Particle-in-cell simulation of high voltage breakdown of large gap in vacuum

Summary form only given. The vacuum is a kind of ideal insulating media. In general, the breakdown voltage of a vacuum gap increases with the length of the gap. But for large gaps longer than 10 cm, it would be different. It was thought that the breakdown mechanism had been changed with increasing of the length of the gap and the voltage ¹ . A 15 cm wide coaxial gap in vacuum was simulated with the particle-in-cell code UNIPIC ² . Secondary electron emission, field emission, photonic emission on cathode and positive ion emission on anode were considered by trial, to simulate the high voltage breakdown processes of the gap. In the simulations, the current history and voltage history obtained from experiments were taken as references, so we could adjust the assembly of the emission models. Then the physics of the breakdown was described according to the setting of the models. On the setting, the variation of threshold voltage and time delay of the breakdown with the width of the gap were investigated with series of simulations. Finally the simulation results were compared with Cranberg hypothesis ³ and Latham's theoretical observations ¹ .