Progress in inhomogeneity of critical current and index n value measurements on HTS tapes using contact-free method

Abstract

The development of high temperature superconducting (HTS) tapes has recently made great progress, and Bi-based tapes (1 G) and YBCO coated conductor (2 G) are commercially fabricated with practical length. Application of HTS in electric power apparatuses made important achievement, various superconducting devices were demonstrated in grid, laying solid foundation for their commercialization. However, since their intrinsic microscopic defects such as weak-link, granularity, small second phase likely exist, critical current and index n value of the HTS tapes in practical length are impossible homogeneous, which have significant influences on safety, stability and efficiency of the HTS apparatuses. Therefore, critical current and index n value are two important parameters describing inhomogeneity of HTS tapes, thus two important indices for evaluating quality of practical long HTS tapes. This paper focuses on main progresses in inhomogeneity of critical current and index n value measurements on HTS tapes using contact-free methods. The statistical analytical methods evaluating the inhomogeneity of critical current and index n value are suggested. They can provide essential references for design and operation of HTS apparatuses.