Optimizing Particle Transport for Enhanced Confinement in Quasi-Isodynamic Stellarators

TL;DR

This paper uses gyrokinetic simulations to identify and address particle confinement issues in quasi-isodynamic stellarators, leading to a new optimized design with significantly improved energy confinement.

Contribution

It introduces a novel configuration with reduced mirror ratio that enhances particle confinement and turbulence suppression in quasi-isodynamic stellarators.

Findings

Nearly doubled energy confinement in the optimized design

Suppressed inward thermodiffusion due to magnetic geometry changes

Formation of strongly peaked density profiles

Abstract

Despite significant advances in reducing turbulent heat losses, modern quasi-isodynamic (QI) stellarators -- such as Stellaris -- continue to suffer from poor particle confinement, which fundamentally limits their overall performance. Using gyrokinetic simulations within the GENE--Tango framework, we identify suppressed inward thermodiffusion, caused by unfavorable magnetic geometry, as the primary cause. To overcome this limitation, we design a new configuration with a reduced mirror ratio, which enhances the contribution of passing electrons to the inward particle flux. This facilitates the formation of strongly peaked density profiles, suppresses turbulence, and leads to a substantial improvement in confinement. Our optimized configuration achieves nearly a twofold increase in energy confinement compared to Stellaris, highlighting the crucial role of optimizing particle transport in next-generation stellarator designs.