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HAL Id: jpa-00219140

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Submitted on 1 Jan 1979

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ON THE INLFUENCE OF ELECTRODES ON THE PROPERTIES OF HIGH PRESSURE DISCHARGE

V. Peskov

To cite this version:

V. Peskov. ON THE INLFUENCE OF ELECTRODES ON THE PROPERTIES OF HIGH PRESSURE DISCHARGE. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-333-C7-334.

�10.1051/jphyscol:19797164�. �jpa-00219140�

(2)

JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, page C7- 333

ON M E IFClUENCE OF ELECTRODES ON

M E

PROPERTIES OF HIGH PRESSURE DISCHARGE

V.D. Peskov.

I n s t i t u t e for PhysicaZ ProbZems, Moscow, U.S. S.R.

It i s known, t h a t i n t h e nearelectrode regions of low pressure a r c s t h e r e occur a l o t of e x o t i c phenomena [I] . As f o r t h e high pressure discharges , t h e information about t h e e l e c t r o d e phenomena is very scanty because t h e i n t e n s i t y of v i s i b l e , emission i s u s u a l l y comparable t o t h e ra- d i a t i o n of nearelectrode regions.

Present work i s devoted t o compa;ison of v i s i b l e and V W s p e c t r a (500-10000A) of t h e

e l e c t r o d e l e s s (EL) [2J and electrode (E) HF discharges and d i r e c t c u r r e n t a r c (A) with W , Mo or Cu e l e c t r o d e s i n H2, D2 and r a r e gases a t t h e pressures up t o 30 atm with s i m i l a r dimensions, power, c u r r e n t and o t h e r c h a r a c t e r i s t i c s . Space d i s t r i b u t i o n of t h e luminosity of t h e v i s i b l e l i g h t was measu- r e d by s t e r e o s c o p i c a l system composed of two d i s s e c t o r s . I n t h e

ITUP

and u l t r a s o f t X-ray regions we used t h e two-dimensional coordinate counters. I n t h e whole s p e c t r a l region (30-7000 i) space r e s o l u t i o n was about 0.1 mm.

I.

Exp

- eriments a t

p=l

atm a ) Spectra i n

0

2000-10000

A

region. The s p e c t r a of H2 and D2 discharges have H- continuum and Balmedlines. The diameter of H- emission region was a f e w

mm

l a r g e r compared t o l i n e emission zone. With i n c r e a s i n g of t h e discharge power from 0.5 t o 3 W t t h e plasma parameters v a r i e d i n such a way:

i n

A

- Te from 0.8 t o 1.1 eV, ne - from

5-10 l5 t o loq7 cme3, i n E - Th from 0.7

t o 0.9 ev,

M e

- from 2 loq5 t o loq6 cme3,

a q f m m 0.7 t o 1.2 eV,

Qe

- from

3 . 1 0 ' ~ t o loq5 c i 3

(

, ne -electron

temperature and d e n s i t g , respectively).

One may conclude t h a t i n EL n, i s of some o r d e r s l e s s e r , t h a n equilibrium

Me

c a l c u l a t e d by Saha equation, whereas i n

A

and E t h i s disagreement does not exseed 2.

I n ELone observes a l s o t h e disagreement of about two o r d e r s with Boltzmann law f o r l e v e l population. Due t o low

d e n s i t y t h e e l e c t r o n energy d i s t r i b u t i o n f u n c t i o n has t h e "cut-tail" [3] so the impurity l i n e s in ELwith &

l b

; , El -ioni- z a t i o n p o t e n t i a l of t h e main gas - were not

excited. But even i n t h e regims when e l e c t r o n d e n s i t i e s of a l l t h e types of discharges were equal, i n EL d i f f e r e n t t o

A

and E, l i n e s of i m p u r i t i e s were not

e x c i t e d

(

Te of EL was l a r g e r than i n

A

and E). S i m i l a r r e s u l t s were obtained i n r a r e gases.

a Spectra i n t h e range 500-2000 i I n IT2

and D2 i n

A

with

W

and Mo e l e c t r o d e s t h e highest luminosity was observed on t h e cathode spot with dimensions about

0.'1

mm.

The r a d i a t i o n from Cathode has pulse form with a time of -ps, moreover in some cases we succeeded t o observe by means of coordinate counters t h e pulse jets,flowing from t h e spots t o column (Fig.1) .Theref ore we o b t a i n i n W and Mo e l e c t r o d e s an "ex- plosive" mechanism of emission [I ] .

F i 1 Oscillograms of t h e s i g n a l s (see[41)

*two-dimensional counters observing t h e region of 0.5x0.5 mm a) t = O , b) t=1 ps,

c) t = 2 p s .

Electron concentration i n t h e nearcathode region measured by the coincidence of t h e s i g n a l s from spectrograph and coordinate counters was about loq8 so t h e s e j e t s c a r r y t h e e l e c t r o n s and i o n s i n t o t h e plasma column. Nearelectrode regions emit- t e d t h e i n t e n s e continuum s p e c t r a too.

Bdaximum energy Ed of t h e photons,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797164

(3)

emitted from cathode measured by means of t h e open counter, was about 100 eV f o r the i n t e n s i t y about I phop/s i n 4 T steerdn.

Such r a d i a t i o n corresponds t o the e f f e c t i v e spot temperature about 3 eV. Oa t h e Cu ca- thode a s o c a l l e d "thermal" mechanism of emission [I] i s l i k e l y t o r e a l i z e , because strong f l u c t u a t i o n s i n WV and photons with Ed- 100 eV were n o t observed and the

spot dimension was about 0.2-0.3 mm. I n E discharge near t h e e l e c t r o d e s we d i d not observe s p o t s , but t h e r e were r e g i s t e r e d t h e moving f i l a m e n t s abovt 0.1 mm i n diame- t e r and 0.3 mm i n length. E l e c t r o n d e n s i t y i n t h e filament was about 3-5 times higher than i n t h e background plasma, so in E t h e r e occurs an i n j e c t i o n of the e l e c t r o n s

i o n s and excited atoms from e l e c t r o d e s t o column.

A

s p e c i a l experiment was made t o check t h e influence of the small nearelec- t r o d e region on t h e densitg of e l e c t r o n s and excited atoms. We have introduced i n t o t h e EL f o r a 1 ms t h e

W

wire perpendicu- l a r l y t o t h e e l e c t r i c f o r c e l i n e s

(

in or-

der

not t o d i s t o r t t h e e l e c t r i c f i e l d ) . This procedure provides two or t h r e e f o l d

increase of ne i n t h e pulse. Radioscopy of t h e discharges by means of X-ray gun and with an emission of t h e discharge shows, t h a t i n EL impurity concentration did not exceed 'lom5%, b u t i n

A

o r E it was about 0.1%. S i m i l a r r e s u l t s were obtained i n r a r e gases. We did n o t manage t o record t h e r a d i a t i o n with E j 100 eV in

A

because of t h e strong absorption, but i n the nearelectrode region t h e r e were exci- t e d t h e weak i o n l i n e s , The halfwidth of He11 l i n e (1640 i), measured by t h e coin-

cidence technique f o r t h e s i g n a l s from spectrograph and coordinate counters w a s about 0.5 f;, i.e. temperature was about s e v e r a l eV. When t h e discharge

was switched off within 0.1 ps t h e s p o t s i n

A

disappeared approximately

ig

t h e same i n t e r v a l , but i n E - f o r someps. After- glow time of a l l t y p e s of t h e discharges was nearly t h e same

(

about some p s) i n t h e v i s i b l e region,

and

was about I 0 s

when we increased t h e speed of gas rota- t i o n i n t h e discharge chamber.

2. Experiments a t p ) 1 atm W e did not

-

manage t o d i s t i n g u i s h

VW

and v i s i b l e emis- s i o n of t h e nearelectrode regions in H2 and D2 at p > 2 atm from t h e background

continuum r a d i a t i o n of t h e column. V i s i b l e s p e c t r a of t h e discharges were similar, but i n EL ne w a s 2-3 orders l e s s e r , t h a n in equilibrium. A t t h e same time we observed t h e 5-10 f o l d d e v i a t i o n of t h e l e v e l popu- l a t i o n s from Boltzmann law.

A l l

t h e l i n e s vanished i n r a r e gases a t

p > 5

atm i n

s p e c t r a of EL and only continuum r a d i a t i o n was present. It was, due t d low ne - 1 0 11 cm-3 and t h e absence of t h e e l e c t r o n dis- t r i b u t i o n f u n c t i o n t a i l .

A t

t h e same power volume d e n s i t y i n

A

and in E t h e l i n e s were presented. We succeded t o observe t h e ca- thode spot i n

A

only i n He a t

3 4

1000 i.

The i n t e n s i t y of t h i s ez- by two or- d e r s of magnitude with a c h a r a c t e r i s t i c time about 3-5 p s .

Conclusion This work shows, t h a t i n

A

and E is always more close t o equilibrium t h a n i n EL. I n E and

A

equal

0,

in cont- r a s t t o EL i m p u r i t i e s with E i ~ > E ~ w e r e always excited. Similar r e s u l t s were ob- t a i n e d i n t h e work [53 , where v i s i b l e s p e c t r a of E and EL were compared. Our ex- periments in VUV showr. t h a t i n j e c t i o n of t h e e l e c t r o n s , e x c i t e d atoms and impuri- t i e s in A and E f a c i l i t a t e d t h e e s t a b l i s h - ment of equilibrium.

References

:

1 G.A.Lubimov, V.I.Rahovskiy, Uspehi P i s . Nauk, 125, 665, 1978

3 J - R i c h t e r , X ICPIG, Oxford, I n v i t e d papers, 37, 1971

4 G.D.Bogomolov, Yu.V.Dubmvskiy, V.D.

Peskov, Prib. Tech .Exper, N3, 209, 1978

5 V.M.Bateqia, V.S.Zrodnikov, V,K. Rod- d a t i s , V.P.Chinnow, TVT, '&, 270, 1975 i n V W . It showes t h a t e l e c t r o d e s d i d not

strongly a f f e c t t h e h e a t balance i n

A

and

E. The cooling time s i m i l a r l y diminished

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