Optimum design of helical windings for a toroidal ℓ = 3 stellarator with large separatrix

Abstract

The paper presents the results of a detailed computational study of possible ℓ = 3 stellarator winding configurations in which the separatrix radius and position are maintained constant. It is shown that toroidal effects on both the rotational transform properties and the mechanical forces can be reduced by suitably modulating the winding pitch, which results in considerable savings in the required current and mechanical support. The existence of significant magnetic wells is demonstrated. The results generally favour the use of shallow rather than steep windings and fairly large aspect ratios.