THE EXPERIMENTAL STUDY OF ARC CATHODE MICROSPOTS LIFE-TIME BY THE VELOCITY MlCROPHOTOGRAPHY

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THE EXPERIMENTAL STUDY OF ARC CATHODE MICROSPOTS LIFE-TIME BY THE VELOCITY

MlCROPHOTOGRAPHY

A. Pertsev, V. Shadov

To cite this version:

A. Pertsev, V. Shadov. THE EXPERIMENTAL STUDY OF ARC CATHODE MICROSPOTS LIFE-

TIME BY THE VELOCITY MlCROPHOTOGRAPHY. Journal de Physique Colloques, 1979, 40

(C7), pp.C7-409-C7-410. �10.1051/jphyscol:19797200�. �jpa-00219180�

JOUHNAL DE PHYSIQUE CoZZoque C7, suppZdment au n07, Tomi 40, JuiZZet 2979, page C7- 40s

THE EXPERIMENTAL STUDY OF ARC CATHODE MICROSWTS LIFE-TIME BY THE VELOCITY MlCROPHOTOGRAPHY

A.A. Pertsev, V.P. Shadov.

Moscow U. S. S. R.

I. I n t r o d u c t i o n

There a r e two modes of cathode opera- t i o n , namely d i f f u s i v e and c o n t r a c t i v e i n d i f f e r e n t d i s c h a r g e d e v i c e s . For t h e c o n t r a c t i v e d i s c h a r g e c u r r e n t t r a n s f e r through t h e plasma-cathode l a y e r i s pro- v i d e d by small cathode s p o t s .

The i n v e s t i g a t i o n showed (p.e.

[I ]

), t h a t t h e s p o t s l o c a t e d on t h e cathode

micro-non-informatics,

c o n s i s t of t h e a r r a y of s m a l l e r elements cathode micro- s p o t s . The s t u d y of t h e cathode micro- s p o t s development dynamics and t h e i r pa- r a m e t e r s e n a b l e s one t o c l e a r t h e gene- r a l q u e s t i o n s of n e a r - e l e c t r o d e p r o c e s s e s and t o s o l v e connected a p p l i e d problems.

The l i f e - t i m e of t h e cathode microspot i s one of t h e most important parameters.

According t o some i n v e s t i g a t i o n s k1,2], t h e l i f e - t i m e o f t h e cathode microspot r a n g e s from few t e n t h s of microsecond t o t e n s microseconds.

I n t h e p r e s e n t work cathode m i c r o s p o t ' s l i f e - t i m e have been measured i n t h e p u l s e a r e vacuum d i s c h a r g e s using t u n g s t e n e l e c t r o d e s .

2.

Diagnostic t e c h n i a u e and t h e e x p e r i - mental d e v i c e

The cathode p r o c e s s e s of a r c were r e c o r - ded on t h e photofilm by t h e e l e c t r o n - o p t i c a l c o n v e r t e r w i t h space-time presen- t a t i o n of image.

The space-time four-dimentional a p e r t u r e f u n c t i o n of t h e p r o c e s s

i s

S ( x , y , z , t ) , where S

i s

t h e r a d i o n c e , t h a t was r e p r e -

s e n t e d by 1 6 space two-dimentional fun- c t i o n s S ( x , y ) , of which e v e r y o t h e r one was s h i f t e d w i t h r e g a r d t o t h e p r e c e d i n g f u n c t i o n b y ~ z -the exposure time.

The microspot l i f e - t i m e can be c a l c u l a t e d a s T = n . b Z where n

i s

t h e number of frames c o n t r a c t i n g a microspot. 'The r e f e- r e n c e g r i d was p r o j e c t e d t o t h e image of t h e s t u d i e d p r o c e s s f o r t h e d i f i n i t i o n of t h e microspot s p a t i a l p o s i t i o n on t h e cathode

633.

Pig.1 shows t h e p r i n c i p a l c o n f i g u r a t i o n of t h e e x p e r i m e n t a l d e v i c e . Vacuum sys- tem provided t h e d e p r e s s i o n i n t h e chamber ( I ) , i n which t h e e x p e r i -

- ^loe6

^{T o m}

mental model (2) was i n s t a l l e d .

E l e c t r o n - o p t i c a l c o n v e r t e r

(3)

w i t h mic- rophotographic o b j e c t i v e ( 4 ) was used t o r e e o r d t h e a r c cathode p r o c e s s e s . For e l e c t r i c d i s c h a r g e i n t h e e x p e r i m e n t a l model t h e s t o r a g e l i n e

(5)

was used, t h a t was t r i g g e r e d by t h e i n i t i a t i n g d e v i c e

( 6 ) w i t h s y n c h r o n i z a t i o n c i r c u i t

(7)

.The e x p e r i m e n t a l model (Fig.2) i n c l u d e s t h e

cathode ( c ) i n t h e form of t u n g s t e n w i r e c u t ,

i t s

d i a m e t e r being 1

mm;

t h e l i m i t - i n g ceramic washer ( w ) , t h e anode ( a ) and t h e t r i g g e r i n g gun

(t).

The exposure time of t h e e l e c t r o n - o p t i c a l c o n v e r t e r v a r i e d from 0.05 t o 0.5 micro- second.

3 .

Experimental r e s u l t s

Fig.3 shows t h e copy of t h e t y p i c a l a r c cathode p r o c e s s photo, t h e d i s c h a r g e cur- r e n t 100A. The exposure time a Z =0.2 mic- rosecond t h e i n t e r f r a m e time d e l a y can be c o n s i d e r e d i n s i g n i f i c a n t .

S t a t i s t i c a l Q a t a h a s been o b t a i n e d con- c o n c i r n i n g t h e microspot l i f e - t i m e and i t s dynamics i n p u l s e d i s c h a r g e s a t t h e cathode temperature of about 3 0 0 ' ~ .

Pig.4 shows t h e d e n s i t y d i s t r i b u t i o n d i a - gram of t h e microspot number v i a t h e l i f e - t i m e ( t h e s o l i d ' l i n e ) . The p i c t u r e shows, t h a t t h e l i f e - t i m e r a n g e s from 0.05 t o 2 microsecond a t t h e d i s c h a r g e d u r a t i o n 1 0 mosec.

The most probable l i f e - t i m e

i s

e q u a l t o 0.6 microsecond. When cathodg temperature i n c r e a s e s from 3 0 0 ' ~ t o 1000bK, t h e d i s - t r i b u t i o n diagram changes v e r y s l i g h t l y , but a t h i g e r t e m p e r a t u r e s t h e number of microspots w i t h s h o r t l i f e - t i m e decrea- s e s and t h e number of ones w i t h l o n l i f e-time grows ( F i g .4, broken l i n e $ . A t temperatures up t o 4TO0°K t h e micro- s p o t s c l u s t e r t o a s i n g l e macrospot, e x i s t i n g d u r i n g t h e h o l e d i s c h a r g e time.

4. Discussion

One h a s t o n o t e , t h a t t h e measurements of t h e l i f e - t i m e were c a r r i e d o u t by r e c o r - d i n g t h e l i g h t r a d i a t i o n d u r a t i o n . The cathode flame f o r m a t i o n may be c o n s i d e r e d

as

t h e i n i t i a l phase of

a

microspot deve- lopment. The microspot l i f e - t i m e v a l u e , dependent on t h e c u r r e n t ,

w i l l

exceed t h e measured magnitude by t h e time i n t e r v a l needed t o t h e microspot f i x a t i o n c e n t e r from t h e c u r r e n t s t a r t t o

i t s

t h e r m a l ex- p l o s i o n . According t o [4] t h i s i n t e r v a l

i s

of t h e o r d e r of microseconds f o r a tunn- s t e n e l e c t r o d e a t t h e c u r r e n t d e n s i t y

-

-lo6

A/srna.

The microspot l i f e - t i m e measurement accu- r a c y

i s

l i m i t e d by

an

e l e c t r o n - o p t i c a l c o n v e r t e r exposure time.

For t h e p r e s e n t c a s e

i t i s

e q u a l t o 0.1 microsecond. T h e t ' s why t h e accuracy of t h e most p o s s i b l e l i f e - t i m e measurements

i s

l i m i t e d t o 2 v 0 l e v e l .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797200

I ~XUCQUB El. r . Ku~eawre ~ g e c o n B J I ~ K ~ H X ~ C R ~ B wm. M.,"HayKaw, 1968.

2 . P a x i ~ s e ~ n P i B.H. @ n s a ~ e c ~ u e ocHosn

3,Eer@~oae~ 1D.A. ,roaybb B.H. TBT, 1971, 3, 846.

4. EHHHCOH M.M. PE1;3,1960,b8, 1318.

F i g .I. The experimental u n i t c o n f i g u r a t i o n .

Fig.!!.

The experimental

model.

Fig.4. The microspot d i s t r i b u t i o n on t h e l i g h t - t i m e .

F i g . 3 . The cathode microspot

s

photo.