R-square impedance of ERL ferrite HOM absorber

An R&D facility for an energy recovery linac (ERL) intended as part of an electron-cooling project for RHIC is being constructed at this laboratory. The center piece of the facility is a five-cell 703.75 MHz superconducting RF linac. Successful operation will depend on effective HOM damping. It is planned to achieve HOM damping exclusively with ferrite absorbers. The performance of a prototype absorber was measured by transforming it into a resonant cavity and alternatively by a conventional wire method. The results expressed as a surface or R-square impedance are presented in this paper.