Dielectric window breakdown in oxygen gas: Global model and particle-in-cell approach

Abstract

Dielectric window breakdown is a major issue in the transmission of high power microwave (HPM) radiation. Breakdown at the dielectric window decreases the power transmitted to a target, and if the electron density increases significantly, it can reflect a large fraction of HPM radiation to the source. Dielectric window breakdown from vacuum multipactor to collisional microwave discharge was previously investigated using the particle-in-cell Monte Carlo collision (PIC-MCC) model for noble gases. A global model (GM) with pressure-independent enhanced electron energy distribution function (EEDF) was also developed to study the breakdown in noble gases. In this work, the previous PIC-MCC model and GM are extended to include oxygen cross sections, and used to study microwave breakdown in oxygen. The GM with pressure-independent enhanced EEDF enables more efficient study of parameter space due to its simplicity and speed. The PIC-MCC model and GM indicate that the breakdown time for oxygen is less than that for argon below 500Torr. Above 500Torr, the high collision frequency reduces the effective electron temperature, and the depleted tail leads to faster reduction of ionization than dissociative attachment, and hence longer breakdown times.