Turbulence characteristics of electron cyclotron and ohmic heated discharges

TL;DR

This study uses gyrokinetic simulations to compare turbulence in electron cyclotron and ohmic heated plasmas, revealing differences in instability drives, impurity transport, and the impact of heating methods on plasma behavior.

Contribution

It provides new insights into how auxiliary heating methods influence turbulence characteristics and impurity transport in plasma discharges.

Findings

Trapped electron modes are unstable in both EC and OH discharges.

EC heating reduces impurity peaking and impurity diffusion.

Different drives and collisionalities cause distinct scaling behaviors.

Abstract

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.