Plasma and Fusion Research

Volume 2, S1094 (2007)

Regular Articles

Magnetic Diagnostics of Magnetic Island in LHD

Y. NARUSHIMA, K. Y. WATANABE, S. SAKAKIBARA, N. OHYABU, H. YAMADA, K. NARIHARA, I. YAMADA, T. MORISAKI, S. INAGAKI, Y. NAGAYAMA, A. KOMORI, LHD exp. group and W. A. COOPER¹⁾

National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
1): CRPP Association Euratom / Confederartion Suisse, EPFL, 1015 Lausanne, Switzerland

(Received 13 December 2006 / Accepted 23 April 2007 / Published 20 November 2007)

Abstract

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, φ_n=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 φ_n=1. In case the island width becomes larger than the seed island, measurements show that δb₁ⁿ⁼¹ is non-zero and φ_n=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 φ_n=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.

Keywords

Large Helical Device, magnetic island, magnetic diagnostics, self-healing

DOI: 10.1585/pfr.2.S1094

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References

[1] T. Ozeki and JT-60 team, Plasma Phys. Control. Fusion 45, 645 (2003).
[2] T.C. Hender et al., Nucl. Fusion 44, 788 (2004).
[3] K. Narihara et al., Phys. Rev. Lett. 87, 135002 (2001).
[4] N. Ohyabu et al., Phys. Rev. Lett. 88, 055005 (2002).
[5] N. Ohyabu et al., Plasma Phys. Control. Fusion 47, 1431 (2005).
[6] K. Narihara et al., Rev. Sci. Instrum. 72, 1122 (2001).
[7] A.H. Boozer, Phys. Fluids 27, 2055 (1984).
[8] T. Morisaki et al., Fus. Eng. Des. 65, 475 (2003).
[9] Y. Narushima et al., Proc. 31st EPS Conf. ECA Vol.28G, P-5.113 (2004).
[10] C.C. Hegna and A. Bhattacharjee, Phys. Fluids B1, 392 (1989).

This paper may be cited as follows:

Y. NARUSHIMA, K. Y. WATANABE, S. SAKAKIBARA, N. OHYABU, H. YAMADA, K. NARIHARA, I. YAMADA, T. MORISAKI, S. INAGAKI, Y. NAGAYAMA, A. KOMORI, LHD exp. group and W. A. COOPER, Plasma Fusion Res. 2, S1094 (2007).