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Description
In many high current vacuum arc experiments, anode spot and plume phenomena are widely observed, which is related to the anode melting and evaporation under strong heating from vacuum arc. Anode vapor will then have great influence on the arc column through ionization-recombination process and energy exchange process among atoms, ions and electrons. This work aims to investigate the vacuum arc characteristics and its interaction with anode spot or anode plume based on two-dimensional (2D) magneto-hydro-dynamic (MHD) model. Formation mechanism of anode spot and anode plume modes in vacuum arc is studied based on numerical simulation. Different from previous work, friction forces between ions and atoms are also taken into account. Simulation results show that the expansion behavior of anode vapor depends on the pressure balance between anode jet and cathode plasma. Higher anode temperature can lead to larger neutral atom vapor area (NAVA) dominant by neutral atoms. In front of the atom vapor area, there is an ionization layer which can be corresponding to the “shell” observed in experiments. Inside NAVA, ion temperature and electron temperature are lower than 1.1eV during anode spot mode and anode plume mode due to ionization process and energy exchange. Electric conductivity in this area is also so low that the maximal value of current density is inclined to move to the edge of the anode instead of anode center, which can make the anode temperature distribution more uniform. The transition from anode spot mode to anode plume mode is related to the pressure competition between anode plasma and cathode plasma. If the anode plasma pressure is much larger than cathode plasma pressure, anode plume mode will form. The asymmetric appearance of anode plume is mainly caused by asymmetric anode temperature distribution with respect to the anode spot center. Qualitative comparisons between simulation results and experiments verifies the correctness of simulation.