Experiments of Bending Strain on Reduced-Scale HTS Conductors for Fusion Energy Reactors

High-temperature superconductors (HTS) are considered as a competitive candidate to be used for the heliotron-type fusion energy reactor FFHR. In order to confirm the bending strain behavior of large-scale HTS conductors, degradation of critical currents by bending strain has been examined in liquid nitrogen (at 77 K) for several samples. The experiment started with two types of reduced-scale conductors with four YBCO tapes, one with copper and YBCO tapes distributed uniformly (Type-A) and the other with YBCO concentrated at the center (Type-B). In order to reconstruct the obtained results, another series of experiment were done by bending a single YBCO tape in two forms: soldered on to a single copper tape and embedded in a copper jacket. We found that even the bending strain of 0.5% defined for the whole conductor thickness should not be a problem from the viewpoint of critical current degradation if we adopt Type-B design with HTS tapes located at the center of the conductor.