Development process of impulse surface discharge in vacuum

We investigated the charge activity on alumina dielectrics in the development process of impulse surface discharge in vacuum. We clarified the charge activity in pre-discharge stage by ultra-high speed and high sensitivity measurement. We also measured the fast-framing images of surface flashover propagation synchronously with current waveforms. We found that the charge activities are classified into three stages, i.e. (I) pre-discharge, (II) surface flashover initiation, and (III) expansion, in the development process of surface discharge in vacuum.