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 fastions to the ELM stability and the transient heat loads on plasma facing components.