Field dependence of the critical current density of MgB/sub 2/ conductors between 4.2 K and 30 K up to 20 T

The critical current density (J/sub c/) of the monofilament Monel/Fe/MgB/sub 2/ wire was measured between 4.2 K and 30 K with a Variable Temperature Insert (VTI) in a 20 T superconducting magnet using the analog DC pulse four-wire method with 1 /spl mu/v/cm criterion. The critical current density, J/sub c/ was measured to be 0.16/spl times/10/sup 5/ A/cm/sup 2/ at 4 T at 21 K for a MgB/sub 2/ sample which was annealed at 700/spl deg/C for 5 min and at 900/spl deg/C for 5 min under Ar gas flow. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis were used to characterize the microstructure of the samples.