Development of Direct Joint Process Using Cu Stabilizing Layers of REBCO Tapes

One of the important issues in high temperature superconducting (HTS) power applications is the establishment of safe and highly reproducible connection technology. In the present study, we propose low-temperature solid phase joining technique to make direct joint of REBa ₂ Cu ₃ O _y (REBCO, RE:rare earth elements) tapes, as an alternative to conventional solder joining technique. In this technique, we directly join the copper stabilizing layer. The key point to make direct bonding is to remove the oxide layer on the copper surface and activate the surface. We use citric acids for this process. Subsequently, the bond between copper stabilizing layers is formed by applying pressure and heating. The heating temperature was set to 200 degrees, which prevents deterioration due to oxygen vacancies. Using this technique, we have succeeded in joining REBCO tape with their resistivity as low as 44-53 nΩcm ² , with high reproducibility. SEM-EDS analysis confirmed that Cu is directly bonded to each other without having impurities such as oxygen.