Potential-variation of a time effect on the average of counts in argon at a low pressure subjected to low frequency silent electric discharges

S Salvi, Sushama Pimpale
2005 Indian Journal of Pure & Applied Physics   unpublished
A series of observations at a definite kV (rms) was taken for the time-variation of discharge counts in which the arithmetic mean of counts in dark (∑C D)/n; in light (∑C L)/n and their associated net effect (∑ΔC)/n [= (∑C L)/n-(∑C D)/n] of irradiation were calculated; after that the discharge tube (1) was short aged for 5 min at 2.45 kV (rms) and the discharge was then discontinued; reapplying the same potential kV (rms) to the same tube, the variation with time of exposure to discharge of
more » ... ts was again recorded and (∑ΔC)/n re-determined as previously. It has now been observed that almost always (∑ΔC)/n shows a greater value in the earlier that in the latter series. Thus, several series of experiments were carried out at different values for the applied potential in each of which (∑ΔC)/n was measured as a function of the applied potential increased progressively, at a constant window width of 0.07 kV(rms), to a maximum. Similarly, the results in a series of comparative measurements for two discharge tubes have been reported. It was observed that the increase of (∑ΔC)/n as a result of ageing, i.e. due to previous exposure to the discharge, was very appreciably larger in the case of a discharge tube (1) which had been rendered comparatively insensitive in regard to the average effect of irradiation, than a fresh one which showed the familiar behaviour of an irradiation. The average light effect (∑ΔC)/n decreased with ageing and disappeared finally. It revived to its original value after allowing a period of rest of 24 hr. Threshold voltage, V g , in aged tube was appreciably smaller than that in the freshly prepared one. This is ascribed to a lowering of the electrode surface work function due to ionic bombardment under discharge. + (∑ΔC)/n inverted to-(∑ΔC)/n with ageing and then decreased. The increase in + (∑ΔC)/n with ageing is attributed to an enhanced photo-electron emission caused by the decrease in the work function. The decrease in-(∑ΔC)/n is ascribable to the deconditioning of the adsorption like boundary layer formed during discharge. The results show that-(∑ΔC)/n is associated with a decrease in ionic mobility. This lends support to the Joshi′s theory for the mechanism of-(∑ΔC)/n, n being the total number of readings taken between counts and exposure-time at each voltage.