The authors have fabricated a novel MgB2 superconducting wire using the in-situ powder-in-tube method with fine boron powder (0.25 μm) and coarse magnesium powder (150 μm). The core of the wire has a fibrous structure consisting of numerous discontinuous MgB2 filaments. The critical current density Jc increases as wire size decreases, and the Jc of a 1.00 mm wire is 1.4×104 A/cm2 at a temperature of 20 K in a magnetic field of 4 T.
