LERARYOFCONGRESS
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`0.003 5.2.2.980 4 3
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`9 783540 194620
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`
`
`188 N 3-540-19462-2
`
`TSMC et al. v. Zond, Inc.
`GILLETTE-1012
`Page 1 of 25
`
`

`

`Yuri P. Raizer
`>
`Gas Discharge Physics
`
`GILLETTE-1012 / Page 2 of 25
`
`

`

`Yuri P. Raizer
`
`Gas Discharge Physics
`
`With 209 Figures
`
`
`
`Springer
`
`
`
`
`
`Springer
`
`Heidelberg
`New York
`Barcelona
`
`Budapest
`Hong Kong
`London '
`
`Santa Clara
`
`GILLETTE-1012 / Page 3 of 25
`
`

`

`a
`
`,)
`
`l
`K.» [7 i
`(32 a} Ff L?)
`
`l a a ~22
`
`Professor Dr. Yuri P. Raizer
`The Institute for Problems in Mechanics, Russian Academy of Sciences,
`Vernadsky Street 101, 117526 Moscow, Russia
`
`.
`Dr. John E. Allen
`Department of Engineering Science, University of Oxford, Parks Road,
`Oxford OX1 3P], United Kingdom
`'
`'
`
`Translator:
`
`Dr. Vitaly I. Kisin
`24 Varga Street, Apt. 9, 117133 Moscow, Russia
`
`
`
`
`This edition is based on the original second Russian edition: Fizika gazovogo razryada
`© Nauka, Moscow 1987, 1992
`
`1st Edition 1991
`Corrected 2nd Printing 1997
`
`ISBN 3-540—19462-2 Springer-Verlag Berlin Heidelberg New York
`
`Library of Congress Cataloging—in-Publication Data.
`Raizer, if]. P. (fiJrii Petrovich) [Fizika gazovogo razriada. English] Gas discharge physics / Yuri P.
`Raizer. p. cm. “Corr. printing 1997” — t.p. verso. Includes bibliographical references and index.
`ISBN 3-540—19462-2 (hardcover: alk. paper)
`1. Electric discharges through gases. 1. Title.
`QC7n-R22713
`1997
`537.5’3-d621 96-53988
`
`This work is subject to copyright. All rights are reserved, whether the whole or part of the material is
`concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broad—
`casting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of
`this publication or parts thereof is permitted only under the provisions of the German Copyright
`Law of September 9, 1965, in its current version, and permission for use must always be obtained
`from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law.
`© Springer—Verlag Berlin Heidelberg 1991
`Printed in Germany
`The use of general descriptive names, registered names, trademarks, etc. in this publication does not
`imply, even in the absence of a specific statement, that such names are exempt from the relevant pro-
`tective laws and regulations and therefore free for general use.
`
`
`
`Preface
`
`Gas discharges are of interest to physicists and engineers in a number of fields.
`Several decades ago excellent textbooks were written by von Engel and Stem-
`beck, Loeb, Brown, Kaptsov and several other authors. These books faithfully
`served many generations of students, and specialists still refer to them. Never-
`theless, their usefulness does suffer from the time elapsed since publication: It
`is not that the material they present has become pbgellggeand irrelevant — this
`has happened to a very minor extent, if at‘all. ‘R'athlélr,
`'flfe"siibject has greatly
`advanced both in scope and in depth, and its.e;nphases
`e somewhat shifted.
`Of course, new books have been written, mostly mbnd
`phs devd‘ted to narrow
`branches of gas discharge physics. But these<~ becksgafe’typically. intended for the
`specialist and not so much for the novice inthe fieldw-«W‘M,
`The need for a new textbook that is understandable to a beginner in gas
`discharge physics, and that conveys the right amount of information (even more
`important: information of the right kind) making it also useful to the specialist is
`apparent. With this in mind, our intention has been to produce a book that serves
`both as a textbook, and a handbook.
`From an immense amount of material we have selected, as best we could,
`
`the parts that are required for an understanding of the physics and those points
`that are most frequently needed in research. As a convenient and comprehensive
`volume, the book contains a maximum of useful data: experimental results, results
`of calculations, and reference data; formulas required for estimates have been
`reduced to a form suitable for computations.
`This work was published in Russian in 1987 as a substanfially larger volume.
`The English edition has been abridged at the expense of ancillary material con-
`cerning collisions, elementary processes, plasma radiation, plasma diagnostics
`and other topics, though the chapters dealing with the central themes of discharge
`physics are retained in full, and even expanded by the addition of new data.
`We have decided not to cover actual circuits, techniques, or methods (we will
`cover the ideas, though) of experiments and measurements; instead we concen-
`trate on the physics of the processes of interest. Purely technical applications of
`gas discharges are not discussed for the same reason.
`It would be impossible to give a comprehensive bibliography when covering
`such an immensely wide scope of topics; hence, original papers are cited only
`when recent results are discussed. In all other cases we refer to a book or review
`
`GILLETTE-1012 / Page 4 of 25
`
`

`

`The author is deeply grateful to Professors A. V. Eletsky and L. D. Tsendin,
`who read the Russian version of the manuscript, and Professor J. E. Allen, who
`read the English, for a number of useful comments. In addltlon, theauthor would
`like to thank the translator, Dr. V. I. Kisin, for a fruitful collaboration.
`
`Moscow, April 1991
`
`Yu. P. Raizer
`
`
`
`Contents
`
`1,
`
`................‘ ............................
`Introduction
`1.1 What Is the Subject of Gas Discharge Physics
`............
`1.2
`Typical Discharges in a Constant Electric Field
`...........
`1.3
`Classification of Discharges
`...........................
`1.4
`Brief History of Electric Discharge Research
`.............
`1.5 Organization of the Book. Bibliography ..................
`
`2. Drift, Energy and Diffusion of Charged Particles
`in Constant Fields
`.......................................
`
`2.1 Drift of Electrons in a Weakly Ionized Gas ...............
`2.2
`Conduction of Ionized Gas
`............................
`
`1
`1
`1
`3
`4
`6
`
`8
`
`8
`13
`
`Electron Energy .....................................
`2.3
`2.4 Diffusion of Electrons ................................
`2.5
`Ions ...............................................
`
`I 14
`20
`23
`
`.................................
`2.6 Ambipolar Diffusion
`2.7
`Electric Current in Plasma in the Presence
`
`.............
`of Longitudinal Gradients of Charge Density
`2.8 Hydrodynamic Description of Electrons ..................
`
`3.
`
`Interaction of Electrons in an Ionized Gas
`
`.
`.
`. .
`with Oscillating Electric Field and Electromagnetic Waves
`3.1
`The Motion of Electrons in Oscillating Fields .............
`3.2
`Electron Energy .....................................
`3.3
`Basic Equations of Electrodynamics of Continuous Media .
`.
`.
`3.4 High-Frequency Conductivity
`and Dielectric Permittivity of Plasma ....................
`Propagation of Electromagnetic Waves in Plasmas
`.........
`Total Reflection of Electromagnetic Waves
`from Plasma and Plasma Oscillations ....................
`
`3.5
`3.6
`
`.................
`4. Production and Decay of Charged Particles
`4.1
`Electron Impact Ionization in a Constant Field ............
`4.2 Other Ionization Mechanisms
`..........................
`
`28
`
`30
`33
`
`35
`35
`37
`. 41
`
`43
`45
`
`49
`
`52
`52
`57
`
`
`
`GILLETTE-1012 / Page 5 of 25
`
`

`

`
`
`
`{it
`
`a
`
`r?“
`iii
`
`awawwaa.
`
`..................
`Formation and Decay of Negative Ions
`4.5 Diffusional Loss of Charges
`...........................
`Electron Emission from Solids
`.........................
`4.7 Multiplication of Charges in a Gas via Secondary Emission
`.
`
`63
`67
`68
`72
`
`. Kinetic Equation for Electrons in a Weakly Ionized Gas
`Placed in an Electric Field
`................................
`5.1 Description of Electron Processes
`in Terms of the Velocity Distribution Function ............
`Formulation of the Kinetic Equation
`....................
`5.3 Approximation for the Angular Dependence
`. ..............
`of the Distribution Function
`. . . . .
`.
`.
`. . . .
`.
`5.4 . Equation of the Electron Energy Spectrum ...............
`Validity Criteria for the Spectrum Equation ...............
`Comparison of Some Conclusions Implied
`by the Kinetic Equation with the Result of Elementary Theory
`Stationary Spectrum of Electrons
`in a Field in the Case of only Elastic Losses ..............
`5.8 Numerical Results for Nitrogen and Air ..................
`Spatially Nonuniform Fields of Arbitrary Strength .........
`
`. Electric Probes
`Introduction. Electric Circuit ...........................
`Current—Voltage Characteristic of a Single Probe ...........
`Theoretical Foundations of Electronic Current Diagnostics
`of Rarefied Plasmas ..................................
`Procedure for Measuring the Distribution Function .........
`Ionic Current to a Probe in Rarefied Plasma ..............
`6.6 Vacuum Diode Current and Space—Charge Layer
`Close to a Charged Body
`.............................
`6.7 Double Probe .......................................
`6.8
`Probe in a High-Pressure Plasma
`.......................
`
`76
`
`76
`77
`
`82
`85
`90
`
`93
`
`95
`98
`101
`
`103
`
`104
`
`106
`111
`113
`
`115
`119
`123
`
`. Breakdown of Gases in Fields
`of Various Frequency Ranges
`7.1
`Essential Characteristics of the Phenomenon ..............
`7.2
`Breakdown and Triggering of Self-Sustained Discharge
`in a Constant Homogeneous Field at Moderately Large Product
`of Pressure and Discharge Gap Vlfidth
`...................
`Breakdown in Microwave Fields and Interpretation
`of Experimental Data Using the Elementary Theory ........
`
`7.3
`
`128
`
`128
`
`130
`
`138
`
`............................
`7.5 Optical Breakdown
`7.6 Methods of Exciting an RF Field in a Discharge Volume .....
`7.7
`Breakdown in RF and Low-Frequency Ranges
`.
`.
`.
`.
`.
`.
`.
`.
`
`8.4
`8.5
`
`.
`
`............................
`Stable Glow Discharge
`8.1
`General Structure and Observable Features
`. .
`. .
`.
`.
`.
`. ......
`8.2
`Current-Voltage Characteristic of Discharge
`.....
`Between Electrodes
`...............................
`8.3 Dark Discharge and the Role Played by Space Charge
`in the Formation of the Cathode Layer
`...............
`Cathode Layer ..................................
`Transition Region Between the Cathode Layer
`.......
`and the Homogeneous Positive Column ............
`Positive Column ...................................
`8.6
`8.7 Heating of the Gas and Its Effect
`........
`on the Current-Voltage Characteristic ’ ...............
`Electronegative Gas Plasma ......................
`8.8
`8.9 Discharge in Fast Gas Flow ..........................
`8.10 AnodeLayer
`....
`
`I
`
`I
`
`.
`.
`.
`Glow Discharge Instabilities and Their Consequences
`9.1
`Causes and Consequences of Instabilities ........... '......
`9.2 Quasisteady Parameters
`.
`.
`.- ............................
`9.3
`Field and Electron Temperature Perturbations
`.....
`in the Case of Quasisteady-State Te ....................
`Thermal Instability ..............................
`9.4
`9.5 Attachmentlnstability
`9.6
`Some Other Frequently Encountered Destabilizing Mechanisms.
`9.7
`Striations
`.....................................
`9.8
`Contraction ofthe Positive Column
`
`10.
`
`.....................................
`Arc Discharge
`10.1 Definition and Characteristic Features of Arc Discharge .....
`10.2 Arc Types ........................................
`10.3 Arc Initiation
`.......................................
`10.4 CarbonArcinFreeAir
`.......
`10.5 Hot Cathode Arc: Processes near the Cathode .............
`10.6 Cathode Spots and Vacuum Arc ......................
`10.7 AnodeRegion
`........
`10.8 Low-Pressure Arc with Externally Heated Cathode .
`.
`A .
`.
`I
`10.9 Positive Column of High—Pressure Arc (Experimental Data). '
`10.10 Plasma Temperature and V — 2' Characteristic
`of High-Pressure Arc Columns .........................
`
`151
`160
`161
`
`167
`167
`
`172
`
`175
`178
`
`190
`193
`
`199
`203
`209
`211
`
`214
`214
`217
`
`220
`222
`226
`228
`230
`239
`
`245
`245
`246
`248
`249
`4251
`259
`266
`268
`271
`
`275
`
`GILLETTE-1012 / Page 6 of 25
`
`

`

`,
`
`14. Discharges in High-Power CW C02 Lasers
`14.1 Principles of Operation of Electric-Discharge C02 Lasers
`" '
`14.2 Two Methods of Heat Removal from Lasers
`_
`14.3 Methods of Suppressing Instabilities
`..................
`14.4 Organization of Large-Volume Discharges ..............
`Involving Gas Pumping ...........
`""""""""""
`Appendix ............................................
`References ..................................................
`.
`Subject Index ...............................................
`
`415
`415
`417
`421
`425
`433
`439
`447
`
`ll. Sustainment and Production of Equilibrium Plasma
`by Fields in Various Frequency Ranges
`.....................
`Introduction. Energy Balance in Plasma ..................
`11.2 Arc Column in a Constant Field ........................
`11.3 Inductively Coupled Radio-Frequency Discharge
`..........
`11.4 Discharge in Microwave Fields .........................
`11.5 Continuous Optical Discharges .........................
`11.6 Plasmatrons: Generators of Dense Low—Temperature Plasma ,
`12. Spark and Corona Discharges
`............................
`12.1 General Concepts ....................................
`122 Individual Electron Avalanche
`.........................
`12.3 Concept of Streamers ...............................- .
`.
`12.4 Breakdown and Streamers in Electronegative Gases (Air)
`in Moderately “Wide Gaps with a Uniform Field ...........
`12.5 Spark Channel
`......................................
`12.6 Corona Discharge .......'.............................
`12.7 Models of Streamer Propagation .................. ’......
`12.8 Breakdown in Long Air Gaps
`with Strongly Nonuniform Fields (Experimental Data) ......
`12.9 Leader Mechanism of Breakdown of Long Gaps
`..........
`12.10 Return Wave (Return Stroke)
`..........................
`12.11 Lightning
`..........................................
`12.12 Negative Stepped Leader ..............................
`
`288
`288
`290
`291
`299
`306
`315
`324
`324
`328
`334
`
`338
`343
`345
`352
`
`359
`363
`368
`370
`375
`
`...........
`13. Capacitively Coupled Radio-Frequency Discharge
`13.1 Drift Oscillations of Electron Gas ............... . .......
`13.2 Idealized Model of the Passage of High—Frequency Current
`Through a Long Plane Gap at Elevated Pressures ..........
`13.3 V — i Characteristic of Homogeneous Positive Columns
`. .
`.
`.
`13.4 Two Forms of CCRF Discharge Realization
`......
`and Constant Positive Potential of Space: Experiment
`13.5 Electrical Processes in a Nonconducting Electrode Layer
`and the Mechanism of Closing the Circuit Current .........
`13.6 Constant Positive Potential
`..................
`of the Weak-Current Discharge Plasma
`13.7 High—Current Mode
`............- ......................
`13.8 The Structure of a Medium—Pressure Discharge:
`Results of Numerical Modeling
`........................
`13.9 Normal Current Density in Weak—Current Mode
`.
`and Limits on the Existence of this Mode ................
`
`78
`378
`
`381
`385
`
`.
`
`387
`
`396
`
`400
`403
`
`408
`
`413
`
`
`
`1
`f
`'
`
`'
`
`_
`
`
`
`GILLETTE-1012 / Page 7 of 25
`
`

`

`1. Introduction
`
`1.1 What Is the Subject of Gas Discharge Physics
`
`The term “gas discharge’; originates with the process of discharge of a capacitor
`into a circuit incorporating a gap between electrodes. If the voltage is sufficiently
`high, electric break down occurs in the gas and an ionized state is formed. The
`circuit is closed and the capacitor discharges. Later the term “discharge” was
`applied to any flow of electric current through ionized gas, and to any process of
`ionization of the gas by the applied electric field. As gases ionized to a sufficient
`degree emit light, it has become customary to say that a discharge “lights up,”
`or is “burning.”
`As a rule, the flow of electric current is associated with the notion of a circuit
`composed of conductors. Actually, a closed circuit or electrodes are not needed
`for a directed motion of charges (electric current) in rapidly oscillating elec-
`tric fields, and even less so in the field of electromagentic radiation. However,
`quite a few effects observed in gases subjected to oscillating electric fields and
`electromagnetic waves (breakdown, maintaining the state of ionization, dissipa-
`tion of energy of the field) are not different, in principle, from dc phenomena.
`Nowadays all such processes are referred to as discharges and included within
`gas discharge physics. The fact that electric current flow in open circuits in the
`field of electromagnetic waves is of no general significance. In such cases, the
`dissipation of the energy of the field is described not as the release of the Joule
`heat by electric current, but as the absorption of radiation.
`The modern field of gas discharge physics is thus occupied with processes
`connected with electric currents in gases and with generating and maintaining
`the ability of a gas to conduct electricity and absorb electromagnetic radiation.
`Gas discharge physics covers a great variety of complex, multi-faceted phe-
`nomena; it is full of an enormous amount of experimental facts and theoretical
`models. Before we begin their analysis, it is expedient to single out the main
`types of discharge processes and clarify them.
`
`1.2 Typical Discharges in a Constant Electric Field
`
`A relatively simple experiment introduces us to several fundamental types of
`
`
`
`
`
`GILLETTE-1012 / Page 8 of 25
`
`

`

`
`
`Fig. 1.1. Typical gas discharge tube
`gases at different pressures. The quantifies measured in the experiment are the
`voltage between the electrodes and the current in the circuit. This classical device
`served the study of discharge processes for nearly 150 years, and still remains
`
`If a low voltage is applied to the electrodes, say several tens of volts, no
`visible effects are produced, although a supersensitive instrument would record
`an extremely low current, on the order of 10‘15 A. Charges are generated in the
`gas by cosmic rays and natural ra 'oactivity. The field pulls them to the opposite—
`sign electrodes, producing a current. If the gas is intentionally irradiated by a
`ra 'oactive or X—ray source, a current of up to 10’6 A can be produced. The
`resultant ionization is nevertheless too small to make the gas emit light. A dis-
`charge and an electric current that survive only while an external ionizing agent
`or the emission of electrons or ions from electrodes is deliberately maintained
`—self-sustaining. As the voltage is
`(e.g. by heating the cathode) are said to be non
`because most of the charges
`raised, the non-self-sustaining current first increases
`produced by ionization are pulled away to electrodes before recombination oc-
`all new charges, the current ceases
`curs. However, if the field manages to remove
`to grow and reaches saturation, being limited by the rate of ionization.
`As the voltage is raised further, the current sharply increases at a certain value
`of V and light emission is observed These are the manifestations of breakdown,
`one of the most important discharge processes. At pressure p ~ lTorr and in-
`terelectrode gap L ~ lcm, the breakdown voltage is several hundred volts.
`Breakdown starts with a small number of spurious electrons or electrons injected
`intentionally to stimulate the process: The discharge immediately becomes self-
`sustaining. The energy of electrons increases while they move in the field. Hav—
`ing reached the atomic ionization potential, the electron spends this energy on
`knocking out another electron. Two slow electrons are thus produced, which go
`on to repeat the cycle described above. The result is an electron avalanche, and
`electrons proliferate. The gas is appreciably ionized in 10‘7 to 10‘3 s, which is
`sufficient for the current to grow by several orders of magnitude.
`Several conditions determine how the process develops at higher voltage.
`At low pressure, say 1 to 10Torr, and high resistance of the external circuit (it
`prevents the current from reaching a large value), 'a glow discharge develops.
`This is one of the most frequently used and important types of discharge. It is
`characterized by low current, 2' ~ 10'6 —10’1 A in tubes of radius R ~ 1 cm, and
`fairly high voltage: hundreds to thousands of volts. A beautiful radiant column,
`uniform along its length, is formed in sufficiently long tubes of, say, L ~ 30 cm at
`
`
`
` plagma is very weakly ionized, to :1: = 10'8 «10'6 (where :1: denotes the fraction
`
`of ionized atoms), and is nonequilibrium in two respects. Electrons that
`t
`energy directly from the field have a mean energy E z leV and a temperatsfe
`Te z 10 K. The temperature T of the gas, including the ions is not much
`higher than the ambient temperature of 300K. This state, with widel
`se arated
`electron and.gas temperatures, is sustained by a low rate of Joule lieat Iij'elease
`under conditions of relatively high specific heat of the gas and high rate of 't
`natural cooling. Also as a result of the high rate of charge neutralization ' 1 S
`cold gas, its degree of ionization is many orders of magnitude lower thanmtha
`thermodynarnic equilibrium value corresponding to the electron temperature
`C
`'
`If the pressure in the gas is high (about the atmospheric level) and there—
`srstance of the external circuit is low (the circuit allows the passage of a hi
`current), anarc discharge usually develops soon after breakdown. Arcs typical]gh
`burn at a high current (i > 1A) at a low voltage of several tens of V01tS‘ they
`form a bright column. The are releases large thermal power that can destroy
`the glass tube: Arcs are often started in open air! Atmospheric—pressure are:
`usually form thermodynamic equilibrium plasmas (the so—called low-tem rature
`plasma), With Te w T w 104K and the ionization of a: = 10—3 4 10P—cl
`responding to such temperatures. The are discharge differs essentiall
`fromcfl'i-
`glow discharge in the mechanism of electron emission from the cathdde
`h'
`lei
`is Vital for the flow of dc current of the arc. In the glow discharge eletvftr1c
`:hre knogllted1from the surface of the cold metal by impacts of positive ionsmlli:
`d;331,5.sc arge, the high current heats up the cathode,and thermionic emission
`.
`If p ~ latm, the interelectrode a L > 10cm
`'
`'
`high, sparking occurs. The breakdovgvri)in the gap dbzzirtifb‘yofgfid 1gsrts)uwftfihc::fnttlliy
`plasma channel from one electrode to another. Then the electrodes are as if shorte
`Circuited by‘the strongly ionized spark channel. Lightning, whose “electrodes;
`are a charged cloud and the ground, is a giant variety of the spark dischar e
`finally, a corona discharge may develop in strongly nonuniform fields that g .
`insuffic1ent for the breakdown of the entire gap: A radiant corona appears at shzrr;
`gc
`hlg
`
`1.3 Classification of Discharges
`
`Discharges in a dc electric field can be classified into (a) non—self—sustainin
`
`and (b) self—sustaining types. The latter are more widespread more diversifiedg
`and richer in physical effects; and they are the subject of this, book. Steady and
`(visas-steady self—sustaining discharges contain (1) glow and (2) are discharges
`e have already mentioned in Sect. 1.2 that the cathode processes of two types
`
`GILLETTE-1012 / Page 9 of 25
`
`

`

`Corona has common features with glow and dark discharges. Among transient
`discharges, the (5) spark discharge stands out sharply, among others.
`Many features of purely plasma processes, characterizing breakdown in a dc
`electric field, as well as the glow and are discharges, are typical for discharges in
`rapidly oscillating fields, where electrodes are not necessary at all. It is therefore
`expedient to construct a classification avoiding the attributes related to electrode
`effects, and the following two properties will be basic for the classification: the
`state of the ionized gas and the frequency range of the field. The former serves
`to distinguish between (1) breakdown in the gas, (2) sustaining nonequilibrium
`plasma by the field, and (3) sustaining equilibrium plasma. Frequency serves
`to classify fields into (1) dc, low-frequency, and pulsed fields (excluding very
`short pulses), (2) radio—frequency fields (f N 105 —- 108 Hz), (3) microwave
`fields (f ~ 109 - 10“ Hz, /\ ~ 102 — 10‘1cm), and (4) optical fields (far from
`infrared to ultraviolet light). The field of any subrange can interact with each
`type of discharge plasma. In total, we have 12 combinations. All of them are
`experimentally realizable, and quite a few are widely employed in physics and
`technology. Typical conditions under which each of the combinations can be
`observed are summarized in Table 1.1.
`'
`
`Table 1.1. Classification of discharge processes
`Breakdown
`Noncquilibtium plasma
`Equilibrium plasma
`
`
`Constant electric
`Initiation of glow
`Positive column of glow
`Positive column of high-
`discharge in tubes
`discharge
`pressure are
`
`
`Radio frequencies
`
`Inductively coupled
`Capacitivcly coupled rf
`Initiation of If discharge
`in vessels filled with
`discharges in rarefied
`plasma torch
`’
`
`rarefied gases
`gases
`at
`
`Microwave range
`Breakdown in waveguides Microwave discharges irt Microwave plasmatron
`and resonators
`rarefied gases
`
`
`Continuous optical
`final stages of optical
`Gas breakdown by laser
`
`
`breakdownradiation discharge
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`1.4 Brief History of Electric Discharge Research
`
`Leaving lightning aside, man’s first acquaintance with electric discharges was
`the observation, dating back to 1600, that friction-charged insulated conductors
`lose their charge. Coulomb proved experimentally in- 1785 that charge leaks
`through air, not through imperfect insulation. We understand now that the cause
`of leakage is the non—self-sustaining discharge.
`Occasional experiments were conducted in the 18th century with sparks pro—
`duced by charging a body by an electrostatic generator, and with atmospheric
`
`worked in the Saint Petersburg Medical Surgery Academy in Russia, reported
`the discovery in 1803. The are was obtained by bringing two carbon electrodes
`connected to battery terminals into contact and then separating them. Several
`years later Humphrey Davy in Britain produced and studied the arc in air. This
`type of discharge became known as “are” because its bright horizontal column
`between two electrodes bends up and arches the middle owing to the Archimedes’
`force. In 1831—1835, Faraday discovered and studied the glow discharge. Faraday
`worked with tubes evacuated to a pressure p ~ lTorr and applied voltages up
`to 1000 V.
`The history of physics of gas discharges in the late 19th and early 20th
`centuries is inseparable from that of atomic physics. After William Crookes’s
`cathode ray experiments and JJ. Thomson’s measurements of the e/m ratio, it
`became clear that the current in gases is mostly carried by electrons. A great
`deal of information on elementary processes involving electrons, ions, atoms,
`and light fields was obtained by studying phenomena in discharge tubes.
`Beginning in 1900, J.S.E. Townsend, a student of 1.]. Thomson and the cre-
`ator of a school in the physics of gas discharges discovered the laws governing
`ionization and the gaseous discharge (known as the Townsend discharge) in a uni-
`form electric field. Numerous experimental results were gradually accumulated
`on cross sections of various electron-atom collisions, drift velocities of electrons
`and ions, their recombination coefficients, etc. This work built the foundations
`of the current reference sources, without which no research in discharge physics
`would be possible. The concept of a plasma was introduced by I. Langmuir and
`L. Tonks in 1928. Langmuir made many important contributions to the physics
`of gas discharge, including probe techniques of plasma diagnostics.
`As regards different frequency ranges, the development of field generators
`and the research into the discharges they produce followed the order of increasing
`frequencies. Radio frequency (rf) discharges were observed by N. Tesla in 1891.
`This kind of discharge is easily produced if an evacuated vessel is placed inside
`a solenoid coil to which high-frequency voltage is applied. The electric field
`induced by the oscillating magnetic field produces breakdown in the residual
`gas, and discharge is initiated. The understanding of the mechanism of discharge
`initiation came much latter, in fact, after the work of U. Thomson in 1926—1927.
`Inductively coupled rf discharges up to tens of kW in power were obtained by
`G.I. Babat in Leningrad around 1940.
`The progress in radar technology drew attention to phenomena in microwave
`fields. S.S. Brown in the USA began systematic studies of microwave discharges
`in the late 1940s. Discharges in the optical frequency range were realized after
`the advent of the laser: A spark flashed in air when the beam of a ruby laser
`producing so—called giant pulses (of more than IOMW in power) was focused
`by a lens, this success being achieved in 1963.
`Continuously bunting optical discharges, in which dense steady-state plasma
`
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`GILLETTE-1012 / Page 10 of 25
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`microwave and optical discharges have by now been studied with at least the
`same thoroughness that the discharges in constant electric fields has been during
`nearly 100 years of research.
`The physics of the glow discharge, one of the oldest and, presumably, best-
`studied fields, has lived through an unparallel revival in the past 15—20 years,
`and numerous new aspects of this phenomenon have been revealed. This surge
`of attention was stimulated by the use of glow discharges in electric—discharge
`C02 lasers developed for the needs of laser technologies. Likewise, the applica-
`tion of plasmatrons (generators of dense low—temperature plasma) to metallurgy,
`plasma chemistry, plasma welding and cutting, etc. provided a stimulus for new
`extensive, detailed studies of arc plasma at 1) ~ latm, T ~ 104 K, and of similar
`discharges in all frequency ranges. These, and many other practical applications
`of gas discharge physics place it within the range of sciences that lie at the
`foundation of modern engineering.
`
`1.5 Organization of the Book. Bibliography
`
`A long-standing tradition demands that a general—type book on gas discharges
`begin with a discussion of elementary processes: possible types of collisions of
`electrons and ions with atoms and molecules, the fundamentals of kinetic theory
`of gases, statistical physics, theory of radiation, and so forth. In this book, we
`mostly ignore these topics, Wishing to use to maximum effect the severely limited
`space; besides, these topics “are well represented in the literature, including some
`general textbooks. The reader is expected to have mastered a university general
`physics course, although some required information is cited in direct relation to
`processes to be studied.
`The book starts by describing the behaviour of charged particles of an ionized
`gas in constant and oscillating electric fields. Chapters 2 and 3 treat the behavior
`of electrons in a field in terms of elementary theory. Its essential feature is that
`the attention is focused on one “mean” electron. Averaged behaviour of one
`electron is considered, and when a quantity characterizing the electron gas as a
`whole is to be calculated, all electrons are assumed to have the same mean free
`time between collisions. Chapter 4 briefly discusses the processes of creation and
`removal of charges in a gas placed in the field. This is necessary for avoiding later
`on an infinite number of digressions while presenting discharge phenomena. As
`we remarked previously, here we spend little time on physical details of collision
`processes and reactions. In fact, we have tried to compile a large amount of data
`useful in discharge research. Chapter 5 elaborates a rigorous approach based on
`the kinetic equation, to the velocity and energy distribution functions. Chapter 6
`is devoted to the fundamental. probe method of studying gas discharge plasma.
`These chapters prepare the ground for the following eight chapters, which discuss
`systematically and in detail the discharges of various types in fields belonging
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`For reasons of restricted space, it was necessary to omit mentioning a large
`number of facts from discharge practice and discharge theory. Quite a few of them
`are discussed in available books, including the older ones. We will list several
`popular textbooks and general-type handbooks that treat a number of subjects
`of discharge physics and some elementary processes [Ll—1.10]. The Russian
`version of the present book [1.11] contains a modern treatise, dropped from
`the English edition, of collisions and radiation phenomena in plasmas, useful
`for discharge research. The kinetics and radiation of low-temperature plasmas
`(T N 104 K) are treated in [1.12,13]. A number of fields in the physics of
`discharges are represented in recent volumes of collected papers [1.14,15], in
`which each chapter was written by an appropriate specialist. The data book on
`electron collisions [1.16] is very useful in discharge work. The list of references
`to each chapter of the book cites monographs on elementary processes and on
`various types of discharge.
`The book leaves out all aspects of discharges and plasma behavior in mag-
`netic fields. This is also caused by sh