PROJECT TITLE :
High voltage studies of inverted-geometry ceramic insulators for a 350 kV DC polarized electron gun
Jefferson Lab is constructing a 350 kV direct current high voltage photoemission gun employing a compact inverted-geometry insulator. This photogun will turn out polarized electron beams at an injector take a look at facility meant for low energy nuclear physics experiments, and to assist the development of latest technology for the Continuous Electron Beam Accelerator Facility. A photogun operating at 350kV bias voltage reduces the complexity of the injector style, by eliminating the requirement for a graded-beta radio frequency "capture" section utilized to spice up lower voltage beams to relativistic speed. But, reliable photogun operation at 350 kV necessitates solving serious high voltage issues related to breakdown and field emission. This study focuses on developing effective methods to avoid breakdown at the interface between the insulator and therefore the commercial high voltage cable that connects the photogun to the high voltage power offer. Three types of inverted insulators were tested, in combination with 2 electrode configurations. Our results indicate that tailoring the conductivity of the insulator material, and/or adding a cathode triple-junction screening electrode, effectively serves to extend the hold-off voltage from 300kV to more than 375kV. Electrostatic field maps recommend these configurations serve to supply a additional uniform potential gradient across the insulator.
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