Relevance of collisionality in the transport model assumptions for divertor detachment multi-fluid modelling on JET

A revised formulation of the perpendicular diffusive transport model in 2D multi-fluid edge codes is proposed. Based on theoretical predictions and experimental observations a dependence on collisionality is introduced into the transport model of EDGE2D–EIRENE. The impact on time-dependent JET gas fuelled ramp-up scenario modelling of the full transient from attached divertor into the high-recycling regime, following a target flux roll over into divertor detachment, ultimately ending in a density limit is presented.

A strong dependence on divertor geometry is observed which can mask features of the new transport model: a smoothly decaying target recycling flux roll over, an asymmetric drop of temperature and pressure along the field lines as well as macroscopic power dependent plasma oscillations near the density limit which had been previously observed also experimentally.

The latter effect is strongest for scenarios with strike points on vertical targets and vanishes in case of asymmetric divertor configurations.