A high gradient multilayer vacuum insulator (HGI) with increased resistance to vacuum arcing to improve electrical strength. In an exemplary embodiment, the HGI includes a plurality of conductive and dielectric layers stacked in alternating arrangement so that the edges of the layers together form a vacuum-insulator interface and the stack has an overall length L.sub.S. The dielectric layers each have a thickness I that is less than I.sub.t I t = ( E M E BD ) 2 L S ##EQU00001## where I.sub.t is the transitional dielectric layer thickness below which failure of the vacuum insulator is by vacuum arcing, E.sub.BD is the breakdown field required to initiate vacuum arcing across one of said dielectric layers, and E.sub.M is the breakdown field required to initiate surface flashover across a monolithic dielectric material of length L.sub.S.
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory.