A Novel Way to Dope TI in Nb3Sn Conductor to Reduce A15 Grain Size and 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. Nb3Sn is still the primary superconductor being used for the CERN upgrade, 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/mm2at 16T-4.2K. The above target performance is much beyond the present state-of-the-art. There is a need for 40% improvement of Jc. A simple extrapolation and improvement of existing strand architectures will not be sufficient, a quantum improvement in performance andanevolutionary change in technology is required. We have been working on creating ternary artificial pinning centers (APC) for the tube type Nb3Sn strands which has successfully doubled the layer Jcs, with Bk up to 26.4 T, and we have made 61 restack wires with APC that have been drawn down to 0.25 mm with 25 m subelements. In this Phase II, we will confirm the new methods to make ternary APC wires by doping in the APC tube type Nb3Sn strands. We will continue to optimize the Ternary wire including the selection of precursors, the precursor (e.g., Sn/Cu/oxide) ratios, the I.D./O.D. of Nb-alloy tubes, the powder packing density and the powder quality, thereby increasing non-Cu Jc to 2100 A/mm2 at 15 T 4.2 k and 1600 A/mm2 at 16 T 4.2 k, which will be above the FCC specification. We will make higher count restack strand to get 35 µm filaments at 0.7 mm diameter strand. Commercial applications and other benefits: 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, determination of the age of materials through radiocarbon dating, the sterilizing of medical equipment and food products.