2-dimensional simulation of surface charge distribution on insulator prior to flashover in vacuum

Based on the secondary electron emission avalanche model the Monte Carlo method is chosen to simulate the 2-dimensional surface charge distributions on PMMA and alumina wafers with planar circular and rectangle symmetrical electrodes, respectively. The results indicate that negative charges exist in a small surface region near the cathode and then turn to positive charges in a big surface region away from cathode, and the density and area of negative charges decrease with the increasing applied voltage, while the density and area of positive charges increase. For PMMA insulator with smaller secondary electric emission rate, its positive charge density gets lower. Compared with planar rectangle electrode, the surface electric field of insulator with circular electrode is more nonuniform, and the surface charge density distributes much more nonuniformly. The simulation results approximately agree with other researchers' experimental results.