Physics and Technology of High Current Discharges in Dense Gas Media and Flows [1 ed.] 9781614705857, 9781606922323

Citation preview

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest Ebook

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest Ebook

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

PHYSICS AND TECHNOLOGY OF HIGH-CURRENT DISCHARGES IN DENSE GAS MEDIA AND FLOWS

No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

PHYSICS AND TECHNOLOGY OF HIGH-CURRENT DISCHARGES IN DENSE GAS MEDIA AND FLOWS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

PHILIP RUTBERG

Nova Science Publishers, Inc. New York

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2009by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Available Upon Request ISBN: H%RRN

Published by Nova Science Publishers, Inc.    New York

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

CONTENTS

Preface

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Chapter I

ix Processes in High Current Discharges in Dense and Super Dense Gas Environments 1. Introduction 2. Construction of the Discharge Chambers 2.1 Methods of Diagnostics 2.2 Pressure Measuring 2.3 Roentgen Measuring 3. Large Current Discharge with the Current Increase Rate of 109 A/Sec 3.1 Discharge Character 3.2 Discussion of the Results 4. Large current discharge under the current Increase Rate of (1–3)×108 A/sec 4.1 Discharge in Hydrogen 4.2 Discharge in Helium, Nitrogen, and Argon 5. Large Current Discharge under the Current Increase Rate of (0.6–3)×107 A/Sec 5.1 Electro–Machine Source 5.2 Inductive Storage 6. Large Current Discharge Under The Current Increase Rate of (0.6–1.8)×1010 A /Sec 7. Large Current Discharge under the Current Increase Rate of 6×1011a/Sec 8. Heat Exchange in the Discharge Chamber: Heat Exchange between the Discharge and the Working Gas 8.1 Electrodes 8.2 Peculiarities of the Electrodes’ Erosion 9. Pulse Discharge In The Super Dense Gas 10. Working Characteristics of Large Current Discharges in Pulse Generators of Dense Plasma

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

1 2 4 7 10 11 11 12 15 17 17 22 23 23 25 26 30 31 33 38 41 51

vi

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Chapter II

Philip Rutberg 11. Pulse Plasma Generators 11.1 Pulse Electric Arc Plasma Generators 11.2 Pulse Electric Arc Plasma Generators with Co–Axial Electrodes 11.3 Pulse Plasma Generators with Two Rod Electrodes 11.4 Pulse Electric Arc Plasmatrons with Co–Axial Rod Electrodes 11.5 Pulse Plasma Generators and the Electric Discharge Light–Gas Accelerators of Bodies 12. Conclusion

60 60

Investigation of High-Current Discharges in Gas Environments 1. Introduction 2. Discharges in Gas Environments 2.1. Character of the Discharge 2.2. Discharge in Nitrogen 2.3. Heat Exchange between the Arc and the Working Gas 2.4. On the Opportunity Obtain the Detachment of the Oscillating Temperature of Nitrogen in Decaying Plasma under High Pressure 2.5. Heating by Radiation in Nitrogen 2.6. Discharge in Air and in Water Vapors 3. Electrodes 3.1. Measurements of the Surface Temperature of Electrodes 3.2. Working Regimes of Electrodes 3.3. Investigation of the Electrodes’ Material 3.4. Run–Out of the Electrodes 3.5. Work of Electrodes in the Oxidizing Environments: The Rail Electrodes 3.6. The Core–Type Electrodes 4. The Main Technical Characteristics of Plasma Generators and Their Constructions 4.1 Classification of Plasma Generators 4.2 DC Plasma Generators 4.3 AC Plasma Generators 4.4 Single–Phase Plasma Generators of Alternating Current 4.5 A Single–Phase AC Plasma Generator with an Arc of Direct Action with Power up to 150 Kw 4.6 Multi–Phase Multi–Chamber Plasma Generators of Alternating Current 4.7 Multi–Phase Single–Chamber Plasma Generators of Alternating Current 4.8 Plasma Generators with Rod Electrodes 4.9 High–Voltage One– and Three–Phase Plasmatron

77 77 78 78 85 90

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

61 62 63 65 69

93 95 99 106 106 108 113 115 118 121 122 123 127 130 131 132 133 135 136 139

Contents

Chapter III

vii

5. External Characteristics of Plasma Generators 6. Plasma Technologies 6.1 General Description 6.2 Plasma Pyrolysis and Gasification 6.3 Plasma High-Temperature Oxidizing

139 150 150 154 166

Investigation of Pulse Electric Discharges in Liquids 1. Introduction 2. Experimental Unit and the PED Parameters 3. Erosion of Electrodes and the Nanoparticles 4. Biological Objects and Methods of Investigation 5. Nanoparticles in Dispersions 6. Nanoparticles and Blood Serum 7. Aggregation of Lysozyme on Nanoparticles 8. Bactericidal Action of Water Treated by PED 9. Mechanism of PMRW 10. Influence of Nanoparticles on Tumor Growth In Vivo

173 173 174 179 182 183 186 188 191 194 196

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Index

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

203

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

PREFACE The book is dedicated to results of fundamental investigations in the field of dense lowtemperature plasma and their technical applications. It also includes technical applications of the results in the following areas: 1. Pulse discharges: High-power pulse plasma generators with power up to 10 GW and currents up to 3 MA have been created. Their application in new plasma technologies includes creation of electric-physical systems of bodies, hyper-acceleration on the basis of electric discharge and combined units, blowing of cones, and X-ray and UV generation. 2. Discharge in flows: Stationary AC in three-phase powerful generators from 1 kW up to 80 MW are applied in various media. New plasma technologies are developed on the basis of these plasma generators. These plasma technologies are used for processing and neutralization of highly toxic waste; synthesis-gas (CO+H2) and hydrogen production from organic containing waste; for treatment of coals and slates for application in power engineering; and production of liquid fuels. 3. Pulse discharge in liquids: Creation of devices for bactericidal water treatment, and for generation charged oxide nanoparticles and their applications in medicine (research in the field of biology, genetics, and oncology). Chapter 1 - Investigations have been carried out under the following parameters of discharge: current amplitude jmax 8 12 0.1–2 MA; current increase rate dj/dt 10 ÷10 A/sec; discharge length 0.005–2 msec; initial pressure of the plasma-generating gas P0 0.1–350 MPa; and energy inserted into the gas of 0.1–10 MJ. The working gases were hydrogen, helium, nitrogen, and air. It was shown that a high density of plasma increases the stability and energy content of the discharge. The high density of energy in the discharge channel leads to the appearance of plasma erosion jets from the electrodes cause creation in the near–electrodes zones of an abnormally high voltage drop. A new type of electrode erosion has been discovered that has the form of symmetrical ejection from their entire frontal surface. It was found that at achievement of the Pease–Braginskii critical value of the current under continuous decreasing of the discharge channel radius, correlated oscillations between the voltage and brightness of the channel appear. The critical value of the current under high initial pressure increases up to ~1 MA which is stipulated by decreasing the losses on radiation caused by its absorption in the passage layer of the dense hull of the gas enclosing the discharge channel. On the basis of the channel conductivity, its darkening, and by the presence of the roentgen radiation, it was found that after the beginning of the compression of the discharge channel its temperature is

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

x

Philip Rutberg

greater than 200 eV. It seems that the appearance of the extended high temperature zone existing for a long time is caused by the radiation compression. On the basis of the implemented investigations, powerful pulse plasma generators (the (plasmatrons) with power up to 10 GW have been created, and technologies with their applications were elaborated. In particular, highly effective electric discharge accelerators of bodies with a casting velocity of up to 6 Km/sec were constructed. Chapter 2 - In the current range from 10 to 10,000 A, the conditions were defined for the existence and passage between contracted and diffuse regimes of burning electric arcs for application to multi–phase electric arc systems and in dependence on the gas dynamic parameters in the electric discharge chambers. The main parameters of the arcs (conductivity, concentration of the current carriers, and so on) along with the parameters of the generated plasma jets have been defined. The working gases were hydrogen, argon, helium, nitrogen, CO2, and others. Phenomena in the near–electrode plasma and the character of emission from the electrodes’ surface were investigated. The elaborated and applied complex methods for diagnostics were described. On the basis of the investigations implemented, a set of stationary plasma generators was constructed with a power range from 5 KW up to 6 MW (in inert environment and hydrogen) and to 600 KW (in oxidizing atmospheres). A number of new plasma technologies were created, in particular, for destruction of toxic wastes and pyrolysis and gasification of organic wastes and coals with the aim of generation of electric power and production of liquid fuels. Chapter 3 - The parameters of the electric discharges were: energy of the pulses W of 0.5–10 J; pulse length 0.5–20 μsec; current increase rate dI/dt 106 ÷1012 A/sec; light diameter of the discharge channel ~1 mm. In dependence on the input energy and the rate of its insertion, the motion of the boundaries of the discharge channel leads to the appearance of compression waves. At the beginning stage, a shockwave appears with a propagation velocity of ~5 Km/sec, on whose front the cavitation bubbles occur. As a result of discharges, nanoparticles are created that have a surface electric charge. The distribution functions of the nanoparticles’ mass fraction in water in dependence on the discharge parameters were defined. The high destructive action of ions and nano-particles (which the ion sources) onto a wide circle of microorganisms, spores, and cellular structures was shown.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Chapter I

PROCESSES IN HIGH CURRENT DISCHARGES IN DENSE AND SUPER DENSE GAS ENVIRONMENTS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

ABSTRACT Investigations have been carried out under the following parameters of discharge: current amplitude jmax 0.1–2 MA; current increase rate dj/dt 108 ÷1012 A/sec; discharge length 0.005–2 msec; initial pressure of the plasma-generating gas P0 0.1–350 MPa; and energy inserted into the gas of 0.1–10 MJ. The working gases were hydrogen, helium, nitrogen, and air. It was shown that a high density of plasma increases the stability and energy content of the discharge. The high density of energy in the discharge channel leads to appearance of plasma erosion jets from the electrodes which cause creation in the near–electrode zones of an abnormally high voltage drop. A new type of electrodes erosion has been discovered that has the form of symmetrical ejection from the their entire frontal surface. It was found that at achievement of the Pease–Braginskii critical value of the current under continuous decreasing of the discharge channel radius, correlated oscillations between the voltage and brightness of the channel appear. The critical value of the current under high initial pressure increases up to ~1 MA which is stipulated by decreasing the losses on radiation caused by its absorption in the passage layer of the dense hull of the gas enclosing the discharge channel. On the basis of the channel conductivity, its darkening, and by the presence of the roentgen radiation, it was found that after the beginning of the compression of the discharge channel its temperature is greater than 200 eV. It seems that the appearance of the extended high temperature zone existing for a long time is caused by the radiation compression. On the basis of the implemented investigations, powerful pulse plasma generators (plasmatrons) with power up to 10 GW have been created, and technologies with their applications were elaborated. In particular, highly effective electric discharge accelerators of bodies with a casting velocity of up to 6 Km/sec were constructed.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

2

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

1. INTRODUCTION Nowadays, there is a growth of interest investigation of dense plasma states. It is connected with achievement of extreme parameters in pinch [1,2,3] of fast pulse discharges close to thermonuclear ones and with obtaining equilibrium states under discharge through the frozen deuterium threads [4]. Under such conditions, the high parameters of plasma (even the most advantageous cases) exist as long as one microsecond in volumes not larger than one cubic centimeter, and demand for their realization occurs in very complicated accelerating (“sharpening”) devices and plants. In such discharges, the rate of the current increase (dj/dt) achieves values of 1014 A/sec and larger. The dense plasma states with an electron concentration of 1019–1020 cm–3 and temperature of 104–106 K can be obtained in discharges with the initial concentration of the plasma generating gas of about 1020 –1022 cm–3. The rate of the current increase (dj/dt) for the discharges, in which such values of the parameters are realized, has values of 108 –1012 A/sec, respectively. As power supplies, more simple and cheap devices can be applied (the batteries of capacitors, shock generators, and inductive storages). Plasma of the mentioned parameters can be obtained in volumes up to several cubic centimeters. High values of temperature and concentration of charged particles in such discharges provide an opportunity to use them as the fore–plasma sources in investigations of thermo–nuclear processes as sources of ultra–violet and soft X–ray radiation [5], in various types of electro–physical accelerators, pulse generators of plasma, etc. The discharge channel surrounded by an envelope of hydrogen or helium can be used for simulation of various astrophysical processes (energy transfer by radiation in the outer envelope of stars, oscillation of brightness of stars caused by the output of shock waves onto their surface, and so on [6,7]). The earlier works were devoted mainly to investigations of the volt–ampere characteristics in argon, helium, nitrogen, hydrogen, and air. Although the pressure in the discharge chamber achieved several hundred mega pascals, the current was only on a level 1– 10 A and the inter–electrode gap was equal to several millimeters [8]. Beginning with the 50th, a series of works appeared that were devoted to investigation of high current pulse discharges under high pressure. The pulse discharge in argon, air, and hydrogen with the length of one fourth of the period ~7.7 μsec under the initial pressure of 0.1 MPa and the inter–electrode gap up to 11.1 mm was considered in [9]. The maximal current achieved was 265 kA. The decrease of the electric field strength was observed under the increase of the inter–electrode gap. The velocity of expanding the discharge channel was about 103 cm/sec. It was assumed that this expanding is realized with the shock wave velocity. In [10], the discharge in argon, hydrogen, and helium was investigated by means of the low–inductive capacitors under pressure from 0.1 to 3.5 MPa and discharge length of 1.8–2.1 μsec; the maximal current achieved was hundred kilo amperes, and the inter–electrode gap was fractions of centimeters. The geometry of the discharge channel, its absorption ability, and the intensity of radiation were determined. The maximal temperature (2.5×105 K) was observed in helium. In [11, 12] the pulse discharges in argon, helium, and hydrogen were investigated; under pressure of about 1 MPa, the battery of capacitors discharged through the stationary arc; the plasma was under quasi–stationary conditions. The presence of the intensive radiation of the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Processes in High Current Discharges in Dense and Super Dense Gas Environments

3

continuous spectrum was established. The maximum of this radiation was observed under the pressure of 3–4 MPa. By application of the thermo–compressor, the super high pressures had been created: 20–50 MPa in helium and hydrogen and up to 120 MPa in argon. The pulse discharges were investigated that were initiated by blowing–up the ignition wire. The current achieved 40–80 kA, and the discharge length was about 10–3 sec; practically complete absorption of the discharge energy by the surrounding gas was observed. In [13, 14] the volt–ampere characteristics of the discharge were investigated in the hydrogen and deuterium under pressure of up to 100 Pa (1 mm of the Hg column); the growth of the volt–ampere characteristic was observed due to the discharge column contraction. The picture of distribution of the discharge current had been obtained in the gap of the plasma injector [14] under the pressure of 0.6 MPa in hydrogen, a current of 100 kA, and a time– period length of 6 μsec. In [15] the functions of the radiation expanding in the hydrogen plasma are presented for temperature of (1–2)×104 K and an electron concentration of ne≈ 1016–1017 cm–3. In [16] values of the electron concentration ne ≈1016–1018 см–3 and the temperatures of 3–7 eV had been obtained by application of the discharge in hydrogen, helium, argon, and air under the initial pressure up to 105 Pa and the current up to 30 kA. The stable discharge had been obtained in the xenon–air mixture under a current of about 1 MA with the time of stability about 100 μsec; the discharge was stabilized by its own magnetic field [17]. The work [18] is devoted to investigation of the time of relaxation and the conductivity dependence versus the temperature in dense hydrogen plasma. The discharge in air was investigated under the current up to 400 kA and the rate of its growth was ~2×1011 A/sec; the obtained temperatures were 7.2×104 K. In investigations of processes that occur in the discharge chamber of a pulse plasmatron, the problems of the discharge expanding and the energy transfer to the surrounding gas are somewhat important. The question on the energy exchange was investigated in detail by means of shock and thermal waves. In [19] a model was created that is based on the energy emanation in the discharge channel and the consecutive appearance of the shock wave. The temperature of the shock wave was higher than the temperature of the surrounding gas, but was significantly lower than the temperature of the discharge channel. The heat take–off by the radiation and the thermal conductivity was considered. The character of the shock wave and the velocity of its expanding were experimentally investigated in [20, 21]. In the works [22, 23] mentioned above, the energy transfer is described in the following manner. The shock wave expands the forefront of the thermal wave through the undisturbed matter. The front of the thermal wave does not run down the shock wave. The main part of the energy is emanated at the center (the temperature is 2–5 eV). In [24] another slightly different mechanism of energy transfer was considered for the temperature of 1–5 eV. As a result of the break–down in a neutral gas, a plasma layer occurs. The layer expansion is realized with the constant velocity, which is controlled by the diffusion and ionization processes, and is not accompanied by creation of strong shock waves. The temperature leveling occurs faster than the density leveling. In investigation of the discharge in helium with high initial density [25], the radiation heating of the vapors ionizes the discharge of the wire, with consecutive transfer of the energy to the surrounding gas by collisions under simultaneous presence of the shock waves. The mechanism of the radiation thermal transfer in combination with the thermal conductivity and convection in the non–

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

4

Philip Rutberg

isothermal hydrogen plasma was investigated in [26, 27]. At last, in some works the direct ohmic resistance heating by the passing current was considered [28].

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

2. CONSTRUCTION OF THE DISCHARGE CHAMBERS For investigations of the large current discharges and for generation of the plasma streams, a row of discharge chambers of various types has been created where the following gases were used as the working gas: hydrogen, helium, argon, nitrogen, air, and vapors of lithium hydrate. The majority of experiments were carried out in hydrogen. The electric power sources were the capacitor batteries, inductive accumulators, and the shock wave generators. By the form and location of the electrodes, the chambers can be divided into two types. In the first type, two rod electrodes isolated from the chamber walls are co–axially inserted one against another. In constructions of the second type, the chambers have axially placed ring and rod electrodes. In all types, the explosive diaphragms are used as a fast acting valve [29, 30, 31]. The pulse plasmatron IP–3 [32, 33] performed in the form of a thick–wall cylindrical sleeve (hull) of stainless steel Х18Н10Т and is designed for pressure up to 200 MPa (Fig. 1.1). The inner diameter of the chamber is 5×10–2 m, and the depth is 6.5×10–2 m. The rod electrodes of the diameter (0.7–1)×10–2 m of tungsten or copper with a hollow for arranging the initiating wire are fixed in the brass holders and are inserted into the sleeve volume through the side walls, and the fluoroplastic cone provides isolation and reliable seal of the isolators. The inter–electrode gap was varied during the experiments in the range of (1.5–3) ×10–2 m. The walls of the discharge chamber are thermally isolated by means of the ceramic cylinder made of Al2O3 and tightly arranged with the chamber diameter. Since the strong shock loads onto the isolator appear (the pressure in the chamber achieves the maximal value in 150–500 μsec), a very exact adjustment of the ceramic cylinder diameter to the diameter of the sleeve was needed.

Figure 1.1. Pulse plasmatron IP–3; 1– the current supplier; 2 – the isolator; 3 – the hull; 4 – the electrode; 5 – the diaphragm; 6 – the ceramic cylinder; L1 and L2 – the lens; K – semitransparent mirror; PHM – the photomultiplier; C1–17 – the oscillograph; UM–2 – monochromator; ISP–22 – the spectrograph; SFR – the speed camera. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

5

For investigations of the discharge under various initial parameters, several constructions of the electro–discharge chambers with electrode systems of various geometries were designed and built. For investigations of the discharge with the rate of a current increase of dj/dt~108 A/sec and the initial pressure of the working gas 0.1–4.0 MPa, a generator of the dense plasma was used, a scheme of which is given in Fig. 1.2. The discharge is initiated by the blow–up of the tungsten wire strained between the rammed cylindrical cathode and the anode copper insert. The internal diameter of the discharge chamber is ~100 mm. The amplitude of the current achieved the value 200 kA under the pulse length of ~1 ms.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.2. Pulse plasma torch IMPP–1; 1 – the cathode; 2 – the insulator; 3 – the initiating wire; 4 – the anode; 5 – the diaphragm.

Figure 1.3. Diagnostic discharge chambers with different geometry of the electrode system: a – co– axial, b – axial; 1 – the cathode; 2 – the initiating wire; 3 – the pressure transducer; 4 – the diagnostic window; 5 – the anode.

In the range of the velocities of the current increase of dj/dt (0.6–1.8)×1010 A/sec, the discharges in hydrogen and nitrogen under the initial pressure 5–40 MPa were investigated. The current amplitude achieved the value 2 MA with the discharge length up to ~2000 μsec and the energy imbedding into the discharge volume up to 2 MJ by one discharge. The value of the final pressure close to the limit strength of the construction did not allow one to relax the chamber construction by a window and to carry out the optic measurements under the full

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

6

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

scale experiment. So, for more complete investigations of the discharge physics, the diagnostic chamber was built with the optic windows in two versions of the construction (Fig. 1.3). In the first variant, the investigations were carried out with the electrode system of co– axial geometry (Fig. 1.3а). In the second one, the system had symmetrical axial electrodes (Fig.1.3b); the unique electro–discharge plant with optical windows was built, and this allowed carrying out the optical diagnosis of the discharge in the electrode system with the axis symmetrical geometry (Fig. 1.3b) under the initial pressure of the gas up to 40 MPa, the current amplitude up to 2 MA, and the energy imbedding higher than 500kJ. In investigations of discharge in the air under normal atmospheric pressure and in the helium under the initial pressure up to 15 MPa and with the current increase rate dj/dt up to 1012 A/sec, the discharge chamber of the construction shown in Fig. 1.3 was used. The maximal amplitude of the discharge current was ~600 kA. The length of the half–period of the discharge current was 6–8 μsec. The discharge initiation was realized by the short–circuit of the discharge gap by means of the plasma jet from the injector placed on the anode. The piezoelectric sensor with a stem for measuring the pressure along the axis of the discharge was placed on the cathode. The second piezoelectric sensor was arranged on the wall of the discharge chamber. For investigation of the discharges in super pressure gas, installations with the preliminary adiabatic compression of the gas were built (Fig. 1.4). In the installation shown in Fig. 1.5a, the pressure just before the discharge achieved 400 MPa (and under this, the maximal concentration of the hydrogen molecules before the discharge achieved (3×1022 cm–3), and in the installation shown in Fig. 1.5b, the pressure was 150 MPa. In the installation given in Fig. 1.5a, the amplitude of the discharge current achieved the value 220 kA under the current increase rate ~109 A/sec; for the installation in Fig. 1.5b, the current amplitude was higher than 500 kA under the current increase rate ~1010 A/sec.

Figure 1.4. Discharge chamber for investigation of the fast discharge; 1 – the pressure sensors; 2 – the Rogowsky’s belt; 3 – the diagnostic window; 4 – the plasma injector.

The principle of action of both plants is similar. Before the start, the discharge chamber and the channel of compression are pumped with hydrogen under a pressure of up to 10–20 MPa. At the first stage, the adiabatic compression of the gas is realized by the piston moving under the action of the propellant charge. The start of the capacitor accumulator is realized

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

7

after the achievement of the maximal pressure in the discharge chamber. After this, the heating of the gas is implemented by the electric arc, and the gas flows through the output unit.

a

b

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.5. Combined electro–discharge installations with the preliminary compression of the working gas; 1 – the powder charge; 2 – the piston; 3 – the channel of the compression; 4 – the cathode; 5 – the ignition wire; 6 – the discharge chamber, anode; 7 – the pressure sensor; 8 – the diaphragm; 9 – the nozzle; 10 – the optical diagnostic window.

2.1 Methods of Diagnostics The principal difficulties of investigation of the arcs in such systems with the current up to hundreds of thousands of kilo–amperes under high and super high pressures are joined with the high density of the plasma. Such plasma has a high factor of radiation absorption. In this case, the situation appears when traditional optical methods of diagnostics give the information mainly about the transient and outer regions of the arc. The high thermal and radiation flows practically exclude an opportunity of the contact diagnostics of the dense plasma in such discharges. Moreover, significant technical demands are required for the methods of diagnostic in connection with the high level of the electromagnetic, acoustic, and thermal disturbances following such experiments. In our experiments, high speed photography of the discharge channel was used in the frame–by–frame photo scanning regimes. The brightness temperature of the discharge channel was defined, and its spectrum was registered. The plasma optic absorption factor was defined by its trans–illumination. The scheme for the fast shadow investigations was designed. The generalized schemes of the optic measuring are shown in Figs. 1.6–1.9. The methods were adapted to conditions of measuring in the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

8

Philip Rutberg

powerful pulse discharges in the dense gas. In using each method, several schemes were applied, which aimed to solve concrete experimental problems.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.6. Scheme of the shadow set–up; I – the high-speed camera; II – the adjusting objective; III – the receiving part of the shadow installation; IV – the discharge chamber; V – the collimator part of the shadow set–up; VI – the source of illumination; 1 – the high-speed camera; 2 – the light filters; 3 – the second component of the adjusting objective; 4 – the visualizing diaphragm; 5 – the first component of the adjusting objective; 6 – the receiving objective; 7 – the diagnostic windows; 8 – the arc; 9 – the cathode; 10 – the anode; 11 – the collimator objective; 12 – the unit for the bunch cleaning; 13 – the condenser; 14 – the electro–dynamic shutter; 15 – the laser.

Figure 1.7. Scheme for measuring the brightness temperature; 1 – the high speed camera; 2 – the neutral filters, wide–band green filter, interference filter 5500 Å; 3 – the mirror; 4,8 – the windows; 5 – the arc; 6 – the cathode; 7 – the anode; 9 – the reference capillary Podmoshensky’s source of brightness; 10 – the high speed monochromatic pyrometer.

The shadow method provides the contrast separation of radiation of the probe source (the argon laser) on the background of its own radiation of the discharge. This is carried out by using the spatial filtration of radiation and spectral filtration with interference filters. In measuring absorption, the schemes free of refraction were applied. The laser and the Podmoshensky’s source (the reference source of brightness with the brightness temperature 40,000 K based on high voltage electric discharge through the capillary with the evaporating wall) were used as the trans–illuminating sources. In measuring the brightness by photographic methods, the simultaneous registration was realized in the given spectral range of the discharge with the reference source of the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

9

brightness temperature. For restricting the light flow, neutral light filters and spatial filtration of the light were used. The given spectral range was separated by a combination of the wide– band color and narrow–band interference light filters.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.8. Measuring the optic absorption by means of the trans–illuminating laser; I – the high-speed camera; II– the adjusting optics; III– the discharge chamber; IV – the trans–illuminating source, laser; 1– the high-speed camera; 2 – the light filters; 3 – the third component of the adjusting optic system; 4– the diaphragm; 6 – the first component of the adjusting optic system; 7 – the diagnostic windows; 8– the arc; 9 – the cathode; 10 – the anode; 11 – the electro–dynamic shutter; 12 – the laser; 13 – the plane of focusing.

Figure 1.9. Measuring the optic absorption by means of trans–illumination of the capillary discharge; I– the high-speed camera; II – the adjusting optics; III – the discharge chamber; IV – the adjusting objective; V – the trans–illumination source; 1 – the high speed camera; 2 – the light filters; 3 – the third element of the adjusting optic system; 4 – the diaphragm; 5 – the second component of the adjusting optic system; 6 – the first component of the adjusting optic system; 7 – the diagnostic windows; 8 – the arc; 9 – the cathode; 10 – the anode; 11 – the adjusting objective; 12 – the reference capillary Podmoshensky’s source of brightness; 13 – the plane of focusing.

For measuring the parameters of the generated streams, the helium–neon laser and monochromator with a photomultiplier were arranged at the output of the unit. When the spectrum of the stream was measured, the spectrograph was mounted instead of the monochromator. The optical measuring was carried out on the distance of 30 cm from the diaphragm. Usually, the intensive spectrum was obtained, in which weak lines of the tungsten, copper, and iron presented. The hydrogen line На was also observed. The

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

10

Philip Rutberg

temperature was determined by the measured intensiveness under the assumption of the thermodynamic equilibrium. The pressure at the point of measuring was close to the atmospheric one. Measuring the parameters of the stream was also realized by the diffraction spectrograph with the dispersion of 0.6 nm/mm. Successful measurement was achieved at the half–width of the line На, by which the electron concentration ne on the butt–end of the nozzle had been determined. The value of ne was (2–4)×1016 cm–3 which corresponded to the temperature 10000–12000 K. It is necessary to note that these measurements agree with the results of calculations obtained from the value of the enthalpy of the stream [34].

2.2 Pressure Measuring

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

A number of important data, such as the energy imbedded into the volume of the discharge, the dynamics of motion of the current channel, and creation of the shock and acoustic waves were obtained by using the pulse sensors of pressure. For measuring the pressure, together with using the serial piezoelectric sensors T–500 and T–6000 (they are designed for the pulse pressure of 500 and 6000 atmospheres, respectively, and the transient band of 200 kHz), we designed a piezoelectric sensor (Fig. 1.10) with the stem having a high level of defense against disturbances and a time resolution of 0.6 μsec. In measuring the pressure along the discharge axis, the piezoelectric sensor with transferring quartz or ceramic stems was inserted into the cathode. The load onto the tourmaline element was relaxed by means of acoustic decoupling of the stems and upset of the frontal stem by rubber. The sensor was calibrated by the shock wave method. In comparison of the readout of the sensor with the other measurements, the delay that is joined with the time of propagation of the pressure pulse through the frontal stem of the sensor was taken into account.

Figure 1.10. Scheme of construction of the pulse pressure transducer; 1 – the tourmaline element; 2-the abjuratory; 3 – the sound absorber; 4 – the isolator; 5 – the cable connector. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

11

2.3 Roentgen Measuring

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

In addition to the optical measuring, the special unit for registration of its own soft roentgen radiation from the arc had been created, since in correspondence with the preliminary estimates, the plasma in the compression zone must intensively radiate in the ultraviolet and soft roentgen ranges. The difficulty of this problem was in the fact that it was necessary to protect the detector of radiation against the effect of the high pressure (the initial one of 5–30 MPa and the pulse one up to 500 MPa), the temperature (up to 5000 K), and of the shock waves. For this, a special chamber (Fig. 1.10) was constructed, into which the semiconductor detector of the roentgen radiation was placed; this was the diode SPD– 12UVHS. The engineering solution allows one to use the sensor several times.

Figure 1.11. Scheme of the unit of the sensor of the roentgen radiation; 1 – the hull; 2 – the screen tube; 3 – the isolators; 4 – the sensor of radiation SPD–12UVHS; 5 – the protecting cover; 6 – the cone insertions; 7 – the aluminum foil; 8 – the output nozzle.

By means of this unit, the flow of the roentgen radiation from the discharge channel had been registered. The energy of the quanta registered is about 400 eV and more. According to calculations of the channel temperature (by its envelope darkening and by its conductivity in the process of compression), estimates of the temperature are 200–300 eV. These values agree well with the roentgen measurements.

3. LARGE CURRENT DISCHARGE WITH THE CURRENT INCREASE RATE OF 109 A/SEC Measurements were implemented in the discharge chamber of the plasmatron IP–3 with the rod electrodes, and in the experiments the inter–electrode gap was varied from 15 mm up to 30 mm. The discharge was initiated by tungsten or copper wire with a diameter of 0.1–

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

12

0.15 mm. The capacitor battery designed for energy of 105 J was used as the feeding source. The working gas was always hydrogen under the initial density of (1–20)×10–4 kg/m [32,33].

3.1 Discharge Character Figure 1.12 shows the typical oscillograms of the current and voltage of the discharge. The marginal values of the current and voltage of the discharge were 350 kA and 1800 V. It is necessary to note that the character splash on the voltage curve corresponds to the instant of beginning of the running out of gas. As seen from the oscillogram, the main part of the energy is released during the first half–period.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.12. Oscillograms of the current (1) and voltage (2) of the discharge; the plasmatron IP–3; the hydrogen is the working gas; the initial pressure is 0.6 MPa.

The discharge has a stable character. The average of the optical diameter of the discharge column (we mean the diameter of the half–width of the radial variation of the column intensiveness) was 0.5–0.6 cm. After 10–20 µsec of the beginning of the discharge, a the sausage–type instability of the diameter 0.3–0.4 cm occurs. It is necessary to note that this sausage–type instability remains for some time, at least up to 180 µsec after the beginning of the discharge and does not lead to discharge instability. But during the current decrease in the first half of the period, the disintegration of the discharge column is observed. Keeping in the mind that the current diameter is determined by the electron concentration ne, the current diameter is found by the following dependence:

F(r)= J (r ) , where r is the light radius and J(r) is the intensity. Under this, the diameter of the current channel is determined by the half–width of F(r). This method of determination is correct under the assumption that the plasma radiates mainly the recombination and bremsstrahlung (braking) spectra. The radiation spectrum is continuous. But such a continuous spectrum can be either in the case of recombination and bremsstrahlung (braking) radiation, or in the case of plasma radiation as the black body. The distribution of the intensiveness of the discharge column along the radius is shown in Fig. 1.13. It is seen that, in this case, the plasma does not

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

13

radiate as the black body, since the distribution of the intensity along the radius does not have a rectangular character. The direct measurements of the electron concentration ne by the recombination and bremsstrahlung spectra showed that the concentration varies in the range of (2–4)×1019 cm–3 in the region of its maximum. The electron concentration was determined under the assumption that the average temperature of the discharge column was (0.6–1)×105 K. Under such temperatures and concentrations, the absorption factor in hydrogen in the visible range does not exceed any units of 0.5–3 cm–1. Hence, the discharge column in the wave range of 500 nm and lower does not radiate as the black body. Under this, we take into account that the maximal concentration of copper is not more that 2×1017 cm–3, i.e., less than one percent of the electron concentration ne in the discharge channel, under the diameter 0.15 mm and the length 25 мм of the copper wire initiating the discharge and even under the assumption of the whole sublimation and ionization of the wire material. The conductivity was defined as follows:

σ = j / E, where j is the current density; E is the electric field strength inside the discharge column under the assumption of the uniform distribution of the current over the cross–section of the discharge column. Conductivity versus the current and the initial density of the gas varied in the interval (105–2)×1017 Om–1m–1. Knowing the value σ, the temperature was determined by the following formula [35]:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Т3/2= σ z Λ/0.015 [k peσ]2/3,

(1.1)

where Λ is the Coulon logarithm (Λ= 3–4.5, and the analogical values have been obtained in similar conditions [36] ); z is the effective charge of the ion; and k peσ = 1.96 is the coefficient that takes into account deviation from the ideal conditions [37]. Under this, the value of z is assumed to be equal to one. With taking into account the obtained values of the current, diameter, temperature, and the electron concentration in the discharge column, the magnetic рм and gas–kinetic рr pressure in the column are determined by the following relations: рм= Н22/8 π,

(1.2)

рr=2 ne k Т ,

(1.3)

where Н2 j/2πr is the magnetic field strength of the discharge; k is the Boltzmann's constant; and Т is the temperature of particles in the discharge column. The thermodynamic equilibrium is assumed [35]. The values of the magnetic and gas–kinetic pressures coincide with accuracy up to any units in the range 20–70 МПа. Such a coincidence can be regarded well if one takes into account the inexactness of the determination of the electron concentration and the temperature inside the discharge column [33].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

14

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.13. Distribution of the intensiveness of the discharge column along the radius of its crosssection.

Figure 1.14. Oscillograms of the pressure (1), current (2), and the view of signal from the photo element (3) without opening its diaphragm; the working gas is hydrogen; the initial pressure is 0.5 MPa.

Figure 1.15. Oscillograms of the pressure (1), current (2), and the view of the signal from the photo element (3); the working gas is hydrogen, the initial pressure is 0.5 MPa.

It is necessary to note that in all cases the gas pressure in the discharge chamber was smaller than in the discharge column. The direct measurements on the axis of the discharge column and on the walls of the discharge chamber show that the pressure in the discharge Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Processes in High Current Discharges in Dense and Super Dense Gas Environments

15

column decreases at the instant of its dissipation. The pressure on the axis of the discharge at the maximum of the first half–period is proportional to the square of the current (the measurements were implemented in the range of 70–270 kA) which also applies to balancing the gas–kinetic pressure by the magnetic one, since the magnetic pressure is proportional to the square of the current. This circumstance helps in preserving the stable discharge. As it follows from the pressure and current oscillograms and the glow on the discharge axis (Fig. 1.14), during the first half–period the peak of the pressure is observed. Further, it decreases (at the instant of dissipation of the discharge column) and, after that, its growth begins up to the second peak. After, a new decrease follows, and the pressure reaches a steady state. The pressure values of the second peak and the steady state correspond to the values measured near the wall. The signal from the photo element is also synchronized with the current during the first half–period. As for the pressure in the volume of the discharge chamber that corresponds to the measurements of the sensor arranged on the chamber walls, then, as seen from the oscillogram, the beginning of the pressure growth on the wall is delayed with respect to the pressure in the volume by a time about 200 μsec and achieves the maximum during the second half–period of the current. After, the pressure decreases to some value and during several hundred microseconds practically does not vary (Fig. 1.15). Thus, the first maxima of the current and pressure are shifted in time. Moreover, as seen, the signal from the photo element that indicates the appearance of the heated gas near the wall achieves the maximum synchronically with the pressure growth; this once more confirms the achievement of the pressure maximum at this instant. If the second half–period of the current is absent or is small, then the peak is not observed, but the smooth growth of the pressure occurs up to its saturation with the time delay. Under this, it is necessary to underline that in all cases the time delay of the pressure signal exceeds the delay in the installation and is significantly larger than the time of the passage of the sound wave from the discharge column to the chamber wall. The time shift is present between the current and the pressure in the chamber. The diaphragm opening is realized after the passage of the current maximum in the first half–period after achievement of a certain value of the pressure with taking into account the time delay needed for the diaphragm opening. The sharp decrease of the pressure and appearance of the signal from the photo element correspond to the instant of the diaphragm opening.

3.2 Discussion of the Results The equation of the energy balance in the system can be written in the following way: W=W0+Wp ,

(1.4)

where W=cu2/2 is the whole energy of the system; W0 are the energy losses in the circuit; Wp is the energy absorbed by the discharge; c is the battery capacity; and u is the voltage on the capacitors. It is known that

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

16 W0= j2L0 /2+t ∫ R0 j2dt+ cu20/2,

(1.5)

where J is the discharge current; L0 is the circuit inductivity; R0 is the active resistance of the circuit; u0 is the active voltage on the capacitors. The discharge energy is distributed in the following way:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Wp=Wi+Wk+ Wн+Wп,

(1.6)

where Wi is the energy of molecular dissociation and the atomic ionization of the working body (aj is the ideal number of particles participating in the process; N is the whole number of particles; and Φj is the energy that corresponds to both these processes); Wk is the energy needed for sublimation of the material of the wire that initiates the discharge; Wн = (3/2) kTn is the energy spent onto the heat of the working body; and Wп are the losses of energy in the plasmatron. From the point of view of the energy balance, the processes that occur before the beginning of the diaphragm opening (i.e., during the first 150–300 μsec) are the main interest. Consider the question about the mechanism of the energy transfer from the discharge column to the working gas. The delays in the growth of the pressure on the wall of the discharge chamber with respect to the first half–period of the current indicate the small thermal exchange between the arc and gas at the initial stages of the discharge development. The analogical delay has been noted by authors in [38]. The significant growth of the pressure onto the walls is observed approximately over 180 μsec. In the SFR–gram the dissociation of the discharge column corresponds to this instant. Evidently, the column dissociation is stipulated by the decrease of its own pitch field caused by the current decrease. After the column dissociation, sufficient number of current carriers appears in the chamber volume, and the current flows through the whole volume of the discharge chamber. As a result, in the second half–period of the current, the direct Joule heating increases the energy transfer into the gas that, in turns, leads to the rapid growth of the pressure. As for the energy that evolves during the steady state of the discharge column, it is mainly given up by radiation of the recombination. As the estimates show, the power of the recombination radiation under the conditions of the consideration allows one to give up this energy. A part of this energy is absorbed by the working gas, but the greater part is absorbed by the walls. Under the analogical conditions in [26] in which helium was used as the working gas, any essential decrease of the pressure had not been observed at the achievement of the maximum but, in contrast, in our case the pressure visibly decreased before achieving the plateau. This difference is determined by the type of gas, since in hydrogen the pressure depends more strongly on the temperature due to greater light ionization and the presence of dissociation in the limits of the temperatures achieved. Thus, even a small decrease in temperature leads to a significant decrease of the pressure [29]. Under dj/dt ≈ 10 9 A/sec and the current 70–350 kA, the discharge in air under the cylindrical geometry of the electrodes and the density (1–20)×10–4 kg/cm3 is contracted and is stable until the gas–kinetic pressure in the discharge column is balanced by the pressure of its own magnetic field. The temperature of the discharge column achieves 105 K and the electron concentration ne is ≈(2–4)×10–19 cm–3. Under decrease of the magnetic pressure, the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

17

dissociation of the discharge channel occurs that leads to the intensive ohm heating of the gas in the discharge chamber.

4. LARGE CURRENT DISCHARGE UNDER THE CURRENT INCREASE RATE OF (1–3)×108 A/SEC At the current increase rate dj/dt of (1–3)×108 А/sec, the discharges in hydrogen, helium, nitrogen, and argon were investigated at the initial pressure of 0.1–4 MPa [39]. The capacitor battery, power supply, inductive storages, and shock generators with accumulated energy from 100 kJ up to 10 MJ [29,40] served as a power source. The photo–streaks of the discharge glow in various gases (Fig 1.17) were obtained. The image of the photo–streak corresponds to the middle area between the anode and cathode. The temperatures (7–15)×103 К of the discharge channel and the rate of its expansion (0.8–6.0)×102 m/sec were determined. During estimation of the heat exchange mechanisms between the arc and ambient gas, it was found that for hydrogen the gas heating takes place due to turbulent heat transfer. Various modes of the arc burning under reducing the inter–electrode gap and the growth of amplitudes of the pressure fluctuations of the gas were observed during heating.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4.1 Discharge in Hydrogen After the discharge initiation by the blow–up of the wire and the following pause of the current, in all cases the peaks on the voltage curve are observed which correspond to the breakdown in the vapors of the wire material. The half–width of these peaks varies in the range of 200–300 μsec. During this period, the curve of the current has a form close to sinusoidal which is stipulated by the resistance of the whole circuit of the discharge contour under the rate dj/dt = (1–3)×108 A/sec. The time length of the first half–period is about 2.6 msec. The typical oscillograms of the current and voltage are given in Fig. 1.16.

Figure 1.16. Discharge in hydrogen; the initial pressure is 1 MPa; the oscillograms of the voltage (1), pressure (2), and current (3).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

18

Philip Rutberg

As it follows from the photos obtained by the high–speed scanning, after the blow–up of the wire, gap in the with the time length up to 150 msec is observed, and, further, the widening of the discharge column (Fig. 1.17) up to the diameter of the discharge chamber begins. In some cases, the gap in the intensity is absent or is weakly expressed.

Ar

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

He

Figure 1.17. Photograph of streaks of the discharge channel expansion in hydrogen, helium, and argon.

From the instant of the wire blow–up until the beginning of the column widening, a weak glow is observed over the whole diameter of the discharge chamber; this glow corresponds to the weak shockwave that emanates after the blow–up. After the widening, the intensity of the glow has a non–stationary character, i.e., one observes the gaps in the intensity, the appearance of the vortices and plasmodia. The analogical plasmodia were observed by means of the photomultipliers. The discharges of such a type are called turbulent in the sequel. The velocity ϑ р of the discharge column widening calculated on the basis of the intensity and pressure variations are given in Table 1.1. In the table the following notations are accepted: I – the glow intensity, P – the pressure transducer indications.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

19

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Table 1.1. Rate of the discharge channel expansion in various cases GAS

РINIT, Atm

VEXPANS, m/sec I Р

Н2

1.8 6 10 12.5

–

Нe

1.3 10 15 21

Ar

1.9 5.4 9.6 20

152 210 – 600 244 164 190 192 161 97 76

175 150 200 250 – 200 – – 280 – – –

The rate of the widening decreases under the increase of the initial density. In the case of hydrogen, some evident dependence of the widening rate versus the initial density is not observed in the pressure range under consideration. The smaller values of the rate of the widening of the discharge column obtained by other authors are possibly explained by the smaller density of the energy. The existing gas–dynamic theory of the channel widening [20, 36] does not allow one to explain the experimentally obtained values of this rate. The estimates obtained from the energy balance in the widening column of the discharge with taking into account of the radiation diffusion in the spectral lines are more appropriate to the results of our experiments. Growth of the turbulization under the discharge in the hydrogen is observed after the mentioned widening of the discharge column. It is necessary to note that the turbulization degree near the cathode occurs more apparently than in the discharge column in all cases. Moreover, the turbulization grows also under the increase of the initial density. After expansion of the discharge column over the whole diameter of the discharge chamber on the hydrogen, the decline of the voltage is always observed, and the plateau appears on the voltage curve. The voltage oscillations with amplitudes of 20–30% are observed. In practice, the voltage average value on the plateau varies slightly in the considered range of the inter–electrode gap of 5–18 cm under fixed geometry of the discharge chamber. It is necessary to note that the voltage peak values in the discharge depend on the initial conditions. So, the voltage on the plateau grows under increase of the initial density of the working gas. Actually, if the density of the surrounding gas increases, the heat exchange between the arc and gas is carried out more intensively, which leads to the growth of the electric field strength. Oscillations of the intensity correspond to those of the temperature (we noted that the surface brightness temperature was measured by optic methods).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

20

Figure 1.18. Temperature of the discharge channel for various working gases.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Taking into account the turbulent character of the discharge when determining the average temperature, it is necessary to keep in the mind that the temperature values for hydrogen changed over time in the range (6–10)×103 K. The character dependencies are given in Fig. 1.18. In all cases, the growth of the temperature is observed after the diaphragm opening and beginning the outflow of the gas. Occurrence of the voltage fluctuations and fluctuations of pressure in the chamber corresponds to the observed turbulent mode of burning of the hydrogen arc which results in growth of the gas heating efficiency with reduction of the distance l between the electrodes (Fig. 1.19). Such behavior of the hydrogen arc has been registered at amplitude of the discharge current of 80 kA, inter–electrode anode–cathode gap of 5–30 cm, magnitude of the initial pressure of the hydrogen of 1.6 MPa, and time of the first half–period of the discharge current 2 ms.

l = 29 cm

l = 9 cm

Figure 1.19. Growth of the amplitudes of the pressure oscillations for the discharge in hydrogen under decrease of the gap between the electrodes.

The discharge in hydrogen differs from the discharges in other gases by significantly higher summary voltage drops near the electrodes. These values were obtained by extrapolation to zero of the discharge gap length and are approximately U ~1 kV (Fig. 1.20). The values of these near–electrode drops for nitrogen, helium, and argon are about 250 V under the large values of the current.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

21

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.20. Dependence of voltage drop at the arc versus the length of the inter–electrode gap; 1 – for hydrogen, the current is 110 kA; 2 – for helium; 3 – for nitrogen; 4 – for argon; 5 – for the wire vapors; in 2–5 the current is 150–180 kA.

260μs

280 μs Figure 1.21. Shadow pictures of the gas motion in the discharge volume and corresponding distribution of density in g/cm–3; the tungsten electrodes are 6 mm diameter; in the inter–electrode gap is 12 mm; the working gas is air; the anode is at the left; the cathode is at the right; the maximal value Imax of the current is 110 kA.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

22

Philip Rutberg

With the increase of the atomic gas number, in which the discharge takes place, the degree of the discharge turbulence decreases and plays a lesser part in heat exchange between the arc and gas. So in photographic streaks the discharge glow for helium can still be seen, but for the argon the channel expands symmetrically without ejections. Growth of the reduction pressure oscillation is observed under decrease of the inter– electrode gap. The occurrence of such oscillations is connected with formation of electrode jets and results in better heat exchange. For example, we have found an increase in efficiency of the energy transfer from the arc to gas under decrease of the inter–electrode gap. Interaction of jets from the electrodes is observed in the high–speed photos of the discharge in the diagnostic chamber. The jets from the electrodes found during investigations in the diagnostic chamber are also present in the chamber shown in Fig. 1.3. They are one of the reasons for turbulence occurrence. The additional reason for turbulence occurrence is interaction of the electrode jets and initiation of the plasma plate (Fig. 1.27). The other reason causing the efficient gas mixing in the chamber volume can be its inflow by erosion electrode jets (Fig. 1.21). Recent investigations carried out in the diagnostic chamber have shown that the high voltage drops near the electrodes in hydrogen are also stipulated by the jets appearing at high energy densities near the electrodes.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4.2 Discharge in Helium, Nitrogen, and Argon The picture of developing the discharge in these gases differs from to the one in the hydrogen that is stipulated by the character of the heat exchange between the arc and the surrounding gas [39]. In the cases of discharge in nitrogen and argon in contrast to the one in the hydrogen, the smooth decrease of the voltage is observed after the voltage peak till to the instant of the diaphragm’s opening. For the discharge in helium and argon, the voltage curve has no apparently expressed plateau, but, nevertheless, it is close in form to the voltage curve for the discharge in hydrogen. The forms of the voltage curves in the other gases are similar each other, but they essentially differ from those of the discharge in hydrogen. This can be explained by the fact that the heat exchange in helium is similar to that of hydrogen. Until the instant of the diaphragm’s opening, the most expressed turbulence is observed in helium. In other gases, the degree of turbulence is expressed very slightly and decreases under increase of the atomic number. At the instant of the diaphragm’s opening, the turbulence degree increases abruptly, which is explained by the abrupt increase in the outflow velocity. Here, the character of variation of the surface brightness temperature differs from the case of the discharge in hydrogen. As a consequence of the fact that for discharges in the gases under consideration the turbulence is significantly smaller than hydrogen and the heat exchange in hydrogen is considerably higher, until the diaphragm’s opening, the average temperature in the arc is higher than for the discharge in hydrogen. This is so in spite of the fact that the voltage drop in these gases is smaller than in the hydrogen. The character curves of temperature versus time were given above in Fig. 1.18. It is seen that until the instant of the diaphragm’s opening, the temperature oscillations in these gases is significantly smaller than for hydrogen.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

23

5. LARGE CURRENT DISCHARGE UNDER THE CURRENT INCREASE RATE OF (0.6–3)×107 A/SEC The discharge was realized in the plasmatron chambers with the cylindrical and the butt electrodes. The working gases were hydrogen, hydrogen mixture with lithium vapors, and nitrogen. The inductive storage and the shock generators were used as a power source [39].

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

5.1 Electro–Machine Source In [40, 41] the electro–machine source of power was used. In contrast to supplying from the capacitor battery (where the time length of the power pulse did not exceed (2–3)×10–3 sec), the main energy imbedding was realized during the first half–period (1–2)×10–3 sec, and in the case of the shock generators, the time of the arc burning was (2–7)×10–2 sec. Variation of the arc current has sinusoidal character and is determined by the parameters of the power source. The current can achieve its maximal value both in the first and second half–periods depending on the angle of switching the arc. Because of the large inductivity of circuit, the rate of the current increase is small at (0.6–0.8)×107 A/sec. The curve of the voltage drop (Fig. 1.22) can be divided into several character parts that are determined by conditions of the arc burning. For 300–500 μsec a blow–up occurs which initiates blow–up of the wire and the breakdown in its vapors. Under this, the splash of the voltage achieves the value 6–16 kV from the generator, and the half– width of the voltage peak is 100–160 μsec. Further, for 3–15 μsec until the diaphragm’s opening, the voltage on the arc is constant (on average) with a slight tendency to decrease (1.8–7.9 kV depending on the initial density). Voltage fluctuations are observed with a frequency of 4–21 kHz (which correspond to acoustic frequencies) and an amplitude that consists of 15–25% of the average voltage of burning. At the instant of the diaphragm opening, the character voltage splash is observed that corresponds to the beginning the gas outflow. After this, the voltage of burning decreases, since the gas density decreases as a result of its outflow. Further, after the passage of the current through zero, the voltage changes its sign, and the repeated breakdown of the inter–electrode gas takes place. The voltage of the peaks in the repeated ignitions is smaller than the voltage of the initial breakdown. It is necessary to note that if the lithium or lithium–hydrate dopant is added into the hydrogen, the voltage peak of the repeated ignition is not observed, but the smooth passage through zero occurs and a voltage increase on the arc is realized. This phenomenon is explained by the presence of the easily ionized dopant that maintains the high conductivity of the gas. In some cases, the diaphragm opening occurs in the second half–period, and then the repeated ignition is observed before the gas outflow. Here, in contrast to the discharge on the capacitor battery, the arc voltage before the diaphragm opening increases appreciably as the inter–electrode gap (under the same other conditions) increases.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

24

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.22. Oscillograms of the voltage under supply from the electro–machine units; the working gas is hydrogen, Umax = 5.4 kV; j max = 180 kA; density p is 0.872 kg/m3; the inter–electrode gap is l = 20 cm.

After the discharge column widening, the pressure in the chamber grows as the discharge current grows, and, as a rule, the pressure achieves its maximum synchronically with the current maximum in the first half–period. After the diaphragm opening, the pressure decreases as the gas outflows, but the arc burning continues for several half–periods until the current ceases. Thus, until the diaphragm opening, energy is used, as a rule, for a quarter of the period (5 мс), but as the gas outflow continues, the energy imbedding also continues. This can maintain the needed temperature of the gas. So, it is possible (if necessary) to provide the heating of the gas flowing through the discharge chamber, i.e., to enlarge the length of the working cycle of the system. This can be done by a simple changing of the chamber construction. In some experiments, when the diaphragm was not broken and the arc burning continued in the closed volume, oscillations of the pressure were observed; they were joined with the current time–oscillations. In the second half–period the pressure increased proportionally to the growth of the imbedded energy. During the third half–period (i.e., after 20 msec), the growth of the pressure retarded or even completely ceased in spite of the additionally imbedding energy. In the case when the current was switched off after the first or second half–period, the decrease of the pressure in the chamber began approximately over 25–30 msec after the maximum achievement. It is necessary to note that the effective absorption of the energy increases as the initial density of the gas increases, and this effects the efficiency (η) of the system. The addition of dopant metal vapors (inparticular of lithium or copper) into the hydrogen leads to an analogous result, but to a larger degree. With the growth of specific energy, the temperature of the gas also grows with simultaneous decrease of the system efficiency (η). But after achievement of the value 5×10–17 J/atom and until the value 4×10–16 J/atom, the efficiency gives over to decrease. As for the temperature, it continues to grow, but significantly more slowly. Actually, the increase of the specific energy leads to increase in concentration of impurities as a result of ablation of the discharge chamber walls, and to an increase in the number of heavy molecules, which causes a decrease in the temperature.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

25

5.2 Inductive Storage

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Inductive storage was also used as the power supply [42, 43]. The rate of the current increase in this case was (1–3)×107 A/sec/. But over 0.5–3 msec after achievement of the nominal value, the current pulse maintained a constant character for 6–15 msec that allowed one to investigate the process under quasi–stationary conditions. The total energy imbedded into the discharge until the diaphragm opening achieved 5×105 J. The value of the discharge current reaching a steady state was in the range 10–90 kA; the average value of the voltage drop in the inter–electrode gap was 0.56–1.7 kV for hydrogen and 0.8–2.2 kV for nitrogen. The depth of the voltage modulation was 10–20%. The peaks of the voltage at the breakdowns achieved amplitudes of 2.3–6 kV. The initial pressure in the implemented experiments was 0.5–3 MPa for hydrogen and 1–6 MPa for nitrogen. The typical oscillograms of the current, voltage, and pressure are given in Fig. 1.23.

a)

b)

Figure 1.23. Oscillograms of the pressure (1), current (2), and the voltage (3) in the discharge chamber under supply from inductive storage; a) the working gas is nitrogen, the initial pressure is 2 MPa, the inter–electrode gap l is 18 cm; b) the working gas is hydrogen, the initial pressure is 1 MPa, the final pressure is 50 MPa, and the inter–electrode gap l is 13 cm.

After blow–up of the initiating wire and the repeated breakdown, to which the peak of the repeated ignition corresponds to the voltage oscillogram, the expansion of the discharge channel occurs with a velocity of 102 m/sec. Since the diameter of the discharge chamber is 8.4 cm, the current channel achieves the chamber walls approximately over 0.5 μsec. The first and second peaks on the pressure oscillograms correspond to the beginning of the nitrogen dissociation. Under increase of the initial pressure in the chamber, these peaks shift to the direction of the higher pressures. Under the initial pressure of 50–60 MPa, the peaks are not observed, i.e., no appreciable dissociation of the nitrogen occurs. In spite of the fact that the pressure in the chamber increases during the process of the gas heating (dependently on the current and the initial pressure of the nitrogen) by 5–40 times, the voltage on the inter–electrode gap after the repeated breakdown until the instant of the diaphragm’s opening changes not more than 20%, but the current (for each concrete case

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

26

Philip Rutberg

of the initial density) maintains a constant level. At the instant of the diaphragm opening, the character splash of the voltage is observed which is caused by the beginning of the gas outflow with the Mach number M > 1. Conductivity and optic properties of the discharge, apparently, are determined as earlier by the significant content of the wire material in the plasma. The mass–average temperature was determined on the basis of the pulse pressure. According to the optic measurements, the brightness surface temperature on the discharge in the nitrogen was (13–14)×103 K. In the discharge chambers with the cylindrical and butt–end electrodes under the rate of a current increase of (0.06–3)×108 A/sec and a current up to 350 kA, the widening of the discharge column with a velocity of 102 m/sec occurs after the initiation of the discharge by the blow–up of the ignition wire. The discharge has a diffusion character. Concentration of the current carriers is determined mainly by ionization of the wire material. The turbulent character of the discharge is also observed. The turbulence is especially expressed in the hydrogen, in which the range of the density is (0.85–42)×10–4 kg/m3. In helium, nitrogen, and argon, the turbulence is expressed slightly and decreases as the gas atomic number increases. The temperature of the discharge column is in the range of (7–14)×103 K. The character of the discharge is maintained also in the quasi–stationary stage under supply from the shock wave generators and from the inductive storage.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

6. LARGE CURRENT DISCHARGE UNDER THE CURRENT INCREASE RATE OF (0.6–1.8)×1010A/SEC In the range of the rate dj/dt (0.6–1.8)×1010 A/sec [44, 45, 46], discharges in hydrogen and nitrogen were investigated under the initial pressures of 5–40 MPa. The investigations were carried out both under operation of a powerful electric discharge plasma generator and in a specially developed diagnostic chamber (Fig. 1.4). The value of the discharge current reaches 1.6 MA, and the energy imbedding into the discharge volume is 2 MJ. A very difficult problem of the discharge initiation and support of the hydrogen arc burning was solved under the initial pressure of 20–40 MPa (Fig.1.24). After initiation, the arc is pushed out from the gap by the gas–kinetic and magnetic pressure, moves along the electrodes, and heats the gas in the chamber. The mode of the multiple breakdowns seems to be the most interesting one (Figs. 1.24 and 1.25). In this case, the arc moves along the inter–electrode gap, and after its extinction the further ignition in the inter–electrode gap is realized (Fig. 1.25). This mode was investigated in detail in the diagnostic chamber. For the discharge in nitrogen, taking into account the low arc mobility, it was possible to estimate the discharge channel temperature directly in the chamber of the electric discharge generator. For hydrogen it was done in the diagnostic chamber at lower values of the discharge current, amplitude, and pressure. The temperature of the discharge channel in nitrogen was estimated on the basis of oscillograms. The sharp fluctuations in the pressure oscillogram can be explained by the motion of the cathode spots of the first type (Figs. 1.24b or 1.25). The thermal cathode spot of the second type with common molten bath takes place near the maximum of the discharge current. Thus, the voltage drop in the inter–electrode gap decreases sharply.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

27

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

a)

b) Figure 1.24. Discharge oscillograms in the chamber of the power electric discharge launcher; а) on hydrogen, the initial pressure is 40 MPa; b) on nitrogen, the initial pressure is 20 MPa.

The arc temperature was estimated on the basis of its conductivity. The most complete researches of the discharge were carried out in the diagnostic chamber at the current amplitude up to 500 kA. The origin of heterogeneities in the current channels can be seen in the photos of the discharge in the diagnostic chamber already until the 12th μsec. Conductivity of the channel was determined at the 28th μsec when the discharge had not yet lost the compact form. At this instant, five channels with an average current density of 3.0×104 A/cm2 are observed, which is typical for the arc discharges with thermal cathode spots. The arc temperature is ~18×103 K that corresponds to the temperature measurements in the transitive zone between the arc and surrounding gas on the half–width of the D–lines of the sodium absorption К 5890, 5896 Ǻ observable on the background of the continuous spectrum of radiation of the arc at (11–14)×103 K.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

28

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.25. Arc motion along the inter–electrode gap in the mode of multiple breakdowns.

More rough estimates of the discharge channel temperature in hydrogen on the basis of its conductivity at the instant of the first maximum of the current gives the value of (25–30)×103 К. Inaccuracy in determination of the temperature is connected with inaccuracy in determination of the geometrical sizes and the uncertainty of the metal vapor concentration in the arc. The temperature of the discharge channel for the discharge in the nitrogen is about 50×103 К. In the latter case, it was assumed that the arc burns near to the place of the initiation in metal vapors of the electrodes. The recent investigations have shown that the steady condition of the discharge channel at the instant ~200 µsec is connected with the occurrence of the powerful electrode jets. Dependence of the field intensity in the discharge channel versus the material of the electrodes indicates the influence of the jets. Two types of jets connected with formation of spots of various types, depending on time of the electrode warming–up, current density, dimensions and material of the electrodes, etc., are observed. The jets of the first type are connected with formation of the fast-moving spots on the electrodes. Two types of jets can exist simultaneously. For the first time it was possible to observe the anode and cathode jets through the expanding semitransparent discharge channel (Fig.1.26). The jets of the second type flow out from the general molten bath of the electrode, which is formed after its warming–up (Fig. 1.27).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

4 μs

20 μsec

8 μsec

24 μsec

29

16 μsec

28 μsec

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.26. Formation of the cathode and anode jets during expansion of the semitransparent discharge channel in hydrogen; 1 – the cathode, 2 – the anode.

a)

b)

Figure 1.27. Computational modeling of gas heating by shock waves for fast discharge in helium at the initial pressure of 15 MPa; Р0 is the pressure on the discharge axis; Р1 is the pressure on the wall; a) the discharge chamber radius is 2 cm; b) the discharge chamber radius is 1 cm [48]. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

30

One of the reasons for the high near electrode voltage drops can be the interaction of the jets with the surface of the opposite electrode or between each other. Another possible reason of the high voltage drop in the near electrode areas can be non– coincidence of the current and jet rates. The additional electric field strength E stipulated by the rate u across the arc magnetic field B will be, as it is known, E = u × B,

B =

μJ . 2πr

For estimations of the jet rate of about 104 m/sec, the current j ~105 A, and the radius r ~ 3⋅10–3 m (that corresponds to the experimental data), the density estimate is E~103 V/cm.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

7. LARGE CURRENT DISCHARGE UNDER THE CURRENT INCREASE RATE OF 6×1011A/SEC The discharges in the air at atmospheric pressure and in helium at pressure up to 15 MPa were investigated under the rate of the current increase of dj/dt = 6·1011 A/sec [47]. The maximal amplitude of the discharge current was ≈600kA. The measurements of the pressure along the discharge axis on different diameters have allowed one to estimate distribution of the current density along the channel radius. Comparison of the pressure on the axis averaged on two diameters, 0.2 and 0.4 cm, was carried out for the discharge in the air. Distribution of the current density along the radius uniform at the discharge current amplitude of 144 kA. Under increase of the discharge current amplitude up to 290 kA, the current density on the smaller radius was higher. In this case, the average pressure at the diameter of 0.2 cm was 171 MPa. Based on this pressure value and assuming that the plasma density at the central part did not exceed 1019 cm–3, it was determined that the temperature at the center was not lower than 105 K. A clear visible, uniformly melted, bulging zone with a diameter of 0.4 cm can be seen on the hemispherical cathode under increase of the discharge current up to 500 kA. Occurrence of the bulging zone at the higher currents agrees with the assumption of the current density increase at the central parts of the discharge. After the discharge current maximum, there is a sharp increase of velocity of the discharge channel expansion caused by decrease of the magnetic pressure value. If the average density of particles in the discharge channel before the beginning of the stage of the magnetic confinement corresponds to the average density of the discharge channel at the stage of the thermal wave, then by estimations for the discharge in air, the density in the channel is several times below atmospheric. Therefore, the possible temperature of the discharge channel under the discharge current amplitude of 500 kA can reach 5×105 K. The average pulse pressure of 436 MPa was registered for the discharge in helium under the initial pressure in the chamber of 10 MPa, a discharge current amplitude of 570 kA, and a discharge diameter of 0.4 cm. Theoretical calculations show that the temperature on the channel axis is ~105 K [48].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

31

The gas heating in the discharge chamber is carried out due to the shock wave energy. Thus, the coincidence of the experimental and calculated curves of the pulse pressures on the axis and on the wall of the discharge chamber (Fig. 1. 27) is obtained [47, 48]. The power shock waves moving away from the discharge channel are formed under the fast energy imbedding (rate of current increase is ≥1012A/sec) when the super high pressure discharge is generated. Thus, the energy emitted by the channel is absorbed by the front of the shock wave. The calculations [48] show that it is possible to increase the discharge channel temperature by focusing the energy of the reflected shock waves along the discharge axis and realizing the additional pulse of the current at the instant of focusing.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

8. HEAT EXCHANGE IN THE DISCHARGE CHAMBER : HEAT EXCHANGE BETWEEN THE DISCHARGE AND THE WORKING GAS The appearance of oscillations of the voltage and pressure in the chamber [29, 49] corresponds to the discovered turbulent regime of the arc burning in hydrogen. This leads to the growth of effectiveness of the gas heating under decreasing the gap between the electrodes. The increase of the pressure oscillations is observed [14] under decreasing the gap between the electrodes (Fig. 1.19). Such behavior of the arc in hydrogen was registered under a current amplitude of 80 kA, an anode–cathode of gap 5–30 cm, a value of the initial pressure of hydrogen of 1.6 MPa, and a length of the first half–period of the discharge current of 2 msec. With an increase of the atomic number of the gas, in which the discharge is realized, the level of the mentioned turbulence decreases and plays a smaller role in the heat exchange between the arc and gas. So, in the photo–streak pictures of the discharge in helium, the turbulence can be seen, but for argon, the widening of the discharge channel is realized symmetrically without spews. First of all, most interesting is the mechanism of the energy transfer from the discharge into the gas in the case corresponding to the turbulent regime of the arc burning in hydrogen. The density of the normal atoms in the discharge zone is usually about 1019–1020 cm–3; but in the volume occupied by the discharge, the density is higher approximately by an order. Since the discharge zone occupies a part smaller than the half–volume of the discharge chamber, as a consequence the main mass of the working gas is placed out of the discharge zone. The energy of radiation is

WR = σT4St, where σ = 5.668×10–5 Erg/cm2·sec·grad4 is the Steven–Boltzmann constant; S is the average square of the discharge surface anf t is the time of the energy transfer. For hydrogen under the condition that the plasma radiates as the absolute black body with surface temperature of ~104 К, the power of the radiation will be ~6×104 W/cm2. For the typical case corresponding to the initial pressure of 10 atm, these values are S = 250 cm2, t ≈ 1 msec, and, consequently, WR ≈ 1.5×104 J. Thus, the maximal value of the energy transferred by the radiation from the whole square of the discharge surface cannot exceed

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

32

10% of the total energy. It is necessary to note that, actually, the discharge radiates as the absolute black body only in the wave band approximately up to 5000 Å, and this means that the energy of radiation is smaller. The energy dissipated in the acoustic oscillations can be estimated in the following way: the space–average density of the acoustic energy is Wac=0.5ρva2=0.5(pm)2/ρ(vac)2, where va is the amplitude of the oscillation velocity; pm is the amplitude of the pressure in the acoustic wave; ρ is the gas density; and vac is the sound velocity in the gas. In the case under consideration, these values are pm ~50 atm, vac ~5×105 cm/sec, and Wac ≈ 5 J/cm3, and if to assume that the oscillations occur in the part of the chamber volume occupied by the discharge, then the whole energy stored in the acoustic oscillations will be not greater than 3×103 J; therefore, it is approximately any percentage of the summary of energy of the discharge. It is possible that the main mechanism, which is responsible for the energy transfer, is the turbulent mode. Let us show it. The energy transferred by the mentioned mechanism is estimated as

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

WT=κT∇TSt. The strong turbulence can be supported by the jets from the zone of the burning arc to the cool gas. As our investigations showed, the intensive anode and cathode plasma jets are formed in the discharges with the current of 105–106 A. The electrode plasma jets interact with each other, effectively intermix the surrounding gas, and provide implication of the gas into the arc. The Reynolds number, which is necessary for the effective turbulent heat exchange, must be 106–108. The Reynolds numbers calculated by the experiment data in our case are of the values 107–108. The factor of the turbulent thermal transfer is

κT = ρCvDТ, where DT ≈ lTv is the factor of the turbulent diffusion; lT is the character size corresponding to the size of the discharge; and v is the average velocity of the propagation of the heterogeneities. For the surface temperature of the discharge ~104 K, lT ≅ 4 cm, and v ≅ 104 cm/sec, we obtain DT ~4×104 см2/с and κT = 0.85×10–3·4·104 ≅ 102 W/cm·grad. Hence, the power of the thermal flow is qT = κT∇T = 102×104 ≈ 106 W/cm. Taking into account the average square of the discharge and the time of the thermal transfer, one can conclude that the turbulent transfer can completely provide the necessary transfer of the energy of the value 1.5×105–5×106 J into the gas. The following facts reveal the prevailing role of the turbulent transfer. For the discharge in argon where the level of the turbulence is lowest, the mass–average temperature of the gas

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

33

in the volume is significantly lower in spite of the temperature of the discharge surface being larger. Therefore, the heat exchange is worse than when under the presence of the developed turbulence.

8.1 Electrodes The metal evaporated from the electrodes or ejected from them in the form of melt influences both the arc discharge parameters (such as the electric field strength and the radiation and dynamic characteristics of the discharge [50, 51,52]) and the parameters of the working gas (the heat capacity, thermal conductivity, density, and viscosity), thereby affecting the heat transfer in the discharge chamber [53,54,55]. Studies of the processes in the discharge chambers of the high-power pulsed plasmatrons (including the processes occurring at the electrodes) are also of considerable interest for the physics of high current gas discharges. Along with the integral erosion, an important parameter characterizing the processes occurring in the discharge chambers of the pulsed plasmatrons is the mass ratio between the evaporated metal and that ejected in the form of melt (the so–called ejection coefficient). In [56] it was pointed out that, in the current range of 70–800 kA, the ejection coefficient is independent of the electric charge and amounts to 40% for copper, 40% for molybdenum, and 20% for titanium. Another parameter characterizing the electrode material erosion is the erosion resistance Re [56]

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Rе =

сТ m , кUe

where c is the heat capacity, Tm is the melting temperature, k is the ejection coefficient, and Ue is the electrode voltage drop. The erosion of one of the electrodes was observed to change substantially when changing the material of the opposite electrode. This is explained by the increase (or decrease) in the intensity of action of the electrode jets from the opposite electrode due to a change in the metal atomic mass. These observations agree with the results of [57], where the electrode erosion was found to depend on the inter–electrode gap. In [58], where the fusion of metal–ceramic materials was investigated, it was found that the energy deposited in these materials is smaller than that deposited in homogeneous materials. The authors of [58] attributed this effect to the surface thermal flows, which act to fix cathode spots in regions with more favorable conditions for evaporation and electron emission. Moreover, in this case, no continuous melting pool is formed; as a result, the intensity of the molten metal ejection and, correspondingly, the rate of electrode erosion are reduced. In [57, 59], the erosion and destruction of the electrode material at currents of 230–500 kA were investigated. The ejection of metal from the melting pool was attributed to the interaction of the magnetic field with the currents flowing in the liquid metal. Thus, the above brief survey of works devoted to electrode erosion in the high current discharges allows us to conclude

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

34

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

that the main mechanisms responsible for the electrode material erosion are the ejection of metal from the melting pools, metal evaporation, and the formation of electrode jets. The results of our experiments show that, at charges of up to 700 Coul, the total mass of the eroded electrode material depends linearly on the charge (Fig. 1.28). In [55], the erosion of copper, molybdenum, and titanium electrodes in pulsed oscillatory discharges was measured as a function of the charge at currents of up to 0.8 MA and charges of up to 70 Coul. It was found that, at charges in the range of 10–40 Coul, the erosion increased in a jump–like manner, while at charges larger than 40 Coul, the measured dependences were linear for all the metals under study. Thus, taking into account that, in this work, the specific erosion is used as a quantitative characteristic of the erosion process, it follows from Fig. 1.28 that the electric charge does not affect the dependences presented below.

Figure 1.28. The total electrode erosion versus the electric charge.

Figure 1.29. Specific erosion of the cathode and anode materials.

Figure 1.29 shows the measured specific erosions of electrodes made of D16 aluminum alloy, alloyed steel, molybdenum, copper, chromium, tungsten, W + Ni + Fe Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

35

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

pseudo alloy, Mo + W + Cu pseudo alloy, and W + Ni + Cu pseudo alloy in the high– power pulsed plasmalrons and electric–discharge accelerators [55]. The specific erosions shown in Fig. 1.29, as well as the dependences presented below, were obtained by processing the data from more than 200 experiments. Figure 1.29 presents the averaged experimental data obtained at the discharge current of 0.8 MA, the electric charge of 360 Coul, and the average working gas temperature of 2300 K. Note that the specific anode erosion is higher than the cathode erosion by approximately 4.5 times. Presumably, this is related to the fact that the area of the anode arc spots measured by the autograph method is larger than that of the cathode spots by approximately the same factor. Moreover, the anode voltage drop is also considerably higher than the cathode one; therefore, the energy released at the anode should be greater [60]. Analysis of the experimental data shows that the specific erosion depends both on the discharge current and the average working gas temperature.

Figure 1.30. Specific erosion of the cathode materials versus the discharge current.

Figure 1.30 shows the specific erosion of various cathode materials versus the discharge current amplitude. It is seen that all the dependences are ascending and that W + Ni + Cu pseudo alloy possesses the highest erosion resistance while the erosion resistance of aluminum is lowest. However, an advantage of D16 aluminum alloy (in contrast to, e.g., copper and steel) is that it is not deposited on the inner surface of the accelerator channel wall. Therefore, it can be used as a cathode material in experiments in which ultra high launch velocities are not required. Figure 1.31 shows the specific erosion of anodes made of steel, copper, tungsten, W + Ni + Fe pseudo alloy, and W + Ni + Cu pseudo alloy versus the current amplitude. Here, similarly to Fig. 1.30, the dependences are also ascending, and steel possesses the lowest erosion resistance (in these experiments, aluminum was not used as the anode material). The use of steel is reasonable when the average temperature of the working gas exceeds the boiling temperature of steel (3000 K). In some experiments, we used anodes made of L62 brass; however, since the specific erosion of brass anodes turned out to be too high (about 180 mg/Coul), we did not use such anodes even with inserts made of W + Ni + Fe pseudo alloy.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

36

Philip Rutberg

Figure 1.31. Specific erosion of the anode materials versus the discharge current.

The mass–average temperature of the working–gas in the range 1000–4500K significantly affects the physical and chemical properties of the electrode materials, including their specific erosion. Figure 1.32 shows the specific erosion of cathodes made of aluminum, steel, molybdenum, W + Ni + Fe pseudo alloy, Mo + W + Cu pseudo alloy, and W +

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Ni + Cu pseudo alloy versus the average temperature of the working gas.

Figure 1.32. Specific erosion of the cathode materials versus the average gas temperature.

Figure 1.33 shows the specific erosion of anodes made of steel, copper, W + Ni + Fe, W + Ni + Cu, and Mo + W + Cu pseudo alloys as well as of anodes covered with plasma– deposited tungsten and its mixture with carbon versus the average temperature of the working gas.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

37

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.33. Specific erosion of the anode materials versus the average gas temperature.

As seen from the above figures, in all four groups of dependences the tungsten– containing alloys possess the highest erosion resistance while aluminum, steel, and copper possess the lowest erosion resistance. In all cases, the dependences of the specific erosion versus the current and working gas temperature are nearly linear. It should be noted that the degree to which the gas temperature affects the specific erosion is different for anodes and cathodes. Thus, the average specific erosion for all the cathode materials in the temperature range under study increases approximately by 2.5–3.5, while for the anode materials it increases by 3–5. In our opinion, this difference may be caused by the intense thermal impact of the high temperature gas flow escaping from the discharge chamber onto the anode, since the latter is placed at the nozzle part of the discharge chamber, while the cathode is placed at the bottom of the discharge chamber and is practically not subjected to the thermal impact exerted by the gas flow. Thus, the basic processes governing the erosion of the electrodes in our experiments are the ejection of the electrode material from the melting pools and its evaporation. Due to the high density of the energy flux (up to 10s W/cm2), the melting pool with a diameter close to the diameter of the arc spot is formed in several microseconds [61]. Ejection of the melt begins after the Ampere force (balancing the gas–dynamic pressure in the melting pool) ceases to act on the surface of the molten metal due to the displacement of the arc spot along the electrode surface [2, 4]. Estimates show that at a current of 0.7 MA, a current pulse duration of 1 ms and an arc spot diameter of ~2 cm, the depth to which the cathode material is molten is about 1.5 mm [61]. This corresponds to a specific tungsten erosion of 10 mg/Coul, which agrees well with the experimental data (Fig. 1.35). Moreover, under small inter–electrode gaps (QJ, then the channel loses energy and contracts. Therefore, the condition of the beginning of the channel contraction is in satisfaction of the inequality

r 2 ni f (T ) ≥ 5.7 ⋅ 1014 .

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

From this relation,

r 2 ni f (T ) = 5.7 ⋅ 1014 , the value T was defined, by which using

equation (1.9), the critical value of the current jcr was found. The results of calculations of jcr for various conditions are presented in Table 1.3. In the table, the value of this current is compared with the experimental value je, under which the contraction of the channel begins. The darkening of the discharge begins 10–15 μsec earlier than the contraction. For this interval, the arc temperature increases up to ~4×105 K, but the brightness temperature at the wave length 694 nm decreases to ~ 2×104 K. Table 1.3. Calculation of the arc parameters

Environment

Initial pressure, MPa

NIR2, cm–3

T, eV

jcr, kA

H2

30

1018

40

659

H2

30

3×1018

39

1120

6 21

18

23 62

750 1025

H2 He

3×10 3×1018

je, kA 775 (in 10 μsec) 1200 (in 10 μsec) 700 770, 1050

As a consequence of the beginning of the radial contraction, the fast growth of the temperatures begins. Until this instant, the third equation of system ((1.9) already is not satisfied πr2qf(t)>jE), and for estimation of the channel temperature the results of the Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

50

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

calculations from [37] were used. Under this, the temperature of the discharge channel is 3×106 K. In our opinion, the decrease of the brightness of the discharge channel during its compression, which is observed in the visible part of the spectrum, is joined with the appearance of the absorption layer (as a result of its heating by the soft X–ray radiation) surrounding the channel. The brightness of the channel decreases after achieving the maximum, but further remains at the constant level that corresponds to brightness temperature Тbr= (10–15)×103 K. This means that the transient zone heated by the soft X–ray radiation glows itself, but the radiation from the discharge channel is completely absorbed. The presence of the soft X–ray radiation from discharge channel had been registered by the semiconductor sensors. In Fig. 1.44 the data on registration of X–ray radiation from discharge channel under the initial pressure of the hydrogen 5 MPa are presented. The preliminary estimates show that the energy of the registered quanta must be about 370 eV and larger.

Figure 1.44. Discharge in hydrogen under the initial pressure 6 MPa; the dependencies of the X–ray signal at the channel center, the brightness temperature at the wavelength 694 nm (Tbr) at the channel center, the current (j), and the voltage (V) versus the time are given; steel electrodes with a diameter of 20 mm were used; the between–electrode gap was 10 mm.

The results of investigations of pulse arcs in the wide range of parameters are presented. The velocities of the energy imbedding, the type of gas, its initial density, and the geometry of the discharge chamber have the largest influence on the discharge characteristics. The most essential factor affecting the properties of the discharge is the current increase rate dj/dt, and the results of the investigations are systematized by this parameter. For dj/dt ≥ 1010 A/sec, the discharge is followed by the creation of a strong shock wave. Under this, the pressure in the discharge essentially differs from the outer pressure in the discharge chamber, and the thermal transfer in the plasma is realized by the radiation thermal conductivity. Under comparatively small velocities of the energy imbedding, the current increase rate is dj/dt ≤ 108 A/sec, the amplitude of the shock waves is not large, and the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

51

pressure in the discharge at each instant approximately coincides with the pressure in the chamber. The thermal tapping from the arc is determined by the turbulent thermal conductivity of the gas and by the radiation going out free from the discharge. The near–electrode domains in the high current arcs are the sources of the high speed jets of the plasma. These jets significantly change the parameters of the discharge itself and essentially change the heat exchange in the volume, the character of the gas motion, and the erosion of the electrodes. The regime of contraction on the stage of the current growth had been registered; this regime is joined with the achievement of the critical Pizza–Braginskii value of the current. The critical current, under which the contraction of the discharge channel begins, has a value of 100–200 kA in the vacuum. In the discharges with the initial pressure of 5–30 MPa, this value increases up to ~1 MA. This is stipulated by decreasing the radiation losses which are caused by the radiation absorption in the transient layer of the hydrogen or helium. The increase in the critical current is also a consequence of the growth of the number of ions of the metal in the channel cross–section. The presence of the dense envelope from the gas surrounding the channel allows one to regulate the arc parameters by choosing the type of the gas and by changing the value of its initial pressure [81].

10. WORKING CHARACTERISTICS OF LARGE CURRENT DISCHARGES IN PULSE GENERATORS OF DENSE PLASMA

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The working parameters of the pulse plasmatrons and some properties of the large current discharges under consideration can be estimated on the basis of the obtained dependencies of the outer parameters [29].

Figure 1.45. The electric field strength versus the initial pressure of the hydrogen; 1 and 3 – the maximal strength for electrodes of W and Cu; 2 and 4 – the average strength through the half–period for electrodes of W and Cu.

In the discharge chambers with the rod electrodes under the conditions of contracted discharge, the dependencies of the electric field in the discharge column have been obtained versus the initial pressure in the chamber for the tungsten and copper electrodes. Moreover, the curves both of the maximal values of the electric field strength and its average value Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

52

Philip Rutberg

through the first half–period are given in Fig. 1.45. As seen, the strength slowly increases as the initial pressure increases which, apparently can be explained by the more effective heat exchange between the arc and the working gas. Greater strength under using the tungsten electrodes is explained by the smaller quantity of the ionized atoms.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.46. Dynamic volt–ampere characteristics of the discharge in the plasmatron IPM–3.

Figure 1.47. The final pressure versus the initial density; j = 270 kA; Ubat = 4 kV; the working gas is hydrogen; 1 – the maximal pressure; 2 – the pressure on the plateau.

Typical dynamic volt–ampere characteristics for various values of the initial pressure are given in Fig. 1.46. Since in the considered case the charge is contracted and the cross–section of the discharge channel is limited, the conductivity is proportional to Т2/3 under the conditions of complete ionization and, consequently, the current density and conductivity must increase. This fact stipulates the rising character of the volt–ampere characteristics. The

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

53

decrease of the resistance in the back parts of the characteristics is joined with the decay of the discharge channel and, consequently, with the decrease of the current density.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.48. Enthalpy (1) and the average mass–temperature (2) in the discharge chamber versus the initial density; the working gas is hydrogen.

Dependencies of the maximal pressure and the pressure on the plateau measured near the chamber wall versus the initial density are presented in Fig. 1.47. The growth observed under increase of the initial density is joined with more effective absorption of the gas energy. Compensation the heat losses is realized due to the flowing current of the discharge. In comparison with the maximum, the slow increase of the pressure on the plateau is defined by the growth of the heat losses on the wall as the density increases and, also, by the fact that the discharge current decreases until this instant. Dependencies of the enthalpy and the mass–average temperature in the discharge chamber versus the initial density are presented in Fig. 1.48. The enthalpy is found by the initial density and the final pressure, but the temperature is calculated according to the tables from [82]. The enthalpy decrease under the growth of the initial density in a close volume is joined with the fact that the energy desorbed in the chamber grows nore slowly than the gas mass, but the temperature fall is determined by the enthalpy decrease. In chambers with cylindrical electrodes where the processes are prolonged, the rates of the current and column temperature increase are significantly smaller. In Fig. 1.49, the typical dynamic volt–ampere characteristics in the plasmatron chamber are shown for various gases under feeding from a capacitor battery. It is seen that the characteristics are falling. If to take into account the comparatively low temperature (6– 14)×103 K) of the discharge column (which is stipulated by a slow imbedding of the energy), the conductivity grows as the current and the temperature increase; and this determines the form of the characteristics. The dependence of the average effective voltage on the arc versus the maximal value of the current has the same character (Fig. 1.50). It is necessary to note that the maximal value of the current under feeding from the shock generator achieved 300 kA and, under this, the hydrogen density was 4.1 kg/m3, and the average voltage drop on the arc was 8.5 kV.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

54

Philip Rutberg

Figure 1.49. Dynamic volt–ampere characteristics of the discharge in the plasmatron in various gases; 1– argon; 2 – helium; 3 – nitrogen; and 4 – hydrogen; the initial pressure is 1 MPa.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

But when the Coulomb interactions begin to prevail (which depends on the current increase) and, also, under appearance of significant impurities of the electrodes’ material W and La (which determines the electron concentration in the discharge), the character of the dependence changes and the voltage grows as the current increases. Under feeding from the electro–machine source when the energy delivering is slowest, the impurities appear earlier, and the electron concentration at the process beginning achieves significant value. In this case, the volt–ampere characteristics are presented in Figure 1.50 below.

Figure 1.50. Dependence of the average voltage drop versus the maximum current; the working gas is hydrogen; a) the feeding source is a capacitor battery: 1 – current density ρ ≈ 0.83 kg/m3, length of charge column l = 10 cm; 2 – ρ ≈ 0.6 kg/m3, l = 17 cm; 3 – ρ ≈ 0.9 kg/m3, l = 5 cm; 4 – ρ ≈ 0.44 kg/m3, l = 10 cm; b) the feeding source is a shock generator: l = 18 cm, 1 – ρ ≈ 0.92 kg/m3; 2 – ρ ≈ 3.27 kg/m3; 3 – ρ ≈ 1.62 kg/m3

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

55

The variation of the volt–ampere characteristics is worthy to be considered in detail also in the case of energy feeding from the inductive condenser. In reality, the process goes under the stationary current, and the time of the pressure leveling is smaller that in the gas– dynamic time (~10–3 sec). The process can be regarded as quasi–stationary on the pressure, i.e., the pressure becomes even through the cross–section of the discharge chamber. Under conditions of the discharge in nitrogen (T ≈ (10–12)×103 К, ρ ≈ 80 MPa), the molecules dissociate completely. It is assumed that the total energy of the electric field is transferred into electron gas which, in turn, transfers one part of the energy to the gas of the heavy particles by means of collisions, and the rest of the energy is spent for the radiation. The electron heat–capacity can be neglected in calculations, since it is small under conditions of the large current discharges and large density [35]. Keeping in the mind that the light diameter of the discharge is close to the chamber diameter (in the ranges of the parameters under consideration), the problem can be simplified. To the same simplification, some arguments (following from consideration of the equilibrium levels) lead, which show that the main portion of the energy desorbing from the discharge is given off in the narrow near–wall zone. From this it follows that the temperature in the discharge zone scarcely varies along the radius, but in the near–wall zone it decreases linearly to the wall temperature TR. Then, practically all current passes through the discharge zone. So, assuming that the field is homogeneous and the gas density is constant through the cross– section, we can write

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

I= πRo2 σee,

(1.10)

where I is the current; Ro is the discharge radius; σe is the conductivity; and E is the strength of the electric field. Then, under constant Ro, the form of the volt–ampere characteristic is wholly determined by the conductivity (Figs. 1.50 and 1.51).

Figure 1.51. Volt–ampere characteristics of the discharge in the nitrogen under feeding from the inductive condenser; the initial pressure is of 2 MPa; the discharge gap is 18 cm; the circles are from the experiment; the lines are from theoretical calculations; 1 – R = 2 cm, Т0 = 10000 К; 2 – R = 2 cm, Т0 = 12000 К; 3 – R = 2.5 cm, Т0 = 10000 К. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

56

Philip Rutberg

Taking into account considered characteristics, it is possible to estimate the main parameters of the discharge that are interesting in the design of the pulse plasmatrons. It is worthy to give several additional dependences that characterize the working parameters of the pulse plasmatrons IMPP–1, IMPP–2. Dependence of the voltage drop versus the length of the discharge gap in nitrogen under the fixed initial pressure and the constant current from the inductive condenser is shown in Fig. 1.52. As seen here, the near– electrode voltage drop is similar to the voltage drop under the large currents, in this case of feeding from the capacitor battery.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.52. Dependence of the voltage drop on the discharge gap under feeding from the inductive condenser; the working gas is nitrogen; the initial pressure is 2 MPa; the current is j = 45 kA.

In Fig. 1.53, dependences of the effective voltage on the arc versus the initial density of the working gas are given for various values of the current and under feeding from the capacitor battery and from the shock generator and, also, dependence of the electric field strength versus the initial density under fixed values of the current and length of the inter– electrode gap is given for the case of feeding from the inductive condenser (Fig. 1.54). As seen, the voltage grows as the density increases; and the character of variation is maintained independently of the type of the power source, i.e., independently of the rate of the energy imbedding into the discharge.

Figure 1.53. Dependence of the average voltage drop versus the density in the plasmatron IMPP–2; the working gas is hydrogen; a) the feeding source is the capacitor battery: 1 – jav ≈ 84 kA, l = 5 cm; 2 – jav ≈ 76 kA, l = 10 cm; 3 – jav ≈ 36 kA, l = 17 cm; 4 – jav ≈ 70 kA, l = 17 cm; b) the feeding source is the shock generator: 1 – jav ≈ 37 kA, l = 18 с cm; 2 – jav ≈ 105 kA, l = 18 cm.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

57

Actually, the effectiveness of the energy absorption by the working gas increases which, in the turn, leads to the growth of the voltage on the arc. The dependences of the enthalpy, the specific power, and the efficiency of the energy transfer from the arc into the working gas versus other parameters of the discharge are very essential. Figure 1.54 shows dependence of the electric field strength versus the initial pressure in the discharge chamber; the working gas is nitrogen.

Figure 1.54. Dependence of the electric field strength versus the initial pressure in the discharge chamber; the working gas is nitrogen; l = 18 cm; j=45 kA.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.55 shows the dependences of the enthalpy versus the effecting current under feeding from the capacitor batteries and the shock generator.

Figure 1.55. Dependence of the enthalpy versus the effective current; the working gas is hydrogen; 1 – the feeding source is the shock generator: l = 20 cm, ρ = 3 kg/m3; 2–4 – the feeding source is the capacitor battery: 2 – l = 10 cm, ρ = 0.6 kg/m3; 3 – l = 10 cm, ρ = 0.8 kg/m3; 4 – l = 15 cm, ρ = 0.6 kg/m3

Figure 1.56 shows dependences of the specific power versus the effective current for different gas density and gaps between electrodes the working gas is hydrogen. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

58

Figure 1.56. Dependence of the specific power versus the effective current; the working gas is hydrogen; 1–3 – the feeding source is the shock generator; the discharge gap is l = 20 cm: 1 – ρ = 1.0 kg/m3; 2 – ρ = 1.5 kg/m3; 3 – ρ = 3.0 kg/m3; 4–5 – the feeding source is the capacitor battery: 4 – ρ = 0.7 kg/m3, l = 10 cm; 5 – ρ = 0.7 kg/m3, l = 17 cm.

It is very interesting to consider dependence of the efficiency versus the specific energy (Fig. 1.57) and the dependence of the enthalpy versus the specific energy; the working gas is hydrogen (Fig. 1.58) under various numbers of parameter A (1.11). To estimate the influence of the geometric parameters of the discharge chamber and the time of heating on the heat losses [83], it is advisable to use the following parameter:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

A = St2 /V,

(1.11)

where t2 is the time of the discharge burning until the diaphragm’s opening; S is the square of the inner surface of the discharge chamber; V is the chamber volume; A is the energy loss decrease. The efficiency of the chamber with smaller A is larger than for the chamber with the larger A.

Figure 1.57. Dependence of the efficiency versus the specific energy; the working gas is hydrogen; 1 – the feeding source is the capacitor battery, Аt = (0.7–1.1)×10–3 sec/cm; 2–4 – the feeding source is the shock generator, 2 – Аt = (2–3)×10–3 sec/cm; 3 – Аt = (3–4)×10–3 sec/cm; 4 – Аt = (6–8)×10–3 sec/cm. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

59

Figure 1.58. Dependence of the enthalpy versus the specific energy; the working gas is hydrogen; 1 – the feeding source is the capacitor battery, Аt = (0.5–1)×10–3 sec/cm; 2–4 – the feeding source is the shock generator, 2 – Аt = (2–3)×10–3 sec/cm; 3 – Аt = (6–8)×10–3 sec/cm; 4 – Аt = (9–10)×10–3 sec/cm.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.59 shows dependence of the energy transfer from the arc into the gas; the working gas is nitrogen; the feeding source is the inductive condenser, namely under DC.

Figure 1.59. Dependence of the energy transfer from the arc into the gas; the working gas is nitrogen; the feeding source is the inductive condenser; l = 18 cm; 1) I = 45 кA; 2) p = 3 MPa.

It is evident that the growth of the current leads to increase of the specific power. And under this, in using both the capacitor battery and the shock generator, the increase of the specific power is larger as the initial density of the gas is larger. This can be also explained by more effective absorption of the energy by the working gas as the density increases, and, also, by the relative decrease of the quantity of impurities in the discharge chamber. To estimate the influence of the geometric sizes of the discharge chamber and the time of the heating on heat losses, it is advisable to use the parameter А (see formula (1.11)). As seen from Fig. 1.57, the efficiency for the conditions corresponding to Аt1 is higher than for Аt2, and for the conditions corresponding to Аt3 efficiency is higher than for Аt4. The same character of variation has the dependence of the enthalpy versus the specific energy imbedding for various values of Аt. For the discharge in nitrogen under feeding from the inductive condenser, the increase in the efficiency is also observed as the initial density and current grow. The efficiency growth is also observed as the length of the discharge gap grows. It is worthy to note that for the discharge in hydrogen and under the increase of the inter–electrode gap larger than 8–10 cm (under the currents up to 80 kA and the initial pressure 0.6–1 MPa), a small decrease in the efficiency is observed; under extension of the discharge gap up to 20 cm, the efficiency falls

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

60

Philip Rutberg

by 10–15%. This phenomenon can be explained by the fact that for the discharge in hydrogen the turbulent heat exchange between the arc and the gas plays the main role, but the turbulence is more developed under the smaller length of the discharge gap and under the larger initial pressure of the hydrogen. Similar phenomena are also present in the discharge in helium where the degree of the turbulence is also large; but in discharges in nitrogen and argon, the turbulence is weak or absent, and the heat exchange by radiation plays the main role. Thus, it is possible to conclude that for the discharge in hydrogen, it is advisable to increase the inter–electrode gap larger than 10 cm, but for the discharge in nitrogen and argon, a high efficiency can be achieved for the gap length of 25–32 cm.

11. PULSE PLASMA GENERATORS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

11.1 Pulse Electric Arc Plasma Generators High current electric arc units (pulse plasma generators) hold great interest. They can be used for obtaining plasma flow with large enthalpy and a high level of energy. If the shock tube is used as the first stage, such generators can create a plasma flow of very high purity. Moreover, they can be used as an element (a unit) of the electric discharge light–gas busters for acceleration of bodies [84, 85]. Such a generator is comprised of a discharge chamber filled with a working gas with a given initial pressure and separated by a diaphragm from a low–pressure chamber. Between the electrodes placed in the discharge chamber, the electric discharge is initiated by the ignition wire or some other way. As a result of the energy feeding from the supply source into the gas, its temperature and pressure increase in the discharge chamber, and, as the consequence, the diaphragm is broken and the expanding gas flow obtains a high velocity. For obtaining a hyper–sound flows, the aggregation of the electric arc generator with a shock generator is optimal. Under this, the electric arc discharge is used for heating the pushing gas until the instant of the diaphragm blow–up; the diaphragm isolates the gas to be pushed from the electric and gas– dynamic influences. The velocity in the gas plug is determined by the sound velocity in the pushing gas–plug under its temperature. It is advisable to use light gases as the pushing body, in particular, hydrogen and helium. But due to difficulties of the stabilization of the arc burning and large heat flows onto the walls of the discharge chamber and onto the electrodes, it is rather difficult to use hydrogen as the working body. Only a small number of constructions are known that work with hydrogen, and designed for comparatively low energy levels. The units of such a kind can be classified by: the type of working gas, the value of the energy imbedding, the pressure, and so on. The most advisable classification seems to be that realized by the constructive features; and the most common characteristics include the form and location of the electrodes which mainly determine the character of the discharge processes and the heat exchange. By these features, the electric arc heaters can be divided into four types, and each of them has its own constructive and exploitation advantages and drawbacks (Fig. 1.60).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

61

Figure 1.60. Schemes of the electric arc plasmatrons: a) with the co–axial electrode; b) with the self– stabilizing length of the arc; c) with two rod electrodes; d) with the ring and rod electrodes; 1 – the electrode; 2 – the ignition wire; 3 – the isolator; 4 – the electric protecting liner; 5 – the electrode–liner; 6 – the nozzle unit; 7 – the diaphragms; 8 – the protecting plate.

11.2 Pulse Electric Arc Plasma Generators with Co–Axial Electrodes

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Units of this type (Fig 1.61) are comprised of a steel cylindrical discharge chamber into which the co–axial electrode assembly is inserted through the frontal flange. The assembly is comprised of central and outer electrodes isolated each from other and, also, from the hull of the discharge chamber and the ignition trigger device that initiates the discharge at the initial instant. After the ignition, the arc burns between the central and outer electrodes.

Figure 1.61. The discharge chamber [83]; 1 – the protector; 2 – the electrodes; 3 – the protecting plate; 4 – the diaphragms; 5 – the nozzle unit.

The inner surface of the discharge chamber is protected from the influence of high temperature by the protecting liner. The gas flows out the discharge chamber through the nozzle arranged in the back flange, and by this, a flow with a high velocity is created. In some designs, to protect the gas from contamination by the products of erosion of the electrodes and liner, a protecting screen is arranged at the front of the nozzle.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

62

Philip Rutberg

Typical examples of this group are the electric arc chamber of the shock tube Hotshot– 1 [86], the discharge chamber of the tube [83], and the discharge chamber of the hypersonic pulse aerodynamic tube MAC designed by the McDonnel company [87, 88, 89]. The pulse electric arc plasmatrons with the self–stabilizing length of the arc have a central electrode–liner. The discharge in the systems of such a type (Fig. 1.62) burns between the outer electrode of the co–axial electrode assembly and the electrode–liner that is isolated from the metal wall of the discharge chamber. The arc length can vary since the arc moves along the surface of the electrode–liner. The arc ignition is realized by the explosive fuse arranged between the inner and outer electrodes of the electrode assembly or by the ignition wire between the rod electrode and the electrode–liner.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.62. Discharge chamber 50–М [82]; 1 – the isolator; 2 – the fuse; 3 – the electrode; 4 – the electrode–liner; % – the nozzle unit; 6 – the diaphragm; 7 – the hull of the nozzle unit; 8 – the protecting plate; 9 – the hull of the electrodes’ unit.

Typical systems of such a type are the discharge chambers 50–О and 50–ОМ in the Hotshot–2 plant [83], the plant Tunnel–F [83], and others [90, 91]. The co–axial conic discharge chamber can be classified ny this type of plant [92]. This discharge chamber is implemented in the form of the steel conic hull with a central conic aluminum electrode arranged with a graphite tip and outer ring electrode, the inner surface of which is made of stainless steel. The discharge chamber is separated from the tube with gas pushed by the diaphragm.

11.3 Pulse Plasma Generators with Two Rod Electrodes Two rod electrodes are inserted into the discharge chamber one against the other in the radial or co–axial positions; the electrodes are isolated from the walls of the discharge chamber (Fig. 1.63).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

63

Figure 1.63. Discharge chamber 8A [86]: 1 – the valve; 2 – the electrodes; 3 – the diaphragm; 4 – the nozzle; 5 – the trigger (the initiating unit); 6 – the liner.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

For ignition of the arc, the electrodes are connected by the ignition wire. From influence of high temperatures, the chamber is protected by the changeable dielectric liner. The advantages of constructions of this type are the following: • • • •

the high dielectric speed of isolation; the simplicity of the arc stabilization stipulated by the small inter–electrode gap; the relative simplicity of introducing and changing the electrodes; the simplicity of manufacturing the discharge chamber.

• • • •

The chamber has the following drawbacks: the relatively small voltage drop on the arc; the poor heat exchange between the arc and the gas; the low efficiency (as a result of the small length of the arc); the tense regime of the electrodes work (the high density of the current).

Application of plants of such a type is advisable with a small volume- discharge chamber, relatively small energy imbedding, and short time length of the discharge (0.5–3 msec). The most powerful systems of such a type are the discharge chambers of the aerodynamic tubes 8А and 16А [86], and the arc chamber of the pulse tube (ARC–1) ONERA [93]. In the discharge chamber in [93], the problem of the isolating liner is solved originally; it is comprised of several layers: the inner enameled cuff, the layer of the isolating material, and the outer steel sleeve.

11.4 Pulse Electric Arc Plasmatrons with Co–Axial Rod Electrodes These systems are the most widely used design of the pulse plasmatrons (Fig. 1.64).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

64

Figure 1.64. Improved discharge chamber [94]; 1 – the electrode; 2 – the diaphragm; 3 – the ignition wire.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The rod electrode is inserted into the discharge chamber through the butt–end flange. The electrode is sealed and isolated from the chamber walls. The ring electrode is placed at the outlet of the discharge chamber. The inner surface of the chamber is isolated by the liner made of a dielectric material. The ignition wire is fixed between the electrodes; in some cases the wire has a spiral form. The explosive diaphragm is placed after the ring electrode at the outlet of the discharge chamber. The discharge chamber is implemented either in the form of the cylinder, or in the form of the truncated cone with bases of different radii which allows better agreement with the low pressure of the chamber. This construction has the following advantages: • • •

• •

the large voltage drop on the arc due to its significant length; the large energy imbedding; the good heat exchange between the arc and the gas, since the arc occupies the main part of the discharge chamber volume. The drawbacks of this construction are: the difficult ignition and stabilization of the arc; the significant heat flow onto the walls of the discharge chamber due to the large length of the arc.

The latter drawback can be partially eliminated by changing the discharge chamber geometry (by increasing the inner diameter of the chamber under the same volume). Constructions of this type are advisable to use with a large-volume discharge chamber, thousands of cubic centimeters, significant energy imbedding, and a relatively long time of discharge (up to tens of milliseconds) [95–108]. The electric discharge chambers with a low density of energy are used to increase the time of the gas outflow [29].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

65

In this type of electric arc plasmatrons, the plants can be classified into those that have ring or rod electrodes separated by diaphragms, which are opened at the discharge ignition, and the rod electrode is overblown by the flow of the working gas [100]. The density of the gas in the discharge chamber decreases after the diaphragm’s opening. This type of chamber is used in accelerators. In Saint Petersburg (Russia), a row of pulse plasmatrons of various types was created for work under various levels of pulse pressure and energy imbedded into the arc using hydrogen, helium, argon, and nitrogen as the working gas. These plasmatrons have the following main parameters: the power is 200–6500 MW; the currents are 0.3–2.5 MA; the energy imbedding is 0.1–10 MJ; the pulse pressure is 70–650 MPa; and the average mass temperature of the plasma is (4–20)×103 K [29,84].

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

11.5 Pulse Plasma Generators and the Electric Discharge Light–Gas Accelerators of Bodies The method for gas heating by means of a power pulse electric arc and the plants designed on basis are widely known. Thus, during the 1950s, at the Arnold Engineering Development Center (Tullahoma, Tennessee, USA), several aerodynamic tubes were built in which the electric arc heaters (the plasmatrons) were used as gas sources. In these plasmatrons, the capacitor batteries and the shock generators were used as the power sources [41, 108]. There, the first light–gas accelerator was created which accelerate bodies with a mass of 3.8 g up to a velocity of 3000 m/sec. Later, analogical plants were built at the French–German Research Institute (Saint–Lois, France), in IEE of RAS (Saint Petersburg, Russia) [109–112], and by the firm GT–Devices Inc. (Alexandria, Virginia, USA) [113]. Aside from the peculiarities of constructions of the electric discharge accelerators, the processes occurring in the discharge chambers are common for accelerators of all types. It was established that the multi–pulse regime is the most effective to transfer the energy of the electric arc into the internal energy of the gas. This regime is characterized by the multi– breaks of the inter–electrode gap with the consecutive creation of the arc. The velocity of motion of the arc fore frontier, which moves in a cool gas, is about 1500 m/sec, and 3000–4000 m/sec in heated gas. The products of the electrodes’ erosion, which are in the vapor state, compose a gas mixture with hydrogen, in which the sound velocity is lower the higher the concentration of metal atoms, i.e., the higher the molecular mass of the gas mixture. The molecular mass μmix of the gas mixture is calculated taking into account the fact that approximately 20% of the eroded metal is in the vapor phase: n

μmix = 1/ Σ gi/μi,

(1.12)

gi = Мi / Мmix,

(1.13)

i

where gi are the mass parts of the mixture; Мi and Мmix are the mass of the i–th component and the mass of the whole mixture; and μi is the molecular mass of the i–th component. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

66

Philip Rutberg

Dependence of the molecular mass of the gas mixture versus the ratio of the mass of pure hydrogen to the mass of the metal eroded from the electrodes is shown in Fig. 1.65.

Figure 1.65. Molecular mass of the working gas versus the ratio of the mass of pure hydrogen to the mass of the metal eroded from the electrodes.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

As seen from this figure, the values of the molecular mass of the gas mixture are in limits from 2.05 amu (which corresponds to the value of the molecular mass of the practically pure hydrogen) to 3.4 amu (which is a little smaller of the atomic mass of helium). The statistically mean value of the molecular mass of the working gas is equal to 2.5 amu. Thus, for the mean–statistical experiment, this parameter of the working gas is of 25% higher than the molecular mass of pure hydrogen. Dependencies of the sound velocity in pure hydrogen and under its contamination by the products of the electrodes’ erosion versus the mass–average temperature are presented in Fig. 1.66.

. Figure 1.66. Sound velocity in pure hydrogen and in the working gas versus the temperature; 1 – the pure hydrogen; 2 – the working gas (the mixture).

The following fact draws attention. In Fig. 1.66, the curve for pure hydrogen (1) and the majority of the points belonging to the curve of the working gas (2) practically coincide in the temperature range up to 2000 K. But further, the curve of the working gas (2) goes Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Processes in High Current Discharges in Dense and Super Dense Gas Environments

67

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

slightly below, and the degree of its deviation grows as the temperature increases. It is joined with the fact that in calculation of the molecular mass of the working gas (as a mixture of hydrogen with the atoms of the metal), the part of the vapor–wise fraction in the total mass of the eroded metal was assumed to be equal to 20% without taking into account its growth as the gas temperature increases. But, as seen, such dependence exists, and it must be taken into account under high temperatures. This dependence is stipulated by the increase of the metal mass, which is in the vapor state under the mass–average gas temperatures exceeding the temperature of melting the electrodes’ metal. A typical example of electric discharge accelerator is one built in the IEE RAS (Russia) [5, 6, 7]. A sketch of the discharge chamber of an accelerator is presented in Fig. 1.67 and an exterior view of the stand of the light–gas accelerator in Fig 1.68. Here, the discharge chamber of the co–axial type has an easily–removed electrode assembly (2, 3, and 8), which is placed in the holder (16). This construction simplifies the plant servicing and increases the lifetime of the basic elements of the accelerator (1).

Figure 1.67. Discharge chamber of the accelerator; 1 –the hull; 2 – the cathode; 3 – the body to be accelerated; 4 – the diaphragm; 5 – the isolation of the electrodes’ holder; 6 – the sealing rings; 7 – the ignition element; 8 – the anode insert; 9 – the changeable input sleeve of the barrel; 10 – the fixing nut; 11 – the ring for the holder removing; 12 – the lock; 13 – the electrodes mount; 14 – the isolating insert; 15 – the nut; 16 – the electrodes holder; 17 – the bandage; 18 – the protecting ring; 19 – the nut of the diaphragm; 20 – the supporting insert.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

68

Figure 1.68. Exterior of the stand of the light–gas accelerators.

Velocity, m/s

From the beginning of experiments and until now, this accelerator has the world’s best mass–velocity characteristics (the ratio of the accelerated body and its velocity) among plants of this type. With some changes and improvements, the accelerator has been in use for more than ten years implementing experiments. In Fig. 1.69, the graph of dependencies of the casting velocity of the bodies versus their masses is shown for the internal energy of the gas from 0.2 MJ up to 2.0 MJ. 6000 5500

0,2 - 0,5 MJ 0,5 - 1,0 MJ 1,0 - 2,0 MJ

5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0

0

50

100

150

200

250

300

350

Mass, g

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 1.69. Velocity of the bodies casting velocity versus their masses.

The curves are drawn on the basis of the data from more that 200 experiments carried out on the accelerator with volume of the discharge chamber from 0.5 dm3 up to 1.5 dm3 and under the initial pressure of hydrogen from 10 MPa up to 42 MPa [114]. For this electric light–gas accelerator, the efficiency η (written in percentages) is determined as the product of three coefficients:

η= ηe ηT ηk × 100, where ηe is the ratio of the electric energy imbedded into the arc to the energy accumulated in the power source; ηT is the ratio of increment of the internal energy to the energy imbedded into the arc; and ηk is the ration of the kinetic energy of the accelerated body to the internal energy of the working gas [115]. Dependence of the efficiency of the accelerator with a 4 meter length versus the velocity of the bodies’ casting drawn on the basis of the experimental data is shown in Fig. 1.70. The statistical mean value of the efficiency in the velocity range from 1000 m/sec up to 6000 m/sec is 6–19%, and in some experiments its value achieved 20– 28%.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Efficiency, %

Processes in High Current Discharges in Dense and Super Dense Gas Environments

69

25

20

15

10

5

0 1000

2000

3000

4000

5000

6000

Velocity, m/s

Figure 1.70. Dependence of the efficiency versus the velocity.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

12. CONCLUSION Thus, the factors have been determined that allow additional opportunity for increasing the effectiveness of the operation of electric discharge accelerators of bodies; the main factor is the initial pressure of the working gas. Accelerators have been designed and built to allow one to accelerate bodies of a mass of 0.3 g up to the velocity of ~9000 m/sec and mass of 300 g up to a velocity of ~2000 m/sec. These accelerators have a simple construction and high reliability. Analysis of the basic methods for casting bodies with high velocity, and comparison of these methods with the results of investigations of the pulse plasmatrons allow one to conclude that the application of plasmatrons as the discharge chambers of the electric discharge accelerators affords an opportunity to obtain the hydrogen parameters for accelerating the bodies with a mass of tens of grams up to velocities of 3000–6000 m/sec with efficiency up to 28%. Moreover, it is possible to conclude that the electric discharge methods for acceleration of bodies are competitive in comparison with any other method of acceleration.

REFERENCES [1] [2] [3]

Matzen, Keith M. Z Pinches as Intense X–ray Sources for High–energy Density Physics Applications; Phys. Plasmas, May 1997, vol. 4, No.5, pp. 1519–1527 Spielman, R. B.; Deeney, C.; Chandler, G. A. et al. Tungsten Wire–array Z–pinch Experiments at 200 TW and 2 MJ; Phys. Plasmas, May 1998, vol. 5, No. 5, pp. 2105– 2111 Vikhrev, V. V.; Korolev, V. D. Neutron Generation from Z–pinches; J Plasma Phys. Reports MAIK Nauka/Interperiodica distributed exclusively by Springer Science+Business Media LLC: M, 2007 v. 33 № 5 pp. 356–380

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

70 [4]

[5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

[15] [16] [17] [18] [19] [20] [21] [22]

Philip Rutberg Sethian, J. D.; Robson, A. E.; Gerber, K. A.; De Silva A. W. Enhanced Stability and Neutron Production in a Dense Z–Pinch Plasma Formed from a Frozen Deuterium Fiber; Phys. Rev. Lett., 1987, vol. 59, pp. 892–900. errata: Phys. Rev. Lett. 1987, vol. 59 p. 1790 Pikuz, S. A.; Shelkovenko, T. A.; Sinars, D. B.; Hammer, D. A. Time Characteristics of X–Radiation of X–Pinch; Fizika Plazmy; 2006, vol. 32 № 12 pp. 1106–1120. Remington, B. A. High Energy Density Laboratory Astrophysics; Plasma Phys. Control Fusion, 2005, vol. 47 pp. A191–A203 Ryutov, D. D.; Remington, B. A.; Robey, H. F.; Drake, R. P. Magnetohydrodynamic Scaling: From Astrophysics to the Laboratory; Phys. Plasmas, 2001, vol. 8, pp. 1804– 1816. Sipailov, G.A.; Khorkov, K.A. Surge Power Generators; Energiya: M., 1979, 127 p. (in Russian) Suits, C.G. Measurement of Some Arc Characteristics at 1000 Atmospheres Pressure; J.Appl.Phys.,1939, vol.10, No 3, pp.203–206. Allen, J.E.; Gracs, J.D. High Current Spark Channels; Brit.J.Appl. Phys.,1954, vol.5, No12, pp.446–453. Fischer,H. Simple Submicrosecond High Source with Extreme Brightness; J.Opt.Soc., 1957, vol.47, pp. 981–984. Borovik, E.S.; Mitin, R.B.; Knyazev, Yu.R. Long Arcs of High Pressure; Zh. Tekh. Fiz; Nauka: Leningrad, 1961, vol. 31, №11, pp. 1329–1336. (in Russian) Mitin, R.B. Stationary and Pulse Arcs of Superhigh Pressure and Their Diagnostic Methods; Properties of Low Temperature Plasma and Its Diagnostic Methods; Nauka: Novosibirsk, 1977, pp.105–138. (in Russian) Breusov, L.N. Longitudinal Gradient of Positive Column Potential in Н2 and D2; Zh. Tekh. Fiz; Nauka: Leningrad, 1969, vol.ХХХIV, issue 6, pp.1143–1145. (in Russian) Valkov, Yu.A.; Zbrailova, N.L.; Skvotsov, Yu.V. Magnetic Field and Plasma Density in the Gap of the Pulse Plasma Injector; Zh. Tekh. Fiz; Nauka: Leningrad, 1970, vol.XL, issue.4, pp.772–780. (in Russian) Osovets, S.M.; Pavlov, E.I.; Sinitsun, V.I. Development of Instability in Z–Pinch; J Experimental and Theoretical Physics, 1973, vol. 64, issue 4, pp. 1228–1236. (in Russian) Pushnov, A.V. Dependence of Parameters of the Quasistationary Discharge Stabilized by Discharge Walls of Current, Initial Pressure and Tube Radius; J Teplopfisica Vysokih Temperatur, 1978, vol. 16, №5, pp. 914–921. (in Russian) Giterman, B. P.; Zenkov, D.I.; Pavlovski, A.I.; Petrov, N.N.; Smirnov, E.N. Investigation of Power Quasistationary Discharge at Megaampere Currents; Zh. Tekh. Fiz; Nauka: Leningrad, 1982, vol. 52, issue 10, pp. 1983–1986. (in Russian) Leurg, W.B.; March, N.H. Resistivity of Structureless Hydrogen Plasma Dew to Weak Electron–ion Interaction; Plasma Phys.,1977. vol. 19. № 3, pp. 277–281. Braginsky, S.I. To the Theory of Development of the spark channel; J Experimental and Theoretical Physics, 1958, vol. 34, issue 6, pp.1548–1557. (in Russian) Sobolev, N.N. Research of Electric Explosion of Thin Wires; J Experimental and Theoretical Physics, 1947, vol.17, pp. 986–997. (in Russian) Vanuokov, M.P.; Isaenko, V.I.; Khazov, L.D. Research of the Light Phenomena Connected with Development of the Spark Channel; Zh. Tekh. Fiz; Nauka: Leningrad, 1973, vol. 64, issue 4, pp. 1245–1251. (in Russian)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Processes in High Current Discharges in Dense and Super Dense Gas Environments

71

[23] Basov, N.G.; Borovitch B.P.; Zuev, V.S., et al. High–Current Discharge in Gases, Part 1; Zh. Tekh. Fiz; Nauka: Leningrad, 1970, vol. XL, issue 3, pp.516–522. (in Russian) [24] Basov, N.G.; Borovitch B.P.; Zuev, V.S., et al. High–Current Discharge in Gases, Part 2; Zh. Tekh. Fiz; Nauka: Leningrad, issue 4, pp. 805–813. (in Russian) [25] Ivanov, A.A.; Parail, V.V.; Soboleva, T.K. Thermal Wave of Ionization in System with Current.; J Experimental and Theoretical Physics, 1973, vol.64, issue 4, pp. 1245– 1251. (in Russian) [26] Mullaney, G.J.; Ahistrom, H.G. Energy Transfer Mechanism in Shock Tube Arc–Heated Drivers; AIAAJ, 1969, vol. 7, No 7, pp. 1353–1356. [27] Mandell, D.A. Conduction, Convection and Radiation in a Nonisothermal Hydrogen Plasma; J Quant. Spectroscopy and Rad. Transfer, 1969, vol.9, pp. 1535–1562. [28] Kelley, I.G.; Levine, M.A.; Besse, A.L.; Tatarian, A. Evaluation of the Driver Chamber Efficiency of an Arc–Driven Shock Tube. Shock Tube Symposium; Phys. Fluids,Suppl., 1969, pp. 76–78. [29] Glebov, I. A.; Rutberg, Ph. G. High–Power Plasma Generators; Énergoatomizdat: M., 1985 [30] Geidon, A.; Girl, I. Shock Tube in the Chemical Physics of High Temperatures; tr. from Engl.; Mir: M, 1966, p.131. (in Russian) [31] Nealy, J.E. An Experimental Study of Ultraviolet Radiation Behind Incident Normal Shock Waves in CO2 at Venusian Entry Speed. – AISS Pap, 1975, No 1150, pp.1–12. [32] Antonov, G.G.; Borodin, V.S.; Zajcev, A.I.; Rutberg, Ph.G. Some Problems of Investigation of High–Current Discharge in the High–Pressure Chamber; Part 1; Zh. Tekh. Fiz; Nauka: Leningrad, 1972, vol. XLII, № 10, p. 2121–2126. (in Russian) [33] Bogomaz, A.A.; Borodin, V.S.; Zaitsev, A.I.; Rutberg, Ph.G. Some Problems of Investigation of High–Current Discharge in the High–Pressure Chamber; Part 2; Zh. Tekh. Fiz; Nauka: Leningrad, 1973, vol. XLIII, № 7, pp. 1507–1512. (in Russian) [34] Rutberg, Ph.G.; Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A.; Pinchuk, M.E. Some Results of Researches of Powerful Pulse Discharges in Dense Gas Media; online publication http://hal.archives–ouvertes.fr/hal–00003134/fr/ [35] Granovsky, V.P. Electric Current in a Gas. Steady Current; Nauka: M, 1971, 543 p. [36] Marshak, I.S.; Doinikov, A.S.; Zhiltsov, V.P.; et al. Pulse Light Sources. Ed. by Marshak, I.S.; Energiya: M, 1978, 472 p. (in Russian) [37] Azizov, E. A.; Bogomaz, A. A.; Levchenko, B. P.; Rutberg, Ph. G.; Yagnov, V. A. High–Current Discharge in Nitrogen with an Inductive Storage Bank; Technical Physics, (USA), Feb.1979, vol. 24, No. 2, pp. 255–256 [38] Ivanov, V.V.; Rozanov, A.G. About Discharge Pressure in a Pulse Tubular Lamp; J Teplofizika Vysokikh Temperatur; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.: M 1972,vol. 10, № 5, pp. 1102–1104. (in Russian) [39] Bogomaz, A.A.; Borodin, V.S.; Levchenko, B.P.; Rutberg, Ph. G. Investigation of the High–Current Discharge in Dense Plasma Generators; Zh. Tekh. Fiz; Nauka: Leningrad, 1977, vol. 47, № 1, pp. 121–133. (in Russian) [40] Levchenko, B.P.; Rutberg, Ph. G. Construction and Investigation of the Power Pulse Plasma Generators ; in book Generators of Plasma Jets and High–Current Arcs; Nauka: Leningrad, 1973, pp. 9–20. (in Russian) [41] Glebov, I. A.; Kasharsky, E.G.; Rutberg, Ph. G. Synchronous Generators in Electrophysical Installations; Lexinton Books, Printed in USA, N 0–669–05434–8, 1982, p. 186.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

72

Philip Rutberg

[42] Azizov, E.A.; Bogomaz, A.A.; Levchenko, B.P.; et al. High–Current Discharge in Nitrogen at Power Supply from Inductive Energy Storage; Zh. Tekh. Fiz; Nauka: Leningrad, 1979, vol XLIX, № 2, pp. 441–443. (in Russian) [43] Basset, J. Arcs Electriques Sous Tres Hauters Pressions Gazeuses. Electr. Compt. Rend, 1942,vol.114, No 15, p. 715–716. (in French) [44] Rutberg, Ph. G.; Bogomaz, A. A.; Budin, A. V.; Kolikov, V. A.; Kuprin, A. G. Heating of the Gas with High Initial Density by Power Electric Arc; Izv. Akad. Nauk; Énerg, 1998 No 1 p. 100. [45] Rutberg, Ph.G.; Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A.; Kuprin, A.G.; Pozubenkov, A.A. Experimental Study of Hydrogen Heating in Powerful Electric Discharge Launcher; Journal of Propulsion and Power, 1997, vol. 13, No 5, pp. 659– 664. [46] Savvateev, A. F.; Bogomaz, A. A.; Budin, A. V.; Kolikov, V. A.; Rutberg, Ph. G. Investigation of Electric Discharge in Gas of Superhigh Density with Preliminary Adiabatic Compression; High Temperature; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.: M, 2003 v. 41, № 5, pp. 580 –585. [47] Andreev, D. A.; Bogomaz, A.A.; Rutberg, Ph. G.; Shakirov, A. M. High–Current Discharge of Z–pinch Type in Dense Media; Zh. Tekh. Fiz. Nauka: L, 1992 vol. 62 No. 6 p. 74–82. (in Russian) [48] Dubovenko, K. V. Interaction of Shock Waves with Channel Plasma of High–Current Discharge in the High–Pressure Chamber; Zh. Tekh. Fiz. Nauka: L, 1992 vol. 62 No. 6, pp. 83–93 [49] Bogomaz, A.A.; Budin, A. V.; Kolikov, V. A.; Pinchuk, М. E.; Pozubenkov, A. A.; Rutberg, Ph. G. Investigation of Influence of the Arc Surrounding Gas on the Voltage Drop Near the Electrodes; Trans XVIII Int Conf Physics of the Extreme Substance Conditions– 2003; Chernogolovka, 2003, pp. 162–163. (in Russian) [50] Tsvetkov, I. V. Influence of the Electrode Erosion on the Plasma Characteristics in Power Railgun aunchers; J Fizika Plasmy, 1993, vol. 19, issue 10, pp. 1281–1288. [51] Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A.; Pinchuk, М.E.; Pozubenkov, A.A.; Rutberg, Ph.G. Influence of Cathode and Anode Jets on the Properties of a High– Current Electric Arc; Technical Physics; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.: M, 2002, vol. 47, № 1, pp. 26–33 [52] Rutberg, Ph.G.; Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A. Powerful Pulse Generator of Dense Plasma with High Concentration of Metals Vapor; Int J of Impact Engineering, 1995, vol.17, pp.93–98. [53] Mesyats, G. A. Pulsed Power; Kluwer Acad. Plenum Publ.: New York, 2005 [54] Mesyats, G. A. Electronic Emission from Ferroelectric Plasma Cathodes; Uspekhi Fizicheskikh Nauk RAS, vol. 178, №1, January 2008. (in Russian) [55] Budin, A.V.; Kolikov, V.A.; Rutberg, Ph.G. Influence of the Current Magnitude and Working Gas Temperature on Electrode Erosion in the Discharge Chambers of High– Power Pulsed Plasmatrons; Technical Physics; Pleadis Publishing, Ltd: M, 2007, vol.52, No.8, pp.1011–1015. [56] Belkin, G. S.; Kiselev, V. Ya. Electrode Erosion at High–Current Pulse Discharges; Zh. Tekh. Fiz. Nauka: Leningrad, 1966, vol. 37, issue 2, pp. 384–389 [57] Donaldson, A.L.; Kristiansen, M.; Watson, A.; Zinsmeyer, K.; Kristiansen E.; Dethlefsen, R. Electrode Erosion in High Current, High Energy Transient Arcs; IEEE Trans on Magn, Nov. 1986, vol. mag.–22, No.6, p.1441. [58] Belkin, G. S.; Danilov, M. E. Investigation of Characteristic Features of Electrical Erosion of Metal–ceramic Materials; Elektrichestvo, 1972, No. 8, p.45 (in Russian)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Processes in High Current Discharges in Dense and Super Dense Gas Environments

73

[59] Watson, A.; Donaldson, A.L.; Ikuta, K.; Kristiansen, M. Mechanism of Electrode Surface Damage and Material Removal in High Current Discharges; IEEE Trans on Magn, Nov. 1986, vol. mag.–22, No.6, pp.1799. [60] Baksht, F. G.; Borodin, V. S.; Voronov, A. M.; Zhuravlev, V.N.; Rutberg, Ph.G. Probe Measurements in the High_Current Arc of High_Pressure; Zhurnal Tekhnicheskoi Fiziki; Nauka:L, 1990, vol. 60, issue 11, pp. 190–193. [61] Rutberg, Ph.G.; Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A.; Pinchuk, M.E.; Pozubenkov, A.A. Features of the Electrode Erosion for Discharge–current Amplitudes above 105 A; Doklady Physics, 2003, vol. 48, No.1, pp.1–4 [62] Davis, W.D.; Miller, H.C. Integrated Ion Flux Emitted from the Cathode Spot Region of a Diffuse Vacuum Arc. J. Phys. D.: Appl. Phys., vol. 25, pp. 686–693, 1992. [63] Budin, A.V.; Kolikov, V.A.; Levchenko, B.P.; Leont’ev, V.V.; Makarevich, I.P.; Rutberg, Ph.G.; Shirokov, N.A. The Electrode Material Erosion in Power High–Current Hydrogen Plasma Generators; J Teplofizika Vysokikh Temperatur; MAIK Nauka/Interperiodica,Pleiades Publishing, Inc.: M, 1994, vol. 32, № 4, pp.628–630. [64] Krinberg, I.A.; Zverev, E.A. The Spatial Structure of Cathode Plasma Jets in a Vacuum Arc; Fizika Plazmy; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.:M, 1999, № 1, pp. 88–95 (in Russian) [65] Nemchinsky, V.A. The Anode Spot of High–Current Vacuum Arc; J Zhurnal Tekhnicheskoi Fiziki; Nauka: L, 1982, vol. 52, pp.35–42 (in Russian) [66] Plutto, A.A.; Rozkov, V.N.; Kapin, A.T. High Speed Plasma Flow in Vacuum Arcs; Zh. Eksp. Teor. Fiz., vol. 47, Issue 8, pp.494–507, 1964. [Sov. Phys. JETP 20, 328 (1964)]. [67] Rutberg, Ph.G.; Bogomaz, A.A.; Budin, A.V.; Kolikov, V.A.; Pinchuk, М.E.; Pozubenkov, A.A. Investigation of Anode and Cathode Jets Influence on Electric Arc Properties with Current up to 500 kA; IEEE Trans. Plasma Sci., April, 2003, vol. 31, № 2, pp. 201–206. [68] Bogomaz, A.A.; Budin, A.V.; Pinchuk, M.E.; Rutberg, Ph.G.; Savvateev. A.F. High– temperature Arc in Dense Gas; Journal of High Temperature Material Processes, (An International Quarterly of High Technology Plasma Processes), vol. 8, issue 4, 2004, pp. 617–626. [69] Budin, A. V.; Savvateev, A. F.; Rutberg, Ph. G. A Two–Stage Launcher–Accelerator Working on Hydrogen; Instruments and Experimental Techniques, 2004 No. 4, p. 534 (Prib. Tekh. Eksp. 2004 № 4, p. 125). [70] Budin, A. V.; Losev, S. Yu.; Pinchuk, M. E.; Rutberg, Ph. G.; A. F. Savvateev. An Experimental Stand for Studying a High–Current Discharge in a Dense Gas // Instruments and Experimental Techniques. 2006 v. 49 № 4 p. 549 [71] Budin, A. V.; Losev, S. Y.; Pinchuk, M. E.; Savvateev, A. F.; Rutberg, Ph. G. Electric and Optic Parameters of the Discharge in High Density Gas; Proceedings EML–13, Potsdam, Germany, May 22–25 2006, paper #102F, 10 p. Telekh, V. D. The [72] Koryshev, O. V.; Nogotkov, D. O.; Protasov, Yu. Yu.; Thermodynamic, Optical, and Transport Properties of the Working Media of Plasma and Photon Power Plants; MGTU im. N.E. Baumana: M, 1999. [73] Braginskii, S. I. About Behavior of Completely Ionized Plasma in the Strong Magnetic Field Zh. Eksp. Teor. Fiz. 1957, vol. 33, issue 3, p. 645. (in Russian) [74] Pease, R. S. Equilibrium Characteristics of a Pinched Gas Discharge Cooled by Bremsstrahlung Radiation; Proc. Phys. Soc. B, 1957. vol. 70, pp. 11–23 [75] Koshelev, K. N.; Pereira, N. R. Plasma Points and Radiative Collapse in Vacuum Sparks; J. Appl. Phys., May 1991, vol. 69, No. 10, pp. R21–R44

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

74

Philip Rutberg

[76] Kalinin, Yu. G.; Kingsep, A. S.; Smirnov, V. P. et al. Experiments on Implosion of Heterogeneous Multiwire assemblies at the unit C–300; Pl. Phys. Reports, 2006, vol. 32, No 8, pp.714–726 [77] Blinnikov, S. I.; Imshennik, V. S. The Dynamic of Radiation Collapse Subject to Enrichment by Admixture and Simple Model of the Plasma Focus; J Fiz. Plasmy, 1982 vol. 8. No 1. p. 193. [78] Voronov, A. M.; Gorjachev, V. L.; Zhuravlev, V. N. Spectroscopic Diagnostic of the Pulse Arc of High Pressure; Pis’ma v Zh. Tekh. Fiz, 1993, vol. 19, No. 14, pp. 35–37 [79] Zel’dovich, Ya. B.; Raizer Yu. P. Physics of Shock Waves and High–Temperature Hydrodynamic Phenomena; Academic, New York, 1966. [80] Zamyshlyaev, B. V.; Stupitskioe, E. L.; Guz’ , A. G.; Zhukov, V. G. Composition and Thermodynamic Functions of Plasma; Handbook; Énergoatomizdat: Moscow, 1984. [81] Bogomaz, A.A.; Budin, A.V.; Losev, S.Yu.; Pinchuk, M.E.; Pozubenkov, A.A.; Rutberg, Ph. G.; Savvateev, A.F. Attainment of the Pease–Braginskii Current in an Ultra–High–Pressure Discharge; Plasma Physics Reports; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.:M, 2008, vol.34, No.5, pp.366–375. [82] Vargaftik, N.B. Handbook on Thermalphysic Properties of Gases and Liquids; Fizmatgiz: M, 1963, 708 p. (in Russian) [83] Blick, J.A. Further Development of Capacitance and Inductance – Driven Hotsho Tunnels; Proc.Sec.Symp. on Hypervelocity Techniques. N.Y., 1962, pp.47–86. [84] Turchi, P.J.; Rutberg, Ph.G.; Kulishevich, A.K.; Hohman, W.; Kamhawi, H.; I.G.Mikellides, P.G. Mikellides, C.S. Schmahl, R.J. Tegtmeyer and Gibson, J.P. Development of a High Power, High Pressure Plasma Flow Facility; 30th AIAA/ASME/SAE/ASEE Joint Prop Conf, June 27–29, 1994, Indianapolis. IN. AIAA– 94–3236, pp. 1–14 [85] Dannenberg, R.; Silva, A. Operation of the High–Pressure Chamber with Electroarc Heating Either in a Mode of Effective Energy Transfer to the Pushing Gas, or in a Mode of High Current Generation; Rocket Technics and Astronautics, 1972, vol.10, № 12, pp. 13–15. (in Russian) [86] Lukashevitch, D; Garris, W.; Jekson, R, et al Development of Capacitor and Inductive Pulse Wind Tunnels; in book Technics of Hypersound Researches; Mir: M, 1964, pp. 212–281 (in Russian) [87] Rotert, R; Sivier, K. Hypersound Pulse Wind Tunnel with a Stock of Energy of 7 MJ; in book Technics of Hypersound Researches; Mir: M, 1964, pp.282–297. [88] Phillips, G.R.; Pugatshew, A. Improvement of Shock Speed in an Electrothermal Diaphragm Shock Tybe; J.Phys.Sci. Instrum. Great Britain, 1975, vol. 8, No. 11, pp. 913–914. [89] Rudolph, L.; Jahn, R.; Clark K.; Onset Phenomena in Self–Field MPD Aec Jets; e.a AIAA/DGLR 13. Electric Propulsion Conf. San Diego N 78–653, 1978. [90] Bianchetta, F.; Sivier, K.R. Operating Experience with the M.A.C. Hypervelocity Impulse Tunnel; Proc. Sec.Symp. on Hypervelocity Techn., N.Y., 1962, pp.87–128. [91] Bout, D.; Post, R.; Presly, H. Ionizing Shocks Incident upon a Transverse Magnetic Field; Phys. Fluids, 1970,vol.13, No 5, pp. 1399–1400. [92] Rudderow, W.H. Development of High–Performance Shock Tube; J. Appl. Phys.,1972, vol. 43, No 2, pp. 373–379. [93] Celly, Levin, Bess, et al.. Improved High–Pressure Chamber of Shock Tube with Electric Arc Discharge; Proboru dlya Nauchnukh Issledovani, 1967, vol. 38, № 5, pp. 641–645. (in Russian) [94] Konotop, V.A. Basic Data on Wind Tunnels and Gas–dynamic Units; Trans CAI, BNTI, 1968, pp. 148–151. (in Russian)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Processes in High Current Discharges in Dense and Super Dense Gas Environments

75

[95] Gladushev, M.K.; Gorelov, V.A.; Chernushov, V.M. Electric Discharge Tube TER–M for Researches in Astrophysics; Trans CAI, 1975, issue 1656, pp. 74–83. (in Russian) [96] Menard, W. A High Performance Electric Arc–Driven Shock Tube; AIAA J., 1971, vol.8, No 10, pp. 2096–2098. [97] Livingston, F.R.; Menard, W. Toward Understanding the Conical Arc – Chamber Driver; Proc.Ninth Intern. Shock Tube Symp. Stanford,California, 1973,p.664–667. [98] Grabovsky, V.; Durran, D.; Spenser, D. Pulse Source of Hot Gas for Pulse MHD Accelerator; Raketnaya Tekhnika I Kosmonavtika, 1967, vol.5, № 10, p. 100. (in Russian) [99] Grabovsky, V.; Durran, D.; Mairela, H. Characteristics of Magnetogasodynamic pipe on 500 kJ; Raketnaya Tekhnika I Kosmonavtika, 1969, vol. 7, № 10, pp. 28–37. (in Russian) [100] Camm, J.C.; Rose, P.H. Electric Arc–Driven Shock Tube; Phys. Fluids, 1963, No 5, 6, pp. 663–678. [101] Dannenberg, R.E. A Conical Arc Driver for High–Energy Test Facilities; AIIA J., 1972, vol. 10, No 12, p.1692. [102] Peng, T.K; Likvornik, D.A. Electrodischarge Pipe with Low Density of Energy in the High Pressure Chamber; Pribory dlya Nauchnuch Issledovanii, 1967, № 5, pp. 115– 116. (in Russian) [103] Meskan, O.A.; Light G.C. Time–resolved Spectroscopic Measurement of Electric–Arc Shock Tube Driver–Gas Temperature; Bull. Amer. Phys. Soc., 1968, Ser. 11, vol. 13, No 5, p. 795. [104] Korolev, A.S.; Frolov, Yu.K. Investigation of Pulse Arc Discharge of High Power in Closed Gas Volume; in book Trans VI Int Conf on Low Temperature Plasma Generators; Frunze, 1974, pp.216. (in Russian) Investigation of Gas Ionization at Flow of Models in a Hypersound Pulse Wind Tunnel; Trans CAI, 1975, issue 1656, pp.94– 101. (in Russian) [105] Korolev, A.S.; Sergeev, V.N. Use of Argon in Pulse Wind Tunnels for Expansion of Area of Modelling of M and Re Numbers; Trans CAI, 1980, issue 2043, pp. 162–173. (in Russian) [106] Leibowitz, L.P. Development of an Annular Arc Accelerator Shock Tube Driver; Proc. Ninth Intern. Shock Tube Symp. Stanford, California, 1973, pp. 678–689. [107] Elckins, R.T.; Baganoff, D.A. Composite Model for a Glass of Electric–Descharge Shock Tubes; Ibid., pp. 652–663. [108] Stollenwerk, E.J.; Perry, R.W. Preliminary Planning for a Pypervelocity Aeroballistic Range at AEDC; AGARDograph, No. 32, 1959, p.200. [109] Rutberg, Ph.G.; Glukhov, A.M.; Kolikov, V.A.; Levchenko, B.P. Electrical Light Gas Gun as an Effective Hypervelocity Launcher; Proc 6th Intern Conf on Megagauss Magnetic Field Generation and Related Topics, Nov 8–11, 1992, Albuquerque, New Mexico, USA, p.182. [110] Rutberg, Ph.G.; Budin, A.V.; Kolikov, V.A.; Levchenko, B.P.; Leontiev, V.V.; Makarevich, I.P.; Shirokov, N.A. Electrical Light Gas Launcher Performance Research; Proc 4th European Symposium on Electromagnetic Launch Technology, Celle, Germany, May 02–06, 1993, pp. 1–5. [111] Rutberg, Ph. G.; Budin, A. V.; Kolikov, V.A.; Bogomaz, A .A.; Makarevich, I.P. Hypervelocity Electric Discharge Accelerator. IEEE Trans on Magnetics, Jan 1997, v. 33, No. 1, part 1, pp.305–309. [112] Budin, A.V.; Kolikov,V.A.; Rutberg, Ph.G. The Programmed Capacitor Storage Discharge and Other Factors Influencing on Launch Velocity and on Performance of an

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

76

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Electrodischarge Accelerator. IEEE Transactions on Plasma Science, August 2006, vol. 34, No. 4, pp. 1553–1560. [113] Massey, D.W.; Tidman, D.A.; Goldstein, S.; Napier, P. Experiments with a 0.5 Megajoule Electric Gun System for Fairing Hypervelocity Projectiles from Plasma Cartridges; Final Report GTD 86–1, GT–Devices, Alexandria, VA, March 1986. [114] Budin, A.V.; Kolikov, V.A.; Kumkova, I.I.; Rutberg, Ph.G. Factors Affecting the Velocity of Launching Bodies by Means of an Electric–Discharge Light–Gas Accelerator; High Temperature; Pleades Publishing, Ltd: M, 2008, vol. 46, No. 2, pp. 143–147. [115] Budin, A.V.; Kolikov, V.A.; Rutberg, Ph.G. Efficiency of Energy Transformation in the Electric–Discharge Light–Gas Launcher; J Teplopfisika Vysokikh Temperatur; MAIK Nauka/Interperiodica, Pleiades Publishing, Inc.: M, 2008, vol. 46, № 2, pp. 1–5. (in Russian)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Chapter II

INVESTIGATION OF HIGH-CURRENT DISCHARGES IN GAS ENVIRONMENTS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

ABSTRACT In the current range from 10 to 10,000 A, the conditions were defined for the existence and passage between contracted and diffuse regimes of burning electric arcs or application to multi–phase electric arc systems and in dependence on the gas dynamic parameters in the electric discharge chambers. The main parameters of the arcs (conductivity, concentration of the current carriers, and so on), along with the parameters of the generated plasma jets, have been defined. The working gases were hydrogen, argon, helium, nitrogen, CO2, and others. Phenomena in the near–electrode plasma and the character of emission from the electrodes’ surface were investigated. The elaborated and applied complex methods for diagnostics were described. On the basis of the investigations implemented, a set of stationary plasma generators was constructed with a power range from 5 KW up to 6 MW (in inert environment and hydrogen) and to 600 KW (in oxidizing atmospheres). A number of new plasma technologies were created, in particular, for destruction of toxic wastes and pyrolysis and gasification of organic wastes and coals with the aim of generation of electric power and production of liquid fuels.

1. INTRODUCTION Development of science and sophistication of its methods lead to the appearance of new technologies and new instruments and plants for their realization. Nowadays, various plasma technologies are one of the fastest developing branches. In these technologies, so-called plasma is used as the working body, i.e., some ionized gas, in which the quantity of positively- charged particles is compensated by the same quantity of negatively-charged ones independently of the quantity of the presenting neutral particles. For creation of new technologies of this type, a dense low–temperature plasma is the most interesting (we do not touch questions connected with the high–temperature plasma usually considered in investigations of the thermonuclear processes). Under the dense low temperature plasma, we understand plasma in the temperature range from ~103 K up to ~106 K and with concentration of particles from n =1015 up to 1022 in a

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

78

cubic centimeter. Together with the application of lasers, shock waves, and so on, the most effective way for obtaining such plasma is by using large current discharges, in particular, powerful electric arcs with a current from amperes up to several million amperes. Physics and techniques of stationary and quasi–stationary discharges in gas flows are of the principal interest, specifically discharges both of constant and alternative currents, in which the maximal value of the current does not exceed several tens of thousand amperes. Discharges of such a type are mostly used in practice, since with their usage stationary plasmatrons of dense plasma have been created. In their turn, these plasmatrons become the main elements in a wide range of new technologies. The pulse large current discharges are characterized by the following parameters:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

• • • •

the maximal currents achieve several mega amperes; the time length ranges from microseconds up to milliseconds; the initial pressures of the cold gas extend up to tens of Pascals; the final pressures (as a result of the imbedded discharge energy) can achieve about one hundred thousand Pascals.

Such parameters allow one to obtain plasma with extreme parameters. The stated values are intermediate between the parameters of the classic low-temperature plasma and those corresponding to thermonuclear plasma. On the basis of investigations of such discharges, pulse generators have been created with dense plasma of extreme values of parameters. These systems (plants) are also used in new technologies. The large current discharges in liquids have several characteristics common with discharges in the super dense gas environments, but they have to be classified as a special type of discharge. With their help, successful realization was achieved in prolonged bactericide cleaning of water without application of any chemical reagents, effective obtaining oxide nanostructures with wide range of parameters, application of charged nanostructures in medical investigations, etc.

2. DISCHARGES IN GAS ENVIRONMENTS 2.1. Character of the Discharge The main processes in plasma of the stationary burning arc are widely known, and, therefore, there is no necessity to discuss this question. The electric arc burning in a gas flow has several particularities [1–4]. Investigations of discharges were carried out in cylinder working chambers and in electric discharge chambers of AC plasmatrons.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

79

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.1. Diagnostic chamber; 1 – quencher with cooling jacket (height 4 m); 2 – water inlet; 3 – plasma torch chamber; 4 – peephole; 5 – exhaust line; 6 – place for quencher gas–liquid atomizer mounting; 7 – extender of the diagnostic.

In all cases under consideration, the incoming gas to the working chamber generates a relatively cool layer near the chamber walls. In this layer, the concentration of the charged particles decreases acutely and, thus, an insulating zone is created. As a result, the positive– charged column of the arc does not touch the walls. The nitrogen (N2), hydrogen (H2), helium (He), argon (Ar2), CO2, air, water vapors, and others are used as the working gas. Under effect of the flow of the working gas, the arcs are extended towards the butt–end of the electric arc chamber. The contracted column of the arc is blown out of the inter–electrode zone by the gas flow. In the case of our investigation (with relatively high pressures), it is necessary to assume that the contraction of the arc column happens because of the non–homogeneity of the gas temperature over the cross–section of the discharge and, as a result, it leads to the non– homogeneity of electron concentration [5]. Contraction [2] of the positive column leads to the decreasing velocity of the ionization front [5] and in the presence of the gas flow, leads to shifting the region of ionization and blowing it out of the column, i.e., to the appearance of the so-called “hunch arrow”. The hunch arrow is mainly determined by the diffusion of the charged particles from the column channel extended by the gas flow. There exists the critical value of gas flow under which the breakdown of the gas happens along the chord of the positive column. Note that the arcs burn in the electric arc chamber which has the form of a truncated cone the arc length is actually bounded by the butt–end of the electric arc chamber of the plasmatron, since at the minimal cross–section of the chamber, the concentration of the charged particles is always sufficient to provide the breakdown.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

80

Figure 2.2. Discharge in the gas flow.

In the alternative current arcs, the electron concentration in the arc plasma decreases after passage of the current through zero at the instant of the discharge end. It is described by the following equation: dne / dt = – α n e2 – Da∇2 ne – hYa ne ,

(2.1)

where ne is the electron concentration, α is the recombination factor, Da is the factor of the ambipolar diffusion, h is the probability of adhesion, and Ya is the frequency of collision with molecules that capture the electrons. Since in the high-pressure large-current arcs the recombination predominates, it is possible to neglect the diffusion and adhesion. Therefore, dne / dt = – α n e2 .

(2.2)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Integrating (2.2) with the initial condition ne (t0) at t0 =0 up to t1, we obtain t = t1 ne ( t1) = ∫ d n/ d n e2= α∫ d t , n(t ) ∫ dn n(t 0 )

1

d ne2 = − α ∫ dt , 0

and from this 1 / ne ( t1) –1/ ne (t0) = α t1 , and ne ( t1) = n(t0) / 1 + n ( t0) α t1 ,

(2.3)

where ne(t0) is the initial electron concentration; t1 is the decay time of the arc; ne(t1) is the electron concentration at the instant t1; and α is the recombination factor. According to [10, 58], this factor is assumed to be α = 10–11–10–12 cm3/sec for argon in the large current arcs. As known, the time (t1) of the voltage increase for the repeated ignition has value about 10–3 sec under using the current of the industrial frequency 50–60 Hz. As seen from (2.3) independently on the initial electron concentration, the arc plasma could not possibly decay to the rather small value of the electron concentration during the time t1. But, since the plasma is blown out of the inter–electrode gap with velocity of about 103–104 cm/sec (this is determined by the velocity of the working gas), it causes deionization of the inter–electrode gap. In the three–phase regime of the arc burning, a smoothing of peaks of the repeated ignition is observed (Fig. 2.3).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

81

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.3. Current and arc voltage oscillograms in one phase of the three–phase regime of the arc burning; 1 – current, 2 – voltage; j = 200 A; U = 30 V; the frequency is 50 Hz; the gas consumption is 30 g/sec.

This can be explained by the large electron concentration in the discharge gap that appears due to diffusion and radiation, since at least one of the three arcs burns at any instant in the three–phase regime. In some cases it is reasonable to inject an electron flow into the inter–electrode gap from an independent source. As a result, the passage to the arc regime of burning is realized not in the jerk–wise form (as under the breakdown), but smoothly as the voltage increases on the discharge gap. As seen from Fig. 2.3 in the three–phase regime work of the plasmatron, the curve of the voltage is closer to sinusoid than in the one–phase regime. From analysis of the arc voltage oscillograms in the three–phase regime, it follows that the voltage curve becomes closer to sinusoid. Thus, in the three–phase regime of the plasmatron, its power factor is closer to unit than in the one–phase regime under the same conditions. As a result, the electromagnetic energy realized in each phase (under the three– phase regime) is greater than the energy realized in the one–phase regime. This fact is confirmed by directly measuring the power in the arcs. This consideration allows one to conclude that the three–regime ignition of the plasmatron arc is conducive to its stable burning since, after the passage of the current through zero, it is not necessary to increase the voltage for repeated breakdown of the arc. Moreover, under the three–phase regime of burning, the form of the voltage curve is close to sinusoid, which essentially enhances the energetic characteristics of the plasmatron. Hence, from the viewpoint of achievement of the maximal power in plasmatrons working on the alternative current, it is advisable to use multi–phase systems with the arcs burning in one working chamber but not to apply separate one–phase systems, as done previously in some constructions until now. It is necessary to note that in arcs burning in environments of atomic inert gases, it is more difficult to provide output of significant electromagnetic power than with using the molecular gases or air. This is explained by the fact that in this case the field strength in the arc column is relatively low. Particularly, in the argon arcs under pressure close to atmospheric, the electric field strength varies in limits of 1–7 V/cm depending on the current, and under the pressure growth, the strength increase is minimal (see the Fig. 2.4).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

82

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.4. Dependence of the longitudinal electric field in the arc column for various gases versus the current; P = 1 Atm for various gases [5,6].

It is possible to enlarge the power imbedded into the arcs by means of increasing the voltage drop on the arc or the value of the arc current. Since the field strength is low on the argon arcs, it is difficult to increase the voltage drop on the plasmatron arc. It is necessary also to note that the argon possesses somewhat lower enthalpy than the molecular gases (especially under relatively high temperatures). This is explained by the fact that in heating the molecular gases, a large amount of energy is spent for dissociation of the gas molecules. But in heating the one–atom gases (argon is just of this type), no energy is spent for the gas dissociation. For example, at the temperature of 8000 K, hydrogen and nitrogen, which are molecular gases, have the enthalpy approximately three and five times (correspondingly) larger than argon at the same temperature. Under these conditions, the enthalpy is 2500 Kcal⋅m–3 for argon, 7200 Kcal⋅m–3 for hydrogen, and 12500 Kcal⋅m–3 for nitrogen [7]. Thus, it is more difficult to imbed energy into the argon plasma flow than by using molecular gases. For further estimates of energy, it is advisable to define the current j density in the arc column and, also, possible electron concentration ne, and possible temperature of the arc j=neϑee,

(2.4)

where ϑe=f(E/p) is the velocity of electron drift in the field and ϑe is significantly smaller the heat velocity; E is the electric field strength; p is the pressure. Under conditions considered in [8]

ϑe=1.22×107 E /К p.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.5)

Investigation of High Current Discharges in Gas Environments

83

In the presence of the Maxwell distribution, the coefficient К tends to 1 as the pressure growth. For estimation of the needed value of ne and the arc temperature T corresponding to this concentration, it is necessary to take into account that in the diffuse regime under relatively low temperature Т~(6–7)×103 К, the electron concentration is defined by ionization of atoms of the electrode’s material, but in the contracted regime under Т~(10–12)×103 K, this concentration is defined by ionization of the working gas . Having estimated the temperature and the square of the arc surface, it is possible to define the part of energy removed from the arc by radiation. This radiation is partially absorbed by the relatively cool gas in the volume of the discharge chamber of the plasmatron. The unabsorbed part of the radiation goes onto the walls of the discharge chamber. Knowing the distance from the discharge surface to the wall of the discharge chamber, the pressure and temperature of the cool zone, it is possible to calculate the absorbed light energy. For the atomic gases, the complete absorption is equal to the sum of absorption in all spectral lines and, besides, it is necessary to take into account the absorption joined with ionization of atoms due to the effect of the radiation. Since the temperature of the cool zone is not too high (not higher than 4000 K) and the gas pressure does not exceed several mega Pascals, it is possible to regard the contour of the absorption line to be dispersion. In this case, the absorption factor at its maximum is defined in [8,9] by the following relation: Коп=5.6×10–13f12 N1 λ2 /∆ λ.

(2.6)

In the case when the line contour is Doppler, we have

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Коo=3.46×10–13f12 N1 λμ/ Т,

(2.7)

where f12 is the force of the oscillator, N1 is the concentration of atoms at the absorbing level; λ is the wave length, ∆λ is the half–width of the line, μ is the molecular mass, and Т is the temperature. As a rule, under low pressure and temperature of about several thousand grades, it is necessary to take into account both the Doppler and dispersion contour. The energy absorbed in the volume dldSn per time unit is equal to [10] ∞ / dW =cdldSn∫ К νρ (ν )d ν , (2.8) 0 where c is the light velocity; dl, dSn are the length and square of the volume, correspondingly; ρ(ν) is the density of radiation; and ν is the frequency. Assuming ρ(ν) to be constant in frames of this line and taking into account that ∞ dν= π e

2

∫ Кν

mc

f12 N1,

e

0 Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

84 we obtain dW =cdldSn ρ(ν ) π e

2

/

mc

f12 N1,

(2.9)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

e

where e is the electron charge; and me is the electron mass. To estimate the complete absorption over the whole volume of the emitter, it is necessary to implement the integration both over the volume or surface (if the emitter is the black body) of the emitter and the absorbing volume. From (2.9) it is seen that the energy absorbed depends on the concentration of atoms in the absorbing level; i.e., to calculate the energy absorbed, we have to know the population in these levels. Estimates show that the concentration of atoms even on the first excited level is small in comparison with the atoms’ concentration at the normal state and, therefore, the absorption from the first excited levels will be smaller than that from the main state. For example, in helium under the pressure 0.1 MPa and T~103 K, concentration in the first excited level is approximately N1 ≈1019 e–190 cm–3; i.e., this is evidently smaller than 1010, if recalling that the absorption factor is sufficiently large under the concentration 1010–1011. Therefore, the absorption from the excited levels of inert gases can be ignored, and it is possible to assume that the main part of the energy is absorbed in the resonance lines where the absorption factor is larger than 10 cm–1 and, as a result, the resonance radiation is closed in the arc. All other radiation goes onto the walls of the plasmatron. Thus, to estimate the losses in radiation, it is sufficient to subtract the radiation in the resonance lines from the whole radiation. But the additional growth of energy absorption by the working gas is possible. As a consequence of sublimation of the electrodes’ material, their atoms distribute over the volume of the discharge chamber and absorb the energy radiated by the hot zone of the discharge. After this as a result of collisions, the energy of the metal’s atoms is delivered into the working gas. It is possible that the absorption in the lines of the copper plays a significant role. As for the energy delivered by the convective heat exchange, in this case the known methods for calculation of the heat exchange in the turbulent flows can be applied [11,12]. For the case of constant current they are considered in detail in [13,14], and the main results of these works can be used for necessary estimations. Since in the three–phase systems the heat exchange between the working gas and the wall is realized under strong turbulence and large heterogeneity of temperatures, it is difficult to solve this question. Note that the turbulent heat exchange always presents when the molecular gases (hydrogen or nitrogen) are used and, as a result, the main part of the energy contained in large whirls is determined by the energy of dissociation of the gas molecules. The temperature in the zone of the arc burning is sufficient for dissociation. But after entering the whirl into the surrounding gas, the whirl’s temperature does not exceed 2000– 4000 K, and to deliver the energy of the dissociated gas to the gas to be heated, the main part of the gas must recombine before the whirl disappears. The process of recombination of atoms N into the molecule N2 with participation of the third body Мm develops according to reaction of the following type [15]: N+ N+ Мm ↔

N2 + Мm.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.10)

Investigation of High Current Discharges in Gas Environments

85

It is possible to write dN2 / dt = k N N Мm– kd N2 Мm, where k is the constant of creation of the molecule from atoms kd is the constant of dissociation of the molecule under the initial conditions N2(t)|t=0 =N2(0); 1/[c−N2(t)]2 −1/[c−N2(0)]2 =2kt. The whirl lifetime of interest is equal to tb=l/ϑn,

(2.11)

where l is the character size (as a rule, it is equal to the distance from the arc burning zones to the walls of the discharge chambers) and ϑn is the velocity of the turbulence propagation. If during the time smaller than t the larger part of atoms recombine into molecules (i.e., the quantity of atoms decreases in any time), then the main part of the accumulated energy emanates.

2.2. Discharge in Nitrogen

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Since from the viewpoint of practical application the molecular gases (first of all, nitrogen, air, and, water vapors) are of the most interest, let us consider the discharge in the nitrogen flow.

a)

b)

Figure 2.5. Typical discharge in nitrogen; a) contracted discharge, р = 0.43 MPa, G = 0.2 kg/sec, j = 1 kA; b) diffuse discharge, р = 0.13 MPa, G =0.2 kg/sec, j = 1 kA. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

86

Philip Rutberg

The character of the further burning of arcs in the chamber is stipulated by a number of factors. Two character regimes are observed: the diffuse and contracted ones. 1. In a diffuse regime, the arcs occupy a significant part of the volume of the discharge chamber. The discharge has an explicitly turbulent character. The pulsing plasmoids are observed, and the acute oscillation of the pressure and the voltage pulsations on the arc are seen. The typical photograms of this regime are presented in Fig. 2.5b. This regime remains in the range of pressures 0.1–0.5 MPa in the discharge chamber under the consumption of the gas at 0.1–10 kg/sec. The operative values of the current were varied in the range of 1–20 kA. In small systems, the range of the current variation was J ~0–0.5 kA and the consumption was 1–6 g/sec. For the nitrogen the depth of modulation of the pressure was 10–15%. Oscillation with the character frequencies is also observed in the voltage oscillograms. Modulations with the frequency ~300 Hz are caused by the three–phase source of the power supply. The voltage oscillations with the frequency 1–6 kHz can be explained by propagation of the sound waves. The voltage oscillations with the frequency 8–30 kHz are possibly caused by oscillations of the discharge column. It is necessary to note that under the growth of the current, the frequency of the oscillations identified with the sound waves rises, since the arc temperature increases. Particularly, under the current increase from 50 to 500 A (argon was the working gas), the frequency of oscillations changes from 0.6 to 1 kHz. 2. Under the pressure increase, the discharge transforms into the contracted regime (Fig. 2.5a); the pressure is below or equal to 3.5 MPa, nitrogen is the working gas. The diameter of the plasma column decreases to the sizes close to the diameter of the emitting surface of the electrode. The density of the arc current and the voltage drop on the arc increase. The arc column oscillates. In some cases, two arc columns might grow from one spot. The splitting of the discharge channels might appear. Values of the current diameter in the arc column and its length varied during the half–period, since the data mentioned correspond to the mean values from the ranges of their variation. The current density and electric field strength were calculated by the light diameter of the discharge column under the assumption of the uniform distribution of the current over its cross–section (the difference between the current and light diameters of the gas flow, apparently, is not large [16]). The values of the electric field strength in the contracted regime are larger than those in the diffuse regime. It is necessary to note that the values of the electric field strength in the discharge column sufficiently correspond to the results obtained by other authors under the similar conditions [17]. Moreover, as seen from Fig. 2.6, the voltage drop on the arc changes slightly after the passage into the contracted regime under the conditions considered.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

87

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.6. Voltage drop on the arc; nitrogen is the working gas; j = 4 kA; G = 2.3 kg/sec.

Directly measured values of the arc temperature and electron concentration sufficiently coincide with ones calculated on the basis of the obtained conductivity and are close to the values of thermodynamic equilibrium. In the turbulent regime such accordance is absent; the conductivity and concentration of the electrons correspond to a temperature higher than the measured one. It can be explained by the fact that the conductivity is determined by the presence of metallic vapors that have been delivered from the electrodes rather than by the ionization of the working gas. This is also confirmed by the fact that in this case the spectrum is completely determined by radiation of the metallic vapors. Actually, the main source of the current carriers of the arc in the diffuse regime is the metal when the arc temperature is (5–7)×103 K. This is characteristic for such a regime. The concentration of the metal in the arcs’ zones achieves the value n0(W) = (1014–1015) cm– 3 . According to the Saha equation

(2.12) where I″ is the ionization potential (for the Copper ICu″ = 7.72 eV, for tungsten Iw″ = 7.98 eV). For the conditions typical for the diffuse regime with the pressure 0.2–0.3 MPa, the concentrations ne are presented in Table 2.1. Table 2.1.

Т, 103K ne, cm–3

4 6×1012

5 6×1013

6 2×1014

7 8×1014

The values of ne (Table 2.1) are rather approximate, in particular, due to uncertainty of the ratio of the statistical weights (it was assumed that Gi / G0 ≈1). At any rate, the concentration ne must not exceed 1015 cm–3. In the contracted regime under the temperature Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

88

Td ≈ (9–12)×103 K, the processes of ionization of the gas (nitrogen) will be determinative. Concentration of the nitrogen ions in the arc will be

(2.13) where x = x(T) is the degree of dissociation for the nitrogen; TN = 14.58 eV. Calculated values of concentration ne are shown in Table 2.2. Table 2.2.

Т, 103 K ne, cm–3

8 2×1015

9 9×1015

10 3×1016

11 2×1017

Under the discharge

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

where j is the current density. Accordingly to [18], the drift rate νe depends on the electric field strength Е, п0, and T. For the diffuse discharge in nitrogen, the character values of the current are I = (3–5)×103 А, the electric field strength is E ≈ 50 V/cm, and the square of the current cross–section of the discharge zone is SI ≈ 50 cm2, р = 0.2–0.3 MPa. The needed concentration of the electrons is presented in Table 2.3. Table 2.3.

Т, 103 K ne, cm–3

4 1.3×1015

5 1015

6 1015

7 0.9×1015

For the contracted discharge under I = (4–5)×103 A, SI ≈ 1 cm2, E ≈ 70 V/cm, and р = 0.6 MPa, the concentration of the electrons is presented in Table 2.4. Table 2.4.

Т, 103 K ne, cm–3

8 5.2×1016

9 4.8×1016

10 4.6×1016

12 4.3×1016

Comparing the shown results, one can conclude that to provide the needed ne under considered conditions, the temperature in the contracted discharge must be Tarc > 104 K, and that in the diffuse discharge Tarc < 7×103 K, which sufficiently corresponds to results of the experiment. As for the turbulence, it is evident that the tangent supply of the gas is one of the factors causing the turbulent regime of the arc burning. Under the conditions considered, the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

89

values of the Reynolds numbers were Re ≈ 2×(103–104), which points to the growth of the turbulent regime. The degree of the turbulence increases under the rise of consumption of the working gas. Non–uniform ejection of the metal from the electrodes facilitates the growth of the turbulence. Together with the gas–dynamic reasons, this determines the non–uniform (on time) glow of the arcs under the turbulent regime of burning. Moreover, the turbulence may be caused by other factors [19]. According to [20], the flow rate in the discharge zone for the turbulent regime with taking into account small values of М1 and М2 will be

(2.14) where υ0 is the velocity of the windward cool gas; Tarc and T0 are the temperatures in the arc zone and the cool gas; М1 and М2 are the Mach numbers in the windward cool gas and in the discharge zone. In particular, in the plasmatrons with nitrogen, the values of υ0 changed in the range of (1–4)×10 m/sec, and υ ≈ (1–2.5)×102 m/sec. Thus, the value

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

(2.15) was 0.1–0.6 which corresponds to a high growth in turbulence. The rate of the pulsations’ rise υp (which have isotropic character) changed in the range of (1–15)×103 cm/sec depending on the consumption and pressure of the working gas. As already mentioned, the contraction of the arc column appears when the pressure rises. Under this, the pinch column is unstable and oscillates with the velocity υ0с≈102 m/sec. The cause of the contraction possibly relates to the fact that under the pressure rise the diffusion of the metal into the volume around the arc decreases, but at the same time under the pressure rise, the difference between the absorption factors of the radiations into the arc and into the environmental gas increases. These mechanisms lead to an increase of the energy concentration close to the axis of the arc discharge and to the corresponding growth of the conductivity. Actually, the growth of the density of the metal vapor leads to the higher concentration of the electrons, and, hence, to the growth of the conductivity. Simultaneously, the increase of the value of the energy absorbed by the discharge causes the heating of the central part of the discharge column. As a result of the mentioned phenomena, the contraction of the arc discharge occurs which is similar to the thermal contraction according to the mechanisms considered in detail in [21]. The passage to the contracted regime is followed by the step–wise change of the current density, temperature, and the conductivity. It is necessary to keep in the mind that under the significant increase of the gas consumption (i.e., in spite of the more intensive cooling of the discharge channel) the degree of the turbulence increases, and this may lead to the fact that the passage to the contracted regime occurs under higher pressure.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

90

Philip Rutberg

2.3. Heat Exchange between the Arc and the Working Gas By calculating the estimates of the heat exchange for nitrogen or another gas with a large enthalpy, it is possible to consider the following mechanisms of the energy transfer: the heating by radiation, heat conduction from the arc’s zone, forced convection (the (turbulent heat transfer); and heating (up to the arc temperature) of the gas portion blown through the arc’s zone. From this, the power spent by the arc on the gas heating is .

(2.16)

In the case of the diffuse regime of the arcs burning when the temperature in the discharge column does not exceed (5–6)×103 K, it is possible to neglect the heating by radiation from the point of view of the energy transfer from the arcs to the environmental gas. Then we have for the heat conduction

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

(2.17) where λ is the heat conduction factor; Sarc is the square of the zone of the arc’s heat output taking into account the three–phase regime of burning and ∇Т is the temperature gradient at the boundary of the heat output zone. Keeping in mind that λ ≤ 2.3 10–2 W/(cm K), Sarc ≈ 500 cm2, and ∇Т ≈500 K/cm, the value Рh–cond ≈ 5.75 kW can be neglected. Thus, in the case of the diffuse regime, only two factors really affect the gas heating: forced convection (turbulent heat transfer) and the heating of gas portion blown through the arc’s zone. To intensify the process of the gas heating under its interaction with the arc, it is necessary to assume that the gas molecules intensively exchange energy when colliding, and the times of relaxation of the energy and excitation and, also, the rate of atomic recombination is smaller than the time of the presence of the molecules in the plasmatron volume. Otherwise, a significant part of the energy will be carried away from the discharge chamber by the gas flow. Under the conditions considered, it is possible to assume that almost the entire energy of the discharge (excluding the losses on the electrodes) is transferred into the working gas. Actually, the time of recombination of the atoms into the molecules under conditions considered is 2×10–5 sec [15]. The time of exchange by kinetic energy and by rotation is still smaller [15]. It is necessary to note that the presence of the metal (with the density пw =1014–1016 cm–3) in the volume of the discharge chamber corresponds to the mentioned processes. Tungsten having a significantly larger mass than nitrogen, can play the role of a “peculiar wall”, and the colliding of the nitrogen with the tungsten atoms must lead to the transfer of the energy of the excitation into heat and also facilitate the recombination processes. As for the part of the energy output in the discharge chamber on account of the transfer into heat under the relaxation of the oscillation, its exact estimation is hampered. This is so because there are no sufficiently reliable data on the dependence of the section of this process

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

91

on the temperature. Thus, a part of the cool gas passes through the arc by the turbulent flows and is heated up to the arc temperature. After, the energy of this gas by means of the mentioned mechanisms redistributes in the rest mass of the working gas; and this leads to heating up to the average temperature. The discussed results allow one to write (2.18) where Qbl is the mass of the gas blowing through the arc for a time unit;, Harc is the enthalpy of the gas in the arc, and H0 is the enthalpy of the gas entering the arc. Then we have for the power transferred by the forced convection (2.19) where k is the factor of the turbulent heat transfer. As it is known (2.20)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

where ρarc is gas density in the arc, Ср is the isobaric heat capacity, υfl is the average velocity of the flow , and LT is the character size of the turbulence. For the conditions under consideration, LT≈10–20 cm. It is convenient to represent the flow rate υfl in the following form: , where А0=const. Then (2.21) Taking into account that

, the resultant consumption through the plasmatron is calculated ,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.22)

92

Philip Rutberg

where ρ0 is the density of a gas coming into the arc and S0 is the square of the plasmatron cross–section before the zone of the arc’s burning. It is possible to write

(2.23) or

(2.24)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

As it follows from the results of the experiment, the ratio of the gas consumption to the power output on the arcs determines the regime of the stable burning of the arcs. Under insufficient power of the power supply source, the following phenomena are possible: an unstable regime of the arc burning and the disruption and collapse of the arc. As a rule in powerful plasmatrons, such a regime appears under values of the arc current jarc lower than 2.1 kA.

Figure 2.7. Dependence of the parameter Q/P versus the arc temperature Tarc calculated according to (3.9); with (1) and without (2) taking into account the convection, correspondingly.

If Q/P > 0.45 (kg/sec) /MW, then the disruption of the arc occurs in the diffuse regime. This can be understood from the above discussion. Actually, the dependence of the ratio P/Q versus the temperature Tarc (Fig.2.7) shows that a stable regime is possible in the segment A–B when the temperature does not fall below 5×103 K, and the thermal ionization of the tungsten vapors can provide a sufficient number of current carriers. The value Q/P > 0.45 (kg/sec)/MW corresponds to the value ∼2 kJ/g ≈ 2000 K ≈ 0.2 eV, and taking into account that the significant part of the working gas passes through the zone of the discharge, this value of Q/P is apparently insufficient for the stable regime of burning the arcs. In the case of the contracted arc, the influence of the heat conduction and the convection both can be neglected, since the arc’s square is essentially smaller than that in

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

93

the diffuse regime. The column of the contracted arc moves between the electrodes with the velocity υc ≈102 m/sec in the volume with the cross–section square S' smaller than 30 cm2. The windward cool gas will be heated by blowing through the mentioned volume under satisfaction of the following condition:

,

(2.25)

where Larc is the length of the contracted arc, Larc ≈20 cm; d is the diameter of the arc column, ≈1 cm. Under the conditions considered, it must hold υо < 102 m/sec, and as was mentioned, υо ≤ 4×10 m/sec. Moreover, in the case of the contracted arc, it is impossible to neglect the influence of the radiation. As it will be shown below, the part of the energy put out from the column by the radiation achieves the value α ≅ 0.1–0.2. Then it is possible to write for the specific power in the case of the contracted discharge

(2.26)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

2.4. On the Opportunity to Obtain the Detachment of the Oscillating Temperature of Nitrogen in Decaying Plasma under High Pressure The supersonic regime of flow–out in the channel with the cross–section (2.2× 22) · 10–2 m2 and a length of up to 0.5 m establishes from (25–30)×10–3 sec until the instant of ending the current pulse of the plasmatron near the maximum of the pressure in the fore– nozzle chamber (р0 = 3–5 МPa with the deceleration temperature Т0=1000–1800 K). Under this in dependence on the working conditions of the plant, the parameters of the process have the following values: static р pressure 10–30 GPa, temperature 250–300 K, velocity (0.9– 2.0)×103 m/sec, and average mass consumption 0.2 kg/sec. The conductivity current Iσ was registered by means of brass electrodes inserted into the channel at a distance of 21.5×10–2 m from the nozzle fence and under the voltage 100 V on these electrodes. The measurements showed that the level of the electro–conductivity averaged over the cross–sections does not vary along the channel length but monotonically decreases during 5×10–2 sec after the end of the plasmatrons’ work [22]. The electron concentration in the supersonic flow of nitrogen was calculated by means of the volt–ampere characteristics of the non–self–maintained discharge burnt up in the channel. In dependence on the experiment conditions, this concentration is ne=1010–1011 cm–3. The degree of ionization of the plasma corresponding to these values of ne of 10–6–10–7 which in many orders exceeds the equilibrium value. Taking into account the losses on the recombination during the process of the gas–dynamic extending [23], the level of ionization in the fore–nozzle mixing chamber must be at least one order larger, and the electron concentration must be ne ≅ 1014–1015 cm–3.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

94

Such values could not be explained by the equilibrium processes. It is essential that for the pressure and temperature realized in the experiments, the time of conservation of the non– equilibrium in the fore–nozzle mixing chamber of more than two orders exceeds the time of the oscillating relaxation of pure nitrogen. It is necessary to note that analogical phenomena have been observed also under the subsonic regime of flow–out in the low temperature nitrogen plasma. In connection with these phenomena, it is interesting to investigate the processes in the fore–nozzle chamber. Spectroscopic measurements showed that the spectra of AlI, CaI, CaII, NaI, FeI, CrI, WI, AIO, and LaO delivered from the plasmatrons are excited. Mainly, lines are observed in which the upper levels have energy that does not exceed 40,000 cm–1. The temperature of excitation measured by the lines FeI has a value of 2700±200 K, and the temperature measured by the lines CrI is 2600±200 K. The resonance lines NaI λ=5889.95 Ǻ and CaI λ=4226.73 Ǻ have large re–absorption and widening (the half–width is of any angstroms). The temperature has been measured by these lines and with the assumption that the radiation in these lines corresponds to the radiation of the black body. The temperatures calculated in this way were 2700 K for NaI and 2800 K for CaI. Thus, the temperatures of excitation measured by different methods coincide up to the errors. The deceleration temperature Т0 measured by the tungsten–rhenium thermocouple of the diameter 100 nm was 1600±100 K under these conditions, but one calculated by the balance of energy imbedded into the plasmatron arcs did not exceed 1300 K (under the assumption of the 100% heat efficiency, the specific energy imbedding was Е/G=1.2 ± 0.2 MJ/kg during the heating process). The temperature obtained from the thermocouple measuring exceeds a little the values from the balance calculations. This confirms the absence of the equilibrium in the fore–nozzle chamber. Figure 2.8 shows the intensity of the glow of the resonance line NaI and the oscillogram of the discharge current Ipl of the plasmatron. It is seen that the time length of the glow is several tens of milliseconds after the end of the discharge current just as the time of conservation of electrons n, exceeds the time of the VT–relaxation ny more than two orders. Thus, a process must exist that is able to support non–equilibrium in the plasma for the significant time after the end of the current. The most probable mechanism seems to be the creation of molecules during the recombination of atoms 2N + N2 → N2* + N2,

(2.27)

where N are nitrogen atoms and N2 , N2* are the nitrogen molecules in the main and oscillating–excited states.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

95

Figure 2.8. Intensity (in relative units with time) of glow of the resonance line NaI and the oscillogram of the discharge current Ipl of the plasmatron.

The following solution of the relaxation equation corresponds to reaction (2.27):

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

N(t)=N(O)/1+2k N(O) N2t,

(2.28)

where N(O, and N2 are the initial concentration of nitrogen atoms and molecules, and k is the constant of the reaction [24]. Under pressure 5 MPa and T ≤ 2000 K, it follows from (2.28) that the time of equilibrium establishment between the nitrogen atoms and molecules exceeds 20 sec. Thus, the nitrogen atoms created in the plasmatrom arc are able (under mixing with the nitrogen molecules in the fore–nozzle chamber) to support the non–equilibrium state of the gas for a long time. In turn, this phenomenon leads to deviation of the gas temperature from the excitation temperature. Taking into account the lifetime (not exceeding 10–5 sec) of the excited states of the metal, it is possible to assert that the excitation of the metal is realized by the excited nitrogen. Under thus, the nitrogen oscillating temperature must either equal or exceed the excitation temperature of the metal. So, it has been shown that the detachment of the nitrogen oscillating temperature ~1400 ±300 K is obtained under the nitrogen blowing through the plasmatrons in the fore–nozzle chamber for the pressure 3.0–5.0 MPa and gas–kinetic temperature 1300±300 K.

2.5. Heating by Radiation in Nitrogen For nitrogen, the state А3∑+и is meta–stable. The first permitted band corresponds to the passage from the state α′P. The maximum wavelength of this passage is 140 nm. Thus, nitrogen will effectively absorb the radiation beginning from this wavelength [25]. For the marginal estimates, we assume that the plasma radiates as the black body and that the whole energy of the radiation with a wavelength shorter than 140 nm is absorbed by the gas. Now for the temperature of the arc column 104 K, we calculate the part of the energy in the wavelength from zero up to 140 nm. This part will take 2×10–2 of the whole energy, i.e., it equals 1.17×107 W/m2, whereas the whole power of the radiation is 5.7×108 W/m2 for the temperature Т = 104 K.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

96

Philip Rutberg

It is evident that such a value of the energy absorbed cannot heat the gas up to any temperature of thousands of degrees. Moreover, note that in this case the resonance passages are used, and since the pressure is about 0.1 MPa and higher, the value of the absorption factor of the resonance radiation is large, and the radiation goes out not farther than a thin layer adjoining with the plasma. Thus, the nitrogen gas environment cannot be heated by the radiation, since the main part of the radiation passes through the environment, but the radiation of the short wavelength is absorbed by the thin layer and heats it. The picture can crucially change if one takes into account presence of the impurity of nitrogen dioxide. This dioxide effectively absorbs radiation in the visible and near ultra–violet ranges, i.e., it is able to absorb the main part of the radiation of the discharge column. The cross–section of the absorption in NO2 achieves 6×10–19 cm2. If the proportion of this impurity to the nitrogen is about 10–3, then the absorption factor (under р = 0.5 MPa) will be approximately 0.1 cm–1. Under the average distance Lu between the arc and the wall approximately 10 cm, such a value of the absorption factor gives коLи =1, i.e., the essential absorption exists. Having noted that under this the radiation distributes rather uniformly over the whole volume, one might conclude that this mechanism of gas heating is one of the possible ways in the case in which the mentioned concentration of NO2 is approximately 10– 3 . But this is unlikely under the conditions considered. Therefore, it is necessary to consider some other mechanism. In the volume of the plasmatron there is an impurity of the tungsten vapors with a concentration of 1014–1015 cm–3, which also can absorb radiation. By the data from [26], the cross–section of the energy transfer from the resonance-excited atom to a molecule is 10–16 cm2. Under the gas pressure 0.5 MPa and the temperature 3000 K, the number of collisions that lead to the energy transfer from the resonance excited atom to the molecule will be 10. Thus, the average lifetime of such an atom will be 10–7 sec, which is comparable to the lifetime of the resonance states, but in many cases this value is even smaller, since it is necessary to take into account the resonance absorptions. So, the energy transferred from the arc column to the tungsten atoms by the radiation will be mainly transferred to the nitrogen molecules, which leads to the heating of the working gas. It is also necessary to take into account that practically all radiation passages in the tungsten atoms run down f the lower levels, which are closely placed to the main state (below the values are given in cm –1) Main level……...………………… 0, 1st level…………………..……… 1670 2nd level…………………….…… 3326 3rd level……………………….… 4839 4th level…………………….…… 6219 It is seen that the distance between the levels (in the scale of the energy) has the order of the heat energy. This means that these levels are strongly joined to each other through the mechanisms of colliding. Therefore, with a large degree of probability, one can expect that the ideas mentioned about the resonance transfer of the energy from the main level can be extended also onto the first excited levels. Thus, one may expect that in the nitrogen heating practically all such lines, whose radiation lies in the visible and ultra–violet ranges; and these are just the ranges participate where the maximum of the radiation lies under the temperatures

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

97

considered. The same scheme of lower levels applies to the tungsten ion. Therefore, everything described about the tungsten atom extends to the tungsten ion. Thus, it is possible to note that nitrogen can be heated by means of the energy transfer from the excited tungsten atom to the nitrogen molecule. The next step is to estimate a part of the energy that can be radiated by the arc in the line spectrum on the tungsten’s lines under the temperature 104 K. A rough estimate can be obtained in the following way: if to assume that the contour in the center of the line is the Doppler one, then under Т = 104 K and concentration of the atoms of 1014–1015 cm–3, the absorption factor will be a little lower but. nevertheless, sufficient to consider that the line radiates like the black body. So, one can adopt that the radiation is contained in a collection of narrow spectral ranges, whose envelope corresponds to the distribution. The whole energy of the radiation can be found by determining the width of each spectral range (the line’s width) and their number. To find the number of lines, it is sufficient to choose (on the curve of the Plank radiation) such interval of wavelengths in which the main part of the energy is radiated. For Т = 104 K, this interval lies between 140 and 600 nm. In this spectral range, approximately 2500 tungsten lines are placed. If their half–width is known, then the output of the radiation can be estimated by the number of the lines. The half–width of each line depends of the form of radiation. It is easy to show that under the large value of the absorption factor the half–widths of the dispersion contour will be larger than the Doppler contour. Actually, let us take the lines with the Doppler and dispersion contours. Then the distribution of the intensity in the lines can be described as follows:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

for the Doppler contour

(2.29) and for the dispersion contour

.

(2.30)

Here, Jо is the intensity at the center of the line, v0 is the frequency at the center of the line;, β = μ/2RT, μ is the molecular mass, R is the universal gas constant, Т is the temperature, с is the light velocity, γ is the parameter of extending, v is the current frequency. It is known that under increase of the absorption factor, the intensity of the output radiation decreases approaching the value that is in equilibrium with the gas temperature. The top of the line’s contour becomes flat. The frequency range, in which the top is flat, can be determined by regarding that in these frequencies the line radiates as the black body, i.e., the absorption factor is rather large. Let the absorption factor be such that the variation of the intensity at the line’s center in comparison with the intensity on the frequency v will equal 105. From these demands, determine the value v – v0

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

98

Philip Rutberg

for the Doppler contour ,

(2.31)

and for the Lorentz contour

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

(2.32)

Comparing these two formulas, it is easy to see that under the equal variation of the intensity inside the line, the width of the radiation shelf is by two orders wider for the dispersion contour than one for the Doppler contour. Therefore, it is possible to make a conclusion that the following is very important for estimation of the radiation: the lines with dispersion distribution of the intensity under the large value of the absorption factor radiate more energy than the lines with the Doppler distribution of the intensity. The width of the line in the plasmatron has been measured, and its mean value is X – Хо – DX = 0.03 nm. Then the whole width of the radiating range will be equal to the product of the lines’ number by 0.3 nm, which is 75 nm. The whole range of the wavelength, in which the main part of the radiation is included, is equal to 140–600 nm. Therefore, the part of the radiating range in comparison with the whole range is 16%. If to assume that over this range the intensity is distributed uniformly (with the error up to 100%), one can conclude that approximately 8–16% of the energy is radiated through the linear spectrum. Now consider the role of the continuous spectrum in the radiation. Above it was noted that nitrogen is not able to heat directly the continuous radiation. So, the process of absorption of continuous radiation by the tungsten atoms that are in the gas remains to be considered. It is absolutely evident that this radiation will be absorbed, on one hand in the limits of the half–width of the line; and, on the other hand, the ultra–violet part of this radiation can be completely absorbed ionizing the tungsten atoms. The estimates show that the absorbed energy is not able to completely heat the gas, since from the experiment it follows that the effective (by measuring) temperature of the black body in the continuous spectrum of the arc does not exceed 4500 K. This does not give a sufficient amount of the energy for essential heating of the gas. Moreover, it is necessary to take into account that in the visible and near ultra–violet spectrum, tungsten absorbs only in the spectrum lines.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

99

2.6. Discharge in Air and in Water Vapors In comparison with the discharges in nitrogen, discharges in these environments have several peculiarities joined, first of all, with the complicated molecular content of these environments. Taking into account the presence of a great deal of the oxidizing component in these mixtures and from the viewpoint of the electrodes’ resource, it is advisable to use copper and its alloys with iron as the electrodes’ material. Moreover, it is necessary to limit the current value by 1500 A and, at any rate, not to exceed this constraint. The estimate of parameters of the processes in the arc discharge of the plasmatron is possible under assumption of the local thermodynamic equilibrium. This takes place, because the electric parameters of the plasmatron arc discharge (note that these parameters are determined with respect to the gas–dynamic system of the electric arc) are subjected to essential changes in the time intervals of approximately one millisecond in length. But the characteristic time lengths of the gas–phase reactions are of several orders smaller under temperatures higher than 2000–3000 K [15, 16]. The current density in the arc (under assumption of the homogeneity of the conductive area over its cross–section) is calculated as follows [27]:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

j

=

I S

пр

,

where Scon ,cm2, is the square of the cross–cection of the conducting area. Let us estimate the needed number of current carriers for providing such a density. As it is known [28], the current density consists of the electron and ion components , (A/cm2),

(2.33)

where ne, ni, cm–3, is the quantity of electrons and positive ions in the volume unit; e (Coul) is the electron charge (1.6×10–19); and ve, vi (cm/sec) is the drift velocity of electrons and ions in the electric field. The role of ions is mainly in the neutralization of the spatial charge of the electrons, and the plasma current is mainly carried by the electrons. Then neglecting the diffusion of electrons from the discharge channel, it is possible to equate the density of the electron current to the average current density calculated by dividing the current by the cross–section square of the discharge channel. The drift velocity can be estimated knowing the ratio of the electric field strength to the whole number of the particles [29–31] which, in turn, depends on the temperature and pressure. The whole number of the gas in the volume unit is

N=

P k .T

,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

100

where p, Pa, is the pressure; k, J/Coul, is the Boltzmann constant; and T, K, is the temperature. For conditions under consideration, the drift velocity of the electrons is ve~6·105 cm/sec. Thus, the needed electron density must be the order on

n≈ e

j e.v

.

(2.34)

e

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

To determine where the electrons of the conductivity appear from, it is necessary to consider the mixture of the plasma-generating air with the vapors of the electrodes’ metal in the temperature range close to the arc temperature. Electrodes for plasmatrons of this type are made of copper or (in some particular cases) special alloy (70%Cu+30%Fe). To simplify description, let us suppose that the electrodes are made of copper. The values Q of the metal erosion estimated experimentally are ~(10–6–10–5) g/Coul in these work regimes [32]. Thus, let us take the value GCu = 1.3 g/hour for calculation of the mixture content. This reasoning holds also for consumption of the plasma-generating gas, but, additionally, it is necessary to exclude from consideration the near–wall layer of the channel, since the air in this layer has a significantly low temperature and cannot be taken into account in calculation of the mixture of gases participating in the discharge. Therefore, the volume consumption of the plasma-generating air passing through the burning area per a time unit is calculated

G≈ v

2 S пр , 3 S к G общ

G =G.ρ m

(2.35)

,

v

(2.36)

where Sds, m2, is the square of the arc discharge; Sch, m2, is the channel square; Ggen, m3/hour, is the consumption of the plasma-generating gas through the plasmatron; Gm, kg/hour, is the air mass consumption; and ρ, kg/m3, is the air density, 1.18 kg/m3 at 300 K. The mass of the copper is

m = Cu

G G +G

,

Cu

m

(2.37)

Cu

and its volume (under normal conditions) is

m r =r .μ Cu

Cu

см

,

Cu

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.38)

Investigation of High Current Discharges in Gas Environments

101

where µmx, g/mol, is the molecular mass of the gas mixture; and µCu, g/mol, is the copper molecular mass. Knowing the volume of the copper, it is possible to calculate the concentration of the copper particles in the volume unit

N =r .N Cu

Cu

.

The level of ionization αCu of the copper atoms under the temperature T can be defined from the Saha equation. The number of electrons in the discharge obtained by the copper ionization is

n ( )= α . N e Cu

Cu

Cu

,

that is,

n( ) . 100% n e Cu e

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

of the needed number of the current carriers. This parameter can be more exactly defined if the equilibrium content of the mixture is known under a given temperature. The calculations could also detect other “deliverers” of electrons into the discharge. Such a calculation was implemented by the computer program CHEMICAL WORKBENCH v.3.4 of the company Kinetic Technologies on the model of the thermodynamic equilibrium reactor; the program is based on a search of the minimum of the Gibbs free energy. The calculation results are shown in Fig. 2.9.

Figure 2.9. Equilibrium content of the mixture of air and copper vapors versus temperature.

As seen from Fig. 2.9, the equilibrium content of the air and copper vapors has the following components in the region of the temperature of 5000 K: N2 – 70.3% mass; O2 – 0.09%; N – 4.4%; O – 22.2%; NO – 1.6%; Ar – 1.3%; Cu – 0.007% (because of its small value, this component is not shown in the figure). The oxygen has practically dissociated

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

102

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

completely, but the nitrogen dissociation has just begun. This equilibrium mixture contains an essential part of the nitrogen oxide. The potentials of the first ionization of these species are the following: N2 – 15.58 eV; O2 – 12.06 eV; N – 14.54 eV; O – 13.614 eV; NO – 9.25 eV; Ar – 15.755 eV; Cu – 7.726 eV; and W – 7.8 eV. As the most probable “deliverer” of the other needed electrons, the oxide NO could be that which possesses the lowest (after the copper) ionization potential. In spite of athe fact that the order of its ionization is low under these temperatures, its presence and effect in the gas mixture is rather essential. The next candidate could be oxygen molecules, but under the temperature 5000 K they are almost completely in the dissociation state and the potential of ionization of the atom oxygen is significantly higher than 1 eV. Figure 2.10 gives the calculation results of the volume concentration of electrons and positive ions. The graphs confirm the conjectures made earlier. In the temperature region of about 3000 K, the main mechanism delivering the electrons into the gas is the copper vapors ionization. The ionization of NO dominates in the interval of 3000–7000 K. In the range higher than 7000 K, the ionization of both the atom nitrogen and oxygen dominate.

Figure 2.10. Dependence of the equilibrium volume concentration of electrons and positive ions in the mixture of air and copper vapors versus the temperature.

The picture presented agrees well with the data from other authors [33,34] and allows one to define a more exact estimate of the temperature in the discharge area. The temperature ~5000 K corresponds to value of the electron concentration ne = 7×1013 cm–3 found earlier. Under this temperature the copper is ionized up to ~17% of copper mass, the proportion of the “copper” electrons in ne is ~13%, and the nitrogen oxide is ionized up to ~0.3% of the whole mass and amounts to ~87% of the electrons. But the proportion of the copper electrons in ne decreases to ~12%, since the level of the oxide NO ionization increases up to ~0.8%, provides ~88% of the electrons. The difference in the copper ionization level found earlier from the data for the equilibrium content is explained by the fact that in the previous estimate the effect of the mixture components was not taken into account and the copper was considered separately. This ionization of copper vapors plays a crucial role in providing the conductivity under temperatures lower than 3000 K. Such regimes are possible at the initial stage of the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

103

discharge when the arc is short and the surrounding gas is not yet heated, and, also, at the instant of the repeated breakdown of the discharge area when the current passes through zero. These estimates and calculations are somewhat approximate and allow one to estimate only the orders of values of the basic parameters of the processes that take place in the discharge chamber of electric arc plasmatrons of this type. In particular, the drift velocity of electrons has been estimated with insufficient accuracy, and in these estimates the ion current was not taken into account, but it can have a value of 10–30% [35, 36]. Discharge in water vapors. The content of the gas discharge plasma is more complicated than that of air. It is advisable to consider the content of the vapor plasma having mind the most appropriate material for the electrodes (Cu and Fe) and for typical ratios of

m mH O Cu

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

2

and

m mH O Fe

(see Figs. 2.11–2.12 and Figs. 2.13–2.14).

2

Figure 2.11. Charged particles.

Figure 2.12. Neutral molecules and atoms. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

104

Results show that the concentration of charged particles is determined by the presence of metal vapor up to ~5200K, but under higher temperature the concentration is stipulated by ionization of Hydrogen atoms. Ionization potential is I″Cu –7.72 eV; I″Fe –7.9 eV, H –13.6 eV. For the content of the vapor plasma

( m = 6,5 × 10 ) mH O Cu

−5

.

2

For the content of the vapor plasma

( mFe = 6,5 × 10−5 ) mH 2O

.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.13. Charged particles.

. Figure 2.14. Neutral molecules and atoms.

For comparison, it is possible present the content of the more simple helium plasma (Figs. 2.15, 2.16).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

For the content of the helium plasma

( mCu = 1,0 × 10 ) m He −4

105

.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.15. Charged particles.

Figure 2.16. Neutral molecules and atoms.

For a mixture of helium with copper vapor (ratio ~ 10–4), the concentration of charged particles is determined by copper ionization up to ~ 8700K, with higher temperature – resulting from ionization of helium atoms (He″ –15.6 eV ).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

106

3. ELECTRODES 3.1. Measurements of Surface Temperature of Electrodes The measurements of temperature at electrodes’ surface were performed by means of a special device with a long-focus achromatic lens. The description of results and data obtained are presented below [37].

a)

b)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.17. Operating modes of rod electrodes of the AC plasma generator.

Figure 2.17 shows electrodes during the work with the spot (a) and in the regime of the emitting surface (b). It is seen that the significant part of the electrode surface is not covered by the plasma of the arc. Therefore, it is possible to measure the temperature of the electrode outside of the electrode spot. This measuring was carried out by the following two methods. 1. The brightness temperature of the electrode image was measured by means of a pyrometer. For passage to the true temperature of the electrode, the reference light source with the known temperature was put at the place of the electrode. The absolute value of the electrode temperature can be determined by a choice of brightness of the reference source corresponding to the brightness of the electrode. 2. It was found that for measuring possible slow oscillations of the electrodes’ temperature, it is expedient to apply the following method: the image of the electrode is projected onto the slit of the monochromator, which separates the narrow spectral interval around the range 100–800 nm which corresponds to the band of the maximal sensitivity of the photomultiplier; the signal after the photomultiplier is delivered through the amplifier to a recorder or to the electronic oscillograph; a region outside of the arc spot is chosen. It was shown experimentally that the temperature of the electrode out of the spot generally is practically the same over the whole surface. In the case where the plasma glow overlays the glow of the arc, oscillations would be seen on the screen of the oscillograph. But such oscillations have not been observed. This is evidenced that the temperature of the working electrode is relatively stable in time, and the intensity of radiation of the plasma is negligible in comparison with the intensity of the radiation of the electrode. Therefore, measuring the temperature outside of the spot, it is necessary to take into account pyrometer error, which may occur under the oscillations of the temperature over time.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

107

Using the Plank formula and taking into account that exp(c2/λT) ≥ 1 (where c2 = 1.43884 cm×K is the constant of the black body radiation), the ratio of energies of the radiation for temperatures T1 and T2 is obtained

(2.39) From (2.39) it follows that the mentioned small variations of the temperature must lead to large variations in radiation intensity. This allows one to determine the temperature oscillations rather exactly. Photography of the electrodes was implemented from the screen by means of the high–speed cine camera SKS arranged at the place of the pyrometer. To separate the linear spectrum of the plasma glow from the continuous spectrum of the spot, the collection of filters was used. This collection allowed separating the range of acontinuous spectrum radiated by the electrodes. To exclude completely the influence of the plasma glow before the electrodes, this method was developed. The described method used allows the opportunity to select (by means of objective lenses with an opaque screen at the center) the radiation of the spaced source of the length

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

,

(2.40)

where f is the focal distance of the objective lens (in the experiments f = 160 cm); r is the radius of the source and; r0 is the radius of the opaque screen on the objective lens. By the lens L arranged with diaphragm of a diameter of 80 cm, the radiation was projected onto the spectrograph ISP–51 with the UF–90 camera or onto the monochromator. This allowed one to reduce maximally the influence of the radiation given by the arc column. To assure that the radiation emanated mainly from the electrode surface, it was necessary to establish the negligibility of the part of the continuous spectrum of the plasma. The whole spectrum of the radiation was photographed in the visible range, and the continuous part of the spectrum was analyzed. The linear spectrum of the radiation practically coincided with the spectrum of radiation of the tungsten, thorium, or lanthanum (depending on the material of the electrode). Therefore, the continuous spectrum did not affect determination of the temperature of the surface, and by means of the photo–electric method, it was possible to measure the time variation of the temperature. The temperature is calculated as follows:

,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.41)

108

Philip Rutberg

where λ1 and λ2 are the wavelengths, cm; ελ1 and ελ2 are the emission of the tungsten; and rλ1 and rλ2 are the energies of radiation of the black body. Simultaneously, the time–summary spectrum was fixed, but according to the method of processing, measurements were possible which allowed determination of the temperature with a margin of error of about ten percent. Determination of the temperature of the surface by the time–summary radiation is connected with strong dependence of the radiation on the temperature of the electrodes’ surface. In the cases under consideration, the temperature close to the maximal one was measured. Moreover, the temperature of the electrode surface was also measured by a sharp decrease the radiation intensity after the fast switch–off of the current. Nevertheless, all of the drawbacks of this method, it allowed one to exclude the contribution of the plasma radiation.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

3.2. Working Regimes of Electrodes It is evident that the processes involving electrodes are essential for the work of the whole electric arc plasma generator. The stable working regime depends considerably on these processes, and, in particular, on the presence of the emitting spot or on the emission from the greater part of the electrode. In the creation of alternative current plasmatrons, especially those designed for work with gases, which do not contain oxygen, it is reasonable to take the high–melting metals (first of all, doped tungsten) as a material for the electrodes. This gives the opportunity to assure the work of the electrodes under high temperatures and, by this, to relieve the conditions for the repeated ignition of the arc after the passage of the current through zero. Moreover, in some cases, this allows one to provide the regime of the thermo– emission which leads to decrease of the current density and to decrease of the electrodes’ run–out. To rise the emissivity of the electrodes, tungsten doped with thorium, yttrium, or lanthanum is used [29,38]. Under a large current density, the temperature of the electrodes’ surface achieves such values, under which oxides dispart in some cases. Nevertheless, the electrodes can also work for any hours in such a stressed regime, since the disparting oxides are compensated by diffusion of the thorium, yttrium, or lanthanum from the inner layers of the electrodes; and under this, the rate of the diffusion rises under the rise in temperature. These cases are possible (under strong currents) when the electrode surface is depleted of the dopants, and the tungsten works alone. The case of the alternative current. For the alternative current of the 50 Hz frequency, it was found that under small current (lower than 200 A), a spot occurs on the surface of the electrode. Under the current growth, the passage from the emitting spot to the emitting surface is observed (Fig. 2.21). This passage depends only on the temperature of the electrode surface and occurs jump–wise. It is necessary to note that according to [39] one observed the dependence of the variation of the current density on the cathode geometry (made of tungsten doped by the thorium) and the value of the discharge current.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

109

Under presence of the spot, the temperature of the surrounding part of the electrode surface is 2000 K or lower. This temperature is practically constant over this part of the surface, i.e., from this part the contribution to the emission current can be neglected. The radius of the spot is 0.6−0.8 mm. Knowing the distribution of the radiation power along the spot on a given wavelength, it is possible to determine the radial distribution of the temperature along the spot. Actually, it is possible to write for the radial distribution of the temperature

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

(2.42) where λ is the wavelength, cm; ε is the emission of the tungsten on the corresponding wavelength; the measurements were implemented in the spectrum range 434, 452, and 470 nm; and z is the radiation energy of the black body. The effective mean temperature of the spot changes in the range of 3200–3400 K. At the center of the spot a melting region of the radius r = 0.1–0.2 mm exists where the temperature achieves a value equal or more 3800 K. In this case, the most probable mechanism of the emission is the thermo auto–electron emission (the T–F–emission) which is able to provide the observed density of the current at the spot. A similar mechanism in the rise of the current density up to 105–106 A/cm2 in the arc discharges was discussed by a number of authors [36,38]. If the current grows on account of the ohm heating and the temperature rise of the environmental gas, the temperature of the electrodes’ surface increases; and at the temperature of 2800−3000 K, the passage from the spot to the emitting surface is observed. In some cases, the appearance of two spots at one electrode was observed in the transient region. The passage to the regime without the spot was realized in all types of plasmatrons when the temperature achieved a corresponding temperature.

Figure 2.18. Dependence of electrode surface temperature versus the working current (working gas – argon, gas consumption 2.1 g/sec).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

110

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.18 presents the dependence of the electrode surface versus the working current for one- and three-phase regimes of the electrodes’ work for the PPT–type plasmatrons. It is seen that under the one–phase regime the electrodes are heated lower than under the three–phase regime at the same value of the current. This seems to be natural, since under the three–phase regime of burning the temperature of the environmental gas is higher than under the one–phase regime. This is due to the larger amount of the electro– magnetic power allotted in the plasmatron arcs. Moreover, under the three–phase regime of burning, the electrode is heated for a longer time than under the one–phase regime, since one of the three arcs of the plasmatron burns continuously. It is necessary to note that in the implemented experiments, the spot remained under the increase of the current value up to 300−400 A (in absolute value) and more and with the intensive water cooling of the electrodes. At the same time, for the current lower than 200 A but under heating the electrode up to the mentioned temperature (in the case of using the hydrogen or helium as the working gas at high pressures), the spot disappeared. Therefore, the passage from the regime of burning with the spot to the regime without the spot under the conditions considered depends exclusively on the temperature of the electrode. The dependence of the current density on the electrode surface versus the current of the arc is shown in Fig. 2.19 [40].

Figure 2.19. Dependence of current density on the electrode surface versus the arc current for plasmatrons PPT and EDP.

Under the current rise from 50 to 120 A, the bright visible spot was on the electrode surface. At a current increase to approximately 200 A, the passage from the spot to the emitting surface is observed. At this level of current, the appearance of two spots was observed on one electrode. The next range of current corresponds to the regime when the major part of the heated surface is emitting. Under the square of the emitting surface, the surface of the electrode that has been heated up to the temperature shown in Fig. 2.18 is implied. Under the larger currents 2−16 kA (in the EDP–type of plasmatron), the regime of the emitting surface remains, although the temperature of the electrodes’ surface increases.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

111

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

In the regime without the spot, the significant part of the electrodes’ surface emits, and under the current rise, the emitting square increases. In this regime the emission has a mainly thermo–electron character (the T–emission). Under the passage to the T–emission, the current density falls sharply. But due to the fact that the electrodes are composed of bars each with a diameter of 1 cm and the heat exchange between the bars is weak (as a rule, one bar is mainly heated), their temperature rises under the current growth. The density of the thermo–emission current also increases. Under very high current (10−20 kA) the appeared spots with a diameter close to the bar diameter move over the electrodes’ surface with a velocity of ~60 m/sec. Under this, the surface melts, the heat exchange between the bars increases, the major part of the surface is heated, and the diameter of the emitting surface also increases; but its temperature decreases a little in spite of the current rise. The temperature of the emitting surface in the regimes corresponding to the T–emission can provide the current density that is observed in the experiments.

. Figure 2.20. Dependence of the thermal emission current versus the surface temperature.

Figure 2.20 gives the dependences of the thermo–emission current versus the temperature of materials used in the cathodes. The values of the Richardson constant and the output–work were assumed to be ones obtained on the basis of the analysis of the data from [38]. Following from the results obtained, the largest values of the voltage of the repeated ignition after the current passage through zero correspond to the regime of burning under presence of the spot. Under the passage to the regime of burning without the spot, the ignition voltage decreases. When the current rises, the peaks of the repeated ignition are smoothed. This phenomenon can be explained by the growth of electron concentration in the inter– electrode gap. From the results obtained, it is possible to conclude that the arcs in the plasmatron of the alternative current burn more stably in the regime without the cathode spot when the major part of the electrode surface emits. The case of the direct current. Similar regimes of the electrodes’ work were observed under work on the direct current. The cathode was made of an insert pressed into the block– shell with cooling water. The temperature of the cathode was regulated by changing the length and diameter of the insert (l = 2÷10 mm, d = 2÷6 mm), and also by the value of the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

112

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

current. The following regimes, which depend on the temperature of the cathode surface were observed. 1. Under the temperature exceeding 3000 K, a significant part of the electrode surface emits. The intensive lines II La are observed in the radiation spectrum near the surface. The current density is large and achieves (2−4)×103 A/cm2. In this case, the most probable regime is one with thermo–emission, and the emission is stipulated by La and La2O3. 2. When the temperature of the surface grows to 3600−4500 K, the electrode surface melts, the emitting square increases, the lanthanum lines disappear, and the tungsten emits. Correspondingly, the current density falls and oscillates in the range (0.7−2.5)×103 A/cm2. In the case of a more intensive cooling of the cathode, the surface temperature decreases and the cathode spot appears on its surface. At the center of the spot in the zone of the tungsten melting, the temperature achieves the value 3700−4300 К. The lanthanum lines are absent; the current density increases again and achieves the values 103 A/cm2. Under this, the mechanism of the thermo–emission (the T–F–emission) is the most probable. In some cases, the regime with a “dark spot” at the center of the emitting surface appears. The temperature of the spot does not exceed 3500 K, and before the dark spot appears, the lines of the lanthanum ions are strong in the spectrum. Apparently, the dark spot consists of melted lanthanum. Around the dark spot, a ring of melted tungsten is created, on whose surface the temperature of 3800 K is a little higher than in the dark spot. The lines of the lanthanum are not observed over the ring. The current density achieves the value ~105 A/cm2. In this case, thermo–emission is the most probable mechanism. Besides the regimes described, transient regimes were observed, in particular, ones involving motion of the cathode spot.

a)

b)

Figure 2.21. Temperature distribution over the cathode surface

The estimates show that, in the case of the lanthanum dopants, the distribution of the temperatures can have a cavity at the center and the maximum at some distance from it (Fig. 2.21). The maximum is stipulated by the energy of the output–work of the dopants’ electrons, by the flow of the ions, and by the sizes of the doped zone. Under this, the smaller the output–work, the lower the temperature at the center of the cavity. Thus, with the work under the direct current, the cavity of the temperature at the center of the spot can be explained by the heterogeneity of the output–work on the cathode surface that appears as a result of the diffusion and sedimentation of the lanthanum on the cathode in the region of the spot. Creation of the dark part of the surface in the cathode spot can appear only under higher temperatures if one does not consider the heterogeneity in the cathode properties.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

113

Certainly, this picture will be essentially corrupted in the work under the alternative current due to the continuous change in the electrode polarity.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

3.3. Investigation of the Electrodes’ Material For assertion of the emission character and, also, the factors affecting the break–up of the electrodes, the material from the electrodes’ surface (before and after the work under various regimes) was taken and subjected to investigations. For research of the chemical compound, Auger–spectroscopy was used. The investigations were carried out on the electron–ion spectrometer of the firm Leibold Hereaus with the electrostatic analyzer of the high resolution ΔE/E = 104. For registration of the spectra, the species were placed into the vacuum chamber (during the work of the electronic gun, the residual pressure was p = 10–14 MPa). The survey of the spectra was implemented under E r = 4 kV, I r = 0.03−0.08 mA, and the amplitude of modulation E m = 1–5 V. During the research of the chemical compound of the electrodes’ surface at various depths, the species were etched by a beam of the argon ions under Er = 4 kV, Ir = 1 μA, argon pressure in the chamber p ≈ 10–9 MPa, and the etching velocity 5−2 nm/min. The scanning was realized over the square 5×5 mm [41]. The Auger–spectra of the electrode made of WY–30 were measured before the work; the spectra of the same electrode surface were measured after its work in the plasmatron of the alternative current; the spectra of the near–surface regions of this electrode (before and after the work) were measured in the process of step–wise etching. Some peaks remained unidentified. It is seen that during the process of etching the intensity of the peaks С and О generally falls, but the intensity the tungsten peaks rises. The peaks identified as belonging to the dopants (La, Y, and Nd) behave differently for the initial and used electrodes during the evaporating of the surface by the beam of the ions. It is seen from the spectra that the relationship between the intensity peaks of various elements and, then, between the concentrations of the corresponding atoms are different on the surface of the initial species and the used one. From the relationship of the intensities, it is possible to find the atomic concentration of each element CA. For С and О the concentration was determined by the peak KLL of the Auger–passage, for Y and Fe the LMM peak, and for other elements the peak MNN of the passage was used. It is possible to conclude that the surface of the initial species contains an appreciable quantity of C and O (from 6 to 8 atoms of C and 3–5 atoms of O fall on 10 atoms of W), and their quantity decreases during etching. The thickness of the layer consisting of C is about 100−200 nm. The splash of oxygen appears at the depth 250–400 nm. The distribution of the dopants can be considered uniform through the whole volume for the initial species of all batches made of tungsten WL–10 of small diameter (2–6 mm) doped by lanthanum. Under this, 2–4 atoms of the lanthanide fall on 100 atoms of W, which approximately corresponds to the technical norms. For the electrode made of tungsten WY–30 doped by yttrium (with a diameter of 40mm), and for tungsten doped by lanthanum (with a diameter of 10 mm), the rare–earth metals were not detected at the depth is distributing about 600 nm when etched. This is

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

114

Philip Rutberg

possibly connected with the difficulty in distributing the dopants uniformly in manufacturing species of a relatively large size. The surface of the used species became more enriched by the oxygen, carbon, rare–earth metals, and other dopants. For example, on the surface of the electrode made of WY–30, the following quantities of other dopants fell on one atom of W: 103 atoms of C, 25 atoms of О, 118 atoms of Y, 110 atoms of Еu, and 69 atoms of Fe. Investigation of the sub–surfaces of the used electrodes showed that the distribution of the rare–earth dopants through the depth varies for different electrodes. This is possibly connected with the different regimes of their work. For example, the concentration of the rare–earth dopants in the species made of WL–10 (this was the cathode used in the plasmatron of the direct current; neodymium and lanthanum were detected) has a maximum at the depth of 100−200 nm. In the electrode made of WL–10 used under the alternative current, lanthanum was detected with the maximum of the distribution at the same depth. The dopant content in the electrode made of WY–ЗО (Y, Fe, and Eu) falls rather sharply with an increase in depth inside the species from the surface. The carbon in the used species presents at a depth of up to 300–500 nm, and under this, dependence of its concentration on the time of etching has the same character as that of the initial species. It may be supposed that some part of the carbon was absorbed by the surface layer with a depth of any number of nanometers. This is evidenced by the sharp fall of the carbon concentration at the beginning of the etching and reduction of this fall under further etching. It was detected that many of the Auger–peaks shift relative to the initial positions during the etching of the surface. This may be evidence of the different state of the valency of the elements oxidizing at various depths. But this question needs more detailed investigation. By the data of the quality and quantity of Auger–analysis implemented for the material of the initial electrodes and those used for various lengths of time, it is possible to make some preliminary conclusions. In the initial species of the large diameter of 10−40 mm, the rare–earth dopants are distributed non–uniformly. The enriching of the surface layers by the rare–earth metals is provided on account of the inner regions. Under the temperature rise of the electrode after the discharge ignition, the diffusion factor of the dopants increases, and they go out from the volume onto the surface. In the initial species of the small diameter 2−6 mm, the rare–earth metals are distributed comparatively uniformly, and in the process of the long work of the electrode, they go out continuously onto the surface. Similar phenomena were observed in the electrodes that worked under the direct current. The results of investigations of electrodes made of tungsten doped by yttrium showed: 1) in addition rare–earth elements, the significant inclusion of other elements, in particular, Fe; and 2) the fast heating of the working electrode, must lead to the non–uniform thermal expansion of the inclusions in comparison with the main mass of the tungsten or even to their boiling. The corresponding data on the thermal expansion are represented in Table 2.5.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

115

Table 2.5

T, K kW (2×10–6) kFe (2×10–6)

15 00

1000

1100

1200

1700

4.9

5

5.1

5.5

5.9

14.7

15.5

22.5

22. 4

22.0

320 0 8. 8

Such behavior of the inclusions may lead to fissure and cleavage of the electrode material which is actually observed in the work of the electrodes of the large diameter made of tungsten doped by yttrium. As follows from the results obtained, oxygen always presents in the sub–surface regions of all species, both the initial and used ones. The conditional temperature of boiling for the rare–earth elements is upwards of 3687°C (for ТhО2 ), 3827°C (for Y 2 O3 ), and 3457°C (for La 2 O3 ) with the output–work of 3, 3.3, and 2.96 eV, correspondingly. Thus, it is natural to assume that in the case when the temperature of the electrode surface is lower than the temperature of break–up of the oxides, the current of the emission is stipulated by the output–work of the corresponding oxides, which allows providing the minimal run–out of the material of the electrodes.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

3.4. Run–Out of the Electrodes The question about the run–out of the electrodes is of the great interest. This is so from the point of view of creation of plasmatron constructions of the direct and alternative current that work for a long time, since the resource the electrodes is of the crucial matter. In some cases, it is advisable to provide the uniform evaporation of the metal from the electrode. The peculiarity of the electrodes working in systems of the alternative current is in the fact that each of the electrodes is alternately served by the cathode and anode, and the run–out of the electrodes is presented by the summary run–out of both the cathode and anode. As it follows from the fulfilled experiments, the run–out of the electrodes depends on: 1) the quantity of the impurities containing oxygen in a relatively largeamount, since the electrodes out quickly because of the oxidizing of the tungsten; if it is necessary to use environments containing oxygen, the electrodes must be defended by a protecting gas (argon, nitrogen, or hydrogen); 2) the oscillations of the voltage on the arc and peaks of the repeated ignition after the current passage through zero; 3) the density of the gas, the character of the emission of the electrode’s, and the temperature of their surface. The question on the balance of energy on the electrodes was considered by some authors in detail [38,42]. As for the investigated plasmatrons of the alternative current, it is evident

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

116

Philip Rutberg

that the energy transferred to the electrodes by radiation and by Joule heating is comparatively small [42]. Propagation of heat in the electrodes and its bleeding by the cooling liquid and by the vortex of the working gas is strongly hampered in the short–time regime. It is possible to state that only a small part of the desorbed energy is spent for evaporation of the material of the electrode. Variation of the electrodes’ mass was determined by weighting on the analytical balance. Before the investigation, the electrodes were degassed. The values of the run–out were determined at each point by averaging over 10 experiments. The fast rise of the run–out was observed at the temperature close to the temperature of break–up of the emitting dopants. Under the conditions optimal from the point of view of the run–out decrease, i.e., at the temperature 2800–3000 K and the current density 500 A/cm2 , the specific run– out of the value 10 –8 –10 –7 g/Coul was by three orders lower than that of 10–6–10–4 g/Coul at the temperature of the dopants’ break–up. Actually, as it follows from the analysis of the data obtained, the minimal run–out is observed in the case when the regime of the thermo–emission takes place and the rare–earth dopants’ oxides remain (of ThO2 , Y2 O3 , and Lа2Оз). Because of the accelerated diffusion, the atoms of the rare–earth elements come in a satisfactory quantity, and the current from the cathode is provided by the low out–work of the oxides. In this case, the specific run–out is 10 –8 −10 –7 g/Coul. Under the rise of in temperature of the electrode surface, the oxides are brokenup. But the rare–earth dopants (which have outputwork lower than that of tungsten) remain on the surface in a satisfactory quantity. The regime of the thermo–emission remains, but is mainly provided by the dopants. In this case, the run–out rises and is of the value 10–7–10–5 g/Coul. Under the larger rise in temperature due to an increase of the current or changing the cooling regime, the rare–earth dopants evaporate from the surface. The regime of the thermo– emission remains, but now it is provided by the output–work of the tungsten. In this case, the run–out is maximal and achieves 10 –6 −10 –4 g/Coul. Under the regime corresponding to the presence of the cathode spot, thermo– emission is realized. The melting temperature in the spot zone is high, and in spite of the small size of the spot, the run–out is 2×10–8−3×10–7 g/Coul, which is a little larger than in the regime of the thermo–emission where the current is provided on account of the rare–earth elements. In the case when a regime is observed and the dark spot (due to lanthanum) appears, regime of thermo–emission is realized from the spot that is sufficient for the observed density of the current. On account of the diffusion of lanthanum from the inner layers of the electrode, its quantity is sufficient for providing the observed regime. Under such a regime, the run–out is minimal and has a value of only (2−6)×10–9 g/Coul. Moreover, it was confirmed experimentally that in the presence of the voltage peaks of the repeated ignition in the one–phase regime of the arcs of the alternative current and the peaks of the voltage oscillations on the arc, the run–out of the electrodes’ metal is larger than that under the absence of such peaks. A similar increase in run–out was observed under the work with a direct current when the amplitudes of the voltage pulsations exceeded 15%.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

117

The peaks of the voltage oscillations on the arc with an average amplitude of 30% and a frequency of 8 kHz occur under a current larger than 1 kA and an arc column length more than 20 cm; under the smaller values of the current and length, such oscillations are absent completely. It is possible to assume that tungsten begins to emit, caused by the break–up of the mono–layer of the oxide due to the temperature rise under the current increase. In turn, to provide the same density of the current, it is necessary to raise the temperature of the emitting surface, which causes the burn–up of the tungsten layer. The process repeats cyclically, causing voltage oscillations on the arc which correspond to the rise of the voltage drop on the cathode. It is assumed that in this case the additional run–out of the electrode metal is mainly realized in its cathode phase due to the mechanism similar to the cathode sputter on account of the splashing of the melted particles of the electrode. If at some point on the electrode an additional energy E appears, that is not bled in time, and around which a temperature field of the value T is created, then it is possible to calculate the mass of the melted metal as follows:

M = 0.31 к

E cT

,

(2.43)

0

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

where c is the specific calorific capacity of the electrode material, for tungsten the averaged value of this parameter is с = 0.175 W/(g×К), and Tо is the melting temperature of the electrode material. The balance of the energy bled additionally on the cathode is determined by the ions and consists of the ions’ kinetic energy , and the energy of neutralization on the cathode surface . Therefore, ,

(2.44)

where α+≈ 1 and αn ≤ 0.5 are the corresponding coefficients of accommodation (according to [40]) Uс/ is the average drop of the cathode potential under the peaks of the repeated ignition and pulsations of the voltage on the arc, t is the time of existence of the peaks and pulsations, and f is the frequency of the impulses. Then using (2.44) and taking into account the difference between the evaporation temperature Te of the electrode metal and the achieved temperature Тr–o of the run–out, we obtain

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

118

Philip Rutberg .

(2.45)

In the regimes under consideration, the ratio of the electronic current by the ionic one is assumed to be [35] approximately equal to 10. It is necessary to note that the energy additionally bleeding on the cathode in all cases is smaller than the energy determined by means of the oscillograms of the current and voltage. This is somewhat natural since not all of bled energy is transferred to the cathode. The additional values of the run–out obtained experimentally under the presence of the peaks of the repeated ignition (due to the energy bled as a result of the pulsations) and the values of the run–out calculated by (2.45) are (1−5)×10–7 g/Coul. These values are related to the regime of the work under the presence of the spot. In comparison with the three–phase regime of the arcs’ burning, these values are approximately two times larger. Although such a coincidence results can be regarded as satisfactory, the results obtained must be considered cautiously, first of all, because of the rough estimates of the voltage drop on the cathode and the value of the ionic current, and also, because of the approximate presentation of the mechanism of the energy transfer to the cathode. As a conclusion, note that in estimating the specific run–out of the electrodes under a large current, it is necessary to keep in mind the large consumption of working gas (1−10 kg/sec), which hampers cleaning the electrodes of oxygen impurities.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

3.5. Work of Electrodes in the Oxidizing Environments: The Rail Electrodes If air or other oxidizing environments are used as the working gases, the erosion of tungsten and tungsten-containing alloys increases by two orders. So, it is advisable to use electrodes made of the copper or copper-containing alloys, intensively cooled, and working in the regime of the arc location point moving along the electrode’s surface. The motion can be realized on behalf of the “railtron” effect and the gas–dynamic forces. The value of acting on the arc is directly proportional to the value of the arc current and the gas flow velocity (Fig. 2.22). As a result, successful construction of electrodes was achieved with a work resource of several hundred hours. In Fig. 2.22, F is the force acting onto the electric arc:

F = IBl sin α , where I is the value of the current, А; B is the value of the magnetic induction, T; l is the length of the wire, m; and α is the angle between the direction of velocity of the arc motion and the induction.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

119

Figure 2.22. Model demonstrating the interaction of the current in the cross–section diamagnetic wire (1) with the magnetic field excited by the currents in the rails (2) of the railtron.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Continuous motion of the arc discharge and the arc location–point along the electrode’s surface constrains the time of its presence at one place and, by this, decreases the value of the erosion. Calculations of the non–stationary heat exchange of the arc with the electrode’s surface (taking into account the evaporation and melting) show that minimal erosion is achieved in the case when the time of the arc localization at the same place does not exceed the time of the heating up to the melting state around the arc location–point. For example, this time is approximately 10–4 sec for currents of about 102–103 A. The velocity of motion of the arc location–point along the electrode’s surface varies in the range of 103–104 cm/sec. Several types of rail electrodes have been designed for work in plasmatrons of alternative current. Two of them are shown in Fig. 2.23.

a)

b)

Figure 2.23. Electrode with symmetric (a) and asymmetric (b) position of the cooling channel.

A series of experiments have been implemented on investigation of electrodes surface wear. On the basis of the results, a new construction of electrodes has been designed, application of which has allowed one to obtain a continuous work duration of electrodes in the three–phase alternative current plasmatron of more than several hundred hours. The value of specific wear in these experiments varied from ~3.1×10–6 g/Coul up to 0.7×10–6 g/Coul [43].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

120

It is also necessary to note other factors influencing the working resource of the rail electrodes. When air is used as the plasma generating gas, the following phenomenon is observed. As the dense layer of the scale (the heat conductivity of this layer is lower than that of pure copper) grows, the time for which the spot of the arc location point remains without motion, increases. As a result, the probability of its appearances in the caverns in the metal is increased Cracks appear on the electrode surface, which insert into the body of the metal and lead to the breakthrough of the liquid from the cooling channel of the electrode into the electric arc chamber of the plasmatron (Fig. 2.24).

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.24. Surface of the plasmatron electrode after work.

The presence of carbon particles in the inter–electrode gap leads to a decrease in the initial breakdown voltage; in turn, this decreases the size of the working zone of the electrode, i.e., the run of the arc becomes shorter, and the wear of the electrode in this zone increases because of the growth of the heat load. During the work, the electrode surface becomes ragged at the place of contact with the arc and takes the form of merged half–spheres of a diameter of 1–3 mm, and a thin layer of the copper oxides is observed on the frontiers of their mergence. Since the electrode erosion depends both on the power of the heat source and the duration of its application, the design of advantageous conditions for the directed motion of the location points of the arc must lead to a decrease in the heat influence and corresponding erosion of the electrodes.

50×, non–etched

100×, etched

Figure 2.25. Photos of the microstructure surface layer of the electrode. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

121

The local melting begins at the thermodynamically unstable frontiers of the grains. The appeared liquid phase that appears is pressed up onto the surface of the metal by thermal expansion. Figure 2.25 presents the microstructure of the surface layer of the electrode in the zone of maximal wear on the non–etched and etched specimens. As seen Fig. 2.25, the deep caverns in the melted–out metal are on the electrode surface; these caverns end in cracks going inside the metal. A thinned, oxidized and, in some places, melted layer of a depth of up to 200 nm is observed. But the metallographic investigation dos not show any changes in the metal structure in the internal part of the electrode. A similar structure is typical for the pure brands of copper subjected to plastic deformation and annealed under temperatures not lower than 600°С. The character of structure of the internal zones does not allow one to suppose that the metal of the internal surface of the electrode had been subjected to temperatures close to the temperature of melting for an essentially long time. This is proven by the absence of zones with the melted grains or over–burns in the internal part of the electrode. But by data obtained from roentgen–spectral analysis, in the surface layer there is an increased concentration of sulfur, which exceeds by 3–4 times the admissible one for such a brand of metal, of 0.010–0.021% ; and of carbon, which usually is not present in copper in noticeable quantities, 0.04–0.21%. These facts allow one to conclude the following: •

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

• •

the melting of the electrode material does not happen in the working process, but the temperature just on the surface is close to the melting point in a thin film of 10–15 μm, which appears in the zone of maximal thermal load; the contact temperature on the internal surface of the electrode, which contacts the cooling water, does not exceed 200–250°С; the breakup of the electrode happens not as a consequence of melting and local burn– through of its material, but rather because of losing the fastness of the electrode under the nfluence of high temperatures and chemical reactions; for example, a copper–carbide layer can appear that possesses worse thermo– and electro– conductive characteristics in comparison with pure metal.

As a result, it is possible to emphasize the most important parameters affecting the value of the electrodes’ resource: the velocity of the arc motion, the distance between electrodes, the current value, the state of the electrodes’ surface, their material, peculiarities of construction, and, the impurities in the working gas.

3.6. The Core–Type Electrodes Core electrodes of various types are used in high-voltage plasmatrons of middle power that work in oxidizing environments [44]. Figure 2.26 presents the typical core–type electrode.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

122

2

Figure 2.26. Design of core type electrode: 1 – electrode,

1

2 – cooling channel.

Since in these plasmatrons the voltage drop on the arc is several thousand volts (approximately 1000–3000 V), the value of the working current is relatively low. As a rule, it does not exceed 30 A. In such a construction, the arc location point on the electrode surface is practically fixed, and the thermal flows inserting into the electrode are very large. To provide a needed resource of electrodes, their very intensive cooling is necessary. Moreover, one has to choose materials optimal for work under concrete conditions. The results of the tests implemented show that the alloys of copper and iron have the best characteristics. These are the (Cu+Fe)– alloy having a specific wear of (4–6)×10–6 g/Coul, and the (Cu+Fe+Y203)–alloy (with added dioxide of yttrium) having specific wear of (5–6)×10–6 g/Coul. For comparison, the specific wear of the copper under the analogical conditions is ~6×10–4 g/Coul, and for stainless steel the value is (0.7–1.6)×10–5 g/Coul.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4. THE MAIN TECHNICAL CHARACTERISTICS OF PLASMA GENERATORS AND THEIR CONSTRUCTIONS The first arc plasma applications were developed at the beginning of the twentieth century in Germany and Norway for nitrogen oxide production and existed until the end of this century while they were superseded by new economically efficient and productive technologies. In 1911 plasma was used for metal fusion in the furnace. The arc torch with gas squeezing of the arc column was patented in 1921. The arc stabilized by water vortex was proposed in 1922. One of the first methods of electric cracking of natural gas was realized in Germany in 1940. Plasma technologies have been widely developed diuring the last 50 years of the twentieth century due to the development of research in the field of gas discharge. Plasma was used in the following industries: • • • • • •

plasma metal processing and plasma metallurgy [45,46] ; material reduction [45] ; various technologies of changing the surface properties of metals [47] ; various kinds of coatings by plasma method [48] ; production of disperse and ultra disperse powders of various materials [49,50] ; and plasma ignition of dust–coal fuel [51].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

123

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

At the middle of the last century, plasma generators (also called plasmatrons or plasma torches) were developed for solution of such special research problems as pumping powerful gas–dynamic lasers, blowing cones in the wind tunnels, and laboratory modeling the conditions of thermal loadings on elements of space vehicles. Now plasma is investigated not only as an interesting physical phenomenon, but is also widely used in various practical applications. Low temperature plasma (T < 104 K) has begun to be used for material processing: melting and foundry, cutting and welding, coating, hardening, for testing of materials’ properties, and, for creation of new materials. Thin carbon films with diamond–like structure and crystal diamonds are grown in the hydro–carbonic plasma environment rich with radicals, under pressure from torr units to atmospheric pressure. Earlier, during the 1950’s methods of diamond synthesis were based mainly for creating conditions with very high levels of pressure and temperature. During recent decades, plasma-based technologies (the methods of pyrolysis, plasma high temperature oxidizing, gasification, and high–temperature plasma mineralization) have emerged in processing of waste materials of various types: neutralization and destruction of dangerous chlorine–fluorine–containing compounds, treatment of flying ash, and plasma high-temperature oxidizing of organic–containing waste (MSW–municipal solid waste, coal, wood, and so on) with synthetic gas generation aiming for renewable energy or synthetic liquid fuels production. Plasma generation for various practical applications is also carried out different ways, depending on the requirements of its structure (the determined by the plasma-forming environment), requirements of the flow rate, and physical parameters (temperature, pressure). So, for example, for deposition of thin carbon films, installations can be used that have power of any kilowatts and operate on the basis of microwave (2.45GHz) or radio–frequency (13.56MHz) plasma reactors maintaining conditions in a comparatively small volume, and sometimes using plasma generators [50,52].

4.1 Classification of Plasma Generators Large-current arc discharges and plasma generators developed on their basis are key elements of new plasma technologies. The existing designs of plasma generators can be divided into two basic groups: DC plasma generators [53,54] and AC plasma generators [55,61]. DC Plasma Generators. Internal energy of the electric arc is transformed into the internal energy of the working gas in a plasma generator. It is realized by the gas heat exchange with the arc discharge column. The flow of the arc column is used by the stream of the plasma–forming gas to intensify the heat exchange process. At the same time, the gas flow thermally insulates the chamber walls from the heat flows, but does not prevent heat transfer by radiant flux from the arc column towards the plasma generator walls. Complete thermal insulation of electrodes is impossible due to the electrical contact between the arc and the electrode surface. In the contact area, especially in the presence of arc spots and significant current values (>102А), the density of the heat flow reaches 109–1010 W/m2. Under these conditions, the long-time operation of electrodes is only possible if they are made of refractory materials (tungsten, molybdenum, hafnium, etc.) and cooled at the place of electrode joint with chamber case of the plasma generator. Electrodes are made of copper or

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

124

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

steel, and they need strong cooling if oxidizing media (air, etc.) are used as a plasma generating gas. In this case, for increasing the life of the electrode it is necessary to provide conditions under which the arc spots will continuously move along the electrode surface. If so, this reduces the need for the electrodes’ cooling, and the average temperature of electrodes’ surface lower than the melting point. The electric arc erosion is insignificant (10– 6 –10–4 g/Coul) at the locations of the arc spots due to short life span (≤10–4 sec). There are two ways of realizing the arc spot motion in DC plasma generators: by gas dynamics and by the effect of the magnetic field action on the current. Physical processes in the positive arc column (electric conductivity, thermal conductivity, radiation, etc.) determine the heat transfer into the plasma-generating gas blowing through the arc. The erosion and life span of the electrodes are mainly determined by phenomena near the electrode. The basic section of the column is blown by the transverse flow of the plasma-generating gas. Small sections of the arc near the electrode’s surface are not blown over. Complex non–equilibrium processes in these thin electrode layers cannot be controlled by any modern diagnostics. That is why theoretical methods would be of great use. The volt–ampere characteristic is an integral characteristic of the arc in the plasma generator as well as in free-burning arcs. The fundamental difference between the volt–ampere characteristic of the plasma generator electric arcs and the free-burning arcs or the arcs stabilized by the walls lies in the fact that their character and value of the average strength of the electric field E depend on total gas flow rate. In most cases the volt–ampere characteristics are low dropping. This is true for the range of the current I = 200–600 А. The typical scheme of a DC plasma generator is presented in Fig. 2.27.

… Figure 2.27. Scheme of DC plasma generator.

The arc column is optically transparent and radiates as a volumetric emitter at a plasma temperature of ~104 К and density of particles ~10–19 cm–3. Under stable conditions, in cylindrical column shape and intensive turbulent heat exchange, the share of the radiant convective heat exchange to the channel walls is insignificant, and the plasma generator has an efficiency of 0.6–0.8. This mode of arc burning is realized at relatively low currents and relatively large arc lengths in DC plasma generators with a power of 100–200 kW. That is why DC plasma generators have the following peculiarities: •

The exclusive characteristic of all powerful DC plasma generators is the relatively long discharge chamber comparatively small internal diameter. In this case, the working gas is fed along the whole length of the working chamber. It causes arc

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

•

•

125

contraction, and its surface temperature, as a rule, is higher than 10000–15000 K. That is why the basic heat exchange between the arc and the working gas is realized by radiation, and the energy losses are insignificant. Application of the direct current, as a rule, requires the ballast resistor connected in series with the arc. It is used for stable arc burning at dropping the volt–ampere characteristic and for control of the arc current. But it causes additional active power losses. The power supply system for DC plasma generators is comparatively expensive (the most expensive part is the thyristor equipment).

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

AC Plasma Generators. Single–phase and multi–chamber AC plasma generators (Fig. 2.28) have the same specific features as DC plasma generators; besides, the necessity arises to provide repeated ignition of the arc after the current passage through zero. Under this situation, the multi–phase plasma generators are preferable.

Figure 2.28. Scheme of AC plasma generator.

Let us note the following peculiarities of AC plasma generators: •

•

• •

Single–chamber multi–phase AC plasma generators provide simultaneous burning of several arcs in one chamber. The chamber can have a spherical form, which is optimal from the point of view of the energy loss decrease on the chamber walls. Several arcs can burn simultaneously in one chamber, and at the expense of electron diffusion (and, also, due to the additional electron injection into the chamber volume), a sufficiently vast area (volume) with high concentration of current carriers can be formed. This results in diffusion character of arc burning; in this case the temperature is rather lower than at contracted mode of burning. The diffusion mode of arc burning provides smooth current transition through zero, and the current curve form is close to sinusoidal. Two mechanisms are basic for gas heating at the diffusion mode: forced convection and blowing of some gas through the arc. The energy of the gas heated at the expense of excitation energy relaxation and atom recombination is redistributed among the remaining gas, which results in heating up to the average mass temperature. In this case, the losses are rather low (there are practically no radiation losses), and the transformation coefficient of the discharge energy into the gas energy is high.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

126 • •

Under variation of the current value, which is connected with arc instability, the AC power supply system automatically reacts by increasing the additional voltage and suppresses this instability. power supply system of a multi–phase plasma generator using commercial frequency (50–60 Hz) is significantly cheaper and simpler than power supply systems of DC arcs. Besides, it can be made of standard industrial components.

Maximal parameters of AC plasma generators developed in the United States operating in a long time mode have reached up to 3 MW (Westinghouse) and in Russia up to 2 MW, and in short time modes up to 80 MW (Russia) with the thermal efficiency of 60–90%. Descriptions of typical power plasma generators are presented below. Plasma generators with rod electrodes are intended for heating the inert gases: nitrogen and hydrogen at pressure 0.1–6 MPa. The flow rate in nitrogen is 0.01–10 kg/sec. Heating is carried out up to temperatures of 2000–6000 K with the thermal efficiency of 60–85%. The power range of these plasma generators is from 100 kW up to 80 MW [40]. It is necessary to take into account that in some constructions of DC plasma torches of high power that are working in long–term modes, the cathode unit (as the most widely used one) is protected by additional blowing/input of inert gases N2 or Ar. But this makes the whole system more complicated and increases the price. The following scheme shows comparative characteristics of the DC and AC powerful plasma torches.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

POWERFUL PLASMA TORCHES PROVIDE SUFFICIENT POWER DENSITY 102 ÷ 104 J/cm3 AT REQUIRED POWER AND GAS DENSITY

OBTAINED PARAMETERS

DC POWER FLOWRATE LIFE TIME ENVIRONMENT

up to 3 MW up to 100 g/s 100-1000 hr AIR, N2, H2, Ar, He

AC POWER FLOWRATE LIFE TIME ENVIRONMENT

up to 3 MW (up to 1 MW for air, O2) up to 100 g/s up to 1000 hr AIR, O2, N2, H2, Ar, He, CO2

Figure 2.29. The main parameters of DC and AC plasma generators.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

127

POWERFUL PLASMA TORCHES

DC

AC PECULIARITIES

• THE ARC IS CONTRACTED - ARC SURFACE TEMPERATURE IS HIGHER THAN 10,000÷15,000 К • BASIC HEAT EXCHANGE BETWEEN THE ARC AND THE WORKING GAS IS AT THE EXPENSE OF RADIATION AND ENERGY LOSSES ARE INSIGNIFICANT • ADDITIONAL ACTIVE POWER LOSSES BECAUSE OF BALLAST RESISTANCE CONNECTED IN SERIES WITH THE ARC FOR STABLE ARC BURNING AND ARC CURRENT CONTROL • POWER SUPPLY SYSTEM FOR DC PLASMA GENERATOR IS COMPARATIVELY EXPENSIVE (EXPENSIVE THYRISTOR EQUIPMENT).

•• HIGH HIGH COEFFICIENT COEFFICIENT OF OF TRANSFORMATION TRANSFORMATION OF OF THE THE DISCHARGE DISCHARGE ENERGY ENERGY INTO INTO GAS GAS ENERGY ENERGY (HIGHER (HIGHER THEN THEN 70-90 70-90 %) %) •• POSSIBILITY POSSIBILITY TO TO CONTROL CONTROL THE THE MODE MODE OF OF ARC ARC BURNING BURNING (DIFFUSE (DIFFUSE OR OR CONTRACTED) CONTRACTED) AT AT TEMPERATURES TEMPERATURES 6,000-20,000 6,000-20,000 КК •• INSIGNIICANT LOSSES RESISTANCE OF INSIGNIICANT BALLAST НЕЗНАЧИТЕЛЬНЫЕ BALLAST LOSSES CURRENT LIMITING REACTORS) RESISTANCE OF CURRENT LIMITING REACTORS) •• CHEAP CHEAP AND AND RELIABLE RELIABLE POWER POWER SUPPLY SUPPLY SYSTEMS SYSTEMS WITH WITH THE THE POSSIBILITY POSSIBILITY TO TO USE USE STANDARD STANDARD POWER POWER EQUIPMENT EQUIPMENT

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.30. The peculiarities of DC and AC plasma generators.

It is necessary to note that in this work we do not consider so-called plasmatrons with removed arc. In such units one electrode (as a rule, the cathode) is blown by the gas flow, but the second electrode (as a rule, the anode) is a conducting fusion (molten metal), on which the arc is shortened. Actually, such units are included in some of types of electro–metallurgic furnaces with all their properties, so they are not discussed in this work. To be more conveniently oriented among the large variety of models of plasma generators that have been developed nowadays, they can be divided into several groups by their properties. By the current used, the electric arc plasma generators are divided into DC plasma generators and AC plasma generators. By operation time, they can be pulse or stationary. By the working body character, they can work with the neutral, reduction, or with oxidizing environments. Moreover, in each group of plasma generators mentioned above, it is possible to point out the groups that differ by constructive and other features. For example, they can differ by the type of the discharge chambers, material and form of the electrodes, a form of working gas supply, or a principle of the arc stabilization. Discharge stabilization can be carried out by various ways, for example, by organization of a gas flow, or by axial or tangential working gas supply in the electric arc chamber of the plasma generator. The method of stabilization by the walls of the electric arc chamber assumes arc squeezing by the cooled cylindrical inserts isolated from the electrodes.

4.2. DC Plasma Generators DC plasma generators with a linear scheme developed for formation of coverings, processing surfaces, and production of new materials is presented in Fig. 2.31. This plasma generator works on air at atmospheric pressure. The cathode material is hafnium. The basic element of the power supply is the thyristor converter with a power of 330–350 kW, maximal current of a 500 A circuit, maximal voltage drop of 700 V, and a 20 kV oscillator used for arc ignition.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

128

Philip Rutberg

Figure 2.31. Schematic diagram of a linear section DC plasma generator; 1 – cathode; 2 – interelectrode insertion; 3 – intermediate anode; 4 – stepped anode.

Among the variety of direct current plasma generators, it is necessary to note modern commercial models.Currently, Westinghouse presents plasma generators MARC–3 and MARC–11 (Fig. 2.32).

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

. Figure 2.32. Plasma generators MARC–3 (left) and MARC–11 (right) [58].

Figure 2.33. Schematic diagram of the Westinghouse DC plasma generator [53].

The MARC–3 plasma generators have been developed for use in such commercial applications as ash vitrification, waste destruction, etc. This plasma generator has a self– Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Investigation of High Current Discharges in Gas Environments

129

stabilizing arc system operating in both modes: with the arc of direct action and with the arc of indirect action. The temperature of the heated gas is 1500–5000°C; the power is 5–300 kW; the working gases are air, oxygen, nitrogen, CO, hydrogen, etc., the life time is 200– 1000 hours (depending on the working gas type). The model MARC–11 is used in the foundry and steel industries. Its electric arc system is self–stabilizing. This plasma generator operates in a mode with the arc of indirect action. The temperature of the heated gas is 1500– 10000°C; the power is 300–1500 kW; and the working gases are air, oxygen, nitrogen, CO, hydrogen, etc. The design of this plasma generator is presented in Fig. 2.33. It comprises two water– cooled cylindrical electrodes with the internal working surface arranged coaxially within a short distance. The arc discharge rotates inside with high speed under action of the magnetic field created by the solenoids. The working gas is supplied into the inter–electrode gap (about 1 mm). Under the power supply, the arc is initiated between electrodes and blown by the working gas into the internal space. The arc current interacts with the magnetic field formed by the solenoids located around both electrodes, and the arc rotates with a speed of 1000– 3600 rev/min. The high rotation speed of the arc in combination with the high working gas flow rate assists good heat exchange between the arc and working gas and also increases the electrode life. From the side of the gas outlet, the plasma generator case warmed to a high temperature is arranged with a flange for fastening and can also be equipped a ledge for building into the furnace a fire–resistant lining or a specialized reactor. The plasma generator is connected to the thyristor power supply of direct current with an adjustable current output. The basic elements of the power supply are the transformer, thyristor bridge, inductor (smoothing reactor), control and protective automatics, and, a control system. Power elements of the power supply systems can be arranged with air or water cooling. The cooling system of the closed type with pumps that provide high pressure includes heat exchanges and is designed on absorption of 30% of the plasma generator power. The working gas is fed under pressure of more than 6 bars. A photograph of a DC plasma generator with hollow electrodes developed in Korea (the working gas is air) [56] is shown in Fig. 2.34.

Figure 2.34. DC plasma generator with hollow electrodes; the current is 200 A, the flow velocity is 200 norm.l/min, the diameter is 16 mm, and the power is 120 kW.

The majority of models of DC plasma generators are designed under the linear scheme, but other variants are also possible. It depends on the application, for which the plasma generator is developed. For example, the V–shaped form of the anode and cathode arrangement with proper supply of the plasma-generating gas (argon) is presented in Fig. 2.35. Here, the processing material is fed directly into the discharge zone.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

130

Philip Rutberg

Figure 2.35. V–shaped plasma generator of direct current.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

As for electrodes of this plasma generator, they can be made from metal or any other solid conductive material. A DC plasma generator with water stabilization of the discharge has been developed in the Czech Republic [57]. It is used for investigation of thermal plasma generated at the interaction of the arc discharge with the water vortex and, also, for studying the stability and structure of a plasma jet with extreme values of density, temperatures, and speed. A photograph of this plasma generator is presented in Fig. 2.36.

Figure 2.36. Plasma generator with water discharge stabilization

Recently, a new type of plasma generator with a combination of water and classical gas stabilization of the discharge, and a plasma generator with a rotating anode and fixed cathode with a power of 50–160 kW has been investigated [58].

4.3. AC Plasma Generators AC plasma generators with power in the hundreds of kW and more are the most competitive ones, and they are mainly examined in this work. The existing designs of AC plasma generators can be divided into three basic groups: single–phase plasma generators,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

131

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

multi–chamber multi–phase plasma generators, and single–chamber multi–phase plasma generators (Fig. 2.37).

Figure 2.37. Schematic designs of AC plasma generators; the single–phase: 1 – with ring electrodes, 2 – with rod and ring electrodes, 3 – with cylindrical electrodes (linear); the multi–chamber multi–phase: 4–6 – with cylindrical electrodes, 7 – with rod electrodes; the single–chamber multi–phase: 8, 9 – with ring electrodes, 10 – with tubular electrodes, 11–13 – with rod electrodes.

4.4 Single–Phase Plasma Generators of Alternating Current The single–phase AC plasma generator shown in Fig. 2.38 is a linear plasma generator with cylindrical electrodes using a power supply of alternating current. In this type of plasma generator, the working gas is usually supplied tangentially. The tangential supply of the working gas ensures moving of the basic arc spots along the surface of the cylindrical electrodes, stabilizes the arc, and sets it along the plasma generator axis [54]. The design with the central rod electrode and ring or toroidal electrodes is another variant of a single–phase plasma generator. Usually, the arc is stabilized by the imposed magnetic field rotating the arc in the inter–electrode gap. As a rule, the axial working gas suppy is used in plasma generators of this design.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

132

Philip Rutberg

.

Figure 2.38. Single–phase plasma generator of "MARC" type; 1 – electrodes, 2 –solenoids, 3 – insulators.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4.5 A Single–Phase AC Plasma Generator with an Arc of Direct Action with Power up to 150 Kw One of the important problems of the AC plasma generator is the repeated ignition of the arc at the instant of the current passage through zero. Here, it is solved by addition of current impulses at each instant of passage of the current curve through zero. The basic characteristics of this plasma generator are: the current varies from 100 up to 500 A, the voltage is from 180 up to 300 V, the network frequency is 50 Hz, and argon is used as the plasma forming gas (with the flow rate 10 norm.l/min). Parameters of the current pulses are a current of 5–15A, voltage of 100 V, and the current front is 2 μs with a duration of 300 μsec. The central rod electrode is made of tungsten with an addition of 2% (mass) La2O3. Its diameter is 13 mm, the length is 11 mm. The external electrode is made of copper; its diameter is 10 mm. It is located at a distance of 40 mm from the plasma generator nozzle. The nozzle diameter is 10 mm. A schematic drawing of the installation is shown in Fig. 2.39 [59].

Figure 2.39. Schematic diagram of a single–phase plasma generator, and the form of an experimental installation.

Designs of single–phase plasma generators consisting of two toroidal electrodes, between which the electric arc burns, are also widespread. In these types of plasma Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

133

generators, a cross–section arc is used which is blown by magnetic rotation in the inter– electrode gap. The solenoids creating the magnetic field are arranged around the electrodes in such a way that the vector of magnetic field induction is directed perpendicularly to the arc current. The working gas is supplied into the inter–electrode gap and moves out through the nozzle located perpendicular to the electrode plane. The basic disadvantages of single–phase plasma generators are the significant pulsations of parameters of the working gas expiring from the plasma generator nozzle ,problems in heating the working gas up to high temperatures necessity, the of using the auxiliary devices (the high frequency ignition and the arc of direct current "on duty") for providing repeated ignition of the arc, and the non–uniform loading of a power line when these types of high-power designs are used.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4.6 Multi–Phase Multi–Chamber Plasma Generators of Alternating Current Powerful systems of such a type are designed for working in short–terms modes. This type of plasma generator consists of various combinations of several single–phase plasma generators using a multi–phase network of alternating current with wye– or triangle– connection (in the case of the three-phase network). There are designs consisting of three separate single–phase plasma generators. Connection of three single–phase plasma generators working in the common mixing chamber is probable, and of connection with the chamber vary. In particular, the combination of single–phase plasma generators located under 120° on the diameter of the common mixing chamber is probable. The plasma generator is connected with the three–phase network under the floating zero circuit. The zero point of all arcs is in the mixing chamber. The arc burns between the cooled copper electrode and zero point in each phase of the plasma generator. The wye–type plasma generator shown in Fig. 2.40 belongs to this type. The wye–type plasma generator usually contain: three identical arc chambers located under the angle 2π/3 to each other and a common mixing chamber 1; the number of arc chambers can be greater. Each arc chamber has a face cover, back–plate, chamber–electrode, and confusor. The electrodes are connected to the phases of the feeding electric system. Each electrode is separated by the electric insulators from the back–plate and confusor. The working gas fed through them tangentially provides the gas–vortex arc stabilization on the axis of the discharge chamber. The basic amount of gas is supplied between the electrode and confusor, and the additional flow (no more than 10 % of the basic one) is introduced between the electrode and back–plate with the purpose of prevention of the arc end closing onto the back–plate. The heated gas leaves the plasma generator through the nozzle of the mixing chamber, the axis is perpendicular to the figure plane. Each electrode is arranged with solenoids. Under the action of the solenoid magnetic field, rotation of the near electrode (radial) parts of the arc increases the electrode’s lifetime. The electrodes, confusors, mixing chamber, and outlet nozzles are cooled by water. At the start of the plasma generator, the voltage is supplied on electrodes and simultaneously in each arc chamber from a special power source; the auxiliary high– frequency low–power discharge between the confusor and special needle tungsten electrode is ignited. The high–frequency discharge closes onto the electrode–confusor interval, and under

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

134

Philip Rutberg

the action of the applied voltage the breakdown formatting the arc is realized. After the basic arc ignition, its closing part located in the confusor moves downstream under the action of aerodynamic forces. Since the confusors of all three arc chambers are electrically connected, there is closure of the lower ends of the arcs onto the stream under the scheme "star" with zero point "on metal". After passage of the confusors, the arcs’ ends are loop–shape extended and blown by a gas stream into the mixing chamber and become isolated each from other in its central area. Thus, the confusors and mixing chambers become electrically neutral.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.40. Plasma generators of the wye–type; at left: schematic of three–chamber plasma generator: 1 – mixing chamber, 2 – back–plate, 3 – chamber–electrode, 4 – confusor, 5 – solenoid, 6–8 – instrumentation, А, В and С – power terminal; at right: photo of the six–chamber plasma generator [60].

The basic characteristics of plasma generators of the wye–type according to the data in [61] for three–chamber models with outlet nozzle diameter of ~1.4–3 cm at the linear line voltage Uc~6–10 kV are the arc current is I~0.13–0.85 kA; the total power is (S = √3UcI) ~1.35–14.7 MVA; thus, the total power imbedded into the arcs is ~0.2–5.9 MW; the gas temperature in the mixing chamber is ~2700–5700 K; and the thermal efficiency as the ratio of the thermal power of the outgoing jet to the input power is ~0.42–0.85. For six–chamber plasma generators with a diameter of outlet nozzle of ~1.4–3 cm at the linear line voltage of the arc of 10 kV, the characteristics are the following the arc current is ~0.73–0.92 kA; the total power is ~26.5–33.4 MW; thus, the total power imbedded into the arcs is ~11.4– 18.4 MW; the temperature in the mixing chamber is ~ 3700÷4500 К; the thermal efficiency is ~0.22–0.56; and the regime is short–term. It is necessary to note that mixture of the working gas streams in the mixing chamber realized in the wye–type plasma generators provides a considerable decrease in the temperature pulsations and stream enthalpy at the outlet. However, the greater surface of the electric arc chambers and mixing chamber in plasma generators leads to greater losses of heat and, hence, to a decrease the whole efficiency of the system. There are applications created by a principle of the wye–type plasma generator, e.g., a multi–phase electric arc heating system where single–phase AC plasma generators are connected under the wye scheme (Fig. 2.41).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

135

Figure 2.41. Multi–phase electric arc heating Westinghouse system for working in short-term modes; the left diagram depicts of the installation; the right one is an electric diagram of the plasma generator supply.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Plasma generators with power of 3500–10000 kW with hollow electrodes and magnetic stabilization of the arc (1000 round/sec) are supplied from the electric system of industrial frequency with a voltage of 4 kV. A powdered solid substance is supplied into the mixing chamber. It is subjected to chemical or physical transformation; the bottom part of the mixing chamber is a chemical reactor.

4.7. Multi–Phase Single–Chamber Plasma Generators of Alternating Current The plasma generators of this type have a specific feature: the electrode system of the plasma generator is mounted in one common electric arc chamber. The electrode systems of multi-phase single–chamber plasma generators can be executed in the form of rings, tors or cores [62]. In the case of using the toroidal ring electrodes (Fig. 2.42), the first and the last electrode, as a rule, are connected to one phase. The electrodes are usually divided from each other by the heat–resistant insulating gaskets. The arc stabilization and rotation is carried out either by the magnetic field by means of the solenoid located on the plasma generator case or by creation of the tangential gas vortex installing the arc column on the axis of the electric arc chamber and moving the basic arc spots along the electrode surface. In this case, the electrodes are water–cooled and made of copper or steel. The large electrode surface results in significant thermal losses, which in turn decreases the system efficiency. The plasma generator with a predionizer is a modification of the plasma generators of this type. Moreover, there are four electrodes connected in the AC network; the ring electrode is located in the same electric arc chamber, and, also, the face electrode connected to the DC power supply is located in a back flange of the plasma generator.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

136

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.42. Electric arc heater from NOL laboratory; 1 – ring electrodes, 2 – current leads, water inlet, 3 – silicone insulator, 4 – nozzle unit.

Another commonly used group of single–chamber multiphase plasma generators are plasma generators with rod electrodes (one of the models is shown in Fig. 2.43). In this case, as a rule, materials with high fusion temperature and good emission properties are used for electrodes which provide steady work of the arcs of alternating current. The power supply of these plasma generators is carried out under the triangle– or wye–scheme (for three phases). Usually, the tangential submission of the working gas or the tangential–axial combination is realized in designs of single–chamber multi-phase plasma generators of this type. The electrodes can be introduced into the arc chamber in the planes perpendicular to the plasma generator axis, at an angle to it, or parallel, but sometimes, besides the tangential working gas supply, the additional axial blast is organized on the periphery of the arc chamber. The earthed case of the electric arc chamber can be used as the zero point. If so, the arcs burn between the rod electrodes and the case. The presence of several AC arcs burning simultaneously in one chamber allows one to create simple and reliable plasma generators transforming the energy of the electric current into thermal energy with a high efficiency of 0.8–0.9.

4.8. Plasma Generators with Rod Electrodes Plasma generators with the electrodes. Plasma generators with rod electrodes are intended for heating the inert gases nitrogen and hydrogen at a pressure of 0.1–6 MPa. The flow rate on nitrogen is 0.01–10 kg/sec. The heating is implemented up to temperatures of 2000–8000 K with a thermal efficiency of 70–90 %. The power range of these plasma generators is from 100 kW up to 80 MW. The design of such a plasma generator is shown in Fig. 2.43 [40]

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

137

Figure 2.43. Three–phase electric–arc plasma generator; 1 – chamber; 2 – gas supply loop; 3 – electrode tip; 4 – insulator; 5 – current lead; 6 – water inlet.

Plasma generators with rail electrodes. A three–phase plasma generator with rail electrodes is intended for operation on air and other oxidizing media with a power of 0.1–1.0 MW. One type of plasma generator with rail electrodes is shown in Fig. 2.44 (the power is 500 kW).

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

gas

w ater

Figure 2.44. Plasma generator with rail electrodes (the power is 500 kW); 1 – case; 2 – electrode; 3 – injector.

Application of the electro–dynamic motion of the electrical arc in the field of its own current (the rail–gun effect) is the basis of operation of these plasma generators. The arcs after inter–electrode breakdown move along the tubular electrodes up to their end. The plasma injector is used for repeated ignition of the arc. It provides concentration of electrons of ne ~10–14–10–16 cm–3 in the inter–electrode gap. This is sufficient for ignition of the basic arcs at a comparatively low voltage of the power supply of ~300–500 V. The appeared arcs move along the electrodes with a velocity of 10–30 m/sec depending on the current magnitude and inclination angle of the electrodes. The three–phase system of electrodes and their configuration allow one to avoid arc extinction and current interruption. Thus, the rail–gun effect provides distribution of the thermal load along the electrode length. The intensive water cooling of the tubular electrodes made of copper alloys allows one to pass strong currents with an essential increase of the electrodes’ lifetime and to minimize the gas medium contamination. The arcs with a combustion regime of diffuse character occupy a large share

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

138

of the discharge chamber, making it possible to produce a thermal efficiency of the plasma generator up to 90% depending on the operation conditions [63,64]. The main parameters of plasma torches described above are presented in Table 2.6. Table 2.6. The IEE RAS AC plasma generators

Parameter

400–1200

200–600

Up to 2.5

Up to 5.0

Up to 2.5

0.2–1

H2, He, Ar, N2

H2, He, Ar, N2

H2, He, Ar, N2

H2, He, Ar, N2

Air, CO2, water steam, H2, He, Ar, N2

Gas flow rate, kg/sec

Up to 0.04 (Ar)

Up to 2.0 (N2)

Up to (N2)

Gas heat content, J/kg·106 Efficiency, % Power supply

2.0–6.0

1.2–5.3

1.2–6

Up to 85 Three– phase electrical network

Up to 85 Three– phase electrical network transformer generators

Up to 90 Three– phase electrical network transformer generators.

Current (effective), A Voltage (effective), V Pressure in the chamber, MPa Working gas

Up to 200

Up to 2000

Up to 10000

80–570

2000–6400

2000–9000

30–240

250–450

0.1÷ 0.2

Rail Type Electrodes 100–1000

Up to 80000 Short–term mode 10000– 26000 500–2000

POWER IN ARCS, KW

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Rod Type Electrodes

3

Up to 20 (Ar), 10 (N2), 0.5 (H2) 1–12 100– 140(H2) Up to 90 Turbo– generator

200–1500

2–14

70–90 Three– phase electrical network

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

139

4.9. High–Voltage One– and Three–Phase Plasmatron

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.45. Three–phase high–voltage electric arc plasmatron of alternating current with the rode electrodes for work on the air; 1 – case; 2 – discharge channel and arc; 3 – water cooling jacket; 4 – arranging flange; 5 – collector for distribution of the protecting gas; 6 – collector for distribution of the plasma generating gas; 7 – electrode; 8 – water cooling holder of electrodes; 9 – insulator; 10 – sealing bush.

A scheme of the high–voltage three–phase plasmatron (injector) is presented in Fig. 2.45. It has face–end electrodes and is intended for work on air [63]. The high–voltage supply of 4–6 kV provides stable ignition and burn of the arc with its length of about 60 cm. The case has a water cooling jacket; the gas supply into the electrodes’ channels is implemented tangentially. The voltage is given onto the central electrodes and breaks down the air gap between the tip of the electrode and the case, and the electric arc appears in the gap of each channel. Due to the tangential gas flow, these arcs are shifted to the edges of the channels and are shorted onto themselves. Thus, only the tips of the electrodes participate in the work. If an arc ceases, the process of shorting repeats.

5. EXTERNAL CHARACTERISTICS OF PLASMA GENERATORS One of the basic external properties of plasma generators is the current–voltage characteristic of the arc discharge that determines dependence of the voltage drop on the arc column. Moreover, the character of the current–voltage characteristic change depends on the type of working gas, its speed, flow rate, and pressure in the electric arc chamber of the plasma generator. The character of the voltage drop on the anode and cathode is basically determined by the processes occurring at these electrodes, and this drop slightly influences a kind of current–voltage characteristic under a significant voltage drop on the arc. In the case of application of the vortex gas stabilization in plasma generators at high currents and flow rates of the working gas, part of the gas stream is intensively blown through the arc. Another part of the gas flows around the arc column which leads to reduction of its cross–section and, under certain conditions, to a significant increase of the voltage drop of the arc. Under the current increase in the arc column limited to the diameter,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

140

the current density increases. But the conductivity varies slightly, since under the ionization degree increase, the total cross–section of the ions’ flow increases, and the Coulomb interaction starts to prevail. This is especially true for the inert gases in which, due to the Ramsauer effect near 104 K (approximately corresponds to the temperature in a strong current arc), the dispersion section by electron atoms prevail. In the contracted mode where concentration of particles is determined by ionization of the working gas, there comes approximate equality of electronic and gas temperatures occurs with the achievement of certain ions’ concentration. Actually, the value σ of conductivity can be written in the following way: σ =Кσ · e 2 ne / me ·Fef ,

(2.46)

where ne is the electron concentration, me is an electron mass, Fef is the effective frequency of electrons’ collisions with the neutral particles and ions, Кσ is a non–dimensional function having a complicated dependence on the temperature Те, and ni < Qi> / n < Qk>. Here, Те is the electron temperature; ni, n is concentration of ions and neutral particles, correspondingly; is the Maxwell mean transportation cross–section; and is the Coulomb cross– section. In the cases of our interest, for the arcs in argon, the value Кσ changes insignificantly [65], and under increase of the ionization degree, it closes asymptotically to the value 1.95. As known,

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

1/ Feff.= τ =1/ < υe> ( < Qk >n + < Qi > ni ),

(2.47)

where τ is the time of the pulse transmission and is the mean thermal velocity of electrons. Substituting the value Feff into (2.47), we obtain the following expression for conductivity in the column of the argon arc: σ = Кσ · e 2 ne / me < υe > ( < QAr >n + < Qi > ni ).

(2.48)

According to the data from [65], the value for argon can be calculated by the following formula: = 10–15 (Те –0,1) cm2,

(2.49)

and the value = 3.6 ·10–4 Те –2 lnΛ cm,

(2.50)

where lnΛ = 23,1– ½ ln ne+3/2 ln Те .

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

(2.51)

Investigation of High Current Discharges in Gas Environments

141

As it follows from (5.3), the value of the conductivity will be mainly determined by the Coulomb interactions under satisfying the following condition:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

n ≤ ni.

(2.52)

Under conditions of our interest (the arc with a current in hundreds of amperes and more, which is stabilized by the argon flow), the possible temperature in the arc plasma is 1– 1.8×104 К. As shown in [27], when the electron concentration achieves a special value, equality occurs between the electron and gas temperatures for argon under ne ≈ 5×1015 cm–3, and the Saha formula can be used for definition of degree of ionization and concentration of charged particles. According to calculations implemented by formulas (2.48)–(2.51) in the considered range of temperature, the term has a value of about 10–15 cm2 and slightly (0.9–1.7·×10– 15 см2) depends on the temperature change. The term under the considered conditions has a value of about 10–13 cm2 (for concentrations ne=1015–1017 cm–3). Having substituted these values into (2.51), it is possible to conclude that the conductivity will be determined mainly by the Coulomb interactions under the values of concentrations of the charged particles of about 1016 cm–3. Thus, the conductivity of the arcs will change insignificantly, but the current density will riseunder the current increase providing the achievement of concentration ne of a value of ~1016 cm–3 and preservation of the arc cross–section constant. As a result, corresponding to the Ohm law, the electric field strength in the arc column will increase. Therefore, the volt– ampere characteristic will be growing. But if the cross–section of the arc increases, the volt– ampere characteristic will be either flattening, or falling depending on variations of the current density. From this discussion, it can be concluded that in the plasmatron with vortex stabilization under a sufficient gas flow rate and an increase in the current, the volt–ampere characteristic can be obtained as flattening (at the beginning) and, further, as growing. In the case whereby the velocities of the working gas (which stabilizes the arc) are not large, the cooling of the arc column is insufficient. Therefore, the diameter of the arc column increases as the current grows. In this case, the volt–ampere characteristics are falling.

Figure 2.46. Typical volt–ampere characteristic of the arc in the DC plasma generator; the arc length is 40 mm, the working gas is air; the working gas flow rate is Q. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

142

Philip Rutberg

Above, data are presented for typical characteristics of the powerful DC plasma torches and two types of AC plasma torches: PPT with power from 100 kW to 1MW, and EDP with power from 2 MW to 80MW; at higher currents the falling character of the curves becomes more well–defined (Fig. 2.46). Figures 2.46 – 2.50 present the typical external characteristics of powerful DC plasma generators [66].

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.47. Dependence of arc voltage on the air flow rate at d = 6 mm; the curve corresponding to H = 1240 A/cm is marked by symbols • , I = 3000 A , l = 40 mm; the curve corresponding to Н = 2300 A/cm is marked by symbols Δ , I = 6000 A, l = 10 mm.

Figure 2.48. Current–voltage characteristics of the arc for l = 40 mm, Н = 1240 A/cm, dlim = 6 mm; the curves are marked by symbols: О – for G = 65 g/sec; – for G = 20 g/sec; • – for G =10 g/sec; and – Δ for G = 0.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

143

Figure 2.49. Dependence of thermal efficiency versus the flow rate for the two–arc plasma generator with magnetic stabilization.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.50. Current–voltage characteristics of the discharge in the plasma generator with the arc in supersonic channel.

The condition of the thermodynamic balance is realized with sufficient accuracy in the contracted arc discharge column. Thus, with an increase in the current under constant cross–section of the arc column, the conductivity will change slightly. Hence, with an increase in the current density, the intensity in the arc column will also increase, and the current–voltage characteristic will look like an increasing function. If the arc cross–section increases and the current density decreases, the current–voltage characteristics will be flattening or falling depending on the current density change. Both static characteristics (reflecting time–average relations of changing parameters) and dynamic characteristics (connected with change of process of the arc burning in time) should be considered in the analysis of results of measurements. For the work of the AC plasma generator of the examined type, the static current–voltage characteristics hold the main interest, since they characterize dependence of the time–average effective voltage value on an arc versus the time–average effective value of the current. Figures 2.51 – 2.56 show the current–voltage characteristics of plasma generators of the PPT, EDP–5 and EDP–80 types for work on air, nitrogen, helium, hydrogen, argon, and on various sorts of mixtures. The pressure and working gas flow rate changed over a wide range. The determining factor of change of the curve character was the current value and its density. Actually, in plasma generators of the EDP–80 and EDP–5 type (the geometrical size of the electric arc chambers of plasma generators of these types differ slightly), the current– voltage characteristics have (at the beginning) a falling character (Fig. 2.52). This could be explained by the fact that in the range of these working currents of 2–8.5 kA, the conductivity increases together with the current increase. The current–voltage characteristics are growing in the EDP–80 plasma generator (Fig. 2.53) at an essentially larger working current (12–25 kA). That is, when the current increases its density increases also, and the Coulomb interaction starts to prevail, but the conductivity varies a little. Both these processes were observed (in the low-power plasma generators of the PPT type due to the small dimensions of the electric arc chamber) already in the range of the current change of 50–500 A, and the current–voltage characteristics have a falling character at their initial parts. But further, when the current increases (and its density increases also), the growth of the current–voltage characteristics is observed [40,55].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

144

Philip Rutberg

Figure 2.51. Current–voltage characteristics of plasma generators of the PPT type; for various working gases the curves are marked by symbols: О – for Н 2 ,G = 0.08 g/sec, р = 0.4 MPa; Δ – f o r a i r , G = 1 g / s e c , р = 0 . 1 1 M P a ; □ – f o r N 2 , G = 7 g/sec, р = 0.4 MPa; • – for Не, G = 0.04 g/sec, р – 0.2 MPa; ∇ – for Ar, G = 6.2 g/sec, р = 0.1 MPa; and ◊ – for Аг, G = 4.2 g/sec, р = 0.1 MPa.

Figure 2.52. Current–voltage characteristics of the EDP plasma generator; for various working gases the curves are marked: 1–3 – for nitrogen, 1 for G = 2.5 kg/sec, р = 1.7 MPa, 2 for G =2.1 kg/sec, р = 0.5 MPa; 3 – for G = 1.9 kg/sec, р = 0.22 MPa; 4–5 for helium, 4 – for G = 0.15 kg/sec, р = 1.1 MPa, 5– for G = 0.05 kg/sec, р = 0.2 MPa.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

145

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.53. Current–voltage characteristics of EDP–80 plasma generator (the w o r k i n g g a s i s n i t r o g e n ) ; 1 for G =10 kg/sec, р = 0.5 MPa; 2 for G = 5 kg/sec, р = 0.2 MPa.

Figure 2.54. Dependence of the voltage drop on the arc versus the working gas flow rate for the plasma generator EDP (the w o r k i n g g a s i s n i t r o g e n , I = 3000 А); the curves are marked for various values of the pressure: – for p = 0.16 MPa; Δ – for р = 0.3 MPa; and O – for р =0.57 MPa.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

146

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.55. Dependence of the effective voltage on the arc versus the gas flow rate of the plasma generator EDP (the working gas is nitrogen; I d = 3.5 kA).

a)

b)

c)

Figure 2.56. Dependence of the effective voltage on the arc versus the gas flow rate of the plasma generator EDP–80; the curves are presented for various working gases: a) for ni t r o g e n ; b) for argon; c) for hydrogen.

Consider the influence of the working gas pressure in the electric arc chambers of the plasma generators of various types under approximately the same values of currents and other equal conditions. The voltage drop increases with the pressure increase, but the general character of its dependence on the flow rate (Figs. 2.57, 2.58) maintains. An increase in the voltage drop on the arc with a pressure increase could be explained by increase of the heat transfer from the arc due to convective processes and radiation. A more impressive dependence of the voltage drop versus the pressure corresponds to the higher values of the currents, since in this case the Coulomb interaction prevails.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

147

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.57. Dependence of the voltage drop on the arc versus the pressure in the discharge chamber of the plasma generator EDP (the w o r k i n g g a s i s n i t r o g e n , If = 3000 A); the curves are marked: □ – for G = 70 g/sec; Δ – for G =110 g/sec; • – for G =200 g/sec; and О – for G = 270 g/sec.

Figure 2.58. Dependence of the electric field strength versus the pressure in the plasma generator EDP (the w o r k i n g g a s i s hydrogen; I =4 kA; G= 50 g/sec).

The efficiency coefficient (η) of transformation of the arcs’ energy to gas flow energy grows with power increase (Fig. 2.59), because the arcs are occupying the volume of the discharge chamber more and more as the energy increases, which results higher efficiency of the heat exchange. In summary, it is necessary to discuss the dependence of the efficiency of the three–phase plasma generators (i.e., the ratio of the energy imbedded into the working gas to energy input into in the arc) on the system parameters.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

148

Figure 2.59. Dependence of the efficiency coefficient versus the power of the plasma generator EDP–80.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

As a rule, the plasma generators with the rail electrodes working on oxidizing media have characteristics different from those presented above. By measuring the electrical parameters of the plasma torch operation (the currents, voltages, and power in the arcs) and determining losses for the cooling system, it is possible to estimate the thermal efficiency of the plasma torch by the following formula:

,

(2.53)

where P is the power in the arcs, W is losses in the cooling system, and (P – W) is the energy spent for the working gas heating.

Figure 2.60. Dependences of the working gas (air) enthalpy of the three–phase plasma torch with rail electrodes at atmospheric pressure versus the gas flow rate; the curves are indicated in accordance with the settings of the power source on short–circuit currents (the experimental data). Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

149

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The curve was formed by the results of a number of experiments. The thermal efficiency for air over the range of flow rates 25–50 g/sec is close to 70%. Figure 2.60 presents the curves of the working gas enthalpy corresponding to different settings of the power source on short–circuit current. Here, the enthalpy was determined taking into account the thermal efficiency

, (2.54) where P is the power in the arcs, η is the thermal efficiency of the plasma torch, Q is the working gas flow rate, and HTo is the initial enthalpy of the plasma-generating gas. The curves are drawn over the points received as a result of the numerical (mathematical) processing of the experimental data. Using the air as a working gas in the range of flow rates 25–70 g/sec, a three–phase plasma torch with rail electrodes can provide the energy input of about 1.5–12.5 MJ kg−1 ensuring a long lifetime of continuous operation (without replacement of the electrodes) of more than one hundred hours. Knowing the working gas enthalpy, it is possible to estimate the average mass temperature of the jet at the plasma torch outlet. The average mass temperature of the jet can be controlled by adjusting the power source and varying the working gas flow rate [55]. The adjustment range is from 1500 to 6000 K with the use of air as the working gas, which is optimal for a number of technological applications. Obtaining the volt–ampere characteristics of the arc and taking into account the factors influencing their modification are essential for the arc characteristic as a whole. The static volt–ampere characteristics for various values of the flow rates of the working gas (air) are shown in Fig. 2.61. The data were obtained at a plasma torch working under the 50 Hz electric network. The main numbers were calculated at time intervals of 500 ms on the instantaneous values registered with a frequency of 10 kHz. The curves are drawn as a result of implementing the polynomial regression of the third order.

Figure 2.61. Static volt–ampere characteristics of the three–phase plasma torch with rail gun electrodes for various flow rates of the working gas (air) at atmospheric pressure (the experimental data) versus the arc current.

The volt–ampere characteristics appear to have a growing character that suggests the prevalence of the Coulomb collisions. The magnitude of the voltage of the arc burning is Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

150

combined from a potential drop on the arc column plus the anode and cathode potential drops. The near electrode processes mainly determine the character of the anode and cathode potential drops. Such factors as the velocity variation of the working gas flow and its pressure have a major influence on the parameters of the arc column. The current density magnitude essentially influences the nature of the processes in the arc column.

6. PLASMA TECHNOLOGIES

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

6.1. General Description One of the most apparent and urgent needs throughout the world is waste treatment. Waste treatment is one of the most ancient and, at the same time, most up–to–date areas of human knowledge. In various stages of history, the efforts of many generations of experts in the field of public health services were directed at elimination of unsanitary conditions of human existence. It became especially important at the end of the nineteenth century, when the theory and practice of public health services reached an understanding of the necessity to improve living conditions and household activities. New problems connected with a radical modification of the character of waste occurred. Growing amounts of paper, plastic, and glass components appeared as waste products. Some substances accumulated in huge amounts during industrialization. It caused immediate disastrous effects and justified anxiety regarding the far reaching consequences. Even with rigid standards adopted in the developed countries, the disposal of wastes at landfills and polygons and their burial in the ground and under water do not guarantee neutralizing of their harmful action. The industrial development was accompanied by magnification of the negative impacts on the environment and people of diverse toxic chemical substances, which are formed at the stage of production as wastes or become unsuitable after application. It has become obvious that such toxic agents retain for a long time, accumulate, migrate, and transform. Of special concern are synthesized organic substances that have no analogs in nature. A number of such substances steadily increase accordingly to the development of chemistry, chemical technologies, and related branches.

Figure 2.62. Comparative diagram of thermal processes; combustion: the process is exothermal, the oxidation is stochiometric with air excess, and the waste has a great amount of organic matter; gasification: the process is self–sustaining, partial combustion at oxygen deficit; pyrolysis: the process is endothermic with an exterior power source at lack of oxygen.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

151

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The problem of waste treatment has become very important in recent decades. The whole industry of waste treatment must be transformed. Research on decontamination and utilization of waste has begun. The whole variety of thermal processes used for waste treatment is presented in Fig. 2.62. Widely-used methods of thermal processing of waste have a number of basic disadvantages, especially the creation and emission into the atmosphere of large amounts of toxic substances: drag–out ash that contains heavy metals, soot, carbon monoxide, oxides of sulfur and nitrogen, chlorine compounds, and, such super-toxic substances as dioxins and furans. The slag also contains unburned carbon and polyaromatic substances. Existing techniques produce large amounts of toxic substances. That is why it is necessary to comply with strict emission requirements by using extremely expensive purification plants, which considerably increases operating costs. Low ecological and economic indexes of such techniques have resulted in the search for and creation of new methods for waste treatment. Such methods use processes of high temperature mineralization of waste under the action of isothermal plasma obtained by blowing some gas through an electrical arc. The range of temperature variation in such processes is rather wide and extends from 2000 to 10000 K. The time of complete waste transformation under conditions of such plasma–chemical processes is 0.01–0.5 sec depending on the nature of the waste and the process temperature. The effectiveness of thermal energy input for simultaneous stimulation of chemical and physical modifications of a substance is represented in Fig. 2.63.

Figure 2.63. Diagram of effectiveness of thermal energy input.

Figure 2.63 shows the difference of plasma heating in comparison with heating by a natural fuel. The plasma processes ensure high and effective temperatures of processing, which cannot be reached by other methods of heating. Dissociation of combustible products gains practical significance only at temperatures above 1800°C, which is connected with energy consumption necessary for molecule decay into atoms. The most widespread components of gases of industrial technologies are СО2, СО, Н2О, О2, N2, and Н2. Carbon dioxide dissociates morea easily, but atomic hydrogen is the most difficult to process. At temperature increase (higher than 1800 K) processes of dissociation and their heat consumption gain greater importance. In particular, dissociation determines limiting the temperature to about 3000 K which is accessible in the combustion of cold fuel in oxygen. Thus, the dissociation process limits the technological possibilities of

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

152

chemical energy of fuel and, therefore, does not allow attaining the needed high temperatures. The level of 3000 K is an upper limit of accessible temperature in industrial waste treatment using traditional kinds of fuel. Traditional combustion does not allow the possibility to decompose products of elementary molecules, thus, creation of resin and unburned carbon takes place in usual combustion systems. Realization of technological processes with higher temperatures is possible only by using the electrical energy. Plasma dissociation allows one to achieve complete decomposition of practically all known organic and many inorganic compounds into the elementary atoms and molecules of the substances processed. Under these conditions, thermodynamically stable two-to threeatom compounds (such as oxides, hydrides, halogenides, etc.) can be formed in dependence on the chemical nature of the waste and plasma-generating gas. Different amounts of energy consumption are needed for ionization of atoms of various substances. The degree of ionization at a given temperature depends mainly on the content of elements with low ionization potential in a gas medium. The sensible thermal ionization can take place at temperatures of 5000–15000 K. The gas stream of high temperature (obtained at the expense of dissociation and ionization processes) has a high energy content. The heating ability of such stream action onto a substance as surface reaches values of 1–2 orders higher than its own heating ability, which can be reached by using some fuel. The last circumstance allows one to accelerate many technological processes connected with handling various materials. In comparison with traditional combustion, plasma–chemical plants have a number of essential advantages [29, 67–69]:

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

• • • • • • • •

the possibility of regulating the temperature in the basic reactor in the range from 1000 up to 10000 K; deep destruction of waste with simultaneous decrease of volume of exhaust gases; the significantly smaller “weight–dimension” characteristics of the reactor and the unit in comparison with the furnace plants; the possibility of complete automatic control of the process; minimal expenditures of time and means in remedial maintenance of the high temperature plasma generators; more complete conversion of carbon into oxides CO and СО2; application of inexpensive electrical energy already available; the by–products of plasma processing are easily predicted, harmless, and are acceptable from the point of view of environment protection.

It is expedient to use plasma–chemical installations for combustion of relatively small amounts of concentrated super toxic substances of the Ist and IInd class of hazard, hazardous medical waste, and, for pyrolysis of halogen–containing gaseous, liquid and solid waste. It is especially expedient to use such plants directly at the site of formation or storage of super toxic waste. Under these conditions, it is possible to use both stationary and mobile plasma– chemical plants. Use of plasma technologies allows the realization of a more purposeful and pure process and reaching the following results:

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

•

•

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

•

153

in the problem of synthetic gas generation, there is a much higher conversion of carbon into СО and СО2 due to the higher temperature of the process, and, consequently, the higher effectiveness of processing the primary raw material into synthetic gas (syngas); a much higher velocity of chemical processes in the reactor due to the high thermal and chemical activity of low-temperature plasma because of a rather high density of energy; the possibility of an essential decrease of toxic substances at the expense of peculiarities of realized physical–chemical processes and the possibility of control by these processes [29].

Realization of physical–chemical processes requires imbedding a significant amount of energy at a high specific density into the reactor. Realization of these processes has become possible due to successes in the creation of reliable and cheap generators of dense plasma as a necessary part of a technological process. The determining factor of the gasification process is heat supply into the working zone of the gas generator for endothermic effective compensation of reactions of carbon with CO2 and H2O. The method of heat supply and type of blasting are determined by the specified structure of the produced gas consisting mainly of CO and H2 and containing a minimum of the ballast nitrogen. The most reasonable working gas in the plasma generators is air, which is applied in the treatment of organic–containing waste and coals contained in the waste to be neutralized (e.g., medical waste). Organic–containing waste and coals are transformed into syngas (CO + H2) for further use in gas turbines and diesel generators for energy production or synthetic liquid fuel production. Application of plasma heating in the pyrolysis and gasification processes of a solid fuel is an alternative to using pure oxygen as a component of the blast. The plasma processes provide high and effective working temperatures that cannot be achieved by some other methods of heating. The high-temperature gas flow has the high enthalpy due to the inside processes of dissociation and ionization. The heating ability of such a flow in action on the surface of the processed substance is up to one to two orders higher than the heating ability, which can be achieved by using some common fuels. This allows one to accelerate the technological processes of waste treatment [29,70]. The important peculiarity of the plasma processes is their high selectivity which allows the creation of prescribed products with insignificant creation of the by–products [71,72]. For example, under gasification of various coals in the plasma of water vapors, the gas obtained has more than 95% of СО and Н2 and does not contain impurities of resin, fenols, and polycyclic hydrocarbons [71, 73]. The syngas (the mixture of CO and H2) obtained from solid organic wastes by plasma high temperature gasification concedes in the calorific value to the natural gas (only 5–10 MJ/m3 in contrast to 30–35 MJ/m3). But application of the syngas as the working body in the gas–energetic cycles becomes competitive under the constant rise in prices of natural mineral energy fuels. The effectiveness of the contemporary technologies for producing thermal and

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

154

Philip Rutberg

electric energy on the basis of the gas fuel (for example, in the combined steam–gas cycle) achieves 84–90% (~35% on the energy output and ~49% on the thermal output). Thus, these indices are essentially higher than those under simple fuel burning with the consecutive utilization of the heat of the produced gases in the boiler and producing electric energy by means of the steam turbine. The gas obtained by the mentioned gasification after its cleaning from impurities can be used as a raw material in many technologies of organic synthesis. This gas is used for producing spirits (methanol, ethanol, etc.), ammonia, and motor fuels. The mentioned facts are confirmed by a real boom of development of these technologies throughout the world [74–79]. Below, we give a short review of the most characteristic and representative methods for organization of processess of the high temperature gasification of organic wastes.

6.2. Plasma Pyrolysis and Gasification

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Consider the plasma–gasification in the reactor with a bath of melt created by joule heat and free–burning arc. the Integrated Environmental Technologies, LlC has elaborated a technology called the plasma enhanced melter (PEM), by which it is possible to treat solid industrial, medical, and weak radioactive waste [80,81]. The method is realized in a reactor of the chamber type (Fig. 2.64), in which two groups of graphite electrodes are placed.

Figure 2.64. Scheme of the reactor by IET, LLC.

Two sources of energy are used in this treatment process. The alternative current source and the first group of electrodes comprise a zone of joule heating, which creates a bath of melt on the reactor’s bottom. The energy is imbedded directly into the melt through sunken electrodes. The melt is created by an inorganic component of the wastes and itself is a glass–

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

155

wise mass with current conductivity. The direct current source and electrodes of different polarities comprise the plasma arc zone. The stable plasma arc is formed between the surface of the melt bath and the rod electrodes. The wastes are input directly into the plasma–arc heating zone where the organic components dissociate under the leak of oxygen and create СО, Н2, N2, HCl, and Н2S. The inorganic oxides are dissolved in the melt bath, but the metal components precipitate on the reactor’s bottom. The electrodes are made of graphite sections with a length of 0.6 m and diameters of 0.15 m. Every two to three weeks it is necessary to enlarge the electrodes, which provides the temperature of the melt bath. The direct current electrodes, which input energy into the plasma–arc heating zone, need an addition of one section every two to three days. Here, the treatment process is implemented under a temperature of 1100–1400оC and, in essence, is close to pyrolisis. As a result, the syngas, glassed slag, and restored metals are obtained in the reactor’s output. In the technological scheme, the wet method for gas cleaning is used. In the first stage, the acid gases and dust particles are removed. In the second stage the acid residuals and aerosols are removed. The cleaned syngas containing mainly Н2 and СО is used further for producing electric energy. In a typical experimental result in treatment of municipal solid waste, the syngas has the following contents (in %): N2 – 44; Н2 – 25.6 ; СО – 17.2; СО2 – 11; Н2О – 5; СН4 – 3.5. A liquid fuel production plant using the same technology is suggested for obtaining liquid fuels from municipal and industrial wastes.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Plasma–pyrolisis with output in the form of glassed slag. The company Vanguard Research, Inc. (VRI, United States) has constructed the technology, plasma energy system (PEPS), for treatment of solid municipal and industrial wastes [82]. Here, plasma–pyrolysis with syngas output is realized (Fig. 2.65).

Figure 2.65. Technological scheme of the PEPS.

The reverse system for scrap delivery excludes jamming and the appearance of hang– ups, and this makes the system especially safe and reliable. The scraps in packed or placer form are delivered into the auger by the mechanical pusher. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

156

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The chamber–type reactor is heated by a plasmatron up to a temperature of 1650 оC, at which the dissociation of the organic part of the waste is performed and glassing of the slag is realized. The syngas goes out of the reactor with a temperature of 1040 оC and is cooled quickly by water to prevent reactions that can create complex organic compositions like dioxins. The gas produced as a result of pyrolysis (for example, of medical wastes) contains carbon, metal particles, and acid gases, which have to be removed before the gas will be used further. The volume of the output gases is 10 times smaller than under burning the same quantity of wastes. The exhaust fan delivers the gas into the quencher and scrubber for cleaning. After the cleaning, the gas congested with water is mixed with a natural gas or methane and is transformed in the thermal oxidizer to correspond to the nominal atmospheric contents. The high temperature in the reactor and high energetic contents of the obtained gas provide an opportunity to obtain electric energy and to minimize permanent and exploitation outlays. The syngas obtained can be used in a gas turbine for rotating the electric generator while delivering the produced electric energy into the PEPS–system or into the consumer net. The second method of application of syngas is in producing overheated vapor by burning the gas in the boiler–utilyzer, or by using the heat exchanger mounted in the flow of the obtained gas.

Figure 2.66. IEE RAS plant for plasma gasification of wastes.

Here, the harmful ejections into the atmosphere are significantly lower than the admissible ones determined by the standard norms (СО – 15.1 mg/ nm3, HCl – 1.06 mg/nm3, NО – 55 mg/nm3; SO2 – 7 mg/hm3, and dioxins – 1.19×10–8 mg/nm3). VRI, Inc. built a row of stationary plants with a performance of 5 to 15 tons per day and a mobile module treating from 3 to 5 tons per day.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

157

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Here, the plasmatron of 500 kW power with a direct current arc works on air or nitrogen, and the power is provided by a diesel–generator of 1 MW power. The IEE RAS experimental installation. In the IEE of RAS (Saint Petersburg, Russia) an experimental plant has been built to research the processes of plasma gasification of various solid hydrocarbon wastes (tires, wood, refuse-derived fuel, coal, etc.) with application of air and air–vapor plasma generators of alternative current [29,83,84]. A general view of the plant is presented in Fig. 2.66. Its principal scheme is shown in Fig. 2.67

Figure 2.67. Principal scheme of the IEE RAS plant.

The shaft–type reactor works by the reversal scheme of gasification with removal of the solid slag. When the energy is delivered through plasmatron 2, the process of partial oxidizing of the hydrocarbon waste by air is realized. Under this, hydrogen is evolved and carbon monoxide is created. Further, the gas obtained passes into the afterburner where the hydrogen and carbon monoxide are oxidized completely. Here, the afterburning is initiated by the low-power plasmatron 4 of and is implemented under an intensive air blast. Further, the products of burning are cleaned and ejected into the atmosphere. Concentrations of the gas components (CO, CO2, CH4, H2, H2O, O2, N2, NO, NO2, and Ar) were measured by means of a time–of–flight mass spectrometer. To check the accuracy of measuring, an infra–red Fourier spectrometer was used. Consider some details of arrangement and principle of operation of the reactor module (Fig. 2.68).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

158

Philip Rutberg

Figure 2.68. Reactor schematic diagram; 1 – loading valve; 2 – tank for primary biomass preparation; 3 – plasma generator; 4 – reactor shaft; 5 – blast holes; 6 – thermocouples; 7 – gas duct (product–gas outlet); 8 – fire grate; 9 – hydro lock.

For the primary heating of the reactor, charcoal is the most suitable material, since it is free of flying fractions, condensation of which on the cold parts of the system can cause violation of operation of the cleaning system. Under the working regime, the biomass is delivered into the system, passes from region 2 to the zone of the plasma input, and is subjected to the following changes: under gradual heating up to a temperature of 500–550°C, the flying components are removed from the biomass; after separating the flying components, a solid residual is created. But its low caking quality, low reaction ability, and high heat stability prevent complete gasification if the process is implemented by the usual (not plasma) methods. At this stage of gasification, for example, when the wastes of technically dry wood are treated, charcoal is produced (of the following approximate mass contents: C – 87.2%, H – 3.4%, O – 9.4%), and 26.4% of the flying components are separated. The process of outlet of the flying components is completely achieved in the shaft near the holes of the plasma in– blast. Further, in the input plasma zone of the reactor, pyrolysis begins, i.e., the thermal destruction and oxidizing–reduction reactions (with the oxidizing ones prevailing), rates of which depend on the enthalpy and consumption of the blast. The plant can be arranged by one to two plasmatrons. As a result, H2, CO, H2O, CO2, and other components are produced, the

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

159

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

phase state of which is stipulated by the morphological contents of the substance to be gasified and by the average temperature in this zone of the reactor. But some types of waste (for example, tires) contain inorganic substances with high temperature of melting and evaporation. So, these substances remain in the condensed form. Moreover, the products of incomplete oxidation of the heavy hydrocarbons and coke residuals are produced. Further along the reactor axis there is a zone of complete destruction with prevailing reduction reactions where the heavy hydrocarbons are transformed into light ones (with their oxidizing), but H2O and CO2 are reduced to H2 and CO on the hot coke residuals. The plasma blast is supplied into the ring distributor which provides homogeneous distributed input of the oxidizer. The reactor is arranged with a system of delivering the additional vapor or air blast into various zones. This allows one to increase significantly the performance of the plant. The check of the temperature regime is implemented by thermocouples, which are evenly placed along the reactor height on the shaft wall. In the steady–state working regime of gasification along the reactor height, the non–uniform field of average temperature is established, which has a maximum. The take–off of the produced gas is implemented through gas duct 7. At the bottom part of the reactor, the process of removal of the solid slag is realized through the slots in the rotating grate–bar screen, onto which the column of the substance to be treated rests.

Figure 2.69a. Syngas composition at the reactor outlet.

Figure 2.69b. Heat value of the product–gas.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

160

Figures 2.69a and b show the experimental results of gasification of wood wastes, effluent gases and their heat values. Under this, the specific enthalpy of the supplied air plasma was relatively low. The syngas contents correspond to the calculated equilibrium composition at 1000 K (H2 – 24.3, CO – 27.2, N2 – 39.3, CO2 – 5.2, CH4 – 0.5, and H2O – 3.2% vol.), and conversion on carbon and hydrogen is about 81.1% and 85.4%, respectively. The maximal deviation of all real concentrations from the calculated ones does not exceed 3%. One can see some experimental results in Table 2.7. Table 2.7. Some characteristics of the product–gas

Material

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Charcoal Charcoal (with steam blast) Wood waste

Conversion (%) on C H 95.4 75.4

Heat value, MJ/nm3 4.31

Specific gas yield, nm3/kg 4.98

4.75

4.22

88.7

85.2

5.88

3.14

81.1

85.4

The high (in comparison with the other modes mentioned above) magnitude of the heat value of the syngas produced from wood is caused by a more than triple (in relation to charcoal) increase in the molar share of hydrogen; and a simultaneous decrease in the share of nonflammable impurities (nitrogen, argon, carbonic gas) of 48.9% compared with 62.3% for air gasification of charcoal and 57.7% for air vapor. At the same time, the specific gas yield from wood is significantly lower. Obviously, due to the high content of oxygen and hydrogen in wood, less air is required less air for its destruction and gasification , than for gasification of charcoal of the same weight. For better charcoal gasification the specific plasma enthalpy should be increased and the vapor blast supply should be increased as well. Coal gasification for liquid fuel production. It is known that the organic component of coal contains approximately fifteen times more oxygen than hydrogen. But for producing liquid fuels from the products of gasification (that contain the main components of synthesis, i.e., CO and Н2), it is necessary to have the ratio Н2 / СО from one to two. Such a ratio can be obtained by the addition of water vapor into the gas generator that inevitably leads to an increase of energy expenditures for gasification. This energy can be obtained from the waste treated by its burning, i.e., with producing carbon dioxide (СО2). For obtaining appropriate working temperatures in the reactor, such a mechanism can be only arranged on the vapor–oxygen blast. For example, this can be realized by the Lurgi method (in which the vapor mass exceeds two times the organic mass of the coal), and the gas obtained has a ratio of the synthesis products of ~2 / 1. On the whole, this leads to growth of the obtained gas mass containing the ballast water vapor and carbon dioxide and to reduction of its temperature. Drying and washing such a gas and obtaining the initial working vapor inevitably lead to uncorrectable loss of power. Moreover, after the drying, the condensed liquid contains hydrocarbon products of gasification that decrease the effectiveness of the process. The plasma–chemical method is an alternative one for gasification whereby the plasma plays the role of carrier of the additional energy and oxidizer. The air (or the air enriched by oxygen) and the water vapor (but in decreased quantities) can be oxidizers. Under this, it is

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

161

possible to obtain higher temperatures in the reactor and to improve the quality of the product–gas under approximately the same specific output in comparison with the vapor– oxygen process. Optimization of the regime parameters of the vapor–oxygen plasma gasification in the IEE RAS plant allows one to obtain syngas with an intermixture of ballast gases of about ~5 %. But additionally arranged recuperation of the heat can decrease the energy expenditures. Comparison of experimental and theoretical data for air plasma confirms the correctness of the computational proposal, and it is possible to expect that in further experiments on vapor–oxygen gasification the computational results will be confirmed experimentally. Comparative analysis of plasma gasification with classic technologies shows that plasma gasification is implemented under significantly higher temperatures of 1800–1200ºC (under normal pressure). As a consequence, the expenditure of the vapor blast and the output of the ballast gases (including the acid ones) are decreased five times, and, the oxygen consumption also decreases, but the losses of carbon in the slag residual are practically absent (not more than 3%). Therefore, the specific output of liquid fuel is higher. Moreover, additional drying of the product–gas (after the gasification) and its cleaning from the resin components are not necessary. In the whole, producing the liquid fuel by the plasma process is ecologically clearer, more effective, and energetically preferable, since the specific flows of the treated harmful substances are decreased but the useful ones are increased. These considerations are affirmed by the experimental data presented in Table 2.8.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Table 2.8. Variants of coal gasification in water vapor plasma with a secondary oxygen blast

Indices Consumption of the plasma generating gas, g/ton Plasma temperature, °C Consumption of the secondary oxygen blast, kg/ton Syngas output under 25°C, m3/ton Water output in the gas cooling to 25°C, kg/ton Summary output of Н2 + CО, kg/ton Н2 СО СО2 Gas contents under 25°C, % vol.: Н2О СН4 N2 Others 3 Gas heat of burning (the minimal), MJ/m

Values of indices in variants of gasification 1 2 3 425 412 500 2900 3150 2990 354 244 271 2540 2450 2650 11 — — 1462 1458 1480 46.9 48.5 49.2 46.9 48.5 45.1 1.5 — 1.2 3.2 — 3.2 — 1.7 — 1.4 1.2 1.2 0.1 0.1 0.1 10.08 10..8 10.11

Plasco Energy Group. In Canada, RCL technology has been elaborated for the plasma gasification of various types of wastes (municipal, biological, etc.) using the direct current Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

162

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

plasmatrons and with preliminary heating (using some natural gas) the vapor delivered into the plasma–chemical reactor. According to the authors’ data, the following optimal parameters of the product–gas were obtained: Н2 – 41.2%, СО –29.7%, N2 – 17.0%, СО2 – 8.3%, СН4 (methane) – 3.2%, О2 –0.3%, acetylene –0.2%, and ethylene – 0.1%. Under this, the conversion ratio is defined as the energy available in the product–gas to the electrical energy imbedded into the process that created the product–gas; the conversion ratio is 4.3 / 1. The quantity of the electric energy spent on one ton of the municipal solid waste is 612 kW×hour, and the energy content of the syngas produced was 10.51 MJ/nm3 [85]. On the basis of these investigations in June, 2007 in the Ottawa suburbs, a full–scale plant for waste treatment [86] was started. A photograph of the plant is presented in Fig. 2.70. The product– gas obtained is used for production of electrical and thermal energy.

Figure 2.70. The PEG plant for waste treatment.

Technology of the Startech Environmental corporation. The Startech Environmental Corp. (United States) has elaborated a technology for treatment of liquid and solid wastes [87]. The a photograph of the plant is shown in Fig. 2.71; the plant is called the plasma waste converter.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

163

Figure 2.71. Photograph of the Startech plant and the reactor scheme.

The plant treats municipal and industrial wastes, as well as, paints, solvents, and oils. Its performance is 200 kg/hour. The technology is based on the process of plasma pyrolysis using a direct current plasmatron of 200 kW power. The plasma-generating gas is air. The scheme of the technological process is presented in Fig. 2.72. PC G plasmaconverter gas

Gas blower standard industrial ne twork

power supply

s

Plasma gas supply

PC G 50°С cooling He a t e xc hange r

steam (if nec essar y)

Used coal charcoal filter

pump Cooling water

Plasmatron

waste

P C G 50°С

external regeneration or destruction

Spraying water

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

P CG 1200°С Automatic feed of waste continuous)

plasma waste

cyclone

que nc hing

PC G 150°С

filter

quenching /treatment

(PWC) ash

collector Of vitrified slag

water

ash

minerals

draina ge

Tre a tm e nt in PWC

Figure 2.72. Scheme of the technological process in the Startech plant.

The wastes are delivered from the depository into the gate feeder and, further, into the reactor in small portions. If necessary to deliver a liquid, additional dosing pumps and air–jets are used. In the plant, plasmatron with an arc of indirect action is used which can be arranged in a fixed position on the cover or can be moved inside the plasmatron by some external mechanism. The wastes are delivered into the reactor of the chamber type, where they are subjected to the action of high-temperature plasma. As a result, the pyrolysis of the waste organic components is realized under temperature of 1600 °С with the production of a high– calorific syngas. In the bottom part of the reactor, melt is accumulated. Because of the density difference, stratification of the melt occurs. The minerals are accumulated in the surface layer, but the metals are collected on the bottom. The obtained product–gas goes out from the reactor under a temperature of 1200°C and is delivered into the scrubber–cleaner, and after cleaning, the gas can be used as a fuel for

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

164

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

producing electric energy. The typical contents of the syngas is the following (in %vol.): CO – 22-32; CO2 – 2-5; H2 – 20-45; O2 – 3-5; N2 – 15-35; the general range of CH is 5-10. The pure syngas is also used as a raw chemical. The metals and ceramic silicates are removed from the reactor. In the treatment of solid wastes, their volume is decreased by 300 times. PYROARC technology. ScanArc (Sweden) [88] has elaborated the PYROARC technology for treatment of solid, liquid, or gas wastes. The peculiarity of this process is in its two–stage implementing. The solid wastes are loaded into the shaft furnace where gasification of the organic components is carried out, and the inorganic components are melted into the slag. This gasification of the solid wastes is based on the thermal energy created by a partial burning of carbon and carbon monoxide. This is realized in the gasifier with the counter–flow under effective thermo exchange between the entering material and the removing gases. The preliminary heated air or oxygen is used as the gasifying agent. The gas produced is further subjected to pyrolisis in the plasma reactor. As a result of the process, the syngas, slag persistent to leaching, the molten metal, and a small quantity of secondary dust are created. The reactor is the main part of the plant (Fig. 2.73). The fuel gas obtained in the shaft generator contains resins and hydrocarbons and is delivered into a mixing zone at the front of the plasma generator. The secondary gas (air and vapor) is input for checking the oxidizing level of the syngas obtained. After the mixing zone, a special zone is situated for expanding and equalizing the temperatures up to 1200–1300°C, and for initiation of the decomposition reaction.

Figure 2.73. Scheme of the PYROARC reactor.

A variant is possible when the liquid and gas wastes are delivered into the mixing zone bypassing the gasifier, are mixed with the air plasma, and are decomposed in the reactor for to producing the syngas components. A pilot plant with a performance of 300 to 700 kg/hour of solid wastes and from 50 to 500 kg/hour of liquid and gas wastes has been built in the city of Hofors (Sweden). In the plant, a direct current plasmaron with an arc of indirect action is used. The plasmatron power is 1 MW and air is the working gas. The syngas obtained has a calorific power of about 4 MJ/m3 and contains a summary value of СО and Н2 of about 35–40%. This gas is used in the gas turbine for obtaining electrical energy or, under burning in the boiler, for producing overheated vapor.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

165

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Collaborative plant of the Westinghouse Plasma Corporation and Hitachi Metals, Ltd. The Westinghouse Plasma Corp. (United States) [34, 89] has created a technology and, in collaboration with Hitachi Metals, Ltd. (Japan), built (in several Japanese cities) plants with various performance in the treatment of solid municipal and other wastes. The principal technological scheme of the process is presented in Fig. 2.74. The reactor is the vertical shaft type. Several plasmotrons of direct current are placed in the bottom part of the reactor. Moreover, there is a reserve plasmatron. Air is the plasma generating gas. The solid municipal wastes are delivered from the top together with limestone and coke and, under this, the latter materials create a “coke cushion” on which the wastes are loaded. The plasmatrons heat the bottom part of the reactor up to a temperature of 1500°C, and under action of the air heated in the plasmatrons, partial burning of the coke is realized with the production of СО2 and СО. These gases react with the excess coke and the substances contained in the solid wastes. Under this, the main components of the fuel gas, i.e., СО, Н2, and СН4 are produced. Due to action of heat, the melting zone is created whereby the inorganic part of the waste is transformed into slag. After accumulation, the slag is removed from the reactor. Thus, the products of the waste treatment are syngas and glassed slag.

Figure 2.74. Principal scheme of the Westinghouse–Hitachi technological process.

Further, the fuel gas is delivered into the afterburner where its burning is realized with the input of additional air. The time of afterburning is 2.5 sec and the temperature is over 1000°C. The energy obtained is used for producing the overheated vapor in the boiler. The effectiveness of the energy obtained is more than 20%, the produced electricity is used in the same plant, and this creates the closed cycle of the treatment. The chimney gases from burning are delivered into the scrubber–cleaner and, after filtration, are removed into the atmosphere. The contents of the harmful impurities in the output gases are the following: dioxins are lower than 0.01 ngr/nm3, dust is lower than 0.01 g/nm3, sulfur–oxide is lower than 20 ppm, HCl is lower than 30 ppm, and NO is lower than 50 ppm. Figure 2.75 shows the plant for plasma treatment of 165 tons per day of crushed car materials or 300 tons per day of solid municipal wastes. This plant was started in 2003 in the city of Utashinai (Japan). The plant produces about 8 MW of energy.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

166

Figure 2.75. Plant treating 300 tons of wastes per day in the city of Utashinai (Japan).

After analysis of a variety of existing technologies for waste treatment, one can conclude that the plasma technology for waste treatment will be needed, since it provides the preferable production mechanism of fuel gases, which do not condensate under usual temperature. In such a process, the vapor–gas products of the low-temperature decomposition of the initial raw material must be subjected to deep secondary pyrolysis, and the solid residual enriched by carbon must be gasified for producing the gases of the prescribed contents. The prescription of the contents is understood as follows: •

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

• •

a minimal content (ideally, the complete absence) of resin condensing under usual temperature in the vapor–gas mixture at the reactor output; a minimal ballasting of the output gas by nitrogen and by other ballast components; a maximal content of thermo–valuing components (СО and Н2) in the output gas under the lowest possible expenditure of energy throughout the process.

6.3 Plasma High-Temperature Oxidizing Waste combustion is a process taking place at high temperature (higher than 600°C) and results in complete decomposition of organic compounds. But not all combustion technologies can be recommended for some types of waste. There are wastes (military, medical, chemical, etc.) requiring temperatures higher than 1200°C. Their calorific value cannot provide high temperatures during the waste combustion itself. That is, why it is necessary to use additional fuel for organization of combustion. The application of plasma technology solves these problems with the method of high-temperature oxidizing [29,89]. Plasma destruction and neutralization of liquid super toxic agents. A plant for plasma destruction of liquid waste has been developed and constructed in the IEE RAS (Fig. 2.76) [67,90,91]. Plasma treatment of toxic liquids is carried out in two chambers mounted in series (two–reactor diagram) – a tunnel primary furnace and a cyclone reactor–afterburner. Delivering the waste into the primary furnace is carried out with the use of a twisted plasma jet, into which liquids dispersed beforehand by compressed air are injected. Input into a plasma jet of solvents to be treated is designed for improvement of the process of ignition of difficult-to-conbust and incombustible liquids. The process of combustion or gasification depends on the proportions of supplied fuel; the air–water process

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

167

can take place in the primary furnace. The processes are implemented under temperatures of 1200–1300°C.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 2.76: Flow–sheet of the plant for plasma destruction of liquid toxic substances: reactor–primary furnace; 2 – the single–phase plasma torch (up to 10 kW); 3 – reactor–afterburner; 4 – three–phase plasma torch (up to 30 kW); 5 – quenching chamber; 6 – gas cleaning system

The gases from the primary furnace move with a high velocity into the cyclone reactor–afterburner. Here, under temperatures of 1400–1500°C, the final oxidation of the initial substances and products of their incomplete oxidation is performed. For this purpose a tangential stream of hot air from the plasma torch is fed into the reactor. A significant stay– time of flue gases in the afterburner (~2 sec) ensures the complete mineralization of the organic substances. After the reactor–afterburner, the flue gases are quickly cooled to temperatures of 380– 400°C by water injection and by the input of cold air. Plasma high-temperature oxidizing of hazardous medical wastes. A plant for the plasma high-temperature oxidizing of hazardous medical waste has been developed and now is under construction at the Institute for Electrophysics and Electric Power of RAS (Fig. 2.77) [89,91,92]. Hot air

Medical waste

Water Air Carbamide

Air Air Water Air Water

4 Air

1

Water

Water Air

Air

Sodium

4

2 3

5

6

7

9

8

10

11

13

12

Air Slag

13

14

14

Figure 2.77. Schematic diagram of the plant for plasma treatment of hazardous medical waste; 1– loading chamber; 2 – rotary kiln; 3 – slag unloading chamber; 4 –plasma torch; 5 – afterburner; 6 – quenching chamber; 7 – quencher; 8 – recuperator; 9 – wet scrubber with Venturi; 10 –– demister; 11 – filter; 12 – stack; 13 – fan; 14 – pump.

The solid medical waste is supplied in the cardboard boxes measuring 457×457×559 mm and is placed on a site of temporary storage or in a special room equipped with a refrigerator.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

168

Philip Rutberg

The waste plasma oxidizing is performed in a rotary furnace. The waste is supplied into the furnace periodically through a gas–tight gate. The process in the furnace is performed under deficit of oxygen. The factor of the air excess is α = 1.0–1.2. The temperature of the flue gases at the furnace outlet is kept at a level of 1100– 1250°C due to the heat of the waste combustion itself and the hot air from the plasma torches installed at the end face of the furnace feed head. The plasma torches are used also for initial heating of the furnace at the start–up and maintaining the necessary temperature in the furnace during stoppage of the combustion process. The slag is removed from the furnace into a device for slag quenching filled with water. After quenching and cooling, the slag is delivered for burial. The flue gases from the rotary furnace go into the afterburner, which serves for combustion of the carbon oxide that is contained in the flue gases, residuals of hydrocarbon, and the mechanical carbon in the form of coke particles, and the soot is removed from the furnace. The high temperature in the afterburner (1200–1300°C) and sufficient continuous stay–time of the flue gases (~2 sec) ensure decomposition of the stable organic compounds and prevent the existence of super toxic compounds, i.e., dioxins. The temperature regime in the afterburner is supported due to the heat contents of the flue gases incoming from the furnace, the feeding of the hot air (1700°C) from the plasma torch, and heat from the combustion of the fuel residuals that are contained in the flue gases. The supply of additional air and water into the chamber is designed to increase the quality of afterburning and ensure the possibility of temperature regulation. Then the flue gases are delivered to the systems of cooling and cleaning. In conclusion, it is necessary to underline that the plasma technology of gasification allows one to transform fuel energy (including the energy of organic wastes) into useful energy in the most complete way. Implementation of this process under temperatures of 1200°C and higher allows one to obtain the product–gas with minimal content (up to the complete absence) of liquid fractions (resins) and harmful impurities. The high temperature of the process facilitates the detoxifying and homogenization of the slag, which makes possible its further utilization in various technological processes.

REFERENCES [1] [2] [3] [4] [5] [6] [7]

Finkelnburg, W., Maecker, H. Electrische Bögen und Thermisches Plasma, Handbuch der Phisik; Bd. XXII, 1956; pp. 254–444. Baranov, V.Yu.. Ph.D.T hesis; Moscow, 1967. (in Russian) Engel, A. Steenbeck M. Electrische Gasentladungen; Berlin, 1934. Rutberg, Ph.G. Three–phase Plasma Generator, Some Questions of Investigation of Gas–discharge Plasma and Creation of Strong Magnetic Fields, L, Nauka, 1970, pp. 8– 19. (in Russian) Suits C.G.; Phys. Rev., 1939, p.55, p. 561. Fransis, G. Ionization Phenomena in Gases. London Butterworths Scientific Publication 1960. Witting, G. Grundlagen und Anwendungen der Plasma–verfahren. Schweissen und Schneiden. 1962, Bd.14. No.5.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

[20] [21]

[22]

[23] [24] [25] [26] [27] [28] [29] [30] [31]

169

Bates, D.R., Dalgarno A., in Atomic and Molecular Processes, Ed. D.R. Bates, Academic Press, 1962, 904 p. Kasabov, G.A.; Eliseev, V.V. Spectroscopic Tables for Low Temperature Plasma; Handbook. Atomizdat: –M, 1973, 160 p. (in Russian) Frish, S.E. Optic spectra of Atoms; Fizmatgiz:L.–M., 1963, 640 p. (in Russian) Schlichting H.; Entstehung der Turbulenz, Springer, Berlin,1959. Bradshaw, P. An Introduction to Turbulence and Its Measurement; Pergamon Press: Oxford,1971. Zhukov, M.F.; Koroteev, A.S.; Uryukov B.A. Applied Dynamics of Thermal Plasma; Nauka: Novosibirsk, 1975, 296 p. (in Russian) Zhukov, M.F. (ed.) Basis of Calculation of Plasma Generators of Linear Circuit Published by Institute of Teplophysics: Novosibirsk, 1979, 146 p. (in Russian) Zeldovich,Ya.B.; Raizer Yu.P. Physics of Shock Waves and High Temperature Hydrodynamic Phenomena; Physmathgis: M., 1963, 632 p. (in Russian). Granovsky,V.P. Electrical Current in Gases. Settled Current; Nauka: M., 1971, 543 p. (in Russian). Jordan, G.R.; Bowman, B.; Wakelam D. Electrical and Photographic Measurement of High–Power Arcs. J.Appl.Phys. 1970, vol.3, №7, pp.1089–1099. Brown, S.C. Basic Data of Plasma Physics, The Fundamental Data of Electrical Discharges in Gases; American Institute of Physics: New York, 1994, 323 p. Nedospasov, A.V.; Hait, V.D. Oscillations and Instabilities of Low Temperature Plasma; Nauka: M. 1979, 178 p. (in Russian). Loicyansky, L.G. Mechanics of Liquid and Gas; Nauka: M., 1970, 736 p. (in Russian). Duchne, A.M. Theory of One–dimentional arc contraction; in book Some Problems of Investigation of Gas–discharge Plasma and Creation of Strong Current Magnetic Fields; Nauka: L., 1970, pp.84–94. (in Russian). Alexandrov, V.D.; Antonov, G.G.; Borodin, V.S.; Velikhov, E. P.; Golubev, V.S.; Pobedonostsev, O.A.; Pozubenkov, A.A.; Rutberg, Ph.G. About Possibility of Obtaining of Nitrogen Oscillation Temperature Variation in Decaying Plasma of High Pressure; Doklady RAS, 1983, vol. 269, №4, pp.843–845. (in Russian) Biryukov, A.S. Proceedings of FIAN, 1975, vol. 83, p.13–16. Shui, V.H.; Appleton, J.P.; J.C. Keck.; J. Chem.Phys., 1970, vol. 53, pp. 2547–2558. Borodin,V.S.; Grigoriev, M.A.; Kiselev, A.A.; Rutberg, Ph.G. Investigation of the Basic Physical Processes in Power Electric Arc AC Plasma Generators; TVT, 1978, vol.16, №6, pp.1285–1296. (in Russian) Smirnov, B.M., Ions and Exited Atoms in Plasma, M.: Atomizdat, 1974, pp. 221–257 (in Russian). Kolesnikov, V.N. Arc discharge in Inert Gases; Proceedings of FIAN, 1964, vol. XXX, pp. 157. (in Russian). Somerville, J.M. The electric arc, Methuen and Co. Ltd,: London,1959. Rutberg, Ph.G. Plasma pyrolysis of toxic waste; Plasma Physics and Controlled Fusion, PII: S0741–3335(03)55956–5, 45 (2003), pp.957–969. Braun, S. Elementary processes in gas discharge plasma; Gosatomizdat: M., 1961, 323 p. (in Russian) Khaksli, L.; Crompton, R. Diffusion and drift of electrons in gases; Mir: M., 1977. (in Russian)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

170

Philip Rutberg

[32] Vinogradov, S.E.; Kuznetsov, V.E. et al., Theoretical Analysis and Experimental Test of Wear Mechanizm of Two–layer Electrodes for Low Temperature Plasma Torches; Voprosy Materialovedeniya, 2006, №1(45), pp. 1–7. (in Russian) [33] Ochkin, V.N. Spectroskopy of Low Temperature Plasma; Fizmatlit: M., 2006, 472 p. (in Russian [34] Laux, C.O., T.G. Spence, C.H.Kruger, R.N. Zare, Optical diagnostics of atmospheric pressure air plasmas; Plasma Sources Science and Technology, 2003, №12, pp. 125– 138. [35] Ecker, G. Electrode Components of the Arc Dicharge; Ergebn. exakt. Naturq., 1961. Bd. XXXIII. p.104. [36] Libin, Sh. I. About Cathode Breakdown in Pulse Discharge in Inert Gases; Radiotechnika I Electronika, 1959, №6, pp. 1026–1032(in Russian) [37] Borodin, V.S.; Rutberg, Ph.G. About Emission of Tungsten Electrodes in Plasma Generators of Alternating Current; TVT, 1968, №3, pp.566–568. (in Russian) [38] Amosov,V.M.; Karelin, B.A.; Kubyshkin, V.V., Electrode Materials on Base of Hard Meltings Metals; Metallurgy: M.,1976, 223 p. (in Russian). [39] Neurath, P.W.; Gibbs, T.W. Arc Cathode Emission Mechanisms at High Currents and Pressures; J.Appl..Phys., vol. 34, №2, pp.277–283. [40] Glebov, I.A.; Rutberg, Ph.G. Powerful Plasma Generators; Energoatomizdat: M., 1985. (in Russian) [41] Korsukov, V.E.; Patrievsky, P.V.; Rutberg, Ph.G.; Tutina, N.M., About Operation of Power Electric Arc Gas Generators; JTF, 1986, vol. 56, issue. 9, pp.1724–1729. [42] Rich, J.A. Resistance Heating in Arc Cathode Spot Zone, J.Appl.Phys., 1961, vol.32, №6, pp.1029–1031. [43] Rutberg, Ph.G.; Safronov, A.A.; Kuznetsov, V.E.; Popov S.D.; Surov A.V. Research of Erosion of Water Cooling Electrodes of Powerful AC Plasma Generation. Progress in Plasma Processing of Materials 2001. Editor Fauchais, P. Library of Congress Cataloging in Publication Data 2001 by Begell House Inc. Printed in the USA 1234567890, pp. 229–234. [44] Vinogradov, S.E.; Rybin, V.V.; Rutberg, Ph.G.; Safronov, A.A.; Shekalov, V.I.; Shiryaev, V.N.; Kuznetsov, V.E. Investigation of Mechanisms of Electrode Wear of Plasma generators; Voprosy Materialovedeniya, 2002, №2 (30). (in Russian) [45] Plasma Technology in Metallurgical processing; Editor Feinman J. A Publication, Iron and Steel Society, Inc. Printed in the USA. Copyright 1987. [46] Fujimoto H.; Tokunaga H.; Iritani, H. A high–powered A.C. Plasma Torch for the Arc Heating of Molten Steel in the Tundish; Plasma Chem. Plasma Processing, 1994, 14, pp. 361–82. [47] Kudinov, V.V. Spray Application. Theory, Technology and Equipment; etallurgiya:M., 1992, 431 p. (in Russian) [48] Usov, L.N.; Borisenko, A.I. Plasma use for production of high–temperature coverings; Nauka: Leningrad, 1965, 34p . (in Russian) [49] Rykalin, N.N.; Shorshorov, M.H.; Kudinov, V.V.; Galkin, O.A. Characteristic Features of Physical–chemical Processes for Composite Material Production with the Help of Plasma. In book Plasma Processes in Metallurgy of Non–organic Materials; Nauka: Moscow, 1973, p. 186–187 . (in Russian) [50] Maruyama, K.; Ohkouchi, K.; Goto T. Jpn.J.Appl.Phys., 1994, 33, p. 4298. [51] Copsey, M, Plasma Technology for the Destruction of Hazardous Wastes; Proc.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of High Current Discharges in Gas Environments

[52] [53] [54] [55]

[56] [57] [58]

[59]

[60] [61] [62]

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

[63]

[64] [65] [66] [67]

[68] [69] [70]

171

Technical Conf. Plasma for Industry and Environment (BNCE Oxford), 1990, No 6–1. Mucha, J.A.; Flamm, D.L.; Ibbotson, D.E. J.Appl.Phys, 1989, 65, pp. 3448–3452. URL: http://www.westinghouse–plasma.com Maniero, D.A.; Kienst, P.F.; Hirayama C. Electric Arc Heaters for High–Temperature Chemical Processing, Westinghouse. Engr. 1966, 26, №3, pp.66–72. Rutberg, Ph.; Safronov, A.; Popov, S. et al. Multiphase Stationary Plasma Generator Working on Oxidizing Media; Plasma Physics and Controlled Fusion; Institute of Physics Publishing: London U.K, 2005, vol.47, pp.1681–1696. Department of Nuclear Engineering, Seoul National University. http://fusma.snu.ac.kr. The Institute of Plasma Physics, Czech Republic. http:// www.ipp.cas.cz Hrabovský, M.; Konrád, M.; Kopecký V; Sember V., Properties of Water Stabilized Plasma Torches. Ed. Solonenko, O.P. – Cambridge, Cambridge Inter. Science Publishing 1998, 16 p. Mikimasa Iwata; Masatoyo Shibuya; Effect on Transferred ac Arc Plasma Stability of Increasing Ambient Temperature and Superimposing Pulse at Current Zero Point; J.Phys. D: Appl. Phys. 32 ,1999, pp. 2410–2415. Printed in the UK. http://www.ipclub.ru/users/ kerc/developments/last_dev.htm USA, Patent 4.013.867. Mar.22.1977, Polyphse Arc Heater System. Anderson, J. Gasodynamic Lazers: Introduction: Ed. Polak, L.S.; Mir: M., 1977, 316 p. (in Russian) Rutberg, Ph.G.; Kumkova, I. I.; Kuznetsov, V. E.; Popov, S. D.; Rutberg, A. P.; Safronov, A. A.; Shiryaev, V. N.; Surov, A. V. High–Voltage Plasma generators of Alternating Current with Rod Electrodes Stationary Operating Media; 2007 IEEE Pulsed Power Conference (PPPS–2007) Digest of Technical Papers 1976–2007, June 17–20, 2007, Aibuquerque, New Mexico, USA, IEEE Catalog Number 07CH37864C, pp.1556–1559. Popov, S.D.; Rutberg, Ph.G.; Safronov, A.A. Characteristic Features of Application of Plasma Generators of Alternating Current at Operation in the Plasma Reactor; Teplofisica Vysokich Temperatur, 2007, vol. 45, №1, pp 5–11. (in Russian) Kasabov, G.A. Ph.D. thesis; Moscow, 1967. (in Russian) Koroteev, A.S.; Mironov, V.M.; Svirchuk, Yu.S. Plasma generators: designs, characteristics, calculation; Mashinostroenie: M, 1993, 295 p. (in Russian) Rutberg Ph.G., A.A. Safronov, A.N. Bratsev, B.M. Laskin, V.V. Shegolev, Scientific– engineering foundation of plasma–chemical technological treatment of toxic agents (TA) and industrial super–toxic agents (ISA), in Environmental Aspects of Converting CW Facilities to Peaceful Purposes, McGuire R. and Compton J.C. (eds.), 2002, P.211– 222. Tendler M., Ph.G.Rutberg, G. Van Oost, Plasma based waste treatment and energy production, Plasma Physics and Controlled Fusion, v.47, A219–A230, (2005). Choi Kyung–Soo, Park Dong–Wha, Pyrolysis of waste tires by thermal plasma. 13th International Symp. On Plasma Chemistry ISPC 13 1997 (Pekin University Press), vol. 4 p.2447–51. Environmental Technologies Handbook. Government Institutes. An imprint of Scarecrow Press Inc. Lanham, Maryland. Toronto. Oxford. 2005. pp.161–192. ISBN0– 86587–980–X.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

172

Philip Rutberg

[71] Zhukov М.F., R.A. Kalinenko, A.A. Levitsky, L.S. Polak, Plasma–chenical treatment of coal M.: Nauka, 1990, 200c (in Russian). [72] Imris I., A. Klenovcanova, P. Molcan, Energy recovery from waste by the plasma gasification process // Archives of Thermodynamics, 2005, Vol. 26, №2.– p. 3–16. [73] Nishikawa Hiroshi et al., A treatment of carbonaceous wastes using thermal plasma with steam // Vacuum, 2004, 74, №3–4, С. 589–593. [74] Hrabovsky M., M. Konrad, V. Kopecky et al., Pyrolysis of wood in arc plasma for syngas production // High Temperature Material Processes, 2006, Vol. 10, №4, p.557– 570. [75] A. van der Drift, H. Boerrigter, Synthesis gas from biomass for fuels and chemicals // Report ECN–C–06–001, SYNBIOS conference, May 2005, Stockholm, Sweden. [76] http://www.eer–pgm.com [77] http://www.plascoenergygroup.com [78] http://www.geoplasma.com [79] http://www.peat.com [80] http://www.inentec.com [81] Waste Gasification – Test Result from Plasma Destruction of Haradous, Electronic and Medical Wastes, W.J. Quapp, D. Lamar, N. Soelberg. IT3/03 Conference, May 12–16, 2003, Orlando, Florida. Pp.1–14. [82] http://www.enersoltech.com [83] Distinctive Features of Biomass Gasification Using AC Plasma Generators working on Air: A.N. Bratsev, V.E. Popov, V.B. Kovshechnikov,V.A. Kuznetsov, I.I.Kumkova, A.A. Ufimtsev and S.V. Shtengel, 2007 IEEE Pulsed Power Conference (PPPS–2007) Digest of Technical Papers 1976–2007, June 17–20, 2007, Albuquerque, New Mexico, USA, IEEE Catalog Number 07CH37864C, ISBN 1–4244–0914–4, Library of Cogress 81–644315. [84] Rutberg Ph.G., Some Plasma environmental technologies developed in Russia, Plasma Sources Science and Technology, PII: S0963–0252(02)39431–3, 11(2002), p.159–165. [85] Carter G.W., A.V. Trangaris (Resorption Canada Limited) Plasma Gasification of Biomedical Waste. Proceedings of the international simposium on environmental technologies: plasma systems and applications. 1995, Atlanta, USA, p. 239–250. [86] Plasco Energy Group. Canada. Corporate Summary Presentation. November 2007. [87] http://www.startech.net [88] http://www.scanarc.se [89] Hitachi Metals Reports. “Plasma Direct Melting Plant”, No. E–321, 03 2002. [90] G.Rutberg Ph., A.A.Safronov, A.N.Bratsev, B.M.Laskin, Treatment of C1–F Organic Toxic Compounds, 1st IAEA Technical Committee Meeting on Applications of Fussion Energy Research to Science and Technology. October 30 – November 3,2000 Chendu, P.R. China. P.22–27. [91] Rutberg Ph.G., A.A. Safronov, A.N. Bratsev, V.E. Popov, S.D. Popov, A.V. Surov, V.V. Shegolev and M.M. Caplan, Plasma Furnace for Treatment of Solid Toxic Wastes, Progress in Plasma Processing of Materials 2001. Editor Pierre Fauchais. Library of Cataloging in Publication Data 2001 by Begell House Inc. ISBN 1–56700–165–3 Printed in the USA,pp.745–750, (2001). [92] Rutberg Ph.G., A.N. Bratsev, A.A. Safronov, A.V. Surov, V.V. Shegolev, The Technology and Execution of Plasmachemical Disinfection of Hazardous Medical Waste, IEEE Transactions on Plasma Science, v.30, #4, August 2002 ISSN 0093–3813, pp.1445–1448, (2002).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Chapter III

INVESTIGATION OF PULSE ELECTRIC DISCHARGES IN LIQUIDS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

ABSTRACT The parameters of the electric discharges were: energy of the pulses W of 0.5–10 J; pulse length 0.5–20 μsec; current increase rate dI/dt 106 ÷1012 A/sec; light diameter of the discharge channel ~1 mm. In dependence on the input energy and the rate of its insertion, the motion of the boundaries of the discharge channel leads to the appearance of compression waves. At the beginning stage, a shock wave appears with a propagation velocity of ~5 Km/sec, on whose front the cavitation bubbles occur. As a result of the discharges, nanoparticles are created that have a surface electric charge. The distribution functions of the nanoparticles’ mass fraction in water in dependence on the discharge parameters were defined. The high destructive action of ions and nanoparticles (which are the ion sources) onto a wide circle of microorganisms, spores, and cellular structures was shown.

1. INTRODUCTION A great many works [1] are devoted to the investigation of the large current discharges in water and the technological applications. In particular, discharges of such a kind were used for forming and treatment of metals, and for other goals [2,3]. It is necessary to apply large current discharges and significant energy imbedding in these technologies. In this work we consider another class of fast discharges in liquids with a small amount of energy in the pulse and relatively small currents. Such discharges are interesting for the bactericide cleaning of liquids, generation of the nanostructures of various types (in particular, oxide nanostructures), in biology, and medicine. Medical investigations in recent decades have shown that the sharp rise of oncological and cardiovascular diseases results from chlorine disinfection of water [4–6]. It was revealed that chlorinated potable water contains steady macro–radicals, which provoke the occurrence and development of these and other serious diseases [7]. This points to the importance and urgency of works that are directed to searches for alternative and safe methods of water disinfection. Moreover, studies of pulsed electric fields'

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

174

Philip Rutberg

influence on human cells and organic tissue, including cancer tissue [8], are currently being implemented. There are some methods for water and air purification from microbe and other pollutions that use electric energy. The most effective are pulse electric fields [9,10], glow discharge [11,12], streamer/corona discharge [13,14], gliding discharge [15], barrier discharge [16], and pulse spark discharge [17–20]. All methods aforementioned have approximately equal efficiency for microbes' destruction because, in all of those cases, the acting factors are almost the same: UV radiation, OH radicals, H2C greater than 2, Os, etc. However, the pulsed electric discharges (PEDs) have essential advantages in comparison with the others: first, intensive shock waves and, second, the effect of prolonged microbial resistance of water (PMRW). Due to the latter property, water treated by PED is the bactericidal agent. Although investigations of PED, electric fields, corona discharges, and other methods of water disinfection have been carried out for more than 30 years, unresolved problems still exist in this area, in particular, the origin of the PMRW phenomenon [21,22]. When confirmation of the absence of a negative action of electric methods on human beings was obtained, their application in medicine, pharmaceuticals, the food industry, and other areas was widely anticipated [23,24]. Currently, those electric methods in disinfecting the drains of hospitals and industrial enterprises can be used. Thus, the goal of this investigation is in defining the opportunities of PED for safer disinfecting of water and other possible applications.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

2. EXPERIMENTAL UNIT AND THE PED PARAMETERS Figures 3.1a and b show a diagram and photograph of a unit for electric–discharge treatment of water. The unit provides a continuous operation for months due to the feeder (7), which keeps the inter–electrode distance constant by means of a supplying wire (9) into the discharge chamber (6). It is necessary to compensate for the increase of the inter– electrode gap because of the electric erosion of electrodes’ metal. The unit is supplied by the electric pulse generator (Fig. 3.2), which allows treatment of water solutions and dispersions with a resistivity of no lower than 500 Ohm. The pulse generator operates in the following way: the main voltage (220 V, 50 Hz) is applied to the rectifier Vdl–Vd4 and the filter (Ci, L1) through autotransformers 7 and T2 (220/600 V). Since C1 > C2 (C1 and C2 are the capacities of the respective capacitors) and throttle L1,2 is inserted into the charging circuit of capacitor C2, the switching thyristor Vd5 causes the capacitor C2 to charge up to a voltage exceeding the voltage on Cl. After the thyristor Vd6 has been switched on, the capacitor C2 is discharged through the primary winding of high–voltage pulse transformer T3, the secondary voltage of which is applied to the discharge gap, causing its breakdown and the formation of a discharge channel. Investigation of PED parameters, together with the physical, chemical, and bactericidal properties of treated water have shown that the optimal PED's parameters are the following: duration: 1–20 μseс; energy: 0.2–1.0 J/pulse; current increase rate: 106–109 A/sус; and pulses frequency: 50–100 Hz [25]. The types of electrode system are "wire to plate" or "wire to wire" with an inter–electrode gap of ~10 mm and with a diameter of the channel for water passage of ~10 mm.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

a)

175

b)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.1. Unit for electro discharge treatment of water a); 1 –the water to be treated; 2 – the pump; 3 – the part for water treatment; 4 – the treated water; 5 – the generator of electric pulses; 6 – the discharge chamber; 7 – the feeder of wire; 8 – the plate; 9 – wire; b) photo of the electro discharge plant).

Figure 3.2. Scheme of the discharge power supply.

I, A U, V I

U

t, μsec Figure 3.3. Oscillograms of the current and voltage of the discharge pulse versus time; j – the current; U – the voltage. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

176

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The maximum bactericidal action of treated water is obtained with electrodes made of silver, copper, or their alloys. In Fig.3. 3, the typical oscillograms of the current and voltage at pulse duration of 20 μsec are presented. Figure 3.3 shows that, before the breakdown of the inter–electrode gap during 5 μsec, the current increases up to 7 A and voltage up to 35 kV (the signal of voltage was flattened). After the breakdown during the discharge column formation, the current increases up to its maximum of 43 A, and, at this time, the voltage decreases from ~1 kV to zero at its average magnitude of ~700 V. The energy of a single pulse is ~0.4 J, and power is ~20 kW. It is known that the widening of the discharge column during the early stage results in generation of a shock wave [26–29], behind the front of which the cavitation bubbles are formed (Fig. 3.4.a) (see also [30]).

a

b

Figure 3.4. Glowing area at early stage of discharge (a) and the discharge current (b).

In our investigation, the velocity of the frontier of the glowing area (from our point of view, the velocity of the shock wave) had been registered for a time less than 0.3 μsec, with a current increase rate of 5μsec×106 A/sec, and imbedded energy of 0.2 J/pulse (Fig. 3.4.b). The velocity is more than 5×103 m/sec [31]. Essentially lower (< 1500 m/s) velocities of shock wave propagation [26–27] are explained by the high decrement of the shockwave velocity. Moreover, the measurements in those two works were carried out at later stage of the process than in our case, i.e., for a time significantly greater than 1 μsec [27] or with an inter–electrode gap that is significantly farther than 10 mm from the plasma channel [27]. The shock waves in water have a high gradient of pressure at their fronts, so, for the size of a bacterium, the difference in pressure is enough to damage the bacterial membrane and to destroy it [32].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

177

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.5. Oscillograms of a current and pressure under the "slow" a) and the "fast" b) discharges.

Figure 3.6. Spectrum of the discharge radiation (intensity in relative units) .

Comparison of the pulse pressure for the same energy of pulses was carried out for two kinds of electric discharges: the "slow" one with a duration of 20 μsec and a current increase rate of dj/dt = 5×106 A/sec, and a "fast" one with a duration of 1 μsec and a current increase rate of 2×109 A/sec. Figures 5a and b show that the increase of discharge

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

178

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

power results in a proportional increase of the pulse pressure. Therefore, for the "slow" discharges, the amplitude of the shock wave measured at the wall of the discharge chamber is ~0.5 MPa and for the "fast" ones it is ~4 MPa. Hence, the destroying effect on bacteria of the "fast" discharges is higher than that of the "slow" ones under the equal energy of the pulses [33]. To determine the temperature of plasma, the registration of the discharge spectra by diffraction spectrometer was carried out. Figure 3.6 shows the distribution of relative intensity of the discharge column radiation with electrodes of 70% silver and 30% copper alloy. The temperature of the discharge column, which was estimated by comparison of relative intensities of radiation in the lines, is ~104 K. Under this temperature, the discharge column is a source of UV radiation in a wide wave range, from 200 nm and greater [34,35]. The UV radiation, being absorbed by water, produces H2C greater than 2, Os, and OH radicals [36,37], which destroy microbes and some organic compounds. The photographs of a 13 mm–long discharge channel (Fig. 3.7) were taken with a ZhLV–2 high–speed camera, at 1.7 μsec and 5.1 μsec after the beginning of the breakdown. Using these photos and the current–voltage characteristics, one can estimate the conductivity of the discharge plasma at the instant close to the current peak.

a

1.7 μsec

b

5.1 μsec

Figure 3.7. Photographs of the discharge channel in different instants: a) 1.7 μsec and b) 5.1μsec.

The average magnitude of specific electric conductivity is ~103 (Ω×m)–1. The following parameters of the discharge column were estimated the diameter is ~1 mm, the length is 10–13 mm, and the resistance is 15–20 Ω.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

179

Figure 3.8. Specific electric conductivity of plasma versus its temperature for various pressures.

Figure 3.8 shows the plasma electric conductivity versus its temperature for various pressures, which were calculated under assumption of thermodynamic–equilibrium structure. Thus, from Fig. 3.8, the temperature of the discharge column at pressures of 0.5–6 MPa is (0.9–1.1)×104 K, which is in accordance with the data above.

3. EROSION OF ELECTRODES AND THE NANOPARTICLES

80

Specific erosion, mcg/C

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

To find out the mechanism of PMRW, the physical and chemical properties and bactericidal activity of water treated by PED were investigated. At the initial stage of investigation, electrodes of various metals and their alloys were used. Figure 3.9 shows the specific erosion of some of those metals and alloys.

70 60 50 40 30 20 10 0

1

2

3

4

5

6

7

8

Electrode metal

Figure 3.9: Specific erosion of electrode materials: 1 - W+Cu; 2 - Cr3C2+Cu; 3 - Ag+Cu; 4 - Fe; 5 - Mo+W+Cu; 6 - W+Ni+Fe; 7 - Cu; 8 - W+Ni+Cu.

We used the data obtained for rough estimation of the total mass strength of the nanoparticles in water. Furthermore, after the connection between the properties of electrode materials and bactericidal action of the treated water was found, the investigations were concentrated on three metals: silver, copper, and iron. The first two metals were chosen because

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

180

Philip Rutberg

their ions have the highest toxicity to bacteria and so are useful for practical applications, and iron was chosen for comparison with the first two metals.

Dimension of particles, nm

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.10. Distributions of dimension of the average values of mass fractions of silver, copper, and iron particles.

It was confirmed by mass spectrometry with inductively connected plasma that the electrodes' erosion produces particles of metal in water. Consequently, the "Coulter N4" analyzer of sub–micrometer particle size was used for determination of the distributions of the particles’ mass fractions in size. Fig. 3.10 shows plots of distributions in size of the average values of mass fractions of silver, copper, and iron particles at the imbedded energy of 5 and 10 J/ml. The plots show that the sizes of all particles ranged from 5 up to 1000 nm, and the maximal mass fraction is of "small" particles of about 10 nm in size (hereafter nanoparticles), and that the mass fraction of these nanoparticles decreases with increase of the imbedded specific energy. Figure 3.11 shows electronic microscopy photos of silver (Fig. 3.11a) and copper (Fig. 3.11b) nanoparticles and the clusters they have formed. Investigation by special liquid chromatography, electronic paramagnetic resonance, spectroscopy in UV, and visible spectra of the water treated by the copper electrodes shows that the material of nano–particles is not metal but its oxides of Cu2O and CuO. Thus, it was found that the water treated by PED with the copper electrodes is a dispersion containing both nanoparticles of the electrodes’ metal, ions Cu+ and Cu++, which are in dynamic concentration equilibrium [38]. After the dispersion, the nanoparticles were extracted and then put in the deionized water; about 1 hour later, it was detected that the ion concentration reached the initial level; hence, the conclusion can be made that the oxide nanoparticles are sources of ions. The mass strength of silver, copper, and iron nanoparticles in a dispersion versus the imbedded energy at complete decomposition of the nanoparticles to the ions at pH = 2.5 had been determined by means of chromatography (Fig. 3.12).

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Investigation of Pulse Electric Discharges in Liquids

Figure 3.11. Photograph of the nanoparticles and their clusters; (a) of silver; (b) of copper.

Figure 3.12. Mass strength of silver, copper, and iron nanoparticles in dispersion versus the energy imbedded into the discharge. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

181

182

Philip Rutberg

By capillary electrophoreses, it was also found that the nanoparticles have a negative specific surface electric charge of (0.4–1.6)×10–2 Coul/m2 and a volume-specific charge of (0.01–2.6)×10–2 Coul/ml.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

4. BIOLOGICAL OBJECTS AND METHODS OF INVESTIGATION Interaction of human blood serum with nanostructures. The object of the investigation was the interaction of nanostructure water dispersions and biological objects, namely, standard human blood serum. Before the tests, the samples of serum (of 3500 g) were centrifuged for 15 minutes. After that, one part of nanostructure dispersion (distilled water for the control sample) was added to three parts of serum, and then this mixture was diluted 20 times with physiologic solution. The biological effect of nanostructure dispersion by the changes of sub–fractional distribution of serum was determined. Human blood serum sample preparation. The samples of serum were exposed for 30 minutes at room temperature. Blood clots (of 3500 g) were separated on a centrifuge for 15 minutes and after that the serum samples were diluted 20 times with a standard isotonic phosphatic buffer with ionic force corresponding to the solution of 150 mM NaCl. Lysozyme sample preparation. Chicken egg white lysozyme (CEWL) (Sigma, USA) solution in 25 mM TrisHCl buffer (pH 7.0) at final CEWL concentration 1 mg/ml for incubation with nanostructure dispersions was used. The protein plus nanostructure mixtures were incubated for 1 hour at room temperature with gentle stirring. Dynamic light scattering. From here and below, we define monomers as the smallest oxide nanoparticles, the clusters as aggregations of the nanoparticles, and the over–molecular complexes are the aggregations of nanostructures, albumins, and lipoproteins. Measurements of the nanostructure sizes by means of the laser correlation spectrometer of quasi–elastic light scattering (LCS–03) were carried out. The quasi–elastic light scattering method is based on interaction of monochromatic coherent light with particles in liquid. Information about the size of the particles is contained in a spectrum of fluctuations of the light scattered on the particles. At a choice of measuring modes, the task of maximal adequate resetting to the true size of nanoparticles and over–molecular complexes had been fulfilled. Nanoparticle sizes are most precisely reset when their lorentzian is determined by not less than five points on a half width and when the range of measurement is not less than the half widths of the lorenzian [24]. Thus, if there is a need to produce particles of the hydrodynamic radius (Rh) ranging from 4 to 500 nm, the lorentzian halfwidth of which is 40–2000 Hz, the frequency 20000 Hz is optimum at the resolution of 10 Hz to one channel (2000 points of a spectrum). The conditions mentioned above require the “smoothness” of the spectrum to be no more than 0.03. Because fluctuations of measured points in a spectrum practically always have random character, it is possible to expect that the “smoothness” is inversely proportional to a square root of the total number of the spectrum copies. Thus, the number of copies should be ≥ 1000, and to accept the unknown factors this number should be ≥ 2000. The measurement of every sample in each point was carried out no less than five times and then the data of measurements were averaged.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

183

The definition of concentration sensitivity limit of the method of consecutive dilutions of initial dispersions with distilled water by 2, 4, 8, 16, 32 and 64 times was carried out. This limit for all investigated metals uses dilution of 16 times. Transmissive electronic microscopy (TEM). A drop of the nano–structure dispersion to carbon–coated copper grids was placed for 30 sec. The excess of liquid by the filter paper from the grids was removed. The grids at ambient temperature were dried, and then were examined with a JEM–100S (JEOL, Japan) transmission electron microscope. Atomic force microscopy (AFM). A drop of the nanostructure dispersion was applied to the surface of a hydrogel–coated slide (Perkin–Elmer, USA) and dried for 1 hour at room temperature. Samples were examined with NT–MDT Solver Bio Scanning Probe Microscope (NT–MDT, Russia) in a semi–contact mode using cantilever NSG01–03 (NT–MDT, Russia) at Biophysics of Macromolecules Laboratory.

5. NANOPARTICLES IN DISPERSIONS

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

During the investigation, the main attention was focused on Ag, Pt, and Cu nanostructures. AFM examination of the smallest Ag nanoparticles shows that some of them are already clusters (Fig. 3.13).

a)

b)

c) Figure 3.13. Examination of the Ag nanoparticles; a) 3D–image; b) 2D–image; c) profiles of the silver clusters. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

184

The platinum, as well as the silver, forms clusters of various sizes; thus, the platinum nanoparticles sticking is weaker than that of the silver ones. Figure 3.14 shows that the platinum monomers are almost absent, and the height of the clusters is not more than 10 nm. This can be the result of the weak coupling of the monomers in the clusters, and during sedimentation on a substrate, they stick to the preformed clusters originally present in the dispersion in the form of flat structures.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

a)

b)

c) Figure 3.14. Examination of the Pt nanoparticles; a) 3D–image; b) 2D–image; c) the profiles of the platinum clusters.

The copper clusters are largest and steadiest among the investigated ones. The nanoparticles in the copper clusters are gathered as a “bunch of grapes”; their size is up to 600–1000 nm (Fig. 3.15). Sizes of the nanoparticles and distributions in size of the nanoparticle sub–fractions were determined with an LCS–03 spectrometer. The distributions in size of the oxide nanoparticles are polymodal and for various metal have from three to five characteristic peaks: ~10 nm; 30–100 nm; 100–200 nm; 200–1000 nm; ≥1000 nm (Fig. 3.16) [38].

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

a)

185

b)

c)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.15: Examination of the Cu nanoparticles; a) 3D–image; b) 2D–image; c) profiles of the copper clusters

a)

b)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

186

Philip Rutberg

c) Figure 3.16. Distribution of Ag (a), Cu (b), and Pt (c) nanostructures in dispersion.

For application of oxide nanoparticles in medical and biological investigations, it is important to know their electric parameters. So by capillary electrophoris it was found that the nanostructures have the negative surface electric charge of (0.4–1.6)×10–2 Coul/m2 and the volume specific charge of (0.01–2.6)×10–2 Coul/ml [38].

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

6. NANOPARTICLES AND BLOOD SERUM Due to the revealed mechanisms of nanostructures’ effect on biological objects, a study of the oxide and metal nanostructures and macro–molecular complexes of blood serum interaction was performed recently [39]. Blood serum, as well as many tissue liquids, is a highly concentrated solution of macro–molecules, basically proteins. In such solutions, the forming of macro–molecular complexes of various sizes and various degree of stability takes place. These complexes can be formed because of both a relatively weak non–covalent interactions, and of strong specific interactions, such as, for example, the antigen – antibody interactions resulting in the formation of immune complexes. It can have both normal physiological character and be the basis for pathological conditions, as in case of superfluous formation of the immune complexes [40] or beta–amyloid oligomers found in Alzheimer’s disease [41]. It is evident that documentation of the formation of such complexes in biological systems can be a model for the study of the nanostructures’ effect on biological systems and can give useful information on many normal and pathological processes in a human organism. Figures 3.13–3.16 show that the nanostructures of almost all metals in water dispersion are clusters. It is possible to distinguish the groups with rather weak (Ag, Pt) and relatively strong (Cu) coupling. In the first group, the contribution of large clusters with Rh > 2000 nm does not exceed 5%, and in the second group clusters with Rh 500–1000 nm dominate. Figure 3.17 represents distributions obtained for various conditions. In the distributions of the particles in standard blood serum, there were mainly components with three Rh: 9–10 nm; 30–40 nm; and 130–160 nm (Fig. 3.17a). The first peak corresponds, basically, to the albumin and antibodies, the second one corresponds to the low–density lipoproteins, and the third peak corresponds to the immune complexes.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

187

a)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

b)

c)

d) Figure 3.17. Distributions of the particles in standard blood serum a) and serum with the nanostructures of b) Ag, c)Cu, and d)Pt.

After adding the nanostructure dispersions to the standard blood serum, two groups of particles with a large Rh appeared. T the first one had a size of ~500 nm, and the second one Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

188

Philip Rutberg

had a size of ≥ 1000 nm (Fig. 3.17b, c, and d). The formation of the over–molecular complexes of serum components and nanostructures lasts up to 40 minutes after the nanostructure dispersions were added. Although for the Ag nanostructures (the first group) the formation of the relatively small over–molecular complexes with an Rh of about 500 nm is typical, the fraction of the largest particles with an Rh ≥ 1000 nm takes place, too. The total contribution of those complexes does not exceed 8%. Both the small and large over– molecular complexes characterize the second group (Cu, Pt). Their total contribution does not exceed 20%. Many processes that take place in blood are specific to some diseases. For example, loading capacity of serum albumin can be used as a marker for specific stages of cancer or some conformational diseases such as Alzheimer’s [42]. In this connection, we began to investigate the protein aggregative ability of the oxide nanostructures as a possible marker for diagnosis of non–native proteins or components changed by disease. It is known that blood serum is a multi–component system with equilibrium among its components, but on the metal surface the native structure of proteins is changed, which leads to their aggregation[43]. Since the various oxide nanostructures attract protein aggregations in specific ways, one can make out the native or non–native conformations of the protein over–molecular complexes using the value Rh found by means of the dynamic light scattering method.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

7. AGGREGATION OF LYSOZYME ON NANOPARTICLES Previously we have found the conditions in which lysozyme in water solution is a monomer of single Rh ~20 nm. Then, to determine the peculiarities of the protein – nanostructures interaction, the lysozyme solution in distilled water (as the control sample) and mixtures of lysozyme and nanostructures dispersions were used (see the subsection on lysozyme sample preparation). Figure 3.18 shows the distribution of particles in the initial lysozyme solution (Fig. 3.18a), in the nanostructures dispersions of Ag (Figs. 3.18b), and in the over–molecular complexes of Ag (Figs. 3.18c).

a)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

189

b)

c)

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.18: Distributions of particle in the initial lysozyme solution (a), nanostructures dispersion of Ag (b) overmolecular complexes of Ag (c)

Figure 3.19 shows the TEM images of Ag, Cu, and Pt nanostructures and their over– molecular complexes. The nanostructures and over–molecular complexes of Ag (a, b, and c), Cu (d, e, and f), and Pt (g, h, and i) are shown in Fig. 3.19. Here, cases a, d, and g are related to the nanostructures themselves; b, e, and h are related to the over–molecular complexes; c, f, and i are related to the over–molecular complexes after negative contrasting by PVA (the horizontal line corresponds to the size of 100 nm). The TEM images (b, e, and h) show the blurred outline of the oxide nanostructures, which is evidence of the protein layer’s presence on the nanostructures’ surface. After the negative contrasting by PVA, the white spots around the nanostructures appeared (g, h, and i), which are opaque under the electron beam. These spots are the protein clusters on the carbon– coated grid surface, making it invaluable for PVA. The nanostructures of all investigated metals in dispersion are monomers and clusters. There are five sub–fractions of nanostructures of the following sizes: ~10 nm, 30–60 nm, 100–160 nm, 200–1000 nm, and larger than 1000 nm. The AFM images show that the Ag nanostructures in dispersion are monomers or clusters of 2–4 nanoparticles. The Pt nanostructures are monomers, and flat clusters (thickness of 1 nanoparticle). The Cu nanostructures form, basically, large clusters of the “bunch of grapes” type. The result of the interaction of nanostructures of investigated metals with blood serum is the agglutination of albuminous and lipoprotein structures of blood serum on nanostructures’ surfaces. Thus, the higher the concentration of nanostructures in blood serum, the larger the over–molecular complexes that are formed.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

190

a)

b)

c)

d)

e)

f)

g)

h)

i)

Figure 3.19. TEM images of the nanostructures and over–molecular complexes

The stages of over–molecular complexes formation are as follows small aggregations of albuminous and immunoglobulin, aggregations of lipoproteins, and large aggregations with hydrodynamic radius ≥ 1000 nm. The interactions of the nanostructure of all metals with the serum of blood are of the same type and have differed only quantitatively. These distinctions are connected with the sizes of nanostructure aggregations in the dispersions. Obtained results, taken together with data available from literature, lead us to the possibility of using such nanostructures for diagnosis of some conformational diseases.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

191

8. BACTERICIDAL ACTION OF WATER TREATED BY PED As explained above, the bactericidal activity of water treated by PED depends on the imbedded energy and the properties of the metal electrodes. The bactericidal activity of water was determined as log10(Nf / Nt), where Nt is the initial concentration of bacteria and Nf is the final concentration of viable bacteria after PED treatment, as shown in Fig. 3.20.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.20. Dependence log10(Nf / Ni) versus the imbedded energy for E. coli

Plots show that water treated by silver electrodes has the highest bactericidal activity in spite of the mass strength of iron and copper which is higher than that of silver under the same imbedded energy (Fig. 3.20). This is because of silver have the highest toxicity to bacteria. The ions of metals are arranged in the following order in terms of their toxicity: toxicityAg > toxicityCu > toxicityCd > toxicityZn, Pb > toxicityAgMn,Fe > toxicityMg > toxicityCa [44]. Since both the mass–strength of the nanoparticles and the bactericidal activity of the treated water are proportional to the imbedded energy, there is also a connection between the bactericidal activity and the mass–strength of the nanoparticles. Moreover, the bactericidal activity is proportional to the mass strength of the nanoparticles. The antimicrobial activity of water has also been examined with Klebsiella pneumonia, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhimurium, Serratia marcescens, Citrobacter freundii, Bacillus subtilis, Candida albicans, and Ulocladium chartarum. In all of those tests, we have obtained similar results. Figure 3.21 shows the ratio of the final concentration Nt of viable E coli to the initial concentration Nt (106 ml–1) versus the imbedded energy, which is obtained in a plant equipped with one or four discharge chambers, connected serially along the water flow.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

192

Philip Rutberg

Figure 3.21. Ratio of the final concentration Nf of viable E. coli to the initial concentration Nt versus the imbedded energy at one chamber a) and four chambers b).

It was found that for the same imbedded energy, the PED treatment of water in several discharge chambers connected this way is more effective than by one chamber (Fig. 3.21). Comparison of the plots (Fig. 3.21) shows that the final concentration Nf of viable E.coli to the initial concentration Ni (106 ml–1) for the imbedded energy of 2.5 J/ml is decreased from 3×10– 3 ml–1 after one discharge chamber up to 10–4 ml–1 after four chambers. This difference may be explained by the multiple actions of the shock waves onto bacteria and by mixing the treated water in the second case. Since the treated water can be considered as the bactericidal agent, it was necessary to determine its bactericidal activity versus the ratio of dilution of the treated water by the initial one. Figure 3.22 shows the final concentration of E. coli versus the ratio of dilution for the imbedded energy of 10 J/ml, the initial concentration of bacteria of 7.9×103 ml–1, and for the time of exposition of 24 h.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

193

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.22. Final concentration of E. coli versus the ratio of dilution for the imbedded energy of 10 J/ml; the initial concentration of bacteria is 7.9 x 103 ml–1; the time of exposition is 24 hours.

Figure 3.23. Rate of destruction of the spores U. chartarum for the imbedded energy of 10 J/ml.

The rate of destruction of the fungus U. chartarum spores treated by PED with titanium, iron, and silver electrodes and then exposed in treated water is shown in Fig. 3.23 [45]. The presented curves are the exponent functions, and in a period from 15 min to 3 h, all spores were destroyed. The rate of destruction of E. coli in water treated by copper electrodes for the imbedded energy of 10 J/ml and the initial concentration of bacteria of 3.8×103 ml–1 and 5.1×106 ml–1 is presented in Fig. 3.24. The presented curves are the exponent functions, and in 5 min, in dependence on the initial concentration of bacteria, from 80% up to 100% had been destroyed.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

194

Philip Rutberg

9. MECHANISM OF PMRW It has been shown above the two groups of factors that cause bactericidal action of PED in water: 1. UV radiation and shock waves, which act during the discharge time; these are factors of the “current” action; 2. hydrated electrons, OH radicals, H2C greater than 2, nanoparticles, and positive ions of the electrodes’ metal, which act after the treatment; these are factors of the “post” action.

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Figure 3.24. Rate of destruction of E coli for the imbedded energy of 10 J/ml.

Figure 3.25. Differences of the final concentration of viable spores in two kinds of treated water versus the imbedded energy; Ni contains only the ions; Nin contains both the ions and nanoparticles.

Since hydrated electrons exist for ~0.5 ms and OH radicals and H2C>2 for no more than several days, it is evident that they cannot be considered as the factors causing PMRW, which is of several months duration. Thus, only the nano–particles and positive ions of the metal, which are produced by erosion of the electrodes, are responsible for PMRW.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

195

To reveal the role of the nanoparticles in PMRW, experiments were carried out on inhibition of growth of U. chartarum fungus spores in two modifications of the same treated water: 1. containing both ions and nanoparticles; 2. containing only ions (after the removal of the nanoparticles).

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

The water was treated by means of silver, copper, and iron electrodes under the specific imbedded energy of 1.5, 3.0, 6.0, 8.0, and 12 J/ml. Figure 3.25 shows the differences of the final concentrations of U. chartarum viable spores versus the imbedded energy, where Ni is the final concentration of spores in the water containing (after the removal of the nanoparticles) only the ions, and Nin is the final concentration of spores in the water containing both the ions and nano–particles. Plots of differences between the final concentrations of Ni and Nin (under the initial concentration of spores of about 103 ml–1 and after ten days of incubation) show that the fungicide effect is higher when both the ions and nanoparticles are in the water. The differences are maximal when the material of the electrodes is iron, i.e., the metal with the lowest toxicity of its ions. In this case, the bactericidal effect of the nanoparticles themselves is highest, whereas, under the higher toxicity of the ions, this difference is lower. Moreover, these differences decrease as the imbedded energy increases, i.e., as the ion and nanoparticle concentration increases.

Figure 3.26. Nanoparticles of Cu on the cell wall of E. coli (×105).

Thus, the nanoparticles in the water increase its bactericidal action. This may be explained by two reasons. First, during the time of the incubation, the nanoparticles maintain the concentration of ions at the same level. Second, the nanoparticles themselves (by means of their surface electric charge) participate in killing the spores.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Philip Rutberg

196

The most probable mechanisms of the bactericidal action of the nanoparticles on bacteria are penetration of the nanoparticles inside the bacteria [46], cooperative action of the toxic ions emitted by nanoparticles, and the surface electric charge of nanoparticles [48]. By electronic microscopy, it was detected that the single nanoparticles and their clusters settle onto bacteria cell walls. In contrast to the data presented in papers [46,48], Figure 3.26 shows that the nanoparticles do not penetrate inside the bacteria, but, adsorbing the ions, remove the concentration balance between the ions and nanoparticles. This, in the turn, causes the additional emission of ions from the nanoparticles. As a result, when the nano–particles approach close to bacteria, directed streams of toxic ions appear, which produce the bactericidal effect.

10. INFLUENCE OF NANOPARTICLES ON TUMOR GROWTH IN VIVO Successful of investigation into the scope of experimental and clinic oncology are manly stipulated by the intensive insertion of developments of fundamental physics and chemistry [49]. Nanoparticles, nanotubes, nanocapcules, dendrymers, and nanoconductors comprise an incomplete list of high–technology achievements. These objects are applied to: • •

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

•

investigation of the direct delivering of the anti–tumor medicines and radioactive markers into cancer cells; strengthening the cytotoxic action of the chemical species during the treatment of cancerous neoformations; creation of new methods for the precise detection of transformed cells, proteins, DNA, and separate genes [50,51].

In particular, the prospective nanotechnological approaches in oncology investigations are joined with the application of the nanoparticles having new physic–chemical and biological properties [52]. It is known that the nanoparticles and ions of silver have their own cytotoxic activity [53,54] and, also, demonstrate a prolonged anti–microbial effect having been pigmented onto the silicon structures [55]. The results of microbiological investigations confirm that the interaction of silver ions with molecules of the out–cell lipo–protein matrix leads to an increase in the permeability of the plasmatic membrane of the microbe cells and to their death [56]. For investigation of anti–tumor activity, silver water dispersion (SWD) was used with maximal array of the small nanoparticles. The anti–tumor effect of the SWD was investigated on 19 inbreeded white male rats of the mass 250–300 g, which were divided into two groups. The first group for the experiments consisted of 9 rats, and the second control group consisted of 10 rats. The cellline of the lymph sarcoma had been obtained from the bank of a experimental tumors. Immediately after the tumor transplantation, the SWD together with the physiological solution was injected two times daily into the animals of the experimental group, but in the control group only the physiological solution was injected. Necropsy was carried out on all dead animals with consecutive histological research.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Investigation of Pulse Electric Discharges in Liquids

197

The growth of Plyss lymphsarcoma was observed in all animals beginning the third day after tumor transplantation (Fig. 3.27).

Average size of the tumors, сm

7

n=3

Check group: LP, PS Experiment: LP, WD

6

Experimental group: LP, WD, No.2

*

Experimental group: LP, WD, No.3

5 4

*

n=3

3 2 1 0 1

3

6

8 10 15 20 Time after the tumor transplantation, days

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Fig. 3.27. Growth of Pliss lymph sarcoma (LP) in rats in the control group with injection of physiological solution (PS), and in the group with injection of water dispersion of nanostructures of oxide silver (WD). * – defferences are trustworthy at p < 0.05; n – number of surviving animals in the group.

In the control group the average size of the tumors increased from 0.7±0.1 cm (the 4th day) up to 6.3±0.7 cm (the 19th day). The sizes of the tumor on the 10th day in the experimental group were authentically smaller in comparison with the check group: 3.1±0.5 cm in the experimental group and 4.4±0.3 cm in the control group; p < 0.05. Under this, the average lifetime of animals in both groups was practically the same: 19.6 ±1.5 days in the experimental group and 19.3±1.5 days in the control; p > 0.05. It is necessary to note that in two animals in the experimental group (beginning the 8th day) the regressive character of the tumors’ growth was observed. Under the morphological research of the tumor tissue in the control group the homogeneous fields of the cancerous lymphoma were observed. In the experimental group the tumor tissue differed by a large content of detritus, the prevailing the dystrophic changed atypical cells, and the expressed fibrosis. In investigation of contents of Ag, Fe, Zn, Cr, Sb, Hg, and Co in the DNA preparations from the benign (fibroadenoma) and the cancerous (adenocarcinoma) tumors of the human milk glands, a decreased content of silver was authentically discovered in the DNA of the cancerous cells [56]. It is assumed that the cytostatic action of silver is a result of the active physical chemical interaction of the metal atoms with the functional groups of the inner– cellular proteins, and the bases and phosphate groups of the DNA [57]. The prolonged injection of the SWD in our experiments, apparentlty, rebuilds the concentration of the silver atoms in the tumor cells, which leads to the physical–chemical stabilization of the DNA molecular structure in the tumor cells. Thus, as a result of the implemented investigations, it had been discovered for the first time that the water dispersion of nanoparticles of silver oxides demonstrates anti–cancer

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

198

Philip Rutberg

properties in vivo. The observed cytostatic effect was confirmed by the authentic decrease of the growth, cytodistrophic changes, and fibrosis of the transplanted Pliss sarcoma in rats under regular injection of the water dispersion of nanoparticles of the silver oxides. The role of silver atoms in the mechanisms of the stabilization of the DNA molecular structure, inhibition of tumor growth, and/or reversion of the cancerous phenotype of cells demands further investigation on the tissue, cellular, and the molecular levels [58].

REFERENCES [1] [2] [3] [4] [5] [6]

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

[7]

[8]

[9] [10] [11]

[12] [13]

Naugolnuch, K.A.; Riy, N.A., Electric Discharges in Water; Nauka: M, 1971, 155 p. (in Russian) Okyn’, I.Z., Zhurnal Tekhicheskoi Fiziki, 1971, vol. 41, issue. 2, pp.302–307. (in Russian) Shneerson, G.A., Zhurnal Tekhicheskoi Fiziki, 2003,vol 73, issue 3, pp.100–101. (in Russian) Zoeteman, B. C.; Hrubec, J.; de Greef, E.; Kool, H. J. Mutagenic Activity Associated with By–Products of Drinking Water Disinfection by Chlorine, Chlorine dioxide, Ozone and UV Irradiation; Environ. Health Perspect; Dec. 1982 vol. 46, pp. 197–205. Gottlieb, M. S.; Carr, J. K.; Moms, D. T. Cancer and Drinking Water in Louisiana: Colon and Rectum; Int. J. Epidemiology; Jun. 1981, vol. 10, No. 2, pp. 117–125. Price, J. M. Coronaries, Cholesterols, Chlorine; Banhadlog Hall, Tyliwch, Landridloes: Pyramid Publications Ltd., 1984, pp. 32–33. Voejkov, V. L.; Asfaramov, R. R.; Rozental, V. M. By–products Dangerous to Health in Chlorinated Water, Ways of Their Detection and Elimination; Proc. 3rd Int. Conf. Ecopolis: Ecology and Steady Development City; Moscow, 2000, Nov. 24/25, p. 226. (in Russian). Beebe, S. J.; Fox, P. M.; Rec, L. J.; Sommers, K.; Stark, R. H.; Schoenbach, K. H. Nanosecond Pulsed Electric Fields (nsPEF) Effects on Cells and Tissues: Apoptosis Induction and Tumor Growth Inhibition; Proc. 28th Int. Conf. Plasma Sci. and 13th IEEE Int. Pulsed Power Conf., Las Vegas, NV; 2001 Jun. 17–22, pp. 211–215. L. Kulskij, A.; Savluk, O. S.; Dejnega, E. G. Influence of an Electric Field on Processes of Disinfecting of Water; Naukova Dumka: Kiev, Ukraine; 1980, 125 p. (in Russian). Schoenbach, K. H.; Peterkin, F. E.; Kldew, R. W.; Beebe, S. J. The Effect of Pulsed Electric Fields on Biological Cells: Experiments and Applications; IEEE Trans. Plasma Sci, Apr. 1997, vol. 25, No. 2, pp. 284–292. Efremov, N. M.; Adamiak, B. Y.; Blochin, V. I.; Dadeshev, S. J.; Dmitriev, K. I.; Semjonov, K. N.; Levachov, V. F.; Jusbashev, V. F. Action of a Self–Sustained Glow Discharge in Atmospheric Pressure Air on Biological Objects; IEEE Trans. Plasma Sci., 2000, Feb. vol. 28, No. 1, p. 238. Montie, T. C.; Kelly–Winterberg , K.; Roth, J. R. An Overview of Research Using the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) for Sterilization of Surfaces and Materials; IEEE Trans. Plasma Sci., Feb. 2000, vol. 28, No. 1, pp. 41–50. Lisitsyn, I. V.; Nomiyama H.; Katsuki S.; Akiyama H. Water Treatment by Pulsed Streamer Discharge; Proc. 12th IEEE Int. Pulsed Power Conf., Monterey, CA, Jun. 27– 30, 1999, pp. 468–471.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Investigation of Pulse Electric Discharges in Liquids

199

[14] Abou–Ghazala, A.; Katsuki, S.; Schoenbach, K. H.; Dobbs, F. C.; Moreira, K. R. Bacterial Decontamination of Water by Means of Pulsed–Corona Discharges; IEEE Trans. Plasma Sci, Aug. 2002, vol. 30, No. 4, pp. 1449–1453. [15] Yan, J.; Du, C.; Li, X.; Sun, X.; Ni, M.; Cen K.; Cheron, B. Plasma Chemical Degradation of Phenol in Solution by Gas–Liquid Gliding Arc Discharge; Plasma Source Sci. Technol, Nov. 2001, vol. 14, No. 4, pp. 637–644. [16] Lei, X.; Rui, Z.; Peng, L.; Li–Li, D.; Ru–Juan Z. Sterilization of E. col! Bacterium with an Atmospheric Pressure Surface Barrier Discharge; Chin Phys; Jun. 2004 vol. 13, No. 6, pp. 913–917. [17] Edebo, L.; Selin I. The Effect of Pressure Shock–wave and Some Electrical Quantities in the Microbicidial Effect of Transient Electric Arcs in Aqueous Systems; J. Gen. Microbiol; 1968, vol. 50, pp. 253–259. [18] Gorjachev, V. L.; Rutberg, Ph. G.; Fedjukovich, V. N. The Electric Method of Water Treating. A Condition of a Problem and Prospect; Appl. Energy, Russian J. Fuel, Power Heat Syst., 1998, vol. 36, No. 2, pp. 40–55. [19] Gorjachev, V. L.; Bratsev, A. N.; Fedjukovich, V. N.; Rutberg, Ph. G.; Greene, H. W.; Chism, P. E. Method and Apparatus for Water Decontamination Using Electrical Discharges; U.S. Patent 5464513, Nov. 7, 1995. [20] Efremov, N. M.; Adamiak, B. Y.; Blochin, V. I.; Dadeshev, S. J.; Dmitriev, K. I.; Semjonov, K. N.; Levachov, V. F.; Jusbashev, V. F. Experimental Investigation of the Action of Pulsed Electrical Discharges in Liquids on Biological Objects; IEEE Trans. Plasma Sci, Feb. 2000, vol. 28, No. 1, pp. 224–229. [21] Muzirthuck, N. T. Disinfection of Water by Ions of Heavy Metals in the Electric Field in Small Towns; Hygiene Sanitation, 1990, No. 1, pp. 24—27. (in Russian). [22] Kolikov , V. A.; Kurochkin, V. E.; Panina, L. K.; Rutberg Ph. G. Pulsed Electrical Discharges and Prolonged Microbial Resistance of Water; Dokl. Biol. Sci., Jul. 2005, vol. 403, No. 1–6, pp. 279–281. [23] Roodenburg, B.; Morren, J.; de Haan, S. W. H.; Wouters, P. C.; de Jong, G.; Pol, I. E.; Creygthon, Y. L. M. High–Voltage Arc Pulser for Preservation of Liquid Food; Proc. Eur. Pulsed Power Symp, Oct. 2002, pp. 22–24. [24] El–Hag, A. H; Jayaram, S. H.; Griffiths, M. W. Inactivation of Naturally Grown Microorganisms in Orange Juice Using Pulsed Electric Fields; IEEE Trans. Plasma Sci, Aug. 2006, vol. 34, No. 4, pt. 2, pp. 1412–1415. [25] Goryachev, V. L.; Rutberg, Ph. G.; Fedioukovitch, V. N. Electrophysical and Ecological Properties of Pulse–periodical Discharge in Water with Pulse Energy of 1 J; Proc. Environ. Appl. Adv. Oxidation Sci. Int. Symp., San Francisco, CA, Feb. Mar.1996 , pp. 123–124. [26] Touya, G.; Reess, T.; Pecastaing, L.; Gibert A.; Domens P. Development of Subsonic Electrical Discharges in Water and Measurements of the Associated Pressure Waves; Phys. D, Appl Phys, Dec. 2006, vol. 39, No. 24, pp. 5236–5244. [27] Lu, X.; Pan, Y.; Liu, K.; Liu, M.; Zhang, H. Early Stage of Pulsed Discharge in Water; Chin. Phys. Lett., Nov. 2001, vol. 18, No. 11, pp. 1493–1495. [28] Mikula, M.; Panak, J.; Dvonka, V. The Destruction Effect of a Pulse Discharge in Water Suspensions; Plasma Sources Sci. Technol, 1997, vol. 6, No. 2, pp. 179–184. [29] Camell, M. T.; Alcock, R. D.; Emmony, D. C. Optical Imaging of Shock Waves Produced by High–Energy Electromagnetic Transducer; Phys. Med. Biol; Nov. 1993, vol. 38, No. 11, pp. 1575–1588. [30] Hubert, P.; Debus, J.; Jochle, K.; Simiantonakis, I.; Jenett J.; Spoo, J.; Lorenz, W. J.; Wannenmacher, M. Control of Cavitation Activity by Different Shockwave Pulsing Regimes; Phys. Med. Biol; Jun. 1999, vol. 44, No. 6, pp. 1427–1437.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

200

Philip Rutberg

[31] Kolikov, V.; Pinchuk , M.; Leks, A.; Rutberg Ph.G. High–Speed Diagnostic Pulsewise–Periodic of Electric Discharge in a Water; Proc. 27th Int. Congr. High– Speed Photography and Photon. //Abstract Collection. Xi'an, China, Sep 17–22, 2006. [32] Vilkov, K. V.; Grigor'ev, A. L.; Nagel, Y. A.; Uvarova, I. V.; The Antimicrobial Action of High–power Electric Discharge in Water. Part 2. Experimental Results; Tech. Phys. Lett., Apr. 2004, vol. 30, No. 4, pp. 281–283. [33] Rutberg, Ph. G.; Bogomaz, A. A.; Goryachev, V. L.; Remennyi, A. S. The Effectiveness of a Pulsed Electrical Discharge in Decontaminating Water; Sov. Tech. Phys. Lett., Jun. 1991, vol. 17, No. 6, pp. 448–449. [34] Ampilov, A. M.; Barkhudarov, E. M.; Bark,Y. B.; Zadiraka, Y. V.; Christofi, M.; Kozlov, Y. N.; Kossyi, I. A.; Kop'ev, V. A.; Silakov, V. P.; Taktakishvili, M. I.; Temchin, S. M. Electric Discharge in Water as a Source of UV Radiation, Ozone and Hydrogen Peroxide; Phys. D, Appl. Phys; 2000, vol. 34, No. 6, pp. 993–999. [35] Sun, B.; Kunimoto, S.; Igarashi, C. Characteristics of Ultraviolet Light and Radicals Formed by Pulsed Discharge in Water; Sep. 2006, Phys. D, Appl. Phys, vol. 39, No. 17, pp. 3814–3820. [36] Lukes, P.; Locke, B. Plasmachemical Oxidation Processes in a Hybrid Gas–liquid Electrical Discharge Reactor; Phys. D, Appl. Phys., Nov. 2006.vol. 38, no. 22, pp. 4047–4081. [37] Rutberg, Ph. G.; Goryachev, V L.; Ufimtsev, A. A. Photolytic Properties of a Pulsed Discharge in Water; Tech. Phys. Lett.; Feb. 1998, vol. 24, No. 2, pp. 122–123. [38] Rutberg, Ph.; Kolikov, V.; Snetov, V.; Stogov, A.; Noskin, L.; Landa, S.; Arutunjan, A. Pulsed Electric Discharges in Water and Oxide Nanoparticles; Digest of Technical Papers 1976–2007; Omnipress: Madison, 2007, pp. 1244–1247. [39] Rutberg, Ph.; Kolikov, V.; Snetov, V.; Stogov, A.; Noskin, L.; Landa, S.; Arutunjan, A. Water Treated by Pulsed Electric Discharges and Its Effect on Biological Objects; Proceedings of the XXVIII International Conference on Phenomena in Ionized Gases; Published by Institute of Plasma Physics AS CR: Prague, Czech Republic, 2007, 3P16–10, pp. 1322–1325. [40] Wiwanitkit, V. Effect of Immune Complex on the Biomechanics of Blood Flow in Common Glomerulonephritis Diseases; Ren. Fail., 2006, No. 28, pp. 541–542. [41] Taboada, P.; Barbosa, S.; Castro, E.; Mosquera, Amyloid V. Fibril Formation and Other Aggregate Species Formed by Human Serum Albumin Association; J. Phys. Chem. B Condens. Matter Mater. Surf. Interfaces Biophys.; 2006, Oct 26; No. 110, pp. 20733– 20736. [42] Kazmierczak, S.C.; Gurachevsky, A.; Matthes, G.; Muravsky, V. Electron Spin Resonance Spectroscopy of Serum Albumin: A Novel New Test for Cancer Diagnosis and Monitoring; Clin. Chem.; No. 52, 2006, pp. 2129–2134. [43] Krasnoslobodtsev, A.V.; Shlyakhtenko, L.S.; Ukraintsev, E.; Zaikova, T.O.; Keana, J.F. W.; Lyubchenko, Y.L. Nanomedicine, Protein Misfolding Diseases, Nanomedicine; 2005, No. 1, pp. 300–305. [44] Siegel, H.; Siegel, A. Metal Ions in Biological Systems. Concepts on Metal Ion Toxicity; Marcel Dekker: New York; 1986, vol. 20 [45] Bogomolova, E. V.; Gorjachev, V L.; Kolikov, V A.; Kulishevich, A. I.; Kurochkin, V E.; Panina, L. K.; Rutberg, Ph. G.; Julaev, P. G. About the Mechanism Fungicidal Actions of the Water Treated by Pulsed Electric Discharges; Mycology Phytopathology; 2003, vol. 37, No. 5, pp. 19–25. (in Russian). [46] Sondi, I.; Sondi, B.Silver Nanoparticles as Antimicrobial Agent: A Case Study on E. coli as a Model for Gram–negative Bacteria; Colloid Interface Sci, 2004, vol. 275, No. 1, pp. 177–182.

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Investigation of Pulse Electric Discharges in Liquids

201

[47] Kolikov, V A.; Kurochkin, V E.; Panina, L. K.; Rutberg, A. Ph.; Rutberg, Ph. G.; Snetov, V N.; Stogov, A. Y. Prolonged Microbial Resistance of Water Treated by a Pulsed Electrical Discharge; Tech. Phys., Feb. 2007, vol. 52, No. 2, pp. 263–270. [48] Rutberg, Ph. G., Kolikov, V. A.; Kurochkin, V. E.; Panina, L. K.; Rutberg, A.Ph. Electrical Discharges and the Prolonged Microbial Resistance of Water, IEEE Trans. Pl. 2007, vol.35, № 4, pp.111–118. [49] Hanahan, D.; Weinberg, R.A. The Hallmarks of Cancer; Cell, 2000, vol. 100, No. 1, pp. 57–70. [50] Kim, K.Y. Nanotechnology Platforms and Physiological Challenges for Cancer the Rapeutics; Nanomedicine; 2007, vol. 3, No. 2, pp. 103–110. [51] Cuenca, A.G.; Jiang, H.; Hochwald, S.N.; Delano, M.; Cance, W.G.; Grobmyer, S.R. Emerging Implications of Nanotechnology on Cancer Diagnostics and Therapeutics; Cancer; 2006, vol. 107, No. 3, pp. 459–466. [52] Ferrari, M. Cancer Nanotechnology: Opportunities and Challenges; Nature Reviews Cancer, 2005, vol.5, No. 3, pp. 161–171. [53] Kim, J.S.; Kuk, E.; Yu, K.N.; Kim, J.H.; Park, S.J.; Lee, H.J.; Kim, S.H.; Park, Y.K.; Park Y.H.; Hwang, C.Y.; Kim, Y.K.; Lee, Y.S.; Jeong, D.H.; Cho, M.H. Antimicrobial Effects of Silver Nanoparticles; Nanomedicine, 2007, vol. 3, No. 1, pp. 95–101. [54] Baker, C.; Pradhan, A.; Pakstis, L.; Pochan, D.J.; Shah, S.I. Synthesis and Antibacterial Properties of Silver Nanoparticles; Journal of Nanoscience and Nanotechnology; 2005, vol. 5, No. 2, pp. 244–249. [55] Furno, F.; Morley, K.S.; Wong, B.; Sharp, B.L.; Arnold, P.L.; Howdle, S.M.; Bayston, R., Brown, P.D.; Winship, P.D.; Reid, H.J. Silver Nanoparticles and Polymeric Medical Devices: a New Approach to Prevention of Infection; Journal of Antimicrobial Chemotherapy; 2004, vol. 54, No. 6, pp. 1019–1024. [56] Sondi, I.; Sondi, B. Silver Nanoparticles as Antimicrobial Agent: a Case Study on E. coli as a Model for Gram–negative Bacteria; Journal of Colloid and Interface Science; 2004, vol. 275, No. 1, pp. 177–182. [57] Andronikashvili, E.L. Malignization and Change of Some Physical and Chemical Properties of Bio–Macro–Molecules and Nano–Molecular Structures; Biofizikas, 1987, No. 5, pp. 782–799. [58] Blagoi, Yu.P.; Galkin, V.L.; Gladchenko G.O.; Kornilova, S.V.; Sorokin, V.A.; Shkorbatov, A.G. Chellates of Nucleinic Acids in Solutions; Naukova Dumka: Kiev; 1991, 270 p. (in Russian) [59] Rutberg, Ph.G.; Dubina, M.V.; Kolikov, V.A.; Moiseenko, F.V.; Ignatieva, E.V.; Volkov, N.M.; Snetov, V.N.; Stogov, A.Yu. Effect of Nanaparticles of Silver Oxide on the Tumoral Growth in vivo; DOKLADY RAS, 2008, (to appear)

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved. Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

INDEX 2 2D, 183, 184, 185

3 3D, 183, 184, 185

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

A absorption, 1, 2, 3, 7, 8, 9, 13, 24, 27, 48, 50, 51, 53, 57, 59, 83, 84, 89, 94, 96, 97, 98, 129 AC, 78, 106, 123, 125, 126, 127, 130, 131, 132, 134, 136, 138, 142, 143, 169, 170, 172 accelerator, 35, 39, 65, 67, 68 accommodation, 117 accuracy, 13, 103, 143, 157 acetylene, 162 achievement, 1, 2, 7, 15, 16, 24, 25, 46, 51, 81, 140, 141 acid, 155, 156, 161 acoustic, 7, 10, 23, 32 acoustic waves, 10 acute, 86 adenocarcinoma, 197 adhesion, 80 adiabatic, 6, 42, 43 adjustment, 4, 149 aerosols, 155 AFM, 183, 189 Ag, 179, 183, 186, 187, 188, 189, 197 agent, 164, 174, 192 agents, 150, 166, 171 agglutination, 189 aggregation, 60, 188 air, 1, 2, 3, 4, 6, 16, 21, 30, 79, 81, 85, 100, 101, 102, 103, 118, 120, 124, 127, 129, 137, 139, 141, 142,

143, 144, 148, 149, 150, 153, 157, 159, 160, 161, 163, 164, 165, 166, 167, 168, 170, 174 alloys, 36, 37, 99, 118, 122, 137, 176, 179 alternative, 78, 80, 81, 108, 111, 113, 114, 115, 116, 119, 153, 154, 157, 160, 173 aluminum, 11, 34, 35, 36, 37, 62 Alzheimer, 186, 188 ammonia, 154 amplitude, 1, 5, 6, 20, 23, 26, 27, 30, 31, 32, 35, 38, 39, 44, 45, 50, 113, 117, 178 amyloid, 186 Amyloid, 200 animals, 196, 197 anode, 5, 6, 7, 8, 9, 17, 20, 21, 28, 29, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 47, 67, 115, 127, 128, 129, 130, 139, 150 antibody, 186 antigen, 186 antimicrobial, 191 anxiety, 150 application, 3, 69, 77, 78, 85, 119, 120, 129, 139, 150, 152, 153, 156, 157, 166, 174, 186, 196 ARC, 63 arc plasma, 80, 122, 137, 141, 143, 172 argon, 2, 3, 4, 8, 17, 18, 20, 21, 22, 26, 31, 32, 54, 60, 65, 77, 79, 80, 81, 82, 86, 109, 113, 115, 129, 132, 140, 141, 143, 146, 160 ash, 123, 128, 151 astrophysical, 2 asymptotically, 140 atmosphere, 151, 156, 157, 165 atmospheric pressure, 6, 30, 43, 123, 127, 148, 149, 170 atoms, 31, 52, 65, 67, 83, 84, 85, 90, 94, 95, 96, 97, 98, 101, 103, 104, 105, 113, 114, 116, 140, 151, 152, 197, 198 attention, 66, 183 atypical, 197 averaging, 116

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index

204

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

B Bacillus, 191 Bacillus subtilis, 191 bacteria, 178, 180, 191, 192, 193, 196 bacterium, 176 ballast, 125, 153, 160, 161, 166 barrier, 174 batteries, 2, 4, 57, 65 battery, 2, 12, 15, 17, 23, 53, 54, 56, 57, 58, 59 behavior, 20, 31, 47, 115 bell, 44 benign, 197 beta, 186 biological, 161, 182, 186, 196 biological systems, 186 biology, 173 biomass, 158, 172 black, 12, 13, 31, 84, 94, 95, 97, 98, 107, 108, 109 black body, 12, 13, 31, 84, 94, 95, 97, 98, 107, 108, 109 bleeding, 116, 118 blood, 182, 186, 187, 188, 189, 190 boiling, 35, 114, 115 Boltzmann constant, 31, 100 brass, 4, 35, 93 breakdown, 17, 23, 25, 79, 81, 103, 120, 134, 137, 174, 176, 178 bremsstrahlung, 12, 13, 43, 46, 47, 48 bubbles, 173, 176 buffer, 182 burn, 79, 111, 117, 121, 125, 136, 139 burning, 17, 20, 23, 24, 26, 31, 32, 47, 58, 60, 77, 78, 80, 81, 84, 85, 86, 89, 90, 92, 100, 110, 111, 118, 124, 125, 136, 143, 149, 154, 156, 157, 160, 161, 164, 165 burns, 28, 43, 61, 62, 81, 110, 121, 132, 133

C California, 75 Canada, 161, 172 cancer, 174, 188, 196, 198 Cancer, 198, 200, 201 cancer cells, 196 cancerous cells, 197 Candida, 191 capacity, 15, 55, 117, 188 capillary, 8, 9, 182, 186 carbide, 121 carbon, 36, 114, 120, 121, 123, 151, 152, 153, 156, 157, 160, 161, 164, 166, 168, 183, 189

Carbon, 151 carbon dioxide, 160 carbon film, 123 carbon monoxide, 151, 157, 164 cardboard, 167 cardiovascular, 173 cardiovascular disease, 173 carrier, 160 casting, 1, 68, 69 cathode, 5, 6, 7, 8, 9, 10, 17, 19, 20, 21, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 44, 46, 47, 67, 108, 111, 112, 114, 115, 116, 117, 118, 126, 127, 128, 129, 130, 139, 150 cathode materials, 35, 36, 37 cavitation, 173, 176 cell, 195, 196 ceramic, 4, 10, 33, 72, 164 CH4, 157, 160 channels, 27, 86, 139 charcoal, 158, 160 charged particle, 2, 77, 79, 104, 105, 141 chemical, 36, 78, 113, 121, 135, 150, 151, 152, 153, 160, 162, 164, 166, 170, 171, 174, 179, 196, 197 chemical energy, 152 chemical interaction, 197 chemical properties, 36, 179 chemical reactions, 121 chemical reactor, 135, 162 chemicals, 172 chemistry, 150, 196 Chemotherapy, 201 China, 172, 200 chlorine, 123, 151, 173 chromatography, 180 chromium, 34 classical, 130 classification, 60 classified, 60, 62, 65, 78 cleaning, 8, 78, 118, 154, 155, 156, 158, 161, 163, 167, 168, 173 cleavage, 115 closure, 134 clusters, 180, 181, 182, 183, 184, 185, 186, 189, 196 CO2, 71, 77, 79, 138, 153, 157, 158, 159, 160, 164 coal, 122, 123, 157, 160, 161, 172 coatings, 122 coke, 159, 165, 168 collaboration, 165 collisions, 3, 55, 84, 96, 140, 149 combustion, 137, 150, 151, 152, 166, 168 commercial, 126, 128 compensation, 153

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Index components, 99, 101, 102, 126, 150, 151, 155, 157, 158, 160, 161, 163, 164, 165, 166, 186, 188 composition, 159, 160 compositions, 156 compounds, 123, 151, 152, 168 compression, 1, 6, 7, 11, 40, 42, 43, 44, 45, 50, 173 computer, 101 concentration, 2, 3, 6, 10, 12, 13, 16, 24, 28, 41, 42, 43, 47, 48, 54, 65, 77, 79, 80, 81, 82, 83, 84, 87, 88, 89, 93, 95, 96, 97, 101, 102, 104, 105, 111, 113, 114, 121, 125, 137, 140, 141, 180, 182, 183, 189, 191, 192, 193, 194, 195, 196, 197 concrete, 8, 25, 122 condensation, 158 conduction, 90, 93 conductive, 99, 121, 130 conductivity, 1, 3, 11, 13, 23, 27, 28, 33, 43, 48, 50, 52, 53, 55, 77, 87, 89, 93, 100, 102, 124, 140, 141, 143, 155, 178 configuration, 137 confinement, 30 conformational, 188, 190 conformational diseases, 188, 190 Congress, 170 conservation, 94 construction, 5, 6, 10, 24, 64, 67, 69, 118, 119, 121, 122, 167 consumption, 81, 86, 89, 91, 92, 93, 100, 109, 118, 151, 158 contamination, 61, 66, 137 contractions, 44 contracts, 49 control, 38, 125, 129, 152, 153, 182, 188, 196, 197 control group, 196, 197 controlled, 3, 124, 149 convection, 3, 90, 91, 92, 93, 125 convective, 84, 124, 146 conversion, 152, 153, 160, 162 cooling, 79, 89, 110, 111, 112, 116, 119, 120, 121, 122, 124, 129, 137, 139, 141, 148, 161, 168 copper, 4, 5, 9, 11, 13, 24, 33, 34, 35, 36, 37, 51, 84, 99, 100, 101, 102, 105, 118, 120, 121, 122, 123, 132, 133, 135, 137, 176, 178, 179, 180, 181, 183, 184, 185, 191, 193, 195 copper oxide, 120 copyright, iv corona, 174 corona discharge, 174 correlation, 182 costs, 151 Coulomb, 46, 48, 54, 140, 141, 143, 146, 149 Coulomb interaction, 54, 140, 141, 143, 146 coupling, 184, 186

205

covalent, 186 cracking, 122 critical current, 51 critical value, 1, 46, 49, 79 crystal, 123 cycles, 153 cyclone, 166, 167 cytotoxic, 196 cytotoxic action, 196 Czech Republic, 130, 171, 200

D death, 196 decay, 53, 80, 151 decomposition, 152, 164, 166, 168, 180 decontamination, 151 decoupling, 10 defense, 10 deficit, 150, 168 definition, 141, 183 degree, 19, 22, 24, 37, 60, 67, 88, 89, 93, 96, 140, 141, 152, 186 delays, 16 delivery, 38, 155 demand, 2 density, 1, 3, 7, 12, 13, 16, 19, 21, 23, 24, 26, 27, 28, 30, 31, 32, 33, 37, 39, 43, 44, 50, 52, 53, 54, 55, 56, 57, 59, 63, 64, 65, 82, 83, 86, 88, 89, 90, 91, 92, 99, 100, 108, 109, 110, 111, 112, 115, 116, 117, 123, 124, 130, 140, 141, 143, 150, 153, 163, 186 deposition, 123 destruction, 33, 77, 123, 128, 152, 159, 160, 166, 167, 174, 193, 194 detachment, 95 detection, 196 detoxifying, 168 detritus, 197 developed countries, 150 deviation, 13, 67, 95, 160 diagnostic, 5, 6, 7, 8, 9, 22, 26, 27, 79 diamond, 123 diamonds, 123 diaphragm, 4, 5, 7, 8, 9, 14, 15, 16, 20, 22, 23, 24, 25, 58, 60, 62, 63, 64, 65, 67, 107 dielectric, 63, 64 diesel, 153, 157 diffraction, 10, 178 diffusion, 3, 19, 26, 32, 79, 80, 81, 89, 99, 108, 112, 114, 116, 125 dioxins, 151, 156, 165, 168 direct action, 129

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index

206

direct measure, 13, 14 discharges, 2, 3, 4, 5, 6, 7, 17, 18, 20, 22, 26, 27, 30, 32, 33, 34, 38, 41, 43, 51, 55, 60, 78, 99, 109, 123, 173, 174, 177 diseases, 173 disinfection, 173, 174 dispersion, 10, 83, 97, 98, 140, 180, 181, 182, 183, 184, 186, 189, 196, 197 displacement, 37 dissociation, 16, 17, 25, 82, 84, 85, 88, 102, 151, 152, 153, 156 distilled water, 182, 183, 188 distribution, 3, 12, 13, 21, 30, 83, 86, 97, 98, 109, 112, 113, 114, 137, 139, 173, 178, 182, 188 distribution function, 173 DNA, 196, 197, 198 dopant, 23, 24, 114 dopants, 108, 112, 113, 114, 116 doped, 108, 112, 113, 114, 115 Doppler, 83, 97, 98 dosing, 163 dry, 158 drying, 160, 161 duration, 37, 119, 120, 132, 174, 176, 177, 194 dust, 122, 155, 164, 165 dynamic theory, 19

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

E E. coli, 191, 192, 193, 195, 200, 201 earth, 113, 114, 115, 116 ecological, 151 economic, 151 effluent, 160 egg, 182 electric arc, 7, 60, 61, 62, 65, 77, 78, 79, 99, 103, 108, 118, 120, 123, 124, 127, 129, 132, 134, 135, 136, 139, 143, 146, 169 electric charge, 33, 34, 35, 173, 182, 186, 195, 196 electric conductivity, 124, 178, 179 electric current, 136 electric energy, 68, 154, 155, 156, 162, 164, 174 electric field, 2, 13, 19, 30, 33, 41, 42, 43, 44, 45, 47, 51, 55, 56, 57, 81, 82, 86, 88, 99, 124, 141, 147, 173, 174 electric power, 4, 43, 77 electrical, 123, 137, 138, 148, 151, 152, 162, 164 electricity, 165 electromagnetic, 7, 81 electron, 2, 3, 10, 12, 13, 16, 33, 48, 54, 55, 79, 80, 81, 82, 83, 84, 87, 93, 99, 100, 102, 109, 111, 113, 125, 140, 141, 183, 189 electron beam, 189

electron charge, 84, 99 electron density, 100 electron gas, 55 electronic, 106, 113, 118, 140, 180, 183, 196 electrons, 80, 87, 88, 89, 94, 99, 100, 101, 102, 103, 112, 137, 140, 169, 194 electrostatic, 113 emission, 33, 77, 108, 109, 111, 112, 113, 115, 116, 136, 151, 196 endothermic, 150, 153 energetic characteristics, 81 energy consumption, 151, 152 energy density, 41 energy emission, 39, 40 energy transfer, 2, 3, 16, 22, 31, 32, 41, 57, 59, 90, 96, 97, 116, 118 engineering, 11, 171 Enthalpy, 53 envelope, 2, 11, 39, 49, 51, 97 environment, 38, 77, 96, 123, 150, 152 environmental, 89, 90, 109, 110, 172 equality, 43, 48, 140, 141 equilibrium, 2, 38, 40, 55, 93, 94, 95, 97, 101, 102, 124, 160, 179, 180, 188 equilibrium state, 2, 95 equipment, 125 erosion, 1, 22, 33, 34, 35, 36, 37, 38, 39, 40, 43, 45, 46, 47, 51, 61, 65, 66, 100, 118, 119, 120, 124, 174, 179, 180, 194 estimating, 118 etching, 113, 114 ethanol, 154 ethylene, 162 European, 75 evaporation, 33, 34, 37, 115, 116, 117, 119, 159 evidence, 114, 189 excitation, 90, 94, 95, 125 expenditures, 152, 160, 161 experts, 150 exploitation, 60, 156 explosive, 4, 62, 64 extinction, 26, 137 extrapolation, 20

F feeding, 12, 53, 54, 55, 56, 57, 58, 59, 60, 133, 168 fibroadenoma, 197 fibrosis, 197, 198 filters, 8, 9, 107 filtration, 8, 9, 165 fire, 129, 158 flight, 157

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index floating, 133 flow, 9, 11, 28, 32, 37, 60, 61, 64, 65, 78, 79, 80, 81, 82, 85, 86, 89, 90, 91, 93, 94, 112, 118, 123, 124, 126, 127, 129, 132, 133, 136, 138, 139, 141, 142, 143, 145, 146, 147, 148, 149, 150, 153, 156, 164, 191 flow rate, 89, 91, 123, 124, 126, 129, 132, 136, 138, 139, 141, 142, 143, 145, 146, 148, 149 fluctuations, 17, 20, 23, 26, 182 flue gas, 167, 168 fluorine, 123 focusing, 9, 31 food, 174 food industry, 174 France, 65 fuel, 122, 151, 152, 153, 154, 155, 157, 160, 161, 163, 164, 165, 166, 168 fungicide, 195 fungus, 193, 195 fungus spores, 195 furnaces, 127 fusion, 33, 39, 40, 122, 127, 136

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

G gas turbine, 153, 156, 164 gases, 1, 4, 17, 20, 22, 23, 53, 54, 60, 77, 81, 82, 83, 84, 85, 100, 108, 118, 126, 129, 136, 140, 144, 146, 151, 152, 154, 155, 156, 160, 161, 164, 165, 166, 167, 168, 169 gasification, x, 77, 123, 150, 153, 154, 156, 157, 158, 159, 160, 161, 164, 166, 168, 172 gasifier, 164 generation, 4, 77, 123, 153, 173, 176 generators, 1, 2, 4, 17, 23, 26, 60, 65, 77, 78, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 142, 143, 144, 146, 147, 148, 152, 153, 157, 170, 171 genes, 196 Germany, 73, 75, 122 Gibbs, 101, 170 Gibbs free energy, 101 glass, 150, 154 glow discharge, 174 goals, 173 government, iv grades, 83 grains, 121 grapes, 184, 189 graph, 68 graphite, 62, 154, 155 Great Britain, 74 grids, 183

207

groups, 37, 123, 127, 130, 154, 186, 187, 194, 196, 197 growth, 2, 3, 15, 16, 17, 19, 20, 24, 31, 44, 45, 49, 51, 53, 57, 59, 67, 81, 83, 84, 86, 89, 108, 111, 120, 143, 160, 195, 197, 198

H H2, ix, 49, 79, 138, 153, 157, 158, 159, 160, 164 hafnium, 123, 127 halogen, 152 handling, 152 harmful, 150, 156, 161, 165, 168 head, 168 health, 150 health services, 150 heat, 3, 16, 17, 19, 22, 31, 32, 33, 39, 51, 52, 53, 55, 58, 59, 60, 63, 64, 82, 84, 90, 91, 93, 94, 96, 98, 111, 116, 119, 120, 123, 124, 125, 129, 134, 135, 138, 146, 147, 151, 153, 154, 156, 158, 160, 161, 165, 168 heat capacity, 33, 91 heat conductivity, 120 heat loss, 53, 58, 59 heat transfer, 17, 33, 90, 91, 123, 124, 146 heating, 3, 7, 17, 20, 24, 25, 29, 31, 41, 42, 50, 58, 59, 60, 65, 82, 89, 90, 91, 94, 96, 98, 109, 110, 114, 119, 125, 126, 133, 134, 135, 136, 148, 151, 152, 153, 154, 155, 158, 162, 168 heavy metals, 151 heavy particle, 55 height, 79, 159, 184 helium, 1, 2, 3, 4, 6, 9, 16, 17, 18, 20, 21, 22, 26, 29, 30, 31, 41, 45, 46, 47, 48, 51, 54, 60, 65, 66, 77, 79, 84, 104, 105, 110, 143, 144 heterogeneity, 84, 112 high pressure, 2, 3, 7, 11, 31, 41, 43, 47, 79, 110, 129 high resolution, 113 high temperature, 1, 37, 61, 63, 67, 82, 108, 121, 123, 129, 133, 151, 152, 153, 154, 156, 159, 166, 168 high-speed, 8, 9 histological, 196 homogeneity, 79, 99 homogeneous, 33, 55, 159, 197 hospitals, 174 House, 170, 172 household, 150 human, 150, 174, 182, 186, 197 human milk, 197 hydrate, 4, 23 hydrides, 152 hydro, 123, 153, 158, 159, 164

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

208

hydrocarbon, 157, 160, 168 hydrocarbons, 153, 159, 164 hydrodynamic, 182, 190 hydrogen, 1, 2, 3, 4, 5, 6, 9, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 38, 40, 41, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 56, 57, 58, 59, 60, 65, 66, 68, 69, 77, 79, 82, 84, 110, 115, 126, 129, 136, 143, 146, 147, 151, 157, 160

ionization, 3, 13, 16, 26, 52, 79, 83, 87, 88, 92, 93, 101, 102, 104, 105, 140, 141, 152, 153 ions, 43, 47, 48, 51, 88, 99, 102, 112, 113, 117, 140, 173, 180, 191, 194, 195, 196 iron, 9, 99, 122, 179, 180, 181, 191, 193, 195 isolation, 4, 63, 67 isothermal, 4, 151 isotropic, 89 ISPC, 171

I

J

IAEA, 172 illumination, 7, 8, 9 images, 189, 190 immunoglobulin, 190 impurities, 24, 38, 40, 54, 59, 115, 118, 121, 153, 154, 160, 165, 168 in vivo, 196, 198, 201 inclusion, 114 incubation, 182, 195 indices, 154, 161 induction, 118, 133 inductor, 129 industrial, 80, 126, 135, 150, 151, 154, 155, 163, 171, 174 industrial wastes, 155, 163 industrialization, 150 industry, 151 inequality, 49 inert, 77, 81, 84, 126, 136, 140 inhibition, 195, 198 initiation, 6, 17, 22, 26, 28, 164 injection, 125, 167, 197, 198 inorganic, 152, 154, 155, 159, 164, 165 insertion, 128, 173, 196 instability, 12, 126 instruments, 77 insulation, 123 insulators, 132, 133 integration, 84 intensity, 2, 12, 18, 19, 28, 33, 44, 94, 97, 98, 106, 107, 108, 113, 143, 177, 178 interaction, 22, 30, 33, 90, 119, 130, 182, 186, 188, 189, 196 Interaction, 22, 70, 72, 182 interactions, 186, 190 interference, 8, 9 international, 172 interval, 13, 42, 49, 97, 102, 106, 133 Investigations, 1, 41, 78 ionic, 118, 182

January, 72 Japan, 165, 166, 183 Japanese, 165 JEM, 183 Jordan, 169 Joule heating, 16, 43, 116 Jun, 198, 199, 200

K killing, 195 kinetic energy, 68, 90, 117 Korea, 129

L L1, 4, 174 landfills, 150 lanthanide, 113 lanthanum, 107, 108, 112, 113, 114, 116 laser, 8, 9, 182 lasers, 78, 123 law, 48, 141 LCS, 182, 184 leaching, 164 lead, 12, 55, 77, 89, 90, 96, 107, 114, 115, 120, 137, 160, 190 lens, 4, 106, 107 lenses, 107 life span, 124 lifetime, 67, 85, 95, 96, 133, 137, 149, 197 light scattering, 182, 188 linear, 34, 37, 98, 107, 127, 128, 129, 131, 134 lipoprotein, 189 lipoproteins, 182, 186, 190 liquid chromatography, 180 liquid fuels, 77, 123, 155, 160 liquid phase, 121 liquids, 78, 166, 173, 186 literature, 190

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index lithium, 4, 23, 24 living conditions, 150 localization, 119 location, 4, 60, 118, 119, 120, 122 London, 168, 169, 171 long work, 114 losses, 1, 15, 16, 43, 47, 48, 51, 53, 84, 90, 93, 125, 134, 135, 148, 161 Louisiana, 198 low-power, 143, 157 low-temperature, 78, 153, 166 lymph, 196, 197 lymphoma, 197 lysozyme, 182, 188, 189

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

M Madison, 200 magnetic, 3, 13, 15, 16, 26, 30, 33, 38, 39, 40, 43, 48, 110, 118, 119, 124, 129, 131, 133, 135, 143 magnetic field, 3, 13, 16, 30, 33, 43, 119, 124, 129, 131, 133, 135 maintenance, 152 manufacturing, 63, 114 margin of error, 108 Mars, 71 Maryland, 171 mass spectrometry, 180 mathematical, 149 matrix, 196 measurement, 10, 182 mechanical, 155, 168 media, 124, 137, 148 medicine, 173, 174 melt, 33, 37, 154, 155, 163 melter, 154 melting, 33, 37, 67, 108, 109, 112, 116, 117, 119, 121, 123, 124, 159, 165 melting temperature, 33, 116, 117 melts, 111, 112 metallurgy, 122 metals, 34, 108, 113, 114, 122, 155, 163, 164, 173, 179, 183, 186, 189, 190, 191 methane, 156, 162 methanol, 154 MHD, 75 microbes, 174, 178 microbial, 174, 196 Microbial, 199, 201 micrometer, 180 microorganisms, 173 microscope, 183 microscopy, 180, 183, 196

209

microstructure, 120, 121 microwave, 123 military, 166 mineralization, 123, 151, 167 minerals, 163 mirror, 4, 8 mixing, 22, 94, 95, 133, 134, 135, 164, 192 mobility, 26 modeling, 29, 123 models, 127, 128, 129, 134, 136 modulation, 25, 86, 113 molecular mass, 65, 66, 67, 83, 97, 101 molecular structure, 197, 198 molecules, 6, 24, 41, 43, 55, 80, 82, 84, 85, 90, 94, 95, 96, 102, 103, 104, 105, 152, 186, 196 molybdenum, 33, 34, 36, 123 monochromator, 4, 9, 106, 107 monomer, 188 monomers, 182, 184, 189 morphological, 159, 197 Moscow, 74, 168, 170, 171, 198 motion, 10, 21, 26, 28, 38, 51, 65, 112, 118, 119, 120, 121, 124, 137, 173 MSW, 123 municipal solid waste, 123, 155, 162 MVA, 134

N NaCl, 182 nanometers, 114 nanoparticles, 173, 179, 180, 181, 182, 183, 184, 185, 189, 191, 194, 195, 196, 197 nanostructures, 78, 173, 182, 183, 186, 187, 188, 189, 190, 197 nanotubes, 196 natural, 110, 115, 118, 122, 151, 153, 156, 162 natural gas, 122, 153, 156, 162 Nd, 113 neglect, 80, 90, 93 neodymium, 114 neon, 9 network, 132, 133, 135, 138, 149 neutralization, 99, 117, 123, 166 New Mexico, 75, 171, 172 New York, 72, 74, 169, 200 Ni, 34, 35, 36, 179, 191, 192, 194, 195, 199 nitrogen, 1, 2, 4, 5, 17, 20, 21, 22, 23, 25, 26, 27, 28, 54, 55, 56, 57, 59, 60, 65, 77, 79, 82, 84, 85, 86, 87, 88, 89, 90, 93, 94, 95, 96, 97, 98, 99, 102, 115, 122, 126, 129, 136, 143, 144, 145, 146, 147, 151, 153, 157, 160, 166 nitrogen dioxide, 96

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index

210 nitrogen gas, 96 NO, 96, 101, 102, 157, 165 normal, 6, 31, 84, 100, 161, 186 normal conditions, 100 norms, 113, 156 Norway, 122 nuclear, 2

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

O observations, 33 oils, 163 oligomers, 186 oncological, 173 oncology, 196 online, 71 optical, 6, 7, 9, 11, 12 optics, 9 organic, 77, 123, 150, 152, 153, 154, 155, 156, 160, 163, 164, 166, 167, 168, 170, 174, 178 organic compounds, 166, 168, 178 organic matter, 150 organism, 186 organization, 127, 154, 166 oscillation, 2, 22, 32, 86, 91 oscillations, 1, 19, 20, 22, 24, 31, 32, 86, 106, 107, 115, 116, 117 oscillator, 83, 127 oscillograph, 4, 106 oxidation, 150, 159, 167 oxide, 78, 102, 117, 122, 165, 168, 173, 180, 182, 184, 186, 188, 189, 197 oxide nanoparticles, 180, 182, 184, 186 oxides, 108, 115, 116, 151, 152, 155, 180, 197 oxygen, 101, 102, 108, 113, 114, 115, 118, 129, 150, 151, 153, 155, 160, 161, 164, 168 oxygen consumption, 161 oxygen plasma, 161 Ozone, 198, 200

P paints, 163 Pap, 71 paper, 73, 150, 183 paramagnetic, 180 parameter, 33, 50, 58, 59, 66, 92, 97, 101, 117 particles, x, 13, 16, 30, 42, 77, 99, 101, 103, 104, 105, 117, 120, 124, 140, 155, 156, 168, 180, 182, 186, 187, 188, 194, 195, 196 Pb, 191 peat, 172

performance, 156, 159, 163, 164, 165 permeability, 196 pH, 180, 182 pharmaceuticals, 174 phenotype, 198 phosphate, 197 photographs, 178 physics, 6, 33, 196 physiological, 186, 196, 197 piezoelectric, 6, 10 PII, 169, 172 pitch, 16 plants, 2, 6, 63, 65, 68, 77, 78, 151, 152, 156, 165 plasma current, 99 plasmatrons, 1, 33, 51, 56, 61, 62, 63, 65, 69, 78, 81, 89, 92, 93, 94, 95, 100, 103, 108, 109, 110, 115, 119, 121, 122, 123, 127, 158, 162, 165 plastic, 121, 150 plastic deformation, 121 platinum, 184 play, 90 pneumonia, 191 polarity, 113 polygons, 150 polynomial, 149 pools, 34, 37 poor, 63 population, 84 powder, 7 powders, 122 power, 1, 2, 16, 17, 23, 25, 27, 31, 32, 33, 35, 43, 46, 48, 56, 57, 58, 59, 65, 68, 77, 81, 82, 86, 90, 91, 92, 93, 95, 109, 110, 120, 121, 123, 124, 125, 126, 127, 129, 130, 131, 133, 134, 135, 136, 137, 142, 147, 148, 149, 150, 157, 160, 163, 164, 175, 176, 178, 200 preparation, 158, 182, 188 pressure, 1, 2, 3, 4, 5, 6, 7, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 27, 29, 30, 31, 32, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 54, 55, 56, 57, 59, 60, 64, 65, 68, 69, 80, 81, 82, 83, 84, 86, 87, 89, 90, 93, 94, 95, 96, 99, 100, 113, 123, 126, 129, 136, 139, 143, 145, 146, 147, 150, 161, 176, 177 prevention, 133 prices, 153 probability, 80, 96, 120 probe, 8 production, 77, 122, 123, 127, 150, 153, 155, 160, 162, 163, 165, 166, 170, 171, 172 program, 101 propagation, 10, 32, 85, 86, 173 property, 174

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index protection, 152 protein, 182, 188, 189, 196 protein aggregation, 188 proteins, 186, 188, 196, 197 pseudo, 35, 36 Pseudomonas, 191 Pseudomonas aeruginosa, 191 public, 150 public health, 150 pulse, 1, 2, 3, 4, 5, 8, 10, 11, 23, 25, 26, 30, 31, 37, 50, 51, 56, 60, 62, 63, 65, 69, 78, 93, 127, 140, 173, 174, 175, 176, 177 pulse discharge, 2, 8 pulses, 132, 173, 174, 175, 177 pumping, 123 pumps, 129, 163 purification, 151, 174 PVA, 189 pyrolysis, 77, 123, 150, 152, 153, 155, 156, 158, 163, 166, 169

Q quanta, 11, 43, 48, 50 quartz, 10

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

R radial distribution, 109 radiation, 1, 2, 3, 7, 8, 11, 12, 16, 19, 27, 31, 33, 39, 43, 46, 47, 48, 50, 51, 55, 60, 81, 83, 84, 87, 90, 93, 94, 95, 96, 97, 98, 106, 107, 108, 109, 112, 116, 124, 125, 146, 177, 178 Radiation, 70, 71, 73, 74, 95, 200 radical, 150 radio, 123 radioactive waste, 154 radius, 1, 12, 14, 29, 30, 39, 43, 47, 55, 107, 109, 182, 190 rail, 119, 120, 137, 148, 149 random, 182 range, 4, 5, 8, 13, 15, 17, 19, 20, 25, 26, 33, 34, 36, 37, 43, 45, 50, 66, 68, 77, 78, 86, 89, 97, 98, 100, 102, 106, 107, 109, 110, 112, 119, 124, 126, 136, 141, 143, 149, 151, 152, 164, 178, 182 RAS, 65, 67, 72, 138, 156, 157, 161, 166, 167, 169, 201 rats, 196, 197, 198 raw material, 153, 154, 166 reagents, 78 reality, 55 reasoning, 100

211

recalling, 84 recombination, 12, 13, 16, 43, 48, 80, 84, 90, 93, 94, 125 recombination processes, 90 recovery, 172 reduction, 20, 22, 114, 122, 127, 139, 158, 159, 160 refractory, 123 regression, 149 regular, 198 regulation, 168 relationship, 113 relaxation, 3, 90, 91, 94, 95, 125 reliability, 69 renewable energy, 123 research, 113, 122, 123, 157, 196, 197 residuals, 155, 159, 168 resin, 152, 153, 161, 166 resins, 164, 168 resistance, 4, 16, 17, 33, 35, 37, 53, 174, 178 resistivity, 174 resolution, 182 retention, 39, 45 Reynolds number, 32, 89 rhenium, 94 rings, 67, 135 roentgen, 1, 11, 121 room temperature, 182, 183 rubber, 10 Russia, 65, 67, 126, 157, 172, 183 Russian, 70, 71, 72, 73, 74, 75, 76, 168, 169, 170, 171, 172, 198, 199, 200, 201

S SAE, 74 Salmonella, 191 sample, 182, 188 satisfaction, 49, 93 saturation, 15 scattering, 182 science, 77 scrap, 155 search, 101, 151 searches, 173 sedimentation, 112, 184 selectivity, 153 Self, 74, 198 semiconductor, 11, 50 semiconductor sensors, 50 sensitivity, 106, 183 sensors, 6, 10 separation, 8 series, 2, 119, 125, 166

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

212

Index

serum, 182, 186, 187, 188, 189, 190 serum albumin, 188 services, 150 shape, 124, 134 shock, 2, 3, 4, 10, 11, 17, 23, 26, 29, 31, 39, 50, 53, 54, 56, 57, 58, 59, 60, 62, 65, 78, 173, 174, 176, 178, 192, 194 shock waves, 2, 3, 11, 29, 31, 50, 78, 174, 176, 192, 194 short-term, 135 sign, 23 silicates, 164 silicon, 196 silver, 176, 178, 179, 180, 181, 183, 184, 191, 193, 195, 196, 197 simulation, 2 slag, 151, 155, 156, 157, 159, 161, 164, 165, 167, 168 smoothing, 80, 129 smoothness, 182 SO2, 156 sodium, 27 solid waste, 152, 162, 164, 165 solutions, 174, 186 solvents, 163, 166 soot, 151, 168 spatial, 8, 9, 99 species, 102, 113, 114, 115, 196 specific surface, 182 spectra, 12, 13, 94, 113, 169, 178, 180 spectral analysis, 121 spectroscopy, 113, 180 spectrum, 3, 7, 9, 12, 27, 39, 50, 87, 97, 98, 107, 108, 109, 112, 182 speed, 4, 7, 8, 9, 18, 22, 51, 63, 107, 129, 130, 139, 178 spheres, 120 stability, 1, 3, 130, 158, 186 stabilization, 60, 63, 64, 127, 130, 133, 135, 139, 141, 143, 197, 198 stages, 16, 150, 188, 190 stainless steel, 4, 62, 122 standards, 150 Staphylococcus, 191 Staphylococcus aureus, 191 stars, 2 steady state, 15, 16, 25 steel, 34, 35, 36, 37, 42, 45, 46, 50, 61, 62, 63, 124, 129, 135 storage, 23, 25, 26, 41, 152, 167 stratification, 163 streams, 4, 9, 134, 196

strength, 2, 5, 13, 19, 30, 33, 41, 42, 43, 44, 45, 47, 51, 55, 56, 57, 81, 82, 86, 88, 99, 124, 141, 147, 179, 180, 181, 191 subsonic, 94 substances, 150, 151, 152, 159, 161, 165, 167 suburbs, 162 sulfur, 121, 151, 165 Sun, 199, 200 supply, 17, 24, 25, 26, 60, 86, 89, 92, 125, 126, 127, 129, 131, 135, 136, 137, 138, 139, 153, 160, 168, 175 surface layer, 38, 114, 120, 121, 163 surface properties, 122 surface region, 113, 115 surviving, 197 Sweden, 164, 172 switching, 23, 174 symbols, 142, 144 symmetry, 40 synthesis, ix, 123, 154, 160 synthetic, 123, 153 systems, ix, x, 5, 7, 62, 63, 77, 78, 81, 84, 86, 115, 126, 129, 133, 135, 152, 168, 172, 186

T technological, 149, 151, 152, 153, 155, 163, 165, 168, 171, 173 technology, 154, 155, 161, 162, 163, 164, 165, 166, 168, 196 TEM, 183, 189, 190 temperature gradient, 90 Tennessee, 65 theoretical, 55, 124, 161 theory, 150 thermal, 3, 7, 16, 26, 27, 30, 32, 33, 37, 43, 50, 89, 92, 111, 114, 121, 122, 123, 124, 126, 130, 134, 135, 136, 137, 140, 143, 148, 149, 150, 151, 152, 153, 156, 158, 162, 164, 171, 172 thermal destruction, 158 thermal efficiency, 126, 134, 136, 138, 143, 148, 149 thermal energy, 136, 151, 162, 164 thermal expansion, 114, 121 thermal load, 121, 123, 137 thermal plasma, 130, 171, 172 thermodynamic, 10, 13, 87, 99, 101, 143, 179 thermodynamic equilibrium, 10, 13, 87, 99, 101 thermonuclear, 2, 77, 78 thin film, 121 third order, 149 thorium, 107, 108 time, 1, 3, 10, 12, 15, 17, 18, 20, 22, 23, 24, 28, 31, 32, 38, 44, 45, 46, 50, 55, 58, 59, 63, 64, 78, 80,

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Index 83, 85, 89, 90, 91, 94, 95, 99, 100, 106, 107, 108, 110, 114, 115, 116, 117, 119, 120, 121, 123, 126, 127, 129, 140, 143, 149, 150, 151, 152, 157, 160, 165, 167, 168, 175, 176, 192, 193, 194, 195, 197 time resolution, 10 tissue, 174, 186, 197, 198 titanium, 33, 34, 193 total energy, 25, 32, 55 toxic, 77, 150, 151, 152, 153, 166, 167, 168, 169, 171, 196 toxic substances, 151, 152, 153, 167 toxicity, 180, 191, 195 trans, 7, 8, 9 transducer, 5, 10, 18 transfer, 3, 16, 32, 37, 43, 50, 65, 90, 91, 96 transformation, 125, 135, 147, 151 transition, 125 transmission, 140, 183 transparency, 45 transparent, 43, 47, 48, 124 transplantation, 196, 197 transportation, 140 tubular, 131, 137 tumor, 196, 197, 198 tumor cells, 197 tumor growth, 198 tumors, 196, 197 tungsten, 4, 5, 9, 11, 21, 34, 35, 36, 37, 38, 39, 40, 42, 44, 45, 51, 87, 90, 92, 94, 96, 97, 98, 107, 108, 109, 112, 113, 114, 115, 116, 117, 118, 123, 132, 133 turbulence, 22, 26, 31, 32, 60, 84, 85, 89, 90, 91 turbulent, 17, 18, 20, 26, 31, 32, 51, 60, 84, 86, 87, 89, 90, 91, 124 turbulent flows, 84, 91

U Ukraine, 198 Ultraviolet, 71, 200 uncertainty, 28, 87 uniform, 13, 30, 38, 39, 86, 89, 113, 114, 115, 133, 159 United States, 126, 155, 162, 165 universal gas constant, 97 URL, 171 users, 171 UV, 174, 178, 180, 194, 198, 200 UV radiation, 174, 178, 194

213

V vacuum, 47, 51, 113 values, 2, 3, 11, 12, 13, 15, 19, 20, 26, 31, 32, 39, 41, 44, 45, 48, 51, 52, 56, 59, 66, 78, 86, 87, 88, 89, 92, 93, 94, 96, 100, 103, 108, 111, 112, 116, 117, 118, 123, 130, 141, 145, 146, 149, 152, 160, 180 vapor, 28, 38, 47, 65, 67, 89, 103, 104, 105, 156, 157, 159, 160, 161, 162, 164, 165, 166 variation, 12, 22, 55, 56, 59, 86, 97, 98, 107, 108, 126, 150, 151 vector, 133 vehicles, 123 velocity, 1, 2, 3, 18, 22, 25, 26, 30, 32, 38, 47, 60, 61, 65, 66, 68, 69, 79, 80, 82, 83, 85, 89, 91, 93, 97, 99, 100, 103, 111, 113, 118, 119, 121, 129, 137, 140, 150, 153, 167, 173, 176 Virginia, 65 viscosity, 33 visible, 13, 30, 50, 96, 98, 107, 110, 180 vitrification, 128 vortex, 116, 122, 130, 133, 135, 139, 141 vortices, 18

W wall temperature, 55 waste, 123, 128, 150, 151, 152, 153, 156, 157, 159, 160, 162, 163, 165, 166, 167, 168, 169, 171, 172 waste products, 150 waste treatment, 150, 151, 152, 153, 162, 165, 166, 171 wastes, x, 77, 150, 153, 154, 155, 157, 158, 161, 163, 164, 165, 166, 172 water, 78, 79, 85, 103, 110, 111, 121, 122, 129, 130, 133, 135, 136, 137, 138, 139, 150, 153, 156, 160, 161, 166, 167, 168, 173, 174, 175, 176, 178, 179, 180, 182, 186, 188, 191, 192, 193, 194, 195, 196, 197 water vapor, 79, 85, 103, 153, 160, 161 Watson, 72, 73 wave propagation, 176 wavelengths, 97, 108 wear, 119, 120, 121, 122 Weinberg, 201 welding, 123 Westinghouse, 126, 128, 135, 165, 171 wet, 155, 167 wind, 123 wind tunnels, 123 windows, 6, 8, 9 wood, 123, 157, 158, 160, 172

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest

Index

214 wood waste, 160 working conditions, 93

Y X

yield, 160 yttrium, 108, 113, 114, 115, 122

xenon, 3 X–ray, 2, 50, 69

Z

Copyright © 2008. Nova Science Publishers, Incorporated. All rights reserved.

Zn, 197

Physics and Technology of High Current Discharges in Dense Gas Media and Flows, Nova Science Publishers, Incorporated, 2008. ProQuest