Superconducting Joints Between ${\hbox {MgB}}_{2}$ Wires and Bulks

In many superconducting applications the feasibility of a persistent mode operation is a prerequisite of acceptance of the superconducting solution. Regarding the High Temperature Superconducting oxides, this persistency is obtained only for the bulks and, when realized for large samples as for the BSCCO-2212 material, allows the transport of very limited superconducting currents, with densities of the order of some kA/cm². Instead we were able to maintain in a MgB, ring a persistent current corresponding to several tens of kA/cm². Designing large superconducting systems, based either on wires or on the bulk materials, as the magnets for MRI or for magnetic separation it will be important to realize persistent superconducting joints between the parts, allowing to sustain the high currents needed for these power applications. In the framework of the MgB₂ material development and using the liquid Mg infiltration technique, we have explored the possibility to join wires with bulks and bulks between themselves. The persistency of the joints has been verified by the measurement of the levitation forces of the superconducting system in presence of a permanent magnet and by direct transport current measurements. How to apply the joining technique to the magnet manufacturing is presented.