The initiation of arcs by ion bombardment

The arcing behaviour of a number of refractory metals and graphite has been examined by negatively biasing specimen electrodes in the presence of a pulsed rf discharge. The main object of this work was to select anode materials for gas-filled valves which would reduce their tendency to arc-bank under severe commutation conditions. The voltage at which about 5% of the pulses resulted in an arc, at an argon ion current density of 1·2 kA m −2 , was used as a figure of merit. Of the materials examined, tungsten was the best with a figure of merit of 15 kV and graphite the worst with 6 kV. A good correlation was obtained between the results and the published values for the vacuum arc voltages.