The bates polarized electron source

A polarized electron source, based on photoemission from GaAs, has been developed and installed at the MIT Bates Linear Accelerator Center. A multichamber vacuum system houses up to four GaAs crystals simultaneously, and is contained in a Faraday cage to provide about 300 keV in electrostatic acceleration. A modulated cw krypton ion laser is used to achieve stable operation during 15 μs pulses with a repetition rate of 600 Hz. The source has produced pre-injected peak currents in excess of 17 mA, and accelerated peak currents of 8 mA. The source has a calculated transverse phase space of 10−3πmec − cm. Developed for initial us in a parity violation measurement in elastic polarized e-12C scattering, the first beam polarization measurement was 0.36 ± 0.04, as determined by Møller scattering at 250 MeV. Subsequent beam polarization measurements have yielded polarizations as high as 0.40 ± 0.03.