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Study of the Influence of Helical Bending Strain and Perpendicular Self-Field on Critical Current Degradation for Multilayer YBCO Tapes

An experimental investigation of the critical current (Ic) degradation of multilayer twisted yttrium barium copper oxide (YBCO) tapes in self-field was performed. The influence of the number of tape layers (N) and twist pitch (P) on critical current was researched. The results showed that the influence of helical bending strain and perpendicular self-field on critical current degradation was a comprehensive process. No critical current degradation was found when there was just one layer and the twist pitch was over 20 mm. However, the situation would change when the number of tape layers increased. The critical current degradation would increase with increase in helical bending strain or perpendicular self-field. The critical current degradation can reach a maximum of 24.6% when the helical bending strain was 0.23% and the number of tape layers was 5. A mathematic formula was set up to express the comprehensive influence of helical bending strain and perpendicular self-field on critical current degradation. The results can provide an important theoretical foundation for the application of high temperature superconducting tapes and the design of YBCO cables.