EXPERIMENTAL INVESTIGATION OF RADIO-FREQUENCY DISCHARGE IN HELIUM

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EXPERIMENTAL INVESTIGATION OF

RADIO-FREQUENCY DISCHARGE IN HELIUM

V. Godyak, A.S. Khanneh

To cite this version:

V. Godyak, A.S. Khanneh. EXPERIMENTAL INVESTIGATION OF RADIO-FREQUENCY DISCHARGE IN HELIUM. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-125-C7-126.

�10.1051/jphyscol:1979761�. �jpa-00219467�

JOURNAL DE PHYSIQUE CoZZoque C7, s u p p l d m e n t a u n 0 7 , Tome 40, J u i Z Z e t 1979, page C7- 125

EXPERIMENTAL INVESTIGATION OF RADIO-FREQUENCY DISCHARGE IN HELIUM

V.A. Godyak, A.S. Khanneh.

Moscou S t a t e U n i v e r s i t y , Department o f P h y s i c s , Moscou, U. S . S. R.

In paper / 1 / it was noted t h a t an in- crease i n RF discharge voltage brought ab- out a qualitative change i n the discharge and in the discharge 1uminocity.In / 2,3 / it was shown t h a t t h i s change i n regime (from d t o ) was accompanied by a sharp increase i n the discharge current.

Given below a r e the r e s u l t s of the ex- perimental investigat ion of plasma parame- t e r s and volt-ampere c h a r a c t e r i s t i c s of RF discharge over a range of external conditi- ons under which both regimes of discharge were realized.Yleasurements were carried out i n a Helium f i l l e d cylindrical tube of radius

R

tjcm with two plane titanium ele- ctrodes placed inside it 7.7cm apart .The

M(K) here d i f f e r s from the Shottky's d i s t r i - bution can be explained according t o / 6 / by the f a c t t h a t the e l e c t r i c f i e l d i n pla- sma and thus the ionization frequency are functions of the

x

-co-ordinate .For \j, 7

ky

( -regime) the a x i a l d i s t r i b u t i o n of pla- sma density a t pressures more than I t o r r showed a maximum near the boundary (Fig.1)

.

If the pressure increased t h e maximum was observed t o move towards the boundary,whi- l e i t s value increased and a t p =6torr the value of maximum was about 20.0n going from d t o. the -regime,the electron te- mperature dropped t o a f r a c t i o n of i t s for- mer value between 1.5 and 0.5V depending on the pressure (Fig.2).

electron temperature Ve and the plasma ^de- ~ = 3 t o r r

Ve, v -

x= 3 c m n s i t y f l were obtained ^f com the electron ^{a - X = O} branch of the volt-ampere curve of the La-

ngmuir probe / 4 /.In calculating I? t h e

f i n i t e n e s s of the r a t i o of the probe radi- ^\ us ( Tp ^{-5 1} O - ~ C ~ ) t o the electron mean

f r e e path was taken i n t o accouat / 5 /.The

discharge current was measured using a Ro- 1

\;9x

govsbyls coil.0n increasing the discharge 2 4 lo3

voltage t o a c r i t i c a l point

V ,

= which 0 1 2 3 X. cm depends on %he gas pressure P and t h e f r e -

quency f , a rediatrLbution of discharge luminosity was observed.For voltages

V ,

⁴

VAr

⁽ -regime) over the range of values of and i n v e ~ t i g a t e d , the a x i a l distri- bution of plasma density

n(%)

is constant, except near the bounda~g where it sharply decreases (Fig.1) .The electron temperature was close t o the temperature of the plasma i n the positive c o l m ~ of t h e direct-cur- r e n t discharge, taking value a between 6-3V depending on the pressure.The f a c t t h a t

Fig.1 Fig.2

The observed changes are i n accordance with the hypothesis put forward i n / 1 /, according t o which when L/, i s large enough

(V,

> Vdr physical processes on the ele- ctrode ^and i n the sheath are similar t o those i n the cathode f a l l region of the glow discharge.In this case gas ionization is mainly brought about the beam of high energy electrons injected from the sheath / 7 /.The plasma density a t t a i n s a maximum near the boundary ( a s r e s u l t of damping

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979761

of the ^beam) and the electron temperature is relatively low a s i n a non-autonomous dischargebhe experimental values of the plasma density a t the center nc and the

discharge current

I/p ,

are plotted in Fig,3,4 and 5,It can be seen here t h a t the- se curves are different f o r & and -re- gimes .The perpendicular l i n e s i n Fig .3,4 show the voltage x y

.

^'

In the d -discharge, when L/, i s not too low: M.-.

V,f2

^;

5 -

^V! and decreases with in- increase in pressure and

J/f - ^{k f} .

the

r

^{-diseWse n (4)}

^{, %}

^(P) a n d f ; O ) practically cease t o depend on their res- pective variables.The sharp increase of

I

noted in / 2,3 / i s seen here when P i s large enough and f i s small.According t o / 7 / t h i s takes place when the crossing over t o

b/

-regime leads t o large decrease of the sheath thickness ^and thus to a dec- rease in the discharge impedance.

Gy

^as a function of gas pressure is shown on Fig.6.

It i s seen here that this pressure depen- dence i s similar t o that of the cathode f a l l in the glow dischargeithe minimum va- lue o f Vdy i s close t o the normal cathode f a l l .

The behavior o f the discharge parame- t e r s Ve

,

^M

, ^I

^and

V !

agrees quali- tatively with the theoretical analyeis of

y

-dischsrge carried out i n / 7

/.

I ^{I 1}

loz 2 4 ^lo3 2

1 0 C.M./ledu~c~u;, )I(T'P,

u,

^970, 1951,

2 0 i'. H.

3 a c ~ e ~ u e p

u

ap.,

P a 3 u o t e x ~ u ~ a u

%'eK T P O H U K ~ ,

5,

^{1709, /96o'}

3.

H. ^9.

~ Y ~ H K O ,

q,

^{h? rep. 06kj. U MOfleK.}

~ U 3 U K U , 160, 1978.

4.V.A.God3ak & all,PRoc.XII Int~Conf oPhe- nom, Ioniz, .Gases, ¹ Og,Eindhoven, 1 975.

5. 6.M 3axr7~06a u

ap.,X(Te

3 , 4 4 2 , 1960.

6,8.P,Allis & all,P~s.Bev0,84~5~9,1951 7.Author1s report in t h i s ~onference.