Influence of pre-existing negative surface charges on secondary electron emission avalanche evolution in vacuum surface flashover of spacecraft

Surface charging of dielectric materials is commonly observed in spacecraft under complex space environments. The accumulated charges on dielectric surfaces can modify the local electric-field distribution and subsequently affect secondary electron emission avalanche (SEEA), which plays a critical role in vacuum surface flashover. However, the influence mechanism of pre-existing surface charges formed before discharge initiation on the subsequent SEEA evolution remains insufficiently understood. In this work, a 2-spatial- and 3-velocity-dimensional particle-in-cell model is employed to investigate the effect of pre-existing negative surface charges near the cathode on vacuum surface flashover development. Different levels of localized negative surface charge densities are introduced as initial charging states, and their effects on electron emission, avalanche evolution, surface charge accumulation, and electric-field redistribution are systematically analyzed. The results demonstrate that the pre-existing charge of dielectric surfaces can strongly regulate subsequent vacuum flashover behavior, providing new insights into the coupling mechanism between surface charging and SEEA development in spacecraft and vacuum insulation systems.