Characterization of I_c Degradation in Bent YBCO Tapes

In this paper, the I_c degradation of bent YBCO tapes has been experimentally studied. The I_c characteristics in length direction was measured through a non-contact, continuous I_c measurement equipment (Mcorder), which is suitable for all kinds of high temperature superconducting (HTS) tapes. The detailed J_c mapping of bent tapes was investigated by a Hall microscopy equipment (Mcorder 2-D), which scans the fields distribution on the surface of the films or bulks. A 4.1-m-long YBCO tape was wound on a 4.5-mm-diameter core with YBCO face outside or inside. The critical current of the YBCO tape before and after winding was measured lengthwise. And the 2-D J_c map of the samples of degraded sections was measured. The result shows that the smallest safe bending diameter is larger than 14 mm and smaller than 4.5 mm, for YBCO face outside and inside, respectively, which indicates that the YBCO face is recommended to be inside in bending cases. The relation between critical current of YBCO face outside bent tapes and diameters was fitted to a sigmoid-like function, to help further development where YBCO face outside bending is unavoidable.