Increased core ion temperatures in high-beta advanced scenarios in ASDEX upgrade

Non-inductive advanced tokamak scenarios are a possible way for future nuclear fusion power plants to run in non-pulsed operation. In these scenarios, the ohmic current is replaced on the one hand with a current driven by external sources such as NBI and ECRH and on the other hand with a substantial bootstrap-current. The bootstrap current is produced in the presence of pressure gradients. This means, to increase the bootstrap-current-fraction, it is advantageous to have regions where ITG turbulence is reduced. To be able to extrapolate from non-inductive scenarios done in smaller present day devices, it is important to have transport models that allow the user to reproduce these experiments and accurately capture the physics behind the reduction of turbulent transport. One commonly used model is the quasi-linear gyrofluid transport model TGLF, which is well tested in standard scenarios. However, in the past, TGLF has failed to reproduce the peaked ion temperature profiles of certain advanced scenario shots.

In this article, progress in overcoming this issue of TGLF will be discussed. Results of a recent publication are reproduced in which TGLF was able to match the experimentally measured peaked ion temperature profiles. In these simulations, we find the E × B-shear to play an important role in the reduction of ITG turbulence. In contrast to that, experimentally we find the E × B-shear to have no effect on the formation of such regions of decreased turbulent transport. This finding is in line with simulations using the gyrokinetic code GENE. A new approach of modelling these advanced scenarios in TGLF is introduced, allowing us to match the peaked ion temperature profiles without depending on the E × B-shear. (paper)