A review of critical current measurement methodologies for HTS: IEC 61788 standards and data analysis

The precise characterization of critical current, I_c is fundamental for the design and stable operation of large-scale high-temperature superconducting (HTS) applications, such as fusion magnets and power cables. However, unlike low-temperature superconductors (LTS), HTS materials exhibit complex voltage-current characteristics governed by thermal fluctuations and flux creep, leading to significant measurement uncertainties. This paper provides a comprehensive review of the international standards for I_c measurement, specifically the IEC 61788 series, with a particular focus on the transition from Nb-based conductors to REBCO coated conductors (IEC 61788-26). The theoretical background of the E-J power law model is analyzed and various definition criteria of critical current are evaluated to highlight the engineering implications of criterion dependency. Furthermore, key technical requirements for reproducible data, such as atmospheric pressure correction and current transfer length, are discussed in detail. Finally, this paper addresses the engineering gap between standardized short-sample tests and actual magnet performance, examining critical issues including screening currents, self-field effects, and mechanical stress in large-scale systems.