Fast Electrical and Optical Diagnostics of the Early Phase of Dielectric Surface Flashover

With a new experimental setup we attempt to acquire information on the physical mechanisms involved in the early phase, of dielectric surface flashover in vacuum. The device uses a cable discharge into an impedance matched, coaxial, surface flashover test chamber in a micro-torr vacuum, operated in self-breakdown mode with a dc charging voltage. Novel techniques for current measurement provide resolutions in the milliampere and subnanosecond range for the preflashover current. They are supplemented by voltage measurements, measurements of the self-luminosity, and soft X-ray diagnostics. Preliminary results support the existence of a secondary electron avalanche above the surface and electron stimulated outgassing before flashover occurs.