Extrusion of Tin Hole in Subelements for Internal-Tin Nb3Sn Superconductor

73042S03-I Nb3Sn superconductor is a key enabling technology that will determine the feasibility of high-energy hadron colliders for high energy physics research. However, the cost of Nb3Sn superconductor is ten times higher than that of other superconductors. The high cost comes not from materials, but from the necessity to fabricate the multi-filament wire in small batches. Batch size is limited by two key process steps: (1) wrapping a Ta diffusion barrier and a copper sheath around the wire subelement, and (2) boring a hole for a Sn core in the center of the subelement. Both steps must be done before drawing the subelement to its finished dimension. This project will develop an improved extrusion process in which the Sn hole is provided in the subelement by extruding over a tapered mandrel. It will then be possible to prepare long lengths of extruded subelement, and increase the billet size by a factor 20 for follow-on drawing. Phase I will develop a tapered mandrel for use on a commercial extruder, with provisions to preserve the internal configuration of the Nb rods within the subelement. Subelement billets, using Nb rods in the inner regions and dummy Fe rods in the outer regions, will be prepared. Extrusions will be performed, and the process will be optimized to maintain internal configuration. Finally, a billet will be extruded using all-Nb rods. Commercial Applications and Other Benefits as described by awardee: The current cost of Nb3Sn superconductor (~$1,000/kg) is prohibitive for most applications where it could be used to advantage. This technology should reduce the cost by a factor of about 2, bringing it into practical interest for the high-field magnets used for high-energy particle accelerators, magnetic confinement fusion, NMR spectroscopy in structural biology, MRI imaging systems, and magnetic levitation transportation.