A Polarized Electron RF Photoinjector

70802S02-II Future linear colliders require high brightness, polarized electron/positron beams for high energy physics experiments. Although photoelectrons with over 80% polarization have been produced in dc guns, the transverse emittance of the polarized electron beam from the dc gun is not low enough to meet the brightness and luminosity requirements of linear colliders. This project will develop a radio frequency (RF) photoinjector with a Plane Wave Transformer (PWT) design. Its unique features will include high vacuum (10-11 Torr), low peak field (55 MV/m, for the survivability of an activated GaAs photocathode), and emittance-compensating solenoids (to allow the polarized electron beam to achieve this low emittance of 0.6 -1.0 mm-mrad, for charge per bunch of 1-2 nC). Phase I demonstrated the feasibility of a polarized electron PWT photoinjector. Beam dynamics simulations showed that excellent beam quality can be achieved by operating the PWT at a low accelerating gradient, and that the possibility of back bombardment of field emitted electrons onto the photocathode is greatly reduced. The vacuum design and the load lock design were completed. Phase II will fabricate and test a PWT photoinjector with an activated GaAs cathode, integrated with a load lock for the photocathode. Commercial Applications and Other Benefits as described by awardee: In addition to its potential as a polarized electron source for future linear colliders, a high vacuum PWT photoinjector should find use in high brightness light sources such free electron lasers, 4th generation synchrotrons, and Compton x-ray sources for applications in medicine, industry and research.