Pedestal and ELM Characterisation of Highly Shaped Single Null and Quasi Double Null Plasmas in JET
Simultaneous high confinement and density are routinely achieved in steady state conditions for ~20tE in JET with highly shaped plasmas. The normalised parameters required for the Q=10 inductive operation of ITER, namely H98 ~1, density > 85% nGR and bN~2 with q95~3, are obtained in lower SN plasmas with dsep ~ 0.4 ­ 0.5. These plasmas are characterised by an ETB with Type I ELMs. Above a certain pedestal density (typically nped>80nGR), the Type I ELM frequency decreases to few Hz, while the Type I ELM prompt energy losses do not increase or even decrease compared to those a lower density, and H98 does not decrease any longer with density. The change in fELM corresponds to enhanced energy and particle losses between ELMs, attributed to the presence of an additional edge relaxation mechanism, identified, by analogy with other experiments, as type II ELMs. Steady state Type II ELMs regime has been obtained in AUG, for plasma configuration near to double null (QDN), high pedestal density and q95>4 for bp~1. The possible requirement of QDN plasma geometry to achieve Type I ELM suppression is of some concern for the extrapolation of this regime to ITER, since ITER is not designed to accommodate high particle fluxes or power fluxes to the top x-point region.