2020/03/03 by Carlos Paz-Soldan · 1 citation
Physics and Astronomy · #physics.acc-ph #physics.plasm-ph
paper · pdf · doi:10.1017/s0022377820001208
arxiv created 2020/03/03 · arxiv updated 2020/10/28
The rapidly emerging technology of high-temperature superconductors (HTS) opens new opportunities for the development of non-planar non-insulated HTS magnets. This type of HTS magnet offers attractive features via its simplicity, robustness, and is well-suited for modest size steady-state applications such as a mid-scale stellarator. In non-planar coil applications the HTS tape may be subject to severe minor-axis bending strain (εbend), torsional strains (εtor) and transverse magnetic field components (B_⊥), all of which can limit the magnet operating space. A novel method of winding angle optimization is here presented to overcome these limitations. Essentially, this method: 1) calculates the peak εbend and B⊥ for arbitary winding angle along an input coil filamentary trajectory, 2) defines a cost function including both, and then 3) uses tensioned splines to define a winding angle that reduces εtor and optimizes the εbend and B_⊥ cost function. As strain limits are present even without B_⊥, this optimization is able to provide an assessment of the minimimum buildable size of an arbitrary non-planar non-insulating HTS coil. This optimization finds that for standard 4 mm wide HTS tapes the minimum size coils of the existing HSX, NCSX, and W7-X stellarator geometries are around 0.3 - 0.5 m in radius. For coils larger than this size, permitting a finite (yet tolerable) strain allows reduction of B_⊥. This enables a reduction of the HTS tape length required to achieve a given design magnetic field or equivalently an increase in the achievable magnetic field for fixed HTS tape length. The distinct considerations for optimizing a stellarator coilset to further ease compatibility with non-insulated HTS magnets are also discussed.