Helical reactor design FFHR-d1 and c1 for steady-state DEMO

•More than 10 years’ operation is feasible using the inboard WC shield, where the total TBR is 1.18 with 90% 6Li.•The divertor targets can be efficiently shielded, expanding the range of material choice (e.g., Cu alloys).•Flinabe blanket mixed with metal powder is proposed to increase hydrogen solubility and thermal efficiency.•Helical coils by connecting segments of 100 kA-class YBCO high-temperature superconductors is proposed.•A multi-path strategy on FFHR-d1 is introduced with sub-ignition options for “before demo, compact and component-test”.

NIFS launched the Fusion Engineering Research Project (FERP) in preparation for DEMO by starting the redesign of the LHD-type helical reactor FFHR-d1. In the first round, the main parameters were selected. The second round is preparing detailed three-dimensional (3D) design of the superconducting magnet support structures, and 3D neutronics analyses, where the diverter targets can be efficiently shielded from fast neutrons. A new Flinabe blanket mixed with metal powder was proposed. Fabrication of helical coils by connecting half-helical-pitch segments of 100 kA-class YBCO high-temperature superconductors is proposed as a promising method. Also in progress is improvement of the first round of the core plasma design, ignition start-up analyses, and fueling scenario. As a consequence, a multi-path strategy on FFHR-d1 has been introduced with versions of -d1A, -d1B, and -d1C, where design flexibility is expanded to include subignition with options FFHR-c1 for “before demo, compact, and component-test.”