Parametric Study for Low-Resistance Joint of REBCO Coated Conductor Tapes Using Ultrasonic Welding

Nowadays, although it is available to produce a 1-km-long coated conductor (CC) tape, it is still not sufficient in length to fabricate cables or coil windings. Therefore, a joint for long CC tapes having a low joint resistance is essential in fabricating coils, magnets, and power cables. Various techniques, such as soldering and diffusion joining have, been tried and reported. A practical and good joint for CC tapes should be cost effective and meet both purposes of electrical and mechanical connections with low contact resistance without critical current degradation. In this study, Cu-surround GdBCO CC tapes adopting a stainless steel substrate was joined by an ultrasonic welding (UW) method. The CC tapes were joined by splice joint with face-to-face configuration. In order to improve the electrical contact at the UW joined part, tip patterns of horn and anvil were varied, and their effects on joint characteristics were investigated. The critical current I-c and joint resistance R-j of the UW joined CC tapes were measured at 77 K and self-field.