Temperature distribution dependence on refractory anode thickness in a vacuum arc

The time dependent anode temperature was measured in a hot refractory anode vacuum arc (HRAVA) sustained between a consumed water-cooled cylindrical Cu cathode and nonconsumed cylindrical W anodes with d=5, 10, 15, 20 and 30 mm thickness. Arc currents of I=130, 150, 175 and 200 A were applied for periods up to 210 s and an inter-electrode gap of 10 mm. The anode temperature was measured using high-temperature thermocouples at different points in the anode body. The visual radiation emitted by the plasma plume was recorded with a digital camera. The anode temperature increased with time, reaching a steady state value which slightly increased with arc current. When d was increased from 5 to 30 mm, the time for the anode front surface to reach the steady state increased from 40 to 140 s, while this temperature decreased from 2525 to 2325 K (I=175 A). Thus minimizing d advantageously minimizes the start-up transient when using the radially expanding HRAVA plasma plume for thin film deposition.