Tomography of m=1 mode structure in tokamak plasma using least-square-fitting method and Fourier–Bessel expansions

A method is discussed for reconstruction of the emissivity profile from projections. The emissivity profile is expanded into Fourier–Bessel expansions, of which coefficients are determined by the use of least-square-fitting method with the help of the Akaike information criterion. Tomographic reconstruction of the m=1 mode structure is obtained in JIPP T-II tokamak during the precursor oscillation of the sawtooth crash. The m=1 mode structure fits Wesson model rather than the Kadomtsev model.