Prebreakdown Conduction in Vacuum Gaps under Switching Impulse Excitations

Abstract

The present investigation concerns prebreakdown conduction in vacuum gaps under slow impulses. Hemispherical, plane, and needle electrodes have been used in a vacuum emvironment of better than 0.1 mPa. The gap spacings were 0.5, 1, and 1.5 mm. The front times ranged from 200 ps to 5 ins. The results indicate that prebreakdown currents were smaller than the highest sensitivity of 10-7 Afor front times of about 1 ins. For larger front times, breakdown currents were observed, which increased with front time. The voltagecurrent relationship appears to follow Fowler-Nordheim theory but Fowler-Nordheim plots are branched. The high magnitudes may be attributed to ion-assisted field emission based on which a model has been developed, that agrees substantially with experimental results. Applicability of non-metallic type of emission is discussed.