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

The critical current density ( J(c)) 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 mu V cm(-1) 1 criterion. The critical current density, Jc, was measured to be 0.83 x 10(4) A cm(-2) at 3 T at 21 K and 0.66 x 10(4) A cm(-2) at 8 T at 4.2 K for the MgB2 sample, which was annealed at 700 degrees C for 30 min with 5.8 degrees 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.