Investigation of onset of plasma formation at anode of fast-pulsed high-voltage vacuum diode

Abstract

The mechanism by which plasma forms in a fast pulsed high vacuum diode has been greatly studied. For the most part, efforts have been concentrated on plasma formation at the cathode. Recently, investigators improved the popular explosive emission model, taking into account the ion current density and surface heating through ion bombardment. This model provides total current densities of the order necessary for exploding whiskers on the cathode surface, and explains the cathode spot phenomena. The general belief is that a fast pulsed high voltage diode event is dominated by cathodic processes, and little research into plasma formation at the anode has been conducted. This study presents experimental results which support the above model applied to both the cathode and anode regions of the diode. It is shown here that plasma formation does indeed take place in the anode region, and, that the formation occurs nearly simultaneously with plasma formation at the cathode. Also, photographic evidence of postbreakdown cratering on the anode surface, similar to the cathode spot phenomena, will be presented.