Impulse Electrical Breakdown Fields of Short Vacuum Gaps

Prebreakdown currents for a long-duration impulse voltage were measured as a function of a wide range of gap spacing using a . air of plane-parallel copper electrodes in a vacuum of 3xlO Pa. The field-emitted component of the prebreakdown current was found to follow the Fowler-Nordheim field emission theory and the field enhancement factor at the cathode was determined from the Fowler-Nordheim plot. The B was found to increase from 15 to 230 with increasing electrode separation in the range from 0.003 to 2.5 mm. The breakdown voltage and the average field strength were also measured in the same gap range. It was found that the average field strength decreased from 700 kV/mm to 33 kV/mm with increasing electrode separation, however, the critical microscopic electric field at breakdown is determined to be (10.2±1.5) X107 V/cm in the range investigated.