The reactive Mg-liquid infiltration to obtain long superconducting MgB$_{2}$ cables

An alternative “in situ” process to the MgB2 wire manufacturing is represented by the Reactive Mg-Liquid Infiltration (Mg-RLI) process [1], in which the precursor wire is constituted by a metallic sheath encasing a central Mg rod, surrounded by the B powders. We demonstrated that this peculiar “internal Mg” assembly is able to produce very dense superconducting material of high critical current density, with an acceptable fill factor, up to 0.28. Furthermore the Mg-RLI allows also to easily dope the MgBB2 material either by carbon or nanoSiC powders. In order to realize long cables with this technique, two different approaches may be applied. The first one relies on the assembly of thin wires, fine enough that the liquid Mg cannot freely percolate along the wire during the reaction, and the second one relies on the assembly of thick hollow wires, reacted with a continuous supply of Mg to avoid deficiency of Mg in some part of the precursor wire. Both techniques have been demonstrated feasible and the relative usefulness is discussed. As far as the large superconducting magnets are concerned, either for future physics applications or for fusion reactors, it will be evident the great advantage of the low weight of the MgB2B wires, other than their good performances at intermediate high magnetic fields: typically of the order of 4T at temperatures of about 20K.