Kinetic numerical simulation of anode sheath of vacuum arcs

Abstract

Anode activity is critical in high-current vacuum arcs in vacuum interrupters. If the anode temperature gets too high, an evaporation of metal vapor from an anode melting pool may lead to a formation of anode spots, which would lead to a failure of current interruption of vacuum interrupters. The input energy from an arc column to an anode surface is adjusted by an anode sheath. The objective of this paper is to develop a numerical simulation model of the anode sheath of vacuum arc by using a Particle-in-Cell method. A low-current case and a high-current case of arcing are simulated. The physical parameters of electrons and ions are obtained from magnetohydrodynamic simulations, and are set at the simulation boundary of the current model. The sheath thickness is 2∼4 Debye length, and the anode potential fall is about 1.5∼3 V for both case. It is found that the acceleration of ions by electric field in the anode sheath is more significant for the high-current case. This also adds to the energy flux into the anode surface.