Anode crater formation by pulsed arcs

Abstract

Anode damage due to short−duration (3 ns−1 μs) arcs between a tungsten cathode and copper, gold, palladium, and platinum anodes has been studied. The electrode arrangement was mounted inside the specimen chamber of a scanning electron microscope so that the surfaces to be discharged, the interelectrode spacing, and the resultant damage were readily observable. The effects of arc current and arc duration on crater dimensions were studied. Anode crater diameters were found to vary as the square root of the arc current for fixed arc duration. A weak dependence of anode crater diameter on arc duration was found at constant current for arcs lasting less than ∼100 ns. The depth of cratering was also measured and relationships between the crater diameter and depth were found for platinum and gold anodes. Large differences in arc crater diameters were not found for each of the anode metals, despite the differences in their thermal properties. The transition from anode to cathode arcs with increasing gap could also be observed and was found to occur between 1.3 and 2.1 μ for a plantinum anode.