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Turbulence characteristics of electron cyclotron and ohmic heated discharges

Turbulence characteristics of electron cyclotron (EC) and ohmic heated (OH) discharges has been analyzed by electrostatic gyrokinetic simulations with GYRO [J. Candy, R.E. Waltz, Journal of Computational Physics 186, 545-581 (2003)] aiming to find insights into the effect of auxiliary heating on the transport. Trapped electron modes are found to be unstable in both OH and the EC heated scenarios. In the OH case the main drive is from the density gradient and in the EC case from the electron temperature gradient. The growth rates and particle fluxes exhibit qualitatively different scaling with the electron-to-ion temperature ratios in the two cases. This is mainly due to the fact that the dominant drives and the collisionalities are different. The inward flow velocity of impurities and the impurity diffusion coefficient decreases when applying EC heating, which leads to lower impurity peaking, consistently with experimental observations.