Helical Coil Optimization in DESC

We present novel results of quasisymmetric vacuum equilibria created from simple coilsets, consisting of only planar TF coils and helical coils lying on a circular torus winding surface. These results are obtained from improvements in helical coil optimization made in the DESC software code suite. A Python-based, automatic-differentiable version of REGCOIL has been developed and added to the DESC code, with improved capabilities for easily finding helically closed current potential contours, and for finding current potentials on the winding surface while accounting for coils external to the winding surface (such as planar TF coils). Engineering constraints such as maintaining a minimum coil-plasma distance, and choosing helical coils that best approximate the current potential under the constraint of carrying equal current, are also enforced during the design and optimization process.

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