Advancements in the Reactive Liquid Mg Infiltration Technique to Produce Long Superconducting MgB2 Tubular Wires

The possibility to manufacture superconducting MgB₂ wires, applying the reactive liquid Mg infiltration (RLI) process, was demonstrated several years ago, obtaining wires characterized by hollow cores. The short samples of these wires gave transport critical currents in line with the best powder in tube (PIT) wires produced by "in situ" technique. Nevertheless the extension of the RLI technology to long superconducting wires initially was prevented owing to difficulties in controlling the liquid magnesium dynamics during the reaction. Now we succeed in controlling the reaction and in the manufacturing wires or tubular long manufacts. For tubular manufacts having large diameter, of several millimetres, useful for current leads or relatively short resistive current limiters, the liquid Mg is also supplied continuously during the reaction, to refill completely the core of the tube. For thin wires, with diameter of the order of a millimetre or less, useful for magnets and racetrack winding and other filamentary manufacts, the movement of liquid Mg is counteracted by the liquid metal surface tension. Concerning the superconducting characteristics of the wires, we have explored some key variables effective on the quality of the crystalline MgB₂: they include the choice of the original Boron powders and the addition of doping elements.