Ultra-fast imaging of pulsed-field surface-flashover along an alumina dielectric in vacuum

Pulsed-field surface-flashover events have been studied for a regime based on a cylindrical alumina insulator (94% Al/sub 2/O/sub 3/), having two concentric planar electrodes on its end-face. Voltage-pulses, typically of 20 kV amplitude (500 kV /spl mu/s/sup -1/ time rate-of-rise), were applied to the radial insulator-electrodes M-I-M regime. Real-time optical recordings of surface-flashover events were made using an ultra high-speed framing camera, with temporal resolutions of up to 5 /spl mu/s per frame; A high spatial resolution (586/spl times/385 pixels) facilitated the detailed recording of optical-emission phenomena associated with the surface-flashover of the alumina. The initiation of surface-flashover in the alumina dielectric is discussed in terms of explosive electron-emission from localised defect-centres within the ceramic.