Development and Testing of an Advanced HOM Absorber Design for SRF Accelerators Using Dielectric-Coated Graphite

Effective methods are needed to dampen and extract power from higher order modes (HOM) in superconducting radio frequency (SRF) particle accelerators. DOE is interested in the development of innovative manufacturing and material processing technologies needed to fabricate robust broadband HOM absorber structures capable of effective operation through the entire ambient-to-cryogenic operating environment of superconducting particle accelerators. In this project, Ultramet will team with Cornell University’s SRF Group to develop advanced HOM absorbers for use in superconducting accelerator systems. Building upon previous research in HOM absorber development by Cornell and others in the accelerator community, Ultramet’s experience and expertise in advanced materials and process technologies will be applied to identify appropriate materials and develop fabrication methods to meet the critical HOM design criteria to be specified by Cornell. Ultramet will adapt advanced chemical vapor deposition (CVD) processes and manufacturing capabilities to fabricate testable advanced-design HOM absorbers. The core design concept of the advanced HOM absorber to be developed in this project is based on previous research performed by Cornell and will include encapsulating the exterior surface features of a graphite core with a non-porous well-adhered ceramic dielectric material (10-200 μm thick) formed by CVD. An integrally bonded high thermal conductivity CVD tungsten backing surface (200-400 μm thick) will be deposited on the dielectric-encapsulated graphite core to facilitate attachment to a parent component or test setup. Cornell will perform RF absorption characterization of the HOM absorber materials and test units to evaluate efficacy at ambient and cryogenic temperatures to guide advanced ring-style HOM absorber design optimization and build efforts planned for Phase II. The medical, food, security, and energy industries are among those benefiting from the proliferation of accelerator technology. Ultramet’s CVD-based advanced HOM absorber technology to be developed in this project will improve beam and thermal stability, allowing increased system efficiencies to promote substantial accelerator system cost reductions.