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The paper reviews recent theoretical and experimental results focussing on the identification of the key factors controlling ELM energy and particle losses both in natural ELMs and in the presence of external controlling mechanisms. Present experiment and theory pointed out the benefit of the high plasma shaping, high q(95) and high pedestal density in reducing the ELM affected area and conductive energy losses in Type I ELMs. Small benign ELMs regimes in present machines (EDA, HRS, Type II, Grassy, QH, Type III in impurity seeded discharges at high delta) and their relevance for ITER are reviewed. Recent studies of active control of ELMs using stochastic boundaries, small pellets and edge current generation are presented. (c) 2004 Elsevier B.V. All rights reserved.

In this paper we investigate differences of the ELM behaviour between RF and NB heated H-mode discharges in JET. The main result of this investigation is that the edge pedestal pressure with NB heating is higher than with RF heating for equal power fluxes crossing the separatrix. This can be explained by a higher population of fast ions in the edge region in the case of NB heating. Using data from NB heated steady-state H-modes we derive a scaling law for the width of the transport barrier. We find that the barrier width is proportional to the poloidal Larmor radius, which in turn is controlled by the ion population with the highest energy in the plasma edge.

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.