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Author(s):
M. Nunami, R. Kanno, S. Satake, H. Takamaru and T. Hayashi
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Title:
Development of Computational Technique for Labeling Magnetic Flux-surfaces
Date of publication:
Mar. 2006
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Key words:
Large Helical Device, magnetic island, flux-surface, Poincare plots, annealing method
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Abstract:
In recent Large Helical Device (LHD) experiments, radial profiles of ion temperature, electric field, etc. are measured in the m/n = 1/1 magnetic island produced by island control coils, where m is the poloidal mode number and n the toroidal mode number. When the transport of the plasma in the radial profiles is numerically analyzed, an average over a magnetic flux-surface in the island is a very useful concept to understand the transport. On averaging, a proper labeling of the flux-surfaces is necessary.
In general, it is not easy to label the flux-surfaces in the magnetic field with the island, compared with the case of a magnetic field configuration having nested flux-surfaces. In the present paper, we have developed a new computational technique to label the magnetic flux-surfaces. This technique is constructed by using an optimization algorithm, which is known as an optimization method called the simulated annealing method. The flux-surfaces are discerned by using two labels: one is classification of the magnetic field structure, i.e., core, island, ergodic, and outside regions, and the other is a value of the toroidal magnetic flux. We have applied the technique to an LHD configuration with the m/n = 1/1 island, and successfully obtained the discrimination of the magnetic field structure.
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