Modelling the Effect of Charge Transport on Surface Flashover in Vacuum

To explain the phenomenon of surface flashover, the prevailing theory, secondary electron emission avalanche (SEEA), usually applies the assumption of pre-existing positive surface charges. However, for dielectrics on an operating spacecraft, the surfaces are usually negative charged by the space plasma. Thus, the assumption of pre-existing positive surface charges needs to be reconsidered. In our previous experiments, the dielectric surface first suffered electron irradiation, and electrons would deposit on the surface. To illuminate how the surface flashover initiates on a negative charged surface, we established a twodimensional charge transport model, considering impact ionization process in the dielectric surface layer to simulate charge evolution in the pre-flashover stage. The results showed that when the applied voltage was low, homocharge would accumulate in the vicinity of the electrodes, reducing the electric field. When the applied voltage increased to a critical value, impact ionization of the dielectric sub-surface layer began, and positive charge appears in the vicinity of the cathode. The breakdown voltage we obtained from this model was close to our experimental flashover voltage.