Low-Temperature CVD Process Development for Forming Niobium Layers on Copper

Innovative process development is needed to reliably deposit high-quality superconducting niobium films possessing near-bulk niobium performance capabilities on the interior surface of less costly copper accelerator component structures such as cavities, complex couplers, and nosecones as an alternative to solid bulk niobium. Fabrication technologies for cost-effective high-Q, high-field, superconducting radio frequency (SRF) cavities are needed for the economic viability of future accelerator facilities. Extensive research is being conducted by the worldwide particle accelerator community to develop effective alternatives to bulk niobium, including the application of superconducting films on alternative lower-cost material cavity structures, such as copper and aluminum, possessing acceptable performance characteristics. Statement of how this problem or situation is being addressed: Ultramet, in collaboration with Cornell University’s SRF Group, continues to mature innovative SRF cavity/component fabrication techniques combining chemical vapor deposition (CVD) process technology and mandreling procedures that minimize many costly, time-consuming, and often performance-limiting fabrication steps currently used. What is to be done in Phase I? Enabling low temperature CVD film process technology will be developed to form niobium layers of moderate thickness on structural copper possessing material and performance properties comparable to bulk niobium materials. Process variables critical for material optimization, future process scaling, and accelerator cavity and component fabrication efforts will be identified. Commercial applications and other benefits: Ultramet’s CVD-based niobium SRF cavity and component fabrication processes are uniquely well-suited for the near-net-shape fabrication and coating of complex niobium accelerator component geometries that are difficult or impossible to form by conventional deep drawing, hydroforming, and spin-forming methods. The proposed research is a necessary step toward the commercial and scientific application of advanced accelerator component-forming technologies that will represent a significant technical milestone in developing reliable fabrication techniques for reproducible high-performance niobium-coated copper accelerator components offering substantial cost reductions for SRF programs worldwide. Key words: superconducting radio frequency (SRF) cavity, niobium, copper, chemical vapor deposition, high-energy physics, nuclear physics, accelerator