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P: Fachverband Plasmaphysik

P 17: Poster II

P 17.18: Poster

Freitag, 3. September 2021, 14:00–16:00, P

Causality study on the drift-wave turbulence -- zonal-flow coupling at the TJ-K stellarator. — •Nicolas Dumérat, Bernhard Schmid, and Mirko Ramisch — IGVP, University of Stuttgart

We present a set of two non-parametric methods used for inferring causality amongst parameters measured in the same complex system. Convergent cross-mapping, a forecasting approach is introduced, based on time-delay embedding and state space reconstruction. This method showed good results for measuring the strength and direction of influence of causal relationships in synthetic datasets. A second method, called transfer entropy, is also investigated, the basis of which is the measurement of information flow between variables. The use of these methods allows for the identification of causal links between variables and can be extended to turbulence studies. In this frame, it is known that zonal flows are driven by the localized tilting of ambient turbulent structures. This deformation of the eddies can be caused by existing shear flows and measured experimentally via Reynolds stress. Langmuir probe measurements from the TJ-K stellarator are then used as experimental inputs for the presented methods. The results support the theoretically expected causal connection of eddy tilting to zonal-flows occurance.