Recent Progress on JET Towards the ITER Reference Mode of Operation at High Density

Recent progress is summarized towards obtaining high density and high confinement in JET as required for the ITER reference scenario at Q=10. Plasmas with simultaneously confinement H98(y,2)=1 and densities up to n/nGW ~1 are now routinely obtained. This has been possible (i) using plasmas at high (d~0.5) and medium (d~0.3-0.4) triangularity with sufficient heating power to maintain Type I ELMs (ii) with impurity seeded plasmas at high (d~0.5) and low (d0.2) triangularity (iii) with an optimised pellet injection sequence, keeping energy confinement and raising the density and (iv) by carefully tuning the gas puff rate leading to plasmas with peaked density profiles and good confinement at long time scales. These high performance discharges exhibit Type I ELMs, with a new and more favourable behaviour observed at high densities, requiring further studies. Techniques for a possible mitigation of these ELMs are discussed, and first promising results are obtained with impurity seeding in discharges at high triangularity. Scaling studies using the new data of this year show a strong dependence of confinement on the upper triangularity, the density and the proximity to the Greenwald limit. MHD instabilities observed and methods to avoid these in high density and high confinement plasmas are discussed.
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