We use the joint resistance evaluation system developed at NIMS, as shown in the figure above. We perform current decay measurements using a superconducting closed-loop sample. The sample is fabricated by connecting both ends of a high-temperature superconducting wire with a superconducting joint. Typical measurement results are shown in the figure below. When a magnetic field of 0.2 T is applied, since the loop current is lower than the current-carrying capacity of the joint, persistent current is observed. The resistance value is found to be sufficiently low. However, at 0.5 T, the loop current is higher than the current-carrying capacity. This results in the current decay and higher resistance.

We analyze the current decay and the joint characteristics, including the resistance value, using physical models for conventional superconducting materials. This study contributes not only to a fundamental understanding of superconducting joints but also to enabling reliable persistent-mode operation of high-temperature superconducting magnets.