Power exhaust and detachment with varying outer leg length using turbulence simulations and experiments designed for validation

The comparison of simulations of plasma turbulence carried out with the GBS code, employing its latest multi-component plasma–neutral model, against a dedicated set of TCV discharges (TCV-X23) designed to investigate high-density divertor conditions characterised by strongly reduced target heat flux with respect to attached conditions, is presented. The TCV-X23 scenario, based on L-mode plasmas with a long outer divertor leg at low toroidal field, provides a well-diagnosed reference for boundary turbulence studies, including Thomson scattering, Langmuir probes, infrared thermography, and Gas Puff Imaging. GBS simulations reproduce the main experimental trends at the outer midplane, including density shoulder formation, and capture key features of turbulence evolution from low to high density, such as increased fluctuation levels, filament size, and radial velocity. The analysis highlights the central role of charge-exchange–driven momentum losses in detachment, and shows that turbulence is enhanced in cold, high-collisionality regions, consistent with ballooning theory. While discrepancies between simulation and experimental results remain at the targets, most likely due to enhanced neutral penetration resulting from the reduced size of the simulations and simplified transport coefficients, this work demonstrates that GBS can accurately reproduce the main turbulence trends across attached and detached regimes.