On criteria of discharge triggering by macroparticles in vacuum

Free particles in vacuum are known to reduce electric insulation in industrial devices drastically. The paper suggests a combined criteria of breakdown using a concept of charge loss by cold emission when a macroparticle is traveling across a vacuum gap. The concept allows the avoidance of infinite field strength when the particle comes very close to the electrode. Experimental data on macroparticle-induced breakdowns are presented. The data imply the existence of two requirements for discharge initiation by the particle. They seem to be appreciable electric field and a certain nonvanishing distance of the particle to the opposite electrode.