Evaluation of Joining Resistivity of Solder-Processed Face-to-Face Double-Stacked REBCO-Coated Conductors Under the Influence of Current Blocking Obstacles in the Tape Strands

During the fabrication of commercial REBa<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Cu<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub><italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> (REBCO; RE: rare-earth element)-coated conductors (CCs), inhomogeneities with low critical current (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>) are occasionally introduced, which may result in electromagnetic instability, particularly at low temperatures. To mitigate the degradation of the current carrying capabiity caused by these defects, we developed long face-to-face double-stacked (FFDS) CCs via reel-to-reel solder bonding process. Previously, we successfully fabricated 400-m-long FFDS CCs via this process and investigated their mechanical properties. However, the current transport properties are still unclear. In this study, we investigated the interfacial resistivity of the FFDS CCs made by the continuous soldering process, and it was confirmed that the joint resistivity is consistently between 40 to 50 nΩcm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> where the joint distances were changed to 3.5, 5.0, and 11.6 cm. In addition, the effect on the current carrying capability was also examined by using model samples in which we introduced artificial defects with almost 50% drop of local <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>. It has been demonstrated demonstrated that the transport current can be recovered at almost 85 to 90% of a defect-free CCs, with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> nearly two times of the strand, thanks to the current sharing effect through the solder joints. Namely, the interface resistivity of 40–50 nΩcm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> by our process was sufficiently small to obtain a current sharing effect and suppress the influence of the local inhomogeneity effectively.