Field dependence of the critical current density of MgB2/Cu wire for coil development

The critical current density (Jc) of monofilament Cu/MgB2 wire was measured between 4.2 and 30 K with a variable temperature insert (VTI) in a 20 T superconducting magnet using the DC pulse four-wire method with a 1 µV cm−1 criterion. The critical current density, Jc, was measured to be 0.83 × 104 A cm−2 at 3 T at 21 K and 0.66 × 104 A cm−2 at 8 T at 4.2 K for the MgB2 sample, which was annealed at 700 °C for 30 min with 5.8 °C min−1 heating rate under 4% H2–Ar gas flow. Scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and x-ray diffraction (XRD) analysis were used to characterize the microstructure of the samples.