From CS and TF model coils to ITER: Lessons learnt and further progress

Central Solenoid (CS) and Toroidal Field (TF) model coils have been developed in order to establish technologies required to the ITER magnets. All of the development goals have been achieved, including the operation at 13 T, 46 kA and pulsed charging at 1.2 T/s in the CS model coil and the stable operation at 10 T, 80 kA under the ITER relevant stress condition in the TF model coil. Based on these results, further activities are now being performed, in extensive collaboration with industry, to optimize coil designs, to improve performances and to mitigate technical risks during the manufacture of the ITER magnets. One of the activities is to establish production capability of Nb3Sn strands having higher critical current density which was redesigned based on the detailed assessment of the conductor performance in the model coil experiments. Strands fulfilling the ITER requirement have successfully been obtained. Another set of activities are full scale manufacturing demonstrations on jacket material for CS and structural materials for TF coil. So far, large forged blocks of JJ1 and ST316LN and thick hot rolled plates of ST316LN were successfully produced as a trial fabrication for the TF coil structures. Experience in the TF model coil indicated a need to improve manufacturing processes for radial plate and a significant progress has also been obtained in this area. Achievements from these activities will provide a firm technical basis for ITER magnet construction including that for industry.