High Performance Lossy Dielectric HOM Absorbers for SRF Cavities

Recently developed high thermal conductivity aluminum nitride (AlN) based lossy dielectrics can replace the toxic beryllia (BeO) based lossy dielectrics as high order mode (HOM) absorbers in superconductor radio frequency (SRF) cavities in linear accelerators and in microwave tubes. AlN-based lossy dielectrics must be joined metallic copper members in these applications. However, lack of suitable metallization and brazing technologies hampers the insertion of AlN-based lossy dielectrics into SRF cavities and other vacuum electron devices. This project will develop a family of vacuum compatible robust joining technologies to attach AlN-based lossy dielectrics to copper members for SRF cavities and power microwave tubes. The Phase I project successfully demonstrated the target joining techniques. The Phase II project will expand the Phase I development by investigating the reliability and repeatability of the joining techniques developed in Phase I, fabricating prototype S-band test assemblies, and carrying out S-band cold and hot cavity tests to compare the performances of the prepared test assemblies. Commercial Applications and other Benefits as described by the awardee: SRF cavities in linear accelerators and medium-to-high vacuum electron devices (microwave tubes) would benefit from the AlN-based lossy dielectric HOM absorbers that are robustly joined to Cu components. Commercial applications include linear particle accelerators for scientific research; x-ray sources for medical diagnostic and treatment devices; klystrons and gyrotrons to supply microwave energy to improve the performance of chemical processes and materials processing; klystrons for direct broadcast satellites; gyrotrons for magnetic fusion based on electron cyclotron heating; and microwave communications.