Speaker
Description
Particle and power exhaust remains one of the major challenges for burning plasma operation in next generation tokamaks and stellarators. Plasma detachment via impurity seeding is a possible solution which has been widely explored on present devices and which is the default approach adopted on ITER. For future devices, predictive modeling is the only tool available both for divertor design and scenario development. While 3D plasma boundary models are essential for stellarators, 2D (axisymmetric) models are typically applied for tokamaks. Nevertheless, 3D models can also be necessary for tokamaks in order to account for non-axisymmetric magnetic perturbations (for edge localized mode control), toroidally localized gas puffing or non-axisymmetric plasma-facing components (PFCs).
Recent improvements of the 3D plasma boundary model EMC3-EIRENE will be presented. In particular, an extension of the coupling between the plasma and neutral gas codes allows for a more realistic treatment of impurity recycling and pumping. Specifically, this includes reflection of impurity neutrals on baffles which has not been included up to now. Furthermore, the new version can account for additional neutral-neutral collisions (such as D-Ne, D2-Ne and Ne-Ne), and it can evaluate charge state resolved impurity fluxes to PFCs (e.g. for subsequent erosion studies). The gas puff can be feedback controlled in order to match a given impurity concentration at the separatrix or total radiated power. Furthermore, a core source for He ash can be included. Simulations for ITER under burning plasma conditions with Ne seeding show a strong asymmetry between the inner and outer divertor targets with the old code version where a sudden onset of deep detachment is found at the inner divertor target. Conversely, a more gradual onset of detachment is found with the improved code which includes transport of - and collisions between - neutral impurities below the dome, and this is found to be more in line with corresponding SOLPS-ITER simulations.