Ambipolar Diffusion Process in Low Pressure Electronegative Gases

Transition of the Arc Discharge in Low Pressure SF₆

Abstract

The transition of the constricted arc to diffused glow discharge in low pressure, 5 to 30 Torr, SF6 was investigated. Some illuminating cases of the enhancement of spectral emission and simultaneous expansion of the plasma column are presented. The mechanism of this transition is attributed to the formation of negative ions and subsequent enhancement of electron diffusion, which is illustrated by the decrease of the density of the current carrying electrons from 3.4×10¹4 cm^-3 for the constricted arc to1×10¹³ cm^-3 for the diffused glow discharge, and the increase of the drift velocity from2×10⁷CM/S to7×10⁷cm/s.