Comparisons and physics basis of tokamak transport models and turbulence simulations

Abstract

The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed ITER tokamak, are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a DIII-D H-mode experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed.

Modern gyrokinetic formulation of collisional and turbulent transport in toroidally rotating plasmas

“…Gyrokinetic theories and simulations are powerful means to investigate microinstabilities and turbulence in fusion and astrophysical plasmas (Krommes 2012;Garbet et al 2010;Idomura et al 2006;Dimits et al 2000;Schekochihin et al 2009). Linear and nonlinear gyrokinetic equations for particle distribution functions were originally derived by recursive techniques combined with the WKB representation (Hazeltine and Meiss 1992;Rutherford and Frieman 1968;Taylor and Hastie 1968;Antonsen and Lane 1980;Catto et al 1981;Frieman and Chen 1982).…”

Energy dynamics in a simulation of LAPD turbulence

“…In some of these cases, nonlinear wavenumber transfers can increase or cause drive, 26,27 while in other cases zonal flow effects decrease drive. 28,29 In order to avoid the pitfalls of relying too heavily on linear stability calculations in forming conclusions on turbulence characteristics, it is useful to perform turbulent simulations and diagnose them with energy dynamics analyses. Energy dynamics analyses track energy input into turbulent fluctuations and energy dissipation out of them.…”

High-resolution magnetohydrodynamic equilibrium code for unity beta plasmas

“…This translates into a resolution of 1 point per mm. This is an exceptional result that is especially useful for inputs to gyro-kinetic codes [32,33] which require a precision comparable to the Larmor radius of the ions, i.e. 2-3mm.…”