Simulation research on the development of vacuum flashover through outgassing and discharge

A particle-in-cell and Monte-Carlo collision (PIC-MCC) model is constructed in order to emulate the development of surface flashover on insulator in vacuum, which involves secondary electron emission avalanche (SEEA), outgassing, and ionization. It is found that multipactor first expands from cathode to anode, subsequently, an ionization avalanche due to increased local pressure occurs near anode and leads to gas breakdown. The spatial distribution of electrons is presented in both saturated secondary electron emission (SSEE) stage and the initiation of gas breakdown stage. Time evolution of electron, ion, desorbed gas molecule and surface charge are investigated in detail. Also the influence of applied voltage and insulator length on flashover are studied carefully. Simulation results show that higher applied voltage enhances the electron collisions on insulator and the speed of pressure build-up. Meanwhile, longer insulator is more vulnerable under the same applied electric field on account that electrons are further accelerated in a greater distance, possessing higher energy and triggering consecutive ionizations more rampantly.