Notes on constricted and unstable positive columns in electronegative gases†

Abstract

A survey has been made of experiments on constricted and unstable positive columns in electronegative gases at relatively low pressure. A provisional division of columns is proposed into those where large negative ions or massive negatively charged particles are present, and those where only small molecular or atomic ions occur. Some new experimental results are described for iodine. Diffuse columns have properties like those of diffuse columns in electropositive gases, modified by the presence of negative ions. Filamentary highly-concentrated discharges appear to be arcs. Attention is called to Kracik's helical perturbation theory of instability. Seeliger and Sommermeycr's theory of unstable columns, in which the core and wall are supposed to be uncoupled by loss of electrons through attachment, is developed further. A method is proposed for assessing the contribution of massive particles to instability by supposing that they provide surfaces distributed through the volume of the discharge on which recombination can occur. Possible causes of the dependence of constriction on composition in a gas mixture are considered.