Comparisons and Physics Basis of Tokamak Transport Models and Turbulence Simulations

The predictions of gyrokinetic and gyroouid 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 eeects of diierences in the physics content of the various models and on the fusion-relevant gures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simpliied plasma model and geometry which is an idealization of the plasma conditions and geometry in a fusion-reactor-relevant (DIII-D) experiment. Most of the models show good agreement in their predictions and assumptions for the linear growth rates and frequencies. There are some diierences associated with diierent equilibria. However, there are signiicant diierences in the transport levels between the models. The causes of some of the diierences 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.