Development of Internal Tin Nb₃Sn Conductor for Fusion and Particle Accelerator Applications

Performance improvements are needed for large-scale applications of Nb3Sn, such as ITER or LHC upgrades. The highest critical current density (Jc) values are achieved in distributed-barrier strand made by the Restacked Rod Process, which can reach 12 T, 4.2 K Jcvalues of 3000 A/mm2, with high residual resistivity ratio (RRR) values. For purposes of accelerator magnet stability, it is desirable to combine high Jcwith a small effective filament diameter ( Deff) . Initial experiments show reducing Defffrom 80 mum to 40 mum leads to a 10% reduction in Jc. For fusion applications, a single-barrier design with well-spaced filaments is used to achieve the low hysteresis losses that are required. The status of our fusion strand development program is presented, including results for strand made using Nb-47 wt%Ti rods to supply Ti dopant. Such strands can reach 12 T, 4.2 K Jc> 1000 A/mm2, with losses3.