Production of Seamless Superconducting Radio Frequency Cavities from Ultra-Fine-Grained Niobium

75616B Superconducting radio frequency cavities, used in high energy accelerators, are produced by the sheet metal forming of multiple sections, which are then joined by high-vacuum, electron-beam welding. The welding procedures are very expensive and produce flaws and contamination that limit cavity performance. Simpler approaches, based on the shaping of seamless tubes, have been hindered by limited formability and performance-limiting surface roughness. This project will develop a technique for manufacturing superconducting radio frequency cavities from highly formable, seamless niobium tubes. The seamless tubes will be produced from billets of ultra-fine grained niobium processed by equal channel angular extrusion. In Phase I a novel billet processing method, equal channel angular extrusion, was used to refine the grain structure of bulk niobium. Analytical results revealed a significant improvement in this bulk material over the currently used sheet metal. In Phase II, the process will be scaled-up to process full size billets, produce 150 mm diameter seamless tubes, and produce and test full-scale superconducting radio frequency (SRF) cavities for the International Linear Collider (ILC). Commercial Applications and Other Benefits as described by the awardee: The demand for RRR niobium for SRF Cavities is expected to reach 1,000,000 pounds by 2012, at a cost approaching $250M for sheet metal, with another $150M or so for welding. The technology developed in this program should eliminate welding costs and offer a higher quality product at a substantial cost advantage. Sales could well approach a hundred million dollars for the International Linear Collider program alone. Lower cost, higher performance accelerators also would have applications in other fields: over 10,000 accelerators are now used worldwide for medical diagnostics, advanced materials characterization, communications, military devices, structural biology, pharmacology, and environmental studies.