SMuK 2023 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 12: Poster II

P 12.26: Poster

Mittwoch, 22. März 2023, 17:30–19:00, HSZ EG

Causal coupling between small-scale fluctuations and zonal flows at the stellarator TJ-K — •Nicolas Dumérat and Mirko Ramisch — IGVP, University of Stuttgart, Germany

Convergent cross mapping (CCM) is a causality inference technique used to identify causal links and directions of influence between variables. In this work, Langmuir probe measurements of plasma potential and density fluctuations across TJ-K’s whole poloidal cross section are used as input for the CCM to map causal links between turbulent phenomena across distant flux surfaces.

Thus, zonal potential (ZP) structures are found to be causally related to density fluctuations in the core, which could reflect equilibrium density modulation via transport regulation by ZP through the shearing of drift-wave structures. Causal coupling between plasma potential and ZP fluctuations has been found to exhibit a strong bi-directional relation around the region of both maximum Reynolds stress and turbulent particle transport. Moreover, ZP is found to be caused by small-scale density and potential fluctuations with density dominating over potential. This is in line with vortex tilting and subsequent zonal flow drive in consequence of strong density-potential coupling drift-wave turbulence. The expected predator-and-prey relationship between background turbulent structures and zonal flows is unveiled with CCM and further analysis concerning its poloidal locality is under investigation.