Two dimensional thermal model of a refractory anode in a vacuum arc

A thermal 2D model for cylindrical graphite and molybdenum anodes is presented. The model includes the heat flux from the plasma to the anode surface, the radiation from the whole anode surfaces and the temperature dependent thermophysical coefficients of the anode material. Arcs equipped with 32 mm diameter and 10-30 mm long anodes, with 175 and 340 A currents, and duration up to 200 s are analyzed The results of the 2D calculations indicate that the temperature of the anode active (front) surface is distributed relatively uniformly, and the rate of anode temperature of rise is larger for short (10 mm) anodes than for long (30 mm) anodes. The maximal active surface temperature depends weakly on anode length. The temperature of the rear surface, when the anode length is increased from 10 to 30 mm, is larger for a graphite anode than for molybdenum. The anode active surface temperature of short anodes is ∼2000 K, indicating that the vacuum arc can operate as a hot refractory anode vacuum arc.