STATUS OF THE POLARIZED SRF PHOTOCATHODE GUN DESIGN

A polarized SRF photocathode gun is being considered as a high-brightness electron injector for the International Linear Collider (ILC). The conceptual engineering analysis and design of this injector, which is required to deliver a large emittance ratio, is presented. The delivered beam parameters we predict are compared to the required performance after the ILC damping ring. The analysis indicates that it may be possible to save cost by eliminating the damping ring though higher values of the emittance ratio are still to be demonstrated. INTRODUCTIONS Advanced Energy Systems, Inc. (AES) is collaborating with Brookhaven National Laboratory (BNL) to investigate the generation of polarized electron beams using a Superconducting Radio Frequency (SRF) photocathode electron gun. The use of an RF gun with a magnetized cathode in place of a DC gun for the ILC may reduce the requirements for emittance damping rings. Maintaining adequate lifetimes for the Gallium Arsenide (GaAs) cathode material requires vacuum levels in the 10 -11 torr range. While vacuum levels around the 10 -9 torr range are common in normal conducting RF guns, the cryogenic pumping of the cavity walls of an SRF gun should maintain vacuum in the range needed for GaAs cathode longevity. The AES/BNL team is developing an experiment to study the quantum lifetime of a GaAs cathode in an SRF cavity, and to investigate long-term cavity performance in the presence of the cesiated cathode. We review the performance of the existing AES/BNL 1.3 GHz and 703.75 MHz SRF photocathode guns. We then discuss efforts to develop a 350 MHz photocathode SRF gun capable of generating polarized electron beam for the ILC injector.