Synopsis:Bronze-processed Nb 3 Sn wires have been used in practical applications of high-field magnets and large-scale magnets. Since the 1980s, Furukawa Electric Co., Ltd. has been developing and manufacturing many high-performance bronzeprocessed Nb 3 Sn wires. This paper describes our recent activity in development of the bronze-processed Nb 3 Sn wires. The non-Cu critical current density of the ITER-type strand was 1,150 A/mm 2 at 12 T and 4.2 K, which is 1.8 times higher than that of the ITER-CS model coil 15 years ago. High-strength Nb 3 Sn wires reinforced with Cu-Ni/Nb-Ti or Cu-Nb composites have been successfully fabricated for high-field magnets. Enhancements of the superconducting properties resulting from pre-bending effects were demonstrated with Cu-Nb reinforced Nb 3 Sn wires. Mass production of practical cables for JT-60SA CS coils have been completed in exact accordance with the specifications. In addition, experimental manufacture of ITER-CSJA1 cables was properly carried out. Furthermore, a novel type of aluminum-alloy jacketed Nb 3 Sn conductor has been developed using the friction stir welding (FSW) technique.

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The Cu-Nb/Nb 3 Sn wires have much higher superconducting properties under large mechanical stresses compared to conventional Cu/Nb 3 Sn wires. In the developments of the Cu-Nb/Nb 3 Sn Rutherford cables for 25 T cryogen-free superconducting magnet with Tohoku University, we succeeded in improving both superconducting performance and mechanical properties by prebending treatment using the React-and-Wind (R&W) method. Subsequently, we have made many prototypes of Cu-Nb/Nb 3 Sn wires that satisfy the properties required for various Nb 3 Sn coil applications. As a result, we established technologies related to Cu-Nb/Nb 3 Sn wires such as higher strength, higher critical current density, rectangular shape, enamel coating, thinner wires for small radius bending, and stranded cables. We also confirmed the effectiveness of Cu-Nb/Nb 3 Sn wires not only in the R&W method but also in the W&R method. This paper describes the development progress and future prospects of Cu-Nb/Nb 3 Sn wires.