Nb3Sn conductor development for fusion and particle accelerator applications

Future large-scale applications of superconductors, such as ITER or possible LHC upgrades, will likely use Nb3Sn conductor. Although the strand requirements for fusion and particle accelerators do have some overlap, there are significant differences that may require a variety of manufacturing approaches. Oxford Instruments, Superconducting Technology (OI-ST) produces high performance Nb3Sn wire via several different "internal Sn" routes. Recently, research at OI-ST has produced strand made by the restacked rod process that has achieved 12 T, 4.2 K non-Cu critical current density (J(c)) values of 3000 A/mm(2). This high J(c) level was achieved by a combination of optimized Cu, Nb, and Sn ratios and improved heat treatment schedules. Similar conductors developed for high field use have shown engineering current density (J(E)) values well over 150 A/mm(2) at 23.5 T, 1.8 K. OI-ST is also involved with research for the High Energy Physics National Conductor Program. Results on distributed barrier internal Sn composites made entirely by hot extrusion are also described. This process is being developed for the production scale-up of internal tin Nb3Sn strand. Finally, the state of development of composites having low AC losses will be described. Such conductors are being developed for possible future fusion applications.