Arc Physics

311 Pages·1968·8.835 MB·English

by  Max F. Hoyaux (auth.)

Volume 8
APPLIED PHYSICS AND ENGINEERING
An International Series
Arc Physics
Arc Physics
Max F. Hoyaux
Associate Professor, University of Pittsburgh
Consultant, Westinghouse Electric Corporation
Adjunct Professor, Carnegie-Mellon University
Pittsburgh, Pa.
SPRINGER-VERLAG NEW YORK INC. 1968
ISBN 978-3-642-85654-9 ISBN 978-3-642-85652-5 (eBook)
DOl 10.1007/978-3-642-85652-5
All rights reserved.
No part of this book may be translated
or reproduced in any form without
written permission from Springer-Verlag.
© 1968 by Springer-Verlag New York Inc.
Softcover reprint of the hardcover 1st edition 1968
Library of Congress Catalog Card Number 68-24015
Title Number 3898
The scientific world owes the existence of this book
TO MY WIFE
Her kindness, love and understanding made it possible
Her rate of expense made it mandatory,
Preface
On first acquaintance the electric arc discharge appears to be both
visually attractive and a relatively simple phenomena to understand. To
those of us engaged in prolonged study of this discharge, it remains a
constantly exciting phenomena but we become only too aware of its complex
nature and the difficulties in interpreting its bulk properties. This is particu
larly true when the arc exists in a practical device and is subjected therefore
to extreme conditions.
In recent years the possibilities for the beginning of a fuller understanding
of the complexities of the arc has arisen out of the excellent research and
development work of scientists and engineers throughout the world. Much
of this work has been stimulated not only by the need for the development
of practical devices but also by the interest in thermonuclear fusion, mag
netohydrodynamic generation and space exploration. In much of this work,
the arc discharge has been a common feature as a source of study of high
temperature plasma. As a result of this increased interest in the arc, the
expert and would-be expert is now faced with the problem of assessing
extensive newly published information on arc properties. Thus there is the
need for texts which present to the engineer and researcher a review and
summary of the present situation. This book is a valuable contribution to
this task.
Professor Hoyaux, whose own research has contributed much to our
knowledge and understanding of arc discharges, has achieved success in
presenting the present state of arc physics by his concise, clear and stimulating
review of the subject. This is a book which will be of value to students and
experts alike. It will encourage those who are deterred by the complexities
of arc phenomena and satisfy those who are engrossed in the subject.
Liverpool, England March 1968 H. EDELS
vii
Foreword
This is an introduction, on the elementary level, to the theory of the
electric arc.
The simplest theoretical models are described, both for the high-and low
pressure arc, in order of increasing difficulty. Indications are given about
how to pursue the study towards higher degrees of sophistication. It should
never be forgotten that the physics of the electric arc is tremendously
complicated and that many simplified pictures are hardly more than "neces
sary evils."
The general properties of the plasmas and electric discharges are not
recalled here; the reader who has an insufficient knowledge of such topics
should first consult a book such as S. C. Brown, Basic Data in Plasma
Physics (M.I.T., 1959) or A. von Engel,IonizedGases, 2nd ed. (Oxford, 1965).
Some knowledge of the dynamics of charge carriers is also necessary. The
treatment by W. P. Allis, Motions of Ions and Electrons, in the 1956 edition
of the Handbuch der Physik (Springer, Berlin) is excellent, although slightly
above the requirements of arc physics. Descriptions of arcs and industrial
applications are not given here. The reader may consult, for instance,
J. D. Cobine, Gaseous Conductors (McGraw-Hill, 1941) and many others.
This author does not believe in extended bibliographies, which have be
come a sport for some writers. The bibliographies given here include only
recent or basic contributions and outstanding reviews. But the reader
interested in further digging will find indications of where such ev,:tended
bibliographies may be found.
This book aims at actual problem solving rather than developing attrac
tive mathematical theories; as such, it is expected to be controversial in some
respects. For instance, some good spirits will criticize the complete dropping
of second order magnetic effects (influence of particle path curvature, tensor
character of the mobility). The author knows how fashionable they are now
adays among plasma physicists, but, after 27 years of experience in the
industrial applications of arc physics, he is still waiting for the first case of
practical interest where they are anything but a useless source of mathe
matical complications. Besides, their rigorous introduction in ambipolar
viii
Foreword ix
phenomena is subjected to unsuspected difficulties. Similarly, he has the
greatest admiration for the modern sheath theories, but he is still waiting
for his first case of quiescent sheath in an industrial or semi-industrial device.
Eventually, the chapter devoted to post-arc phenomena, introducing the
plasma collective phenomena in highly simplified models, will probably be a
fiery object of discussion.
We hope however that this book will appeal to all those involved in prob
lems of arc physics and technology, both on the industrial and the scientific
level, without being really experts (as yet) in the subject.
Acknowledgements: the author wishes to acknowledge direct and indirect
contributions by a number of people. First of all, he owes to Professor
Richard L. Longini, of the Carnegie-Mellon University, the authorization
to disclose a hitherto unpublished model of the cathodic spot, object of many
fruitful discussions during the years 1967 and 1968. He wants also to thank
Professor Harry Edels, of the University of Liverpool, England, and his
colleagues of the Westinghouse Research and Development Center, namely
Drs Emmerich, Frost, Lowke, Swanson, Kimblin, Orville, Ludwig, Jen,
Wutzke and many others, for minor, but appreciated, contributions to this
book. His appreciation goes also to his old master, Professor Rene Ledrus,
the first man who taught him arc physics more than 25 years ago, and to the
typists, Miss Lois Blair, of the Westinghouse Research and Development
Center, and Miss Claudia Schumann, of the Carnegie-Mellon University,
who typed the pre-print from which this book was made.
M.H.
Contents
Preface v
Foreword viii
Chapter 1. Introduction. 1
Chapter 2. The Arc as Part of an Electric Circuit. 13
[2-1] Ignition of an Arc . 13
[2-2] Maintenance of the Arc 18
[2-3] Maintenance of the Cathodic Spot 20
[2-4] Arcs in Parallel . 20
[2-5] Extinction of the Arc . 21
[2-6] Reignition of the Arc . 23
[2-7] Hysteresis Phenomena in the Arc. 24
[2-8] The Electric Arc in A-C 26
[2-9] Rectification. 26
PART I:. THEORY OF THE POSITIVE COLUMN
Introductory Remarks 31
Chapter 3. The Cylindrical Indefinite Positive Column in a
Fixed Neutral Gas. 33
[3-1] High-Pressure Arc . 33
[3-2] Low-Pressure Arc . 67
Chapter 4. General Theory of the Arc Plasma. 98
[4-1] Low-Pressure Arc of Non-Cylindrical Shape 105
[4-2] High-Pressure Arc of Non-Cylindrical Form in a Fixed Gas 118
xii Arc Physics
[4-3] General Theory of the High-Pressure Arc Plasma. 130
Appendix-Note Concerning the Thermodiffusion Coefficient 146
PART II: WALL AND ELECTRODE PHENOMENA
Introduction. 151
Chapter 5. Wall Phenomena. 154
[5-1] Ambipolar Diffusion to a Wall 154
[5-2] Bohm's CJ;iterion of Sheath Formation 158
Chapter 6. Anodic Phenomena . 162
[6-1] Convergence of the Lines of Current towards the Anode 163
[6-2] Local Reduction in the Plasma Conductivity . 167
[6-3] Difference between Primitive Field and Actual One 169
[6-4] Anodic Sheath Phenomena 169
[6-5] Anodic Spots 171
[6-6] Hash Phenomena in the Anodic Region. 172
Appendix - Anodic Erosion Phenomena 175
Chapter 7. Cathodic Phenomena. 178
[7-1] The Contracted Column in the Cathodic Region 180
[7-2] Cathodic Sheath Phenomena. 181
[7-3] The Mechanism of Cathodic Emission 186
[7-4] Division of the Cathodic Spot 195
[7-5] Motions of the Cathodic Spot 196
Appendix-Cathodic Erosion Phenomena. 198
Chapter 8. Post Arc Phenomena. 202
[8-1] Decay of the Mterglow Plasma 204
[8-2] Influence of a Voltage Drop Across the Gap 208
[8-3] Influence of Secondary Emission. 217
[8-4] Conditions of Reignition . 222
Contents xiii
PART III: METHODS OF PLASMA DIAGNOSTICS
RELEVANT TO ARC PHYSICS
Introductory Remarks . 227
Chapter 9. Diagnostic Techniques Wideley Used in Arc
Physics 229
[9-1] Optical Methods 229
[9-2] Spectroscopic Methods. 237
[9-3] Electric Probes . 254
Chapter 10. Rapid Survey of the Other Methods of Plasma
Diagnostics . 267
[10-1] Magnetic Probes 267
[10-2] Microwave Techniques 269
[10-3] Miscellaneous Techniques 275
Appendix A. The Langmuir Paradox 281
Appendix B. Steen beck's Minimum Principle. 299