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A study of the X-ray emission from the plasma focus Rankin, Graham Whitelaw 1975

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A STUDY OF THE  X-RAY EMISSION FROM.  THE PLASMA FOCUS by GRAHAM WHITELAW RANKIN B.Sc.,  The  A THESIS  University  SUBMITTED  of  IN PARTIAL  THE REQUIREMENTS  the  Columbia,  FULFILMENT  .1372  OF  FOR THE DEGREE OF  MASTER OF  in  British  SCIENCE  Department of  PHYSICS  We a c c e p t required  this  thesis  as  conforming  to  standard  THE UNIVERSITY  OF BRITISH  December,1975  COLUMBIA  the  In p r e s e n t i n g  this  thesis  an advanced degree at the L i b r a r y I  shall  f u r t h e r agree  for  scholarly  by h i s of  this  in p a r t i a l  the U n i v e r s i t y of B r i t i s h  make  it  freely available  that permission  representatives. thesis  for  It  financial  is understood gain shall  phvsics  The U n i v e r s i t y o f B r i t i s h  2075 Wesbrook Place Vancouver, Canada V6T 1W5  t  e  npn.  Columbia,  I agree  r e f e r e n c e and this  1  f  Columbia  that copying or  not  for  that  study. thesis  purposes may be granted by the Head of my Department  Department o f  a  for  the requirements  f o r e x t e n s i v e copying o f  w r i t ten pe rm i ss ion .  D  fulfilment of  or  publication  be allowed without my  ABSTRACT  The X - r a y studied  using  emission  t i m e i n t e g r a t e d and s t r e a k  plasma f o c u s , a small  plasma  focus  and h o t  bank o f V = 1 2 - 1 5  Measurements emitting  plasma column  have is  which extends  a few c e n t i m e t e r s i n t h e a x i a l  has  v e l o c i t i e s o f b e t w e e n 2-6  expansion for  30-60 In  the f o l l o w i n g 10-30  nsec.  plasma r e g i o n s  velocity.  The d i s t a n c e b e t w e e n t h e s e  w h i c h have  regions  the  stage,  direction, 7  X-ray  little "hot"  cm/sec.  and  emission  occurs  o r no a x i a l spots  and o b s e r v a t i o n s  are c o n s i s t e n t with r e s u l t s  P e a c o c k and M a t h e r . of t h i s  pinch  are  of  half a centimeter.  These measurements emitting  X-ray  nsec.  from small  the o r d e r of  x 10  current  yf.  shown t h a t a d i f f u s e 'early'  The  discharg-  kV, and C = 84  formed i n the  been  plasma  gun d r i v e n by a f a s t  p e r i o d T ~ 2 u s e e w h i c h was p r o d u c e d by  ing a condensor  lasts  has  photography.  volume o f v e r y dense  was c r e a t e d i n a c o a x i a l pulse of  from a plasma  By c o m p a r i n g  experiment i t  i s o l a t e d X-ray  is  of  the  X-ray  obtained  their results  with  by those  concluded t h a t the appearance  sources  is  instability. i i  associated  with the m = 0  of  TABLE OF CONTENTS  Page ABSTRACT  i i  L I S T OF FIGURES  v  ACKNOWLEDGMENTS  •. .  vi  Chapter 1  2  3  INTRODUCTION  1  1 .1  The P l a s m a F o c u s  1  1.2  P r e v i o u s Work on t h e P l a s m a F o c u s .  1.3  Uniqueness  . . .  of the Experiment  3 4  APPARATUS  6  2.1  The F o c u s  6  2.2  The S p a r k  2.3  X-ray  2.4  T i m i ng  Gap  9  Imaging  • • •  . . . .  ^ 15  OBSERVATIONS AND RESULTS  18  3.1  Image M a g n i f i c a t i o n  18  3.2  Spacial  19  3.3  Temporal R e s o l u t i o n .  3.4  X-ray  Resolution  Photographs  i ii  . .  19 19  Chapter  Page  4  DISCUSSION OF RESULTS  23  5  CONCLUSIONS  28  REFERENCES  29  iv  LIST OF FIGURES  F i gure  Page  1  Experimental arrangement  7  2  E l e c t r o d e assembly  8  3  S p a r k gap e l e c t r o d e s  4  Electrical  5  I l l u s t r a t i o n of Optical  6  Pinhole  7  Electro-optical  8  Triggering  9  X - r a y p h o t o g r a p h s and an o s c i l l o g r a m of t h e f o c u s i n g event  21  Schematic events  27  10  circuit  10  o f t h e plasma f o c u s .  . . . . .  arrangement  13 . . . . .  X-ray  camera  arrangement  f o r proposed  v  12  14 16 17  sequence o f  ACKNOWLEDGMENTS  The ing  idea of using  t h e dense p i n c h s t a g e  streak  photography  o f t h e plasma f o c u s  for analyzi s that of  Dr . J . M e y e r . I  would l i k e  plasma f o c u s  t o acknov/ledge t h e b u i l d i n g o f t h e  apparatus  by J a c k B u r n e t t .  To Dough S i e b e r g express  my a p p r e c i a t i o n f o r t h e i r Many t h a n k s  physics  group This  Energy  and A l l e n C h e u c k , technical  I wish to assistance.  t o t h e members o f t h e U . B . C .  for their  helpful  discussions.  work was s u p p o r t e d by a g r a n t  C o n t r o l Board of Canada.  plasma  f r o m t h e Atom  Chapter 1  INTRODUCTION  1.1  The P l a s m a  Focus  The p l a s m a f o c u s electrodes  inside  at a pressure  i s a device consisting  a vessel  of less  than  c o n t a i n i n g a m i x t u r e o f gases several  The f o r m a t i o n o f t h e d e n s e t h e end o f t h e c o a x i a l  the years  concentrated electrodes,  with  plasma f o c u s  T.I. Flippova  studies  on t h e i n i t i a l t h e dynamics  s h e a t h , and t h e f i n a l  torr.  breakdown  dense  focus  stage  on t h e l a t t e r  on t h e n e u t r o n p r o d u c t i o n w h i c h r e s u l t s  A high capacitor  bank  have  between t h e  o f t h e plasma  focus,  and more s p e c i f i c a l l y if a D  2  gas i s  vessel.  voltage  (in this  e x p t . 1 2 - 1 5 kV) f r o m t h e  i s a p p l i e d b e t w e e n t h e i n n e r and o u t e r  trodes of the discharge in the region  i n the 1960's.  o f t h e plasma f o c u s  electrical  observed  o f t h e rundown o f t h e c u r r e n t  recent i n t e r e s t being  used i n t h e d i s c h a r g e  beyond  e l e c t r o d e g e o m e t r y was f i r s t  and s t u d i e d by t h e R u s s i a n , Over  of coaxial  vessel.  This  produces  elec-  a breakdown  a t t h e back o f t h e e l e c t r o d e s n e a r a L u c i t e  1  2  insulator  (see  Fig.  electrode  back  along  ducing have  a "waterfall"  shown [ 1 ]  build-up duced  1).  Current  the  insulator  flow over  that during  there  is  a t t h e back  then flows  t o t h e back  the  plate.  At t h i s  the c u r r e n t  stages  The j , x B_, outward  time the f i l a m e n t a r y  plate  of  x B )  r  is  Q  the o u t e r  greater  nearer  e l e c t r o d e and so  Photographs  by M a t h e r  pattern  inverse  have  pro-  pinch  the outer  p a t t e r n of  inner  force  electrode.  the c u r r e n t  blends  the  force  e l e c t r o d e than  the c u r r e n t  [2]  Studies  9  towards  the  pro-  current  to form a uniform a x i s y m e t r i c d i s c h a r g e . B e c a u s e i r and B„o d e c r e a s e w i t h r a d i u s (5  centre  surface.  filamentary light Z  next d r i v e s  insulator  the e a r l y  a complex  from the  sheath  shown t h i s  has  a  at cant.  appearance  of  the  sheath. The  current  copper  electrodes  called  snowploughing  the physics sheath  limit  has  cm/sec) of  [5]  1.5  x 10  i t overshoots radial  the strong  this  pinch  gas  sheath  i n the annulus of  force  of  [3].  has  sheath  pinch  the  This  effect  describing  The maximum  been r e c o r d e d  to  average have  [4]. arrives  towards force, j t h e gas  the c u r r e n t  it.  models  and e x p e r i e n c e s  one c h o o s e s  s u c h t h a t t h e peak  i n f r o n t of  cm/sec  7  collapse  radial  i t moves down between  l e d to s e v e r a l  When t h e c u r r e n t electrodes  as  accumulates  of the c u r r e n t  velocity  an u p p e r  sheath  at  t h e end o f  a fast  the a x i s x B . Q  as To  (1-4 a  occurs  10  7  result  maximize  m i x t u r e , and t h e  pulse  x  the  at the  voltage time  of  3  radial is  collapse.  In  a d d i t i o n t h e peak  d e t e r m i n e d by t h e  Any  reduction  i n d u c t a n c e of  of  the c u r r e n t  the v o l t a g e  in the inductance, f o r  pulse  supply  network.  e x a m p l e , by u s i n g  several  low i n d u c t a n c e c a b l e s  to d e l i v e r the c u r r e n t from the  capacitor  bank  vessel  a  to the d i s c h a r g e  greater  pinch  cm"  been o b s e r v e d 3  1 .2  plasma  and t e m p e r a t u r e o f  Previous  of  radiation flux and S c h l i e r e n  and  and  have  given  neutron y i e l d s  plasma  densities  Electron keV have  addition,  it  the  neutron emission  total  has  temperature of  keV  1 9  been done  region  [8].  by  observ-  absolute Shawdowgraphs  of  t h e dense  have  plasma  been u s e d t o  the [12],  obtain  of data to both  X-ray  (assuming a thermonuclear  plasma)  of  [4].  the o r d e r (for  by l a s e r  been o b s e r v e d  several  have  The f i t t i n g  temperatures  been o b s e r v e d  10  been u s e d t o d e t e r m i n e  development  [4].  of o r d e r  s p e c t r u m arid t h e  soft X-ray  photographs  pinch  Focus  of d e n s i t i e s  in the  temporal  and  a r e s u l t of the  keV.  i n t e r f e r o m e t r i c measurements  emission  .70  several  the emission  the e l e c t r o n d e n s i t y  have  f o r m e d as  Work on t h e P l a s m a  t h e shape  spacial  in a c h i e v i n g  t o have e l e c t r o n d e n s i t i e s  Measurements ing  result  force.  The d e n s e has  will  that  of  10  deuterium) scattering  cm  1 9  of  approximately  [7].  in a deuterium  per d i s c h a r g e  - 3  requires  In plasma  an  (assuming a thermonuclear  ion plasma  4  [ 6 ] ) . The a s s u m p t i o n clearly  of thermal neutron p r o d u c t i o n i s  v a l i d since there is  production  evidence f o r a nonthermonuclear  i n a d e u t e r i u m plasma f o c u s [ 9 ] . Due t o t h e h i g h  focus  most o f  temperatures reached in the  the r a d i a t i o n i s  i n the X - r a y  X-rays  a r e due t o B r e m s s t r a h l u n g  thesis  devotes  the X-ray focus  1.3  f e a t u r e s of the dense  a t U . B . C . does an X - r a y  Uniqueness What  the U.B.C.  of is  included pinhole  stage  of  pictures  is  photographs the p i n c h .  the X - r a y  (in  and t h u s  emitted,  focus  stage.  and as  The  such  is  is  the X-ray  the f i r s t  experi-  emissions  during  Other experiments which f e a t u r e s of the focus emissions  absorbers  to o b t a i n time  have  with X-ray  monitored  work done on t h e  been t o e x p l a i n t h e o b s e r v a t i o n s  X-ray  inte-  energies  i n a d d i t i o n to c o r r e l a t i o n of  the t h e o r e t i c a l  have  by t h e use o f  i n f o r m a t i o n about the  the v i s i b l e region)  so f a r has  neutron f l u x  This  experiment performed at  that i t of  emission  cameras w i t h v a r i o u s  Most o f focus  lab  the r e c o r d i n g of X - r a y  the X-rays  radiation.  the Experiment unique about t h i s  grated photographs of  not produce neutrons  plasma p h y s i c s  investigated  These  e m i t t i n g plasma.  ment t o t a k e s t r e a k the focus  and l i n e  region.  plasma  i t s main i n t e r e s t t o t h e i n v e s t i g a t i o n o f  emission  primarily  not  framing pulses.  plasma of  t h a t o r i g i n a t e s from a deutrium f o c u s .  the To'  5  explain  the a n i s o t r o p i c  neutron  energy  as  for  example  spectra various  the  and  talists extent in  of  features in this  Bostick.  focus  measure  is  have  field  proposed, models,  processes  occurring  and p o s s i b l e  mechanisms  been s t u d i e d  by s u c h n o t e d  as  Their  P e a c o c k and M a t h e r  observations  discussed  summary  of  and  and s u m m a r i z e d  X-ray experimen-  to a  and p r o p o s e d  been o b s e r v e d  i t was  t h e aim o f  v e l o c i t i e s and l i f e t i m e s o f  to compare  those  the X-ray  at the  i n the  lesser  mechanisms U.B.C.  conclusion  this  experiment  the X-ray  the r e s u l t s  time i n t e g r a t e d photographs  possible  mechanism  obtained with e x i s t i n g for  X-ray  The e x p e r i m e n t was features  a success  temporal  and  time i n t e g r a t e d photography  be f o r m u l a t e d .  models  plasma  with  so  and that a  p r o d u c t i o n c o u l d be f o r m u l a t e d .  and  a result a possible  of  to  emitting  o b t a i n e d by o t h e r e x p e r i m e n t a l i s t s , and t o f i t  compare  As  been  thi s thesi s . In  and  thermonuclear  c o n j u n c t i o n w i t h what has  plasma  have  and  focus. Observations  emission  models  fluxes  t h e beam t a r g e t m o d e l , and o t h e r  w h i c h assume t h e r m a l within  d i s t r i b u t i o n of neutron  the X - r a y s  mechanism  in that the  using  nsec.  streak,  were r e c o r d e d and for  X-ray  spacial  analyzed.  production  could  Chapter  2  APPARATUS  2 .1  The  Focus The e x p e r i m e n t a l  The  a r r a n g e m e n t i s shown i n F i g . 1.  plasma focus i n v e s t i g a t e d in t h i s experiment c o n s i s t s  b a s i c a l l y o f two approximately  coaxial c y l i n d r i c a l copper electrodes  25 cm i n l e n g t h .  The  inner electrode cylinder  o f p o s i t i v e p o l a r i t y has an o u t e r d i a m e t e r inner diameter  o f 2.5  cm.  of  o f 5 cm and  an  The c a t h o d e i s a p e r f o r a t e d  c o p p e r c y l i n d e r o f 10 cm d i a m e t e r .  The o u t e r c y l i n d e r i s  soldered onto a brass disk with a c o n c e n t r i c hole of 6 diameter.  The h o l e a l l o w s the c o a x i a l a s s e m b l y c o n s i s t i n g  o f t h e a n o d e , and a c y l i n d r i c a l P y r e x i n s u l a t o r (5 cm diameter  cm"  and  5 cm l e n g t h ) , w h i c h i s f i t t e d o v e r t h e  inner  anode,  t o be m o u n t e d i n s i d e t h e o u t e r c y l i n d e r ( s e e F i g . 2 ) . The g l a s s s l e e v e and a p l e x i g l a s s d i s k  prevent  premature e l e c t r i c a l breakdown between the o p p o s i t e electrodes. formation  In a d d i t i o n t h e g l a s s s l e e v e a l l o w s t h e  o f an i n v e r s e p i n c h f o l l o w i n g b r e a k d o w n t o  b e t w e e n t h e a n o d e a t t h e s l e e v e end and copper cathode c y l i n d e r .  6  the i n s i d e of  polarity initial occur the  Spark gap Glass Insulator  Inner Electrode Current sheath  cm  84/jf  Outer Electrode (Perforated)  X-ray Film Holder  Evacuated Tube  Image Converter  F i g u r e 1. E x p e r i m e n t a l  arrangement.  8  Coax Cablo lead in  Figure 2.  Electrode  assembly.  9  The  e n t i r e electrode assembly i s f i t t e d i n s i d e a  Pyrex vessel which i s evacuated  and f i l l e d w i t h a gas  o f H y d r o g e n and A r g o n ( a p p r o x i m a t e l y to a p r e s s u r e  10% A r g o n by  mixture  pressure)  o f b e t w e e n .5 t o .8 T o r r .  The e l e c t r o d e a s s e m b l y i s h e l d i n p o s i t i o n i n t h e P y r e x v e s s e l by a b r a s s p l a t e .  The b r a s s p l a t e ( o r  h e a d e r ) a l s o p r o v i d e s an e l e c t r i c a l c o n n e c t i o n c o a x i a l c a b l e s coming from  cable  between  the c a p a c i t o r bank to the  and o u t e r c y l i n d e r i c a l c o p p e r e l e c t r o d e s  the  inner  ( l o c a t e d i n s i d e the  Pyrex v e s s e l ) . The is provided  power r e q u i r e d to p r o d u c e the c u r r e n t  by a b a n k o f s i x , 14 u f c a p a c i t o r s c h a r g e d  a v o l t a g e b e t w e e n 12 and by 30 c o a x i a l c a b l e s are a l l connected  2.2  The S p a r k  15 kV.  ( f i v e c a b l e s f o r each c a p a c i t o r )  to the c a b l e  Gap  an a u x i l i a r y s p a r k g a p .  Inside the spark  are four e l e c t r o d e s .  four electrodes. another  A l l spark  One  e l e c t r o d e (#2  Fig. 3 depicts  firing the  in the diagram) i s con-  i s e l e c t r i c a l l y connected  to the i n n e r p o s i t i v e c y l i n d r i c a l  gaps  can, which houses  to the h i g h v o l t a g e t e r m i n a l of the c a p a c i t o r (#1)  which  header.  a r e t r i g g e r e d a t t h e same t i m e by a p u l s e p r o d u c e d by t h e s p a r k gap,  to  This energy is d e l i v e r e d  E a c h c a p a c i t o r has a s p a r k g a p .  nected  sheath  ( v i a the c a b l e  electrode.  and header)  10  Fi gure  3.  Spark  gap e l e c t r o d e s .  11 Two  other electrodes  (#3 and #4)  between the above mentioned e l e c t r o d e s . (produced  by t h e a u x i l i a r y s p a r k g a p )  t h e o u t e r d i s k s h a p e d e l e c t r o d e (#3) a tungsten  wire  between them.  ( e l e c t r o d e #4), This spark  are  located  A high voltage  i s a p p l i e d between and t h e f i n e p o i n t  so t h a t a s p a r k  p r o d u c e s a U.V.  f l a s h which in turn  a c u r r e n t to s t a r t f l o w i n g  e l e c t r o d e s #1 a n d #2.  r e s u l t i n g plasma short  e l e c t r o d e s #1 and #2 and t h e r e b y  discharges  the  between  circuits  capacitor.  T h i s e l e c t r i c a l a r r a n g e m e n t o f t h e s p a r k gap a f a s t and j i t t e r - f r e e b r e a k d o w n o f t h e c a p a c i t o r This is important  since simultaneous  o f a good f o c u s .  f o r the  ensures  bank.  a r r i v a l of the  pulses at the cable header i s important  of  i s produced  i o n i z e s the a i r and c a u s e s The  pulse  voltage  formation  See F i g . 4 f o r t h e d e t a i l e d e l e c t r i c a l  layout.  2.3  X-ray  Imaging  T i m e i n t e g r a t e d and s t r e a k e d were taken The  simultaneously  imaging  was  approximately  event.  by u s i n g a p i n h o l e X - r a y  at r i g h t angles  17 cm f r o m  photographs  o f t h e same p l a s m a f o c u s  accomplished  Located  X-ray  camera.  to the e l e c t r o d e a x i s  t h e f o c u s ) a r e p i n h o l e s o f .5  (and mm  ( o n e on e a c h s i d e ) w i t h a 1 m i l Be f o i l w i n d o w ( s e e F i g s . 5 and  6).  The  pinhole diameter  Fresnel zones wide.  The X - r a y s  i s of the order of a thousand passing through  the  pinholes  To Plasma Focus electrodes 10 KV 20M :  To other 14 uf capacitors 4K Wv  500p  Trig Pulse  HM—Z I00K«  500p  100 M  5 25M  Charging Unit  5C22 r±-  F i g u r e 4.  Electrical  ferrite core  100 M  c i r c u i t of the plasma  focus.  Polaroid camera Image intensifier Streak unit streak  scintillator  direction  Plasma focus electrodes  plasma  Be foil  pinhole  X-ray  F i g u r e 5.  film  Illustration of optical  arrangement.  14  F i g u r e 6.  Pi n h o l e .  15 t r a v e l down an e v a c u a t e d length) until  hollow  tube (approximately  t h e y h i t i n one c a s e X - r a y  i n t h e o t h e r a t h i n s c i n t i l l a t o r ( 1 . 5 mm) in v i s i b l e - l i g h t . Image C o n v e r t e r through  ( F i g . 7).  2.4  T i m i ng  achieved  image  TRW passed  finally  streak  by p l a c i n g a l i g h t p i p e n e a r t h e end and  the c u r r e n t sheath  passed  l i g h t r a d i a t e d f r o m i t was  pictures above  As t h e l u m i n o u s f r o n t o f  down b e t w e e n t h e e l e c t r o d e s  the  p i c k e d up by t h e l i g h t p i p e  (see  then sent to a p h o t o m u l t i p i i e r which i n t u r n  t r i g g e r e d the d e l a y g e n e r a t o r converter  8606) before  or  an  image i s then  t i m i n g r e q u i r e d t o t a k e th^e X - r a y  the outer p e r f o r a t e d e l e c t r o d e .  F i g . 8) and  producing  in  by a c a m e r a o n t o 1 0 , 0 0 0 A . S . A . p o l a r i o d  film  was  The s t r e a k e d  an i m a g e i n t e n s i f i e r (RCA  The  recording film  T h i s i m a g e i s t i m e r e s o l v e d by a Camera.  being recorded  17 cm  which sent a pulse to the  image  to s t r e a k i t . T h i s m e t h o d was  n e c e s s i t a t e d by t h e  irreproduce-  a b i l i t y i n the d i s c h a r g e ,  because of v a r i a t i o n i n the  pressure,  (due to e l e c t r o d e m a t e r i a l  gas c o m p o s i t i o n  n a t i o n ) , and b a n k v o l t a g e .  T r i g g e r i n g on t h e d l / d t  gas contamipulse  w h i c h i s p i c k e d up by a R o g o w s k i c o i l a t t h e b a c k p l a t e t r i e d but proved  too u n r e l i a b l e .  was  F i g u r e 7.  Electro-optical  X-ray camera.  Power and Trig. Unit  Light pipe  Photo multiplier  Delay Unit  V  Rogowski Coil  T  X-rays  X-ray Film Holder  e  _/  Scintillator Plasma Focus  Image Converter  F i g u r e 8. T r i g g e r i n g  J  Image Intensifier  arrangement.  Chapter 3 OBSERVATIONS AND RESULTS  B e f o r e an i n t e r p r e t a t i o n o f t h e X - r a y  photographs  a r e made, m e a s u r e m e n t s o f t h e m a g n i f i c a t i o n , t h e s t r e a k etc.,  m u s t be d o n e .  T h e f o l l o w i n g d e s c r i b e s how s u c h m e a s u r e -  ments were  conducted.  3.1  Magnification  Image  The m a g n i f i c a t i o n o f t h e t i m e i n t e g r a t e d was o b t a i n e d  by m e a s u r i n g t h e o b j e c t - i m a g e  the focus t o the p i n h o l e and from  white  electrode.  i s on t h e For the  d i s t a n c e s were measured t o t h e  A t t h e s c i n t i l l a t o r ' s s u r f a c e two  t h r e a d s were used as o b j e c t s i n a s e p a r a t e  to d e t e r m i n e the m a g n i f i c a t i o n  parallel experiment  between t h e s c i n t i l l a t o r and  t h e f i l m by m e a s u r i n g t h e r e a l d i s t a n c e b e t w e e n t h e and  that recorded  from  the p i n h o l e to the X-ray  c e n t r e a x i s ( z ) d e f i n e d by t h e i n n e r streak shot the object-image  pictures  distances  f i l m , assuming that the o b j e c t ( i . e . the focus)  scintillator.  speed,  by t h e f i l m .  18  threads  19  3.2  Spacial  Resolution  T h e s p a c i a l r e s o l u t i o n i s l i m i t e d t o 1 mm and i s d e t e r m i n e d by t h e p i n h o l e d i a m e t e r a n d o p t i c a l The s c i n t i l l a t o r t h i c k n e s s (.15  cm)  geometry.  though a f f e c t i n g image  f o r m a t i o n d o e s n o t a f f e c t t h e r e s o l u t i o n due t o t h e comp a r a t i v e l y l a r g e d i s t a n c e (17 cm) b e t w e e n  i t and t h e p i n h o l e .  T h e t i m e d u r a t i o n o f t h e s t r e a k f r o m 50 t o 200 was d e t e r m i n e d by t h e s e t t i n g o f t h e c o n t r o l s on t h e converter unit.  t h r e a d s , one a t t h e b e g i n n i n g streak.  T h i s change  Temporal  was  white  a n d one a t t h e m i d d l e o f t h e  i n d i s t a n c e a s r e c o r d e d by t h e p o l a r i o d  f i l m , and t h e s t r e a k d u r a t i o n , d e t e r m i n e s t h e s t r e a k  3.3  image  The l e n g t h o f t h e s t r e a k on t h e f i l m  o b t a i n e d by t a k i n g two p i c t u r e s o f t h e two p a r a l l e l  nsec.  speed.  Resolution  The t e m p o r a l r e s o l u t i o n o f the s t r e a k i s l i m i t e d by t h e d e c a y t i m e o f t h e p l a s t i c which i s approximately 2 nsec.  scintillator  S i n c e t h e image  has a v e r y l o n g decay time ( o r a f t e r image)  photographs intensifier  i t had t o be  p o s i t i o n e d a f t e r the s t r e a k u n i t o r image c o n v e r t e r i n o r d e r t h a t t h e t e m p o r a l r e s o l u t i o n was n o t  3.4  X-ray  sacrificed.  Photographs Enlargements of the recorded  X-ray p i c t u r e s were  taken such t h a t the f i n a l enlargements of the time i n t e g r a t e d  20 a n d s t r e a k s h o t s h a v e t h e same m a g n i f i c a t i o n ( o r r a t i o o f image to o b j e c t s i z e ) . These measurements combined  with the  photographs  t a k e n h a v e g i v e n t h e f o l l o w i n g r e s u l t s and o b s e r v a t i o n s . Two  streak photographs with their corresponding  t i m e i n t e g r a t e d X - r a y p h o t o g r a p h s a r e shown i n F i g . 9.  From  p i c t u r e s a s t h e s e i t was d e t e r m i n e d t h a t a l o n g e m i t t i n g X-ray r e g i o n of plasma, extending over d i s t a n c e s of order o f c e n t i m e t e r s w i t h l i f e t i m e s o f 30-60 n s e c . i s p r o d u c e d w h i c h m o v e s a x i a l l y t o w a r d s and away f r o m t h e a n o d e v e l o c i t i e s between  2 and 6 x 1 0  7  at  cm/sec.  T h i s X - r a y b u r s t i s f o l l o w e d 10-30  nsec.  latter  by s m a l l i n t e n s e X - r a y e m i t t i n g r e g i o n s e x t e n d i n g o v e r d i s t a n c e s < .5 cm w i t h l i f e t i m e s o f 10-30 n s e c ( s e e F i g . 9 b , c ) . Some o f t h e s e X - r a y e m i t t i n g r e g i o n s e x h i b i t no n o t i c e a b l e axial v e l o c i t y (see Figure 9 f ) .  From s p a c i a l  correlation  with the c o r r e s p o n d i n g time i n t e g r a t e d photographs  (see  F i g . 9 a , c ) t h e s e s o u r c e s show up as v e r y s m a l l d a r k d o t s on the X-ray f i l m i n comparison to the s o f t e r and d i f f u s e  back-  g r o u n d p r o d u c e d f r o m r a d i a t i o n e m i t t e d f r o m an e a r l i e r  time.  T h e d l / d t s i g n a l was d i s p l a y e d on a s c o p e , t h e f o c u s b e i n g i n d i c a t e d by a s u d d e n d i p i n t h e d l / d t ( s e e o s c i l l o g r a m F i g u r e 9e - u p p e r t r a c e A ) .  waveform  The s t r e a k  d u r a t i o n was a l s o m o n i t o r e d a n d a p p e a r s a s a 'gap' i n t h e l o w e r t r a c e ( B ) , on t h e o s c i l l o g r a m . The r e a l t i m e o f b o t h t r a c e s c o i n c i d e w i t h i n 10 n s e c . o f e a c h o t h e r , e x t r e n o u s  (Z = a x i a l d i s t a n c e f r o m t h e e l e c t r o d e s ) F i g u r e 9.  X - r a y p h o t o g r a p h s and an o s c i l l o g r a m o f t h e focusing event.  22  t i m e d e l a y i n t h e e l e c t r i c a l c a b l e s arid t h e e q u i p m e n t i s t a k e n i n t o a c c o u n t when c a l c u l a t i n g t h i s f i g u r e . The d i s c h a r g i n g o f t h e c a p a c i t o r s c r e a t e s siderable electrical  noise.  con-  T h i s n o i s e was e l i m i n a t e d  t h e u s e o f f e r r i t e c o r e s on m o s t o f t h e e l e c t r i c a l  by  cables,  and by t h e u s e o f a l i g h t p i p e f o r d e t e c t i n g t h e p a s s a g e o f the c u r r e n t sheath.  To f u r t h e r m i n i m i z e e l e c t r i c a l  inter-  f e r e n c e t h e t r i g g e r d e l a y u n i t , p h o t o m u l t i p i i e r , and scope were p l a c e d i n a s h i e l d e d room. w a l l s and t h e e l e c t r i c a l  T h e room h a s d o u b l e c o p p e r  p o w e r t o t h i s r o o m was  b e f o r e and a f t e r e n t e r i n g i t .  filtered  Chapter 4 DISCUSSION OF RESULTS  The o b s e r v e d f e a t u r e s o f t h e f o c u s a g r e e w e l l w i t h t h e r e s u l t s o f o t h e r e x p e r i m e n t e r s who h a v e s t u d i e d t h e f o c u s . The t i m e i n t e g r a t e d p h o t o g r a p h s t o t h o s e o b t a i n e d by M a t h e r  [ 1 0 ] , Peacock  taken are s i m i l a r [ 1 1 ] , and B o s t i c k  [13]. Peacock  [ 1 2 ] has o b s e r v e d t h a t t h e s u s t a i n m e n t  time o f t h e p i n c h e d plasma  i s n o t m o r e t h a n 50 n s e c . a n d  corresponds d i r e c t l y to the duration of the i n i t i a l of thermal X-rays.  He a l s o f o u n d t h a t t h e l o c a l  burst  break-up  o f t h e p i n c h i s o f t e n due t o m = 0 i n s t a b i l i t i e s , and t h a t the time between f o r m a t i o n o f the dense p i n c h and i t s break-up i s n o t g r e a t e r t h a n 100 n s e c .  These o b s e r v a t i o n s c o r r e s p o n d  well to the measured l i f e t i m e s o f the heated (X-ray e m i t t i n g ) p l a s m a a s r e c o r d e d by s t r e a k p h o t o g r a p h y Peacock  in this  experiment.  [ 1 4 ] has f u r t h e r o b s e r v e d t h a t t h e q u a s i -  c y l i n d i r c a l compression produces a ' f o u n t a i n ' o f a h o t and d e n s e p l a s m a w h i c h t r a v e l s a x i a l l y away f r o m t h e e l e c t r o d e s with a v e l o c i t y of approximately 10  23  7  c m / s e c , which  agrees  24  w i t h the measured observed r a d i a l  v e l o c i t i e s of 2-6  x 10  7  cm/sec. B o s t i c k [13] observes t h a t the d u r a t i o n of the X-ray e m i s s i o n from small to 30 nsec.  i n t e n s e s o u r c e s i s o n l y 10  T h i s agrees w i t h o b s e r v a t i o n s i n t h i s  But he i n c o r r e c t l y are  individual  triggered  in  assumes t h a t these small  sequence  a l o n g the a x i a l  seen from the s t r e a k photograph clearly  not always the c a s e .  i s the o r d e r o f magnitude e j e c t e d from the a x i a l  epxeriment.  i n t e n s e sources  region.  As i s  ' f i n F i g . 4, t h i s i s  Bostick states that 10  of the v e l o c i t y  of the  cm/sec.  7  plasma  r e g i o n , which i s i n agreement w i t h  t h e , v a l u e s measured by Peacock From a time sequence  and i n t h i s  experiment.  o f shadowgraphs  Peacock  observes t h a t the dense p i n c h breaks up due to a m = 0 instability the  and  t h a t the time i n t e r v a l  between f o r m a t i o n o f  dense p i n c h and onset of the i n s t a b i l i t y ,  the s u s t a i n m e n t  t i m e , i s of the o r d e r of 10 nsec.  He measures f u r t h e r ,  the  the d i s t a n c e between  wavelength  constrictions,  of the i n s t a b i l i t y ,  i s ' o f the o r d e r of h a l f a c e n t i m e t e r .  that  From  time r e s o l v e d X-ray photographs of the plasma  investigated  here (see F i g . 4) one measures time i n t e r v a l s  between the  appearance  of the X-ray e m i s s i o n , s p r e a d i n g over the whole  p i n c h c h a n n e l , and the appearance  of the i s o l a t e d  X-ray s o u r c e s t o be of the o r d e r of 10 n s e c , which to Peacock's  substainment time.  point-like corresponds  The d i s t a n c e between the  25  i s o l a t e d X - r a y s o u r c e s i s on t h e a v e r a g e which c o r r e s p o n d s  to the wavelength  a s o b s e r v e d by P e a c o c k . that the appearance  half a centimer  of the m = 0 i n s t a b i l i t y  These c o r r e l a t i o n s s t r o n g l y suggest  o f the i s o l a t e d X-ray sources i s asso-  ciated with the i n s t a b i l i t y . The f e a t u r e s o f t h e f o c u s o b s e r v e d h e r e a n d by Peacock  suggest that the f o l l o w i n g sequences  events takes place.  of physical  These events a r e d e s c r i b e i n f i v e  stages. The f i r s t s t a g e i s t h e c o l l a p s e o f t h e c u r r e n t sheath o f t h e end o f the e l e c t r o d e s , the B ing  t h e gas mixutre r a p i d l y inward.  by t h e p l a s m a  e  field  compress-  The second s t a g e  starts  b e i n g p i n c h e d , and as a r e s u l t t h e plasma  o b t a i n s an a x i a l motion w i t h v e l o c i t i e s o f t h e oder o f 1 0 cm/sec.  In the t h i r d stage the plasma  and by r a d i a t i v e l o s s e s .  d i f f u s e plasma  forms,  times between t h e decay o f t h e  and the c r e a t i o n o f " h o t " s p o t s .  As a r e s u l t  i s h e a t e d by l o c a l i z e d f i e l d s and X - r a y  occurs again.  Since the pinch f o r c e or the magnetic  f i e l d i s symmetric ing,  instability  r a t e s o f t h e o r d e r o f 10 n s e c , a t i m e w h i c h i s  consistent with the observed the plasma  c o o l s by e x p a n s i o n  S t a g e f o u r s t a r t s when t h e i n s t a b i l -  i t i e s , p a r t i c u l a r l y the m = 0 sausage w i t h growth  7  the plasma  emission B  0  and p e r p e n d i c u l a r to t h e r e g i o n o f p i n c h -  e x p a n d s e q u a l l y away a n d t o w a r d s  the electrode  ( w i t h a p p r o x i m a t e l y t h e same a x i a l v e l c o i t y ) d u r i n g i t s v e r y s h o r t l i f e t i m e , a n d t h u s l o o k s l i k e an a b l o n g  ' d o t ' on t h e  26  streak photograph.  In s t a g e f i v e t h e " h o t " s p o t i n s t a g e  f o u r c o n t i n u e s t o e x p a n d w h i l e a t t h e same t i m e  rapidly  c o o l i n g a n d e m i t t i n g l i t t l e o r no X - r a y s . T h i s sequence the f o r m a t i o n and breakup observed  would e x p l a i n the o b s e r v a t i o n s o f t h e dense f o c u s s t a g e as  i n t h i s and o t h e r e x p e r i m e n t s .  10) i s a p i c t o r i a l  during  summary o f t h e p r o p o s e d  The f o l l o w i n g ( F i g . process.  27  Stage 1  Stage 2  Stage 3  Stage 4 X-rays  Stage 5  S t a g e 1 : gas i s p i n c h e d by B  &  field  S t a g e 2 : plasma i s p i n c h e d , X - r a y e m i s s i o n o c c u r s S t a g e 3 : plasma i s c o o l i n g by e x p a n s i o n and r a d i a t i v e S t a g e 4 : m=0  instability  forms, X - r a y e m i s s i o n o c c u r s  S t a g e 5 : Plasma e x p a n d i n g and  F i g u r e 10.  cooling  Schematic f o r proposed of events.  sequence  losses  Chapter 5 CONCLUSIONS  Measurements of the X-ray e m i s s i o n s from the f o c u s by t i m e i n t e g r a t e d a n d s t r e a k p h o t o g r a p h y  plasma  has y i e l d e d  i n f o r m a t i o n a b o u t the v e l o c i t i e s , l i f e t i m e s and growth  of  the X-ray e m i t t i n g regions. A d i f f u s e X-ray e m i t t i n g plasma, extending s e v e r a l centimeters i n the a x i a l d i r e c t i o n , having v e l o c i t i e s of 2-6 x 1 0  7  observed.  c m / s e c . a n d l i f e t i m e s o f 3 0 - 6 0 n s e c . has T h i s i s f o l l o w e d 10-30  been  n s e c . l a t e r by s m a l l i n t e n s e  X - r a y s o u r c e s w h i c h h a v e l i t t l e o r no a x i a l v e l o c i t y , l i f e t i m e s o f t h e o r d e r o f 10  and  nsec.  The d i s t a n c e b e t w e e n t h e s e s h o r t - l i v e d s m a l l e m i t t i n g r e g i o n s c o r r e l a t e d t o o b s e r v a t i o n s made by  X-ray  Peacock  s t r o n g l y suggest that these X-ray sources are a s s o c i a t e d with the m = 0 i n s t a b i l i t y . A p o s s i b l e model f o r e x p l a i n i n g the s e q u e n c e  of  X - r a y e v e n t s has been p r o p o s e d w h i c h i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n s a n d m e a s u r e m e n t s o b t a i n e d by P e a c o c k Mather. 28  and  REFERENCES  1.  M a t h e r , J . W . , and W i l l i a m s , A . H . , P h y s i c s 2081 (1966).  2.  Mather, J.W., Nucleonics in aerospace - proceedings of t h e 2nd i n t e r n a t i o n a l s y m p o s i u m , C o l u m b u s , O h i o , U . S . A . , 1 2 - 1 4 J u l y 1967 (New Y o r k : Instrument S o c i e t y of America 1968), pp. 290-6.  3.  Pert, 6 . J . , Brit. (1968).  4.  M a t h e r , J . W . , P l a s m a P h y s i c s and C o n t r o l 1ed N u c l e a r Fusion Research V o l . II, Proceedings of a Conference on P l a s m a P h y s i c s and C o n t r o l l e d N u c l e a r F u s i o n R e s e a r c h h e l d by t h e I . A . E . A . a t C u l h a m , 6 - 1 0 S e p t . , 1965, pp. 389-403.  5.  T o e p f e r , A . J . , S m i t h D.R., and B e c k e r , E . H . , P h y s i c s F l u i d s , V o l . 1 4 , #1 (1971 ) .  6.  P e a c o c k , N . J . , et al. 5 t h E u r o p e a n C o n f e r e n c e on C o n t r o l l e d F u s i o n and P l a s m a P h y s i c s , G r e n o b l e , F r a n c e , V o l . I I , 2 1 - 2 5 , A u g . , 1 9 7 2 , p. 6 6 .  7.  D o w n i n g , J . N . , The P h y s i c s p p . 991 -1001 .  8.  Morgan,  9.  B e r n s t e i n , M . J . , and H a i , F . , #6, 317 ( 1 9 7 0 ) .  J . Appl . P h y s i c s ,  of F l u i d s ,  9,  S e r . 2 V o l . 1, 1487  of  3  o f F l u i d s , V o l . 1 8 , #8, 1 9 7 5 ,  P . D . , et al. 3 r d E u r o p e a n C o n f e r e n c e on C o n t r o l l e d F u s i o n and P l a s m a P h y s i c s , N o v o s i b i r s k , U . S . S . R . , 1-7 A u g . , 1 9 6 8 , p. 1 1 8 . 3  29  Physics  L e t t e r s , V o l . 31A  30  10.  M a t h e r , J . 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D . , 3 r d E u r o p e a n C o n f e r e n c e on P l a s m a P h y s i c s and C o n t r o l l e d Nuclear Fusion Research (I.A.E.A. cn-24/ G - 4 ) , N o v o s i b i r s k , U . S . S . R . , 1-7 A u g u s t , 1 9 6 8 , pp. 1-22.  J.W., Peacock, N . J . , W i l c o c k , P.D., T o p i c a l Conf e r e n c e i n P u l s e d High D e n s i t y P l a s m a s , Los Alamos, New M e x i c o , U . S . A . , S e p t . 1 9 - 2 2 , 1 9 6 7 .  

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