DC polyimide surface flashover in vacuum under electron beam irradiation

In this paper, the effects on direct current (dc) surface flashover characteristics of polyimide (PI) in vacuum are experimental studied in the case of electron beam irradiation, accompanied with the theoretical analysis. The results show that the flashover voltage under 0.5~20keV beam electron radiation is higher than no radiation case; the higher energy of the electron is, the higher flashover voltage is. Under constant electron beam energy irradiation, the higher the beam current density is, the lower flashover voltage is. Further experiment shows that the radiation reduces the dielectric permittivity. We infer that, (1) The low energy electron radiation reduces the surface positive charge density of the insulator. The higher the energy of the electron beam is, the lower the secondary electron emission coefficient is. While the radiation induced conductivity (RIC) will lead to reduce the surface accumulation charge. And also the radiation crosslinking and degradation effects make the surface charge difficult accumulation by means of reducing the dielectric constant of the material. These factors all contribute to the increase of dc surface flashover voltage. On the contrary the surface flashover voltage reduces as the low energy initial electron increases. The gas desorption increases with the increasing of leakage current.