Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Experimental investigations of plasmas in electromagnetic shock tubes Simpkinson, William Vaughan 1964

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1964_A1 S5.pdf [ 4.11MB ]
Metadata
JSON: 831-1.0085398.json
JSON-LD: 831-1.0085398-ld.json
RDF/XML (Pretty): 831-1.0085398-rdf.xml
RDF/JSON: 831-1.0085398-rdf.json
Turtle: 831-1.0085398-turtle.txt
N-Triples: 831-1.0085398-rdf-ntriples.txt
Original Record: 831-1.0085398-source.json
Full Text
831-1.0085398-fulltext.txt
Citation
831-1.0085398.ris

Full Text

EXPERIMENTAL INVESTIGATIONS OF PLASMAS IN ELECTROMAGNETIC SHOCK TUBES  by  WILLIAM VAUGHAN SIMPKINSON B.A.Sc,  U n i v e r s i t y o f B r i t i s h Columbia, 1 9 5 7  M.A.Sc., U n i v e r s i t y o f B r i t i s h Columbia, 196,1  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE. REQUIREMENTS FOR THE DEGREE OF  Ph. D •  i n the Department of  Physics  We accept t h i s t h e s i s as conforming t o the required  standard  THE UNIVERSITY OF BRITISH COLUMBIA August, 196*+  In presenting this thesis i n p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library shall make i t available for reference and study*  freely  I further agree that per-  mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It i s understood that copying or publi-  cation of this thesis for financial gain shall not be allowed without my written permission*  Department of The University of B r i t i s h Columbia, Vancouver 8, Canada Date  The U n i v e r s i t y  of B r i t i s h  Columbia  FACULTY OF GRADUATE STUDIES  PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  of WILLIAM VAUGHAN SIMPKINSON' B.A.Sc,  The U n i v e r s i t y  of B r i t i s h . Columbia, 1957  M.A.Sc..,  The U n i v e r s i t y  of B r i t i s h Columbia, 1.961  FRIDAY, AUGUST 28th, 1964, AT 10.00 A.M. IN ROOM 303, HENNINGS BUILDING (PHYSICS)  COMMITTEE IN.CHARGE Chairman?  I . McT. Cowan  B. A h l b o r n  R. F. S n i d e r  A. J . Barnard  L . G. de S o b r i n o  F. L . Curzon  T. Watanabe  External  Examiner;  Department University  R o W. N i c h o l l s  of P h y s i c s ,  of Western  Ontario  EXPERIMENTAL INVESTIGATIONS OF PLASMAS IN ELECTROMAGNETIC SHOCK TUBES ABSTRACT The plasmas produced i n e l e c t r o m a g n e t i c shock tubes have p r e v i o u s l y been s t u d i e d i n t h i s l a b o r a t o r y and elsewhere., In g e n e r a l the temperatures and e l e c t r o n d e n s i t i e s deduced from time"-resolved s p e c t r a e m i t t e d by the plasma do not agree w i t h the v a l u e s c a l c u l a t e d from shock t h e o r y . Photographs taken w i t h a K e r r c e l l s h u t t e r r e v e a l e d t h a t luminous d i s c h a r g e gases w i t h a v e r y i r r e g u l a r f r o n t were d r i v e n down the tube and t h a t no s e p a r a t e shock front: c o u l d be seen ahead. The plasma behind the luminous f r o n t c o n s i s t e d of a m i x t u r e of rest: gas and a c o n s i d e r a b l e amount (~50%) of i m p u r i t y from the d r i v i n g d i s c h a r g e . In the work r e p o r t e d here, f u r t h e r attempts were made to produce shock, heated .plasmas. - V a r i o u s e l e c t r o d e c o n f i g u r a t i o n s were t r i e d but no improvement was observed. Some measure of success was a t t a i n e d w i t h an e l e c t r o d e l e s s d r i v e r on the shock tube. K e r r c e l l photographs showed t h a t w i t h argon i n the tube a shock wave appeared to be formed ahead of the d i s c h a r g e plasma. The shock speed was much slower than the speed of the advancing luminous front, i n the tubes w i t h e l e c t r o d e s . However, no shock wave c o u l d be observed with helium. With argon i n the e l e c t r o d e l e s s tube r a d i a t i o n c o u l d be observed from t h e gas ahead of the shock, wave. Time r e s o l v e d s p e c t r o s c o p i c measurements on t h i s r a d i a t i o n a l l o w e d rough d e t e r m i n a t i o n of e l e c t r o n d e n s i t y and of the p o p u l a t i o n of e x c i t e d s t a t e s of argon atoms and ions ahead of the shock f r o n t . This " p r e h e a t i n g " of the gas i s presumably due t o u l t r a v i o l e t , l i g h t : e m i t t e d from the d i s c h a r g e and the shock plasma. The v a l u e s of e l e c t r o n d e n s i t y and temperature expected behind the shock front; were c a l c u l a t e d from shock t h e o r y , t a k i n g i n t o account: the p r e h e a t i n g of the gas. The expected v a l u e s agreed w e l l w i t h the e l e c t r o n d e n s i t y and temperature determined from s p e c t r o s c o p i c measurements on the shock plaetpa.  The study of the precursor radiation was continued in a shock tube with, electrodes. In this tube the driving discharge was more luminous and the excitation and ionization of helium and argon ahead of the luminous front: could be more readily observed than with the electrodeless tube. The number densities of helium atoms in various excited states were determined from the time resolved line intensities before and after the passage of the luminous front. The ratios of atoms in different: levels differ from the expected ratios for thermal equilibrium conditions-, both ahead of the luminous front: and behind i t . An estimate was made of the time required for the attainment: of equilibrium by electron impact. The calculation indicates that ahead of the luminous front, there is not sufficient time to attain equilibrium. On the other hand., for the high electron density found behind the luminous front, the equilibrium distribution is expected to be reached in times shorter than the observation times,, in disagreement with the behaviour observed.  GRADUATE STUDIES Field  of Study:  Physics  Elementary Quantum Mechanics Waves E l e c t r o m a g n e t i c Theory Nuclear Physics Spectroscopy E l e c t r o n Dynamics Plasma P h y s i c s Advanced Plasma P h y s i c s  W. Opechowf J . C. Sava^ G. M. Volkr J . B, Warr A. M, Croc R. E, Burg, L. G. de Sobrj F. L. Cur  Related Studies: High Speed Gas Dynamics D i g i t a l Computer Programming D i f f e r e n t i a l , Equations E l e c t r o n i c Instrumentation T r a n s p o r t P r o p e r t i e s of Gases  G. V. P a r k i Charlotte Fr C. A, Swanc F. K. Bo R. F. Sn  PUBLICATION, S p e c t r o s c o p i c S t u d i e s of Helium and Argon Plasmas produced by E l e c t r o m a g n e t i c a l l y D r i v e n Shock Wav, Can. J . of Phys. 4 0 , 531 (1962).  ii  ABSTRACT The plasmas produced i n e l e c t r o m a g n e t i c shock tubes have p r e v i o u s l y been s t u d i e d i n t h i s l a b o r a t o r y and elsewhere.  I n g e n e r a l the temperatures and e l e c t r o n  d e n s i t i e s deduced the  from t i m e - r e s o l v e d s p e c t r a emitted by  plasma do not agree w i t h the values c a l c u l a t e d  shock t h e o r y .  Photographs taken w i t h a K e r r c e l l  from shutter  r e v e a l e d t h a t luminous d i s c h a r g e gases w i t h a v e r y i r r e g u l a r f r o n t were d r i v e n down the tube and t h a t no separate shock f r o n t could be seen ahead.  The plasma  behind the luminous f r o n t c o n s i s t e d of a mixture o f r e s t gas and a c o n s i d e r a b l e amount  ^50%) o f i m p u r i t y from the  driving discharge. In  the work r e p o r t e d h e r e , f u r t h e r  attempts were made t o produce shock heated V a r i o u s e l e c t r o d e c o n f i g u r a t i o n s were t r i e d provement was observed.  plasmas. but no im-  Some measure o f success was  a t t a i n e d w i t h an e l e c t r o d e l e s s d r i v e r on the s h o c k tube. K e r r c e l l photographs showed t h a t w i t h argon i n the tube a shock wave appeared t o be formed plasma. of  ahead o f the d i s c h a r g e  The shock speed was much slower than the speed  the advancing luminous f r o n t i n the tubes w i t h e l e c t r o d e s .  However, no shock wave could be observed w i t h h e l i u m . With argon i n the e l e c t r o d e l e s s tube r a d i a t i o n could be observed from the gas ahead o f the shock  iii  wave.  Time r e s o l v e d s p e c t r o s c o p i c measurements on t h i s  r a d i a t i o n allowed rough d e t e r m i n a t i o n of e l e c t r o n d e n s i t y and of the p o p u l a t i o n of e x c i t e d s t a t e s o f argon atoms and ions ahead o f the shock f r o n t .  T h i s " p r e h e a t i n g " o f the  gas i s presumably due t o u l t r a v i o l e t  l i g h t emitted from  the d i s c h a r g e and the shock plasma.  The v a l u e s o f e l e c t r o n  d e n s i t y and temperature expected behind the shock f r o n t were c a l c u l a t e d from shock t h e o r y , t a k i n g i n t o account the p r e h e a t i n g o f the gas.  The expected values agreed w e l l  w i t h the e l e c t r o n d e n s i t y and temperature determined s p e c t r o s c o p i c measurements on the shock  from  plasma.  The study o f the p r e c u r s o r r a d i a t i o n was continued  i n a shock tube w i t h e l e c t r o d e s .  I n t h i s tube  the d r i v i n g d i s c h a r g e was more luminous and the e x c i t a t i o n and i o n i z a t i o n o f helium and argon ahead  o f the luminous  f r o n t could be more r e a d i l y observed than w i t h the e l e c t r o d e l e s s tube.  The number d e n s i t i e s o f h e l i u m atoms  i n v a r i o u s e x c i t e d s t a t e s were determined from t h e time r e s o l v e d l i n e i n t e n s i t i e s b e f o r e and a f t e r the passage of the luminous f r o n t .  The r a t i o s o f atoms i n d i f f e r e n t  l e v e l s d i f f e r from the expected r a t i o s f o r thermal e q u i l i b rium c o n d i t i o n s , both ahead it.  of the luminous f r o n t and behind  An e s t i m a t e was made o f the time r e q u i r e d f o r the  attainment o f e q u i l i b r i u m by e l e c t r o n impact. c a l c u l a t i o n i n d i c a t e s t h a t ahead  The  of t h e luminous  front  t h e r e i s not s u f f i c i e n t time t o a t t a i n e q u i l i b r i u m .  On  iv  the other hand, for the high electron density found behind the luminous f r o n t , the equilibrium d i s t r i b u t i o n is expected to be reached in times shorter than the observation times, observed.  i n disagreement with the behavior  V TABLE OF CONTENTS PAGE Abstract  . . . . . . . . . .  i i  Table o f C o n t e n t s . .  v  Index o f T a b l e s  v i i  Index o f F i g u r e s  viii  A cknow led gme nt s  ix  CHAPTER I. II.  INTRODUCTION. . . . . . . . . . . .  1  THEORY  7  S p e c t r o s c o p i c Theory  7  (a) S t a r k Broadening o f Hydrogen L i n e s . . .  7  (b) Temperature D e t e r m i n a t i o n from Spectral Intensity. . . . . . . . . .  8  Shock Theory. III.  .  15  APPARATUS  S p e c t r o s c o p i c Equipment  . . . . . . . . . .  E l e c t r o n i c A n c i l l i a r y Equipment  . . . . . .  High Speed Photographic Equipment IV.  10  . . . . .  18 20 20 22  EXPERIMENTAL INVESTIGATION Preliminary Investigation . . . . . . . . .  22  E l e c t r o d e l e s s Shock Tube w i t h Argon . , . .  2h  ' (a) Magnetic Probe Measurements (b) Photographic Measurements  . . . . . .  2h  . . . . . . .  25  (c) S p e c t r o s c o p i c Measurements.  . . . . . .  27  vi TABLE OF CONTENTS  (cont'd)  CHAPTER  PAGE  IV. (cont'd) E l e c t r o d e l e s s Shock D r i v e r With Helium . . .  3^  Observations o f P r e c u r s o r R a d i a t i o n With a Co-planar D r i v e r  .  36  (a) Argon (b) Helium V.  3>h  *fl  DISCUSSION AND CONCLUSIONS.  k?  Nature o f Luminous Plasma  h7  Precursor I o n i z a t i o n  h$  Attainment o f E q u i l i b r i u m i n Plasma 51  Investigated  55  C o n c l u d i n g Remarks APPENDIX I.  II.  THEORETICAL LINE STRENGTHS  56  Argon L i n e Strengths..  56  Carbon L i n e S t r e n g t h s  . . . . .  58  Helium L i n e S t r e n g t h s  . . . . . . . . . . .  58  DETERMINATION OF MONOCHROMATOR SPECTRAL SENSITIVITY  III.  . . . . . . . . . . .  59  ROUGH SPECTROSCOPIC ANALYSIS OF CARBON CONTENT OF PLASMA IN SHOCK TUBES WITH AND WITHOUT ELECTRODES  IV.  65  CORRECTION OF MEASURED SPECTRAL LINE PROFILES FOR INSTRUMENTAL BROADENING. . . .  BIBLIOGRAPHY  67 70  VII  INDEX OF TABLES NO. 1.  PAGE k T and N for v e  e  g  = 0.6cm^(sec i n Argon i n  Electrodeless Shock Tube 2.  k T and N for v  s  3.  12 cm k T and N for v  s  e  e  e  e  = l,6cm//Asec  33 i n Argon at  = 1.31cm^/sec i n Argon at  17 cm from Arc  ^1  h. k T and N for Helium at 17 cm from Arc . . . . e  5.  e  (A) Ratios of N at Various Times i n Helium with P =0.1 mmHg. (B) Ratios of N at Various Times i n Helium 0 m  o  5.  o m  with p =0.3 mmHg. o  ^6  6.  Ratios of Carbon to Argon i n Plasmas  66  7.  Standard Voigt P r o f i l e s  69  viii INDEX OF FIGURES NO.  PAGE  1.  One  2.  Schematic of Shock Tube With E l e c t r o d e s  3.  Driver Electrode Configurations  17  h.  Schematic of E l e c t r o d e l e s s Shock Tube . . . . .  19  5.  Electrodeless Driver  19  6.  E l e c t r o d e l e s s D r i v e r C o i l Current  2k  7.  Photographs o f D i s c h a r g e Development i n E l e c t r o d e l e s s Shock Tube w i t h Argon and Helium  26  I n t e n s i t y H i s t o r i e s o f A l , A l l , and H L i n e s Tube With E l e c t r o d e l e s s D r i v e r .  30  8. 9.  D i m e n s i o n a l Shock Waves  10 . . . .  16  in  I n t e n s i t y H i s t o r i e s of A l , A l l , A I I I L i n e s Tube With Co-planar D r i v e r at 12 cm  in 37  10.  Precursor  S i g n a l s from P r o f i l e s of H ^ L i n e . . .  38  11.  P r e c u r s o r I n t e n s i t y H i s t o r i e s of A l l and A I I I L i n e s i n Tube w i t h Co-planar D r i v e r at 17cm .  *f0  12.  P r e c u r s o r I n t e n s i t y H i s t o r i e s of H e l H e l M+71A° and H e l 3888A  5876A ,  Precursor  5016A ,  0  h2  0  13.  I n t e n s i t y H i s t o r i e s of H e l  0  H e l M-922AO, and H e l l U686A°  ^3  Ih.  Apparatus f o r C a l i b r a t i n g Monochromators. . . .  59  15.  S e n s i t i v i t y of J a r r e l - A s h Monochromator w i t h P h i l l i p s 150 CVP P h o t o m u l t i p l i e r S e n s i t i v i t y of J a r r e l - A s h Monochromator w i t h RCA IP 28 P h o t o m u l t i p l i e r  62  16. 17.  S e n s i t i v i t y M u l t i p l i e r f o r IP 28 P h o t o m u l t i p l i e r w i t h Various Supply V o l t a g e s . . . . . . . . .  63 6If  ix ACKNOWLEDGMENTS  I am indebted to D r . A. J . Barnard for his d i r e c t i o n , enthusiastic  interest  and invaluable assistance.  The author is grateful to D r . G. D. Cormack and Mr. C. R. Neufeld who, i n the course of t h e i r own research, designed and constructed much of the apparatus used i n this work. I would l i k e to thank those responsible for administering the President's Research Fund for the f i n a n c i a l assistance given me.  Thanks are also due the  B r i t i s h Columbia Telephone Company for a scholarship awarded me for the year 1962-63.  CHAPTER I INTRODUCTION Much work has been done i n r e c e n t years on plasmas  formed  i n e l e c t r o m a g n e t i c shock t u b e s .  experiments e l e c t r i c a l energy i s stored  In these  i n a charged  capa-  c i t o r bank and r e l e a s e d t o form a d i s c h a r g e i n the shock tube. The c a p a c i t o r bank may be d i s c h a r g e d d i r e c t l y  i n t o the tube  by means of e l e c t r o d e s o f v a r i o u s c o n f i g u r a t i o n s . n a t i v e l y , an e l e c t r o d e l e s s arrangement  Alter-  may be used; the  c a p a c i t o r bank i s switched through one or more c o i l s the tube, i n d u c i n g a d i s c h a r g e i n the shock tube.  outside  The  highly  luminous d i s c h a r g e i s d r i v e n down the tube as a r e s u l t o f e l e c t r o m a g n e t i c f o r c e s and/or from the a c t u a l h e a t i n g o f the gas.  Many workers  (such as McLean et a l (I960), B a r n a r d ,  Cormack, and Simpkinson  (1962)) have conducted  spectroscopic  i n v e s t i g a t i o n s on the plasma behind the advancing  luminous  f r o n t . I n these i n v e s t i g a t i o n s the e l e c t r o n d e n s i t y has been determined from s p e c t r a l l i n e b r o a d e n i n g , and the e l e c t r o n temperature from the r e l a t i v e i n t e n s i t y o f v a r i o u s lines.  spectral  The a c c u r a t e d e t e r m i n a t i o n of e l e c t r o n temperature by  t h i s method r e q u i r e s e q u i l i b r i u m between the e l e c t r o n s and the e x c i t e d atomic and i o n i c s t a t e s .  The  spectroscopically  determined v a l u e s o f the above q u a n t i t i e s were found t o be i n poor agreement w i t h values c a l c u l a t e d t h e o r e t i c a l l y by t r e a t i n g the advancing luminous f r o n t as a shock wave.  -1-  -2Subsequent t o the above work at t h i s  laboratory  f a s t s h u t t e r photographic s t u d i e s of the development of the "shock wave" i n e l e c t r o m a g n e t i c shock tubes were c a r r i e d (Barnard and Cormack, (1963)).  out  These were done f o r many d i f f e r -  ent c o n f i g u r a t i o n s of d r i v i n g e l e c t r o d e s and showed t h a t the shape of the advancing luminous  f r o n t at p o s i t i o n s f a r down  the shock tube bore a r e l a t i o n s h i p t o the shape of the a r c which i n i t i a l l y developed driver section.  between the e l e c t r o d e s i n the  Thus, the luminous  f r o n t d i d not appear t o  be a shock wave but seemed t o be the boundary between a r c heated  gas advancing down the tube and the c o l d r e s t  gas  i n i t i a l l y i n the tube. A more d e t a i l e d e l e c t r o m a g n e t i c shock tubes was t h e o r y used  i n v e s t i g a t i o n of plasmas i n t h e r e f o r e undertaken.  i n t h i s work w i l l be found  i n Chapter I I .  The The  t h e o r y i s on the whole w e l l known and i s o n l y b r i e f l y outlined.  Relevant equations are quoted  from the t h e o r y o f  S t a r k broadening and of e l e c t r o n temperature d e t e r m i n a t i o n from s p e c t r a l l i n e i n t e n s i t i e s . h e a t i n g was  developed  The  standard t h e o r y of  shock  i n a convenient form f o r the case of a  shock propagating i n t o a gas which i s p r e - i o n i z e d t o a s m a l l extent. Chapter I I I d i s c u s s e s the arrangement o f the apparatus employed.  The o p t i c a l , s p e c t r o s c o p i c , and  e l e c t r o n i c equipment are standard items.  V a r i o u s shock  tube  -3d r i v i n g e l e c t r o d e c o n f i g u r a t i o n s are shown, one o f which has been used p r e v i o u s l y (Neufeld (1963)), w h i l e t h e other two were made f o r these experiments.  A l s o shown i s a simple  e l e c t r o d e l e s s d r i v e r designed by the author. The e x p e r i m e n t a l work done i s presented i n Chapter IV.  The work began w i t h a r o u g h  spectroscopic  d e t e r m i n a t i o n o f t h e i m p u r i t y content o f t h e plasma i n t h e tube used by Neufeld (1963).  generated  Carbon was chosen as a  r e p r e s e n t a t i v e i m p u r i t y and the s t r e n g t h o f a carbon l i n e was compared w i t h t h a t o f a l i n e from t h e r e s t gas. T h i s a n a l y s i s shows t h e carbon content o f t h e plasma t o be g r e a t e r than 35%* tried not  Two other d r i v e r e l e c t r o d e c o n f i g u r a t i o n s were  i n an attempt t o reduce the i m p u r i t y c o n t e n t .  T h i s was  s u c c e s s f u l so an e l e c t r o d e l e s s shock tube was b u i l t t o  e l i m i n a t e e l e c t r o d e s and i n s u l a t i n g m a t e r i a l from the i n s i d e of the tube. The second s e c t i o n o f Chapter IV d e a l s w i t h i n v e s t i g a t i o n s c a r r i e d out on t h e e l e c t r o d e l e s s shock tube. Current t r a c e s are presented showing  the two waveforms used  i n the d r i v i n g c o i l current*, i n one o f these the c a p a c i t o r bank i s shorted c a t such a time t h a t o n l y two d i s c h a r g e pulses flow w i t h i n the tube.  Next, photographs  through a K e r r c e l l s h u t t e r are shown. development the  These  o f the d i s c h a r g e , i t s subsequent  tube, and t h e e f f e c t s o f a magnetic  field  taken  i n d i c a t e the t r a v e l down "shaper" put  near the d r i v e r and o f short c i r c u i t i n g the c a p a c i t o r bank at the above time. The photographs r e v e a l that under  certain  experimental c o n d i t i o n s , i . e . w i t h argon i n the tube and s h o r t i n g t h e bank a f t e r two c u r r e n t p u l s e s , a shock f r o n t appears t o advance  ahead  o f the a r c heated gases.  The second s e c t i o n o f Chapter IV continues w i t h an account o f t h e s p e c t r o s c o p i c measurements made o f the i m p u r i t y (carbon) c o n t e n t , e l e c t r o n d e n s i t y , and temperature o f the argon plasma behind t h e suspected shock front.  The carbon content o f t h e d i s c h a r g e i n t h i s tube i s  shown t o be o f the order o f 6%.  A l s o r e p o r t e d a r e rough  s p e c t r o s c o p i c d e t e r m i n a t i o n s o f e l e c t r o n d e n s i t y and temperature made from the l i g h t found t o be coming the plane luminous f r o n t .  from t h e gas ahead o f  I n t e n s i t y h i s t o r i e s o f argon atomic  and i o n i c l i n e s and o f hydrogen l i n e s are presented i n which t h i s " p r e c u r s o r " r a d i a t i o n i s compared w i t h t h a t from a f t e r the luminous f r o n t .  The r e s u l t s o f t h e spectroscopic;measurements  on argon are then compared w i t h the t h e o r y f o r a shock wave moving i n t o a "preheated" gas and good agreement was found. The p r e s e n t a t i o n o f work on t h e e l e c t r o d e l e s s tube c l o s e s w i t h a b r i e f r e p o r t on the r e s u l t s obtained w i t h helium i n the tube.  Photographs  are shown which i n d i c a t e a  much more i r r e g u l a r shaped d i s c h a r g e than i n the case of argon. Some s p e c t r o s c o p i c measurements are i n c l u d e d .  -5The f i n a l s e c t i o n o f Chapter IV d e a l s w i t h s t u d i e s o f the p r e c u r s o r r a d i a t i o n c a r r i e d out u s i n g t h e shock tube w i t h co-planar e l e c t r o d e s .  Intensity histories f o r  s p e c t r a l l i n e s from argon atoms, f i r s t and from hydrogen measurements.  stage ions  are shown from the r e s u l t s o f these  Somewhat more e x t e n s i v e measurements are  presented f o r helium because are  and second  more o f i t s atomic  parameters  known than f o r argon, and i t was b e l i e v e d some  comparisons  could be made between the o b s e r v a t i o n s and t h e o r e t i c a l  cal-  c u l a t i o n s o f times f o r a helium plasma t o r e a c h e q u i l i b r i u m . Chapter IV c l o s e s w i t h a s e t o f t a b l e s o f r a t i o s of p o p u l a t i o n of  certain excited  s t a t e s o f n e u t r a l helium at v a r i o u s times  a f t e r the i n i t i a t i o n  o f the d r i v i n g d i s c h a r g e .  These t a b l e s  c o n t a i n f o r each r a t i o the v a l u e which would be expected at equilibrium.  Even behind t h e luminous  f r o n t t h e observed  r a t i o s depart c o n s i d e r a b l y from the expected v a l u e s .  It i s  f e l t t h a t t h e c a r e f u l study o f the p r e c u r s o r i o n i z a t i o n i s the most s i g n i f i c a n t (McLean  (1961))  c o n t r i b u t i o n of t h i s research.  Other workers  have observed t h i s p r e c u r s o r r a d i a t i o n but t o  the author's knowledge no measurements as d e t a i l e d as those presented here have been  conducted.  The f i n a l chapter o f t h i s t h e s i s c o n t a i n s a d i s c u s s i o n o f the r e s u l t s .  An attempt  i s made t o show from  the r e s u l t s t h a t p h o t o - e x c i t a t i o n i s the dominant mechanism of  e x c i t a t i o n and i o n i z a t i o n ahead of the luminous  front.  Also  -6included  i n Chapter V i s a c a l c u l a t i o n of the time t o e s t a b l i s h  e x c i t a t i o n and  ionization equilibrium  t y p i c a l experimental c o n d i t i o n s .  T h i s i n d i c a t e s that  rium should p r e v a i l behind the luminous h e l p t o e x p l a i n the  by e l e c t r o n impact f o r equilib-  f r o n t and does not  anomalous behavior observed.  c l o s e s w i t h suggestions f o r f u t u r e work.  The  chapter  CHAPTER I I THEORY S p e c t r o s c o p i c Theory ( a ) S t a r k Broadening o f Hydrogen L i n e s Hydrogen l i n e broadening i s used i n these experiments as a measure o f e l e c t r o n d e n s i t y . present as an i m p u r i t y i n the plasmas  Hydrogen i s  studied.  I t can be  shown, t h a t a t the temperatures and d e n s i t i e s a t t a i n e d i n t h i s experiment, the S t a r k e f f e c t i s the dominant  broadening  mechanism f o r the broadening o f hydrogen s p e c t r a l l i n e s (see for  example the review a r t i c l e by R.G. Breene J r . (1957)).  G r i e n , K o l b , and Shen (1959) extended the Holtsmark  (1919)  t h e o r y and computed the p r o f i l e s o f Hydrogen l i n e s f o r d i f f e r e n t e l e c t r o n d e n s i t i e s and temperatures. the  By f i t t i n g  e x p e r i m e n t a l p r o f i l e o f a hydrogen l i n e emitted from a  plasma c o n t a i n i n g e l e c t r o n s , atoms, and s i n g l y charged  ions  one can thus determine the e l e c t r o n d e n s i t y , N . e  I f the plasma should have many stages o f i o n s present, an " e f f e c t i v e " charge d e n s i t y , N the  f i t t i n g o f the p r o f i l e .  e f f  , i s obtained from  (19*+3) one  F o l l o w i n g Chandrasekhar  finds  (1)  where the  N  e f f  = N  X  + 2  3 / 2  N  2  + 3^ N+ 3  ... = ^  i s the number d e n s i t y o f i - t h stage i o n s .  r a t i o s o f the  i / ! ^ 3  2  Provided  a r e known, the e l e c t r o n d e n s i t y may be  -8=  found from  (2)  N  = Hx + 2N  e  2  + 31*3 + ... =  iK;  (b)Temperature D e t e r m i n a t i o n from S p e c t r a l  Intensity  The e l e c t r o n temperature i n a plasma can be determined from the i n t e n s i t i e s o f s p e c t r a l l i n e s i n l i g h t emitted by the plasma provided t h a t thermal e q u i l i b r i u m prevails.  I n the t h e o r y t o be developed here i t w i l l  be  assumed t h a t the e l e c t r o n temperature i s equal t o the e x c i t a t i o n temperature though t h e r e i s some doubt whether t h i s assumption i s t r u e  i n the plasmas encountered i n t h i s work.  The e x c i t a t i o n temperature i s the temperature, T , e x  e x i s t s i f the p o p u l a t i o n s o f the e x c i t e d  which  s t a t e s o f the atoms  or ions i n the plasma are a l l p r o p o r t i o n a l t o Boltzmann f a c t o r s , g exp  TP  (- w ) , where E i s the energy o f the e x c i t e d ^ ex  s t a t e above the ground The c o n d i t i o n s electrons studied  s t a t e and g i t s s t a t i s t i c a l weight.  f o r e q u i l i b r i u m t o be a t t a i n e d  between  and e x c i t e d s t a t e s o f atoms and ions have been  by Griem  (1963).  The a b s o l u t e i n t e n s i t y o f a s p e c t r a l l i n e r e s u l t i n g from a t r a n s i t i o n between the energy l e v e l s E * and E*  o f an i - t h stage i o n i s g i v e n by (see f o r example Condon  and S h o r t l e y  (1935))  ,  (3)  N,(m)  I * _ = -V" m  '  n  g*  64 71^0  -^TT 3 XI  (m,n)  S^m.n)  -9-  where N^m) i s the density of the i - t h stage ions of energy E*,  g  Xj.(m,n) i s  i s the degeneracy of the energy state E * ,  m  the wavelength of the l i n e , c i s the speed of l i g h t , and SMmjn) i s the t h e o r e t i c a l l i n e strength of the t r a n s i t i o n E  m " n (m E  E  strengths  w  i  l  1  a  l  w  a  v  s  b  taken as the upper l e v e l ) .  e  The l i n e  for the helium and argon lines studied i n t h i s  experimental work are tabulated i n Appendix I . At the temperature T we have the following r e l a t i o n involving the N^Cm) and N,(m)  (if)  —i  g  N =  1  m  ±  (- -<2-)  tap  —f—  Z>  :  kT  where Z* is the p a r t i t i o n function for i - t h stage ions and k is the Boltzmann constant.  The r a t i o  of ions i n d i f f e r e n t  stages  of i o n i z a t i o n is given by the Saha equation, N  (5)  2  +JZ Z—7 1  t  N^Z.  +  =  1  2TTm kT e  ~~ (  N  o h  e  /2  3  )  exp (-  E  1  kT  d  ),  where m i s the mass of the electron, h i s Planck s constant J  e  and E  1  i s the i o n i z a t i o n energy of the i - t h stage i o n .  Combining equations  (3), (V), and ( 5 ) and inserting numerical  values we a r r i v e at the r e l a t i o n 1  (6) kT =  —  (  2.303 E ) (  3/ log kT+21.8 log 2  1 0  +  i  1 0  + Et (  ~ Ei)  1  " ±  +  ± \ h  where kT and other energy terms are i n electron  -^*fr > volts.  -10E q u a t i o n ( 6 ) , on s u b s t i t u t i o n o f the observed s p e c t r a l i n t e n s i t i e s and other parameters i s e a s i l y s o l v e d f o r kT by g r a p h i c a l or n u m e r i c a l means.  Shock Theory We w i l l c o n s i d e r here a s t r o n g , one d i m e n s i o n a l shock wave propagating w i t h v e l o c i t y v  s  i n t o a gas at r e s t .  F o l l o w i n g the n o t a t i o n on F i g u r e 1, the s u b s c r i p t q u a n t i t i e s b e f o r e the shock.  0  w i l l denote  The symbols p, T, U, N, N  denote r e s p e c t i v e l y p r e s s u r e , temperature,  e  and v  i n t e r n a l energy per  heavy p a r t i c l e , number d e n s i t y o f ions and atoms combined, e l e c t r o n d e n s i t y , and flow v e l o c i t y .  As we wish t o c o n s i d e r  F i g u r e 1 - One Dimensional Shock Wave  v =0 o  P »T ,U ,N  P,T,U,N  0  0  G  0  the e f f e c t s o f i o n i z a t i o n ahead o f the shock wave we w i l l not immediately p <£ c  invoke the s t r o n g shock approximation where  p and U<^C U and sp the equations f o r c o n s e r v a t i o n s o f mass, 0  linear  (7)  momentum, and energy are (a)  N v  (b)  p-p  (c)  pv = N v ( U - U +  D  = N ( v -v)  s  s  0  = mN v v 0  c  s  s  0  sy_)  -11-  where m Is the mass o f an atom or i o n ( n e g l e c t i n g From E q u a t i o n (7)  mass).  (b) and (c)  p v (U-U) - - ° — = ° oV  mv  Q  (8)  electron  N  2  2  s  To proceed processes o c c u r r i n g  f u r t h e r w i t h t h i s development the  behind the shock must be c o n s i d e r e d .  p r i n c i p a l processes i n t h i s r e g i o n are c o l l i s i o n a l and e x c i t a t i o n .  The  ionization  From the o v e r a l l charge n e u t r a l i t y o f the  plasma we may w r i t e  (9)  N  where  e  = N +2N X  denotes  2  + 3N  3  +  and «6 i s the degree  electrons  t o heavy p a r t i c l e s .  N  ..)=  = N(«C 1 +2«C S +  the f r a c t i o n o f i - t i m e s i o n i z e d  ( oC-_X^) 1  ...  N^U^C^ N«C  atoms  o f i o n i z a t i o n or r a t i o o f The values o f N  e  andoC ahead o f  the shock w i l l always be taken as known. Assuming thermal e q u i l i b r i u m electrons,  (ieT  = T ) , Equations  i o n  Q  (7)  between ions and  ( a ) , (b) and (8)  be supplemented w i t h the e q u a t i o n o f s t a t e  can  and the e q u a t i o n f o r  the i n t e r n a l energy of an i d e a l gas: (a) p = (1+cC) NkT  (10) (b) U = /2 (l+oC)kT + 3  where U Solving  i e  U  i e  i s the i o n i z a t i o n and the e x c i t a t i o n energy per i o n .  Equations  (7)  ( a ) , ( b ) , (8),  (9)  and (10)  for N  Q  -12 p  and v^ and i n t r o d u c i n g n u m e r i c a l v a l u e s , one f i n d s  e  N  (a) N = 0  *C  6  U, (•+(l+-<) + 2 —  - Uj 2 kT  )  (11) 1.92  ,  (b) v = ' s  M  -,  p  ?  <2(l+^)kT+(U -uf)) (1Z  0  )  2  le  "  ° p(N-NJ  °  2N N  2  —  3/2(l+«C)kT+(U -ub-  °  6  le  1 6  2(l+«£)NkT  0  Here M i s t h e atomic weight o f the r e s t gas, kT, U ^ , and e  are i n e l e c t r o n v o l t s , and  P  * t  0  i s a convenient a b b r e v i a t i o n f o r  _ , „  P (  rr  Y2m(U-U ) n  0  N  -  N  0)  D  ° mN s  '  v  0  In Equation  2N N C  (11) (b) o n l y the l i n e a r terms i n — ^ and NkT  have been r e t a i n e d .  The approximation  "Ms  2  2 p  0  «  i s valid i f  2 ((l+oC)NkT)  2 and p  Q  «  mN v n  q  ?  (—-~~),  iei f p  i s s m a l l com-  Q  pared w i t h t h e s t a t i c and dynamic pressures i n the flow  behind  the shock wave. F o r comparison w i t h the values o f kT and N  e  obtained from s p e c t r o s c o p i c measurements i t i s n e c e s s a r y t o express kT and N  e  i n terms o f the o b s e r v a b l e s , v  should be noted t h a t oC^_ and U^g a r e themselves kT and N . e  I n t h i s experiment  the temperature  s  and N „ I t 0  functions of i s o f the order  -13o f a few e l e c t r o n v o l t s and so the e x c i t a t i o n energy o f an i o n , g i v e n by:  ~7  E* =  g i n g  n  ET~ exp (- -*-) kT  i s s m a l l compared w i t h the i o n i z a t i o n energy. the e x c i t a t i o n e n e r g i e s , U^ the  e  Thus, n e g l e c t i n g  can be expressed i n terms o f  :  (12)  U  i e  = £jB?+  ^ (E°+E )+  +*^.(E +...+E " )+...  1  0  2  T  1  where E^" i s the i o n i z a t i o n energy of the . i - t h stage i o n . Assuming thermal e q u i l i b r i u m , the  are g i v e n by the Sana  equat ions  o £ , N (13) _ £ J ^ = — ~ = - ~Z— r  +  1  =  2  Z j  r  +  =  27ttn kT 3. —( ^ 1  -E  r  ( V) ^ exp ( ),  and by  (1*0  £<<^ = 1  o  To s o l v e E q u a t i o n s (11) and  (Ih)  ( a ) , ( b ) , (12),  (13),  f o r kT, N , and the oC^ a method o f s u c c e s s i v e e  approximations was adopted.  I t was found convenient t o r e w r i t e  -llf-  E q u a t i o n (11)  i n the form  (a) kT =  _  8(1+-C)  (15)  (b) N  where B, C, and M  e  =  ° 1+X  (*+(l+*C)+2  6  kT  °)  are g i v e n by  1  M  B = (^U  v  -I'Z—^  ie  f  9 M ^ 3  -  ( 1 + u  1  - lfoj)  1.92  1 6  c  1  8 (N-N )  2  Po  ie+ * i ^ -  - K  -  0  — i ^ r  }  M  (1-  -)  2(1+ oC)NkT  I n s e r t i n g estimated values f o r the P (N-N ) (15) w i t h IT" = U , - — — = kT ° NN x  o  0  2  i n Equations  (12) and  , and M = M gives a f i r s t  0  0  approximation t o kT and N . e  S u b s t i t u t i o n o f these  first  approximations i n Saha's e q u a t i o n y i e l d s b e t t e r values f o r the oC^,  T h i s process i s continued u n t i l s e l f c o n s i s t e n t values  of oC^ are o b t a i n e d , then the values o f kT, N, and U are i n s e r ted  1 i i n the equation: f o r U , M 0  x  and G and the process  repeated.  CHAPTER I I I 'APPARATUS  Shock Tubes Two shock tubes were used i n the e x p e r i m e n t a l work t o be d e s c r i b e d h e r e . q u a r t z t u b i n g , o f 2.5  Both tubes were o f g l a s s and  cm i n s i d e diameter, approximately 100 cm  l o n g , and could be f i t t e d w i t h v a r i o u s e l e c t r o m a g n e t i c d r i v e r s . One tube was used w i t h d r i v e r s o f co-planar and c o - a x i a l e l e c t r o d e c o n f i g u r a t i o n s , and was powered by a condenser a t 5yU.f and charged t o 12 kv.  The d e s i g n , c o n s t r u c t i o n , and  o p e r a t i o n o f t h i s tube were d e s c r i b e d by Neufeld (1963). schematic diagram of the arrangement i n Figure  rated  H  o f the apparatus i s shown  2. The two v e l o c i t y measuring p h o t o m u l t i p l i e r s view  the shock tube through c o l l i m a t e d s l i t s separated by f i v e centimeters.  The time i n t e r v a l between the responses o f the  p h o t o m u l t i p l i e r s was used t o compute the s peed o f a luminous f r o n t o f gas advancing down the tube.  The t h r e e d r i v e r s used  w i t h t h i s shock tube are shown i n F i g u r e  3.  The o t h e r shock tube was used w i t h an electjodel e s s d r i v e r and was powered by a condenser bank o f 9»6 uf, /  charged t o Ik kv, switched through a vacuum spark-gap s w i t c h and w i t h p r o v i s i o n f o r s h o r t i n g the bank a t any time a f t e r the d i s c h a r g e w i t h a second vacuum spark-gap s w i t c h .  -15-  This  shock  F i g u r e 2 -Schematic o f Shock Tube w i t h E l e c t r o d e s  Phillips Quartz Objective Lens  1.50CVP P h o t o m u l t i p l i e r  V e l o c i t y Measuring • Photamitltiplier. Shock Driver  Spark Gap Switch Capacitor Bank  To Gas Metering and Vacuum System  Figure 3 -Driver Electrode Configurations  -18-  tube w i t h i t s condenser  bank w i t h switches and  t i m i n g c i r c u i t s i s d e s c r i b e d by Cormack (1962). diagram  o f the arrangement of apparatus  electronic A  schematic  i s shown i n F i g u r e h  and the d e t a i l s o f the e l e c t r o d e l e s s d r i v e r are shown i n Figure  5. The  arrangement of the v e l o c i t y measuring  s p e c t r o s c o p i c apparatus was  and  the same f o r both shock t u b e s .  S p e c t r o s c o p i c Equipment Time i n t e g r a t e d s p e c t r a used  i n preliminary  i n v e s t i g a t i o n o f r a d i a t i o n from the plasma were obtained using a H i l g e r E l spectrograph. g r a t i n g monochromators, a 500 mm Bausch and  Two Lomb and a 500 mm  J a r r e l Ash were used t o study time  of s p e c t r a l i n t e n s i t i e s .  These monochromators could be  w i t h e i t h e r a P h i l l i p s 150 i n f r a - r e d , o r an RCA  CVP  v i o l e t r e g i o n s of the spectrum.  ments above 6200A . 0  was  16A°/ mm  1.5  A Corning 2-62  ultra  red f i l t e r  order s p e c t r a when u s i n g the  was  instru-  The d i s p e r s i o n o f both the monochromators  throughout  monochromator: was  fitted  p h o t o m u l t i p l i e r ^ s e n s i t i v e i n the  IP 28 f o r use i n the v i s i b l e and  used t o e l i m i n a t e second  variation  the spectrum.  The Bausch and Lomb  capable o f r e s o l v i n g l i n e s o f approximately  A° h a l f - w i d t h separated by k t o 5 A° w h i l e the J a r r e l Ash  instrument could r e s o l v e l i n e s of 0.5 by 0.75  A  0  •  The  A° h a l f - w i d t h separated  l a t t e r monochromator was  used t o o b t a i n  p r o f i l e s o f l i n e s having h a l f widths of approximately 1 A  0  .  -19-  Figure k - Schematic of Electrodeless Shock Tube  Electrodeless Driver Magnetic Pick-up Coil Shorting Switch Timing Circuit  Shock Tube Vacuum Spark Gap Switches  I Shorting Trigger Shorting Switch  To Gas Metering and Vacuum System  Capacitor Bank  Figure 5 - Electrodeless Driver One turn S p l i t Ring Driving /-set 3/16 inch from Driving C o i l  -Mylar Insulation between Conductors and inside rings  -20-  E l e c t r o n i c A n c i l l i a r y Equipment The output of the v e l o c i t y measuring photomultir p l i e r s was fed through shielded cable to the  difference  amplifier on a Tektronix type 551 oscilloscope trace recording camera (Dumont).  f i t t e d with a  The outputs of the  photomultipliers on the monochromators were fed into cathode followers of standard design.  The output of the  cathode  follower was fed through shielded cable to the single input preamplifier. follower,  The r i s e time of the photomultiplier,  cathode  and preamplifier c i r c u i t was of the order of 0.1  microsecond.  The oscilloscope  and the timing unit for the  bank shorting switch were triggered by a pick up c o i l coupled to the current i n the shock tube discharge.  Theophanis (I960)  High Voltage Pulse Units were used to trigger a l l the spark gap switches save the main switch for the electrodeless shock tube.  The Kerr c e l l timing unit was triggered from a  Tektronix 1000:1, 25 kv probe attached across the d r i v e r leads on the shock tube. The variable high voltage (0-1.5 kv) power supplies to the photomultipliers allowed adjustment of spectrophotometer s e n s i t i v i t y to accommodate a great range of spectral i n t e n s i t i e s without changing the entrance  spectrophotometer  slit.  High Speed Photographic Equipment Photographs of the discharges advancing i n the shock tubes were taken with an Avco Kerr c e l l followed by a  -21-  standard Polaroid camera.  The Kerr c e l l high voltage supply was  triggered from a Theophanis unit which i n turn was triggered either by the camera timing unit or from a variable a u x i l i a r y output on the bank shorting switch timing u n i t .  CHAPTER IV EXPERIMENTAL INVESTIGATION  Preliminary  Investigation Previous spectroscopic studies of plasmas i n  t h i s laboratory (Simpkinson (1961), Barnard, Cormack and Simpkinson (1962)) showed many spectral lines from various impurities such as Hydrogen, Carbon, S i l i c o n , and Copper. Time resolved intensity measurements showed that there was no s i g n i f i c a n t time lag between lines from the rest gas and carbon l i n e s , as expected for a shock plasma followed by a d r i v i n g plasma.  The plasma appeared to be a slug driven  from the electrodes sweeping up the gas i n front of  it.  Photographs made through a Kerr c e l l by Barnard and Cormack (1963) supported the above "slug" theory.  The front of the  advancing plasma was not plane, and retained, for tens of centimeters  of i t s t r a v e l down the tube, c e r t a i n character-  i s t i c s caused by the o r i g i n a l discharge between the  electrodes.  It was decided to make a rough spectroscopic analysis of the impurity content of the plasma generated the shock tube which was used i n the above work.  in  Carbon was  a convenient impurity to work with and should be i n d i c a t i v e of the general l e v e l of impurity.  The monochromator entrance  s l i t was focused inside the tube at a point approximately 1 5 cm from the co-planar electrode d r i v e r .  The instrument was  set on the wavelength of a carbon l i n e (CIllf26*7A ) and the 0  oscilloscope  trace compared with that from an argon l i n e -22-  -23( A I I f 8 0 6 A ° ) , i n each case the background signal from a point l  near the l i n e being subtracted from the signal at the l i n e centre.  The results of t h i s analysis with intermediate  culations, w i l l be found i n Appendix IV.  cal-  The r a t i o of carbon  to argon was found to be approximately one t h i r d .  As carbon  was just one of the impurities observed i n this plasma t h i s would mean that the impurity l e v e l could be higher than 50% i n the tube. Next, the two designs of c o - a x i a l d r i v e r s shown i n Figure '3 of Chapter III were t r i e d .  The opening of the  shutter was timed to take pictures of the luminous front at various distances from the d r i v e r s .  Time integrated spectra  were taken at approximately 12 cm from the driver and the v e l o c i t y of the luminous front was measured at various points i n the tube.  These two c o - a x i a l configurations did not y i e l d  encouraging r e s u l t s .  While the luminous fronts produced by  these drivers were a l i t t l e  closer to being plane than those  from the co-planar d r i v e r there was no evidence of a shock wave being formed ahead of the luminous front and there was a three or four fold pressure increase after the f i r i n g ,  as  compared with a two or three fold increase for the co-planar d r i v e r , indicating a high impurity l e v e l .  This was supported  by the great number of impurity lines i n the spectra taken of the luminosity i n the tube.  These configurations were deemed  unsuitable for producing plasma on diagnostic techniques.  which to test  spectroscopic  On the basis of the high impurity  l e v e l and the fact that no shock wave was evident i t was decided to investigate an electrodeless configuration.  -2h-  Electrodeless Shock Driver With Argon The d r i v i n g c o i l configuration shown i n Figure 5 of Chapter I I I was set up with argon gas i n the tube.  All  measurements made with argon were done at an i n i t i a l gas pressure of .500 mm Hg.  The gas could be l e f t  i n the tube for  up to 50 f i r i n g s with no increase i n pressure, i n d i c a t i n g a lack of v o l a t i l e impurities. (a) Magnetic Brobe Measurements The output of the magnetic probe c o i l i n the c i r c u i t between the shorting switch and the d r i v i n g c o i l was fed through a passive integrator network to the  oscilloscope  and showed a damped sinusoidal discharge of period h.Q microseconds with a calculated i n i t i a l peak amplitude of approximately 100 Kiloamperes.  The current waveform when the shorting  switch was activated i s shown i n Figure 6 with the unshorted waveform shown dashed.  Figure 6 - Electrodeless Driver C o i l Current  -100 -  -25The current after the shorting switch actuation time  exhibits  an exponential decay with a r i p p l e due to the bank current o s c i l l a t i n g through the p a r a l l e l c i r c u i t of shorting switch and load. (b) Photographic Measurements Photographs were taken of the development of" the discharge by timing the Kerr c e l l shutter with the variable delay a u x i l i a r y output on the shorting trigger timing c i r c u i t and are shown i n Figure ?."  Pictures .& through £ show the  development of the discharge from a time of 1.6  microseconds  after the onset of the o s c i l l a t o r y current i n the c o i l to approximately 9 microseconds after t h i s time.  The pictures  taken early i n the discharge development have the s p l i t "field shaper" removed to f a c i l i t a t e charge.  Pictures X» i » &  n d  ring  observation of the d i s -  are taken at times near the  second, t h i r d and fourth maxima of ~ dt the tube through the d r i v e r c o i l .  (and hence E«) within *  On each of these maxima  a surge of azimuthal current flows which causes increased l i g h t from the tube at these times.  Each surge of current i s  driven down the tube and r a p i d l y catches up with the front produced by the surge before i t .  It can be seen that the  second surge produces a rather f l a t front whereas the t h i r d results i n an i r r e g u l a r f r o n t . From pictures £ and r i t i s seen that the shaper doesn't affect the front speed. With the condenser bank shorted immediately dR after the second maximum of — a shock front seems to separate dt from the luminous front formed by the second surge of current. This i s evidenced by the plane front with a r e l a t i v e l y homo-  -26Fi.Ture 7 -Pliotof rapha o f ^'.T-chp.v^e Development i n E l e c t r o d e l e s s Shock Tube w i t h Arjfori'and Helium  n  same time a f t e r starts of discharge  same time after starti of discharge  g  arrows i n s.  to u indicate 4: *  separated f r o n t seen in original photos  u  w  k  m  Helium -\ x  4  i  i  -27geneous area behind  i t f o r a d i s t a n c e o f about one centimeter  ( P i c t u r e s £ and J I ) .  P i c t u r e s s. and £ were taken w i t h and  without  at t h e same time a f t e r the onset o f the  the "shaper"  bank c u r r e n t .  Thus the shaper r e s u l t s i n a h i g h e r speed o f  advance o f the d i s c h a r g e o n l y when the bank i s s h o r t e d .  It  was f e l t t h a t the 1cm t h i c k , plane f r o n t e d plasma s l u g obtained w i t h the shaper when the bank i s shorted near the f i r s t negative peak o f c u r r e n t was t h e best t h a t could be obtained J  without  a f a s t e r c a p a c i t o r bank and much more s o p h i s t i c a t e d  driving c o i l configurations.  I n p i c t u r e £ the luminous f r o n t  l i e s a p p r o x i m a t e l y ' 6 . 5 cm from the f r o n t face o f the d r i v i n g coil. 0.6  The speed o f the f r o n t past t h i s point was  cm per microsecond.  spectrograph  approximately  I t was decided t o focus the  s l i t s i n t h i s plane f o r the s p e c t r o s c o p i c  measurements.  (c) S p e c t r o s c o p i c Measurements The entrance spectrograph was focused station.  slit  o f the H i l g e r E l  i n s i d e the tube at the 6.5  cm  E x p l o r a t o r y , time i n t e g r a t e d s p e c t r a were taken i n  the v i s i b l e and near u l t r a v i o l e t , and i n the near i n f r a r e d . The l i n e s seen i n these s p e c t r a were from the A l , A l l , C I I , S i l l , C a l l and N a i l s p e c t r a .  From the above s p e c t r a were  chosen the l i n e s t o be s t u d i e d w i t h the monochromators. The entrance  s l i t s o f both monochromators were p>  then focused  ^  at the c e n t r e o f the tube at the 6.5cm s t a t i o n  N  -28from the front face of the d r i v i n g c o i l .  One monochromator was  moved up or down the tube with r e l a t i o n to the other i n order that the beginning of signals originating from the same spectral l i n e came simultaneously from each monochromator. The monochromators could then be used to observe two spectral l i n e s . the time difference  simultaneously  V e l o c i t y measurements were made by noting between the signals from one of the  monochromators and a collimated photomultiplier displaced a known distance down the tube from the monochromator.  Velocity  measurements were not taken on every shot as i t was found that i f the luminous front arrived at the 6.5 cm station at the same time, i t s v e l o c i t y was the same each time.  Thus,  coincidence between the times of onset of the signal on two separate f i r i n g s could be used as an i n d i c a t i o n of the same shock v e l o c i t i e s for the two f i r i n g s . A l l monochromator responses which were to be used for comparison of spectral i n t e n s i t i e s were converted to a common s c a l e .  This conversion was done by reducing the  response to that which would have occurred at a standard photomultiplier voltage and then d i v i d i n g by the monochromatorphotomultiplier combined studied.  sensitivity  at the wavelength being  The procedures by which the voltage reduction factor  or B s e n s i t i v i t y m u l t i p l i e r  41  and the s e n s i t i v i t y  curve were  obtained are described In Appendix I I . (1) Spectroscopic Impurity Determination The comparison of the i n t e n s i t i e s of the  lines CII-+267A and AII^-806A° gave an estimate of 0.06 for the 0  r a t i o of carbon to argon (see Appendix III for d e t a i l s ) .  Thus,  the impurity l e v e l would appear to be s i g n i f i c a n t l y less i n the electrodeless tube than i n a shock tube with As i t was suspected  electrodes.  that the impurity spectra  came from a layer next to the walls of the tube an experiment was conducted to determine i f this was t r u e .  This was done  by placing an obstruction consisting of an  diameter  aluminum cylinder i n the centre of the tube and examining the time resolved spectra from the flow stagnation region before the obstruction.  The aluminum cylinder was mounted with an  end face 7 cm. from the d r i v i n g c o i l and the monochromator 1  n  entrance s l i t was focused ~ ~ 16 s i l i c o n l i n e , S i l l ^-lBlA  0  i n front of t h i s face.  was chosen to represent  A  the  impurities known to come from the w a l l ; the response of the monochromator to l i g h t from t h i s l i n e did not change when observed with and without the obstruction i n the tube.  The  peak i n t e n s i t y of the l i n e A l l f806&° was seen to be approxil  mately three times greater with the obstruction than without it.  Thus i t would appear that the impurities coming from the  wall do not mix into the homogeneous region of plasma following the plane front seen i n the photographs. (2) E l e c t r o n Temperatures and Densities T y p i c a l time variations of i n t e n s i t i e s for  a pair of A l and A l l l i n e s are shown i n Figure 8.  The  -30F i g u r e 8 - I n t e n s i t y h i s t o r i e s o f A l . A l l and H l i n e s i n tube w i t h E l e c t r o d e l e s s d r i v e r  -31s i g n a l s shown have been c o r r e c t e d f o r monochromator s e n s i t i v i t y v a r i a t i o n w i t h the wavelength and have had the background 1H-.5  s p e c t r a l i n t e n s i t y subtracted.  The A l l s i g n a l at  microseconds shows c l e a r l y the demarcation between the  plane f r o n t e d homogeneous l a y e r seen i n the photographs more luminous d i s c h a r g e gases following,, are of  and the  The strong A l l l i n e s  i n the v i s i b l e r e g i o n o f the spectrum; increased  intensity  these l i n e s w i l l make the gas more luminous than an i n c r e a s e d  i n t e n s i t y i n A l which has i t s s t r o n g e s t l i n e s i n the i n f r a - r e d . In the o b s e r v a t i o n s of the argon s p e c t r a i t was  n o t i c e d t h a t weak e m i s s i o n of both A l and A l l l i n e s  p l a c e w e l l b e f o r e the a r r i v a l of the luminous f r o n t .  took  These  " p r e c u r s o r " s i g n a l s have been observed by other workers  (see  McLean (196l))who have concluded t h a t they do not o r i g i n a t e from l i g h t emitted i n the d i s c h a r g e and by the tube w a l l s .  In  F i g u r e 8 i t i s seen that these s i g n a l s become measureable at about 3«5  microseconds a f t e r the onset of the d i s c h a r g e , t h a t  i s at the second peak of the d i s c h a r g e c u r r e n t . The time h i s t o r y of the  line exhibits a  d i f f e r e n t behaviour i n the p r e c u r s o r r a d i a t i o n as can be seen from F i g u r e 8.  Time r e s o l v e d p r o f i l e s o f t h i s l i n e were  obtained by r e c o r d i n g average time h i s t o r i e s at wavelengths on the broadened  l i n e i n the p r e c u r s o r and i n the plasma  behind the luminous f r o n t . the  p r e c u r s o r i t was  For the much narrower p r o f i l e i n  n e c e s s a r y t o use the J a r r e l - A s h instrument  w i t h a 10 micron entrance s l i t  and a 25  micron e x i t s l i t .  With  -32such narrow s l i t s  the instrument was  capable of measuring  the  p r o f i l e of a l i n e w i t h a whole h a l f - w i d t h g r e a t e r than o5A°, i e . , an i n f i n i t e l y narrow s p e c t r a l l i n e would r e s u l t i n a. measured whole h a l f - w i d t h of .£A°. the measured p r o f i l e  The  i s c o r r e c t e d f o r the above  broadening i s d e s c r i b e d i n Appendix IV. versus  intensity profile  precursor  the l i n e  of the  gas  instrumental  Ai complete wavelength  l i n e shows that i n the  i s q u i t e narrow, though wide enough f o r the  monochromator to measure i t s p r o f i l e , value  procedure by which  ( w i t h i n a f a c t o r of 2)  and hence o b t a i n a rough  f o r the e l e c t r o n d e n s i t y i n the  ahead of the shock wave.  While the amplitude of the  pre-  c u r s o r s i g n a l changes a p p r e c i a b l y w i t h time, i t s b r e a d t h does not.  T h i s means t h a t the electron d e n s i t y does not  change  r a p i d l y ahead of the shock wave. E l e c t r o n temperatures and  densities calculated  from the s p e c t r a l data are d i s p l a y e d i n Table are t h e o r e t i c a l values  The  at 0.6  cm per m i c r o s e c . i n t o a gas  ization  A l s o shown  of e l e c t r o n temperatures and d e n s i t i e s  behind shock waves propagating 0.65  1.  cm per m i c r o s e c .  at the temperature and  and ion-  observed s p e c t r o s c o p i c a l l y from the p r e c u r s o r r a d i a t i o n .  c a l c u l a t i o n s f o r the h i g h e r shock speed were made to show  the expected values  at the upper l i m i t of the v e l o c i t y e r r o r  envelope. The main experimental  errors i n  the.determination  of e l e c t r o n d e n s i t y a r i s e through l a c k of accuracy the l i n e p r o f i l e the a p p r o p r i a t e  and u n c e r t a i n t y i n f i t t i n g theoretical profile.  i n obtaining  the l i n e p r o f i l e  As p o i n t e d out  above,  to  -33Table 1 kTg & N  In  for v  e  Precursor  kTe  = 0.6 cm^ttsec  A f t e r Shock  lev  1.3  5xl0 ^cm"  Ne  g  1  Theoretical, After Shock w i t h Preheating 1.18 (1.23  ev  l.Vxl0 cm" 1 7  3  6.3xlO  3  ev ev)* l 6 c m  "  3  (S.lxlO^cm" )* 3  k  Quantities i n brackets are f o r shock speed of .65  from t h e  cm per microsecond  narrow  profile  aeea i n t h e  t a l value f o r  N  wider E^c l i n e  emmited f r o m t h e  the of  i s e s t i m a t e d w i t h i n a f a c t o r o f .2.  e  p l a s m a b e h i n d the  uncertainty i n matching p r o f i l e s -10$  in N . e  Errors  i n obtaining  p r o f i l e could r e s u l t i n a f u r t h e r c e r t a i n t y of  f o r the The  be  tV~>%  i f the  by  a f a c t o r of  the  front  r e s u l t i n an  experimental  error  line  error giving a total  o b s e r v e d s p e c t r a l i n t e n s i t y r a t i o s are  in  a further  v a l u e s o f kT  shown i n Table 1,  i n measurement are  i n e r r o r by  t20%  i n the  uncertainty  a f a c t o r o f 2. the  i n kT  would  e  error is  e  Thus, f o r  uncertainties  p r e c u r s o r and  un-  shock f r o n t . kT  while  i n the  being  shock.  the  For  e x p e r i m e n t a l v a l u e of  10,  error  could  experimen-  shock  v a l u e o f N$'behind the  r o d u c e d by Ne e  p r e c u r s o r the  due  to  tl%% after  int-  the errors  the  -3»+-  No c a l c u l a t i o n s were made of the s p e c t r o s c o p i c temperature behind the second luminous f r o n t but i t i s apparent from the steep r i s e i n the A l l s i g n a l w i t h no attendent r i s e i n the A l s i g n a l t h a t the temperature i s g r e a t e r behind the second luminous f r o n t than a f t e r the shock f r o n t . E l e c t r o d e l e s s Shock D r i v e r With Helium No worthwhile r e s u l t s were obtained w i t h h e l i u m . T h i s gas having a h i g h e r i o n i z a t i o n p o t e n t i a l i s more d i f f i c u l t t o breakdown and does not give a luminous d i s c h a r g e on the f i r s t maximum o f ~ ^  but does so on the second, t h i r d  dt  -  and f o u r t h maxima each o f which appears v e r y i r r e g u l a r (see p i c t u r e s i t o Zi f o r p r o g r e s s i o n o f discharge i n helium) . The advanced  combined, i r r e g u l a r f r o n t e d d i s c h a r g e  past the 12  per microsecond. d e n s i t y were  cm s t a t i o n at a speed of about 1.25  The s p e c t r o s c o p i c temperature and e l e c t r o n  measured a f t e r the luminous f r o n t u s i n g the  i n t e n s i t i e s of  the l i n e s H e l 5 8 7 6 A , H e l l U 6 8 6 A ° , 0  broadening o f the H e l l ^686A° l i n e . and 5 10 X  cm  cm"-  3  respectively.  and the  These values were 3 A 7 e v  T h i s temperature i s almost  double t h a t o f h e l i u m heated by a shock w i t h the above speed. Observations o f P r e c u r s o r R a d i a t i o n w i t h a Co-Planar D r i v e r From the above work w i t h the e l e c t r o d e l e s s tube i t i s apparent t h a t p r e c u r s o r i o n i z a t i o n and  excitation  must be considered when attempting t o e x p l a i n the processes t a k i n g place b e f o r e a luminous f r o n t advancing i n t o a gas.  -35T h e r e f o r e , at t h i s p o i n t i t was decided t o i n v e s t i g a t e more f u l l y the p r e c u r s o r r a d i a t i o n .  The i o n i z a t i o n ahead o f the  f r o n t was b e l i e v e d t o be due t o the photon f l u x from the f r o n t .  behind  (4Bf83B5g<g^^ T h e shock tube w i t h co-planar  e l e c t r o d e s was chosen f o r t h i s study because i t s d i s c h a r g e i s more i n t e n s e . found  I t was hoped t h a t the h i g h i m p u r i t y l e v e l  i n t h e plasma behind  the luminous f r o n t  i n this  tube  does not p l a y a s i g n i f i c a n t r o l e i n the p r e c u r s o r i o n i z a t i o n . From p r e v i o u s w^rk i t has been e s t a b l i s h e d t h a t the c o - p l a n a r e l e c t r o d e c o n f i g u r a t i o n gives r e p r o d u c i b l e r e s u l t s so readings were made w i t h o n l y one monochromator. The  o s c i l l o s c o p e channel w i t h the d i f f e r e n t i a l a m p l i f i e r f e d  from the two c o l l i m a t e d p h o t o m u l t i p l i e r s was used  to display  the time o f passage o f the luminous f r o n t through  5 cm.  order t o measure  or  In  p r o f i l e s i n the p r e c u r s o r  r a d i a t i o n i t was necessary t o add approximately 2% hydrogen to  the r e s t  for used  gas being used  each f i r i n g ;  as f r e s h gas was used  i n the tube  i n the e l e c t r o d e l e s s tube the same gas was  f o r many shots and s m a l l amounts o f hydrogen and o t h e r  impurities  accumulated. Observations w i t h argon were made a t two  s t a t i o n s i n the tube, 1 2 cm and 1 7 cm from the d r i v e r , w i t h an i n i t i a l p r e s s u r e , p , o f 0 . 6 m m H g . Q  r e a d i n g s were t a k e n at 1 7 cm w i t h p  Q  Some a d d i t i o n a l = ImmHg.  Observations  made w i t h h e l i u m were a l l at the 1 7 cm s t a t i o n and were taken at two p r e s s u r e s , 0.ImmHg and 0 . 3 m m H g .  Helium was  -36chosen f o r c l o s e r study as i t s atomic parameters are b e t t e r known. (a) Argon (1)  Twelve Centimeters From The D i s c h a r g e  At 12 cm from the d i s c h a r g e the speed o f the luminous f r o n t was 1.67  cm per microsecond w i t h p  0  = 0.6mmHg.  The time v a r i a t i o n s o f i n t e n s i t y o f t y p i c a l A l , A l l , and AIII l i n e s are shown i n F i g u r e 9.  These t r a c e s i n c l u d e the  l i n e i n t e n s i t i e s a f t e r the luminous f r o n t f o r comparison I n F i g u r e 9,  w i t h the p r e c u r s o r i n t e n s i t i e s .  on the t r a c e  f o r A l l f806A° i t w i l l be n o t i c e d t h a t the time b e f o r e the l  luminous f r o n t a r r i v a l has been r o u g h l y d i v i d e d  i n t o two  p e r i o d s , c o r r e s p o n d i n g t o two r e g i o n s b e f o r e the luminous f r o n t i n the  shock tube.  There i s a break i n the slope o f  the i n t e n s i t y t r a c e o f A l l and A I I I l i n e s at t h e d i v i s i o n . These r e g i o n s have been l a b e l l e d e a r l y and , l a t e and w i l l be r e f e r r e d t o i n the d i s c u s s i o n . the  precursor  Two t r a c e s on  p r o f i l e In the p r e c u r s o r are shown i n F i g u r e 10,  the l i n e c e n t r e (measured o f f the c e n t r e . before 5«5  The  one on  at 6563.25A°) and the o t h e r , 1 A  0  broadening can not be measured  microseconds a f t e r the beginning o f the d i s c h a r g e .  A f t e r t h i s time i t i s broadened  s u f f i c i e n t l y t o get an  estimate o f the e l e c t r o n d e n s i t y .  T a b l e 2 gives the values  of e l e c t r o n d e n s i t y and temperature i n the p r e c u r s o r immediately b e f o r e , and .5 microseconds before the luminous  -37Fieure 9 - Intensity  h i s t o r i e s o f A l . A l l and A I I I  l i n e s i n tube w i t h Co-planar d r i v e r @ 12 cm from d r i v e r P =0.6 mmHg. o  -38F i g u r e 10  - Precursor Signals  I(t)  Line  /  f r o n t as w e l l as the  electron density  immediately a f t e r the was  from p r o f i l e of  front.  The  and  average temperature  temperature a f t e r the  obtained by averaging the values c a l c u l a t e d  the i n t e n s i t i e s of 5 A l l i n e s ( 8 0 0 6 A ° , 8 0 1 ^ ° ,  front  from p a i r i n g  8l03A°,  8ll5A°,  and 8*f08A°) and 6AII l i n e s (if3-+8A , *+579A°, >+589A°, h76hk°, G  hQ06k°, and  f933A°X  calculated  from averaging r e s u l t s from one  l  The  temperature before the  A l l l i n e s ( A l 8115A and 0  A l l and  A I I I l i n e s ( A l l M-806A and 0  equilibrium  between the  temperatures.  b e f o r e the  the  was  p a i r of A l from one  A I I I 3286A°), and  e l e c t r o n and  Though the  open to doubt i n the density  A l l H-806A°) , and  front  and  pair  of  assuming  atomic e x c i t a t i o n  e x i s t e n c e of such e q u i l i b r i u m  r e g i o n of r e l a t i v e l y low  f r o n t , t h i s assumption was  is  electron made i n the  absence of b e t t e r knowledge of the mechanisms of  excitation.  -39-  As the s e n s i t i v i t y of the monochromator could not be determined i n the u l t r a - v i o l e t , the c a l c u l a t i o n involving AIII 3286A necessitated taking as known the temperature 0  after the luminous front and calculating only the change i n the l a s t term i n the denominator of Equation 6 of Chapter I I . Knowing the change i n t h i s term across the luminous front we can calculate the temperature ahead of the f r o n t .  The per-  centage variations written after the temperature are the maximum spread of the observed values from which the average is  calculated.  Table 2 kT and H for v = 1.67cm/ JU, sec @ 12 cm from Arc i n Argon assuming thermal equilibrium e  s  In Precursor at shock kT We  e  In Precursor, . 5 sec before shock  After shock  1.66 ev (±Ujg)  1.61 ev (±k%)  2.3 ev (±750  lxl0 cm~  3xlO cm"  .97xlO cm"  1 6  3  l5  3  l8  3  (2) Seventeen Centimeters From Discharge At the 17 cm station the v e l o c i t y of the luminous front was 1.31 cm per microsecond at a pressure of 0.600 mmHg. and 0.83/ cm per microsecond at a pressure of 1 mmHg.  Here no  Al signal can be picked up from the precursor r a d i a t i o n .  The  A l l and AIII traces i n the precursor are shown i n Figure 11 for the two pressures.  Table 3. gives the spectroscopic  values  -1+0-  Figure 11 - Precursor Intensity h i s t o r i e s of A l l and AIII l i n e s i n tube with Co-planar d r i v e r @ 17 cm from d r i v e r , Pp - 0,6  and 1 mmHg.  Kt) A  A l l 1+806A  0  20  late precursor  region-*-  1.6 early precurscr region<— 12 p= 0  8 -  .6 mmHg  0 time (yUsec)  Kt)  AIII 3286A°  2.1+  luminous front  1.6 0.6  P = 1 mmHg c  8 time (yUsec) Note - the i n t e n s i t y scales on these two graphs are each i n a r b i t r a r y units and are unrelated as the c a l i b r a t i o n procedure could not be carried out i n the u l t r a v i o l e t  -1+1-  of k T and N e  for  immedlately before the front and after the front  e  a front v e l o c i t y of 1.3 cm per microsecond„  The value of  kT_ i n the precursor was calculated from the change i n intensity r a t i o across the luminous f r o n t , of the same A l l and AIII lines used i n Table 2.  This r a t i o increased by a factor of 19.  The  time h i s t o r y of points on the H^Q l i n e appear the same as i n the case of the 12 cm readings except the l i n e i s narrower. Again the broadening can not be measured more than 1 microsecond before the shock. Table 3 k T and N for v = 1.31 cmZ/^sec at 17 cm from Arc i n Argon assuming thermal equilibrium e  e  s  Precursor kT N  2.06 ev  l.V-8 ev  e  6xlO cm" l5  e  After Shock  3  .9xlO cm~ l8  3  (b) Helium Line i n t e n s i t y time variations at the 17 cm station are displayed i n Figures 12 and 13 for the two pressures 0.1 mmHg and 0.3 mmHg. are  The i n t e n s i t y scales i n these figures  a l l i n the same r e l a t i v e u n i t s .  Table h shows the electron  temperatures and densities after the luminous front and i n the precursor immediately before the front for the above two pressures.  These values were calculated from the  of Hel 5876A and H e l l *+686A° l i n e s . 0  intensity  Calculations of the  -If2-  F i g u r e 12 - P r e c u r s o r R a d i a t i o n I n t e n s i t y H i s t o r i e s f o r Hel5876A . kh71A° and 3888A , , @17 cm from d r i v e r iCt) A Hel5876A A u^TC«r7^ o , f j peak 23P-33D at 13-8 0.8 0  '  ~  0  —  A  0  luminous 0.6 -  front  to peak a t 3«6 , p = 0 . 3 mmHg 0  0.»+ "  p = 0 . 1 mmHg 0  0.2 " 0  0.016 _  3.5  HeI-+-+71A° 2 P^1+3D 3  0.012 k  (/xsec)  *^to peak at 0.55 t o peak a t 0.08 luminous front  0.008 0.00-+ -  3.5  (yKsec) t o peak at 2 . 6  .10. Figure 1^ - Precursor Radiation Intensity H i s t o r i e s for Hel^OieAQ. M?22A° and HeII>+686A @17 cm from d r i v e r Kt) 0  O.oCP  Hel5016A°  to peak a ^ . l l j * / fiat 0  1.0  1.5  2.0  2.5  3.0  3.5  p  e  a  k  0A2  (yUsec)  i(to peak at 0 . 3 1  0.002h  time 3.5  o.ow  HeII^686A 3D 2  0.03  c  - '-+F etc  (yKsec)  fto peak at 3.26  2  luminous front 0.02  0.01  0  o peak time  _L1+-  r a t i o s o f the numbers o f He atoms i n the upper e x c i t e d  states  of the H e l l i n e s observed were made from E q u a t i o n ( 3 ) o f Chapter I I at three s e p a r a t e times i n the p r e c u r s o r and a t the peak o f i n t e n s i t y a f t e r the passage o f the luminous i n Table 5  These are d i s p l a y e d  w i t h the r a t i o which could be  expected w i t h the e x c i t e d s t a t e s i n e q u i l i b r i u m . these r a t i o s a r e i n s e n s i t i v e t o temperature, slowly w i t h temperature.  I t i s seen t h e s t a t e s w i t h p r i n c i p a l compared w i t h  I f the i n t e n s i t y o f the 23p - 1+3D  l i n e i s i n s e r t e d i n E q u a t i o n (6) o f Chapter the H e l l +686A° l i n e t h e temperatures l  increased  Four o f  the others vary  quantum number h are very much under-populated equilibrium conditions.  front.  I I with that of  i n T a b l e h w i l l be  by approximately 0.7 ev. Table h  kT  e  and N  e  for p  0  = O.lmmHg and p - 0.3mmHg a t 17 cm from  Arc i n Helium assuming thermal p = O.lmmHg, v  kT  s  = 5<= 5 cm/ microsecond  e  Precursor  A f t e r Shock  2.32 ev  3 c 6 3 ev  2xl0 5cnr3  2xl0 ' cm"3  1  p =0.3mmHg,  kT N  e  v  s  =  1  7  h .6cm/microsecond  Precursor  A f t e r Shock  2 A 3 ev  3.6 ev  2X10 ^cm 1  e  equilibrium  -3  l+.2xl0 cnf3 17  -1+5Table Ratios  of N _ P  Time from start of Discharge  1.0 /csec.  m  at  0  2.1+ yusec.  5A  Various  =0.1  Times  i n Helium  mmHg.  3«0^osec (luminous , f r o n t ) . i v\,:  3.7 ><sec.  equilibrium  2.2  3.92  l+.OU-  1.73  3.52  1.93  1.81+  033D 0 3  1.96  2.1+1  3.13  2.6  1.667  o^3p 03lp  1.12  1.63  1.3  5.5  3  22.7  J  N  03°D l Q  3  oi+3  N  D  n  N  5  l*+.3  p  3  3  P  N  N  033D  N  OI+1D  N  OI+1D  12.8  63.2  37.9  0.172  0.062  0.107  7A  18  0.265  0.13  1+.17 3.6  before after  1.21 l.V  before after  N  0.63  O,33D  N  Nplf3p N  03 P 3  19.7  12.3  0.159  0.211  1.1+ 1.2  before after  2 before 2.33 after  -1+6-  Table 5B Ratios of N m 0  Time from start of Discharge  V D  2.2  qi+ D  N  o^3  D  n  033P  N  033  N  03lp  n  P  033D  Ol+lD  OI+1D  N  N n  0  3.25 yUsec.  6.9  0 3  lp  033D  OI+3D  O»+3D  033p  N  yusec. (luminous front)  6.2  1+.2 equiliby t t s e c . rium  12.8  5  0.96  1.01+  2.22  2.15  1.97  2.01  1.85  1.02  3.5  3.1  6.95  7.85  25.2  21+.8  0.28  0.271+  12.2  26.2  23.8  16.1  1.1+ b e f o r e 1.2 a f t e r  0.176  0.075  0.081+  0.115  2 before 2.33 a f t e r  N  N  3.5  0.61+6  1  N  N  1.5 yUsec.  at V a r i o u s Times i n Helium, p =0.3mmHg  0.25  3  1.667  3  35.9  1+.17 before 3.6 a f t e r  0.357  1.21 before 1.1+ a f t e r  CHAPTER V DISCUSSION AND CONCLUSIONS  Nature of Luminous Plasma From the work done on shock tubes with d i f f e r e n t configurations of d r i v e r electrodes the impurity concentration i n the luminous slug would appear to be less a function of electrode  configuration than of some other parameter.  Other  workers such as Cormack (1962), and S t a i r and Naff (I960) reach the conclusion that the impurity concentration i s proportional to  J l * t which varies inversely with the ringing 2 <  frequency of the capacitor bank.  The banks available i n t h i s  laboratory did not permit the investigation of the effect of very high voltage, banks on  low inductance, high frequency capacitor  impurity concentration. From the observation of a more or less  i r r e g u l a r luminous front followed by gas which strongly emits impurity spectra i t was concluded that i n a l l the shock tubes with electrodes used i n this laboratory no r e a l shock plasma has been found. In these experiments, the impurity concentration i n the discharge heated plasma was considerably reduced by the use of an electrodeless d r i v e r on the shock tube.  With the  electrodeless d r i v e r , a shock wave appears to be formed i n argon when the d r i v i n g discharge is terminated after two pulses of current within the tube.  The s p e c t r o s c o p i c a l l y measured -k7-  -1+8-  e l e c t r o n temperature o f the r e g i o n behind the shock wave was approximately 20% h i g h e r than the t h e o r e t i c a l v a l u e s obtained from the Rankine-Hugoniot gating into a cold  gas.  equations f o r a shock wave propaHowever, i t was  p o s s i b l e t o measure  approximately the e l e c t r o n temperature and d e n s i t y ahead the shock wave. t i o n s ahead  of  When the s p e c t r o s c o p i c a l l y observed c o n d i -  o f the shock are i n s e r t e d  i n the Rankine-Hugoniot  equations the agreement between t h e o r y and experiment f o r the r e g i o n behind the apparent shock wave become c l o s e r t h a n the approximate e x p e r i m e n t a l e r r o r .  10%,  From t h i s c l o s e agreement  and from the evidence t h a t w a l l i m p u r i t i e s were not found i n the c e n t r a l one h a l f i n c h diameter core o f the p l a n e - f r o n t e d luminous r e g i o n preceeding the more luminous remains o f the d i s c h a r g e we  conclude t h a t a shock wave separates from the  advancing d i s c h a r g e . The attempt t o c r e a t e the above c o n d i t i o n s i n helium was  not s u c c e s s f u l .  The luminous f r o n t s were more  i r r e g u l a r than i n the case of argon and moved at approximately twice the speed. 1961)  Other workers  (Jeanmaire et al 1963» Chang  have found t h a t d i s c h a r g e s advancing above a c e r t a i n  c r i t i c a l speedj dependent  on the g i v e n e x p e r i m e n t a l parameters,  do not e s t a b l i s h shock f r o n t s . the e l e c t r o d e l e s s tube was  0.6  w i t h t y p i c a l shock speeds o f 1.3  The shock speed i n argon i n cm per microsecond as compared t o 2 cm per microsecond i n  the other e l e c t r o m a g n e t i c shock t u b e s . 0.6  cm per microsecond  d r i v e n shock w a y e f  ?  T h i s shock speed o f  i s as slow as t h a t of f a s t m e c h a n i c a l l y  -1+9Precursor  Ionization The s t u d i e s o f the p r e c u r s o r r a d i a t i o n from  argon i n the shock tube w i t h co-planar e l e c t r o d e s permit o n l y a q u a l i t a t i v e d i s c u s s i o n i n the absence of d a t a on the e x c i t a t i o n cross s e c t i o n s f o r the r e l e v a n t energy The i n t e n s i t y measurements made at 17 t h a t an i n c r e a s e i n the i n i t i a l  levels.  cm from the d r i v e r show  pressure d r a s t i c a l l y reduces  a l l s p e c t r a l i n t e n s i t i e s except those j u s t a f t e r the discharge.  initial  T h i s i s most marked i n the case of A I I I where the  i n t e n s i t y at 2 microseconds a f t e r the i n i t i a t i o n o f the d i s charge i s unchanged by the pressure i n c r e a s e and i t i s a l s o s u b s t a n t i a l l y unchanged by moving the o b s e r v a t i o n point 12 cm t o 17  cm from the d r i v e r .  T h i s behavior would  from  seem t o  i n d i c a t e t h a t i o n i z a t i o n o f argon atoms and ions at p o i n t s remote from the luminous f r o n t the  discharge i t s e l f ,  f r e e path.  i s caused by r a d i a t i o n from  and t h a t t h i s r a d i a t i o n has a l o n g mean  With p =0.6mmHg the p r e c u r s o r e x c i t a t i o n o f A l l 0  and A I I I l i n e s begins a steep r i s e at 0.6  t o 0.75  microseconds  before the a r r i v a l o f the luminous f r o n t thus d e f i n i n g the beginning o f the l a t e p r e c u r s o r r e g i o n (see F i g u r e 9 IV).  T h i s r e g i o n i s always about 1 cm t h i c k .  S  Because  Chapter the  l a t e p r e c u r s o r r e g i o n always extends the same d i s t a n c e b e f o r e the  f r o n t we  conclude t h a t i t i s caused by l i g h t which i s  s t r o n g l y absorbed by the gas ahead  of the f r o n t or through  e l e c t r o n s which d i f f u s e out from the f r o n t . the  The t h e o r y t h a t  above behavior i s caused by p h o t o - e x c i t a t i o n i s favoured  -50here over the electron d i f f u s i o n theory.  From the observed  spectroscopic temperature before the luminous front we can calculate a degree of i o n i z a t i o n , oG » of 1.29; the corresponding electron density of 2.62xl0^ cm~ 6  3  is much greater  than the observed electron density of 6x10 ^cm  .  This  apparent deficiency of electrons before the front could be caused by photo-excitation enhancing the populations of the excited states of A l l and AIII ions and thus making the gas appear hotter and more ionized than i t a c t u a l l y i s . In the case of helium the behavior of the precursor r a d i a t i o n i n t e n s i t y l i n e v a r i a t i o n is somewhat similar to that i n argon, having the sharply defined early and late precursor regions i n advance of the luminous f r o n t . The major effect of the reduction of p  Q  from 0.3mmHg to  O.lmmHg was to more than double the thickness of the late precursor region.  Ahother effect of the decreased pressure  was to considerably reduce the intensity of the H e l l l i n e i n the precursor r a d i a t i o n .  Again as i n the case of argon we  have a seeming deficiency of electrons i n the region before the luminous f r o n t .  At the observed spectroscopic temperature  and electron density the gas should be completely i o n i z e d , y i e l d i n g an electron density of at least lxlO^^cm"^ for p =0.3mmHg o  and 0.33X10 cm~ l6  3  for p = 0.1 mmHg. 0  observed, 0.2xl0^cm" , 3  appreciably with p . Q  The electron density  i s much too low and does not change  This l a s t c h a r a c t e r i s t i c would seem to  suggest that the electons come from photo-ionization of wall  -51impurities.  The  more than l i n e a r decrease o f H e l l l i n e »  intensity with p  Q  i s compatible w i t h p h o t o - e x c i t a t i o n  e l e c t r o n i c e x c i t a t i o n should be l i n e a r because the d e n s i t y remains f a i r l y constant w i t h changing  as  electron  p . 0  From Table 5 i t i s seen t h a t a l l the r a t i o s of n e u t r a l helium e x c i t e d  s t a t e populations  which would be expected at e q u i l i b r i u m . luminous f r o n t the t r i p l e t respect  depart from those  F a r ahead o f  s t a t e s are a l l underpopulated w i t h  to s i n g l e t s t a t e s of corresponding p r i n c i p a l quantum  number.  As the f r o n t approaches and  populations  of the t r i p l e t  passes, the r e l a t i v e  states increase  and  the  r a t i o s approach or pass the e q u i l i b r i u m r a t i o s . o f populations  above  The  r a t ioi:  of s t a t e s of quantum number k t o those of  quantum number 3 are always s m a l l e r t h a n would be under e q u i l i b r i u m  expected  Following  Investigated  the work of H. R.  c r i t e r i a f o r " l o c a l thermal e q u i l i b r i u m " homogeneous l a b o r a t o r y  Griem (1963)  plasmas i s t h a t  collisional  t h a t the v e l o c i t y d i s t r i b u t i o n s of the  p a r t i c l e s be thermal. i o n i z a t i o n s and  recomcolliding  S i n c e most c o l l i s i o n a l e x c i t a t i o n s  t h e i r inverses  involve electrons,  e l e c t r o n v e l o c i t y d i s t r i b u t i o n must be t h e r m a l . should be  the  i n time independent  processes be more important than r a d i a t i v e decay and b i n a t i o n and  L  conditions.  Attainment: of E q u i l i b r i u m i n Plasma  and  the  and  the This  condition  s a t i s f i e d here as even at e l e c t r o n d e n s i t i e s as  low  -52as lO^cm""  at a temperature of 1 ev the time f o r e l e c t r o n i c  3  r e l a x a t i o n i s o f the order The  of 1 0 ~ ^ ^ s e c . ( S p i t z e r (1956)).  c r i t e r i o n adopted by Griem t o determine i f c o l l i s i o n a l  processes dominate over r a d i a t i v e processes i s t h a t the for  rate  a given c o l l i s i o n a l process be t e n times t h a t f o r competing  radiative  processes. The  i o n i z a t i o n and o f atoms and  r a t e s f o r c o l l i s i o n a l e x c i t a t i o n and  hence the time t o achieve a given d i s t r i b u t i o n  ions among the e x c i t e d s t a t e s may be c a l c u l a t e d  knowing the cross s e c t i o n s f o r e l e c t r o n i c c o l l i s o n s and temperature and d e n s i t y of the are e a s i l y obtained  electrons.  rates  knowing the t r a n s i t i o n p r o b a b i l i t i e s  between the energy l e v e l s concerned. be made f o r helium as values and  Radiative  i o n i z a t i o n from the  C a l c u l a t i o n s can e a s i l y  o f cross s e c t i o n s f o r e x c i t a t i o n  ground s t a t e are a v a i l a b l e f o r n e u t r a l  helium ( G a b r i e l and,Heddle (I960) and  Francis  (I960)) and may  be e a s i l y c a l c u l a t e d f o r h y d r o g e n i c , i o n i z e d helium and t r a n s i t i o n s between e x c i t e d l e v e l s i n n e u t r a l helium (Seaton (1962)). I n s e r t i n g the a p p r o p r i a t e  cross-section,  G£(E_), where E ^ i s the e l e c t r o n energy, i n the >) " e  we  the  equation  o b t a i n the r a t e of c o l l i s i o n a l t r a n s f e r per atom from  energy s t a t e E . t o E  r  Considering  the n e u t r a l helium  for  =53energy l e v e l 2^P at an e l e c t r o n d e n s i t y e l e c t r o n temperature o f 2ev, we o b t a i n  o f lO-'-^cm" and coll 3  a rate,  R  l p - 3 - D °" L  2  570 X l O ^ s e c " o r a time between c o l l i s i o n s o f 1.75 X 10" 1  3  microsecond f o r t h i s l e v e l , assuming the r a d i a t i o n 2 P-1' S 1  (resonance l i n e ) i s t r a p p e d . valid  a t t h e values o f N  L  The assumption o f t r a p p i n g i s  ( ~ 1 0 c m " ) used i n t h i s work l D  0  3  (see Phelps ( 1 9 5 8 ) ) . The above c a l c u l a t i o n y i e l d s even h i g h e r c o l l i s i o n a l rates  f o r the h i g h e r e x c i t e d  l e v e l s o f helium  because o f t h e c l o s e r grouping o f energy l e v e l s as t h e p r i n c i p a l quantum number i n c r e a s e s . excited  s t a t e s could  therefore  The p o p u l a t i o n s o f the  be expected t o always assume  an e q u i l i b r i u m d i s t r i b u t i o n among themselves at t h e above e l e c t r o n temperature and d e n s i t y under steady s t a t e conditions. The t h e o r e t i c a l time o f r e l a x a t i o n t o c o l l i s i o n a l e q u i l i b r i u m f o r the c o n d i t i o n s before and a f t e r the luminous f r o n t w i l l calculated.  observed  now be  As almost a l l o f t h e h e l i u m atoms must be  i o n i z e d an approximate time f o r t h e plasma t o reach e q u i l i brium between n e u t r a l and i o n i c h e l i u m can be found by i n v e r t i n g the r a t e ,  R  coll I,II ~  R  coll - R l l  j  2  coll coll l , 2 + Rl.lon  p  coll + Ri l s  2  -.coll + i, 3p R  S  T ^  +  R  2  o f c o l l i s i o n a l t r a n s f e r from the ground  0  1  l,23s  T >  1  +  R  C  O  1  1  l,ion>  s t a t e t o the s t a t e s  of p r i n c i p a l quantum number 2 and t o the i o n i z e d s t a t e .  The  r a t e Rx°2^" *  s  the c r i t i c a l r a t e as the energy gap between the  n = 1 and n = 2 l e v e l s i s much g r e a t e r than t h a t between h i g h e r l e v e l s and so the upper l e v e l s are depopulated r a p i d l y ionization.  The r a t e R^ ^" i s r o u g h l y 6% of R ^ ; l,ion 1,2 0  1  00  e l e c t r o n temperature o f 2 ev and 20% o f R ^ ^ 0  N  e  = lO-^cnT  3  a  ^ ^  1  e  a  V  o  towards  t an F  o  r  at the two temperatures, 2 ev and k ev, t h i s  c a l c u l a t i o n y i e l d s times o f 3600 microseconds and Ik- microseconds r e s p e c t i v e l y . As even the time f o r the h i g h e r temperature i s l o n g compared w i t h the time f o r the luminous f r o n t t o t r a v e l from the d r i v e r t o the p o i n t of o b s e r v a t i o n , i t would appear t h a t the plasma observed i n the tube ahead the  luminous f r o n t  i s not i n e q u i l i b r i u m .  of  C o n s i d e r i n g the gas  behind the f r o n t , where the e l e c t r o n d e n s i t y i s o f the o r d e r of  lO^^cm"  3  and the temperature about k ev, we have a  r e l a x a t i o n time o f O.lW  microsecond f o r e q u i l i b r i u m between  helium atoms and i o n s .  Thus the gas f l o w i n g i n t o the luminous  f r o n t can be i o n i z e d by e l e c t r o n impact i n a time of t h i s order which i s short when compared w i t h the r i s e times and f a l l times of the i n t e n s i t y h i s t o r i e s seen here ( t y p i c a l time = 0.6 second).  rise  microseconds, f a l l time t o i i n t e n s i t y = 1 microI t must t h e r e f o r e be concluded t h a t other complex  processes are r e s p o n s i b l e f o r the d e p a r t u r e from e q u i l i b r i u m values o f the p o p u l a t i o n r a t i o s behind the luminous (see  T a b l e 5? Chapter I V ) .  front  -55Concludlne  Remarks In plasmas formed i n e l e c t r o m a g n e t i c  tubes many complex mechanisms are active.,  shock  Only a l i m i t e d  amount o f i n s i g h t i n t o these mechanisms has been gained i n the work r e p o r t e d here and there i s much scope f o r f u t u r e research.  One p o s s i b l e l i n e o f r e s e a r c h would be t o determine  more a c c u r a t e l y the e l e c t r o n d e n s i t y i n the r e g i o n ahead of the advancing luminous f r o n t . has  The work i n t h i s f i e l d  which  been done w i t h microwave probing o f the r e g i o n f a r i n  advance o f t h e f r o n t could be complemented and extended towards t h e f r o n t w i t h s p e c t r o s c o p i c equipment o f h i g h e r r e s o l u t i o n than has been a v a i l a b l e f o r the present ments.  experi-  Another more complex problem would be t o f u r t h e r  study t h e mechanisms r e s p o n s i b l e f o r e x c i t a t i o n o f r e s t gas atoms and ions i n t h e p r e c u r s o r r e g i o n .  As i t Is f a i r l y  c e r t a i n t h a t p h o t o - e x c i t a t i o n and i o n i z a t i o n are the dominant processes,  such a study would have t o b e g i n with an  accurate d e t e r m i n a t i o n  of the s p e c t r a l d i s t r i b u t i o n o f  r a d i a t i o n f a l l i n g on the gas from the d i s c h a r g e advancing luminous f r o n t .  and the  -56APPENDIX I THEORETICAL LINE STRENGTHS The  t h e o r e t i c a l l i n e s t r e n g t h s to be used i n  c a l c u l a t i o n s f o r argon and helium  plasmas w i l l be  taken  d i r e c t l y from published values where a v a i l a b l e . Argon L i n e  Strengths The  "argon l i n e strengths used i n t h i s work  were f o r the most part c a l c u l a t e d from the t r a n s i t i o n b a b i l i t i e s f o r Argon I and The  Argon I I published  pro-  by Olsen  t r a n s i t i o n p r o b a b i l i t y , A, f o r e m i s s i o n of a l i n e  (1963) of  wavelength ^ i s r e l a t e d t o the l i n e s t r e n g t h , S", by  (1)  6^7^  A\ =  where a l l symbols are as p r e v i o u s l y d e f i n e d . l a t i o n s of temperature e t c s t r e n g t h s we  As our c a l c u -  i n v o l v e o n l y the r a t i o s of  w i l l r e w r i t e the above e q u a t i o n  line  in arbitrary  units:  (2) The  S  1  = g  values of A, g , and S ffi  1  X A 3  m  .  f o r the Argon I and  II lines  s t u d i e d i n these experiments are t a b u l a t e d below, ^ i n Angstrom u n i t s i s i n s e r t e d i n E q u a t i o n values.  (2)  to o b t a i n  these  -57A  Line  g  1 9  (Kid?  6  1.70  8  7.^6  7.Mf  2  1.-+3  6.kO  6  3o70  5Ao  If  2.3-+  AIllf806A°  7.86  6  5.2**  AII +933A  1.60  if  7.69  0.510  5  1.31  AII f266A°  AI8011+A  0^796  5  2.05  AIIU-3-+8A  AI8103A  0  2.68  3  if.28  AIllf579A  AI8115A  0  2.22  7  8.31  AII-+589A  1.99  5  5.91  AIlWfA  Al8006A° 0  Al8lf08A°  3o65  l  11.5  0  0  0  0  1  No  &  A  Line  (lio" )  m  G  published values were a v a i l a b l e f o r Argon I I I  l i n e s so the s t r e n g t h of the l i n e used, A I I I 3286A , was  cal-  0  c u l a t e d u s i n g the Coulomb approximation method of Bates Damgaard (1950).  and  The r e s u l t of t h i s c a l c u l a t i o n i s shown  below, w i t h t h a t from the same c a l c u l a t i o n f o r the  line  AII-+806A . 0  S  Line  S  1  = 2.02xlO S l8  (xlO" ) 1 9  AII*f806A° AIII3286A  21.5 0  «f.3-+  25.2  A l s o shown f o r AII f806 i s the value o f S l  (1)  and  2.02x10  1  which from  Equations  (2) can be obtained by m u l t i p l y i n g S by J^t2l 3h 18  2 2 f o r S i n u n i t s o f ( a . e ) (a  T h i s l a s t d e t e r m i n a t i o n of S  = Bohr r a d i u s ) .  Q  1  =  f o r A I I f 8 0 6 A ° can be compared l  with t h a t i n the t a b l e f o r A l and A l l l i n e s .  -58Carbon Line Strength The strength of the carbon l i n e , G.II *267A , 1  0  used i n the impurity determination was calculated from the absorbtion o s c i l l a t o r strength as quoted by A l l e n (1963). The values g -A , , and hence S . 011*4-267 CIlU-267  were found from  1  m  the r e l a t i o n of g f = 1.^99 x 10" n  8  g  m  A.  S  1  CIIH-267A  0  was  found to equal 15.3 > i n the same a r b i t r a r y units as are the values of S  for A l and A l l .  1  Helium Line Strengths The l i n e strengths of neutral and ionized helium l i n e s used i n temperature determinations were also calculated from the absorbtion o s c i l l a t o r strengths quoted by A l l e n (1963).  The strengths of the neutral helium l i n e s  which were used to determine ratios of the numbers of atoms i n various excited stages are calculated from the s e l f consistent (I960).  set of values of A found i n Gabriel and Heddle  The strengths for the lines used are as follows:  Line  Strength  Hel5875A°  32.9  HeII^686A°  126  HelM+71A° HeI3888A°  Hel50l6A° HeI +922A l  0  S  1  * g  t t  2.l8xl0  A  3  2 0  20 0 .327x10 0 .0*+9xl0  20  0.051X10 20 0.115x10 20  A  -59APPENDIX I I DETERMINATION OF MONOCHROMATOR SPECTRAL SENSITIVITY The e x p e r i m e n t a l arrangement  by which the  s p e c t r a l s e n s i t i v i t y was determined i s shown i n F i g u r e l.'lf. The temperature o f the t u n g s t e n source had been determined i n a p r e v i o u s experiment by Robinson (1962).  F i g u r e lh - Apparatus f o r C a l i b r a t i n g Monochromators 1000 w a t t tungsten  @  Red f i l t e r f o r use above 6200A t o remoVe second order pectra 0  -fl)  T=2l+00°KVT^  V=ll5Vdc  Tvm^J^l  ~ 5000  Grating Monochromator  Rotatin mirror  Photomultiplier  A l l mirrors front  To Oscilloscope  silvered  The e x i t and entrance s l i t s were opened  on the monochromator  u n t i l the s i g n a l t o the o s c i l l o s c o p e  was o f the  same order as s i g n a l s obtained from the l i g h t from the shock tubes.  The s l i t s were opened  t o o b t a i n the above l e v e l o f  s i g n a l (with maximum^allowable phot©multiplier  v o l t a g e ) i n the  r e g i o n o f the spectrum where the response o f the monochromaterp h o t o m u l t i p l i e r t o the pulses o f l i g h t from the t u n g s t e n bulb  -60-  was the l e a s t .  The p h o t o m u l t i p l i e r v o l t a g e was reduced  when necessary when responses were being measured i n the o t h e r r e g i o n s o f the spectrum. A semi l o g a r i t h m i c „plot was made o f the responses  o f the monochromator versus i t s wavelength  setting.  The p h o t o m u l t i p l i e r v o l t a g e changes were r e -  flected  i n d i s c o n t i n u o u s jumps i n the response  Because o f the g l a s s envelope  curve.  on the t u n g s t e n b u l b ,  responses were p l o t t e d o n l y f o r 3 8 O O A  0  and above.  This  process was repeated f o r a l l t h e monochromator-phot©multiplier  combinations. Next was p l o t t e d the r a d i a t i o n intensity:.;  curve f o r t u n g s t e n at a temperature  o f 2*+00° K,  -  1(30-  A ((exp where £ i s the e m i s s i v i t y and C  2  ^Tp") -1) = l.^Scm^K  . The  e m i s s i v i t y values f o r t h e v a r i o u s wavelengths were taken from De Vos (195 *-). 1  t o the l i g h t  T a k i n g the s e n s i t i v i t y t o be r e l a t e d  i n t e n s i t y and response by: Sensitivity  Response = Intensity  a semi l o g a r i t h m i c p l o t o f the s e n s i t i v i t y can e a s i l y be obtained by t a k i n g the d i f f e r e n c e between the response and i n t e n s i t y semi l o g a r i t h m i c p l o t s .  As o n l y i n t e n s i t i e s  -61measured w i t h the J a r r e l - A s h monochromator were used i n the c a l c u l a t i o n s of these experiments, s e n s i t i v i t y curves f o r t h i s instrument o n l y are presented i n F i g u r e s 15 and 16. With r a d i a t i o n from the shock tube the v a r i a t i o n o f response and hence o f s e n s i t i v i t y w i t h p h o t o m u l t i p l i e r v o l t a g e can be determined, at v a r i o u s wavelengths.  Changes o f response at low p h o t o m u l t i p l i e r  v o l t a g e s were determined a strong l i n e . wavelength  by s e t t i n g the monochromator on  T h i s v a r i a t i o n o f s e n s i t i v i t y w i t h both  and p h o t o m u l t i p l i e r supply v o l t a g e was  found  t o be q u i t e c o n s i d e r a b l e i n the case o f the IP 28 tube where r e a d i n g s were takne w i t h v o l t a g e s from 500V t o 1100V. The s e n s i t i v i t y v a r i a t i o n f o r the IP 28 p h o t o m u l t i p l i e r i n the s p e c t r a l r e g i o n o f i n t e r e s t i s presented i n F i g u r e 17 i n the form o f a " S e n s i t i v i t y M u l t i p l i e r " .  I n the case  of the 150 CVP p h o t o m u l t i p l i e r , v o l t a g e s from 1500V t o 1800V were used and the " S e n s i t i v i t y M u l t i p l i e r " can be taken as a f a c t o r o f two f o r every 100V increment w i t h l i t t l e v a r i a t i o n w i t h wavelength. I n order t o compare i n t e n s i t i e s o f s p e c t r a l l i n e s i n d i f f e r e n t wavelength  r e g i o n s the response at each  wavelength was d i v i d e d by the a p p r o p r i a t e " S e n s i t i v i t y M u l t i p l i e r " and then f u r t h e r d i v i d e d by the s e n s i t i v i t y f o r the wavelength.  F i g u r e IS  - S e n s i t i v i t y " v s - W a v e l e n g t h f o r Jarre1-Ash Monochromator with P h i l l i p s 150 CVP P h o t o n m l t i p l f e r " P S b t d m u l t i p l i e r v o l t a g e - 1700V  Sensitivity (Arbitrary Units)  F i g u r e 16 - S e n s i t i v i t y v s Wavelength f o r J a r r e l - A s h Monochromator w i t h RCA IP28 P h o t o m u l t i p l i e r "  Sensitivity (Arbitrary „Units)  4000  5000  >A(A°)  -6k F i g u r e 1 7 - S e n s i t i v i t y M u l t i p l i e r vs Wavelength f o r IP28 Photo-  >A  (A°)  -65APPENDIX III Rough Spectroscopic Analysis of Carbon Content of Plasma In Shock Tubes With and Without Electrodes In each analysis a comparison is made between the i n t e n s i t y of the A l l ^806A° l i n e and that of the CII M,267A° line.  The i n t e n s i t y of the argon l i n e A l l +266A° must be l  estimated i n order to correct the i n t e n s i t y observed at H>266A° and obtain a value for the i n t e n s i t y of the CII +267A° l i n e . 1  From equations (3) and (h) of Chapter II and using the l i n e strengths from Appendix I , we obtains  I  AIH4-266A I , o AIH+806A  0  a  _ "  21.9 1+266 =  v X  *+8Q6 T7T2  O Y T 1 e x p  (19.1^-19 A6) k  T  .1+09 @ kT = 1.3ev  = A 5 2 @ kT = 2.2ev So,  taking the i n t e n s i t y observed at +806A° to be e n t i r e l y 1  due to A l l l+806A°, the i n t e n s i t y at *+267A° due to A l l *+266A° can e a s i l y be estimated. observed at h267A°  The remainder of the  intensity  i s taken to be due to CII 1+267A .  s t i t u t i n g the values of I ^ ^ ^ A  0  0  and I ^ j ^ c ^ A  0  Subinto  equation (3) of Chapter I I , solving equations (3) and (1+) for N Q J J and N ^ j j , and taking t h e i r r a t i o we obtain CII t[ AII K  1N  C . 7T* by c a l c u l a t i n g "A N  which can easily be converted into  the r e l a t i v e population of the various stages of carbon and  -66argon ions from Saha's e q u a t i o n . i n T a b l e 6 a r e the measured i n -  Tabulated  t e n s i t i e s at M306AO and *267A°, t h e estimated l  eillf267A° and t h e r a t i o s  N  CII  N  AII  and  intensity of  f o r the two types o f N  A  shock d r i v e r s .  Table 6 R a t i o s o f carbon t o argon i n plasmas. Electrodeless  Electrode  I  lf806A°  =  I  V267A°  =  I  Cim-267lf  N N  1  c  n  ^  ,  l  2  A  I  5  X  ° ° 9  .39  AII  N  C  *A  .36  o=  >f267A ^  I  0  CII *267A l  N N  =  lf806A  2  c  n  0=  1  3  •  5  6  '  9  1  ,  l  f  =  .09  =  .06  AII  Ng NA  -67APPEHDIX IV C o r r e c t i o n o f Measured S p e c t r a l L i n e P r o f i l e s f o r Instrumental Broadening In  order t o o b t a i n t r u e p r o f i l e s o f l i n e s  having a whole h a l f width o f approximately  1 A ° i t i s neces-  s a r y t o c o r r e c t the measured p r o f i l e f o r broadening due t o the instrument being  used.  In  order t o make the above c o r r e c t i o n i t i s  necessary t o solve the f o l l o w i n g e q u a t i o n i n v o l v i n g a convolution  integral:  (A)  (from Unsold,  (1955)).  I n the case at handv.we have the  i n s t r u m e n t a l broadening which we w i l l r e p r e s e n t by the function f  1  (A)  represented by f  (Voigt  a  n  1  d  1  t  n  e  (A).  S t a r k broadening which w i l l be The V o i g t functions'.  (1912)) w i l l s a t i s f y equation (A) w i t h the f o l l o w i n g  r e l a t i o n s h i p between the h a l f  In  order t o use t h i s procedure  widths:  the observed  p r o f i l e and  -68the i n s t r u m e n t a l broadening f u n c t i o n must be f i t t e d t o appropriate Voigt functions.  The  p r e s e n t a t i v e of the i n s t r u m e n t a l low  pressure,  low The  p r o f i l e used as broadening was  re-  t h a t from a  temperature Hydrogen source ( G e i s l e r f i t t i n g of the above two  V o i g t f u n c t i o n s i s f a c i l i t a t e d by the use  profiles  tube).  to  of Tables made  by van de H u l s t and R e e s i n c k (19U-7). These t a b l e s a r e reproduced here (Table 7).  The  widths of the p r o f i l e  be f i t t e d are compared with those i n the t a b l e s at amplitudes l i s t e d and obtained.  the best average V o i g t  the  profile  to  Table 7:  Ordinates i n Terms o l C e n t r a l O r d i n a t e  Parameters B /h x  B2./B2  0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200 0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475 0.500  0.00 0.04 0.09 0.14 0.19 0.24 0.30 0.36 0.43 0.51 0.59 0.69 0.79 0.92 1.07 1.26 1.50 1.83 2.38 3.54  0.8 B /h 2  0.60 0.59 0.57 0.55 0. 54 0.52 0.50 0.48 0.46 0.44 0.42 0.40 0.38 0.35 0.33 0.30 0.27 0.23 0.19 0.13 0.00  Standard V o i g t P r o f i l e s  B^h  2  0.36 0.34 0.32 0.31 0.29 0.27 0.25 0.23 0.21 0.20 0.18 0.16 0.14 0.12 0.11 0.09 0.07 0.05 0.04 0.02 0.00  P  1.06 1.08 1.11 1.13 1.16 1.18 1.20 1.23 1.25 1.28 1.30 1.33 1.35 1.38 1.40 1.43 1.45 1.48 1.51 1.54 1.57  0.7  """"  0.57 0.56 0.56 0.56 0.56 0.56 0.55 0.55 0.55 0.54 0.54 0.53 0.53 0.53 0.52 0.52 0.52 0.51 0.51 0.51 0.50  6.6  0.5 0.4 6.3  6.-  widths i n Terms o f HaJ^-widtft  0.72 0.72 6.71 0.71 0.71 0.71 0.71 0.70 0.70 0.70 0.70 0.69 0.69 0.68 0.68 0.68 0.67 0.67 0.66 0.66 0.66  0.86 0.86 6.86 0.86 0.86 0.86 0.85 0.85 0.85 0.85 0.84 0.84 0.84 0.84 0.84 0.83 0.83 0.83 0.82 0.82 0.82  1.00 1.00 1.66 1.66 1.00 1.00 1.00 1.66 1.66 1.00 1.66 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  1.15 1.15 1.15 1.16 1.16 1.17 1.17 1.17 1.18 1.18 1.18 1.19 1.19 1.19 1.20 1.20 1.21 1.21 1.22 1.22 1.22  1.32 1.33 1.33 1.33 1.34 1.34 1.35 1.36 1.37 1.38 1.39 1.40 1.41 1.42 1.44 1.45 1.47 1.48 1.50 1.52 1.53  1.52 1.53 1.54 1.56 1.57 1.59 1.60 1.62 1.64 1.66 1.68 1.71 1.74 1.77 1.81 1.85 1.88 1.92 1.96 1.98 2.00  o.l  6.o50.02  (b /h)  ;  ±  1.82 1.84 1.87 1.90 1.94 1.98 2.02 2.06 2.10 2.15  2.19 2.24 2.29 2.34 2.40 2.46 2.54 2,64 2.74 2.87 3.00  o.ol  2.08 2.12 2.19 2.25 2.34 2.42 2.54 2.64 2.75 2.87 2.98 3.12 3.26 3.39 3.54 3.70 3.85 4.00 4.13 4.25 4.36  2.38 2.49 2.63 2.79 3.00 3.24 3.52 3.80 4.14 4.44 4.73 5.03 5.32 5.57 5.83 6.07 6.30 6.55 6.76 6.92 7.00  2.58 2.82 3.13 3.56 4,08 4.58 5.05 5.50 5.96 6.40 6.78 7.15 7.52 7.86 8.21 8.55 8.86 9.18 9.50 9.77 9.95  -70BIBLIOGRAPHY  A l l e n , C . W . ( 1 9 6 0 ) , A s t r o p h y s i c a l Q u a n t i t i e s , 2nd ed., Athlone Press. Barnard, A. J . , Cormack, G.D., and Simpkinson, W . V . ( 1 9 6 2 ) , Canadian J o u r n a l o f P h y s i c s kO, 5 3 1 . Barnard, A. J . , Cormack, G.D. ( 1 9 6 3 ) , Proceeds o f VI Annual Conference on I o n i z a t i o n Phenomenon i n Gases, Paris. Bates, D. R., and Damgaard, A. ( 1 9 5 0 ) , A 2if2«  P h i l . T r a n s . Roy. S o c .  101.  Breene, R..G. J r . (1957) ? Reviews Chandrasekhar, S. (19^3)» Reviews  o f Modern Physics 29., 9h. o f Modern P h y s i c s 1.2, 1.  Chang, C.T. ( I 9 6 0 ) , P h y s i c s o f F l u i d s k, 1 0 8 5 . and S h o r t l e y , G.H. (1935) » Theory o f Atomic r . - c c i S p e c t r a , Cambridge U n i v e r s i t y P r e s s . Cormack, G.D. (1962), Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia.  Condon, E.U.,  De Vos, J.C. (195*0 > P h y s i c a 20, 690. F r a n c i s , Gordon  ( I 9 6 0 ) , I o n i z a t i o n Phenomena i n Gases, B u t t e r w o r t h , p. 26.  G a b r i e l , A.H., and Heddle, D.W.O. ( i 9 6 0 ) , P r o c . Roy. S o c . A 258, 12*+. Griem, H. R., K o l b , A.C.. and Shen, K.Y. ( I 9 6 0 ) , P h y s i c a l Review 116, h. See a l s o Naval Research Lab. Report no. 5^55» I 9 6 0 . Griem, H. R. ( 1 9 6 3 ) ,  P h y s i c a l Review 1^1, 1 1 7 0 .  Holtsmark, J . (1919), Z e i t s c h r i f t  f u r P h y s i k 20, 162.  Jeanmaire, P., K l i n g e n b e r g , H., and Reichenbach, H. (1963), Z. N a t u r f o r s c h g . 18a, 318. McLean, E. A., Faneuf, C.E., K o l b , A.C., and Griem, H. R. (I960), P h y s i c s o f F l u i d s 3 , 81+3.  -71N e u f e l d , C. R. (1963), M.Sc. T h e s i s ,  University of B r i t i s h  Columbia. Olsen, H.N. (1963), J . Quant. S p e c t r o s c .  R a d i a t . T r a n s f e r 3,»£9.  Phelps, A.V. (1958), P h y s i c a l Review 110. 1362. Robinson, A.M. (1962), M.A.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia. Seaton, M.J. (1962), i n Atomic and M o l e c u l a r Processes, e d i t e d by Bates, D.R., Academic Press, S t a r r , W.L., Naff, J.T. (I960), Plasma A c c e l e r a t i o n , e d i t e d by Kash, S.W., S t a n f o r d U n i v e r s i t y Press, 52. Simpkinson, W.V. (196l), M.A^Sc. T h e s i s , B r i t i s h Columbia?,. S p i t z e r , L . J r . (1956), Physics  of F u l l y  University of Ionized  Gases,  Interscience. Theophanis, G.A. (I960), Rev. S c i . I n s t s . 31, k2J. Unsold, A\. (1955), P h y s i k der Sternatmospharen. V o i g t , W. (1912), Munch. B e r . 6 0 . 3  Van  de H u l s t  and Reesinck (19lf7), A s t r o p h y s . J . 106, 121.  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0085398/manifest

Comment

Related Items