Moving Striations in Iodine Vapour†

Striations have been observed in the positive column of a discharge through an electronegative gas, iodine, moving from anode towards cathode with speeds between 3 × 102 and 5 × 103 cm see−1. Compared to those commonly observed in electropositive gases, these striations have up to order of magnitude lower velocities and wavelengths. A semi-quantitative theory of electronegative striations is approached in three ways, each taking account of the presence of negative ions : (i) comparing the striations to plasma ion waves, (ii) assuming control by lateral diffusion, and (iii) assuming control by ion-ion volume recombination.