Characteristics of electric discharges in the halogens: the recombination-dominated positive column

Abstract

Models the positive column in strongly electronegative gases, where recombination is the dominant mechanism of charge loss in the volume. The pressure range is taken to be such that mobility governs particle motion. It is related to earlier work in gases like oxygen, where detachment is the dominant loss mechanism and there are many similarities with the case where the attachment/ionization rate ratio P was <1, treated by Daniels, Franklin and Snell (1990). It is shown that P is necessarily less than unity and that it is not physically possible to have a discharge where electron-ion recombination is the only loss mechanism. The structure found is that of a central positive ion-negative ion core surrounded by a conventional electron-positive ion plasma with a sharp transition region of fractional thickness given by the parameter l1/2 where l is a normalized ratio of ion recombination rate beta i and ionization rate nu i given by beta ine0/ nu i where ne0 is the central electron density. Expressions are found for the ion plasma dimensions and the eigenvalue lambda , which relates the ionization rate, discharge radius, ion mobility and electron temperature, and comparison is made with the work of Volynets et al. (1993). The physical characteristics of such discharges are explained by the treatment given for the first time since the problem was formulated in 1949.