Stellarator Coil Optimization Supporting Multiple Magnetic Configurations

Effective and efficient stellarator optimization is of great interest to the nuclear fusion community. Our goal in this work is to develop techniques that can be used to design devices capable of supporting multiple magnetic configurations. We utilize PyPlasmaOpt, a Python package that couples coil and vacuum field optimization, as our base software. Our primary methods for adding flexibility to the coil design are adjusting the currents in the modular coils and adding control coils to the device. We find that changing the currents in the modular coils without the addition of control coils leads to flexible stellarators with complex coil shapes and minute plasma volumes. Adding control coils introduces enough degrees of freedom to achieve multiple magnetic configurations, maintain reasonable coil shapes and low quasisymmetry error, and create larger plasma volumes. We add quadratic flux minimizing surfaces to the optimizations to increase the volumes further. Overall, we achieve greater flexibility by accounting for multiple magnetic configurations during the design.