Effects of interface angle, added powder and applied deformation on the transport current and structure of scarf joints of single- and multi-core unreacted MgB2 wires

The effects of the interface angle and applied deformation on the transport current and structure of scarf architecture joints between single- and multi-core MgB2 wires are studied in this paper. The transport currents of the joints were measured at 4.2 K, external magnetic fields of 2–8 T, and joint’s resistances between 27 and 42 K. Resistive transitions and critical currents of the prepared joints were compared with the transition and critical current of the unjointed MgB2 wires. The interface structure of joined in situ wires was analysed using optical microscopy. Increasing the interface area between the joined wires and optimizing deformation by pressing allows to enlarge the superconducting current path. In-field transport currents of up to 73% of wire’s Ic were measured for joined single-core MgB2/Fe wires. In the case of six-filament wires, the maximal transport current up to 53% of wire’s Ic was reached. The results show that the presented joint technique could potentially be used for superconducting MgB2 coils in a persistent mode.