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Title: Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis

Abstract

Spatiotemporal mode coupling is studied experimentally in a cylindrical plasma device. For that purpose, a bicoherence analysis is applied to spatially resolved measurements of drift wave fluctuations in order to study nonlinear coupling in the wave number spectrum. The use of the k bicoherence is shown to be much more accurate and straightforward than one of the {omega} bicoherence, revealing bicoherence bursts with a characteristic duration shorter than the characteristic period of the signals. It is demonstrated that intermittent structures can be produced during these events.

Authors:
; ; ;  [1]
  1. Max-Planck-Institute for Plasma Physics, EURATOM Association, D-17491 Greifswald (Germany)
Publication Date:
OSTI Identifier:
20860429
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 12; Other Information: DOI: 10.1063/1.2402131; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COUPLING; CYLINDRICAL CONFIGURATION; FLUCTUATIONS; LANGMUIR PROBE; NONLINEAR PROBLEMS; PLASMA; PLASMA DRIFT; PLASMA WAVES; THERMONUCLEAR DEVICES; TURBULENCE

Citation Formats

Brochard, F., Windisch, T., Grulke, O., and Klinger, T. Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis. United States: N. p., 2006. Web. doi:10.1063/1.2402131.
Brochard, F., Windisch, T., Grulke, O., & Klinger, T. Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis. United States. doi:10.1063/1.2402131.
Brochard, F., Windisch, T., Grulke, O., and Klinger, T. Fri . "Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis". United States. doi:10.1063/1.2402131.
@article{osti_20860429,
title = {Experimental evidence of mode coupling in drift wave intermittent turbulence using a wave number bicoherence analysis},
author = {Brochard, F. and Windisch, T. and Grulke, O. and Klinger, T.},
abstractNote = {Spatiotemporal mode coupling is studied experimentally in a cylindrical plasma device. For that purpose, a bicoherence analysis is applied to spatially resolved measurements of drift wave fluctuations in order to study nonlinear coupling in the wave number spectrum. The use of the k bicoherence is shown to be much more accurate and straightforward than one of the {omega} bicoherence, revealing bicoherence bursts with a characteristic duration shorter than the characteristic period of the signals. It is demonstrated that intermittent structures can be produced during these events.},
doi = {10.1063/1.2402131},
journal = {Physics of Plasmas},
number = 12,
volume = 13,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The spectrum cascade by mode coupling in drift-wave turbulence occurs to larger and smaller values of vertical-barkvertical-bar rather than toward lower frequencies. This leads to the dual cascade process; energy cascades to smaller k while entropy (square of the vorticity) cascades to larger k, analogous to two-dimensional hydrodynamic turbulence. However, the speed of energy condensation to k = 0 is much slower than in the hydrodynamic case.
  • Experimental evidence of the nonlinear nature of the broadband edge fluctuations has been obtained in edge turbulence in the Advanced Toroidal Facility torsatron. Whereas little nonlinear wave interaction is found in the scrape-off layer region, three-wave coupling is enhanced in the plasma edge region ([ital r][lt][ital a][sub shear]). The degree of three-wave coupling strongly depends on the plasma conditions; it decreases in the temperature range ([ital T][sub [ital e]][approx]10 eV) where the ionization rates depend strongly on [ital T][sub [ital e]] suggesting a link between ionization source and turbulence.
  • A recently introduced tool for the analysis of turbulence, wavelet bicoherence [van Milligen, Hidalgo, and Sanchez, Phys. Rev. Lett. {bold 16}, 395 (1995)], is investigated. It is capable of detecting phase coupling---nonlinear interactions of the lowest (quadratic) order---with time resolution. To demonstrate its potential, it is applied to numerical models of chaos and turbulence and to real measurements. It detected the coupling interaction between two coupled van der Pol oscillators. When applied to a model of drift wave turbulence relevant to plasma physics, it detected a highly localized coherent structure. Analyzing reflectometry measurements made in fusion plasmas, it detected temporalmore » intermittency and a strong increase in nonlinear phase coupling coinciding with the L/H (low-to-high confinement mode) transition. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • Nonlinear interactions in strong plasma turbulence have been investigated in the vicinity of the Earth`s quasiparallel bow shock by making use of magnetometer data from the AMPTE--UKS (Active Magnetospheric Particle Tracer Explorers--United Kingdom Subsatellite) spacecraft. Using a new and more robust estimator of the bicoherence, it is shown that the large-amplitude monolithic magnetic structures observed upstream the shock front interact with the whistler wave trains that accompany them. A unified picture emerges, in which the whistlers progressively grow from these soliton-like structures through nonlinear interaction, similarly to the dynamical evolution of step-like profiles in the Korteweg--de Vries equation. {copyright} {italmore » 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • The bicoherence of fluctuations in a system of drift waves and zonal flows is discussed. In strong drift-wave turbulence, where broadband fluctuations are excited, the bicoherence is examined. A Langevin equation formalism of turbulent interactions allows us to relate the bicoherence coefficient to the projection of nonlinear force onto the test mode. The dependence of the summed bicoherence on the amplitude of zonal flows is clarified. The importance of observing biphase is also stressed. The results provide a basis for measurement of nonlinear interaction in a system of drift waves and zonal flow.