Instabilities of prebreakdown currents in vacuum II: the nature of the emission sites

Abstract

Prebreakdown electron emission between extended copper electrodes is experimentally studied with a time resolution <100 ns. When taking the current-voltage characteristics sufficiently quickly it is found that after a voltage increment the emission can relax to a lower level with time constants <1 ms. As a consequence, Fowler-Nordheim plots become flat, yielding values of the microscopic field enhancement that are too high. During the deposition of a metal-vapour plasma that originates from neighbouring arc gaps, a steady growth of the emission is observed, which leading to a considerable reduction of the voltage, down to 50% of the initial value. The results are discussed in terms of metallic-field electron emission from atomic structures that are subjected to surface migration under the influence of the electric field. The migration processes can be activated by mechanical shocks. This explains the shock effects found in the preceding paper in this issue.