Development of Internal Tin ${\hbox{Nb}}_{3}{\hbox{Sn}}$ Conductor for Fusion and Particle Accelerator Applications

Performance improvements are needed for large-scale applications of Nb 3 Sn, such as ITER or LHC upgrades. The highest critical current density (J c ) values are achieved in distributed-barrier strand made by the Restacked Rod Process, which can reach 12 T, 4.2 K J c values of 3000 A/mm 2 , with high residual resistivity ratio (RRR) values. For purposes of accelerator magnet stability, it is desirable to combine high J c with a small effective filament diameter ( D eff ) . Initial experiments show reducing D eff from 80 mum to 40 mum leads to a 10% reduction in J c . 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 J c > 1000 A/mm 2 , with losses 3 .