Luminescence characteristics before flashover across alumina ceramic under steady voltage in vacuum

The surface flashover issue has always been a hot topic in the insulation field and it has been reported that various luminescent phenomena occur before flashover under a high electrical field in vacuum, which are closely related to the behavior of charge carriers induced by discharge. However, it is still not so clearly about the intrinsic relationship between the luminescence phenomenon and the mechanism of flashover. This paper studies the luminescence on alumina ceramic under DC and AC excitation in vacuum, and the results show that under a relatively low voltage, the electroluminescence phenomenon on sample surface will be caused by radiative electron-hole recombination following charge injection. The luminescence intensity and spatial distributions for DC and AC voltage are obviously distinctive with each other due to the quite different recombination process. However, when it comes to a relatively higher voltage, making it possible for electrons to release from cathode triple junction due to field-enhanced emission, the cathode-like luminescence process will dominate, which is generated by a self-stabilizing secondary electron emission process and subsequent collision on insulator surface. This study might be helpful to comprehensively reveal the luminescence phenomenon regarding surface flashover.