Development of Nb3Sn superconducting wires for AC use

We have fabricated the powder-metallurgy (P/M) processed Nb3Sn superconducting wires as the first trial for the development of P/M processed Nb3Sn wires for AC use. The Nb content was chosen as small as 22.5wt% so as to avoid the appearance of interfilamentary coupling inside the wire. Nevertheless, the smallest effective diameter deffobtained in the present trial was 37μm, while the average diameter of Nb3Sn filaments was 1μm. The Critical current density Jc of filamentary region was 1.7×10⁹A/m²at 4.2K at 1T. A test coil with the coil length of 160mm, inner diameter of 34mm and outer diameter of 146.5mm was wound by a (3×7)- strand cable of P/M processed Nb3Sn wires in the wind and react method, and a pulse-mode operation was carried out. We have also fabricated the external diffusion (E/D) processed Nb3Sn multifilamentary wires to seek for another possibility for the development of Nb3Sn superconducting wires for AC uses. The wire diameter was 0.15mm, the filament diameter was 0.5μm, the number of filaments was 17935, and the twist pitch was 1mm. The overall critical current density was 1.8×10⁹A/m²at 4.2K and 2T, which is about 3 times larger than that of the corresponding NbTi multifilamentary wires. A test coil with the coil length of 50mm, inner diameter of 20mm and outer diameter 30.4mm was also wound by 3-strand cable of E/D processed Nb3Sn wires in the wind and react method, and 60Hz operation was carried out. The present trial indicates that the superior characteristics of Nb3Sn wires such as high temperature margin and large amplitude availability compared with NbTi wires could be the additional advantageous characteristics of further developed Nb3Sn wires for AC uses.