Erosion of metal cathodes by arcs and breakdowns in vacuum

Abstract

The formation of erosion structures on metal cathodes by arcs and breakdown in UHV was studied experimentally by FEM and SEM and theoretically by a simple model. Nanosecond high-voltage breakdowns and quasi-stationary arcs had analogous effects on the production of surface craters. The existence of sharp micropoints could be proved directly by SEM. In accordance with the experiments the theory shows three distinct stages of crater formation on a nanosecond time scale: initially micropoints explode without strong erosion, then melting occurs with pronounced smoothing of the surface and finally craters are formed by the action of ion pressure. The latter process is connected with the production of a few sharp micropoints at crater boundaries, and of numerous droplets. The results presented here support the non-stationary model of arc cathode spots and the field-emission model of vacuum breakdown.