Scanning Electron Microscope Study of Electrode Damage Due to Nanosecond Arcs

Abstract

The comparison between the observed cathode damage in a short arc (20–100 nsec duration; 0.3 mm long), as observed by a scanning electron microscope, and a model of cathode erosion employing ionic bombardment as the main erosion source leads to the evaluation of the current density in the individual craters comprising the cathode spot. Only order‐of‐magnitude calculations were possible; however, the main feature was that the current density was found to remain almost constant at a value of 1.9×10⁷ A cm⁻² for craters of radius between 0.3 and 1.0 μ. The ratio of the ionic to electronic currents was found to be significantly higher than previously published values for cathode spots.