Optimizing Performance of Hybrid and AT Discharges in Preparation for the ITER Like Wall

Fuelling the AT scenario remains one of the main challenge for its operation in ITER. If the electron density at the last closed flux surfaces is not high enough (typically less 3¥1019m-3), with the peak power loads on divertor targets will be unacceptable high for the given choice of plasma facing materials, namely Be and W. The JET first wall and divertor plasma facing components, currently made of carbon fibre-composite, will be substituted by similar plasma facing components made of beryllium and tungsten, thus the same material choice that will be installed in ITER. With this new first wall, JET could address the fuelling issue for AT scenario and also other limitation such as the neutral beam shine-through limits. Because of the metallic wall, the density control of the scenario is also likely to change. Therefore, recent experiments done in the last JET campaign with CFC, have been carried out with the aim of studying particle fuelling in Hybrid and AT scenario while preserving the confinement in order to obtain density level compatible with the operation with the ITER-Like Wall (ILW). A series of experiments have been conducted injecting deuterium at different level and from different poloidal locations, as well as injecting pellets from the Low Field Side (LFS) and Vertical High Field Side (VHFS). The first experiments were aimed at documenting the difference between different gas injecting locations at a moderate gas influx. The second series of experiments extended gas rates to higher levels while the third series of experiments used pellet injection for comparing the effect of pellets during the main heating phase and during the transient phase at the start of the NBI heating.
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EFDC090647 1.70 Mb