Introduction In JET, the injection of argon simultaneously with deuterium in ELMy H-mode discharges has allowed the achievement of high confinement (H97 1) at high density (ne /nGr 1) in various experimental scenarios [1]. The motivation of this paper is to characterize different plasma configurations with respect to the equilibrium between highly radiative regimes and increase of medium-Z impurity ions in the centre in long lasting discharges. The study of the impurity behaviour allows the identification of high performance regimes with hollow radiation profiles and without impurity accumulation.