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The superconducting joint is one of key technologies to evolve high temperature superconducting (HTS) conductors and their applications. Various joint techniques have been proposed in these years [1]. To evaluate developed joint efficiently, we developed a resistance evaluation system for superconducting joints [2]. The system consists of a superconductor sample with a joint, a copper coil to inject (induce) current to the sample, and a superconducting magnet for external fields applied to the joint. Using this system, joint resistance (R$_j$) ranging 10$^{-15}$-10$^{-7}$ Ω can be quantitatively evaluated as a function of injected current (I$_i$$_n$) magnitude, temperature, and external magnetic field. In addition, I$_c$ and T$_c$ of the joint can be evaluated. In this paper, we report the evaluation results of the REBCO superconducting joint [3]. At 4.2 K without external field, R$_j$ stayed ~10$^{-14}$ Ω at I$_i$$_n$ up to ~300 A. This indicates that the I$_c$ of the joint is sufficiently larger than 300 A. At 77 K, I$_i$$_n$ of ~150 A rapidly decreased to ~116 A and evaluated R$_j$ was ~10$^{-12}$ Ω. This higher R$_j$ is considered to be due to a high load factor of ~100% at the joint. R$_j$ at 4.2 K showed almost no dependence on external field ranging 0 ≤ B ≤ 3 T. Even at 77 K and 3 T, the junction carried I$_c$ of ~17 A and R$_j$ was ~10$^{-12}$ Ω. This work is based on results obtained from a project commissioned by JST-Mirai Program Grant Number JPMJMI17A2, Japan.
[1] G. D. Brittles et al., Supercond. Sci. Technol. 28, 093001 (2015).
[2] K. Kobayashi et al., IEEE Trans. Appl. Supercond. 30, 9000204 (2020).
[3] K. Ohki et al., Supercond. Sci. Technol. 30, 115017 (2017).
