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The stationary advanced tokamak scenario with an internal transport barrier (ITB) for ions and electrons, particles and momentum in combination with an H-mode barrier and flat shear (q0 approximately equals 1) was maintained for 40 confinement times and several internal skin times with H(ITERL-89P) ÎN approximately equals 5. Raising the density by edge gas fuelling close to 50% of the Greenwald density to integrate proper exhaust conditions causes an increase of the threshold power to sustain an ITB and a decrease of Z(eff) below 2. In contrast, a density increase caused by improved core particle confinement as more triangular plasma shapes does not change the ITB onset conditions. No temporal impurity accumulation even with high-Z Ar puffing was observed despite peaked impurity density profiles.

MHD modes contribute to the stationarity of the shear profile. In the ITB/H-mode scenario (1,1) fishbones with a large reconnection area "clamp" the q-value in the vicinity of one and avoid sawteeth during the whole high-performance phase. In ITB scenarios with reversed shear (qmin > 2) fishbones can clamp the current profile development near the q = 2 surface without deteriorating energy confinement, whereas double-tearing modes, acting in a similar form, 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 CD direction. Moreover, reactor relevant T(e) > T(i) operation with temperatures in excess of 10 keV was achieved with internal transport barriers for both electrons and ions simultaneously. ly.

Additional information

Authors: GRUBER O ET AL, Max-Planck Institut f³r Plasmaphysik, EURATOM Association, Garching bei M³nchen (DE)
Bibliographic Reference: Article: Plasma Physics Controlled Fusion, Vol. 42 (2000) pp. A117-A126
Availability: Plasma Physics Controlled Fusion (Journal)
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