A Subgrid Gyrokinetic Model of Electron-Temperature-Gradient Turbulence in Tokamaks

Substantial research has been conducted in validating gyrokinetic models at ion-temperature-gradient (ITG) scales for a variety of experimental magnetic confinement plasmas. Ion-scale gyrokinetic simulations are now able to accurately predict ion transport levels and flux spectra; however, they can often underestimate electron thermal transport levels. Recent multiscale simulations [Howard16, Holland17], while impractically expensive, have shown that the inclusion of electron-scale turbulence can lead to better agreement with experimental heat flux levels and that capturing cross-scale dynamics can be important as well. Therefore, a reduced model of fine-scale turbulence is of interest in modeling future burning plasma experiments such as ITER, where electron-temperature-gradient (ETG) effects can become important [Holland17]. Here we investigate a subgrid ETG model which considers spatially, and possibly temporally, averaging the electron-scale turbulence onto the ITG turbulent state. This method would result in ion-scale simulations which produce better agreement with experimental electron thermal transport levels, while also capturing how the ion-scale turbulence could be affected by finer-scale turbulent interactions. Electron-scale flux-tube simulations are carried out using GENE [Jenko00] and then input into global GEM ITG simulations [Chen04]. Various analytic radial profiles of electron-scale turbulence will also be constructed and tested against flux-tube runs at multiple radial locations in order to simplify the simulation complexity.

Howard N.T. et al 2016 Phys. Plasmas 23 056109

Holland C. et al 2017 Nucl. Fusion 57 066043

Jenko F., Dorland W., Kotschenreuther M., and Rogers B.N. 2000 Phys. Plasmas 7 1904

Y. Chen and S.E. Parker 2003 J. Comput. Phys. 189 463