Development of composite flexible Nb3Sn cables suitable for the react-then-wind approach

This effort introduces the possibility of applying the react-then-wind approach to the construction of large magnet modules by using flexible reacted Nb3Sn cables. The key to the flexibility is that the strands are transposed by twisting, small in diameter, and free from bonds to other strands. Flexible, reacted subcables were made by; 1) cabling of reacted strands, and 2) controlled heat treatment of unreacted cables. The J(c) of these cables, after bending, showed no degradation over the J(c) of the undeformed single strands. Composite flexible cables of Nb3Sn and Cu strands were fabricated eliminating the need for a tin diffusion barrier and Cr plating of the strands. In addition to numerous advantages in the cost and engineering, flexible cables using fine strand appear to provide better stability than conventional cables.