Monte Carlo based simulation on surface charging phenomena of insulators prior to flashover in vacuum

As we know, before flashover across an insulator surface under high electric field in vacuum, there are charging phenomena occurring on the insulator surface, which significantly affect the developing process of flashover. Based on the secondary electron emission avalanche (SEEA) model, and by using the Monte Carlo method, a two-dimensional analysis of surface charge density on cylindrical and conical insulators prior to flashover in vacuum has been performed under unipolar voltage. Typical insulating materials are employed, i.e., machinable ceramic, alumina ceramic, PTFE and PMMA. The influences of secondary electron yield, voltage amplitudes and coning angles on charge distribution are investigated. The results reveal that negative charges exist in a small surface region near the cathode, while the surface charges positive in a larger region away from the cathode. With increasing applied voltage, both the negative charge density and region decrease, and even vanish, whereas both the positive charge density and region increase, and the peaks of both regions move towards the cathode.