Speaker
Description
Polarized electron beams play critical role in fundamental physics research by providing additional observables and opening new channels of discoveries. This discovery potential is well-known and is frequently used in high-energy and nuclear physics research. Recently, more conventional branches of science, such as ultra-fact electron microcopy, started exploitation of unique features of matter interaction with polarized electrons. While there is an active search for efficient sources of polarized electrons, GaAs crystals illuminated by circular polarized IR lasers remain the main “work-horse” in polarized electron sources. All current GaAs polarized sources are limited to so-called DC – or electrostatic- electron guns with maximum voltage of few hundred kilovolts and accelerating gradients of few megavolts per meter. This technology is providing super-ultra-high vacuum conditions necessary for survival of GaAs photo-emissivity, i.e. its quantum efficiency. But this technology limits both the quality and quantity of available beams, and results in ion back-bombardment diminishing quantum efficiency of GaAs photocathodes. These are the reasons why accelerator community was and is attempting to extend this important technology to the realm of the RF (radio-frequency) electron guns, which are capable of accelerating beams to mega-electron-volts and accelerating gradients measured in tens if megavolts per meter. Unfortunately, all previous attempts of operating GaAs photocathodes in RF guns were unsuccessful and their QE was diminishing in few RF cycles. In this paper, we report on first successful operation of GaAs photocathode in superconducting RF gun. We describe in detail all critical steps necessary for this saucerful demonstration, parameters of the accelerator system and the generated electron beam, evolution of the GaAs quantum efficiency, as well as, lessons learned to further improve the systems.
