Development of a 13-T and 40-kA Nb3Al conductor for toroidal coils of fusion reactors

Since Nb3Al is less sensitive against strain than Nb3Sn, we can avoid degradation of the critical current performance due to strain, or any difficulties in the fabrication of the toroidal field (TF) coil, which originate as a result of sensitivity of the critical current of Nb3Sn on the strain. From 1986, therefore, the authors started the development of an Nb3Al strand aiming at the application in TF coils of fusion reactors. The high critical current performance, 600–700 A mm−2 at 12 T and 4.2 K, could then be achieved, which was as good as Nb3Sn. In addition, a large-current Nb3Al cable-in-conduit conductor will be tested, the critical current of this conductor was then evaluated to be 120 kA at 12 T and 4.2 K. These data demonstrate the applicability of the Nb3Al conductor to the ITER-TF coil. In addition, the 13-T and 40-kA class coil, Nb3Al insert coil, was tested to demonstrate the applicability of the Nb3Al conductor, with a react-and-wind technique, to the ITER-TF coil under the framework of the ITER-EDA. The fabrication of the Nb3Al strand for this coil is underway.