Preliminary engineering design of the first wall and X-point divertor of the Helios planar coil stellarator

“Helios” is a two-field-period, quasi-axisymmetric (“QA”) planar coil stellarator power plant that features a novel, toroidally-continuous, non-resonant X-point divertor isomorphic to that of a tokamak with resonant magnetic perturbations. This work describes the preconceptual mechanical and thermal design of a divertor, first wall, and impurity exhaust system for Helios. Toroidally-continuous tungsten-surfaced divertor targets and a central neutral compression dome are cooled by high-temperature helium to withstand a heat flux of 10 MW m −2 , which is maintained via a detached divertor operating regime. V-4Cr-4Ti vanadium alloy is presented as a structural material for coolant channels, due to its high temperatures limits and superior resistance to radiation embrittlement. Impurity exhaust is performed by turbomolecular pumps.