Finding relative negative ions concentration in dc glow discharges during undergraduate laboratory work

Abstract

In this paper, we present a laboratory work implementing a simple method for finding the relative concentration of negative ions in the plasma of a contracted positive column of DC glow discharge. With this method, university students can study processes in gas discharge plasmas in technological gases during their undergraduate laboratory work. The method is based on measuring the positive column radius after the glow discharge transition from a diffuse to a contracted mode. The basics of the physical processes in electronegative plasma and conditions of the positive column contraction are discussed in the paper as well as the practical implementation of the proposed technique. We describe our experimental setup and conditions, and present the experimental data illustrating the method capabilities. Values of the relative concentration of negative ions found with the offered method reasonably agree with other authors’ data obtained by widely accepted diagnostic techniques.