The radiated power limit in impurity seeded JET-ILW plasmas

The total radiated fraction is examined in high density H-mode plasmas (Greenwald fraction of about 85 %) in JET by the variation of the auxiliary heating power of Pheat = 14 MW-29 MW. An achieved radiation fraction of about 75 % at most has been observed in JET-ILW, which is less than the highest achievable (≈90 %) fraction in JET-C during the high radiative power scenarios with N2 seeding. It is shown that the maximal achievable total radiation fraction averaged over ELM cycles has a strong dependence on the radiation efficiency of the ELM energy, θrad: γrad,totalmax=1-fELM×ΔWELMPheat1-θrad. About 50 % and 16 % of the ELM induced diamagnetic energy drop (ΔWELM) radiates during the ELM in JET-C and JET-ILW, respectively, which corresponds to the maximum total radiated powers of γrad,JET-Cmax=0.87 and γrad,JET-ILWmax=0.77. These values of the maximum of the radiative power fractions are in good agreement with γradmax experimentally observed in JET-C (90 %) and JET-ILW (75 %).