Determination of the cathode erosion and temperature for the phases of high voltage discharges using FEM simulations

A discharge produces an energy input in the cathode material, which causes the erosion of the material surface. The principal mechanism of erosion is the formation of craters mainly due to melting. From calorimetric results published in the literature, the amounts of energy delivered to the cathode for the different phases of the discharge (breakdown, arc and glow discharge) were calculated. A FEM model was developed to simulate the temperature distribution and the phase transitions, which allows the definition of molten and evaporated zones. These zones were compared with the volumes of craters done in Pt-samples at air with pressures ranging between 1 and 9 bar and static electrode gaps of 2 mm. The breakdown energy is enough to melt an amount of material, which is responsible for the formation of very flat craters. The formation of deeper overlapped craters observed in experiments can not be produced during the breakdown; they are produced by the arc phase of the discharge. The assumption of the crater area as the area for the energy exchange between plasma and material gives the best results in the simulation. The glow discharge produces only a light heating of the cathode, without any significant erosion.