Heat transport driven by the ITG and ETG instabilities in ASDEX Upgrade H-modes

A study of the properties of the turbulence-driven ion and electron heat fluxes, is presented. Dedicated H-mode experiments taking advantage of the on-axis and off-axis possibilities of both neutral beam injection and electron cyclotron resonance heating available on the ASDEX Upgrade tokamak were carried out. The experimental results are interpreted by comparisons with gyrokinetic calculations. Ion heat transport is, as expected, driven by the ion temperature gradient (ITG) instability with the features predicted by theory: increase of the driven heat flux above a threshold in normalised gradient. In addition the main effects known to impact on the stability of the turbulence, temperature ratio and fast ions population, are exhibited by the experimental results and agree with the gyrokinetic calculations. It is known that the ITG also contributes to the electron heat flux, but that an electron instability can be required in addition when the ITG contribution does not drive the whole imposed electron heating. This situation, investigated by adding electron cyclotron heating, indicates that in the experiments presented here the electron temperature gradient instability develops.