Photographic Observations of Breakdown Mechanism in Vacuum

The results of a high-speed photographic study of the initial stages of discharge development in a point-to-plane gap in vacuum are presented. An image converter camera operating, in a streak mode, up to a speed of 1 mm/ns was used in conjunction with an image intensifier. The first detectable light always appeared at the cathode. The light originating at the anode appears to be from a plasma expanding at thermal velocities. Collapse of the voltage across the gap coincides with the bridging of the gap by anode plasma.