Wideband Microwave Absorbers Cryogenic Vacuum Applications in Accerators

High order mode (HOM) absorbers are very important to stable operation of accelerators. It has been very difficult, especially for superconductor radio frequency (SRF) accelerators, to find a suitable HOM absorber material that not only can function at cryogenic temperatures and vacuum compatible with extremely clean environment but with batch-to-batch repeatability of its electromagnetic properties. Currently available HOM absorber materials either cannot function at cryogenic temperatures, or not vacuum compatible, or suffers from the batch-to-batch inconsistency of their electromagnetic properties. In an earlier program, Sienna Technologies, Inc., in collaboration with JLABS successfully demonstrated a new generation AlN-based lossy dielectric (STL-150D) that meets the requirements of CEBAF loads as a drop-in replacement for the discontinued AlN/GC composite loss loads. Sienna Technologies, Inc. proposes to continue the development of our AlN-based STL-150D lossy dielectrics with batch-to-batch repeatable electromagnetic properties for HOM absorbers for a multitude of accelerator applications. In Phase I, we will investigate a range of chemical compositions to meet the HOM absorber material requirements for a variety of DOE accelerators. We will also demonstrate the batch-to- batch repeatability of absorption characteristics of the developed materials. This will be accomplished by establishing and controlling incoming materials specifications, establishing fully documented strict process controls that conform to commercial manufacturing standards, and exercising in-process quality control steps, and final quality control procedures. Commercial Applications and Other Benefits: The proposed program will provide vacuum compatible AlN-based lossy dielectrics that can absorb microwaves over a broad frequency range from room temperature to cryogenic temperatures of 2 K to 4 K. The new AlN-based lossy dielectrics will provide drop-in replacements for AlN-GC loss loads for CEBAF, and a viable waveguide absorber for high power HOMs for ANL-APS, offers 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 developed products will also help to fill the need for high thermal conductivity lossy dielectrics created by the scarcity of toxic BeO components. The development of non-toxic high thermal conductivity AlN-based lossy dielectric will not only provide cryogenic HOM absorbers for accelerators but also allow vacuum electron device manufacturers to improve their products because of AlNs higher thermal conductivity. The success of this program will also help expand the AlN market beyond high thermal conductivity substrates for electronic packaging, and will help to drive down the cost of aluminum nitride components.