Temperature distribution dependence on refractory anode thickness in a vacuum arc: Experiment

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 thicknesses of d = 5, 10, 15, 20 and 30 mm separated by gaps of 5, 10, 15, and 20 mm. Arc currents of I = 130, 150, 175, and 200 A were applied for periods up to 210 s. 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. The anode temperature decreased with the gap and was higher for thinner anodes. When d was increased from 5 to 30 mm, the time for the anode front-surface temperature to reach the steady state increased from 45 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.