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Abstract

A review is presented of the scenarios and physics of advanced tokamak discharges and the associated technical enhancements leading towards enhanced performance and steady state operation in ASDEX Upgrade. A stationary advanced tokamak scenario with internal transport barriers (ITB's) in combination with an H mode barrier and weak shear (qmin approximately equals 1) was maintained for 40 confinement times and several internal skin times with H(ITERL-89PÎN) approximately equals 5. By raising the triangularity of the plasma shape the performance was increased up to H(ITERL-89PÎN) approximately equals 7.2, but Î is still limited by neoclassical tearing modes. The density was raised to close to 50% of the Greenwald density either by gas edge fuelling, causing an increase of the threshold power to sustain an ITB and a decrease of Z(eff) below 2, or by improved core particle confinement with more triangular plasma shapes without changing the ITB onset conditions. Sufficient helium pumping and no temporal impurity accumulation was observed despite the peaked impurity density profiles. MHD modes contribute to the making the shear profile stationary. In the ITB/H mode scenario (1,1) fishbones clamp the current development near the q=2 surface without causing energy confinement to deteriorate. Double tearing modes act similarly, but lead to substantial confinement losses. Applying central ECRF heating and current drive to beam heated reversed shear ITB discharges shows a substantial effect on MHD stability, affecting the passage of the q profile through qmin=2 and degrading or prolonging the reversed shear phase, depending on the current drive direction. Moreover, reactor relevant T(e) approximately equals T(i) operation with temperatures in excess of 10 keV was achieved with internal transport barriers for both electrons and ions simultaneously. For current profile control ECCD will be supplemented by on-axis fast wave ICCD and off-axis current drive up to 400 kA using NBI

Additional information

Authors: GRUBER O ET AL, Max-Planck Institut f³r Plasmaphysik, EURATOM Association, Garching bei M³nchen (DE);MC CARTHY P J, University College Cork, Association EURATOM-DCU, Cork (IE)
Bibliographic Reference: Article: Nuclear Fusion, Vol 40 (2000) No. 6, pp. 1145-1155
Availability: Nuclear Fusion (Journal)
Record Number: 200012113 / Last updated on: 2000-07-12
Category: PUBLICATION
Original language: en
Available languages: en
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