Influence of ambipolar diffusion on the positive column constriction in a cryogenic discharge

An earlier theory concerning the positive column constriction is briefly summarized. This theory explains the constriction as a thermal effect: due to the heating the gas becomes rarefied near the tube axis and this results in a sharp increase of molecular ion production in the central part of the tube. The production is balanced by the dissociative (volume) recombination and the radial diffusion. The relevant equations are solved numerically for the wall temperature kept at –196 °C corresponding to the cooling of the walls by the liquid nitrogen. On example of this cryogenic discharge the influence of the ambipolar wall diffusion is examined in detail.The authors greatfully acknowledge the stimulating discussions on the subject with Dr.Karl Wojaczek.