Superconducting RF Photocathode Gun for Low Emittance Polarized ELectron Beams

Polarized electron beams are important to high energy physics and nuclear physics experiments. At present, linear colliders and nuclear science machines use DC polarized sources, as these have been proven to provide polarized beams with good cathode lifetimes and acceptable emittances. However, future linear colliders, including the International Linear Collider (ILC), will require emittance damping rings that can be large and expensive. A gun that can produce low emittance polarized beams with a reasonable cathode lifetime can reduce or even eliminate the damping ring requirement. In particular, a superconducting radiofrequency electron gun that uses a gallium arsenide photocathode has the potential to produce polarized electron beams with very low emittances, while still providing for long cathode lifetimes. This project will demonstrate that the cathode lifetimes in a superconducting radiofrequency gun can rival the lifetimes achieved in existing DC guns and that a gun system can be designed with very low electron beam emittances. Using simulations, Phase I showed not only that low emittances can be achieved but also that ion backbombardment, which limits the lifetime of cathodes in DC guns, can actually be less than in DC guns. Phase II will design modifications to the existing cavity and cryostat, which will be used for the lifetime testing. Phase II also will develop a preliminary design for a superconducting radiofrequency gun, which would be suitable for use with the ILC. Commercial Applications and Other Benefits as described by the awardee: In addition to ILC applications, the electron source could be used in other radiation sources to produce high-power, coherent radiation, spanning THz to UV and perhaps beyond, through various mechanisms such as coherent synchrotron radiation and FELs. The source also could find application in defense and as the front end of high-power electron accelerators for materials processing and sterilization.