Improved Internal-Tin Nb3Sn Conductors for ITER and Other Fusion Applications

In the near future, there will be an urgent need for large quantities of Nb3Sn superconductor for the International Thermonuclear Experimental Reactor (ITER), an experimental fusion device. However, the DOE has only a few domestically-located companies that are capable of supplying this need, and two of these are subsidiaries of European companies that have orders and commitments to the EU fusion program. Thus, there is a serious need for a U.S. company that can supply some of this superconductor. This project will demonstrate that a United States company can supply superconductor strands that meet toroidal-field specifications from production-size billets. In Phase I, several lengths of strand were made from two small billets, without any fabrication problems. The aim was to meet the specification for the central solenoid conductor, which has lower electrical loss and slightly lower critical current density. The material produced had a lower critical current density than required, but the reasons for this result were identified and are not thought to be insurmountable. Phase II will focus on reducing the distortion of the filaments, enlarging the billets, controlling the spacing-to-diameter ratio of the superconductor rods, and improving the critical current density. First, small billets will be fabricated to enable the process to be refined and modified to meet the toroidal-field specification. Afterwards, large billets will be fabricated to demonstrate the viability of a domestic strand supplier. Commercial Applications and other Benefits as described by the awardee: In addition to the fusion application, Nb3Sn superconductors should find use in open-area Magnetic Resonance Imaging (MRI), where the patient is more accessible to the surgeon. (MRI is the largest commercial application of low temperature superconductors.) There is also a need for this type of product in High Energy Physics research and in Nuclear Magnetic Resonance