Joint resistance characteristics in ultrasonic weld REBCO CC tapes at various temperatures and magnetic fields

In coil and magnet manufacturing that requires long length 2G coated conductor (CC) tapes, the development of joining methods for CC tapes with zero or low resistance is necessary. Nowadays, although it is said that CC tapes with around 1-km length were produced, it is still inadequate to produce cables and coil windings. Therefore, the development of a stable and reliable joint for long CC tapes having a low joint resistance (R j ) and the understanding of the magnetic field and temperature dependence of R j is essential in the design of high field magnets and coils. In this study, the characteristics of joint resistance in REBCO CC tapes jointed using ultrasonic welding (UW) method were experimentally evaluated in various temperatures and magnetic field. The CC joints were also fabricated by hybrid welding, which incorporates soldering to the UW joint. The magnetic field and temperature dependencies of joint resistance of both types CC joints were measured. The acquired results showed that the joint resistance decreased with a decrease of temperature, and increased slightly as magnetic field applied increased.