DC and pulsed-field electro-optical phenomena from an alumina insulator in vacuum

The optical and electrical characteristics of a cylindrical alumina insulator (94% α-Al₂O₃) have been measured under ultra-high vacuum conditions. A high-resolution CCD camera was used to record real-time optical images of DC prebreakdown luminescence from the ceramic. Further optical images were also recorded of pulsed-field surface-flashover events on the alumina ceramic: an intensified high-speed video technique provided 1 ms frames of surface-flashover events. The DC electro-optical prebreakdown characteristics of the alumina are discussed in terms of solid-state photon emission processes, that are believed to arise from radiative electron-recombination processes at vacancy defects and substitutional impurity centres within the surface-layers of the ceramic. Comments are also made upon the nature of pulsed-field surface-flashover phenomena along a solid insulator in vacuum