Edge turbulence studies across confinement regime transitions at ASDEX Upgrade

Edge turbulence is thought to play an important role in the transition between the low confinement operating regime, L-mode, and high confinement operating regimes such as H-mode. ELM-free high confinement regimes such as I-mode are promising for future reactor operation, but open questions remain about the role of turbulence in regulating transport in I-mode. There are also open questions about changes in edge turbulence leading up to the I-mode and H-mode transitions, which affect access to I-mode, and the relationship with favorable and unfavorable ion ▽B drift configuration. The Correlation Electron Cyclotron Emission (CECE) diagnostic measures long-wavelength electron temperature fluctuations at ASDEX Upgrade with high temporal and spatial resolution. This work presents outer core and pedestal (ρ_pol=0.85-1.0) electron temperature fluctuation measurements in a variety of experiments with L-modes, I-modes, and H-modes in different magnetic configurations. These measurements provide important information on scaling and transitions between confinement regimes. Gyrokinetic simulations of these plasmas with the CGYRO code provide further details about the nature of the turbulence across confinement regime transitions.