High thermal conductivity cryogenic RF feedthroughs for higher order mode couplers
Reece CE., Daly EF., Elliott T., Phillips HL., Ozelis JP., Rothgeb T., Wilson K., Wu G.
The use of higher-order-mode (HOM) pickup probes in the presence of significant fundamental RF fields can present a thermal challenge for CW or high average power SRF cavity applications. The electric field probes on the HOM-damping couplers on the JLab "High Gradient" (HG) and "Low Loss" (LL) seven-cell cavities for the CEBAF upgrade are exposed to approximately 10% of the peak magnetic field in the cavity. To avoid significant dissipative losses, these probes must remain superconducting during operation. Typical cryogenic rf feedthroughs provide a poor thermal conduction path for the probes and provide inadequate stabilization. We have developed solutions that meet the requirements, providing a direct thermal path from the niobium probe, thorough single-crystal sapphire, to bulk copper which can be thermally anchored. Designs, electromagnetic and thermal analyses, and performance data will be presented. ©2005 IEEE.