Novel Type of Aluminum-Alloy Jacketed Nb3Sn Superconductors Manufactured by Friction Stir Welding Technique

New process to compose a reacted Nb3Sn superconducting cable with aluminum-alloys has been developed by using friction stir welding (FSW) technique. The FSW joining process, which takes place in the solid phase below the melting point of the materials, has considerable advantages such as a high strength of welding zone and much lower distortion due to both small heat affects and reliable control of joining depth as compared with conventional welding method. In order to realize practical aluminum-alloy jacketed Nb3Sn superconductors, we have carried out elemental researches by using FSW technique. For a fabrication of aluminum-alloy jacketed Nb3Sn superconductor of a dimension 17 mm(w) x 4.9 mm(t) a Rutherford type superconducting cable having 18 reacted Nb3Sn strands of diameter 1.0 mm was assembled into a set of channel and fitting-covermade of aluminum-alloy A6061-T6 with filling material indium. Then, their joining parts were connected by using the FSW technique. The measurement on critical current (I-c) of the fabricated Nb3Sn superconductor achieved over 9.5 kA at 8 T, 4.26 Keven after bending with a radius of 150 mm in a flatwise direction, which showed no degradation in comparison with I-c values multiplied by number of strands in the cable. As the results, we succeeded in developing novel type of aluminum-alloy jacketed Nb3Sn superconductors manufactured by FSW technique, which have large current capacity, sufficient allowable bending strains for a coil winding and improved contact between a cable and an aluminum-alloy jacket. The developed superconductors will be applicable to react-and-wind superconducting magnets having very large current at high magnetic field such as nuclear fusion reactors and detectors for high energy physics of the next generation.