SBIR-STTR Award

Current, commercially available microwave absorbing materials (terminations) do not provide adequate microwave absorption at the extremely low temperatures (2-50 K) that are required to operate many super-cooled, superconductor-based particle accelerators. Artificial, dielectric, lossy ceramics, with temperature-independent dielectric properties in the microwave frequency range, are being developed. These types of materials would satisfy all of the required properties for accelerator environment applications. The materials are being developed using the concepts of artificial dielectrics, and by identifying the type of conductive phase required in the system to yield temperature-independent, microwave absorption properties. Ceramic, aluminum nitride (AlN) based systems will be created and evaluated with emphasis on the selection of the conductive phase, which will provide low temperature loss and the capability of functioning in the accelerator environment. Due to temperature-independent properties, materials developed using this approach will be universally applicable in microwave absorbing applications such as use in Travelling Wave Tubes, Klystrons, Coupled Cavity Tubes etc., serving commercial and military communication applications. In phase I, at least one artificial dielectric material family (based on AlN) will be designed and (to be determined) conductive phase, and its dielectric properties in the microwave frequency range will be characterized. The fact that it can meet material requirements for use in accelerator environments will also be verified. Additionally, it is planned to further characterize the AlN-C(glassy) dielectric system. Hot pressing will be used as the manufacturing method.

Commercial Applications and Other Benefits as described by the awardee:
These materials should, in addition to cryogenic environments, operate both at room and elevated temperatures, with more predictable properties than other currently available termination materials. Therefore, companies that commercially manufacture microwave amplification devices for communication, both commercial and military, should be able to use the material in their devices. Superconducting accelerators operating at extremely low temperatures should also have a reliable source of microwave absorbing materials to ensure optimal performance by reducing HOM modes during cavity rebuilds and for the design of new accelerators.

Current, commercially available microwave absorbing materials do not provide adequate microwave absorption at the extremely low temperatures (approaching absolute zero) that are required for operation in many super-cooled, superconductor-based particle accelerators. Specifically, the new Next Linear Collider requires a high volume of a lower cost lossy material for incorporation into its accelerator cells. This project will develop a commercial source of lossy materials, based on a ceramic aluminum-nitride (AlN) matrix, with temperature-independent properties. In Phase I, two cryogenically lossy material combinations were identified and confirmed to have temperature-independent dielectric loss properties under cryogenic conditions. Both materials are vacuum compatible and have been bonded to copper. Phase II will initiate material optimization and manufacturing scale-up for these materials. Both material densification hot-pressing and near-net-shape pressureless sintering techniques will be evaluated. Relevant material properties will be measured, and process capability will be determined.

Commercial Applications and Other Benefits as described by the awardee:
The material should have lossy properties at extremely low temperatures for applications such as CEBAF. Larger markets for these materials include microwave tubes both for military applications and for high energy particle accelerators.