High Intensity Polarized Electron Sources

During the 1990s, at numerous facilities world wide, extensive R&D devoted to constructing reliable GaAs photoguns helped ensure successful accelerator‐based nuclear and high‐energy physics programs using spin polarized electron beams. Today, polarized electron source technology is considered mature, with most GaAs photoguns meeting accelerator and experiment beam specifications in a relatively trouble‐free manner. Proposals for new collider facilities however, require electron beams with parameters beyond today's state‐of‐the‐art and serve to renew interest in conducting polarized electron source R&D. And at CEBAF/Jefferson Lab, there is an immediate pressing need to prepare for new experiments that require considerably more beam current than before. One experiment in particular—Q‐weak, a parity violation experiment that will look for physics beyond the Standard Model—requires 180 uA average current at polarization $>80%$ for a duration of one year, with run‐averaged helicity correlated current asymmetry less than 0.1 ppm. Neighboring halls will continue taking beam during Q‐weak, pushing the total average beam current from the gun beyond 300 uA. This workshop contribution describes R&D at Jefferson Lab, dedicated toward extending the operating current of polarized electron sources to meet the requirements of high current experiments at CEBAF and to better appreciate the technological challenges of new accelerators, particularly high average current machines like eRHIC that require at least 25 mA at high polarization.