ANOMALOUS CONDUCTIVITY OF LOW PRESSURE HF DISCHARGE IN MAGNETIC FIELD

JOURNAL DE PHYSIQUE Colloque C7, supptdment

n07, Tome

JuiZZet 1979, page

207

ANOMALOUS CONDUCTIVITY

LOW PRESSURE HF DISCHARGE IN MAGNETIC FIELD

V.G.

Naumovets, L.L. Pasechnik and

I n s t i t u t e for Nuclear Research Ukrainian SSR Academy o f Sciences Kiev, U. S. S . R.

It was e s t a b l i s h e d previously / I / that i n t h e HF discharge t h e superposition of t h e magnetic f i e l d H normal t o t h e a l t e r n a - t i n g e l e c t r i c f i e l d E r e s u l t s i n a redi- s t r i b u t i o n of HF v o l t a g e between t h e aheath and plasma. Due t o t h i s t h e elec- t r i c f i e l d i n the plasma s u b s t a n t i a l l y increses. F u r t h e r i n v e s t i g a t i o n s /2/ ha- v e shown t h a t t h e e l e c t r i c f i e l d E has a maximum a t some value of H, t h e p o s i t i o n of t h e maximum being dependent on t h e pressure. This dependence was explained by t h e d i f f e r e n t i n f l u e n c e of H on t h e conductivity of t h e plasma - ^{GP and of}

t h e sheath - ch . The c a l c u l a t i o n perf or- med agree reasonably with t h e experimen-

t a l dependence l!(H). A t high magnetic f i - e l d s , however, t h e r e e x i s t s some d i s c r e - pancy between t h e measured and calcula- ted values of E. The experimental d a t a

Fig. 1

obtained a t two pressures P of helium a r e presented i n 9ig.l by t h e p o i n t s (a- P = 2.10"~ mm HO; b- P = l . l ~ - ~ m m HG).The measurements were perfollaed with t h e ap- paraturea described i n / I ,2/. The E(H) -

dependences c a l c u l a t e d according t o /2/

a r e given i n fig.1 by s o l i d l i n e s . A t t h e high magnetic f i e l d s t h e s e dependen- c e s a r e i n poor agreement with t h e expe- rimental d a t a , t h e discrepancy being es- p e c i a l l y pronounced a t t h e low pressures.

The agreement between t h e experimental and c a l c u l a t e d d a t a can be s i g n i f i c a n t l y improved i f one assumes a t high R t h a t t h e c o l l i s i o n frequency of electeons - ^{3 ,}

determining t h e value of 6 is easenti- a l l y h i g h e r than t h e c l a s s i c a l frequency

*a "293. ~O'P /3/. The v a l u e of 9 ^{can be}

determined from t h e measurements of t h e phase s h i f t -9 between t h e discharge v o l t a g e and t h e c u r r e n t i n t h e discharge c i r c u i t . A n a n a l y s i s of t h e equivalent c i r c u i t of t h e discharge gap (plasma -

and r e a c t i v e components of t h e plasma conductivity a c r o s s H, Gh -the Weath c o n d u c t i v i t y ) . I n our experiments t h e elec- t r o n cyclotron frequency Ge i s much hig-

15

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797102

her than the frequencies of electron- atom and ion-atom collieions, &a and via ,

and the frequency of alternate electric field - ^Cd . Besides in our experiment the inequality is also fulfilled E44E p, were E -the specific "plasma field"/4/. Under

P

these conditions

and 6 x are ex- pressed as:

e2n mi d2

c--(-.--i) ^{-mi0 me %}

(e and me are the electron charge and mass, n is the concentration of the char- ges in the plasma, mi is the ion mass).

At high H we have usually in our experi- ments 1 6 6 R . Then the expression (1) can be simplified as follows:

(2) As can be seen from (2) 9 is determined

m a i w by y . The dependence (H) which is obtained experimentally (curve 1) and calculated according to (1) under assum- ption that Lf- yea (curve 2) is shown in fig.2. !Phe discrepancy between the measu-

red and calculated C f at high H can be eliminated by inserting instead of L' some ef f eo tive frequency &j depending on H.

The values of l)eff obtained by substitu- ting the measured phase shifts into

Fig.3 (0 - ^P

4.10-~mm HG).

(1) and (2) are presented in fig.3 (curve I). The calculations using $eff allow to describe correctly the behaviour of E(H) in the region of the high H (fig. 1,dashed curve). A n analysis shows that the signi- ficant increase of L' can be due to the exitation of small-scale ion-sound oscil- lations on which the intense scattering of the evaluation of Qeff according to /5/

is shown in fig.3 (curve 2).

References:

1 .V.G.IJaumovets,L.L.Pasechnik,V.V.Yagola, Proc .XI11 ICPIG, Berlin, 1977, p.34-46 2.V.G.Naumovete,L.L.Pa8echaik,V.V.Pagola,

Bisika plasmy,1979,~,N01,187-191

3.V.E.Golant,Svershvysokocharjtotnye meto- dy issledovanya plasmy,Moskva,Nauka, 1968 4.V.L.Ginsburg,lS.V.Gurevich,Uspekhi Fisi-

cheskikh Nauk, 1960,'&,B03,393-428 5.L.I.Grigorieva,A.V.Loginov,A.I.pSatak,

V.L.Sizonenko,B.I.Smerdov,K~B.Stepanov, Proc.4 Conf.Plasma Phys.Contr.Bucl.Fus.

Research,Vienna,l971,vol.III,573-595

Big.2 (o - ^P

HG).