Magnetic Diagnostics of Magnetic Island in LHD

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  • NARUSHIMA Y.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • WATANABE K. Y.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • SAKAKIBARA S.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • OHYABU N.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • YAMADA H.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • NARIHARA K.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • YAMADA I.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • MORISAKI T.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • INAGAKI S.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • NAGAYAMA Y.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • KOMORI A.
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • LHD exp. group
    National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
  • COOPER W. A.
    CRPP Association Euratom / Confederartion Suisse, EPFL, 1015 Lausanne, Switzerland

Description

Characteristics of magnetic islands are investigated by magnetic diagnostics in the Large Helical Device (LHD). The structure of the magnetic island with m/n = 1/1 (where, m and n are poloidal and toroidal mode number, respectively) can be estimated from the perturbed magnetic field appearing when a magnetic island changes. To measure the toroidal profile of the perturbed magnetic field δb1 originating from the plasma, a toroidal array of magnetic flux loops is set up in the LHD. The toroidal profile of δb1 is then spatially Fourier decomposed to determine the amplitude of the n = 1 component, δb1n=1 and its phase, φn=1 which correspond the change of the island width and the toroidal position of the X-point of the island, respectively. Therefore, the information about the magnetic island structure can be obtained from δb1n=1 and φn=1. In case the island width becomes larger than the seed island, measurements show that δb1n=1 is non-zero and φn=1 is temporally constant. A non-zero δb1n=1 can also be observed when the island width becomes smaller than the seed island. In this case, the angle φn=1 shifts by about π[rad] compared with the increasing case and the δb1n=1 is limited to a certain value which corresponding to the magnetic field suppressing the seed island.

Journal

  • Plasma and Fusion Research

    Plasma and Fusion Research 2 S1094-S1094, 2007

    The Japan Society of Plasma Science and Nuclear Fusion Research

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