Numerical study of a nanosecond repetitively pulsed discharge in an Ar–He mixture at near atmospheric pressure

Abstract

An atmospheric pressure nanosecond (few tens of ns) repetitively pulsed discharge (NRPD) in a mixture of helium with a small fraction of a heavier rare gas Rg allows producing a large number density of metastable atoms Rg(1s5), required, for example, for optically pumped rare gas lasers. At the repetition rate of hundreds of kilohertz, the memory effect in this type of discharge becomes important because the initial conditions for the discharge pulse are determined by the afterglow kinetics from the previous pulse. In addition, the overall plasma kinetics is strongly dependent on the dynamics of the cathode sheath formation. Therefore, the characterization of an NRPD requires simulation of the discharge plasma together with its decay during the afterglow across the entire discharge gap. In this work, a periodic numerical solution for the NRPD in the 1% Ar in the He mixture at near atmospheric pressure was found within the frame of extended drift-diffusion approximation. Spatial and temporal distributions of discharge parameters were calculated and conditions for production of Ar(1s5) with the number density ∼1013 cm−3 determined. The influence of atmospheric impurities on the Ar(1s5) yield and the specific heat release was assessed. Results of modeling were compared with available experimental results. The sensitivity analysis of the model to the choice of kinetic constants is presented, and the applicability of drift-diffusion approximation is justified.