The diffuse and channel stages in the overvoltage breakdown of a gas gap

An interrupted discharge has been used to examine the production of light in the breakdown of an overvoltage gas gap in air under conditions of E/p = 90-110 V/cm-mm Hg. It is found that there are two types of discharge, the type being dependent on the number of initial electrons: diffuse when there are many electrons and of channel type when there is a single initiating electron. The observed voltage-fall curves for the first type of discharge agree well with theoretical ones derived from the avalanche theory. A study has been made of the dependence of the delay time and switching time on the relative intensity of the illumination used to produce the initial electrons.