Development of a Robust Quasi-Poloidal Compact Stellarator

Abstract

A compact quasi-poloidally symmetric stellarator (QPS) plasma and coil configuration is described that has desirable physics properties and engineering feasibility with a very low aspect ratio plasma bounded by good magnetic flux surfaces both in vacuum and at β = 2%. The plasma is robust with respect to variations of pressure and the resulting bootstrap current, which leave the bounding flux surface approximately unchanged and thus reduce active positional control requirements. This configuration was developed by reconfiguring the QPS modular coils and applying a new computational method that maximizes the volume of good (integrable) vacuum flux surfaces as a measure of robustness. The stellarator plasma and coil design code STELLOPT is used to vary the coil geometry to determine the plasma geometry and profiles that optimize plasma performance with respect to neoclassical transport, infinite-n ballooning stability up to β = 2%, and coil engineering parameters. The normal component of the vacuum magnetic field is simultaneously minimized at the full-beta plasma boundary.