Multiple resonances of the edge-localized mode (ELM) frequency caused by the application of low n (=1 or 2) magnetic perturbations for ELM control have been observed on JET. With a low n field applied, a strong increase in ELM frequency, fELM, by a factor of ∼4.5 was found in many separated narrow windows of q95 (resonant q95), while the fELM increased only by a factor of ∼2 for non-resonant q95 values. The fractions of increase in fELM with different resonant q95 values are not the same. An analysis of ideal external peeling modes shows that both the dominant unstable peeling mode number and fELM depend on the amplitude of the normalized edge current density as well as the edge safety factor, qa.
Effect of resonant magnetic perturbations with toroidal mode numbers of 4 and 6 on edge-localized modes in single null H-mode plasmas in MAST