Abstract
Several future accelerator projects at Brookhaven for the Relativistic Heavy Ion Collider (RHIC) are based on energy recovery linacs (ERLs) 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. Strong HOM damping was experimentally demonstrated both at room and at superconducting (SC) temperatures in a prototype research and development (R) five-cell niobium superconducting rf (SRF) cavity with ferrite dampers. Two room-temperature mock-up five-cell copper cavities were used to study various damper configurations with emphasis on capacitive antenna dampers. An innovative type of ferrite damper over a ceramic break for an R SRF electron gun also was developed. For future SRF linacs longer cryomodules comprised of multiple superconducting cavities with reasonably short intercavity transitions 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. This paper presents the results of simulations and measurements of several damper configurations.
Highlights
The Collider-Accelerator Department at BNL is actively working on various accelerator projects based on highcurrent superconducting rf (SRF) energy recovery linacs (ERLs): (1) a research and development (R&D) energy recovery linac facility [1]; (2) the envisioned electron-ion collider [2]; and (3) coherent electron cooling [3]
The R&D ERL facility is expected to operate with a high current up to 0.3 A, or with high-charge bunches up to 5 nC
With a highly flexible electron beam return loop lattice, the R&D ERL will serve as a test bed for the technologies and concepts necessary for future high-current ERL-based projects
Summary
The ECX five-cell cavity has very long, large diameter beam tubes which connect to the room-temperature higherorder-mode (HOM) dampers that are installed outside of the cryostat. These HOM dampers use water-cooled ferrite absorbers. The contemplated eRHIC electron accelerator would use SRF linacs based on five-cell SC cavities with highly damped HOMs, similar to that used for the R&D ERL. The HOM frequencies and Q values of the cavity string with its ferrite dampers were obtained with the aid of a network analyzer, Agilent E5701C, from forward scattering coefficient (S21) measurements between the bottom ‘‘6 o’clock’’ BPM probes located at opposite sides of the cavity.
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