The radiated power limit in impurity seeded JET-ILW plasmas

Abstract

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 P heat =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 N 2 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, θ rad : γ rad , t o t a l max = 1 - f ELM × Δ W ELM P heat 1 - θ rad . About 50% and 16% of the ELM induced diamagnetic energy drop (ΔW ELM ) radiates during the ELM in JET-C and JET-ILW, respectively, which corresponds to the maximum total radiated powers of γ rad , J E T - C max = 0.87 and γ rad , J E T - I L W max = 0.77 . These values of the maximum of the radiative power fractions are in good agreement with γ rad max experimentally observed in JET-C (90%) and JET-ILW (75%). PACS numbers: 52.55.Rk, 52.25.Vy, 52.40.Hf, 52.55.Fa