A Novel Way to Dope Ti in Nb3Sn Conductor to Reduce A15 Grain Size and Improve non-Cu Critical Current at High Fields

This proposal is submitted in response to the SBIR/STTR High Energy Physics Topic 26(a), “Superconductor Technologies for Particle Accelerators, (a) High-Field Superconducting Wire Technologies for Magnets”. Grant applications are sought to develop new or improved superconducting wire for high field magnets that operate at 16 Tesla (T) field and higher. The need is for strands that operate at 15 to 25 T. Nb3Sn is still the primary superconductor being used for the HL-LHC project, and is presently considered as the baseline superconductor for the Future Circular Collider (FCC) design study. The minimum target non-Cu Jc for a potential FCC should be greater than 1500 A/mm2 at 16T-4.2K and 2000 A/mm2 at 15T-4.2K. The above target performance is much beyond the present state-of-the-art. There is a need for a 40% improvement of Jc. Our current APC Nb3Sn wires with Ta and Zr doping gave Birrs and Bc2s of up to 28 T, meeting or exceeding those of the best ternary Nb3Sn conductors. The non-Cu Jc of these new Ta-doped APC conductors are above 1500 A/mm2 at 16 T/4.2 K, surpassing the target of the CERN FCC. For our record breaking non-Cu Jc performance of achieving over 1500 A/mm2 at 16T-4.2K, it is important to ensure proper strand performance under deformation, as well as overall conductor robustness, RRR, and long length uniformity. In this Phase IIA, we will focus on exploring strand design considerations aimed at increasing the strand RRR and deformation tolerance while scaling up billet size. One goal is the ability of the strand to undergo the standard Rutherford cabling process without significant degradation.Inthe Phase IIA we propose new ways to optimize this APC strand design including filament shapes and barrier material selection. We will demonstrate high Jc at high fields and long piece length with subelements of 45 m or less with high performance. The other commercial applications of this advanced Nb3Sn strands are high field 7-11T MRI, NMR systems, superconducting accelerators - protron radiation for cancer treatment, SMES, and high field magnetic separation. According to a U.S. EPA article, more than 97% of the 15,000 accelerators in use around the world have commercial applications, e.g. in the diagnosis and treatment of cancer, the locating of oil and minerals in the earth, the processing of semiconductor chips for computers, the determination of the age of materials through radiocarbon dating, the sterilizing of medical equipment and food products.