Hundred-meter-scale MgB2 multi-filament wires with Cu stabilizer fabricated by internal Mg diffusion process

The high stability and current carrying properties of multi-filament long wires are fundamental to applying MgB2 superconducting materials. To ensure the current carrying properties and enhance stability, we utilized the internal Mg diffusion (IMD) process to fabricate different structures of Cu-stabilized, hundred-meter-scale MgB2 wires: 7-filament, 6 + 1-filament, 12 + 7-filament, 18 + 1-filament, 30 + 7-filament, and 36 + 1-filament. We characterized both the current carrying properties and the three-dimensional structure of these wires. The experimental results reveal that the current carrying properties strongly correlate with the integrity of the Nb barrier layer. In the 7-filament wire, the intact Nb barrier layer prevents contamination of the MgB2 superconducting phase, leading to a critical current density (J c) of 4.16 × 105 A cm−2 at 4.2 K and 4 T. This study provides a foundation for the application of MgB2 superconducting wire.