CVD Process Development of Thin Film Triniobium-Tin for SRF Applications

Innovative fabrication technologies for cost-effective high-Q, high-field superconducting radio frequency (SRF) components are needed for the economic viability of future accelerator facilities. The worldwide particle accelerator community continues to investigate alternatives and performance-enhancing modifications to bulk niobium accelerator components via the application of superconducting films. DOE is interested in development of advanced process technologies to deposit superconducting materials such as triniobium-tin (Nb3Sn), which has the potential to exceed the performance capabilities of bulk niobium when formed on the interior surface of existing bulk niobium, or less costly copper, accelerator component structures, enabling substantial fabrication and operating cost reductions for continuous wave and high gradient accelerators. Ultramet, in collaboration with Cornell University’s SRF Group, will build on previous work by Cornell, CERN, JLAB, and others to develop techniques to create well-bonded layers of triniobium-tin on niobium, and potentially copper, substrates via Ultramet’s advanced chemical vapor deposition processing technologies. Chemical vapor deposition (CVD) thin film process technology using pre-alloyed niobium-tin precursor materials will be developed to form triniobium-tin layers on molybdenum substrates as a critical first step in developing CVD processes for Nb3Sn with a tin content of 24% for accelerator component applications. Material characterization including surface resistance and RF performance properties will be measured and results related to prior research. Process variables deemed critical for material optimization, future process scaling, and accelerator cavity and component fabrication efforts will be identified. Ultramet’s CVD-based processing to be developed in this project will represent a significant technical milestone in the surface application of the superconducting material Nb3Sn. The critical temperature of Nb3Sn is 18 K versus 9.2 K for niobium, making Nb3Sn far more efficient and allowing for higher temperature operation of SRF components, avoiding the need for expensive and complex superfluid/ subatmospheric helium operation to enable substantial cost reductions for SRF programs worldwide.