Berlin 2014 – scientific programme

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P: Fachverband Plasmaphysik

P 12: Poster Session - Magnetic Confinement

P 12.6: Poster

Tuesday, March 18, 2014, 16:30–18:30, SPA Foyer

Permutation entropy analysis of density fluctuations in the torsatron TJ-K — •Dong Wang and Mirko Ramisch — Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart

In order to explore the nature of density fluctuations in the edge of magnetically confined fusion plasmas, the technique of permutation entropy and statistical complexity is used. The location of fluctuations on the entropy versus complexity plane classifies the dynamical behaviour of the system. The behaviour can be differentiated between stochastic and chaotic. The latter is supposed to be connected to a specific temporal form of intermittent density events, i.e. blobs, in the scrape-off layer (SOL).

In this contribution, density fluctuations measured with a Langmuir probe in the torsatron TJ-K are analyzed with respect to the dynamical nature. Radial scans are performed across the separatrix to distinguish the dynamics in the inner edge and the SOL. Comparisons with well known test systems indeed point to a qualitative change in the dynamics across the separatrix. In the region of maximum density gradient, the fluctuations are charaterized by minimum entropy. The results will be discussed on separated scales.