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The modification of JT-60 was programmed to be a superconducting tokamak (JT-60SC) that has superconducting toroidal field (TF) and poloidal field coils. The Nb3Al superconductor was developed in order to apply to the TF coil system in JT-60SC. The TF coil conductor was designed with a cable-in-conduit (CIC) type. This conductor was Nb3Al cable jacketed into stainless steel (SS) conduit. As the first step of SS conduit production, the 10 m long round-in-square type tubes were successfully fabricated within eccentricity tolerance of the tube hole (<10%). A 30 m SS conduit was made of three units of 10 m long tubes, which were butt-welded in series. After the welding process, penetrating beads were observed by CCD camera, and it was visually clear that the penetrating beads were successfully controlled by adjustment of back-shielding gas pressure. Therefore, regarding the production of SS conduit, the procedures of fabrication and inspection were established. Then, the inserting of cable into this conduit and compaction were also carried out. Consequently, the 30 m Nb3Al CIC conductor was successfully fabricated, so that a feasibility of mass-producing CIC conductor applied to the real machine was obtained. [Copyright &y& Elsevier]

In the framework of ITER-EDA, a 13 T–46 kA Nb3Al conductor with stainless steel jacket has been developed in order to demonstrate applicability of an Nb3Al conductor with react-and-wind technique to ITER-TF coils. Using a 3.5 m sample consisting of a pair of conductors with 0% and 0.4% bending strain, the critical current performances of the Nb3Al conductors were studied to verify that the conductor achieves the expected performance and the bending strain of 0.4% does not originate degradation. The critical currents were measured at background magnetic fields of 7, 9, 10 and 11 T at temperatures from 6 to 9 K. The expected critical currents were evaluated taking into account the variation of the strain in the cross-section due to the bending strain as well as self-field and non-uniform current distribution as results of an imbalance in the joint resistance and inductances. The calculation results indicate that the current distribution is almost uniform and the experimental results showed good agreement with the expected critical currents. Accordingly, we can conclude that the fabrication process of this conductor is appropriate and the react-and-wind technique using the Nb3Al conductor is applicable to ITER-TF coils. In addition, the critical current of the Nb3Al conductor is expected to be 108 kA at 13 T and 4.5 K, resulting in a sufficient margin against the nominal current of 46 kA. Furthermore, it was found that the decrease in the critical current by thermal strain can be made small by applying the bending strain to the conductor so as to reduce the compressive strain at higher fields, i.e. inner side of the coil, in the conductor cross-section. [Copyright &y& Elsevier]