EFDA-JET-PR(03)41
Dimensionless Pedestal Identity Experiments in JT-60U and JET in ELMy H-mode Plasmas
This paper reports first results of collaborative experiments in JT - 60U and JET to compare ELMy H-modes characteristics in both machines. The JT - 60U/JET identity experiments were explicitly aimed at matching edge pedestal parameters, in plasmas of the same geometry. The similar size of the two devices allows plasma configurations and conditions to be established for which the match of the dimensionless parameters (r*, u*, b and q95) and of the equilibrium geometry is carried out in plasmas that are also almost identical in dimensional terms. The results of the power and density scans at fixed (and matched) Ip - BT indicate that, in a common range of r*, the pedestal electron collisionality ue*, and normalised pressure bp, ped do not match in the two machines. In particular, the range of bp, ped of the JT - 60U ELMy H-modes with Type I ELMs is accessible to JET plasmas only with a Type III ELMs edge, and ue* in JT - 60U is consistently higher by 2 than JET , for the same r*. Comparison of ne and Te pedestal profiles indicates that Te is comparable in the two devices, while JET ne profiles are steeper than JT - 60U. The global energy confinement enhancement factor, (H98 - y(2)) is higher in JET than in JT - 60U, and this difference is possibly attributed to the reduced pedestal pressure in JT - 60U compared to JET. Although a full explanation for the different behaviour of the edge pedestal in the two devices has not yet been found, difference in plasma toroidal rotation magnitude and direction (in JET co-current, in JT - 60U counter-current) and/or fast ion losses may be consistent with the different pedestal properties found in these experiments.