Electron inertial effects in the rarefied regime of a direct-current (DC) breakdown

A multi-fluid moment model, a drift-diffusion (DD) model, and a particle-in-cell/Monte Carlo collision (PIC-MCC) model are compared to investigate direct-current breakdown accounting only for singly charged ions and electrons. The key difference between the moment and DD models is that the electron inertial terms are taken into account in the moment model while the DD models neglect the inertia terms. The breakdown voltage results obtained from the multi-fluid moment and PIC-MCC models are in good agreement with each other over a wide range of pd values, where p is the gas pressure and d is the distance between the cathode and anode. The steady-state electron momentum balance reveals the importance of the electron inertial term at low values of pd , showing the invalidity of the DD approximation under such conditions. The results also show that the main electron energy loss mechanism transitions from volumetric (collisional) losses at high pd regime, which corresponds to low reduced electric field, to convective heat to the anode at low pd regime, where the reduced electric field is high.