Simulations of multipactor breakdown in low-pressure background gas for angled dielectrics in DC

We report on 2D particle-in-cell (PIC) simulations of electrical breakdown incorporating single-surface multipactor with background-gas ionization. The system for study is a semi-infinite, two-electrode Bergeron geometry with an angled dielectric in steady-state fields, with a background gas at variable low pressure. For pressures below a few tens of Pa (a few hundred mTorr), discharges are dominated by multipactor breakdown initiated by a triple-point source; the breakdown condition is well-characterized by an average secondary-emission coefficient greater than unity at the onset of anodic current, otherwise a dark-current develops due to space-charge saturation. The magnitude of the anode current is driven by the development of a multipactor front comprising an enhanced current front followed by a steady-state tail in which dielectric-surface fields no longer support net secondary-emission, resulting in a non-multiplicative arc. Additional avalanche phenomena occur with increased pressure >133.3 Pa (>1 Torr), where space-charge coupling leads to oscillations in an otherwise DC discharge, largely driven by the development and quenching of the multipactor front.