Variation of the critical breakdown field between copper electrodes in vacuo

Abstract

The critical breakdown field, ie the product of field enhancement and (mean) applied electric field at breakdown, between copper electrodes in vacuum is shown to increase with the number of low-current (<1A) conditioning arcs. A similar effect is not observed on materials with smaller ranges of hardness (stainless steel, molybdenum, etc). A hypothesis is put forward that a local hardening of emitting regions occurs in copper due to the mechanical stresses induced into the surface at arc points. Experimental evidence supporting this is presented along with complementary experimental results for deliberately hardened copper surfaces.