High Current Density (Jc), Low A.C. Loss, Low Cost Internal-Tin Superconductors

70027 Although internal tin Nb3Sn superconductors have been shown to have current densities (Jc) close to the objectives of magnet designers for future particle accelerators, the AC losses and costs are too high. This project will combine the best features of the internal tin and modified jelly roll processes to reduce these losses and costs. In Phase I, multiple-barrier restacks were made from single-barrier material and Mono Element Internal Tin (MEIT) processed material, with and without internal fins. Each configuration was tested, and comparisons were made among them. In the material without fins, Jc was maintained, and the losses were significantly reduced¿but not to less than 40¿m as desired. The problem was that in the material containing Ti in the Sn core, strand breakage was experienced when the subelements were small, and the subelement material could not be reduced below 0.8mm. Material without Ti in the core was processed without breakage down to 0.17mm, even though it had Cu in the Sn. Based on these results, Phase II will process multiple-barrier subelement billets, both with and without fins, using NbTa 7.5wt% filaments with no Ti in the cores, and with thicker barriers and larger filaments than used in Phase I. A series of restacks, including ¿double stacked¿ arrays will be made and tested to determine the best combination of billet design and restack procedure. Once this has been determined with small billets, three larger billets will be made and processed to yield material that will be supplied to DOE for testing in magnets. Commercial Applications and Other Benefits as described by awardee: Applications for the technology include open area MRI (MRI is the largest commercial application of low temperature superconductors), small magnets for high field laboratory applications and NMR, and fusion and levitated transportation projects.