Momentum transport studies in ITER-relevant turbulence regimes on ASDEX Upgrade and DIII-D

Understanding momentum transport is essential for predicting the plasma rotation of future fusion devices as ITER or SPARC. This work reports results from the ASDEX Upgrade (AUG) and DIII-D tokamaks, aiming to investigate momentum transport in ITER-relevant turbulence regimes with dominant electron heating (ECH). For both machines, the established momentum transport analysis developed at AUG is employed. Previous work on AUG has suggested dependencies of residual stress on the turbulence regime during the transition from ITG to TEM. For this work, discharges with a mixed-mode turbulence regime were analyzed on AUG. The dominant ECH in these experiments gives rise to residual stress, which causes a counter-current intrinsic torque in the inner plasma core. The intrinsic torque at mid-radius locally exceeds the values of the deposited beam torque. Together with momentum diffusion and convection, this results in hollow rotation profiles, which must be avoided for the stability of future fusion devices. First results are presented on the implementation of the analysis technique on DIII-D to investigate momentum transport in low-torque and, consequently, low-rotation regimes with thorough scans of ECH. Turbulence measurements will be performed to assess the Reynolds stress present. Ultimately, this will allow the community to increase confidence in the extrapolation of rotation profiles for future tokamaks.