Partial discharge characteristics and mechanisms in consideration of charge behavior on alumina dielectrics under AC voltage in vacuum

Partial discharge phenomenon, which is not breakdown but has a potential to lead breakdown, is sometimes observed under AC operating voltage application in vacuum. We aim to investigate the partial discharge on the insulator surface in vacuum by the measurement of charge behavior and light emission. The surface charge distribution reached a quasi-stationary state by repetition of the partial discharge. However, a sudden drastic change of surface charge distribution to another quasi-stationary state was also observed. This behavior could be explained by the sudden increase/decrease of electron emission from the cathode and the distribution of electric field due to the increase/decrease of accumulated surface charge by repetitive partial discharge under ac voltage.