Compact, Low-Cost Higher Order Mode Absorbers Formed by Cold Spray of Metal Matrix Composites

Suppression of higher order modes HOMs) represents a significant challenge for current and future high average power accelerating facilities, such as future colliders, Free Electron Lasers FEL) and Energy Recovery Linacs ERL), which have kW-levels of estimated HOM power per cavity. While current HOM RF absorber materials have satisfied the requirements for cryogenic operation; robust, low-cost manufacturing technologies which can generate large area RF absorbers are needed for future accelerators development. This proposal outlines a method to fabricate novel Al/SiC metal matrix composites for use as RF absorbers. We utilize an innovative, two-step process which includes mechanically alloying metallic and ceramic powder followed by consolidation onto a metallic heat sink using the cold spray process. The low temperatures associated with this fabrication route will result in the formation of nanostructured, non- equilibrium phases with enhanced microwave absorbing properties. Our industrial collaborator has recently developed technology which enables the coating the inside of tubes as small as 50mm [2”] in diameter. Combined, mechanical alloying and inside diameter cold spraying will enable the direct fabrication of HOM RF absorber assemblies. This proposal outlines the synthesis and characterization of cold-sprayed metal-matrix composites for higher order mode beamline absorbers. This includes measuring the metallurgical, RF, vacuum and particulate generation properties of the composite material. The primary deliverable for this phase I will be a 50mmL x 80mm ID copper tube coated on this inside diameter with our RF absorbing composite. In Phase II, further optimization of the RF absorber will be conducted, and a complete HOM beamline absorber assembly based on our cold spray composite will be fabricated using in-house capabilities. Cold spray HOM absorbers could reduce the capital and operational costs associated with superconducting RF accelerators via low-costs RF absorbers and optimized cryogenic thermal management, respectively. This novel, low-temperature powder consolidation process enables the fabrication of non-equilibrium materials which have received significant interests for corrosion and wear applications. We are confident that these composite materials can be similarly engineered to have specific RF properties. If successful, this process could also be applied to high power microwave systems and radar-absorbing aerostructure.