Aluminum Nitride Based Absorber Materials for Toom and Cryogenic Temperatures

Currently available Aluminum nitridesilicon carbide (AlNSiC) composite lossy dielectrics are not suitable as high order mode (HOM) absorbers in superconductor radio frequency (SRF) cavities in linear accelerators operating at cryogenic temperatures. Even though they have favorable dielectric properties at room temperature, AlNSiC composites become totally lossless at cryogenic temperatures due to the freeze out of carriers in the semiconducting SiC component. The loss of absorption capability at cryogenic temperatures makes AlNSiC composite lossy dielectrics unsuitable for SRF cavities. Replacing semiconductor SiC component in AlNSiC composites with a conductor would eliminate the carrier freeze out and prevent the loss of absorption capability at cryogenic temperatures. Sienna Technologies, Inc. will develop an AlNbased composite that maintain its loss characteristics at cryogenic temperatures and with repeatable thermal and electrical properties. In Phase I Sienna Technologies, Inc. will produce new AlN lossy dielectrics with required loss properties that are temperatureindependent over room temperature to 2 K. The new AlN lossy dielectric will have high thermal conductivity equal to or greater than that of AlNSiC and BeOSiC composites. The microstructures of the AlN lossy dielectrics will be characterized using advanced electron microscopy and electron probe microanalysis (EPMA). Prototype AlNconductor composite HOM absorbers will be evaluated for CEBAF and ANLAPS applications. Commercial Applications and Other Benefits: An AlNbased HOM absorber that can operate over a broad temperature range and has high thermal conductivity is a viable product for use both by Federal Government and commercial sectors in linear particle accelerators, high power microwave tubes, space and satellite communications, and wireless communications. The new AlNbased lossy dielectrics will provide dropin replacements for AlNGC loss loads for CEBAF and a viable waveguide absorber for high power HOMs for ANLAPS, and offer an alternative to ferrites for beamline HOM absorbers for a variety of other accelerators such as Cornell ERL, and electron cooler for RHIC at Brookhaven. The new product will also help to fill the need for high thermal conductivity, lossy dielectric components created by scarcity of the toxic BeO components due to the recent EPA ruling.