(IT/2-1Rb) Technology Development for the Construction of ITER Superconducting Magnet System

K. Okuno1), H. Nakajima1), M. Sugimoto1), T. Isono1), K. Kawano1), N. Koizumi1), K. Hamada1), Y. Nunoya1), Y. Nabara1), K. Kitamura1), M. Oshikiri1), K. Takano1), F. Tsutsumi1)
1) Japan Atomic Energy Agency, Naka, Japan

Abstract.  Engineering basis of the ITER superconducting (SC) magnets has been established through the development of the CS model coil (13T, 46 kA) and TF model coil (10T, 80 kA) in the ITER EDA. Based on this achievement, Japan Atomic Energy Agency (JAEA) has started activities in order to further develop the magnet technologies to a full scale level for the ITER construction. In the model coil development, JAEA has developed two types of Nb3Sn strands: bronze process and internal tin process strands. The results of the model coil experiments, however, revealed a significant loss of superconducting performance in a cable-in-conduit conductor under operating conditions. In order to compensate the loss, new requirements have been specified for Nb3Sn strands, and a trial fabrication (about 0.1 ton each supplier) was performed in Japan. Critical current densities of 1,000 A/mm2 and 750 A/mm2 were obtained in the internal tin process strands and in the bronze process strands, respectively, both of which satisfied the ITER requirements (700 A/mm2 in bronze process, 800 A/mm2 in internal tin process). TF coil manufacture consists of three major processes: (1) winding pack manufacturing, (2) structure manufacturing, and (3) encasing of the winding pack and final machining. Detailed procedures and tooling requirements are being finalized for these processes through the studies with industries. Based on these studies, demonstration at full scale level is also being performed. The TF coil uses several kinds of cryogenic steels, depending on the requirements of the mechanical strength. At the highest stress area, grade JJ1 will be used, and at the second highest stress area, grade ST316LN (strengthened SS316LN with nitrogen content of more than 0.17%) will be used. Trial fabrications of these materials are under way to establish the manufacturing route of large scale materials and the manufacturing processes for machining and welding. Database of material properties will also be established in these trials. Yield strengths of the forgings of JJ1 and ST316LN were confirmed to exceed the required values of 1,000 MPa and 850 MPa, respectively. These activities are being performed in extensive collaboration with industries and will provide a firm technical basis to realize the required performance of the magnets while maintaining both planned schedule and cost.

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