MHD Stability Limit Analysis in JET High bN Advanced Scenarios

High bN plasmas with q and pressure profiles ranging from Hybrid to ITB shapes ( min q from 1 to above 2) have been explored in JET experiments on advanced regimes. Various instabilities were observed, including ideal-like modes with toroidal number n = 1 and tearing modes (NTMs) with m/n = 2/1, 3/2, 4/3, up to n = 6. In the hybrid regime in particular, modes with n < 3 had detrimental effects on confinement, and a large part of the experimental effort was spent to reach relatively stable conditions with only n 3 modes. Furthermore, the n = 1 mode was the main obstacle to the prolongation of high bN phases, when this parameter was pushed towards the maximum value in each regime. The n = 1 mode at high bN featured some characteristics in common with the Resistive Wall Mode (RWM), i.e. initial slow growth in the absence of magnetic reconnection, and some others in common with energetic particle modes, like the possible occurrence in the form of fishbone-like bursts.
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