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Submitted on 1 Jan 1979
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INVESTIGATION OF AN EARLY HELIUM AFTERGLOW PLASMA PRODUCED BY A
MICROWAVE SURFAGUIDE
A. Bouvier, S. Abed, B. Charlet
To cite this version:
A. Bouvier, S. Abed, B. Charlet. INVESTIGATION OF AN EARLY HELIUM AFTERGLOW
PLASMA PRODUCED BY A MICROWAVE SURFAGUIDE. Journal de Physique Colloques, 1979,
40 (C7), pp.C7-197-C7-198. �10.1051/jphyscol:1979797�. �jpa-00219503�
JOURNAL DE PHYSIQUE CoZZoque CT, s~ppZ6ment au n07, Tome 40, JuiZZet 1979, page C7- 197
INVESTIGATION OF AN EARLY HELllJM AFTERGLOW PLASMA PRODUCED BY A MICROWAVE SUFWAGUEM:
A. Bouvier, S. Abed, 6. Charlet and A. Bouvier.
E. R. A., C. N. R. S. 302, Laboratoire de Spectroscopie e t de L d n e s c e n c e , Uniuersit6 Claude Bernard, Lyon I 43, Bd du 11 Novembre 1918 69621 ViZZeurbanne, France.
Abstract. P l a s m a i s produced by a microwave s u r f a g u i d e / l / i n a cylindric quartz c e l l filledwith helium a t a p r e s s u r e of 14 t o r r s . A homogeneous plasma i s s o obtained along the axis. Spectrosco- pic diagnostics a r e used t o m e a s u r e during the f i r s t 100 s and in different p a r t s of the c e l l :
a. different atomic and molecular excited l e - v e l s populations
b. the rotational t e m p e r a t u r e of He2 in two electronic s t a t e s e% and
~h
g g
c . a m e a n electronic t e m p e r a t u r e of the c l a s s of e l e c t r o n s which recombine.
Introduction. S p e c t r a l investigation h a s shown that many atomic and molecular levels a r e popu- lated during 1 0 0 ~ s by recombination p r o c e s s e s i n t h e c a s e of non complete Boltzmann equilibrium.
T o d e s c r i b e the variations of populations in t h e s e conditions R . Deloche and col.
12/
have shown that i t is v e r y important t o d e t e r m i n e the r a t i o T,/Tg w h e r e T e i s the electronic t e m p e r a t u r e and T the
g n e u t r a l g a s t e m p e r a t u r e , p a r a m e t e r s we t r y t o d e t e r m i n e i n t h i s work.
E x p e r i m e n t a l methods. The plasma i s observed end on, i n a direction p a r a l l e l t o the a x i s of the c e l l , on a d i a m e t e r , a t a distance r f r o m the a x i s (Fig. 1). T h e intensity of different lines i s analy- s e d by a s y s t e m (Fig. 2 ) including, a Jobin-Yvon monochromator HRS (dispersion 1 2 ~ / n m ) , a 6256 S EM1 photomultiplier, a counter s y s t e m I n t e r - technique IN 90 with a~ multichannel a n a l y s e r and a computer using d i f f e r e n t acquisitions techniques.
The single photon technique w a s the m o s t adequat i n t h i s c a s e because the t i m e resolution could be a s good a s wanted.
Fiq. 2
1. The population of different atomic and mole- c u l a r levels v a r i e s with r and t (Fig. 3 a n d 4).
Along a d i a m e t e r , we obtain one minimum on the a x i s and two maxima on both s i d e s of the a x i s . The amplitudes df the two maxima a r e not identical.
The decay is exponential, the relaxation t i m e va- r i e s with r and is of the s a m e o r d e r f o r atomic and molecular levels.
2. The rotational t e m p e r a t u r e i s m e a s u r e d b y considering the B oltzmann d i a g r a m . Equilibrium is re' a l i s e d f o r a l l the rotational n u m b e r s J except
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979797
f o r one J (J higher = 2) on the w a l l s of the cell. /3/H.R. G r i e m
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P l a s m a Spectroscopy, Ed. Mc Rotational t e m p e r a t u r e v a r i e s only a little with r Graw-Hill Book Company. N. Y . , San F r a n c i s c o , a n d t (A
t /u_ 100 K ) , about 700 K ( F i g . 5 and 6). London (1 974).3. Electronic t e m p e r a t u r e i s evaluated b y using
/4/H.W. Drawin
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2 . P h y s . 228, 99 (1963) t h e o r y of G r i e r n I 3 / and D r a ~ i n ' ~ ' . A p a r t i a l equi-2 . Phys. 225, 483 (1972).
l i b r i u m is r e a l i s e d between e l e c t r o n s (for e l e c t r o - n i c density 10'' o r 1
o1
c m m 3 ) and helium a t o m s i n l e v e l s with quantum number higher than 5 (In f a c t the level 6 D). The electronic t e m p e r a t u r e 3 what i s s o m e a s u r e d i s constant enough during the f i r s t 30)Cs b u t i n c r e a s e s i n the c e l l i n the p a r t n e a r e r the g e n e r a t o r . This m e a n t e m p e r a t u r e k e e p s high enough (1500- 2000 K ) ( ~ i ~ . 5 a n d 6 ).
The r e a s o n i s t h a t a n o t h e r c l a s s of e l e c t r o n s with v e r y high energy c e r t a i n l y e x i s t s during t h i s i n t e r - val.
Discussion. T h e s e m e a s u r e m e n t s a r e i n t e r e s t i n g b e c a u s e they will p e r m i t t o study recombination p r o c e s s e s during t h e e a r l y afterglow when Te i s high enough and when complete Boltzmann equili- b r i u m is not obtained. If T R r e p r e s e n t s the t e m - p e r a t u r e of the n e u t r a l g a s , T , / T ~ v a r i e s a little with t i m e , what explains the different exponential d e c a y s ; but T e and T R v a r y with r what justifies t h e i m p o r t a n t v a r i a t i o n of populations i n the cell.
References.
/1/ M. Moisan, G. Beaudry, L. B e r t r a n d , E.
Bloyet, J.M. Gagne, P. Leprince, J. M a r e c , G . Mitchel, A. R i c a r d , Z . Zakrzewski
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I n t e r n a - tional Conference on Gas D i s c h a r g e s , Swansea , U.K. (Sept. 1976) n o 143, p.382./2/ R. Deloche, P. Monchicourt, M. C h e r e t , F. L a m b e r t
