Abstract
The force-free helical reactor (FFHR) is a conceptual design of a heliotron fusion reactor being developed at the National Institute for Fusion Science. All the coils in the FFHR are made of superconductors. Several cooling schemes have been proposed for the helical coils; of these, indirect cooling is considered a good candidate. In this study, we investigated the possibility of using an indirect-cooled superconducting magnet for the FFHR. In parallel with this design study, we developed Nb3Sn superconductors, jacketed with an aluminum alloy, for use in an indirect-cooled magnet. The results of performance tests of a sub-scale superconductor showed good feasibility for application in the FFHR helical coil. Stress distribution in the helical coil was also analyzed, and the stress and strain were confirmed to be within the permissible range.
