Characterization of the ELMy H-Mode Regime with the ITER-Like Wall in JET
The installation of a full tungsten divertor and a beryllium first wall in JET, the so-called ITER-Like Wall (ILW), provides a unique opportunity to study the influence of the wall materials on the ELMy H-mode regime, the foreseen reference scenario for ITER. With the new ILW, the H-mode regime has been readily achieved with low shape (d~0.25) and high shape (d~0.4) with a small amount of additional heating power, either from neutral beams or ICRH systems (less than 2MW). During the initial development phase, metallic impurity events have been observed but in the course of the further operation their frequency strongly decreased, hinting to a conditioning effect of the plasma wetted surfaces. An example of an ELMy H-mode discharge obtained in JET with the ILW is given in the Figure 1. 10.5MW of NBI power was applied in a 2.0MA/2.1T plasma. The configuration is a low triangularity (d~0.25) with the inner strike point lying on the vertical target (coated tile) and the outer strike point on the horizontal target (bulk tungsten tile). A significant amount of deuterium had to be puffed (~1022D/s) continuously in the divertor during the main heating phase to achieve stable conditions with respect to W accumulation and central radiation as already shown in ASDEX Upgrade. Regular type I ELMs are still observed on the BeII line emission and on the line integrated density at a frequency of about 12Hz. The ELM signature in the radiated power and the Da emission is strongly reduced compared to the carbon wall, suggesting a different deuterium and impurity release from the plasma facing components under the transient heat flux.