Winding angle optimization and testing of small-scale, non-planar, high-temperature superconducting stellarator coils

Abstract

We designed and constructed two non-planar coils with high-temperature superconductors (HTS) based on shapes from the Wendelstein 7-X stellarator. Tape track orientation of the HTS was optimized to reduce the coil size as much as possible while staying within the strain limits of the Gadolinium Barium Copper Oxide (GdBCO) superconductor. This resulted in average coil radii of 0.23 m and 0.48 m at strain limits of up 0.45 % to for the coil shapes that were chosen. The coils were produced by winding the GdBCO tapes onto 3D-printed plastic frames. We confirmed the integrity of the superconducting layer after winding by spatially resolved measurement of the critical current and by energizing the coils in liquid nitrogen. Coil 1 showed a resistance of 1.75 µΩ and did not have any critical current degradation, while coil 5 had a resistance of 195 µΩ and showed only one dropout, attributable to a handling error. We measured the magnetic field of the coil with a 3-axis Hall probe system and found good agreement with predictions. This work demonstrates the manufacturing of small-scale, non-planar magnetic coils from commercially available HTS.