Modelling of the TCV Power EXhaust (PEX) upgrade

The Tokamak à Configuration Variable (TCV) has recently undergone a major upgrade of its plasma-facing components, divertor, and edge-plasma diagnostics. The installation of removable gas baffles allows for variable divertor closure and has demonstrated power exhaust mitigation with increased closure. This upgrade provides a unique and well-diagnosed environment to challenge and validate the numerical models used in the design of fusion reactors.

The reference Power EXhaust (PEX) experiment, a lower single-null ohmic density ramp with I_P = 250 kA and a reverse B_Φ = 1.4 T, is systematically modelled using the SOLPS-ITER edge-plasma code suite. The upstream electron density is scanned across all baffled and unbaffled configurations. For the first time in TCV, input fluxes at the core boundary of the SOLPS domain, anomalous diffusivities, and pinch velocities are evaluated from core-edge integrated modelling, informed by the TGLF code. The work investigates the role of core and divertor target boundary conditions, radial pinch velocities, carbon sources and fluid flux limiters. It explains the divertor density overestimation previously found in TCV edge simulations. As divertor closure increases, the improved exhaust properties observed in experiments are well replicated by simulations. The constraints provided by integrating edge and core modelling and the newly available diagnostic data have significantly enhanced the ability of the model to quantitatively reproduce experimental results.