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A regime of improved H mode energy confinement, the VH mode, was obtained following boronisation of the DIII-D tokamak vacuum vessel. The gradual confinement improvement in VH mode is associated with expansion of the H mode pedestal and reduction of thermal diffusivity in a region just inside the pedestal. Disappearance of density fluctuation bursts is associated with a confinement improvement in the latter region. The VH mode is terminated in a rapid global energy loss which is initiated by a mode with toroidal mode number, n approximately equal to 5, consistent with calculated instability to an edge localised ideal kink. The improved confinement in VH mode is consistent with the extension of the region of the E x B velocity shear turbulence suppression zone further in from the plasma boundary. Expansion of the ideal ballooning second stability region and of the drift reversal stabilisation of trapped particle modes are also considered as possible explanations for the confinement improvement.

Additional information

Authors: OSBORNE T H ET AL., General Atomics, San Diego (US);DOYLE E J, University of California, Los Angeles (US);RETTIG C L, University of California, Los Angeles (US);KONOSHIMA S, Japan Atomic Energy Research Institute, Tokai Research Establishment, Ibaraki-ken (JP);WINTER J, Forschungszentrum Jülich GmbH (KFA) (DE);WROBLEWSKI D, Lawrence Livermore National Laboratory, California (US)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 35 (1995) No. 1, pp. 23-37
Record Number: 199510570 / Last updated on: 1995-04-21
Original language: en
Available languages: en