Ambipolar diffusion process in low pressure electronegative gases - Transition of the arc discharge in low pressure SF6.

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.