Persistent MgB₂ joints for react and wind magnets

Ultra-low resistance joints are a key technology enabling superconducting magnets to operate in persistent mode and to achieve the temporal stability required for nuclear magnetic resonance and magnetic resonance imaging (MRI) applications. High performance superconducting joints are manufactured routinely for Nb-Ti and Nb3Sn magnets, but technologies for joining other technological superconductors are still in the early stages of development. Here we report the use of a simple cold pressing and heat treatment procedure to fabricate persistent MgB2 joints with resistance values <10(-12) Omega between MgB2 wires that have already undergone the full wire reaction process. Trapped persistent currents of 172 A and 160 A were achieved under self-field and 1 T background field conditions respectively at a temperature of 20 K. This corresponds to a critical current ratio of 78% under these conditions, outperforming previously reported joints using fully reacted MgB2 wire. These findings are relevant for the development of commercial MRI magnets with MgB2 wires utilizing react and wind methods.