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In this work the bispectral analysis method and its limitations are discussed. In order to study special features, it is applied to fluctuation data of the scrape-off layer of the tokamak ASDEX. The fluctuations are monitored by the H(alpha)-diagnostic and by probes. The application of the bispectral analysis to data of the ASDEX scrape-off layer leads to some interesting results: in every plasma discharge a significant bicoherence of up to 30% can be detected, which indicates a large nonlinearity in the plasma behaviour. The maximum bicoherence can be located at a position about 2.5 cm outside the separatrix. H-mode discharges can be distinguished from ohmic discharges on the basis of the results from the bispectral analysis. The shape of the predominant plasma events remains the same during different discharge types, but does depend on the plasma parameter studied. The application of the results to a simple plasma model to calculate the power transfer between Fourier components does not lead to clear results.

Additional information

Authors: WEINLICH M, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP III/183 DE (1992) 104 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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