Tuesday, October 23, 2018
On the path toward the clean, sustainable, and safe energy of a fusion power plant, experiment and modeling each contribute something unique. Especially in recent years, the increased cost of constructing new experimental facilities has highlighted the necessity of developing computational models that can accurately predict the performance of future machines. Before one can in good faith use turbulent transport models to predict the performance of future machines such as SPARC, however, one must ensure that these models can correctly reproduce experimentally measured conditions on existing devices.
In particular, recent work at MIT has shown that for some plasmas, one requires incredibly computationally expensive multi-scale gyrokinetic simulations in order to accurately model the plasma, while in other cases significantly faster ion-scale simulations are sufficient. Knowing which type of simulation is required to predict future device performance is vital before one trusts these predictions. This question is answered using a gyro-fluid code, TGLF, to model more than fifteen plasma conditions on both the Alcator C-Mod and ASDEX Upgrade tokamaks. These runs led to the discovery of two physical criteria that distinguish plasmas for which multi-scale simulations are necessary from those for which ion-scale simulations are sufficient.