Optimized superconducting MgB2 joint made by IMD technique

Abstract A novel type of superconducting joining technique has been introduced to join unreacted internal Mg diffusion (IMD) single-core MgB 2 wires. Our method is based on fabricating a small diameter joint mould obtained by deforming an Nb/Cu composite tube with a longitudinal semi-cylindrical Mg and B core into a thick round wire. The small diameter of the joint provided advantages such as rapid cooling, low resistance, and the unique core design inside the joint ensured a uniform MgB 2 phase formation. Scanning electron microscope analysis revealed that the IMD MgB 2 wires had excellent contact with the superconducting MgB 2 bulk material inside the joint. The joint resistance, calculated from the decay of the trapped magnetic field over time, is a quite low value of 6.44 × 10 −16 Ω at 20 K. The transport critical current ( I c ) of the joint is 62 A at 20 K under a self-magnetic field, and the n -value of the joint is 66 at 20 K under 1.5 T. The results showed that the I c of our joint can be determined precisely, regardless of whether the magnetic field is applied from low to high or from high to low value during I – V measurements.