Development of a Prototype Winding Machine for Helical Coils Using High-Temperature Superconducting Tapes

The force-balanced coil, which has a helical winding configuration, enables the reduction of electromagnetic forces. However, in the use of high-temperature superconducting (HTS) tapes, the in-plane curvature of helical coils may cause a decrease in the critical current due to the edgewise bending strain. The objective of this work is to establish the winding technique of helical coils without plastic deformations of HTS tapes, particularly YBCO coated conductors. The authors developed a prototype winding machine for HTS tapes and discussed the feasibility of the geodesic winding pitch, which can minimize the in-plane curvature variations. The assembly of the prototype winding machine has been finished. From the results of the test operation, the torsion control schemes based on the simultaneous four-spindle angle control system are visually confirmed. In order to estimate the applied edgewise bending strain due to the winding errors, the authors investigated the validity of a development view method of helical coils by using a flexible scale attached to the torus surface.