High Thermal Conductivity Aluminum Nitride-Based HOM Absorbers

A family of aluminum-nitride/silicon-carbide (AlN/SiC) composite lossy dielectrics are being developed to replace the toxic beryllia/silicon-carbide (BeO/SiC) composite lossy dielectrics as high order mode (HOM) absorbers in superconductor radio frequency (SRF) cavities in linear accelerators and in microwave tubes. Even though the dielectric properties of AlN/SiC composites match those of BeO/SiC composites, the low thermal conductivity of AlN/SiC composites has prevented their use in high power applications. This low thermal conductivity is caused by the formation of a solid solution between AlN and SiC at processing temperatures. This project will develop an approach to prevent the formation of this solid solution, which will result in a high thermal conductivity (=130 W/m-K), lossy AlN/SiC composite with repeatable thermal and electrical properties. In Phase I, the microstructures of the AlN/SiC composites will be characterized using advanced electron microscopy and electron probe microanalysis (EPMA). Prototype AlN/SiC composite HOM absorbers will be evaluated in the cavity by measuring the resonant frequency and cavity quality (Q) factor over the frequency of interest in the S-band. Commercial Applications and other Benefits as described by the awardee: An AlN-based HOM absorber with high thermal conductivity should be a viable product for use in linear particle accelerators, high power microwave tubes, space and satellite communications, and wireless communications.