Research and development of superconducting helicoids

Superconducting helicoids, i.e., magnets with planar turns, are in the process of being developed. Their main advantages are: high mechanical rigidity, the possibility of current redistribution across the turn width in accordance with magnetic field value, and the possibility of utilizing superconductors in nontraditional forms different from the usual wires, cables, and tapes. In the future this possibility may be of special importance for utilizing high-temperature superconductors. Shortcomings of the superconducting helicoids are also mentioned. They are thermomagnetic instability and electrical losses, both resulting in charging rate limitations. The design and test results of model helicoids are presented: a NbTi coil with ID=180 mm OD=320 mm: a NbTi racetrack with large and short axes of 120 mm and 48 mm, respectively; and a Nb₃Sn coil with ID=46 mm, OD=120 mm. The racetrack winding without any bandages reached its critical parameters almost without training. The charging rate of the Nb₃Sn helicoid was much higher than that of NbTi coils. The total induction of the Nb₃Sn coil tested in a bias field was about 10.5 T