Geometry effects on zonal flow dynamics and turbulent transport in optimized stellarators

TL;DR

This study uses gyrokinetic simulations to show that optimized stellarators, especially quasi-helicalsymmetric and quasi-isodynamic types, exhibit significantly stronger suppression of turbulence and comparable confinement to tokamaks due to their geometry.

Contribution

It demonstrates how stellarator geometry influences zonal flow dynamics and turbulence suppression, highlighting the advantages of QH and QI configurations over QA stellarators and tokamaks.

Findings

QH and QI stellarators show greater turbulence suppression than QA stellarators and tokamaks.

Transport levels and confinement times in QH and QI are similar to tokamaks despite higher linear growth rates.

Zonal flow residuals and nonlinear frequencies are key factors in turbulence suppression.

Abstract

Global gyrokinetic simulations find a strong suppression of ion temperature gradient (ITG) turbulence by zonal flows in stellarators optimized for neoclassical transport. The reduction of the ITG transport by the zonal flows in quasi-helicalsymmetric (QH) and quasi-isodynamic (QI) stellarators are much larger than a quasi-axisymmetric (QA) stellarator or a tokamak, thanks to higher linear residual levels and lower nonlinear frequencies of the zonal flows in the QH and QI. The transport level and energy confinement time in the QH and QI are similar to the tokamak with the same size and temperature gradient, despite the much larger linear growth rates in the stellarators.