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Description
The spherical tokamak (ST), characterized by its low aspect ratio and compact geometry, necessitates a toroidal filed (TF) coil design that typically adopts a sharper D-shape profile. This design is distinguished by its slender and tall configuration with a reduced radius of curvature, which can result in localized magnetic field and stress concentration on coils. Furthermore, the incorporation of a straight segment in the Princeton-D shape presents challenges in applying winding tension, particularly for high-temperature superconducting (HTS) TF coils fabricated from HTS tapes. To address these issues, a novel method for optimizing the TF coil shape in the ST is proposed. First, a semi-analytical code for calculating the magnetic field and the ratio of input current to the critical current on TF coils is developed. Next, a simplified analytical expression is derived to quantify the stress induced by both winding tension and electromagnetic forces. Finally, a genetic algorithm is employed to iteratively refine the coil shape, aiming to minimize the stress and the ratio of input current to the critical current, while ensuring the magnetic field and facilitating the winding process. This method is implemented in the design of the TF coil for the CTRFR-1 spherical tokamak, and its validity is rigorously assessed through comparative analysis with finite element simulations.
