Development of a 30 m long Nb3Al superconducting conductor jacketed with a round-in-square type stainless steel conduit for the toroidal field coils in JT-60SC

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]