Gyrokinetic Simulation of Turbulent Transport for I-mode Edge Plasmas

I-mode is an attractive candidate for tokamak operation with good energy confinement similar to H-mode but poor particle confinement similar to L-mode [1-2]. Additional benefits about I-mode include no impurity accumulation and free of ELMs. Many tokamaks, such as Alcator C-Mod, AUG, DIII-D and EAST, have achieved I-mode operation recently. However, theory and simulation remains insufficient to explain the I-mode formation and its transport behavior. In this work, an electrostatic gyrokinetic simulation using GTC code is carried out for the I-mode physics. Linear simulations find that two comparable instabilities co-exist for both short wavelength and long wavelength modes. The passing electron response cannot be treated adiabatically for those mode numbers close to that of weekly-coherent-mode (WCM), which is shown to account for the I-mode formation and transport behavior. Nonlinear simulations give a turbulent heat transport level consistent with the experimental value. But the particle transport from the simulation remains elusive from the experiment, which requires further investigation. References: [1] D. G. Whyte et al. 2010 Nuclear Fusion, 50(10), 105005. [2] A. E. Hubbard et al. 2011 Physics of Plasmas, 18(5), 056115.