The critical current density (J c ) of monofilament Cu/MgB 2 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, J c , was measured to be 0.83 × 10 4 A cm −2 at 3 T at 21 K and 0.66 × 10 4 A cm −2 at 8 T at 4.2 K for the MgB 2 sample, which was annealed at 700 • C for 30 min with 5.8 • C min −1 heating rate under 4% H 2 -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.

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