Improved Nb3Sn Strand with High Jc and High RRR and Low Effective Filament Diameter

This proposal is submitted in response to the SBIR/STTR High Energy Physics Solicitation Topic 33(a). The need is for strands that operate at a minimum of 15 Tesla (T) field, with preference for production scale ( & gt; 3 km continuous lengths) wire technologies at 15 to 25 T with reduced effective filament diameter, in particular to less than 30 micrometers, which at 1 mm wire diameter would require processing 547 filaments in the strand, while 217 filaments would be required at 0.7 mm wire OD. However, with presently available high Jc internal Sn strands in the 0.7 mm diameter, the filament sizes are too large (about 50 microns). Only Hyper Techs tubular type Nb3Sn type strands has demonstrated the potential of high filament counts (500 plus) to get the filament sizes in the 30-45 micron range of 1-1.5 mm diameter and even smaller for smaller diameter strands. So this Phase I and potential Phase II is to develop a strand requested and needed by national labs for Muon Collider and the CERN upgrade. In this project, our focus is on making high count restack with 547 subelements, 1.0-1.5 mm restack strand with RRR over 100. In our currently produced 547-subelement high count restack strands, the noncopper Jc at 12T-4.2K can exceed 2000 A/mm2 (Jc at 15T-4.2K to 1500 A/mm2) and the filament size could be reduced to 30 m at 1.0 mm strand and 45 m at 1.5 mm strand. In this project, we will focus on improving the strands non-copper Jc while maintain its high RRR. We will make round Nb filaments to form more Nb3Sn phase while keeping high RRR. We will optimize the Cu ratio in the restack strand to improve its cabling property for making into Rutherford Cable. This type of strand in Rutherford Cable form is desired for the CERN upgrade and as well as desired by Fermi Lab for Muon Collider project. During the potential Phase II, we will demonstrate the 1.5 mm diameter, 547 restack strands in piece lengths greater than 3 km, and provide to National Labs like Fermi Lab. Commercial Applications and Other Benefits: The success of this SBIR will lead to a fully stable strand with high Is and Js for DOE-HEP while demonstrating that the strand can be fabricated into a Rutherford cable without subelement breakage and merging for accelerator magnets that are used to understand high energy physics and various medical and industrial applications.