Numerical simulation of high-current vacuum arcs in external magnetic fields taking into account essential anode evaporation

High-current arcs as found in AMF vacuum interrupters have been numerically simulated taking into account the effect of evaporation of metal vapor from the anode surface. The Magneto-Hydro-Dynamic approach is applied. The physical behavior has been studied and the heat flux to the anode determined. Rise of surface temperature and rate of evaporation has been analyzed for arcing with one half wave of 50Hz-AC-current between Cu contacts. The transition from diffuse to diffuse columnar seems to occur when evaporation rate of metal vapor from the contact surfaces exceeds the emission of plasma produced by the cathode spots.