The early phase of dielectric surface flashover

Results of high-temporal-resolution current, luminosity, and X-ray measurements indicate the existence of free electrons during the first phase of dielectric surface flashover. The linearly rising current points to a saturation mechanism of the carrier amplification during this phase. In a subsequent phase, the exponentially rising current, the termination of the X-ray emission, and the build-up of plasma above the surface indicate gaseous ionization processes. The observations are compatible with the standard model for dielectric surface flashover-the saturated secondary electron emission avalanche and electron induced gas desorption