Spherical tokamaks with outboard stellarator windings

Abstract

The possibility of adding stellarator features to the extremely compact configuration of a spherical tokamak (ST) is analysed. This is accomplished by introducing outboard stellarator windings (OSWs). Two types of OSW are studied, a classical stellarator type and a torsatron type, and both are shown to be effective. Numerical calculations are presented for a simplified model of the NSTX tokamak. Among the main potential advantages of using OSWs in a ST are the possibility of noninductive plasma startup or improved inductive operation caused by the existence of closed vacuum flux surfaces and an external rotational transform