Stark broadening of argon and neon resonance line

Greig, J. R.

Griem, H. R.

English

NASA Technical Reports Server

SublarDr-d ta &e 
Bati.mml AammautEcs and Space Adndniatra~oa 
SJmfiinst~fi, De C. 
Department of Physics a d  lClstnsno~ap 
Uxriveroity of Maryland 
Gollege Park, Wrylaad 
Hsas R. Grim 
aad 
J. 1. Gre3-8 
https://ntrs.nasa.gov/search.jsp?R=19700018930 2020-03-12T02:06:49+00:00Z
SEMI-mNUAL STATUS REPORT 
f o r  
Nat iona l  Aeronautics and Space Administrat ion 
NGR-21-002-0 73 
"EXPERIMENTAL AND THEORETICAL INVESTIGATION OF 
PLASMA RADIATION" 
Covering Per iod  
September 1969 - February 1970 
Submitted t o  t h e  
National  Aeronautics and Space Administrat ion 
Washington, D.  C. 
By the  
Department of Physics  and Astronomy 
Univers i ty  of Maryland 
College Park,  Maryland 
P r i n c i p a l  Lnves t i g a t o r s  
Hans R ,  Griem 
and 
J. R. Greig 
This r e p o r t  concludes our  experimental  program i n  t h e  measurement 
of t he  S t a rk  broadening f o r  t h e  resonance l i n e s  of n e u t r a l  argon and neon. 
Table 1 s u m a r i z e s  our  experimental  values f o r  wf, t h e  product of t h e  
S t a rk  broadening parameter and t h e  o s c i l l a t o r  s t r e n g t h  f o r  each l i n e ,  
and t h e  va lues  of w der ived  from t h i s  q u a n t i t y  u s ing  t h e  most r ecen t ly  
measured va lues  of f1'2, t h e  o s c i l l a t o r  s t r e n g t h  f o r  each l i n e .  The 
plasma condi t ions  f o r  t h e  e lec t romagnet ica l ly  dr iven  T-tube source  
used i n  t hese  determinat ions a r e  a l s o  tabula ted .  
Table 1, 
Our method of measurement cons i s t ed  i n  comparing the  s a t u r a t e d ,  
Stark-broadened emission l i n e s  of argon (neon) wi th  those  of Lyman-a and 
Lyman-@ us ing  a  mixture of argon (neon) and hydrogen as  a  f i l l i n g  gas f o r  
I) G.  M. Lawrence, Phys. Rev. z, 40 (1968). 
2)  G.  M. L,awrence, H e  S, L i s z t ,  Douglas Adv. R e s .  Lab:, 
Res. Communication 83 (1968). 
3) H .  R .  Griem, , McGraw-Hill (1964) . 
our T-tube source ,  The va lue  of wf i s  then d i r e c t l y  p ropor t iona l  t o  
t he  r a t i o  of t h e  ground s t a t e  dens i ty  of hydrogen and argon (neon) 
atoms, and t h e  e r r o r  i n  wf is  r e f l e c t e d  i n  t h e  e r r o r  i n  t h i s  r a t i o .  
Fur ther ,  experimental  e r r o r s  a r e  est imated by t h e  dev ia t ion  of t h e  
experimental ly  determined r a t i o  of t h e  o s c i l l a t o r  s t r e n g t h s  f o r  Lyman-a 
and Lyman-@ from t h e  t h e o r e t i c a l  va lue  of 5.26. Trea t ing  these  two 
as  independent e r r o r s  y i e l d  f i n a l l y  t h e  va lue  f o r  t h e  e r r o r  i n  wf. 
I n  argon, N r  is  a  slowly varying func t ion  of e l ec t aon  temperature 
f o r  our plasma condi t ions  (See Table l ) ,  g iv ing  an e r r o r  i n  wf from 
N:/N~ of ~ 7 . 5 % .  Other experimental e r r o r s  amounted t o  u7-8%, g iv ing  
a  f i n a l  e r r o r  o f ~ l l %  f o r  wf. We were n o t  a s  f o r t u n a t e  i n  t he  case  of 
the neon l i n e s ,  however, s i n c e  l i m i t a t i o n s  on our  source forced us t o  
opera te  under condi t ions  where NH/NNe had a  s t r o n g  dependence on 0 0 
e l e c t r o n  temperature con t r ibu t ing  an e r r o r  of ~ 2 7 %  i n  wf, while  o t h e r  
experimental  e r r o r s  were increased  somewhat (ko~-+20%) ,  producing a  f i n a l  
e r r o r  of 440% i n  wf. This was f u r t h e r  comppunded i n  t he  case of t h e  
NeI 743070 l i n e  whose equiva len t  width was of t h e  o rde r  of t h e  instrument  
width.  We es t ima te  wf f o r  t h i s  l i n e  t o  be  accu ra t e  t o  w i t h i n  a f a c t o r  
of 2.  
I n  p r i n c i p l e ,  t h e s e  l a r g e  e r r o r s  f o r  t he  N e I  measurements 
a r e  e a s i l y  reduced i f  w e  (a)  ope ra t e  t he  T-tube i n  a region 
B Ne (kTem1*6 eV) where NO/NO i s  f a i r l y  i n s e n s i t i v e  t o  e l e c t r o n  temperature,  
and (b) i nc rease  t h e  p re s su re  and capac i to r  vo l t age  s o  t h a t  t he  equ iva l en t  
width of NeI 7434 70 i s  a t  l e a s t  a  f a c t o r  of t h r e e  g r e a t e r  than the  
instrument  width.  Unfortunately,  we were n o t  a b l e  t o  ob ta in  such 
condit ions i n  our p re sen t  T-tube. 
A very va luab le  spin-off of our i n v e s t i g a t i o n  was t o  show 
t h a t  values of t h e  e l e c t r o n  temperature obta ined  from t h e  v i s i b l e  l i n e s  
emi t ted  by t h e  source  and those obtained from t h e  f i t t e d  p r o f i l e s  of t h e  
s a t u r a t e d  emission l i n e s  i n  t h e  vacuum u l t r a v i o l e t  agreed t o  w i t h i n  3%. 
Thus these  s a t u r a t e d  UV l i n e s  under our  T-tube condi t ions  could s e r v e  
a s  an i n t e n s i t y  s t anda rd  i n  t h i s  region of t h e  r a d i a t i o n  spectrum. 
Fur ther  i n v e s t i g a t i o n  of t h e  p r o f i l e  of t he  helium ion  
resonance l i n e ,  ~ 3 0 4 1 ,  making d e t a i l e d  allowance f o r  t he  width of 
the instrument  p r o f i l e ,  has  shown t h a t  cont ra ry  t o  our  expec ta t ion ,  
the  measured line-width is  considerably l e s s  (mx.67) than predic ted  
by r ecen t  ca l cu la t ions .  This comparison depends c r i t i c a l l y  on the  
dimensions of the  T-tube plasma and i ts  homogeneity, we a r e  t h e r e f o r e ,  
i n v e s t i g a t i n g  t h e  homogeneity of t he  plasma a t  our ope ra t ing  condi t ions .  
However, i t  is  f e l t  t h a t  a t  l e a s t  p a r t  of t h i s  narrowing can be expla ined  
as  a  f a i l u r e  t o  allow f o r  c e r t a i n  cance l l a t i ons  i n  t h e  broadening 
ca l cu la t ions .  
Cons is ten t  wi th  t h i s  specu la t ion ,  we have found t h a t  p r o f i l e s  
0 
of t h e  o p t i c a l l y  t h i n  hel ium ion  l i n e  A4686A a r e  a l s o  narrower ( ~ 1 0 % )  
than p red ic t ed  by our previous ca l cu la t ion ,  though t o  a  much l e s s e r  
ex t en t .  
We have done a  f e a s i b i l i t y  s tudy  t o  determine t h a t  both Ca I1 
and He I e x i s t ,  with comparable d e n s i t i e s ,  i n  a  slow e lec t romagnet ica l ly  
dr iven shock tube.  Between now and t h e  next  progress  r e p o r t ,  we hope 
t o  measure t h e  Ca I1 resonance l i n e s  and compare them wi th  var ious  
c a l c u l a t i o n s .  When we o b t a i n  agreement, we hope t o  extend the theory 
t o  o the r  s i t u a t i o n s  and check wi th  measurements made by o the r  people.  
F i n a l l y ,  we w i l l  make a  s i m i l a r  experimental and t h e o r e t i c a l  s tudy  
of Mg 11. 
We have inves t iga t ed  t h e  side-on emission i n  t he  f a r  i n f r a r e d  
( 2 0 0 ~  t o  3 5 0 0 ~ )  from a helium t h e t a  pinch plasma, wi th  an i n i t i a l  
f i l l i n g  p re s su re  of 1 8 ~  He. So f a r ,  we have determined t h a t  t he  main 
body of the  emission l i e s  i n  t he  s p e c t r a l  range from 200 t o  2000p, wi th  
a peak emission at about 7 5 0 ~  of approximately 1 0 - ~ w a t t s / p .  Over t h e  
range from 1900 t o  700p, t h e  emission w a s  enhanced from two t o  four  
orders  of magnitude above t h a t  expected from a  1 cm s l a b  of Maxwellian 
plasma of dens i ty  5 ~ 1 0 ' ~ c m - ~  and temperature ~ O ~ O K .  
Concurrently wi th  t h e  f a r  i n f r a r e d  measurements, we observed 
the  He 4922 a l i n e ,  s ea rch ing  i n  p a r t i c u l a r  f o r  evidence of a  s a t e l l i t e  
l i n e .  The r e s u l t a n t  p r o f i l e s  s t rong ly  suggested the  presence of a  
s a t e l l i t e .  Our aim, a t  p re sen t ,  is t o  r e so lve  t h e  He 4922 p r o f i l e  
0 
by comparison with t h e  l i n e  p r o f i l e  of He 38898 which should n o t  
possess  a  s a t e l l i t e .  I n  p a r t i c u l a r ,  we wish t o  c l a r i f y  whether o r  no t  
t h e  observed " s a t e l l i t e s f f  a r e  merely Doppler s h i f t e d  peaks. We a l s o  
0 
plan t o  measure the  H e  40268 l i n e ,  which should have an even s t r o n g e r  
s a t e l l i t e  l i n e  than t h a t  of He 4922i, I n  add i t i on ,  t h e  width of t h e  
allowed component of t he  He 40261 l i n e  should g ive  a  r e l i a b l e  measurement 
of the  e l e c t r o n  dens i ty  of the  plasma. 
The i n i t i a l  work of f i n d i n g  plasma condi t ions  app ropr i a t e  f o r  
observing t h e  high n-a l i n e s  of hydrogen has  been compleeed. By vary ing  
the prehea ter  capac i to r  vo l t age  and the  i n i t i a l  f i l l i n g  p re s su re ,  with 
12 -3 
and wi thout  a  b i a s  bank d ischarge ,  e l e c t r o n  d e n s i t i e s  of 5x10 cm t o  
3 x 1 0 ~ ~ ~ ~ ~  and e l e c t r o n  temperatures of 0 .5 eV t o  5  eV were obtained.  
Absolute i n t e n s i t y  c a l i b r a t i o n s  were made f o r  two of t hese  condi t ions ,  
14 -3 e., f o r  e l e c t r o n  d e n s i t i e s  of approximately 5x1012 and 3x10 cm . 
These r e s u l t s  showed t h a t  t h e  n-a l i n e s  f o r  the  lowest  dens i ty  
condit ion would no t  have s u f f i c i e n t  i n t e n s i t i e s  t o  be  observable wi th  
present  f a r  i n f r a r e d  equipment, b u t  t h a t  t hese  l i n e s  should be  observable 
14 -3 
a t  an e l e c t r o n  dens i ty  of 3x10 crn i f  t he  bremsstrahlung l e v e l  i s  no t  
t oo  high.  For somewhat h ighe r  e l e c t r o n  d e n s i t i e s ,  i t  i s  expected t h a t  
t h e  n-a l i n e  width,  even wi th  t h e  recent  t h e o r e t i c a l  es t imates  p r e d i c t i n g  
much l e s s  b r ~ a d e n i n g  than the  Ing l i s -Te l l e r  e s t ima te s ,  w i l l  be  l a r g e  
enough f o r  t he  l i n e s  t o  have merged. 
Prepara t ions  a r e  now beBng made t o  observe t h e  i n f r a r e d  r a d i a t i o n  
from the  second plasma condi t ion  descr ibed above, over a  broad band, 
u s i n g  t h e  i n f r a r e d  (indium ant imonide)  d e t e c t o r  and a p p r o p r i a t e  f i l t e r s .  
I f  t h i s  shows s i g n i f i c a n t  i n f r a r e d  r a d i a t i o n  i n  t h e  wavelength  
r e g i o n  of i n t e r e s t  ( 5 0 ~ - 3 0 0 ~ ) ,  t h e  i n f r a r e d  s p e c t r o m e t e r  
w i l l  b e  set up t o  r e s o l v e  t h e  l i n e  r a d i a t i o n  from t h e  bremsstrahlung. 
11. THEORETICAL PROGRAM 
The p a p e r ,  "Quantum-Mechanical C a l c u l a t i o n  f o r  t h e  Elect ron-Impact  
Broadening o f  t h e  Resonance L ines  o f  S ing ly  I o n i z e d  Magnesium" h a s  
appeared (Phys. Rev. - A l ,  9 7 ,  1970) ,  w h i l e  t h e  r e p o r t  on c a l c u l a t i o n s  
f o r  p r o f i l e s  of i o n i z e d  h e l i u m  l ines i s  s t i l l  i n  p r e p a r a t i o n .  We are 
p r e s e n t l y  deve lop ing  a  s e m i - c l a s s i c a l  c a l c u l a t i o n  scheme f o r  i s o l a t e d  
l i n e s  t o  f a c i l i t a t e  comparison w i t h  exper iments  and f u l l y  quantum 
mechanical  c a l c u b a t i o n s .  Also,  we are look ing  i n t o  t h e  t h e o r e t i c a l  
i n t e r p r e t a t i o n  of t h e  plasma p o l a r i z a t i o n  s h i f t .  Our l a b o r a t o r y  
o b s e r v a t i o n  of t h i s  e f f e c t  h a s  been  p u b l i s h e d  i n  Phys. Rev. L e t t e r s  
24 ,  3 (1970) . Such s h i f t s  which a r e  i n  a d d i t i o n  t o  s h i f t s  from ~ ~ s u a l  
-
impact broadening mechanisms, may b e  of r a t h e r  fundamental  importance 
because  of t h e i r  i n f l u e n c e  on a b s o l u t e  wavelength  s t a n d a r d s  a t  s h o r t  
wavelengths .  


Experimental and theoretical investigation of plasma radiation Semiannual status report, Sep. 1969 - Feb. 1970

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