ELECTRON ENERGY DISTRIBUTION FUNCTION AND ATOM IONIZATION PROCESSES IN HIGH FREQUENCY DISCHARGE MERCURY-ARGON PLASMA

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Submitted on 1 Jan 1979

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ELECTRON ENERGY DISTRIBUTION FUNCTION AND ATOM IONIZATION PROCESSES IN HIGH

FREQUENCY DISCHARGE MERCURY-ARGON PLASMA

S. Wagner, I. Nisconen

To cite this version:

S. Wagner, I. Nisconen. ELECTRON ENERGY DISTRIBUTION FUNCTION AND ATOM IONIZA- TION PROCESSES IN HIGH FREQUENCY DISCHARGE MERCURY-ARGON PLASMA. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-209-C7-210. �10.1051/jphyscol:19797103�. �jpa-00219073�

JOURNAL DE PHYSIQUE CoZZoque C7, suppl6ment au n07, Tome 40, J u i Z l e t 2979, paqe c7- 209

ELECTRON ENERGY DISTRIBUTION FUNCTION AND ATOM 1-TION PROCESSES

IN HIGH FREQUENCY DISCHARGE MERCURY-ARCON PLASMA

S.D. Wagner, 1.5. Nisconen.

KareZian Pedagogical I n s t i t u t e Petrozavodsk U.S.S.R.

T h i s p a p e r p r e s e n t s t h e r e s u l t s of e l e c t r o n e n e r g y d i s t r i b u t i on f u n c t i o n (SEDP) measurements and c a l c u l a t i o n s .

EEDP were measured by d i f f e r e n t i a t i n g t h e probe c u r r e n t s by a r a d i o method/l/.

The probe s y s t e m c o n s i s t e d of a c y l i n d r i - c a l probe which c o u l d be moved a c r o s s t h e t u b e r a d i u s and a l a r g e a r e z a n t i p r o b e p l a c e d on t h e t u b e s u r f a c e . The whole sy- s t e m was p l a c e d i n t h e c e n t r a l p a r t of t h e d i s c h a r g e t u b e of r a d i u s 1 6 m. Vol- t a g e a t 28 ?dEz was f e d l;o e x t e r n a l e l e c - t r o d e s 26 cm a p a r t from a g e n e r a t o r w i t h a S J - v m e t r i c a l o u t p u t . Measurements were

~ a d e a t mercury v a p o r p r e s s u r e 2 * 1 0 - 4 ~ o r r , a r g o n p r e s s u r e 0.05 and 0.5 T o r r and tube c u r r e n t 100 nA.

The measilred UBBP d i f f e r f r o m Pvla,meli f u n c t i o ~ s of t h e s a x e mean e n e r g y by z d e p l e t i o n of high e n e r g y e l e c t r o n s . A c - r o s s t h e t u b e r e d i u s t h e EdDF d o e s n o t change n a r k e d l y , t h e mean e l e c t r o n energy d e c r e a s e s a b o u t two t i m e s when t h e a r g o n p r e s s u r e i s r a i s e d f r o m 0.05 t o 0.5 T o r r .

For c a l c u l a t i n g t h e EEDF t h e t o t a l e n e r g y i n t e r v a l was d i v i d e d i n t o t h r e e r e g i o n s : t h e r e g i o n w i t h e n e r g i e s l o w e r t h a n t h e f i r s t mercury e x c i t a t i o n poten- t i a l , t h e r e g i o n f r o m t h e f i r s t mercury e x c i t a t i o n p o t e n t i a l t o t h e f i r s t a r g o n e x c i t a t i o n p o t e n t i a l and t h e r e g i o n high- e r t h a n t h e f i r s t a r g o n e x c i t a t i o n poten- t i a l . E s t i m a t i o n s of c h a r a c t e r i s t i c f r e - q u e n c i e s of e l e c t r o n e n e r g y l o s s e s were made f o r a l l t h e s e r e g i o n s . I n t h e f i r s t r e g i o n e n e r g y l o s s e s t a k e p l a c e m a i n l y by e l g s t i c c o l l i s i o n s - b e t w e e n e l e c t r o n s and

a r g o n atoms. I n t h e second r e g i o n u n e l a s - t i c c o l l i s i o n s between e l e c t r o n s and mer- c u r y atoms a r e e s s e n t i a l t o o . I n t h e t h i r d r e g i o n o n l y u n e l a a t i c c o l l i s i o n s between e l e c t r o n s and a r g o n atoms a r e e s s e n t i a l . I n a l l c e s e s e l e c t r o n - e l e c t r o n i n t e r a c t i o n i s n e g l i g i b l e . A k i n e t i c e q u a t i . o n was worked o l l l f o r e v e r y c a s e . The e q u a t i o n s were time-averaged./2/. The u n l o c a l c h a r a c t e r of t h e E3DP was talcen

i n t o a c c o u n t t 0 0 / 3 / . By s o l v i n g t h e k i n e - t i c e q u a t i o n s t h e f o l l o w i n g SCCP were r e - c i e v e d f o r e a c h r e g i o n r e s p e c t i v e l y :

where W

-

,

-

e n e r g g ( 1 I ,5eV) ,

- , J' -

,

-

f u n c t i o n , 9, - a m p l i t u d e v a l u e of h i g h f r e q u e n c y f i e l d s t r e n g t h , e

,

,

-

e l e c t r o n c h a r g e , mass and v e l o c i t y ,

P -

c o e f f i c i e n t i n t h e a p p r o x i m a t i o n f o r t h e r a d i a l p o t e n t i a l 9 (7.) i n t h e c e n t r a l r e - g i o n of t h e

e9(~)=J3(-&)* , do

& -

c o e f f i c i e n t s i n t h e appGbximations f o r t h e f r e q u e n c i e s of u n e l a s t i c and e l a s t i c

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797103

c o l l i s i o n s between e l e c t r o n s and a r g o n

atoms

Jp=Jg(w-w2)

'IJ=8P2V3

Pi ^and

pa

c

io2w

(h)'i _Pa .

The c o e f f i c i e n t s

G

A

,'

F a r e d e t e r m i n e d feom t h e n o r m a l i z i n g c o n d i t i o n and t h e j o i n i n g c o n d i t i o n s of t h e EEDF and i t s d e r i v a t i v e on t h e boun- d a r i e s of t h e d e f i n e d r e g i o n s .

C o n s t a n t s needed f o r c a l c u l a t i o n s were t a k e n f r o m t h e monograph/4/.

Pi.$. 1 and 2 p r e s e n t t h e measured and c a l c u l a t e d EI:,DP. The e x p e r i m e n t a l f unc- t i o n a t a r g o n p r e s s u r e 0.5 T o r r i s i n a c c o r d a n c e w i t h t h e c a l c u l a t e d f u n c t i o n E,/P _2- -4 V/cm-Torr and a t 0.05 T o r r

-

t h e f u n c t i o n i.;,/P2=20 V/cm*Torr.

-2' 0 &s 110 &

Pig.1. 0, =2*1 o - ~ T o r r , P2=0. 5 T o r r . c a l c u l a t i o n : 1 - 2,/P2=2 V/cm-Torr, 2

-

-

-

.

Measured iC!<DF were used f o r d e t e r m i n - i n g t h e r o l e of d i f f e r e n t i o n i z a t i o n p r o c e s s e s i n t h e plasma. The r a t e s of d i - r e c t i o n i z a t i o n of n e r c u r y ( Z ; ) , s t e p w i z e

i o n i z a t i o n of mercury (Z1 ) and argon(Z ₂ ) ,

i o n i z a t i o n of s e r c u r y by t h e Perining e f - f e c t ( Z p ) were c a l c u l a t e d . A s a l l t h e ZLDF a r e in t h e r e g i o n nkj c h is l o w e r t h a n t h e d i r e c t i - o n i z a t i o n t h r e d h o l d of a r g o n i o n i z a t i o n by t h i s p r o c e s s was n o t c a l c u - l a t e d . C a l c u l a t i o n s of s t e p i z e i o n i z a - t i o r ! p r o c e s s e s and i o n i z a t i o n -03' Per;r?in;

e f f e c t w e r e made u s i n g t h e p o p u l a t i o n s of t h e low e x c i t e d l e v e l s of mercury and a r - gon, which were d e t e r m i n e d by t h e r e a b - s o r p t i o n method. The t a b l e g i v e s t h e r e - s u l t s of c e l c u l a t i o n s f o r a u n i t l e s g t h of t h e t u b e .

1 Z1 2

C2 :

z'

T o r r : - 5, s -1

The mos t i x p o r t a n t p r o c e s s e s a r e s t e p - w i z e i o n i z a t i o n of a r g o n and i o n i z a t i o n

of mercc,r$- L~J t h e Penning e f f e c ' t . A com- p a r a x e of t h e si.~rrmarized i - o n i z a t i o n ( z ~ )

w i t h t h e v a l u e d e t e r m i n e d by t h e t u b e wall c i ~ r r e n t d e n s i t?; (Z,.,) was made. The r e s u l t s d i f f e r no n o r e t h a n a f a c t o r of

1.5 - 2.

R e f e r e n c e s :

~ i g . 2 . P ~ = ~ . I o - ~ ~ o r r , P ~ = O . O Z Tory.

c a l c u l a t i o n : 1 - Eo/P2=1 0 V/cm-Torr , 2 - 2 0 , 3

-

-

.

3

/I / S .C.'uilagner ,B.K. I ~ n a t y e v , JTP(USZ1i) ,

47,934(1977)

- --

-

Froc. ~ 1 1 1 ~ ~ I n t e r n . C o d . Phen. I o n i z . g a s e s , C o n t r . P a p e r s , P a r t 1, 333,

~ e r l i n ( 1 9 7 7 ) .

-

/4/ S.C.Broikn, B a a i c Data of Plasma P h y s i c s , Cambridge, I d a s s a c h u s e t t s , E.Y. (1959).

-2

b