Peculiarity of highly radiating multi-impurity seeded H-mode plasmas on JET with ITER-like wall

Abstract

On JET with fully metallic first wall, highly radiative conditions with N2, Ne and Ar as well as their mixture as radiators are approached in high density H-mode plasmas. The confinement increases from H 98(y,2) = 0.65 in unseeded pulses with γ rad ∼ 30% to a value of H 98(y,2) = 0.75 at γ rad ∼ 50% with N2 injection. A degradation of the pedestal profile is compensated by steeper core n e and T e profiles. Further increase of γ rad with increase of the N2 seeding rate leads to a moderate confinement degradation which can be avoided by applying of combined impurity seeding. The enhancement of the plasma performance for the radiation fractions beyond 55% with the maximum value of H 98(y,2) = 0.78 is reached with combined N2 + Ne and N2 + Ar impurity injections. The observed intense, strongly localized radiation at the X-point inside the confined plasma in the scenarios with the highest radiated power fraction is interlinked to complete divertor detachment. In the JET-ILW, the X-point radiation is stable, reproducible and reversible.