2D particle-in-cell/Monte Carlo collisional simulation of the plasma initiation in the vacuum breakdown stage

Abstract

In this paper, the plasma formation in the vacuum breakdown stage is simulated with a 2D particle-in-cell/Monte Carlo collisional model. In this model, the field is solved in a 2D cylindrical coordinate system and particles including electrons, atoms, singly, doubly, triply and fourfold charged ions are traced as super particles, each of which represents many real particles. The plasma quickly builds up from the field emission and evaporation near the field emitter with a local field of about 10 GV m−1. The plasma expands in a hemispherical shape with a high-density gradient in the vicinity of the field emitter. During the discharge, a typical structure including an ion sheath, a quasi-neutral region and an acceleration layer is obtained. The well-pronounced potential hump near the cathode, the high ion velocity in the acceleration layer and ion charge state agree well with results in previous research works. Investigation of the effects of the field enhancement factor and emitter surface temperature shows that more highly charged ions can be obtained in simulations with higher field emission current, while the plasma initiates faster and has higher density with stronger evaporation of neutral atoms.