Ion temperature fluctuations in the ASDEX Upgrade scrape-off layer

The ion temperature in turbulent plasma filaments T i fil is measured by a retarding field analyser during L-mode discharges in the ASDEX Upgrade tokamak. At 2 cm outside the separatrix T i fil ≈ 80–110 eV, which is 3–4 times that of the background ions and 50–70% of the ion temperature at the separatrix. T i fil is reproduced by a fluid model of the parallel filament transport assuming the radial filament propagation speed of 400–1000 m s −1 in the near scrape-off layer, consistent with earlier experimental estimates. The conditional sampling used in experiment to measure T i fil is tested on artificial time series obtained from a gyrofluid turbulence simulation.