Performance of the SLC polarized electron source with high polarization

For the 1992 operating cycle of the SLAC Linear Collider (SLC), the polarized electron source (PES) during its maiden run successfully met the pulse intensity and overall efficiency requirements of the SLC. However, the polarization of the bulk GaAs cathode was low (~27%) and the pulse-to-pulse stability was marginal. We have shown that adequate charge for the SLC can be extracted from a strained layer cathode having P_e~80% even though the quantum efficiency (QE) is <1%. The recent addition of a separate chamber to the PES-which allows cathodes to be loaded into the gun after the vacuum bake and after high voltage (HV) processing without breaking vacuum-increases the reliability for achieving an adequate photoelectron yield. A new SLAC-built pulsed Ti:sapphire laser permits operation of the PES at the required wavelength with sufficient power to fully saturate the yield, and thus improve the e^- beam stability. The performance of the PES during the 1993 SLC operating cycle with these and other improvements is discussed