The nature of high voltage initiation of an electrical arc in a vacuum

Generally the gap voltage at the moment of arc initiation in a vacuum is significantly larger than the voltage in developed arcs. This phenomenon was studied here suggesting a physical model for initially triggered at the bulk cathode plasma and then for appeared transient spot. The model allows calculating the transient energy flux to the cathode and the transient cathode potential drop (CPD). It was shown that the CPD at the moment of spot ignition is relatively large and significantly contributes to the arc voltage at arc ignition. The subsequent voltage decrease can be understood from the transient CPD behavior during arc development. The voltage oscillation in an arc was explained by suggested model taking into account the spot shifting on a cold location.