Multi-machine modelling of divertor geometry effects

The design and construction of advanced divertors has been one of the main topics of tokamak research during the last decade. The design of such divertors has been carried out by using 2-D plasma edge modelling codes. Many of the predictions from the modelling, which guided the optimisation procedure, have been demonstrated experimentally such as: larger operating density range for partially detached plasmas in vertical divertors compared to horizontal ones, improvement of the divertor pumping capability with more closed divertors and corresponding changes in recycling impurity exhaust following predictions. New phenomena that were hinted at by modelling but not clearly quantified, such as the increase in radiative capability of the divertor induced by the geometry, have been measured and understood by 2-D modelling. Divertor flows determined by divertor sources, which are in turn determined by the geometry, show the expected qualitative trends but detailed modelling which includes plasma drifts, not yet carried out, is required to sort out the effects of drifts and particle sources.