Core momentum and particle transport studies in the ASDEX Upgrade tokamak

Abstract

Core momentum and particle transport in ASDEX Upgrade (AUG) have been examined in a wide variety of plasma discharges and via several different methods.Experiments were performed in which ECRH power was added to NBI heated H-modes causing the electron and impurity ion density profiles to peak and the core toroidal rotation to flatten.Turbulence calculations of these plasmas show a change in the dominant regime from ITG to TEM due to the ECRH induced changes in the electron and ion temperature profiles.The impurity and electron density behavior can be fully explained by the changes in the turbulent particle transport.Momentum transport analyses demonstrate that in the TEM regime there is a core localized, counter-current directed, residual stress momentum flux of the same order of magnitude as the applied NBI torque.The initial results from momentum modulation experiments performed on AUG confirm that the Prandtl number in AUG NBI heated H-modes is close to 1 and that there exists a significant inward momentum pinch.Lastly, an intrinsic toroidal rotation database has been developed at AUG which can be used to test theoretically predicted dependencies of residual stress momentum fluxes.Initial results show a linear correlation between the gradient of the toroidal rotation and both the electron density gradient scale length and the frequency of the dominant turbulent mode.