Optimised stellarators with a positive radial electric field

TL;DR

This paper proposes a novel approach to stellarator design that uses optimized magnetic geometry to generate a positive radial electric field, potentially improving impurity control and energy confinement in fusion reactors.

Contribution

It demonstrates that recent advances in stellarator optimization enable creating a positive radial electric field, addressing impurity expulsion and turbulence suppression in fusion plasma.

Findings

Positive radial electric field can be achieved through magnetic geometry optimization.

Such electric fields can help expel impurities from plasma core.

Electric field sign change creates shear flow that may improve confinement.

Abstract

We draw attention to an interesting possibility in the design and operation of stellarator fusion reactors, which has hitherto been considered unrealistic under burning-plasma conditions. Thanks to recent advances in stellarator optimisation theory, it appears possible to create a positive (outward-pointing) radial electric field in the plasma core by carefully tailoring the geometry of the magnetic field. This electric field is likely to expel highly charged impurities from the centre of the plasma through neoclassical transport and thus eliminate, or at least mitigate, a long-standing problem in stellarator physics. Further out, the electric field is expected to suddenly change sign from positive to negative, thus creating a region of strongly sheared flow, which could locally suppress turbulent transport and enhance overall energy confinement.