Experimental Investigation of Complex Bending-Effect on Superconducting Characteristic of YBCO Tape Applied to Force-Balanced-Coil for Superconducting Magnetic Energy Storage Device

In order to minimize the weight of support structures for superconducting magnetic energy storage with relatively large storage capacity, the coil for the storage device is designed based on the virial limit, in which the hoop stress is well optimized but flatwise (FW) and edgewise (EW) bending strains would be applied when we use YBCO thin tape to construct the coil. The complex bending strains supposed to be applied to the tape are experimentally investigated by using newly developed complex bending testing device and sets of strain gauges. Even in the range of the presumed bending radius and tensile stress for the coil winding, several combinations of FW, EW bending, and tensile stress cause specific deterioration of superconducting characteristics. The Rosette analysis by using tri-axial strain gauge revealed that the extremely high shear strain would be in relation to the deterioration. This work will help developing a winding technique without any degradation of superconducting characteristics such as critical current and n value of the fragile material.