GAS TEMPERATURE DEPENDENCE OF AC DISCHARGES BETWEEN ISOLATED ELECTRODES

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GAS TEMPERATURE DEPENDENCE OF AC DISCHARGES BETWEEN ISOLATED ELECTRODES

R. Zahn, S. Müller

To cite this version:

R. Zahn, S. Müller. GAS TEMPERATURE DEPENDENCE OF AC DISCHARGES BETWEEN ISOLATED ELECTRODES. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-319-C7-320.

�10.1051/jphyscol:19797157�. �jpa-00219132�

JOURNAL DE PHYSIQUE ColZoque C7, suppldment au n07, Tome 4O,&<ZZet 1373, page C7- 319

GAS TEMPERATURE DEPENDENCE OF AC DISCHARGES BETWEEN ISOLATED ELECTRODES

R.J. Zahn and S. Mijller.

ZentraZinstitut fiir Elektronenphysik, V Akademie der Wissenschaften der D.D.R., D.D.R. 2 2 GreifswaZd.

Introduction: In /I/ and /2/ the transiti- on was investigated between the bistable pulse mode, which is used in ac plasma displays, and the non-bistable continuous mode in Ne-Penning mixtures by frequency variation of the sinus wave voltage. For the transition frequency ?: of both these discharge modes there is a similarity re- lation with the similarity parameters f/p and pd (f-frequency of applied voltage, p-gas pressure, d-distance of the elec- trodes) in a wide parameter range with constant mixture ratio. The present paper deals with investigations of the influen- ce of gas temperature on the transition between the discharge modes.

Method: The investigations were carried out between glass covered Mo-electrodes with 1 mrn

0

and a 0.1 mm thick insulator.

The distance of the electrodes was varied between 0.2 and 2.5 mm. After usual vacu- um procedure the discharge vessels were filled with mixtures of Ne+l%N2 or Ne+

0.3%N2 at pressures of p0=270 torr and po=450 torr (po

-

gas pressure at 0 OC).

The frequency was varied between 10 and 1000 lcHz. The gas temperature was regula- ted by diping the whole discharge vessel into liquid nitrogen or cooled alcohol of -53 OC. In addition measurements were c a r ried out at room temperature and in a he- ating chamber at higher temperatures. The firing voltage UZ, minimum sustaining vol- tage UL and the actual discharge current were measured. The capacitive current was nulled with a current bridge.

Results and discussion: Fig.1 shows the dependence of firing voltage and minimum sustaining voltage on frequency for po=270 torr gas pressure. The wall temperature of the discharge vessels is used as pameter.

It is shown that the transition frequency between the bistable pulse mode and the non-bistable continuous mode ia characte- rized by a minimal frequency at which the curves of UZ and UL become identical. The pulse mode exists at lower frequencies but the continuous mode occurs at higher fre-

N

quencies. With decreasing temperature f is shifting to smaller frequency values. At low frequencies ( f 4 0 kHz) a variation of gas temperature has a negligible effect on the firing and minimum sustaining voltage.

Because the firing voltage is decreasing in the range of

5

the shift of

?

to smal- ler frequenc,ies is accompanied 'by a decre- asing bistable range. In addition to this influence on the bistable range and

?

there is also an influence on the discharge cur- rent. Fig.2 presents two diagrams, each showing the current oscillograms for two comparable discharges at T=77 K and 300 K but for different frequencies, When the gas density remains constant an increase in temperature leads to a shorter duration of the discharge pulses. The limited in- fluence of gas temperature on the firing

Neffl

240 220 20

Ne+l% N2,d.aZ mrn

-

Fig.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797157

at various gas temperatures for the whole Time scale: pod range. From this shift the relative 2 ps/div. dependence of Q(T) can be obtained.

Table 1

-

^{Q (T 1}

T f/p0

Q

P

re^=^*^

^Q~

Fig. 2 77 77 0.57 2.85 10'~~

300 268 1 5.0 10'16 (from /5/) 500 395 1.14 5.7 10'16 By adaptation of the relative values of Time scale: Q re1 to room temperature values of other 0,5 ps/div. authors data can be obtained about thetem- P

perature dependence of the absolute cross voltage at lower frequencies and the rela-

tively great change of the discharge cur- rent indicate a high incidence of ioniza- tion processes by collisions of heavy par- ticles. Such processes are collisions of excited Ne-atoms with N2-molecules, the Penning ionization being the main ioniza- tion mechanism. In addition, the associa- tive ionization plays a certain role /4/.

In /I/ it was demonstrated that the life time of metastable atoms is important for the existence of the continuous mode. If the life time is changed by variation of gas pressure or mixture ratio the transi- tion frequency

2

is shifted in the same way, i.e.

/Y '12

f) PO -XngvrQp

^with v , = ( V )

and A.

, .& L

P v"4 %

(X-mixture ratio, Tg

-

gas temperature, n

-

gas density at 1 torr and 0 OC, Qp

-

cross section for Penning ionization, m,, g

m2

-

masses of gases 1 and 2). For a con- P' ' I 2 results.

stant cross section Q

F/~;T~

On the other hand from the shift of ?/p, the dependence of Qp(~) can be determined.

Fig.3 illustrates the dependence of ?/p0 on pod. Above a certain pod-value ?/po is independent of pod. This break is in good correspondence with the ion transit time /I/. To the right of the break the ion transit time reaches such a value that on

sedtions for Penning ionization. In Table I Q has been adapted to the values of /5/.

P

Ne *O,3 % N 2

Po = 4 5 0 Torr

lo1 5 lo2

pod porr.c+

References:

/I/ Zahn, R.J., Mtiller, S,, Beitr.Plasma- phys., in print.

/2/ Zahn, R.J., Wdller, S., XIII. ICPIG, Berlin 1977, Contr. Papers, p. 373*

/3/ Arora, B.M., Bitzer, D.L., Slottow, H.G., Willson, R.H., ⁸ Nat. Symp. Inf.

Display, San Prancisco (1967), 1.

/4/ West, W.P., Cook, T.B., Dunning, P..B., Rundel, R.D., Stebbings, R.F.,

J. Chem. Phys. (1975) 1237.

/5/ Pfau, S., Rutscher, A*, Ann. Phys.

3

(1970) 321.

an average the ions are no longer swept out of the volume. The figure illustrates the shifting of f/po(constant gas density) v