A SPECTROSCOPIC STUDY OF THE DC GAS MAGNETRON DISCHARGE

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A SPECTROSCOPIC STUDY OF THE DC GAS MAGNETRON DISCHARGE

V.I. Miljević

To cite this version:

V.I. Miljević. A SPECTROSCOPIC STUDY OF THE DC GAS MAGNETRON DISCHARGE. Jour-

nal de Physique Colloques, 1979, 40 (C7), pp.C7-61-C7-62. �10.1051/jphyscol:1979730�. �jpa-00219289�

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JOOURNAL DE PHYSIQUE CoZZoque C7, suppl6ment au n07, Tom 40, ~ u i Z Z e t 1979, page C7- 61

A SPECTROXOPIC STUDY OF THE DC GAS MAGNETRON DISCHARGE

V.I. Miljevi6.

Boris ~ i d r i z I n s t i t u t e of Nuclear Sciences, Laboratory for Atomic Physics, 11002 Beopad, Yugoslavia.

INTRODUCTION

The properties of ionized gas in a cylindrical diode with axial magnetic field

(gas magnetron diode) depends strongly on magnetic field intensity.

Under the influence of a strong magnetic field in the cylindrical diode elec- trons move on cycloidal paths around the cathode acquiring a velocity component in the anode direztion only after collisions with gas atoms. Electron paths are consi- derably prolonged, thus increasing the probability of excitation and ionization.

In the case of the pulse magnetron diode, filled with argon at low pressure, it has been found that the spectrum con- sists of the lines which correspond to tr- ansitions from energy levels of simple and multiple ionized argon atoms, but atomic

lines have not been registered (for example /1-4/).

In this paper the results of the spectroscopic study of a DC cylindrical magnetron diode, filled wit.1 argon at low pressure, are presented.

RESULTS

A cylindrical diode was uses in the experiments. The anode was 30 mm long and 22 mm in diameter. The directly heated in- cadescent tungsten cathode, 1 mm in dia- meter, was placed along the cylindrical anode axis. An axial magnetic field with the maximum intensity of 1200 G was appl- iedto the system. The experimental set up scheme is shown in Fig. 1. The working conditions were: the anode voltage Ua= 30

-

150 V, argon pressure p=

-

^torr.

Spectra were recorded with a crossed dispersion spectrograph STE 1 operated in the wavelenght range of 2200

-

9000 A with the dispersion 3,7

-

12,8 A per mm. Rela- tive intensities of the spectral lines have been determined by standard photograp- hic photometry methods.

The experimental results have been ob- tained. for the magnetic field BC4B4BC

,

where Bc is the cut off magnetic fie13 in a vacuum diode /5/ and Bcg is the cut off magnetic field in a gas magnetron diode

(i.e. the critical magnetic field when the discharge current cut off occurs). The spectrum contains intense lines of ionized

argon AII, lines A111 moderate intensity, lines AIV weak intensity and atomic tungsten lines (originating from the cathode because of ion bombardment). Atomic argon

lines were not formed even with prolonged exposures.

The part of the spectrum of the DC discharge with reference iron spectrum for working conditions :

is presented in Fig. 2. As it can be s%en spectrum contains only argon A11 lines.

~ l s o , by changing the working conditions, for constant magnetic field,only intensity of the spectral lines is changed.

Because of weak intensities of the A111 and AIV lines only the intensity of ion spectral lines A11 has been analysed.

The dependence of the A11 4880 A spectral line intensity on the square of the discharge current (solid curve) and of the discharge current on the magnetic field in the region 80 G4Bc300 G (dashed line) under the operating conditions: Ua= 30 V, p=10-2torr is presented in Fig.3. The dis-

Fig.1. Experimental set-up

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979730

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charge current density was about 0,2 ~ / c m ~ . The dependence of intensity on the

discharge current is often used for inves- tigation of the excitation mechanism of the spectral lines (for example /6,7/). In the case of direct excitation (cascade transi- tions and other processes are neglected) the dependence of spectral line intensities on the discharge current has linear chara- cter, while in the case of stepwise excitation this dependence is paraboiic (I =ai

+

biz).

In our case the dependence of A11 4880 A spectral line intensity on the square of the discharge current is shown in Fig.3. The low gas pressure (10-2) and

low discharge current density (j=O, 2 ~/cm2) show that intensive excitation of the ion line A11 4880 A should not be expected in stepwise collisions. However, under the infiuence of the radial electric and axial magnetic fields electron paths are consi- derably prolonged. The presence of crossed fields results in the increase of the, so colled, equivalent pressure, and the elec- trons fulfill the conditions for stepwise collisions. In this way the probability for gas ionization and excitation is also inc- reased.

-

^{A 1 1}

-

^{A 1 1}

-

^A11

* irol rence rum

.- A11

4880 A

4847 A

4806 A n refe-

spect-

4765 A

Fig.3. Dependence of the A114880 A spectral line intensity on the square of the discharge current (solid line) and of the discharge current on the magnetic field (dashed line) : Ua=30 V, p=lO-2torr, j=0,2 ~/cm2.

The dependence of the A11 4880 Aspec- tral line intensity on the discharge current when the anode voltage increase is more complex, indicating direct and stepwise excitation. This phenomenon is more expresed in the case of A11 4765 A spectral line. It may be noticed that the upper energy levels of the A11 4765 A spectral line has relatively big direct excitation cross sections.

Further work is in progress.

REFERENCES

/1/ V.Miljevib, D.ToHi6, J.Appl.Phys., 4 1545 (1971).

/2/ D.ToZi6, V.Miljevi6, Int. J. Electr., 30.175 (1971).

/3/ V.Miljevib, Proc.VII1 Yug.Symp.Phys.Ion.

Gases,Dubrovnik,l976,p.332.

. .

~oniz;~ase&,~erlin, 1977,p. 171.

/5/ A.W.Hul1, Phys.Rev.,18,31(1921).

(a) (b (c) /6/ K.I.RozgaEev, Opt.Spectr., 4,549(1958).

/7/ V.M.Zaharova,Yu.M.Kagan,

ZETF

22,400 Fig.2. Part of the magnetron dischar- (1952).

ge spectrum with reference iron spectrum

for: /8/ P.N.Clout, D.W.O.Heddle, J.Phys.B,

4.483 (1971).