Breakdown at the vacuum/dielectric interface is triggered by multipactor and finally realized by plasma avalanche in the ambient desorbed or evaporated gas layer above the dielectric. We have theoretically and experimentally demonstrated that the periodic surface profiles and external resonant magnetic field can prominently increase the high power microwave (HPM) breakdown thresholds.

The recent experiments of diagnosing the snapshot of nanosecond development of vacuum window breakdown are reported in this paper. For a flat-surface window, the light emission from the local plasma is focused in a thin layer above the surface during the HPM pulse, and the light emission lasts much longer than the HPM pulse, the thickness increases and the light weakens. The periodic surface could effectively suppress multipactor demonstrated by a much weaker light emission compared with flat surface.