Modeling of Vacuum Arc in Anode Spot or Anode Plume Modes with Consideration of Different Components

This work investigates the arc behaviors during the anode spot mode with CuCr25 electrodes using a 3D magneto-hydro-dynamic (MHD) model. The components considered in the model include electrons, Cu atoms, Cr atoms, Cu ions and Cr ions. The realistic axial magnetic field (AMF) is generated by cup-shaped electrodes. When the anode surface temperature is high enough, the anode vapor can enter the arc column forming a cool and poorly conducting region, namely the neutral atom vapor area (NAVA). Simulation results show that due to the six-leave shape of the AMF distribution, the current density and the plasma temperature are the highest near the slots. Inside the NAVA, the plasma temperature is very low as a result of ionization process and the energy exchange among ions, atoms and electrons. Similarly, the current density is also considerably low because of low electric conductivity inside the NAVA. The highest atom density and single-charged ion density can be seen in the NAVA, while the double-charged ion density reaches its maximum in front of the NAVA. This is because ions are ionized to higher ionization levels step by step. By comparison, triple-charged ion density is negligibly low and reaches its maximum near the slots due to high electron temperature here.