Influence of the heating profile on impurity transport in ASDEX Upgrade

The transport of silicon has been investigated for various heating scenarios in ASDEX Upgrade H-mode discharges. Inside of r≈a/4, the diffusion coefficient D is either mainly neoclassical or anomalous depending on the heating method. For all investigated scenarios with NBI-heating and off-axis ECRH or off-axis ICRH, the diffusion coefficient is approximately neoclassical, and the effective heat diffusion coefficient χeff is below the neoclassical ion heat diffusion χi,neo in the plasma core. When central ECRH is added, χeff is above χi,neo, and D strongly increases by a factor of 3–10, i.e. becomes predominantly anomalous. For central ICRH, D is above the neoclassical level by a factor of 2. For radii outside of r≈a/4, D is always anomalous and increases towards the plasma edge. For ra/4, we find a clear scaling of D in terms of χeff, where D is about equal or above χeff. A strong inward drift parameter v/D is only observed in the core and only for cases, when the diffusion coefficient is neoclassical. With central wave heating, the drift parameter decreases to small values.