Improvement in the transport critical current density and microstructure of isotopic MgB monofilament wires by optimizing the sintering temperature.

Superconducting wires are widely used in fabricating magnetic coils in fusion reactors. In consideration of the stability of B against neutron irradiation and lower induced radio-activation properties, MgB superconductor with B serving as boron source is an alternative candidate to be used in fusion reactor with severe irradiation environment. In present work, a batch of monofilament isotopic MgB wires with amorphous B powder as precursor were fabricated using powder-in-tube (PIT) process at different sintering temperature, and the evolution of their microstructure and corresponding superconducting properties was systemically investigated. Accordingly, the best transport critical current density (J) = 2 × 10 A/cm was obtained at 4.2 K and 5 T, which is even comparable to multi-filament MgB isotope wires reported in other work. Surprisingly, transport J vanished in our wire which was heat-treated at excessively high temperature (800 °C). Combined with microstructure observation, it was found that lots of big interconnected microcracks and voids that can isolate the MgB grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating MgB wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet.