Transport properties of multifilament MgB 2 long wires and coils prepared by an internal Mg diffusion process

We fabricated a 78 m long six-filament MgB 2 wire using an internal magnesium diffusion (IMD) method. The microstructure and transport performance of this six-filament IMD wire were investigated. Layer J c values as high as 5 × 10 4 A cm −2 at 4.2 K and 10 T are obtained for short samples cut from this long wire. In order to investigate the uniformity and application potential of this long wire produced by an IMD technique, we made two solenoid coils by a wind-and-react method using two wires of 26 m in length cut from this long wire. One coil exhibited J c of 4.5 × 10 4 A cm −2 at 10 T and 4.2 K, which is similar to the short samples. Another coil generated a central field of B o = 1.67 T and a maximum magnetic field of B m = 1.8 T at zero external field. These results demonstrate that the 78 m long multi-filamentary wire has sufficient longitudinal homogeneity for designing MgB 2 coils.