The trigger pulse causes surface flashover, which liberates electrons and vaporized surface discharge material into the inter-electrode gap, which facilitates formation of a vacuum arc, closing the switch. The short switching time suggests electrons from the trigger discharge and the corresponding secondary electrons knocked from the anode as the initiation of the switching operation; the vaporized material travels too slowly through the gap to play significant role. The repeatability of the triggering can be improved by special coating of the surface between the trigger electrode and the cathode, and the jitter can be improved by doping the trigger substrate and modifying the trigger probe structures.