Equilibrium optimization of the Helios planar coil stellarator power plant

Thea Energy, Inc. has developed a preconceptual design for “Helios”, a fusion power plant based on the planar coil stellarator architecture. This paper presents the optimization process that resulted in a two-field-period, low aspect ratio, quasi-axisymmetric, planar coil stellarator with a tokamak-like X-point divertor as the design for Helios. Single-stage optimization tools were developed to efficiently compute free-boundary equilibria generated by planar coil sets. Novel optimization functions were implemented to target equilibria that confine fusion-born alpha particles, are nonlinearly stable at high pressure, and have a feasible divertor. This effort has yielded an attractive preconceptual design for Helios, and this paper reports how the equilibrium properties satisfy all of these high-level requirements for a fusion power plant. The process outlined here promises to yield further improvements on the design with continued optimization.