HIGH FREQUENCY OSCILLATIONS AND ELECTRON BEAM RELAXATION IN HOMOGENEOUS GAS-DISCHARGE PLASMA

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HIGH FREQUENCY OSCILLATIONS AND ELECTRON BEAM RELAXATION IN

HOMOGENEOUS GAS-DISCHARGE PLASMA

L. Pasechnik, L. Romanyuk, N. Svavil’Ny

To cite this version:

L. Pasechnik, L. Romanyuk, N. Svavil’Ny. HIGH FREQUENCY OSCILLATIONS AND ELECTRON BEAM RELAXATION IN HOMOGENEOUS GAS-DISCHARGE PLASMA. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-619-C7-620. �10.1051/jphyscol:19797300�. �jpa-00219290�

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JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment a u n07, Tome 40, J u i Z Z e t 1979, page C7- 619

HIGH FREQUENCY OSCILLATIONS AND ELECTRON

IN HOMOGENEOUS GAS-DISCHARGE PLASMA BEAM RELAXATION

L.L. Pasechnik, L.I. Rornanyuk, N. Ye. Svavil'ny.

I n s t i t u t e f o r Nuclear Research, U k r a i n i a n Academy o f S c i e n c e s , Kiev, U . S.S. R.

The account of different types of in- homogeneities in the theoretical conside- ration of the electron beam interaction with plasma and wave propagation in plasma allows one to observe a number of some remarkable phenomena (oscillation localization and accumulation /1,2/,rapid wave attenuation /3/).An extunple of the beam- plasma system,which is strongly inhomogeneous by a number of parameters is the hot cathode Penning discharge.The present report deals with results of an experimental study of the high frequency oscillations,originating in- the plasma of this discharge and formation of electron velocity distribution function.

Experiments were carried out on an de- vice with Penning cell (fig la).The discharge was realized in a stationary sta- te in He (in dome experiments in &) at a pressure pt8-10-~$5 10-~torr in a homogeneous magnetic field BPO. 01 -0.04T. Para- meters of the beam-plasma system were va- rled:plasma density n=8.10~~$4-10 cmW3, 11

primary electron velocity v0e4. 5 lo8+

3 . logcm-s'l ,ratio of beam and plasma

density

- ns

^=r5loo4+2 loo2; the plasma electron temperature Te=4s8 eV. The con-

n

trol measurements were also carried out in the arc discharge plasma at the same discharge conditions (in this case elec- trode 6 was the anode.) This experiment showed that in both Penning discharge plasma and arc discharge plasma inside the primary electron beam intensive oscil- 'lations are generated in frequency range

f a40 MHzf7.5 GHz whose characteristic spectrum is shown in fig 2.

One can see that the most intensive oscilla-

tions are concentrated in "low frequencyw

Fig. 1 .Experimental devicezl-cathode, 2-au- xiliary cathode,3-diaphragm,4-anod,!5-HF probe, 6-ref lector, 7-screen, 8-stationary analyzer,9-moving amalyzer;b,c-dependen- ces:l-Um(Z) 2-ULp(Z),3-n (2).

(LF) 4031000 MHz and "high frequencyn (HF) 233 GHz parts of the spectrum.

The characteristic features of the ob- tained oscillation spectra indicated that in the studied beam-plasma system flashes (nradioimpulsesn) of the HF field with

&&dare generated,which cause the plasma Pe

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797300

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potential splashes (%video pulsesw) with According to /2/ in the ISfield local- the mean statistic durationZ"-5 ns and ization zone the transformation is possib- the repetition period Tz16+25 ns /4/.The le of the excited waves in Langmuir ones observed rapid selfmodulation of HF field with the subsiquent intensive absorption at the present experiments is possibly of HF power by plasma electrons.Investiga- connected with the peculiarity of wave tion of the space evolution of the elect- generation and absorption /3/ in plasma, ron distribution function showed that ac-

which is inho- mogeneous in deneity .The re ason for the potential Fig.2.0scillation spectrum.a-PIG dischar- ge ;b-part of spectrum (a) ;c-arc discharge.

splashes may be lack of compensation of electron space charge,arising due to stric tion force,because of the ion inertia.

The detailed study of the space distri- bution of the oscilLation intensity in both discharges types showed that the HF range oscillation are always localized in the inhomogeneous density plasma,adaoin- ing to cathode (fig Ib,c,curvea I).The observed characteristics of the HF field

(Zst- is the coordinate of the oscillati- on oocurence,Z-is the half width of the HP field existence range and 8-is the space increment),agree satisfactorily with estimations from theory of the electron beam interaction with inhomogeneous den- sity plasma /2/ (see Table I).Localizati- on of the LF range oscillation is deter- mined by the HP field position and prima-1

r y electron beam velocity (fig lb,c,cu~-

ves 2).

n tually not only primary electron beam relaxation

/ O ' q ~ ~

B takes place in the HF

,..j\---- ;

field localization zone

/Z'q

^.^,^,)\\

-.

but also an effective 0 80 /m t;ev

Fig.3.Electron distribution functi0n.a- PIG discharge, 1-Z=9 mm, 2-2-17 m,3-Z=32mm.

b-1-PIG discharge,2-arc discharge,Z=l40nrm, fa=0.3~,~a=150 V.

heating of plasma electrons (fig 3al.Be- Table I

* ffrc dr schozge

yond the indicat

-

ed zone the ener- gy elec- tron spectrum practically is not changed and has an identical form in both discharges

types (fig 3b).

R E F E R E N C E S : 1.Ya.B.Fainberg,V.O.Shapiro,Zh.Ehksp.feor.

Fiz.

,a,

1389,1964.

2.V.Kopecky,J.Preinhaelter,Plasma Phys., 2,333, 1969.

3.S.?d.Dikman,Pis*ma Zh.Ehksp.Teor.Fiz.,a, 429,1978.

4.L.L.Pasechnik,L.I.Romanyuk,N.Ye.Svavi18 ny,Pis!ma Zh.fekh.Fiz.,4,958,1978.