The role of recycling and impurity production in JET hot-ion H-modes

Abstract The effect of impurity production and recycling on JET hot-ion H-mode discharges is investigated for the MkI and MkII divertors. Analysis of the best of these discharges has been performed with the EDGE2D/NIMBUS codes and the results compared with a wide range of diagnostics. For the very low recycling hot-ion regime, the code predicts that Z eff at the edge (in the upstream SOL) increases with SOL density, and is higher for the MkII than for the MkI divertor. These predictions have been confirmed by the experimental data. The significance of the edge density and edge Z eff for the hot-ion regime is that the loss power has been predicted from neo-classical theory to scale as: P loss  ∼  n edge 2 Z eff,edge . It has now been demonstrated that this is consistent with both the MkI and MkII experimental data. It has been observed that the carbon sources in the MkII divertor are increased relative to those in the MkI divertor. These data are compared with the modelled results from the EDGE2D code, taking into account the change in the chemical sputtering yield with the different base temperatures of the MkI (40°C) and MkII (270°C) divertors.