Influence of a Nitrogen Admixture on the Value and Radial Profile of the Metastable Argon Atom Density in a DC Glow Discharge in Argon

Abstract

Results of measurements of the value and radial profile of the density of Ar(3P2) metastables in a dc discharge in pure argon and Ar + 0.1%N2 and Ar + 1%N2 mixtures are presented. The electric field strength in the positive column of the discharge was also measured. The experiments were performed in a 2‑cm-radius discharge tube at gas pressures of 1, 7, and 60 Torr and discharge currents in the range of 10–50 mA. It is found that, at a pressure of 60 Torr, a nitrogen admixture to argon leads to a significant decrease in the electric field strength in the diffuse discharge, while at P = 1 Torr, in contrast, the electric field increases substantially. The degree to which the nitrogen admixture affects the density of Ar(3P2) atoms on the discharge tube axis also depends on the gas pressure. At a pressure of 60 Torr, the Ar(3P2) density decreases substantially (by three orders of magnitude for the 1%N2 admixture and 1.5 orders of magnitude for the 0.1%N2 admixture), while at a pressure of 1 Torr, the Ar(3P2) densities in pure argon and in Ar + N2 mixtures differ less than twice. It is also shown that, at all gas pressures under study, a nitrogen admixture to argon leads to the broadening of the radial profile of the Ar(3P2) density. The experiments were accompanied by numerical and theoretical studies. For pure argon, the calculations were performed in a one-dimensional (along the tube radius) discharge model, while for the Ar + 1%N2 mixture, in a zero-dimensional model, which allows one to calculate the plasma parameters on the tube axis. The calculated results were used to qualitatively explain the experimentally observed effects.