The search for chaotic edge localized modes in ASDEX Upgrade

Time intervals between edge localized modes (ELMs) from the ASDEX Upgrade tokamak have been analysed to determine whether the ELM dynamics is chaotic (deterministic) or random (noise dominated). Two different methods have been used to detect unstable periodic orbits or unstable fixed points, which are indicators of chaos, in the ELM time series. It has been found that these time series generally are noise dominated, with the notable exception of five individual discharges in which traces of chaos have been detected.