ON IONIZATION INSTABILITIES OF HIGH PRESSURE DISCHARGES

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ON IONIZATION INSTABILITIES OF HIGH PRESSURE DISCHARGES

V. Peskov

To cite this version:

V. Peskov. ON IONIZATION INSTABILITIES OF HIGH PRESSURE DISCHARGES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-335-C7-336. �10.1051/jphyscol:19797165�. �jpa-00219141�

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JOURNAL DE PPYSIQUE Colloque C7, s u p p l i m e n t au n07, Tome 40, J u i l l e t 1979, page C7- 335

ON IONIZATION INSTABILITIES OF HIGH PRESSURE DISCHARGES

V.D. Peskov.

I n s t i t u t e f o r PhysicaZ Problems, Moscow, U. S. S.R.

Recently there was discovered an in- Results : 'Pwo types of the instabilities stability of high pressure dischargesh-&ut were discovered. The first one arises at the mechanism of such instability has not at I?> 3 atm in carefully purified gases been studied. This report is devoted to with diminishing of gas rotation speed.

the experimental investigation of the in- This instability arose in arc and electrode stability in direct current arcs and in HF ID? discharge in %he form of disordered discharges [4] in H2, D2 and rare gases at breakdowns near the main discharge column pressures up to P=30 atm. bended by Arhimed forces (Fig.2a). Ion

~ ~ t : h~ i ~ . l ~ dshows ~ the experimental lines appeared in rare gases simultaneously arrangement. Discharge emission was re- with breakdown. After the breakdown %he vi- gistered by means of stereoscopical sys- sible emission vanished for somers, but in tem composed of two dissectora and two V W one can observe the molecular spectrum fast (

-

^0.1 ^,qs) two-dimensional coordi- of rare gases during some tens of ?so nate counters, visualizing V W and soft

X-ray radiation of plasma in narrow bands from 100 to 2000 A 0 with the space resolu- tion about 0.1 mm.

Fig.1 l-discharge, 2- chamber, 3- pulse lamp,4- camera-obscura with coordinate counters, 5-x-ray counter, 6-spec- t rograph, 7-dissector,

Fig.2 a) scheme

a)

of first type of instability, b) oscillonrams of - arc current ( 1 1, lines ( 2 ) , and molecular ( 3 ) radiation at the 'moment of break-

down, c) oscillo- 6,gram [ 5 1 of sig-

nals from coordinate counter pas-

sed 10 p ^{s after}

breakdown

In electrodeless ID disahargp this in- 8- electria probe, 9-X-ray gun. stability displayed as an oscillations of

discharge dimension with a characteristic Spectra were recorded by the mono-

time about 1Ops. It was suggested [ 6 ] ,

chromator MDR-2 and vacuum spectrograph

that such a breakdown was due to DFS-29. Electric field distribution near

avalanche ionization of excited atoms the discharge was measured bg the probe.

accumulated near the main diecharge

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Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797165

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column. An attempt to calculate such a breakdown has been made in paper [7] .Our measurements with coordinate counters

show, that immedeately before the breakdown the intensity of molecular radiation near the discharge substantionally increases that confirms the accumula.tion of at oms.

To demonstrate experimentally the possibility of this mechanism the following experiment was produced. When discharge came up to the surface we irradiate the region near the column by the colli- mated pulse of radiation with energy

EL ) E d , & ( - f e n and with intensity of the order of -lo2' phot/s ( E; , E a - ^ioni-

zation potentials and first excited level of rare gas atom). Breakdown appeared simultaneously with the radiation pulse.

This experiment proves the hypothesis suggested in [6] because such radiation may ionize only excited atoms, but not normal

.

The second type of instability ap- pears only in HF discharges. It was displayed in the form of rapidly growing ( Ips) filamentary regions (diameter 0 , l - 1 mm) intensively radiating in V W (mainly continuum spectram)- see Fig.3.

Fig.3 Signals from dissector

(a) and coordinate counter (b) during growth of

8) ^--F second type in-

1

t'--7

f stability [ 5 L

usly with filament growth one can observe the weak flashes of ion lines and in

0 D2 weak radiation in interval up to 100 A

.

The lifetime of these filaments was about lops. From both the spectral distribution and its absolute brightness one can eva- luate T,

-

²^-3 eV. Electrical probe measurements show the increase of electric field lines density near the inhomogeneities at the moments of filament growth. We can suggest the following mechanism of this instability. Electron density fluctuati- ons provide the region of enhansed conduc- tivity with local increase of the electric field &

.

As a consequence, there improves the "tail" of electron energy distribution function, increases the electron density, ratio E/p , ^etc.

The filament decay is likely to be connected with swelling and skinning which draw up the overheated region onto the discharge surface.

References :

1 V.Finkelburg, G.Maecker, "Electriches- kie dugi i termich.plasmaw,In.lit,1961 2 J.D.Cobine, D.A.Wibbur, Journ.Appl.Phys,

22, 835, 1951

-

3 V.M.Batenin, P.V.Minaev, High Temp. -

High Press, 2, 597, 1970

4 D.B.Diatroptov, V.D.Peskov, JETP, 6 l , 1038, 1971

5 G.D.Bogomolov, Yu.V.Dubrovskiy, V.D.Pes- kov, frib.Tech.Exper., 3, 209, 1978 6 V.D.Peskov, Zh.Tech.Fiz.,fi, 2552,1975 7 J.D.Daugherty, J.A.Mangano, J.H.Jacob,

Appl.Phys.Lett., 28, 581, 1976 Full scan

PS*

In the visible region continuum luminosity pactically did not change, but sinchrono-