SOLPS-ITER modelling databases of three tokamaks—ASDEX-Upgrade, JET and ITER with fluid drifts activated are compared to understand the dependence of edge plasma performance on machine size and other global parameters. Two medium Z extrinsic radiating impurity species (Ne and N) are considered. It is demonstrated that N is better kept in the divertor region than Ne in semi-detached and detached divertor conditions due to smaller first ionization potential (FIP effect). Together with the fact that Ne radiates more efficiently at higher plasma temperatures, this leads to an increase in the efficiency of Ne for divertor heat load control with increasing machine size. In larger machines such as JET and ITER Ne can be as efficient a radiator as N while for ASDEX-Upgrade Ne easily leads to radiation from the pedestal and loss of H-mode stability. The relative roles of various physical effects are compared for the three tokamaks based on both whole databases and in more details for chosen semi-detached regimes with comparable fraction of radiated power. It is shown that for smaller machines drift effects are more significant and divertor asymmetries more pronounced.
Impurity leakage and radiative cooling in the first nitrogen and neon seeding study in the closed DIII-D SAS configuration