Ionization parameters of high power microwave flashover on dielectric window surface calculated by particle-in-cell simulation for fluid modeling

Abstract

The particle-in-cell (PIC) simulation method is used to get the reliable ionization parameters of high power microwave flashover and breakdown on dielectric surface for fluid modeling. Firstly, the PIC method is presented briefly, including dynamic equations, secondary emission and Monte-Carlo collision (MCC) between electron and gas atom. Secondary, the fluid global model (GM) is introduced including continuity and energy conservation functions. Finally, by using a 1D3V PIC-MCC code programmed by the authors, the ionization parameters are calculated under different microwave electric-field values, microwave frequencies, gas types and pressures for fluid modeling, including ionization frequency, breakdown delay time, average electron energy, electron energy distribution function (EEDF). The numerical results could be concluded as follows. Average electron energy is unrelated to EEDF type. At middle and low gas pressures, electron energy satisfies Maxwell distribution, and ionization parameters are unrelated to EEDF type. At middle and high gas pressures, ionization parameter is related to EEDF type, and the relevant coefficient X of EEDF tends to be of high older. Different gases have different EEDF types, and the relevant coefficient X of EEDF should be corrected by PIC simulation. The value of X is also related to microwave electric-field value and frequency, and its value increases with the increase of microwave electric-field value and the decrease of microwave frequency. In a fixed range (microwave electric-field value below 7 MV/m, and microwave frequency below 40 GHz), at middle and low gas pressures, the average electron energy increases with the increase of electric-field value and the decrease of microwave frequency rapidly, and the ionization frequency increases and then decreases with the increase of microwave electric-field value and frequency respectively; at high gas pressure, the average electron energy increases with the increase of electric-field value slowly, the ionization frequency increases with the increase of electric-field value, and the average electron energy and ionization frequency are unrelated to microwave frequency.