Improvement in the transport critical current density and microstructure of isotopic Mg 11 B 2 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 11 B against neutron irradiation and lower induced radio-activation properties, MgB 2 superconductor with 11 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 Mg 11 B 2 wires with amorphous 11 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 c ) = 2 × 10 4 A/cm 2 was obtained at 4.2 K and 5 T, which is even comparable to multi-filament Mg 11 B 2 isotope wires reported in other work. Surprisingly, transport J c 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 2 grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating Mg 11 B 2 wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet.