Monte Carlo Simulation of Surface Charging on Insulator in Vacuum

Effects of Ceramics Coating on Flashover Inhibition

Abstract

We have studied the effect of ceramics coating on the surface charging of solid insulator in Vacuum by employing Monte Carlo simulation method, in which we analyze the electron multiplication on the surface due to the secondary electron emission process. The simulation consists of a two dimensional field analysis and the analysis of the energy of electrons impinging upon the insulator surface. We firstly discuss variations of the electron energy and the secondary emission rate on ordinary organic insulator (PMMA) and demonstrate the appropriateness of our simulation method, then the charging on coated insulator is analyzed. The insulator is in the shape of a cylinder or a negatively angled conical frustum. The coating with Cr₂O₃ or Al₂O₃ on PMMA insulator has examined. The maximum secondary emission rate of Cr₂O₃ is smaller than 1, however, Al₂O₃ has the rate larger than 6. The simulation for the Cr₂O₃ coated surface shows that only a small part of the cathode side of the surface is charged negative irrespective of the insulator shape. It is found that the density of the negative charge is so high as to make electrons emitted from the cathode junction fly away from the insulator surface. The negative charge on the insulator with Cr₂O₃ thus prohibits interactions between the surface and the electrons from cathode, resulting in reduction of gas desoprion from the surface and in improvement of the insulation ability of the insulator.