Original title: Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Authors: Seidl, Jakub ; Jiráková, Kateřina ; Adámek, Jiří ; Grover, Ondřej ; Horáček, Jan ; Hron, Martin ; Vondráček, Petr
Document type: Papers
Conference/Event: 45th European Physical Society Conference on Plasma Physics, Praha (CZ), 20180702
Year: 2018
Language: eng
Abstract: We have identified two distinct types of turbulent fluctuations in COMPASS plasmas, the high-frequency edge oscillations and low-frequency SOL blobs. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of isat fluctuations is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL. This supports, together with turbulence spreading rate being positive in the near SOL but negative in the edge, the picture presented in [3] that most of the fluctuations that form a positive skewness in the edge region disappear around LCFS and new blobs are formed in the near SOL. Further, we cannot confirm the assumption that the blobs are generated randomly according to a Poisson process. Oscillations of all measured quantities, incl. radial particle flux, in the near SOL are peaked around ∼13 kHz. This seems to correspond to a poloidally rotating structure with a rather large poloidal wave-length ∼ 15 − 20 cm, that at least partly modulates blob generation. Nevertheless, we note that time separation of blobs becomes more random further in the SOL, possibly due to differences in their individual propagation. These observations hold for diverted plasmas, but the situation may be different in limited low-elongation plasmas where the radius of zero skewness was observed to be shifted significantly (several cm) inwards, compared to diverted configuration, and Gamma-like PDF is detected even inside the LCFS. Study of these plasmas is ongoing.
Keywords: plasma; tokamak; turbulence
Project no.: GA16-25074S (CEP), 8D15001 (CEP), LM2015045 (CEP)
Funding provider: GA ČR, GA MŠk, GA MŠk
Host item entry: 45th EPS Conference on Plasma Physics, EPS 2018, ISBN 9781510868441

Institution: Institute of Plasma Physics AS ČR (web)
Document availability information: Fulltext is available at external website.
External URL: http://ocs.ciemat.es/EPS2018PAP/pdf/P1.1103.pdf
Original record: http://hdl.handle.net/11104/0293868

Permalink: http://www.nusl.cz/ntk/nusl-392805


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