SOME REMARKS ON THE NON-EQUILIBRIUM PLASMA DIAGNOSTICS

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SOME REMARKS ON THE NON-EQUILIBRIUM PLASMA DIAGNOSTICS

E. Gippius, B. Iljukhin, V. Kolesnikov

To cite this version:

E. Gippius, B. Iljukhin, V. Kolesnikov. SOME REMARKS ON THE NON-EQUILIBRIUM PLASMA DIAGNOSTICS. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-871-C7-872.

�10.1051/jphyscol:19797421�. �jpa-00219423�

JOURNAL DE PHYSIQUE CoZZoque C7, s u p p l g m e n t au n 0 7 , Tome 40, J u i l l e t 1:979, page C7- 871

SOME REMARKS ON THE NON-EQUILIBRIUM PLASMA DIAGNOSTICS

E.F. Gippius, 6.1. Iljukhin and V.N. Kolesnikov.

L e b e d e v P h y s i c a l I n s t i t u t e , Moscow U.S.S.R.

'Phis r e p o r t completes t h e list of our pa- pers

il,

² ] r e l a t e d t o t h e development of t h e physical base of non-equilibrium plasma spectroscopy. The t r a n s i e n t dense plasma f omed with t h e help of t h e high current pulse discharge i n helium was chosed a s an object of our i n v e s t i g a t i o n s The main p e c u l i a r i t i e s of such plasma d i a g n o s t i c s m e discussed i n review re- portc3-J. I n t h i s paper we consider i n ad- d i t i o n two o t h e r problems of r e l a t i v e l y wide i n t e r e s t . The f i r s t one i s t h e ef- f e c t of expansion of t h e PLPX model v a l i - d i t y region i n t h e case of unhomogeneous plasma. The second i s t r u e time of t h e plasma steady-state establishment.

Experiment a1 conditions.

The coa$ial discharge tube with a 1 cm inner diameter was f i l l e d with s p e c t r a l pure heliuin a t a pressure of 3 t o r r . The amplitude of c u r r e n t pulse was

4.5

k A , l e n g t h being 8 . 5 p s e c . The d e t a i l s of t h e density measurements of e l e c t r o n s (Be), ions ~ e + and ~ e + * a s well a s those of t h e e l e c t r o n temperature Te a r e reported i n r 1 J . During t h e time i n t e r v a l 2+141~( sec He changed i n t h e region (2+6) 1016

and Te decreased from 7.5 t o 2.9 eV. The gas pressure P, on t h e tube w a l l was a l s o measured with t h e help of t h e piezoelect- r i c probe.

&paasion of t n e i-'LITE model v a l i d i t s region.

a number of e f f e c t i v e diagnostic methods a r e based on t h e PLTE modelf4,53. There- f o r e it i s important t o know t h e bounda- r y of t h e region where t h i s model i s va- l i d . This boundzy may be founa with t h e help of some simple c r i t e r i a i n f e r e d by Griemf43 and o t h e r s from balance condi- t i o n s of d i r e c t and ogposite processes.

However accurate c a l c u l a t i o n i n which nore t h a n two processes a r e taken i n ac- count g i v e s i n some c a s e s strongly nar- rowed v a l i d i t y region (UrawinK6J). iEie would l i k e t o note t h 8 t t h e opposite si- t u a t i o n , namely, t h e expansion of t h i s region i s a l s o possible, i f t h e connec- t i o n between t h e ground and excited le- v e l s i s weaked. Vie have observed such case i n ourA experiments.

The i o n composition of t h e i n v e s t i g a t e d plasma i s caused by s t r o n g competition of many p r o c e s s e s L 2 ~ . The ground s t a t e s a r e over populated because of mass t r a n s - f e r and diffusion. That i s enough t o ex- pect t h e excited s t a t e s t o be over popu- l a t e d too. Fig.1 shows t h e expected over population degree P , = ~ ~ / N ; ~ f o r l e v e l n=4 He11 a s a f u n c t i o n of time. I n this c a l c u l a t i o n t h e e l e c t r o n d i s t r i b u t i o n f u n c t i o n Te(v) i s usually assumed a s

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797421

Fig.1.

iWxwe1lia.n. The expected v a l u e of F4 reaches 2, and PLTL model i s v a l i d f o r t h i s l e v e l only a t two o r d e r higher 17ie t h a n t h a t found with t h e help of Grierns c r i t e r i o n . However t h e experimental v a l u e s of P,+ a r e c l o s e t o 1, t h a t i s we o b t a i n r e a l l y a g r e a t e x p a s i o n of t h e r'Lrllk mo- d e l v a l i d i t y region. It i s p o s s i b l e t o o b t a i n t h e same r e s u l t f o r a l l o t h e r atoms, t h e e x c i t e d l e v e l s of which axe s t r o n g l y s h i f t e d , s i m i l a r t o t h a t of HeIi, t o t h e i o n i s a t i o n boundzry ( f o r exanple H, HeI, NeI e t c . ) . T h i s e f f e c t can be e a s i l y explained by t h e non-maxwellien f orm of f e ( v ) due t o plasrna unholaogeneity

.

The steady s t a t e establishment.

It i s u s u a l l y supposed t h a t t h e p l ~ s m a p r e s s u r e becomes n e a l y constant along r a f t e r t h e time t ~ r / w , r being t h e plasma colwnn r a d i u s , w

-

t h e v e l o c i t y of shock (sound) wave. T n i s time corresponds t o t h h t of steady s t a t e establishment. Tnis p o s t u l a t e i s used i n dynamic models of high c u r r e n t p u l s e discharge. It i s a l s o of g r e a t impotance i n automodel approxi-

r

mation.

I n our experiments

t,c

1 s e c , but one

2 i g . 2 .

o r d e r longer t i n e i s r e q u i r e d t o acnieve nearly c o n s t a n t pressure. Fig. 2 shows t h e r a d i a l d i s t r i b u t i o n s of t o t a l pres-

s u r e P ( r ) found from t h e s g e c t r o s c o p i c d a t a a s w e l l a s t h e p r e s s u r e 2w on t h e t u b e w a l l a t so,ae mornen'cs of t i i n e . 2 0 t h a t P ( r ) and Pw t h e i n p u t of rnhgnetic p r e s s u r e i s t a k e n i n t o kccount. The pressure becones nearly constlint along r only a f t e r l 2 p s e c . I h ~ s t h e u s e of auto- model &pproxirn.ztion i s not v a l i d f o r t u e

a n a l y s i s of plasrua s t a t e during t h i s e a r l y s t a g e s .

References.

l.X.F.Gippius, V.N.Kolesnikov. Proc.

XIII-th I C I ? I G , P t . 2,p.475,Berlin, 1977;

K ~ ~ T K M ~ coodq.

no

@ I ~ I ~ K ~ , v ~ ~ A H , N3,17 (1970);

x n c , ~ ,

59t3,1(77t3.

2. L.F.Gippius, E. I. I1 jukhin, V.N.Iiolesni- kov.Proc.XII1-th ICPIG,Pt.2,p.477,Ber- l i n , 1977; Y M ~ M K ~ n n a s ~ b l , 2,13'?7(19'?8).

3. V.N.k;olesnikov, lQ

.a.

Sobolev. P r e p r i n t FIAN,N7(1978).

4.H.Griem. Plasma Spectroscopy.N.-Y.1963.

5.I.Hicnter. Pr0c.X-th ICPIG,Pt.2,37(1971).

6.H.W.Drawin. I n book: P r o g r e s s i n Plas- mas and, Gas E l e c t r o n i c s . V. 1,p. 591, Ber-

l i n , 1975.