Two-dimensional measurement becomes active to explore physics of plasma structure and dynamics. The paper proposes a set of new methods using the Fourier-Bessel function series expansion to characterize the twodimensional images for plasma and illustrates an example of its application to a phenomenon of quasi-periodic oscillations observed with tomography in a linear plasma device PANTA. The analysis provides quantitative relations between the coherent structure and residual random fluctuations of the oscillations. The results suggest that similarity between their spatial patterns should be increased in the phase when both amplitudes become stronger.
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