Internal Tin ${\hbox {Nb}}_{3}{\hbox {Sn}}$ Conductors Engineered for Fusion and Particle Accelerator Applications

Abstract

The critical current density (Jc) of Nb3Sn strand has been significantly improved over the last several years. For most magnet applications, high Jc internal tin has displaced bronze process strand. The highest Jc values are obtained from distributed barrier strands. We have continued development of strands made with Nb-47 wt%Ti rods to supply the dopant, and have achieved Jc values of 3000 A/mm2 (12 T, 4.2 K). Such wires have very good higher field performance as well, reaching 1700 A/mm2 at 15 T. To reduce the effective filament diameter in these high Jc strands, the number of subelement rods incorporated into the final restack billet has been increased to 127 in routine production, and results are presented on experimental 217 stacks. A new re-extrusion technique for improving the monofilament shape is also described. For fusion applications such as ITER, we have developed single-barrier internal tin strands having non-Cu Jc values over 1100 A/mm2 (12 T, 4.2 K) with hysteresis losses less than 700 mJ/cm3 over non-Cu volume. The Jc-strain behavior of such composites is also presented.