Study of YBCO Tape Non-Uniformity Based on the AC Loss and the Magnetic Field Distribution in Current Transport

The simplest models in calculations of AC losses in YBCO tapes assume a rectangular cross-section of the superconducting layer and a constant critical current density. Models that are more complex consider the critical current density depending on magnetic field and its orientation. In some AC loss experiments the observed deviation from theoretical predictions could be explained by a non-uniformity of the superconducting layer across the tape width. Therefore, we try to determine this non-uniformity from the measured distribution of magnetic field in the tape vicinity. The experimental profiles were compared with those calculated by a numerical method based on the critical state model, comprising non-uniformity in the superconductor properties or the layer thickness. This procedure requires less computation time then the model optimization for the purpose of agreement of AC loss calculations with experiments. From the series of magnetic field distributions calculated with different parameters of the critical current non-uniformity, the candidates exhibiting the best agreement with experimental observation have been selected. Practical use of this procedure in the evaluation of tape quality is discussed.