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Description
In-field current transport property is one of the most important properties of high Tc superconducting tapes for practical applications. Usually the current-voltage (I-V) characteristics or critical current (Ic) are characterized by the four probe transport measurement or magnetization measurement using a short piece sample. In a practical application, however, the piece length of the tape strands reach more than hundreds of meters or km scale. This indicates that the influence of positional variation of Ic should also be taken into account to describe the I-V characteristics in a real device. In fact, the characterization of spatial Ic variation attracts much attention as a quality control of the long length tapes. However, the relationship between the spatial Ic variation and the local- and/or global-I-V characteristics are not well established. In this study, we have succeeded in measuring in-field Ic variation as a function of longitudinal coordinate, x, in reel-to-reel manner under external magnetic fields up to 4 T at 77 K and 65 K, respectively. We also obtained position-dependent I-V characteristics by site specified transport measurements using the same sample. We proposed an analytical model to describe the position-dependent I-V characteristics based on the Ic(x) in the long length tape. It has been shown that the analytical expression shows good agreement with the position-dependent in-field transport measurements. Namely, this approach allows us to describe the I-V characteristics as function of B, T, and x including position dependent n-index and localized flux flow dissipation in the long length tape.
Acknowledgements: This work was supported by “JSPS KAKENHI (16H02334)”.