Negative Sections of Moving Striations†

Abstract

An experimental investigation of moving striations in neon discharges at pressures (p) from 2-50 mm Hg has been carried out by rotating mirror photography. Supplementary photoelectric measurements have also been made. The appearance of the discharges has been described in detail. Particular attention has been given to the negative end of the column, where an increase in striation frequency usually occurred at a distance from the anode determined by current and pressure. The behaviour of this‘ branched ’ section was found to be independent of the position of the anode, and its length decreased when either the current or pressure was increased. The velocity of the waves varied as p ^−½ in the unbranched part of the column and was only slightly dependent on anode-cathode spacing except when the latter was small. In the branched region the striations travelled more quickly and the velocity varied in a more complicated way with pressure. Moving striations disappeared from the column with large currents, but periodic fluctuations still persisted in the anode glow. The head of the column, when viewed without time resolution, showed apparently stationary striae decreasing in distinctness towards the anode, but mirror and photoelectric measurements showed that the striae were definitely oscillatory. The appearance here was similar to that which would result if an undamped wave moving towards the cathode were superposed on a damped wave travelling in the opposite direction.