Internal-Tin Nb/Sn Strand with Enhanced Ti Additions aimed at 17 T optimization

The DOE needs improved superconductors to support the high-field-magnet requirements of high energy particle accelerators. The immediate focus is the Large Hadron Collider (LHC) luminosity upgrade in the form of interaction-region quadrupole magnets, which require an evolutionary increase in field-at-windings to more than 15 T. To address this need, this project will develop a high-performance Nb3Sn strand with improved stability. The strand will combine high critical current density (Jc) and high upper critical field (Bc2) with manageable levels of magnetization and stability. Ti and Ta additions to the binary Nb3Sn will serve to increase Bc2 and hence the high-field Jc. The Ti addition will flatten the Jc vs B curve, leading to strands with reduced low-field Jc and hence improved stability during ramp-up to high field. In Phase I, two internal-Sn type billets were designed and processed: one with added Ti only and one with both Ti and Ta. Jc values of 1000 A/mm2 were obtained at 15T, 4.2K. Phase II will optimize the production process, leading to one 7" OD billet of selected design. The development will be accompanied by detailed characterization studies, followed by the production of many kilometers of strand suitable for cabling and coil winding. Commercial Applications and other Benefits as described by the awardee: The new superconducting strand should be applicable to the large market for accelerator and fusion magnets. The largest commercial market would be for clinical MRI systems above 7T. High field magnets (over 7 tesla) also should find use in NMR, high gradient magnetic separation, and superconducting magnetic energy storage (SMES) applications