Berlin 2014 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 12: Poster Session - Magnetic Confinement

P 12.10: Poster

Dienstag, 18. März 2014, 16:30–18:30, SPA Foyer

Estimation of statistical moments for single point measurements in the Scrape Off Layer — •Ralph Kube and Odd Erik Garcia — University of Tromsø, Department of Physics and Technology, Tromsø, Norway

Recent theoretical work argues that time series of the plasma particle density in the scrape-off layer (SOL) may be modelled as a shot noise process. It was shown that the superposition of individual bursts with an exponentially decaying wave form, exponentially distributed waiting times between bursts and burst amplitudes cause the particle density to be gamma distributed, in good agreement to single point measurements in the SOL.

In this contribution we derive expressions for the mean error on estimators for the mean, variance, skewness, and kurtosis for this class of shot noise processes. The number of samples of the time series, N, and the intermittency parameter γ that gives the ratio of the e-folding time of individual burst events to the waiting time between bursts, are free parameters.

We find that the rate of convergence of the estimator for the mean and normalized variance increase with γ and that the e-folding time of the individual burst events further cause a deviation from the N⁻¹ rate of convergence that holds for normally distributed random variables.

Comparing the expressions for the mean-squared error to synthetic time series shows good agreement. We also present a comparison to long ( t≃ 0.3s) single point measurements obtained by a Langmuir Probe and Gas-Puff imaging in the scrape-off layer of Alcator C-Mod.