Beam Pipe HOM Absorber for 750 MHz RF Cavity Systems

Superconducting RF (SRF) systems, used in storage ring and linac applications at DOE facilities, typically contain unwanted frequencies or higher order modes (HOM) that must be absorbed by ferrite and other lossy ceramic-like materials. These materials are brazed to substrates that are strategically located and mechanically attached, often to the drift tube adjacent to the SRF cavity. However, the ferrites and their attachments weaken under tensile and thermal stresses and tend to crack. This project will develop an improved HOM absorber for high-gradient 750 MHz superconducting cavity systems. The work will build on novel construction techniques developed earlier at the SLAC B-factory. In Phase I, numerical modeling will be used to determine the optimum ferrite load required to meet broadband loss specifications. Prototype structures will be fabricated and tested for mechanical strength. Attachment techniques to the metal substrates will range from full compression rings to stress-free ferrite assemblies. Commercial Applications and other Benefits as described by the awardee Better attachment techniques for dissimilar materials, such as ferrite bonding to a metal substrate, are needed for many microwave applications where thermal heat transfer is critical and where a great difference between assembly temperature and operating temperatures exist.