Conceptual design of an indirect-cooled superconducting magnet for the LHD-type fusion reactor FFHR

The large helical device (LHD) has demonstrated that LHD-type reactors are well suited for steady-state power plants. This paper presents a conceptual design of the superconductor and coil for the LHD-type helical reactor (FFHR) superconducting magnet. The magnet of the FFHR consists of continuous windings with a large diameter, twisted configuration and large magnetic energy. The magnet system has a coil major radius of 14 m, magnetic energy of 120 GJ and maximum field of 13 T. We employ an aluminum-alloy jacketed Nb3Sn superconductor and indirect cooling using cooling panels inside the coil. The aluminum-alloy jacket, which has higher thermal conductivity than stainless steel, promotes elimination of steady-state nuclear heating. The cooling panels not only cool the coil indirectly, but also support the electromagnetic force. We have developed a sub-scale (10-kA class) superconductor and measured its current-carrying capacity.