A Subgrid Model for Electron-Scale Turbulent Transport in Global Ion-Scale Gyrokinetic Simulations of Tokamak Plasmas

TL;DR

This paper introduces a subgrid model for electron-scale turbulence in global ion-scale gyrokinetic simulations, enabling more accurate representation of electron heat transport in tokamak plasmas.

Contribution

A novel subgrid ETG model is developed to incorporate electron-scale turbulence effects into global ion-scale simulations, bridging a gap in multiscale plasma modeling.

Findings

The subgrid model accurately captures electron heat flux in global simulations.

ETG turbulence significantly influences ion-scale transport in tokamak plasmas.

Coupling mechanisms between electron and ion scale turbulence are identified.

Abstract

A subgrid electron-temperature-gradient (ETG) model is demonstrated here which averages local electron-scale turbulence from the GENE code over intermediate scales in space and time to include in global ion-temperature-gradient (ITG) GEM simulations. This approach results in ion-scale equations which include the electron heat transport from ETG turbulence and the effects of electron-scale turbulence on the ion scale. Flux-tube ETG Cyclone Base Case simulations are carried out using GENE at different radial locations and a kinetic form of the flux is added to ion-scale global GEM simulations as a source term. Analytic radial profiles of ETG heat flux are constructed and compared to flux-tube results at multiple radial locations. Different ratios of ITG to ETG turbulent heat flux levels are considered and the results of capturing ETG heat transport in global GEM simulations are discussed. Possibilities for coupling of the ETG streamer potential and intermediate-scale zonal flows found in ETG simulations to the ion scale are further discussed.