Superconducting wires are widely used for instance in NMR (Nuclear Magnetic Resonance) devices and MRI (Magnetic Resonance Imaging) devices. Rare earth-based high-temperature superconducting wires (REBCO superconducting wires) have been produced in recent years, and research and development is being conducted in which such superconducting wires are utilized.
Joining of superconducting wires to each other is an essential technical issue with a view for instance to achieving longer wires and realizing a persistent current mode. Low-resistance connection between REBCO superconducting wires is conventionally accomplished by soldering; as is known, however, electrical resistance values of about 10−8Ω are incurred in this technique.
Research has been carried out in recent years for directly joining REBCO superconducting wires to each other. PTL 1 proposes a technique relying on a melt diffusion method. In this technique, the protective layers of two REBCO superconducting wires are removed, and the wires are heated up to the melting point of superconducting layers, while causing the superconducting layers to abut each other and while applying pressure to the latter; thereby, part of the abutting superconducting layers in the thickness direction undergoes melt diffusion, and the superconducting wires become joined to each other as a result. PTL 1 reports that the REBCO superconducting wires can be connected to each other with yet lower resistance than is the case when the wires are joined by soldering.