Estimation of surface flashover threshold in vacuum: from multipactor to discharge plasma

We propose a novel theoretical formula to estimate the surface flashover threshold in vacuum using the intrinsic properties of dielectric material as well as dielectric-vacuum configuration. The method is based on an above-surface model called secondary electron emission avalanche (SEEA), where flashover development can be divided into multipactor discharge, out-gassing and an ionization avalanche which eventually leads to a plasma discharge. The transition from SEE-dominated regime to discharge plasma is supposed to be of significance where gas breakdown takes place within a nonuniform desorbed gas cloud in the vicinity of dielectric surface. Flashover occurs when specific space charge multiplication is achieved, yielding the critical pressure and breakdown voltage. The depiction of previous stages involves the secondary electron emission of dielectric materials, desorption and diffusion of adsorbed gas, ambient temperature, electrode structure, etc. Both particle-in-cell simulation and experiment data can corroborate the obtained theoretical results.