Evaluation and Improvement of Uniformity in km-Class MgB2 Superconducting Wires

An 18-multifilamentary MgB2 wire, classified within the 250 m-class, was produced utilizing a technique to improve the uniformity of powder filling by employing three-dimensional vibrators. A comprehensive evaluation of the fabricated wire revealed that the uniformity of the critical current (I-c) and fill factor, determined through the coefficient of variation, were 2 and 4%, respectively, along the wire direction. Building upon this achievement, a scaled-up MgB2 wire was fabricated, with dimensions of approximately 3 km in length and 0.83 mm in diameter. At 20 K and 2 T, the I-c was measured to be 191 A. The corresponding critical current density (J(c)), determined to be 190,000 A/cm(2), represents a significant improvement when compared to that yielded by the conventional gravity-based powder filling method.