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This paper is the first to define a conceptual design of a fusion power complex with hydrogen storage capability in a superconducting magnet system using cryogenic hydrogen. The fusion power complex realizes a carbon-neutral society by combining a large-capacity power source of renewable energy with the flexibility of energy output. Therefore, the proposed design is positioned as one of the most important next-generation power sources.

The maintenance scheme in the compact helical fusion reactor, FFHR-c1, equipped with the liquid metal divertor, REVOLVER-D (Reactor-oriented Effectively VOLumetric VERtical Divertor) and the cartridge-type molten salt blankets, CARDISTRY-B (CARtridges Divided and InSerTed RadiallY − Blanket), is investigated. The magnetic configuration of the compact variant FFHR-c1 is similar to that of the Large Helical Device (LHD), while the device size is 2.8 times enlarged from LHD and a strong magnetic field strength of ∼8 T at the plasma center is adopted. The maintenance of the REVOLVER-D is simpler than that of the helical divertor with a complicated structure as seen in the LHD. In the REVOLVER-D, showers of molten tin are injected into the ergodic layer at 10 inner ports. To circulate the molten tin, 10 sets of the shower system including a liquid metal pump, ducts, a showerhead, a pool, and a heat exchanger, are installed. These can be replaced with simple up/down motions. The CARDISTRY-B consists of 320 tritium breeding blanket cartridges, which are toroidally segmented every two degrees. These cartridges are maintained by using heavy manipulators with a simple 4DOF motion at a constant toroidal angle.

Thermal properties of alkali bis(fluorosulfonyl)amides, MFSA (M = Li, K, Cs), have been investigated. Binary phase diagrams of LiFSA-KFSA, LiFSA-CsFSA and KFSA-CsFSA systems have been constructed. The eutectic point for the binary systems are 338 K at (xLi, xK) = (0.45, 0.55), 331 K at (xLi, xCs) = (0.40, 0.60) and 333 K at (xK, xCs) = (0.60, 0.40). The eutectic point for the ternary LiFSA-KFSA-CsFSA system is 309 K at a nearly equimolar composition. The electrochemical window of the LiFSA-KFSA at 348 K and LiFSA-KFSA-CsFSA at 325 K are as wide as 6.0 V with the cathode limit being lithium metal deposition. These new inorganic ionic liquids are highly promising for various electrochemical applications.

The Fusion Engineering Research Project (FERP) at the National Institute for Fusion Science (NIFS) is conducting conceptual design activities for the LHD-type helical fusion reactor FFHR-d1A. This paper newly defines two design options, 'basic' and 'challenging.' Conservative technologies, including those that will be demonstrated in ITER, are chosen in the basic option in which two helical coils are made of continuously wound cable-in-conduit superconductors of Nb3Sn strands, the divertor is composed of water-cooled tungsten monoblocks, and the blanket is composed of water-cooled ceramic breeders. In contrast, new ideas that would possibly be beneficial for making the reactor design more attractive are boldly included in the challenging option in which the helical coils are wound by connecting high-temperature REBCO superconductors using mechanical joints, the divertor is composed of a shower of molten tin jets, and the blanket is composed of molten salt FLiNaBe including Ti powers to increase hydrogen solubility. The main targets of the challenging option are early construction and easy maintenance of a large and three-dimensionally complicated helical structure, high thermal efficiency, and, in particular, realistic feasibility of the helical reactor.

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