Structure and Magnetic Field Dependences of Joint Resistance in a Mechanical Joint of REBCO Tapes

Mechanical joints of rare-earth barium copper oxide (REBCO) tapes and stacked tape conductors have been investigated for segmented fabrication of high-temperature superconducting (HTS) magnets for future fusion reactors. To design the optimized joint, we need to predict joint resistance depending on operating conditions and the conductor's structure. The prediction method was proposed in our previous study, taking into account the model of contact resistance, resistance of constituent materials, and interfaces. However, that was just based on data of mechanical lap joints for one kind of REBCO tape and a magnetic field perpendicular to the tape. Therefore, in this paper, we first evaluated joint resistances in mechanical lap joints of Fujikura's and SuperPower's REBCO tapes as a function of temperature and magnetic field with different orientations. The results showed that the joint resistance significantly increased with an increase in magnetic field parallel to the tape at temperatures of 10 K and lower. In addition, the reduction rate of joint resistance for the SuperPower's tape with a decrease in temperature was lower than that for the Fujikura's tape. Based on experimental results for Fujikura's REBCO tapes with different field orientations, we modified the model of contact resistance. Further improvement of the prediction method is still needed for different stabilizer structures and a temperature range around 10 K.