Monte-carlo simulation on improving flashover voltage through electromagnetic methods

Prior to the occurrence of vacuum flashover a stable stage combined with surface charging phenomenon can be achieved which is called the saturated secondary electron emission (SSEE) stage. The effects of the external electric field perpendicular to the insulator surface as well as a magnetic field parallel to the insulator and normal to the applied electric field on flashover phenomenon are studied based on our simulation using 2D Monte Carlo and particle-in-cell (PIC) method under DC condition. The results show that the field dragging electrons down can reduce the surface charge while the field in opposite direction can increase the surface charge. The latter can also delay the formation time of multipactor and increase the flashover voltage. Different distributions of external field are also investigated in simulation which proves that a cathode field is sufficient in mitigating vacuum flashover. It is notable that in certain cases the SSEE stage is still to be achieved with the influence of external electromagnetic field, and the modification of surface charge provides a complete compensation of external field which eventually leads to a stage similar to the situation where no extra field is applied. A theory of equivalent charge layer is therefore proposed to explain such influence on surface charge and a parallel with the situation of preset surface charge can also be drawn accordingly.