A lateral test structure with metalized film electrodes is shown to have distinct advantages over a conventional solid electrode structure for studying the HV characteristics of solid insulators in vacuum. The paper presents results of streak photography and spectral analysis of surface discharge luminosity, and of preflashover activity using time-coordinated current, luminosity, and imaging of light activity emanating from the surface of the stressed dielectric. The preflashover activity, consisting of bursts of time-correlated current and light emission, is associated with randomly distributed emission spots on the surface. It is proposed that the above observations are related to charge trapping and detrapping processes at localized energy levels associated with insulator surface defects.
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