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

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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.