Isotope Effects on TEM-driven Turbulence and Zonal Flows in Helical and Tokamak Plasmas

TL;DR

This study uses advanced gyrokinetic simulations to explore how isotope ion mass influences TEM-driven turbulence and zonal flows in various magnetic confinement fusion devices, revealing new stabilization effects.

Contribution

First-time gyrokinetic simulations of isotope effects on TEM turbulence in realistic three-dimensional magnetic configurations, clarifying the nonlinear impact on transport and flows.

Findings

Isotope mass affects TEM stabilization and zonal flow impacts.

Transport reduction is linked to isotope effects and near-marginal stability.

Universal isotope effects are observed across different plasma configurations.

Abstract

Impacts of isotope ion mass on trapped electron mode (TEM) driven turbulence and zonal flows in magnetically confined fusion plasmas are investigated. Gyrokinetic simulations of TEM-driven turbulence in three-dimensional magnetic configuration of LHD plasmas with hydrogen isotope ions and real-mass kinetic electrons are realized for the first time, and the linear and the nonlinear nature of the isotope and collisional effects on the turbulent transport and zonal-flow generation is clarified. It is newly found that combined effects of the collisional TEM stabilization by the isotope ions and the associated increase in the impacts of the steady zonal flows at the near-marginal linear stability lead to the significant transport reduction with the opposite ion mass dependence in comparison to the conventional gyro-Bohm scaling. The universal nature of the isotope effects on the TEM-driven turbulence and zonal flows is verified for a wide variety of toroidal plasmas, e.g., axisymmetric tokamak and non-axisymmetric helical/stellarator systems.