Prebreakdown phenomena and formation process of the glow discharge in low-pressure Ar gas

Abstract

The prebreakdown phenomena and the formation process of the glow discharge in a low-pressure Ar gas were investigated under a uniform field gap. Prebreakdown phenomena were observed for 0.5 Torr cm⩽pd⩽2 Torr cm (where p is pressure, d the gap distance) in Ar gas under conditions of a slowly increasing voltage. It was observed that the prebreakdown phenomena formed pulse discharges up to the transition to the glow discharge. The amplitudes of the photon and current pulses due to the pulse discharge increased with time, and then decreased as soon as the transition to a steady glow discharge occurred. When the overvoltage or external series resistance was increased, the pulse amplitudes increased with the applied voltage and decreased with the resistance. The characteristics of the prebreakdown phenomena were changed by the shape of the electrodes. The formation mechanism of the glow discharge can be qualitatively explained by that of the streamer in a high-pressure discharge. The transient glow discharge was observed, and its duration increased with an increase in resistance. The instability of the glow discharge was controlled by three factors, namely, Kaufmann’s criterion, the Child–Langmuir law, and the density balance between the production and removal rates of electrons.