Charging Mechanism of Surface Flashover on Polyimide Under Electron Beam Irradiation

The surface flashover along the interface of solid dielectric and vacuum seriously restricts the improvement of the voltage level of vacuum electrical equipment. Surface charging is an important factor in the process of surface flashover, but its mechanism is still unclear. In this article, in situ surface potential measurement is used to measure the surface potential of polyimide radiated by electron beams with different energies, and the charging curves of polyimide at different temperatures are obtained. The experimental results show that the surface potential of polyimide is close to zero after the low-energy electron beam radiation. When the electron beam energy exceeds the critical value, the surface potential is approximately proportional to the electron beam energy. The critical values of different materials are different, such as 1.18 keV for polyimide and 1.86 keV for Teflon. The surface charging characteristic is related to sample thickness, secondary electron yield (SEY), conductivity, permittivity, and so on.