Assessment of alternative divertor configurations in TCV via experiments and interpretative SOLPS-ITER modelling

Alternative divertor configurations (ADCs) are assessed by performing experiments in the TCV tokamak and interpretative SOLPS-ITER modelling, and comparing both with simple analytical models that predict benefits of these configurations for detachment access and control. Thanks to its characteristic shaping capabilities and a complete set of divertor diagnostics, TCV is an ideal testbed to verify the working principles of ADCs as exhaust solutions. SOLPS-ITER modelling, including drifts and impurities, allows for a thorough analysis of the different physical processes at play.

The investigation of ADCs is carried out by isolating geometrical features in the outer divertor, and testing their effect on detachment access and control. These geometrical features include poloidal connection length, poloidal flux expansion, total flux expansion, the presence of a secondary X-point. Dedicated experiments, and corresponding simulations, that cover a wide range of plasma scenarios and detachment strategies, are the basis for a unique holistic assessment of ADC physics. Significant discrepancies with respect to the simplified analytical models are highlighted, and attributed to invalid assumptions or neglected effects, such as those related to parallel flows in the divertor. These are discussed in details, together with their implications for the extrapolation to future fusion reactors.