R and D ERL: HOM Absorbers

Several future accelerator projects at the Relativistic Heavy Ion Collider (RHIC) are based on Energy Recovery Linacs (ERL) with high-charge high-current electron beams. Their stable operation mandates effective higher-order-mode (HOM) damping. The development of HOM dampers for these projects is pursued actively at this laboratory. A strong HOM damping was experimentally demonstrated both at room- and at superconducting- (SC) temperatures in a prototype R and D five-cell niobium SRF cavity with ferrite dampers. A novel type of ferrite damper over a ceramic break for a R and D SRF electron gun also was developed. For future SRF linacs longer cryomodules comprising of multiple superconducting cavities with reasonably short transitions between them are planned. In such a configuration, the dampers, located closer to the cavities, will be at cryogenic temperatures; this will impose additional constraints and complications. Two room-temperature mock-up five-cell copper cavities were used to study various damper configurations. This paper presents results of simulations and measurements for several configurations.