Dielectric surface flashover at atmospheric conditions under high-power microwave excitationa

Due to recent advances in the peak output power densities and pulse widths of high-power microwave (HPM) devices, the ability to radiate this power into the atmosphere is limited by surface plasma formation at the vacuum-air interface. Very little is known about this window flashover under HPM excitation at “air” side pressures from atmospheric down to approximately 90 Torr , and this paper reports one such study at 2.85 GHz and MW ∕ cm 2 pulsed power densities. Due to the high ( ∼ 600 GHz at standard temperature and pressure) elastic collision frequencies of the electrons with the neutral gas molecules and added energy-loss channels through molecule excitation, proven concepts of vacuum flashover, such as multipactoring electrons, have to be abandoned. The observed flashover field is roughly a factor 3 higher in SF 6 compared to air, which is consistent with unipolar volume breakdown data. Quantitative comparisons of HPM flashover data with results from a recently developed computer code are given.