Investigation on novel parameter characterizing surface flashover phenomena in vacuum

Surface flashover in vacuum is a kind of complicated surface and interface phenomena, which seriously restricts the development of high voltage electro-vacuum devices. On the basis of a novel material as machinable ceramic (MC) for vacuum insulation system, which has excellent machinable performance and good surface electric strength, the surface electric property of samples with different preparation technologies is investigated under pulsed voltage excitation before and after erosion with dilute hydrofluoric (HF) acid. Using the surface potential decay method, the surface trap density and energy of each sample are measured, and the influence of acid erosion on trap distribution is analyzed. Based on the concurrent optical and electrical measurements, the surface electric strength of samples with/without erosion is tested in vacuum, and the influence of surface trap density and energy level on flashover performance is analyzed. It is revealed that, the glass phase on MC surface is an important factor for the largely existed traps, and the shallow trap parameters can be employed as a novel parameter to characterize the flashover phenomena. By eroding off the glass phase on the sample with hydrofluoric acid erosion, the concentration of shallow traps can be reduced, thus its flashover stability is greatly improved.