Global Model for High Power Microwave Breakdown at High Pressure

A major limiting factor in transmission of high power microwave radiation is dielectric window breakdown. Dielectric window breakdown from vacuum multipactor to collisional microwave discharge has been investigated using the PIC/MCC model for noble gases. The effect of a wide spectrum of reaction kinetics is very important in molecular gases like oxygen or air. However, it is not practical to investigate breakdown in molecular gases including detailed reaction kinetics using particle simulation due to the computational expense. Therefore, a fast volume-averaged global model was developed for the purpose of investigating the effect of reaction kinetics and plasma parameters for multiple species needed to model molecular gases. Since the global model is a fluid-based model, it requires specification of the electron energy distribution function (EEDF). Most global models assume a Maxwellian distribution for the electron energy distribution function. The electrons, however, are not in equilibrium in most discharges unless the electron-electron collision is dominant. The assumption of a Maxwellian EEDF produces inaccurate reaction rate coefficients for the plasma discharge and results in incorrect plasma parameters especially at high pressure. We examine the effect of the EEDF on the global model and develop a method to find the proper approximation of the EEDF to improve fidelity of the prediction of the high power microwave breakdown at high pressure. An application of the improved global model to oxygen and air breakdown is presented.