A hot-spare injector for the APS linac

Last year a second-generation SSRL-type thermionic cathode RF gun was installed in the Advanced Photon Source (APS) linac. This gun (referred to as "gun2") has been successfully commissioned and now serves as the main injector for the APS linac, essentially replacing the Koontz-type DC gun. To help ensure injector availability, particularly with the advent of top-up mode operation at the APS, a second thermionic-cathode RF gun will be installed in the APS linac to act as a hot-spare beam source. The hot-spare installation includes several unique design features, including a deep-orbit Panofsky-style alpha magnet. Details of the hot-spare beamline design and projected performance are presented, along with some plans for future performance upgrades.