Seamless Nb Tubes for SRF Cavities

Superconducting radio frequency (SRF) cavities used in charged particle linear accelerators, are currently fabricated by expensive deep drawing, welding, and geometry adjustment methods. The RRR pure niobium sheet used typically has a non-uniform and poorly textured microstructure which leads to inconsistent & quot;spring- back & quot; and rough surfaces after deep drawing. Seam welds are structural weak links and locations of operational hot spots, which limit linear accelerator performance. Severe plastic deformatioon (SPD) processing will be used to produce RRR Nb billets with fine-grains and a uniform microstructure to extrude into seamless tube for hydroforming into SRF cavity strings. Careful selection of the plastic strain route and heat treatment conditions during extrusion and subsequent processing steps will lead to a fine grain uniform microstructure with favorable texture in the tube, leading to improved hydroformability and overall lower SRF cavity manufacturing costs. Phase I work includes 1) SPD processing bulk RRR Nb, 2) transforming the microstrructure in RRR Nb tube for better hydroformability, 3) microstructure examination and mechanical testing of processed tube to assess quality for hydroforming into SRF cavities, and 4) design of procedures and scale-up equipment for Phase II. Phase II work will include construction of scale-up equipment for SPD processing bulk and tube RRR Nb, SPD processing prototype scale thin wall Nb tube, hydroforming the processd tube into prototype SFR cavities, and performance testing of the prototype SRF cavities. Cavity manufacturing and performance experiments will enable an evaluation of commercialization potential. A cost/benefit analysis will assess economic viability of the new technology. Commercial Applications and Other Benefits: The commercial application is to apply this technology to the production of Nb tubes for lower cost superconducting radio frequency cavities. Cabot, Wah Chang, Inc., and H.C. Starck, Inc. may be interested in using this technology for Nb tubular products. The processing approach could be applicable to the fabrication of other tube materials including tantalum, titanium and zirconium.