Experimental validation of similarity law for glow discharges in argon at low pressure

Summary form only given. Experimental studies on the similarity law of glow discharges in argon at low pressure (50Pa<; p<;400Pa) were carried out with plane-parallel electrodes. Two geometrically similar gaps were set up by keeping p₁d₁=p₂d₂ and p₁r₁=p₂r₂, where d is the gap length and r is the electrode radius. It was found that the discharges at the pressure of 50Pa is abnormal glow discharge while that at a pressure in the range of 200Pa ~ 400Pa is normal glow discharge, which is in agreement with the results, obtained by other researchers, that the current range for normal glow discharge at very low pressure is so narrow that normal glow discharge can be hardly observed¹. Voltage-current characteristics for 4-cm gap in a pressure range of 50Pa ~ 200Pa and for 2-cm gap of 100Pa ~ 400Pa were measured. The curves of the voltage-current characteristics for both gaps at the pressures higher than 100Pa superimposed onto each other, which indicates that the similarity law is valid for the glow discharges in argon in this pressure range. It is important to find that the similarity law is not valid for the discharges at a pressure lower than 100Pa. The reason for this phenomenon may be that the recombination process at low pressure is forbidden process for the similar discharges².