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.
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