Uniform transport performance of a 100 m-class multifilament MgB₂ wire fabricated by an internal Mg diffusion process

A 100 m long six-filament MgB₂ wire was successfully fabricated using an internal magnesium diffusion (IMD) process. We investigated the transport properties and the uniformity of this long multifilament IMD wire. The MgB₂ layer and the sub-filament region are regular, and the J _c values have a fairly homogenous distribution throughout the wire, suggesting that there were no obvious defects along the length of the wire. The uniformity problem of long multifilament IMD MgB₂ wires can be mitigated by optimizing the starting composite parameters, multifilament geometry, fabricating process and annealing conditions. A layer J _c as high as 1.2 × 10⁵ A cm^-2 at 4.2 K and 8 T was obtained, which was comparable with the highest reported value for a short multifilament IMD wire. The transport layer J _c, non-barrier J _c and J _e values are independent of the wire diameter. In addition, the analysis of the stress-strain characteristics and the n value of the IMD wire is also presented. These results indicate that the long multifilament IMD-processed MgB₂ superconducting wire is suitable for practical applications.