Doping with hafnium to create pinning centers to refine A15 grain size in Nb3Sn conductors

This proposal is submitted in response to the SBIR/STTR High Energy Physics Topic 29(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. Currently Hyper Tech is developing very high performance Nb3Sn strands incorporating artificial pinning centers, using an internal oxidation approach. Our recent APC Nb3Sn wires with Ta and Zr doping demonstrated substantial grain refinement and strongly increased Jc,nonCu, while retaining the high Bc2 valuesof the best ternary Nb3Sn conductors. The non-Cu Jcs of these APC conductors has reached nearly 1500 A/mm2 at 16 T/4.2 K, which approaches the current CERN FCC spec. Their layer Jc reaches 4700 A/mm2 at 16 T/4.2 K -- more than double the present best ternary Nb3Sn conductors. However, at 1% Zr or more added Nb-Ta alloy may have limitation on the final filament size in the conductor when scaling up the billet size due to its fast work hardening and relatively low drawability. Hence, we want to keep searching for new alloys to refine A15 grains as the Zr alloy but have better drawability and could make 35 micros or finer filaments possible. Hf (Hafnium) is a good choice to investigate. In this Phase I, we will focus on involving Hf to our developed APC conductors. We will use HfO2 instead of ZrO2 to refine the A15 grains in Nb3Sn conductor. This approach will dope Hf on the original Nb- Ta alloy material. In this Phase I, we will select 2wt% Hf as the starting composition to not only demonstrate that artificial pinning can be generated in the Hf, Ta doped Nb3Sn strands, but that they can be generated with an approach that can be scaled to high field properties, and long length production (a scalable approach). In this Phase I, we will also make a conductor with filament size of 35 m which will demonstrate its good wire drawability. We will demonstrate long piece length with subelements of 35 m or less with high performance in a proposed follow-on Phase II.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.