An SF6 gas-insulated -500 kV DC conical insulator vacuum feedthrough

A test electrode was biased to -500 kV direct current (DC) by means of a novel SF6 gas-insulated conical alumina insulator feedthrough. The design enables the extreme high vacuum conditions required by spin-polarized electron sources by reducing the photogun vacuum chamber volume compared to coaxial cylindrical insulators. In contrast to conventional inverted-insulator photogun designs that rely on solid dielectric interfaces for high-voltage terminations, the present design employs a pressurized SF6 intervening volume between a conical alumina insulator and a modified commercial epoxy high-voltage cable receptacle. This approach enables the use of commercially available cable hardware while extending the demonstrated operating voltage of solid feedthroughs. A maximum voltage of -500 kV was applied to a test electrode attached to the narrow end of the feedthrough inside a chamber filled with SF6 at 170.3 kPa (10 psig) and later under vacuum to -259 kV, limited by field emission. The results demonstrate that a commercial high-voltage cable combined with a custom-designed SF6 gas-insulated vacuum feedthrough can be used to bias photogun electrodes to -500 kV DC.