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

The effect of impurity production and recycling on JET hot-ion H-mode disch arges is investigated for the MkI and MkII diverters. 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 recycl ing hot-ion regime, the code predicts that Z(eff) at the edge (in the upstr eam SOL) increases with SOL density, and is higher for the MkII than for th e MkI divertor. These predictions have been confirmed by the experimental d ata. The significance of the edge density and edge Z(eff) for the hot-ion r egime is that the loss power has been predicted from neo-classical theory t o scale as: P-loss similar to n(edge)(2)Z(eff,edge). It has now been demons trated 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 inc reased relative to those in the MkI divertor. These data are compared with the modelled results from the EDGE2D code, taking into account the change i n the chemical sputtering yield with the different base temperatures of the MkI (40 degrees C) and MkII (270 degrees C) diverters. (C) 1999 JET Joint Undertaking, published by Elsevier Science B.V. Al rights reserved.