Theory based investigation of Outer Mode to ELM transition in JET-C plasmas

Tokamak high-confinement regimes are normally affected by the presence of often violent edge localised modes (ELMs). ELMs deposit unacceptable peak heat loads causing a severe deterioration of the plasma facing components. Although several ELM control/suppression techniques have been developed, they may not be applicable to future reactors such as ITER and DEMO. Thus a vivid interest has arisen on the development of naturally ELM-free regimes. One of the most promising of such regimes is the so called quiescent high-confinement (QH) mode. In QH plasmas, ELM activity is replaced by dominantly low-n steady mild rotating MHD edge harmonic oscillations (EHOs) localised in the pedestal region. EHOs have been observed in DIII-D, ASDEX-U, JET and JT60 [1]. In JET such a MHD activity is referred to as Outer Modes (OMs) [2].