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Findings of pre-ELM structures through the observation of divertor heat load patterns at JET with applied n = 2 perturbation fields

Resonant magnetic perturbation experiments at JET with the ITER-like wall have shown the formation of radially propagating pre-ELM structures in the heat flux profile on the outer divertor. These appear a few milliseconds before the major divertor heat load, caused by type-I edge-localized modes (ELMs). The formation of the pre-ELM structures is accompanied by an increase in the Dα emission. For some pronounced examples, the propagation appears to end at the positions where an increased heat load is seen during the ELM crash a few milliseconds later. These observations are presented and discussed along with a comparison of a thermoelectric edge currents model.