Development of high copper ratio Nb3Al strands for fusion magnets

A joint project was carried out between the Japan Atomic Energy Research institute (JAERI) and Hitachi Cable, Ltd, to develop long length Nb₃Al strands with a Cu ratio of 4 using the Jelly Roll process with the intention to fabricate a CICC (cable-in-conduit-conductor). The workability of the hydrostatically extruded multifilament rod proved to be very good, comparable that the formerly developed Jelly Roll processed Nb₃Al strands with Cu ratio 2. The strands with Cu ratio 4 show the same Jc 605 A/mm² at 12 T as that for the strands with Cu ratio 2. A CICC is formed through a drawing process. The inserted cables have the pattern of 3×3×3×3×4 with a first triplet composed of 2 Nb ₃Al strands and a Cu strand. The finished 5th stage cable is wrapped with SS304 tape, after which it if drawn inside a 1.9 mm thick SS316L tube to a void fraction of 38% as a demonstration of conductor fabrication feasibility