"Fine grain Nb tube for SRF Cavities"

Superconducting radio frequency (SRF) cavities used in charged particle linear accelerators, are currently fabricated by deep drawing and welding high RRR pure niobium sheet. The sheet typically has a non-uniform and poorly textured microstructure which leads to excessive thinning, unpredictable cavity shape, inconsistent "spring-back", and rough surfaces during cavity manufacture. These factors limit linear accelerator performance and increase cavity manufacturing cost. Equal channel angular extrusion (ECAE) processing will be used to refine and homogenize the microstructure of Nb tube for subsequent hydroforming into SRF cavities. Careful selection of deformation and heat treatment conditions during the processing steps will give a microstructure with a fine and uniform grain size and favorable texture in the tube leading to improved deformability and lower manufacturing costs. Phase I work includes 1) developing equipment and procedures for ECAE processing of high RRR Nb tubing, 2) ECAE processing of tube, and 3) mechanical and microstructural characterization of fine grain Nb tube to assess quality for hydroforming into SRF cavities. Material property comparisons with commercial Nb sheet/tube will be used as a baseline for evaluating project success. Phase II work will include construction of a scaled up tool for ECAE processing of high RRR Nb tube, ECAE processing of 4-6 inch outside diameter Nb tubes, hydroforming of the ECAE processd tube into prototype SFR cavities, and operational testing of the prototype SRF cavities. Cavity manufacturing and performance experiments will assess the improvement in the fabricability and performance of the fine grain Nb tube compared with comparable cavities made from commercial Nb sheet and tube. 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 tube 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 approach used could be applicable to the fabrication of other tube materials including tantalum, titanium and zirconium.