Dependence of Vacuum Electrical Breakdown Field and Field Enhancement Factor on the Number of Apertures Drilled in Small Electrodes

Abstract

Dark current based on field-emission current is considered as a factor causing the vacuum electrical breakdown between the multi-aperture acceleration grids in the JT-60 negative ion source. In this paper, we focused on field enhancement factor which is a key parameter of field-emission from the electrode. Vacuum breakdown tests for small sized electrodes simulating the multi-aperture acceleration grids of the negative ion source was conducted. We obtained field enhancement factor and breakdown field for multi-aperture electrodes, and we investigated the dependence of each parameter on the number of apertures. The results revealed that the increase of the average field enhancement factor after the end of conditioning due to the increase of the number of apertures decreases dielectric strength of the multi-aperture electrode.