Validation of the GBS code against COMPASS experimental data

This work presents the first full-size turbulence simulation of the COMPASS tokamak edge with the three-dimensional, self-consistent, flux-driven, two-fluid Global Braginskii Solver (GBS) code. The simulation is validated against experimental data from a standard L-mode COMPASS discharge, covering the scrape-off layer (SOL) from the outer midplane to the divertor region. The dataset combines four diagnostic systems and provides 43 observable profiles, including electron temperature and plasma potential measurements that enable the first direct comparison of their fluctuations and higher-order statistics in COMPASS. The validation results show good agreement between simulation and experiment in profile shape, magnitude, and fluctuation levels for most outer midplane observables. The parallel heat-flux fall-off length is also reproduced. In the divertor, the mean profiles agree reasonably well in magnitude, but the simulated fluctuation levels remain significantly underestimated. Advanced blob analysis shows that both simulation and experiment lie mainly in the sheath-connected regime, with partial presence in the connected ideal-interchange regime. The remaining discrepancies in the COMPASS simulation are probably a consequence of simplified parameters and boundary conditions, reflecting limitations that are common to fluid turbulence models. Overall, the validation demonstrates that GBS captures the dominant upstream SOL turbulence dynamics, while identifying divertor physics as the main target for further improvement.