High critical current of Cu-sheathed MgB2 wire at 20 K

For large-scale electric power applications of MgB₂ wire, especially at AC environments, development of nonmagnetic sheath material is essential. In this study, Cu-sheathed MgB₂ wire was fabricated using the powder-in-tube method and ultra-fine Mg and B precursor prepared by high-energy ball milling. Lowering the annealing temperature and shortening the annealing time effectively limit the reaction between Mg and Cu. Critical current density of the wire annealed at 700°C for 5 minutes is 4.3×10⁴ A/cm² at 20 K and self-field. Adding excess Mg in precursor further enhances critical current to 250 A at 20 K and self-field. These results demonstrate the potential of Cu-sheathed MgB₂ wires for large-scale applications.