Multi-machine Dimensionless Transport Experiments

Integrated dimensionless confinement studies have been performed recently on JET, C-Mod, JT-60U, DIII-D, and Tore Supra. Analysis of ELMy H-mode identity experiments on JET and C-Mod shows that, despite results indicating confinement falls as density approaches the Greenwald limit, Greenwald fraction is not a relevant parameter for confinement scaling, but that collisionality is. Studies on JT-60U show a fall in ELMy H- mode confinement with increasing β , contrasting with those on DIII-D and JET which showed a negligible effect. Analysis of a multi-machine database indicates that the differing results may be due to a change in β dependency with plasma shape. Tore Supra experiments show a negligible β effect on L-Mode confinement, suggesting that any β dependence observed in ELMy H-modes is related to the edge pedestal. Statistical studies of multi- machine core and edge confinement databases lead to an improved explanation of these results. The impact of these results on the understanding of plasma transport and its extrapolation to ITER will be discussed.