High field microplasma activity along alumina surfaces in vacuum

Certain interesting preflashover activities are observed in this study when alumina ceramic dielectrics are subjected to high voltage pulsed excitations in vacuum. The observed preflashover activities include bursts of time-resolved current and light emission (seen using a PMT), along with distinct spots of luminosity on the insulator surface, observed using an intensified CCD camera. The preflashover microplasma activity is found to depend strongly on the surface preparation of the dielectric and hence on the surface properties (specifically the distribution of defect complexes) of the material. Our results strongly suggest that the preflashover microplasma activity is a precursor to the surface flashover