The magnetic flux coordinates, such as Boozer's coordinates, are the important tool to study the magnetic configurations as well as plasma confinement in the toroidal devices. The coordinate is constructed by the algorithm given by Boozer; the magnetic surface is constructed by tracing a magnetic line of force for long time, until the line covers the surface sufficiently dense. The two dimensional Fourier transform on the magnetic surface is constructed by one dimensional Fourier transform along the magnetic line of force. However, if the rotational transform is near some low order rational number, it is not easy to obtain the reliable results.
The new method proposed in this paper is based on the construction of two dimensional surface; The algorithm construction the generalized magnetic coordinates [1-3] is applied. In the coordinate construction in [2,3] the magnetic surface is not required as the coordinate surface. The method employed in the paper use the same technique as [2-3], but requires the magnetic surface as a coordinate surface. For the toroidal angle variable ζ being suitably chosen, the poloidal angle θ is determined so that the magnetic line of force is a straight line on the θ-ζ plane.
No difficulty relating with the rational surface arises in this method, inasmuch as the nested magnetic surfaces exist.

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