Investigation of breakdown emission sites on the surface of large-area stainless-steel cathodes in vacuum

The paper describes the results of study of prebreakdown emission in vacuum and correlations between prebreakdown emission sites and breakdown of gaps formed by plane-parallel electrodes made of stainless steels. Anode-scanning probe vas used for recognizing emission sites and reconstructing emission maps of 8-cm-diameter plane cathodes. After recognizing emission sites, high-voltage 60-ns 220-kV square pulses were applied with closing a gap until breakdown occurs. Cathode emission sites were found experimentally to be responsible for electrical breakdown at hold-off electric field essentially below 1 MV/cm. In a case of better insulating ability of a vacuum gap, the anode becomes more influencing on electrical insulation of a gap.