Working group report on superconducting magnet for fusion DEMO

Important development issues for fusion DEMO superconducting coil are increasing the magnetic field and current of conductor, as well as increasing the strength of the winding coil structure, cooling structure, and support structure. It is important to promote the development of high-temperature superconducting wire while making compete the improvement of the mechanical properties of Nb₃Sn conductor and the development of high performance Nb₃Al conductor. The most important items to be accelerated are the development of high-strength low-temperature steel and the study for rationalization of the manufacturing cost of the large toroidal magnetic field coil. The provisional values of development target are ever-experienced maximum magnetic field of 15-16T, conductor current value of 100 kA, and demonstration via model coil of full scale size is indispensable for confirmation of superconducting coil performance. Prior to actual machine fabrication, it is necessary to have completed the development of conductor, structural materials, and insulating materials. In addition, to evaluate the superconducting characteristics at 15-16 T and 100 kA, a conductor test method to evaluate the performance degradation due to the electromagnetic force should have been established. At the same time, it should have been examined to fabricate a central solenoid model coil for DEMO in advance, which is to be used as a conductor test device. (A.O.)