[Table of Contents]

Plasma and Fusion Research

Volume 1, 041 (2006)

Regular Articles

Experimental Study of Nonlinear Processes in Edge Turbulence of Toroidal Plasmas
Yoshihiko NAGASHIMA, Katsumichi HOSHINO1), Kenichi NAGAOKA2), Kouji SHINOHARA1), Akihide FUJISAWA2), Kazuya UEHARA1), Yoshinori KUSAMA1), Katsumi IDA2), Yasuo YOSHIMURA2), Shoichi OKAMURA2), Keisuke MATSUOKA2), Akira EJIRI3), Yuichi TAKASE3), Kimitaka ITOH2), Masatoshi YAGI, Sanae-I. ITOH, JFT-2M group1) and CHS group2)
Research Institute for Applied Mechanics, Kyushu University
1)
Japan Atomic Energy Agency
2)
National Institute for Fusion Science
3)
University of Tokyo
(Received 23 February 2006 / Accepted 7 June 2006 / Published 25 September 2006)

Abstract

This paper presents experimental studies of nonlinear processes between meso-scale structures and turbulent fluctuations, by use of bispectral analysis, in the edge region of toroidal plasmas. In ohmically heated plasmas of the JFT-2M tokamak, the drift wave-zonal flow system is investigated by observation of the potential fluctuations. The total bicoherence is composed of two components, i.e., the peak at the geodesic acoustic mode (GAM) frequency and broadband distribution. The biphase is also obtained, which indicates the phase angle of coherent interaction between GAM oscillations and broadband fluctuations. Bispectral functions (e.g., magnitude and phase) give an order-of-estimate agreement for the drift wave-zonal flow systems. Bicoherence analysis is also applied to the edge plasmas of the high-confinement mode (H-mode) of the Compact Helical System (CHS). In the case of CHS plasmas, nonlinear couplings in a system composed of coherent global magneto-hydrodynamic (MHD) oscillations and broadband fluctuations (up to hundreds kHz range) have been observed. Bispectral analysis enhances our understanding of the self-regulation systems of various toroidal plasmas in which strong turbulence and meso-scale structures coexist.

Keywords

nonlinear coupling, bispectral analysis, turbulence, coherent fluctuation, zonal flow-drift wave system, H-mode, JFT-2M, CHS

DOI: 10.1585/pfr.1.041

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This paper may be cited as follows:

Yoshihiko NAGASHIMA, Katsumichi HOSHINO, Kenichi NAGAOKA, Kouji SHINOHARA, Akihide FUJISAWA, Kazuya UEHARA, Yoshinori KUSAMA, Katsumi IDA, Yasuo YOSHIMURA, Shoichi OKAMURA, Keisuke MATSUOKA, Akira EJIRI, Yuichi TAKASE, Kimitaka ITOH, Masatoshi YAGI, Sanae-I. ITOH, JFT-2M group and CHS group, Plasma Fusion Res. 1, 041 (2006).