A Polarized Electron RF Photoinjector

70802 Future linear colliders will require a polarized electron source with large spin polarization (>80%), high quantum efficiency, long cathode life, maximum peak and average current, and low emittance. Currently, polarized electron beams for accelerators are generated using dc-biased electron guns with GaAs photocathodes. The relatively long pulse, on the order of nanoseconds, produced by these sources must be radio frequency (rf) chopped and bunched into the desired pulse (or multi-bunch) shape. Another drawback is that typical dc polarized electron beams also have a larger emittance than what is required. This project will develop a polarized electron rf photoinjector based on a modified plane-wave-transformer (PWT) design. The design would allow for a unique accelerator structure with large vacuum conductance, integrated with a strained GaAs photocathode and suitable for producing a high quality, polarized electron beam of energy greater than 10 MeV. In Phase I, the rf photoinjector will be designed to include a cathode insertion system which maintains a high vacuum integrity as required for the use of GaAs photocathodes. The vacuum requirements of the system will be studied to improve the properties of the PWT gun including, but not limited to, the use of advanced getter material. Beam dynamics for a high rep-rate operation will be studied numerically to determine the operating parameters and performance of the proposed rf gun. Commercial Applications and Other Benefits as described by the awardee: In addition to its potential as a polarized electron beam in future linear colliders, a high-quality polarized electron source should have a ready market in many national laboratories and nuclear physics laboratories around the world. Additional applications include medical imaging, biomagnetic field measurements, and industrial processing of semiconductor materials.