Modeling and simulation of high-current vacuum arc considering the micro process of anode vapor

Abstract

In vacuum arc (VA), when the arc current is very high (usually in the tens of kilo-ampere), the heat flux density injecting into an anode is larger and leads to a higher anode temperature with the increasing of current. The strong anode evaporation drives the evaporated atoms from the anode surface to the arc column. Simultaneously, the anode evaporated atoms impact with the cathode plasma, and then the micro processes as ionization and recombination between anode atoms and plasma will happen. In this paper, the two fluid three-dimensional (3D) magneto-hydro-dynamic (MHD) model of VA considering ionization and recombination processes is built, and the influence of the anode vapor and its micro processes on the arc column is obtained by solving the two fluid MHD equations, which control anode neutral atoms and cathode plasma, respectively. In the model, the ionization of neutral atoms and the recombination of ions are both considered, the mass, momentum and energy exchange caused by the ionization and recombination processes are also considered. Moreover, the influence of ionization and recombination processes on the electromagnetic process of VA is also considered in the model. By numerical simulation, the anode vapor distribution, cathode plasma distribution and VA distribution, such as density, temperature, pressure, etc, are all obtained, and the parameters related to ionization and recombination processes are also obtained. When the anode temperature is high enough, the anode neutral vapor will enter into the arc column, and strong ionization happens at the interface between anode vapor and cathode plasma. Then, the anode vapor will be quickly ionized (usually smaller than a few microseconds) and generate a lot of ions (usually higher than 1021 m−3 orders of magnitude). The anode neutral vapor has the same temperature with the anode surface, which is much lower than the temperature of the arc column, so the anode neutral vapor obviously has a cooling effect on the arc column. Whether anode neutral vapor will enter into the arc column or not, is determined by the balance between anode neutral vapor and cathode plasma.