Observation of the palm tree mode, a new MHD mode excited by type-I ELMs on JET

A new MHD mode has been discovered during type-I ELMy H-modes in the Joint European Torus (JET) tokamak. This mode is excited by the perturbation of the edge plasma due to the edge localized mode (ELM). It is radially and poloidally well localized and has the toroidal mode number n = 1 and the poloidal mode number m = 3. The mode appears in different plasma configurations and in a wide range of global plasma parameters as long as the rational q = 3 surface is located in the ELM perturbed region. A possible explanation for the new mode is as the remnant of a magnetic island created by edge ergodization during the ELM. Consequences for the understanding of the ELM process itself are discussed.