Gyrokinetic studies of core turbulence features in ASDEX Upgrade H-mode plasmas

TL;DR

This study uses gyrokinetic simulations with the GENE code to analyze core turbulence in ASDEX Upgrade H-mode plasmas, validating the model against experimental data and examining the sensitivity of fluctuations to ion temperature gradients.

Contribution

It demonstrates a method to match nonlinear heat fluxes to experiments and highlights the robustness of cross-phases as reliable observables for validation.

Findings

Density and temperature fluctuations are highly sensitive to ion temperature gradient variations.

Cross-phases are more stable and reliable for comparison with experimental measurements.

Nonlinear simulations can be tuned to match experimental heat fluxes within error margins.

Abstract

Gyrokinetic validation studies are crucial in developing confidence in the model incorporated in numerical simulations and thus improving their predictive capabilities. As one step in this direction, we simulate an ASDEX Upgrade discharge with the GENE code, and analyze various fluctuating quantities and compare them to experimental measurements. The approach taken is the following. First, linear simulations are performed in order to determine the turbulence regime. Second, the heat fluxes in nonlinear simulations are matched to experimental fluxes by varying the logarithmic ion temperature gradient within the expected experimental error bars. Finally, the dependence of various quantities with respect to the ion temperature gradient is analyzed in detail. It is found that density and temperature fluctuations can vary significantly with small changes in this parameter, thus making comparisons with experiments very sensitive to uncertainties in the experimental profiles. However, cross-phases are more robust, indicating that they are better observables for comparisons between gyrokinetic simulations and experimental measurements.