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Effect of conductor arrangement on critical current degradation of stack–parallel REBCO conductors at 77 K
Yojong Choi, Seunghyun Song, Myung Su Kim, Geonwoo Baek, Sangjun Oh, and Yeon Suk Choi

Multiple REBCO tapes are often assembled into stacked or parallel conductors to achieve high transport current capacity. However, the current-carrying capability of stack–parallel REBCO conductors cannot be estimated by simply multiplying the critical current of a single tape by the total number of tapes, because self-field effects and current redistribution cause nonuniform critical-current degradation inside the conductor. In this study, the critical current of stack–parallel REBCO conductors was calculated by considering the arrangement-dependent self-field degradation and current redistribution, and a fitting equation was proposed for practical critical-current estimation. The proposed fitting equation showed good agreement with the calculated results, with a mean absolute percentage error of 1.45%. Transient thermal analysis of terminal Joule heating was also performed to determine suitable test conditions under liquid nitrogen cooling, and the temperature rise was limited to less than 0.5 K at the selected current level. Experimental validation was conducted using stack–parallel REBCO conductors immersed in liquid nitrogen, and the measured critical currents and burn-out currents generally followed the calculated trend. These results indicate that the proposed calculation method and fitting equation can provide a practical reference for evaluating fabrication-induced degradation in stack–parallel REBCO conductors.

Keywords: Critical current, stack–parallel conductor, superconducting wire, thermal analysis, self-field effect, current redistribution