Speakers
Description
National Institute for Fusion Science (NIFS) in Japan is considering about FFHR-d1 (Force Free Helical Reactor) for their future R&D project. Its magnet system will be needed a pair of helical typed coils with the major radius of 15.6 m. Since the maximum magnetic field on the helical coil of FFHR-d1 reaches 11.9 T, the NbTi cable is not applicable. The practical Nb3Sn cable was selected for the ITER (International Thermonuclear Experimental Reactor) project and it might be still one of candidate conductor for FFHR-d1 as well. However, the large helical coil shows 3 dimensional complex forming, it is strongly preferable to apply a React and Wind method for the coil winding. Recently, the STARS (Stacked Tapes Assembled in Rigid Structure) conductor fabricated using 2G-REBCO tapes is being investigated by a research group of NIFS and Tohoku University. The 2G-REBCO tape shows a large critical current density at 4.2 K, and also mechanically strong due to the hastelloy substrate. In addition, its thin tape shape may be good advantage to keep a small bending strain with flat-wise direction. In this paper, the RHQT(Rapid Heating/Quenching and Transformation)-processed Nb3Al tapes with 0.2 mm in thickness were fabricated, and their superconducting properties and microstructures were investigated. We propose the Nb3Al conductor as another candidate for FFHR-d1. It is well known that Nb3Al conductor shows an excellent strain tolerance and is promising very much for a React and Wind method for the coil winding. In addition, Cu stabilized long wire with over one kilometer length has already been made by NIMS (National Institute for Materials Science). We will report the transport critical current at 4.2 K of the 0.2 mm thick Nb3Al tape soldered on brass fixtures, which have different radius down to 15 mm. Maximum bending strain corresponds to 0.66% in this study.
