Particle-In-Cell Simulation for Breakdown Initiating Process in Vacuum

Abstract

The initiating process of vacuum breakdown is still unknown despite the efforts of many researchers in the long history of vacuum insulation. This paper reports the results of Particle-In-Cell Monte Carlo Collision simulation in the vicinity of an emitter of the electrons and the neutrals on cathode. The temperature of the emitter T, the product of macroscopic electric field and electric field enhancement factor β·Emac, and the electric field enhancement factor β itself are used as the parameters. It turns out that there are mainly two necessary conditions to increase the current passing through the cathode as the result of the electric field intensification by the approach of the positive ions: sufficient amount of initial field emission electrons and sufficient amount of neutrals at the height where the electric potential increment from the emitter becomes approximately 8 V. The necessary amount of neutrals is estimated to be in the order of 1024/m3. After the increase of the current occurs, the trajectories of the electrons spread sideward direction. The radius of the electron beam when it reaches the anode at the height of 1 mm is roughly estimated to be 50 μm. The starting timing of the current increase becomes earlier as T increases, β·Emac increases, and β decreases. This is because the generation of the positive ions becomes easier with the increase of the neutral density, and the drift velocity of the generated positive ions is determined by the macroscopic electric field.