Spiral Bending Tests of Various REBCO Wires for Development of High-Temperature Superconducting Assembled Conductors

The development of next-generation high-tempe- rature superconducting equipment using the cold heat of liquid hydrogen is expected to achieve carbon neutrality. We have begun to develop small-diameter REBCO assembled conductors forliquid hydrogen cooled superconducting generators and small nuclear fusion magnets. First, the effect of spiral pitch on the strain of the superconducting layer and critical current (
Ic
) maintenance is examined. A spiral bending strain model is constructed and calculated, where the results show that the generated strain depends significantly on the wire substrate thickness and the effect of copper plating thickness is insignificant. The residual strain of the superconducting layer is an important parameter for calculating the
Ic
retention rate from strain, and the
Ic
retention rate calculated differs depending on the wire manufacturer. Spiral bending tests are performed on three types of wires with a former diameter of 4 mm from different manufacturers. Experimental results show the same trend as the calculation results. When selecting wires for use in an assembled conductor, not only the wire geometry, such as the substrate thickness, but also the residual strain of the superconducting layer must be prioritized.