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THE ROLE OF MOLECULAR LINES IN THE STUDY OF PLASMA SATELLITES
A. Piel, F. Pinnekamp
To cite this version:
A. Piel, F. Pinnekamp. THE ROLE OF MOLECULAR LINES IN THE STUDY OF PLASMA SATELLITES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-813-C7-814.
�10.1051/jphyscol:19797392�. �jpa-00219391�
JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, page C7-
813
THE ROLE
OF MOLECULAR LINES IN THE STUDY OF PLASMA SATELLITESA. Piel, F. Pinnekamp.
Rhr-UniversitEt Bochwn, I n s t i t u t fiir ExperimentaZphysik 11, Bochwn, Germany F. R. G.
The measurement o f f l u c t u a t i n g e l e c t r i c f i e l d s i n p l a s m a s by means o f t h e h i g h f r e q u e n c y S t a r k e f f e c t h a s a t t r a c t e d much a t t e n t i o n d u r i n g t h e l a s t d e c a d e . S i n c e t h e i n t e n s i t i e s o f t h e h i g h f r e q u e n c y p l a s m a s a t e l l i t e s h a r d l y e x c e e d ?%
o f t h e main l i n e i n t e n s i t y t h e s e s t r u c t u r e s have t o b e c a r e f u l l y s e p a r a t e d from i m p u r i t y l i n e s . R e c e n t l y Ramette and Drawin / I / r e p o r t e d p l a s m a s a t e l l i t e s o n Hp
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C o n t r a r y t o t h a t s t r u c t u r e s on t h e 447.15 nm h e l i u m l i n e mea- s u r e d u n d e r s i m i l a r c o n d i t i o n s by t h e same a u t h o r s / 2 / were i n t e r p r e t e d a s b e i n g due t o h e l i u m m o l e c u l a r l i n e s . R e p e a t i n g t h e s e expe- r i m e n t s we o b t a i n e d v e r y d i f f e r e n t r e s u l t s . E x p e r i m e n t a l-
The e x p e r i m e n t a l s e t - u p ( f i g . 1 ) i s s i m i l a r t o t h a t i n r e f . /1,2/. The l i g h t from t h e d i s - c h a r g e t u b e ( 1
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470mm, di = 24mm, A 1 e l e c - t r o d e s ) i s o b s e r v e d end-on. The whole s p e c t r u m i s r e c o r d e d s i m u l t a n e o u s l y d u r i n g o n e s h o t on a 5 0 0 c h a n n e l m u l t i c h a n n e l a n a l y z e r (OMA) which r e p l a c e s t h e e x i t slit o f a f=lm g r a t i n g s p e c -Hydrogel) d i s c h a r g e
A t y p i c a l l i n e p r o f i l e o f Hp r e c o r d e d i n t h e a f t e r g l o w 6 p s a f t e r s h o r t c i r c u i t i n g i s shown i n f i g . 2. The d i s c h a r g e c o n d i t i o n s ( I o = 6 0 0 ~ , p =500Pa) were v e r y similar t o t h o s e i n r e f . / I / . S e v e r a l s t r u c t u r e s a p p e a r on t h e l i n e p r o f i l e which c o i n c i d e w i t h t h e p o s i t i o n s o f h y d r o g e n m o l e c u l a r l i n e s t a k e n from t h e wave- l e n g t h t a b l e s o f D i e k e / 3 / . The i n t e n s i t y o f t h e s t r u c t u r e s c l e a r l y e x c e e d s t h e s t a t i s t i c a l e r r o r . 2 5 m o l e c u l a r l i n e s c o u l d b e i d e n t i f i e d . I n o r d e r t o d e t e r m i n e t h e e x a c t p o s i t i o n s o f p o s s i b l e p l a s m a s a t e l l i t e s a t +id t h e p l a s m a
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d e n s i t y was d e r i v e d from Langmuir p r o b e d a t a and t h e s l o p e o f t h e H p l i n e wing /4/. B o t h methods show good a g r e e m e n t , y i e l d i n g a n e l e c - t r o n d e n s i t y o f ne
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1 * 1 0 ~ ~ r n - ~ a t t h e i n s t a n t o f e x p o s u r e . P l a s m a s a t e l l i t e s a r e t h e r e f o r e e x p e c t e d t o o c c u r a t &'A= 20.224 nm, b u t weak s t r u c t u r e s at t h e s e p o s i t i o n s a r e more l i k e l y t o a r i s e from m o l e c u l a r l i n e s . I n a d d i t i o n t h e p l a s m a s a t e l l i t e s s h o u l d b e s u b j e c t t o t h e same S t a r k b r o a d e n i n g-
as t h e main l i n e . There- t r o m e t e r . The e x p o s u r e t i m e was t y p i c a l l y I p sf o r e t h e s h a r p n e s s o f t h e s t r u c t u r e s r e p o r t e d and t h e s p e c t r a l r e s o l u t i o n amounts t o 0.024nm.
i n r e f . / I / up ports t h e i n t e r p r e t a t i o n a s m o l e c u l a r l i n e s .
Exper~ment A R T U R
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F i g u r e 1 : E x p e r i m e n t a l s e t - u p
F i g u r e 2: Hydrogen F i g u r e
3 :
Heliumd i s c h a r g e d i s c h a r g e
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797392
Helium d i s c h a r g e
We r e p e a t e d t h e measurements o f /2/ a t e x a c t l y t h e s a p e d i s c h a r g e c o n d i t i o n s . The p r o f i l e shown i n f i g . 3 i s a n a v e r a g e o v e r
80
i n d i v i - d u a l s h o t s ( e r r o r b a r s w i t h i n d r a w i n g a c c u r a c y ) . No s t r u c t u r e s c o u l d b e r e g i s t r a t e d , a l s o at l a t e r t i m e s no s t r u c t u r e s a p p e a r e d . A s t h e p e a k s i n /2/ were i n t e r p r e t e d a s b e i n g due t o He2 mo- l e c u l a r l i n e s we t r i e d t o measure o p t i c a l t r a n - s i t i o n s o f t h e He2 m o l e c u l e and l o o k e d f o r t h e i n t e n s e e 3 n --+a3t: band a t 465.0 nm. Eveng
w i t h a n e n t r a n c e s l i t o f 1 mm w i d t h o f t h e s p e c t r o m e t e r and by i n t e g r a t i n g t h e l i g h t o f t h e whole t i m e o f t h e d i s c h a r g e , t h e s e s t r o n g m o l e c u l a r l i n e s c o u l d h a r d l y be d e t e c t e d . U s i n g a s t a t i o n a r y R F - d i s c h a r g e He2 l i n e s a r e r e g i s - t r a t e d ( f i g . 4 ) and t h e i r i n t e n s i t y i s shown i n f i g . 5 a s a f u n c t i o n o f t h e p r e s s u r e . I n t h i s d i s c h a r g e m o l e c u l a r l i n e s i n t h e 447.1 nm r e -
-
4g i o n a r e v e r y weak and r e a c h 1 0 o f t h e 447.15 nm l i n e o f He at b e s t . Therefrom we c o n c l u d e t h a t h e l i u m m o l e c u l a r l i n e s do n o t a f f e c t t h e He l i n e at 447.15 nm a t p r e s s u r e s below 1 0 0 Pa, n
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l ~ ~ and ~ mT~4
- ~eJJ i n t h i s l i n e a r p u l s e d d i s c h a r g e .F i g u r e 4: Helium R F - d i s c h a r g e
On t h e o t h e r hand v e r y s m a l l amounts o f h y d r o g e n i n t h e h e l i u m d i s c h a r g e change t h e m o l e c u l a r s p e c t r u m d r a s t i c a l l y . I n a t u b e c o n t a m i n a t e d w i t h hydrogen b e f o r e t h e He2 s p e c t r u m i s com- p l e t e l y s u p p r e s s e d a t 465 nm and a s t r o n g hy- d r o g e n m o l e c u l a r s p e c t r u m o c c u r s . From o u r e x p e r i m e n t s and t h e f a c t t h a t p r a c t i c a l l y a l l p e a k s i n Drawins measurement /2/ c o i n c i d e w i t h h y d r o g e n m o l e c u l a r l i n e s , t h e i n t e r p r e t a t i o n o f t h e s e s t r u c t u r e s a s b e i n g due t o h y d r o g e n m o l e c u l e s seems t o b e more a d e q u a t e , p r o v i d e d t h e d i s c h a r g e t u b e i n / 2 / h a s b e e n i n c o n t a c t w i t h hydrogen b e f o r e .
F i g u r e 5: I n t e n s i t y o f h e l i u m m o l e c u l a r l i n e s a s a f u n c t i o n o f f i l l i n g p r e s s u r e
C o n c l u s i o n s
F o r t h i s t y p e o f d i s c h a r g e i t w i l l b e v e r y d i f f i c u l t t o d i s t i n g u i s h between o b s e r v a t i o n s o f p l a s m a s a t e l l i t e s and m o l e c u l a r l i n e s i n h y d r o g e n d i s c h a r g e s , s i n c e m o l e c u l a r l i n e s w i l l a t l e a s t a r i s e from boundary l a y e r s o f t h e plasma. On t h e o t h e r hand we c o u l d v e r i f y t h a t h e l i u m m o l e c u l a r band s p e c t r a do n o t a f f e c t t h e s t u d y o f p l a s m a s a t e l l i t e s on he- l i u m a t o m i c l i n e s i n h e l i u m d i s c h a r g e s . I n a d d i t i o n h e l i u m m o l e c u l a r l i n e s w i l l b e o f e v e n l e s s i m p o r t a n c e a t l o w e r p r e s s u r e s , which a r e t y p i c a l f o r t u r b u l e n t h e a t i n g e x p e r i m e n t s . Hydrogen i m p u r i t i e s i n h e l i u m d i s c h a r g e s , however, may b e of g r e a t i n f l u e n c e .
R e f e r e n c e s
1 J. Ramet-te, H.W. Drawin
2. N a t u r f o r s c h .
Jla,
401 (1976)2 H.W. Drawin, J. Ramette
2. N a t u r f o r s c h .
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1285 ( 1 9 7 8 )3 H.M. C r o s s w h i t e , The Hydrogen M o l e c u l a r Wavelength t a b l e s o f G e r h a r d H e i n r i c h Dieke Wiley I n t e r s c i . , New York 1972
4 A. P i e l , H. R i c h t e r
a c c e p t e d by 2 . N a t u r f o r s c h . f o r p u b l i c a t i o n