Soft-x-ray tomography of sawtooth oscillations in the JIPP T-II tokamak

Time evolutions of the soft-x-ray tomography of a tokamak plasma have been obtained during sawtooth oscillations by use of the Fourier-Bessel expansion technique. The colder plasma is carried to the center by a hydrodynamic flow, and becomes a new hot spot during the crash phase. The old hot core is pushed out and the new hot spot remains at the center after the crash. The observed sawtooth crash is consistent with neither the Kadomtsev model nor the Wesson model. The crash time is shorter as the current profile is broader.