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Submitted on 1 Jan 1979
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EFFECT OF DISCHARGE RADIATION ON ELECTRODE PROCESSES IN HELIUM
L. Kiselevskii, N. Klygin, A. Makarevich, D. Soloviyanchik
To cite this version:
L. Kiselevskii, N. Klygin, A. Makarevich, D. Soloviyanchik. EFFECT OF DISCHARGE RADIATION
ON ELECTRODE PROCESSES IN HELIUM. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-
465-C7-466. �10.1051/jphyscol:19797226�. �jpa-00219208�
JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuilZet 1979, page C7- 465
EFFECT OF DISCHARGE RADIATION ON ELECTRODE PROCESSES IN HELIUM
L.I. Kiselevskii, N. Ya. Klygin, A.N. Makarevich and D.A. Soloviyanchik.
I n s t i t u t e o f Physics, Byelomcssian Academy of Sciences, Minsk, U. S. S. R.
The t ~ l e ~ ~ i o n i c , a ~ t ~ e l e ~ t r o n i c and seconda- r a n g e d from 1 t o 5 A, w h i l e in t h e p u l s e re- ry i o n - e l e c t r o n e m i s s i o n s a r e u s u a l l y c o n s i - gime t h e s e were 8 k ~ and 100 A, r e s p e c t i v e l y .
& r e d t o be t h e main e l e c t r o n s o u r c e s i n t h e r e g i o n o f e l e c t r i c a r c and s p a r k d i s c h a r g e s . Some o t h e r i m p o r t a n t s o u r - c e s o f e l e c t r o n s , w i t h t h e p h o t o e f f e c t on t h e cathode s u r f a c e among them, c a n be a s
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sumed t o e x p l a i n t h e c u r r e n t s t r e n g t h and c a t h o d e s p o t motion. However, i t i s e x t r e
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mely d i f f i c u l t t o d i s t i n g u i s h t h e r o l e o f t h e p h o t o e f f e c t i n e x p e r i m e n t s , s i n c e t h e f a r - u l t r a v i o l e t r a d i a t i o n e x h i b i t i n g t h e p h o t o e f f e c t o n most m e t a l s i s g r e a t l y a b s o r - b e d by t h e d i s c h a r g e atmosphere.
The s c r e e n i n g e f f e c t o f t h e atmosphere can be s u b s t a n t i a l l y d i m i n i s h e d w h i l e s t u d y i n g a d i s c h a r g e i n i n e r t g a s e s o p t i c a l l y t r a n s - p a r e n t up t o shomt w a v e l e n g t h s .
Our e x p e r i m e n t s have b e e n made i n t h e h e l i - um atmosphere ,whose t r a n s m i t t a n c e i s up t o 4 0 0 A / I / . This c o r r e s p o n d s t o u l t i m a t e l i g h t quantum energy o f
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2 5 eV, markedly p r e v a i l i n g o v e r t h e e l e c t r o n bond energy i n s o l i d s . Vacuum u l t r a v i o l e t q u a n t a t h a t p a s s t h r o u g h t h e atmosphere o f t h e s e g a s e s a r e c a p a b l e o f p r o d u c i n g t h e p h o t o e f f e c t o n a l l a n d a l l o y s . The e l e c t r i c d i s c h a r g e between a f l a t p o l i s h e d c a t h o d e and cone- -shaped anode (Cu,Mu ,W) was s t u d i e d u n d e r t h e c o n t i n u o u s and p u l s e c o n d i t i o n s w i t h a s p a c e between e l e c t r o d e s b e i n g e q u a l t o-
1 0 mm. ' h e d i s c h a r g e chamber a t a p r e s-
s u r e o f
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1 atm was c o n t i n u o u s l y blown t h r o u g h by t h e h e l i u m flow t o remove t h e e l e c t m de c o n t a m i n a t i o n s o f t h e atmosphere.Under s t e a d y c o n d i t i o n s , t h e e l e c t r o d e v o l - t a g e amounted t o 300 V, a n d t h e c u r r e n t
I n t h e s t e a d y c o n d i t i o n s , when t h e atmosphe- r i c p u r i t y i s e n s u r e d , t h e r e a p p e a r e d a d i s - charge w i t h a c o n t r a c t e d column a n d d i s c cathode " 20-30 mm i n d i a / 2 / . The r e a s o n s f o r t h e c a t h o d e d i s c f o r m a t i o n have n o t b e e n e a r l i e r d i s c u s s e d . I t i s i m p o r t a n t t h a t t h e c a t h o d e c u r r e n t c o v e r s t h e whole
d i s c r e g i o n and i t s d e n s i t y c a n n o t be a t t - r i b u t e d o n l y t o t h e above p r o c e s s e s . Both t h e r m i o n i c and a u t o e l e c t r o n i c e m i s s i o n s l i t t l e c o n t r i b u t e t o t h e c u r r e n t d e n s i t y b e c a u s e o f a low cathodb s u r f a c e tempera- t u r e ( s e v e r a l hundreds o f d e g r e e s ) and s m a l l e l e c t r i c c u r r e n t s t r e n g t h . The c o n t - r i b u t i o n o f t h e s e c o n d a r y i o n - e l e c t r o n e m i s s i o n i s a l s o s m a l l due t o a low c u r r e n t d e n s i t y ( f r a c t i o n s Of A / c ~ 2 ).
The i n v e s t i g a t i o n s show t h a t t h e most p r o - b a b l e a d d i t i o n a l p r o c e s s t h a t c a u s e s e l e c t - ron e m i s s i o n from t h e c a t h o d e s u r f a c e o u t - s i d e t h e d i s c h a r g e column i s p h o t o e f f e q t due t o d i s c h a r g e u l t r a v i o l e t l i g h t . The above i s p r o v e d by t h e f o l l o w i n g . The d i s c glow n e v e r a p p e a r s i n t h e main d i s - charge shadow c r e a t e d by t h e d i e l e c t r i c s c r e e n p l a c e d i n t o t h e d i s c h a r g e chamber.
The d i s c glow diarneter c!e?ends on t h e ca- t h o d e m a t e r i a l . I t i s g r e a t e r o n t h e m e t a l s having a h i g h e r e l e c t r o n work f u n c t i o n
( F i g . 1 ) . This i s , p r o b a b l y , due t o t h e f a c t t h a t w i t h p r e s c r i b e d r a d i a t i v e f l u x , a l a r g e r a r e a i s n e e d e d t o yroduce t h e r e q u i -
red c u r r e n t f o r h i g h e r e l e c t r o n work func- t i o n .
Beyond t h e d i s c glow, s m a l l l o c a l 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:19797226
s i t e s s h a p e d a s a corona 0.5-3 mm i n d i a ( F i g . 2 ) can be g e n e r a t e d o n t h e c a t h o d e s u r - f a c e . I t s h o u l d be n o t e d t h a t t h e s e s i t e s were r e g i s t e r e d , b e i n g p a r t i a l l y and comp
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l e t e l Y i s o l a t e d from t h e main d i s c h a r g e . F i g . 1 D i s c glow d i a m e t e r v s c u r
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r e n t o f e m i s s i o n from t h e c a t h o d e a t T=600 K
F i g 2 D i s c h a r g e w i t h l o c a l s i t e s With t h e metal probe p l a c e d f a r from t h e
d i s c h a r g e (up t o 2 0 cm) where t h e g a s i s a t room t e m p e r a t u r e , r e l a t i v e l y l a r g e e l e c t r i c c u r r e n t s up t o SO0 F A a r e r e g i s t e r e d . These c u r r e n t s a p p e a r o n l y when t h e p r o b e i s i n s i g h t o f t h e main d i s c h a r g e . The probe cur- r e n t l a s t s p r o v i d e d t h a t a q u a r t z p l a t e i s mounted i n f r o n t o f t h e p r o b e a n d v a n i s h e s c o m p l e t e l y when t h i s p l a t e i s r e p l a c e d by a g l a s s one.
The k i n e t i c s o f t h e c a t h o d e d i s c i n t h e p u l s e regime s t u d i e d by t h e s t r e a k - p h o t o g -
raphy o f glow (Fig.3) a l s o t e s t i f i e s i n f a - vo r , o f t h e above s t a t e m e n t .
The d a t a show t h a t t h e s p e e d o f r a d i a l s p r e a d o f t h e c a t h o d e d i s c can a c h i e v e t e n s o f km/s, t h a t g r e a t l y e x c e e d s a p o s s i b l e e x p a n s i o n v e l o c i t y o f h e a t e d g a s e s i n t h e d i s c h a r g e . Also, we o b s e r v e d t h a t glow s t a r t s f i r s t i n t h e p e r i p h e r y a n d t h e n co- v e r s t h e r e g i o n s c l o s e t o t h e d i s c h a r g e
shock waves a r e no l o n g e r g e n e r a t e d i n t h e d i s c h a r g e column.
F i g . 3 Streak-photography o f t h e cathode glow: a
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symmetric c a t h o d e glow, b-
asym-m e t r i c c a t h o d e glow
The f o r m a t i o n o f asymmetric c a t h o d e glow c a n be o b s e r v e d , t o o . I n t h i s c a s e time o f t h e s h a p e and p o s i t i o n o f t h e c a t h o d e r e g i o n may be c o n s i d e r e d a s t h e well-known c a t h o d e s p o t moving o v e r t h e cathode s u r f a c e .
The e x p e r i m e n t s &emonst ra8e t h a t t h e s h a p e and k i n e t i c s o f a c a t h o d e s p o t i n t h e h e l i -
wn
d i s c h a r g e a r e a f f e c t e d by some p m c e s-
s e s . Of importance i s a l s o t h e c o n t r i b u
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t i o n o f p h o t o p r o c e s s e s o n t h e c a t h o d e s u r - f a c e , namely, t h e c a t h o d e s u r f a c e photoef- f e c t c a u s e d b y d i s c h a r g e u l t r a v i o l e t r a d i a - t i o n . However, a s m a l l r a d i a t i o n p a t h o f t h e vacuum u l t r a v i o l e t r e g i o n hampers t h e i r
~ b s e r v a t i o n i n o t h e r atmospheres.
R e f e r e n c e s
1 . Samson J. A. R., J. Opt. Soc. Am., 5 4 , 876, 1964
2 . ~ i s e l e v s k i i L. I., Klygin N. Ya.,
~ ~ l ~ ~ i y a n c h i k D. A., Feshchenko 2. P., P w c . ~ 1 1 1 t h I n t e r n a t i o n a l Conference phenomena i n I o n i z e d Gases, B e r l i n , 7977, p . 713
c e n t r e . I t i s a l s o importanf t h a t t h e ca- t h o d e di-sc s t a r t s forming n o t w i t h dis
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c h a r g e break-down b u t much l a t e r when
