Confinement Properties of High Density Impurity Seeded ELMy H-Mode Discharges at Low and High Triangulaity on JET

The ITER-FEAT reference operational scenario for pulsed operation at Q = 10 is ELMy H-mode with a confinement characterized by H98(y,2) = 1 at fGW = n/nGW = 0.85, where H98(y,2) is the enhancement factor over the IPB98(y,2) scaling law [1] and fGW is the Greenwald factor i.e. the density normalized to the empirical Greenwald density limit nGW [2]. Previous experiments on JET and other tokamaks [3] have shown that the energy confinement degrades when raising density towards nGW and that the maximum achievable density for a given confinement is increasing with the triangularity d. Hence the necessity to develop scenarios combining high confinement at high density. However, high confinement is generally accompanied by large type I ELMs of low frequency causing severe transient power loads on the divertor target plates. The power load may be reduced by radiating a substantial part of the energy over greater surface areas. This can be achieved by the seeding of impurities into the plasma, trying to create a radiating mantle. These experiments aim at combining high density, high confinement and good power exhaust by a radiating plasma edge without altering significantly the purity of the plasma center.
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