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Characteristics of the H-mode pedestal in improved confinement scenarios in ASDEX Upgrade, DIII-D, JET and JT-60U

Funded under: FP7-EURATOM

Abstract

Pedestal and global plasma parameters are compared in conventional ELMy H-modes and improved confinement discharges from ASDEX Upgrade (AUG), DIII-D, JET and JT-60U with varying net input power. Both electron and ion pedestal pressures are studied. The pedestal top pressure p{PED} increases moderately with power in all tokamaks, in broad agreement with the power dependence of the IPB98(y, 2) scaling. Higher pedestal pressures are observed in AUG improved H-modes and in JT-60U high beta(pol) discharges at q(95) ~ 6.5 and high triangularity. For all machines and all scenarios a robust correlation between the total and the pedestal thermal stored energy is observed, with the ratio of the two varying between ~0.3 and 0.5. However the relative importance of pedestal and core confinement varies from regime to regime. In AUG the confinement improvement with respect to the IPB98(y, 2) scaling is due to improved pedestal confinement in improved H-modes with early heating and to both improved pedestal and core confinement in improved H-modes with late heating. In DIII-D hybrid discharges the increase in confinement factor compared with conventional H-modes is due to improved confinement in the plasma core. JT-60U reversed shear H-modes have strong internal transport barriers and thus improved core performance. In all four tokamaks improved edge stability is correlated with increasing total beta(pol) and H98(y,2) increases with pedestal beta(pol). The analysed multimachine data set supports a scaling expression for the pedestal stored energy derived under the assumption that the dominant loss term for the pedestal is by thermal conduction in the edge transport barrier region.

Additional information

Authors: MAGGI C F, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);HORTON L D, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);SIPS A C C, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);SUTTROP W, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);GROEBNER R J, General Atomics, San Diego (US);LEONARD A, General Atomics, San Diego (US);LUCE T C, General Atomics, San Diego (US);WADE M R, General Atomics, San Diego (US);OYAMA N, Japan Atomic Energy Agency, Naka-shi, Ibaraki-ken (JP);KAMADA Y, Japan Atomic Energy Agency, Naka-shi, Ibaraki-ken (JP);URANO H, Japan Atomic Energy Agency, Naka-shi, Ibaraki-ken (JP);SARTORI R, EFDA Close Support Unit, Garching (DE);ANDREW Y, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);GIROUD C, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);JOFFRIN E, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);DE LA LUNA E, CIEMAT, EURATOM Association, Madrid (ES)
Bibliographic Reference: An article published in: Nuclear Fusion 47 (2007), pp. 535-551
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/doi:10.1088/0029-5515/47/7/005
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