The effect of the interelectrode gap on some characteristics of the cathode and anode regions of the glow discharge in gases at low pressures

Abstract

The effect of the interelectrode gap on some characteristics of the glow discharge in electronegative gases (oxygen and air) at low pressures (0.1-1 Torr) has been studied in a specially constructed discharge tube with parallel plate electrode geometry. In this tube the interelectrode gap could be varied without altering the discharge pressure or the planarity of the electrodes. The interelectrode gap has been found to have a profound effect, both on the magnitude of the discharge current and its stability. The current decreased to zero, at a constant pressure and applied voltage, as the anode was gradually moved towards the edge of the cathode dark space or drawn away from the cathode beyond the Faraday dark space. This variation of the current has been discussed. Moreover, when the interelectrode gap was such that the discharge current was less than about 70% of the maximum discharge current, highly regular oscillations of frequency in the range 1-6 Hz developed. This behaviour has been explained by the formation of negative ions of the gas and their subsequent decay. When the applied voltage was so low that only a Townsend discharge formed, regular instabilities of low frequency occurred at all interelectrode gap values studied.