Overview of ELM Control by Low n Magnetic Perturbations on JET

概要

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A series of ELM control experiments have been performed on JET aiming at a better understanding of the plasma response to applied magnetic perturbations. The dynamics of the edge profiles with applied n = 1 fields have been studied in the type-I ELM H-mode plasmas. Typically, the pedestal density decreased by about 20 % when the n = 1 perturbation field was applied (So called pump-out effect). However, there is no influence of the n = 1 fields on the recovery rate of the pedestal pressure, but the ELM crash occurs earlier and at a lower level of the pedestal pressure and pressure gradient. The compensation of the density pump-out has been demonstrated using either gas fuelling or pellets injection in low triangularity H-mode plasmas. Strong toroidal rotation braking by more than 60 % has been observed, and found to be independent on the safety factor. The calculated Neoclassical Toroidal Viscosity (NTV) torque profile in the ν regime including the boundary effect is in agreement with the observed torque profile induced by the n = 1 fields on JET. No complete ELM suppression was observed by application of either n = 1 or n = 2 fields with a Chirikov parameter above one at √ Ψ ≥ 0.925, which is one of the important criteria for the design of ITER ELM control coils.