The role of inclusions and surface contamination arc initiation at low pressures

This paper is concerned with the initiation mechanism of electric arcs in low-pressure gas discharge apparatus. It is demonstrated experimentally that arcs are initiated at the sites of inclusions in the surfaces of metal cathode probes exposed to a hydrogen plasma. The presence of relatively volatile extraneous contamination is also necessary, however, for arc initiation to occur under the present experimental conditions (hydrogen ion current density 10 A cm -2 , cathode field 10 5 V cm -1 ). A mechanism for arc initiation involving the production of bursts of cathodic vapour is postulated, in which an essential event is the dielectric breakdown of insulating inclusions.