Three-Dimensional Inhomogeneity of Electron-Temperature-Gradient Turbulence in the Edge of Tokamak Plasmas

TL;DR

This study uses advanced gyrokinetic simulations to reveal the complex three-dimensional structure of electron-temperature-gradient turbulence in tokamak edge plasmas, showing how magnetic configuration influences turbulence behavior and transport efficiency.

Contribution

It provides the first detailed three-dimensional analysis of ETG turbulence structure in tokamak edges, highlighting the impact of magnetic drifts and FLR effects on turbulence localization and transport.

Findings

ETG turbulence varies strongly with magnetic configuration.

Long-wavelength ETG turbulence has low heat transport efficiency.

Multiscale interactions reduce overall ETG transport by approximately 40%.

Abstract

Nonlinear multiscale gyrokinetic simulations of a Joint European Torus edge pedestal are used to show that electron-temperature-gradient (ETG) turbulence has a rich three-dimensional structure, varying strongly according to the local magnetic-field configuration. In the plane normal to the magnetic field, the steep pedestal electron temperature gradient gives rise to anisotropic turbulence with a radial (normal) wavelength much shorter than in the binormal direction. In the parallel direction, the location and parallel extent of the turbulence are determined by the variation in the magnetic drifts and finite-Larmor-radius (FLR) effects. The magnetic drift and FLR topographies have a perpendicular-wavelength dependence, which permits turbulence intensity maxima near the flux-surface top and bottom at longer binormal scales, but constrains turbulence to the outboard midplane at shorter electron-gyroradius binormal scales. Our simulations show that long-wavelength ETG turbulence does not transport heat efficiently, and significantly decreases overall ETG transport -- in our case by $\sim$40 \% -- through multiscale interactions.