Observation of accelerated beam ion population during edge localized modes in the ASDEX Upgrade tokamak

The interaction between fast-ions and edge localized modes (ELMs) is investigated by means of fast-ion loss detector measurements. Fast-ion losses are increased during ELMs exhibiting a 3D filamentary-like behaviour. An accelerated beam ion population has been observed during ELMs in a tokamak for the first time. Tomographic inversion of the measured fast-ion losses reveal multiple velocity-space structures. Attending to the experimental observations, an acceleration mechanism is proposed based on a resonant interaction between the beam ions and parallel electric fields emerging during the ELM crash. The key experimental observations can be qualitatively reproduced by full-orbit following simulations of fast-ions in the presence of the ELM magnetic and electric perturbation fields. Our findings may shed light on the possible contribution of fast-ions to the ELM stability and the transient heat loads on plasma facing components.