• E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu
  BNL, Upton, Long Island, New York
• D. Holmes
  AES, Medford, NY
• E. Wang
  PKU/IHIP, Beijing

RF electron guns with strained super lattice GaAs cathodes can produce higher brightness and lower emittance polarized electron beams, due to the higher field gradient at the cathode surface compared with DC guns. The vacuum in the gun must be better than 10^-11 torr to obtain a sufficient cathode life time with high quantum efficiency (QE). Such high vacuum cannot be obtained easily in a normal conducting RF gun. We report on an experiment with a superconducting RF (SRF) gun, which can maintain a vacuum of nearly 10^-12 torr because of cryo-pumping at the temperature of 4.2K . The GaAs cathode was activated by Cs'O treatment with a QE of 3% and exhibits a long lifetime in a preparation chamber. This cathode will be used in a 1.3 GHz - cell SRF gun to measure the destruction of the QE by ion and electron back-bombardment.

• E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu
  BNL, Upton, Long Island, New York
• D. Holmes
  AES, Medford, NY
• E. Wang
  PKU/IHIP, Beijing

Superconducting RF (SRF) electron guns deliver higher brightness beams than DC guns because the field gradient at the cathode is higher. SRF guns with metal cathodes have been successfully tested. For the production of polarized electrons a Gallium-Arsenide (GaAs) cathode must be used, and an experiment to test this type of cathode is under way at BNL. Since the cathode will be normal conducting, the primary concern is cathode-driven heat load. We present measurements of the electric resistance of GaAs at cryogenic temperatures, a prediction of the heat load, and verification by measuring the quality factor of the gun with and without the cathode.