Effective Cathode Voltage in a Vacuum Arc With a Black Body Electrode Configuration

The energy dissipated in the cathode in a vacuum arc black body assembly (VABBA) is investigated. A closed volume is formed by a water-cooled cylindrical Cu cathode and a cup-shaped W or Ta anode. Cu cathode material is emitted into the closed volume and the anode is heated by the arc. The VABBA confined and evaporated macroparticles while the plasma is extracted through small anode apertures. Arc currents are $I=175\hbox {--}250~{\rm A}$ and the arc time is 150 s. The effective cathode voltage $U_{\rm cef}$ is determined calorimetrically, using a thermocouple probe. It is observed that $U_{\rm cef}$ increases with time from ${\sim}{\rm 6.5}~{\rm V}$ for cold anodes (i.e., during conventional cathodic arcing) to a steady-state value of ${\sim}{\rm 11.2\hbox {--}12.0}~{\rm V}$ when the anode is sufficiently hot and the arc operated in the VABBA mode.