Properties of Vacuum-Insulated Single-Crystal Tungsten Electrodes in High Electric Fields. Part II. Nature of Prebreakdown Currents

Abstract
The nature of the emission currents associated with electropolished single-crystal tungsten electrodes in vacuum insulation has been studied. Schottky-Richardson curves indicate that the emission current is thermionic at voltages above 1.5 kV, this conclusion being supported by Fowler-Nordheim curves which show no evidence for field emission. It is uncertain whether the emission currents below 1.5 kV are of the thermionic or field-emission type. The origin of the thermionic currents can be associated with various surface structures on the electrodes, notably slip plane ledges and surface hole ledges, as discussed in Part I. Polycrystalline electrodes were not studied in detail, but appear to be associated with field emission.