Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
JET radiative mantle experiments in the ELMy H-mode regime have produced high confinement plasmas with densities close to the Greenwald limit. In the septum configuration, high performance plasmas (H_97*f_GWD >0.8) were obtained with two gas injection phases: continuous D_2 and Ar fuelling, followed by the "after-puff" phase when both gases injection rates are reduced. Confinement degradation is observed when Ar accumulates in the plasma core. This correlates with disappearance of sawtooth activity, when q(0) becomes greater than unity. In order to improve the q(0) stationarity, 1-3MW of ICRH power was added to the main NBI heating. The RF resonance layer was located on axis to increase the central electron temperature, keeping q(0)<1. Sawteeth were maintained and core impurity accumulation was prevented, resulting in quasi-steady state, high performance discharges with high Ar content. Sawteeth loss, followed by discharge degradation, is also a common observation in JET plasmas with peaked density profiles. The use of ICRH in these discharges, to avoid loss of confinement, is assessed.