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Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal
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2005
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Image ReconstructionX-ray SpectroscopyEngineeringPlasma PhysicsMagnetic Confinement FusionSynchrotron Radiation SourceX-ray ImagingRadiographyX-ray TechnologyMagnetohydrodynamicsInstrumentationRadiation ImagingSawtooth OscillationSoft X-ray SignalRadiologyHealth SciencesPhysicsMedical ImagingSawtooth OscillationsHt-7 TokamakSynchrotron RadiationX-ray Free-electron LaserNuclear AstrophysicsPrecursor OscillationX-ray DiffractionX-ray OpticTomography
It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate two-dimensional (2D) images of sawtooth oscillation on the HT-7 tokamak using the Fourier–Bessel harmonic reconstruction method and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasi-interchange mode. The characteristics of them=1/n=1 mode structure observed in the soft x-ray tomography are as follows: the magnetic surface is made up of the crescent-shaped ``hot core'' and the circular ``cold bubble''. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.