m/n=1/1m/n=1/1 mode behavior during sawtooth activity in LHCD plasmas on the HT-7 tokamak

Different types of m/n=1/1m/n=1/1 mode during the central relaxation oscillations are observed in lower hybrid current drive (LHCD) plasma on the HT-7 tokamak. In this Letter, the difference of the mid-mode and the precursor on the sawtooth oscillation are reported using two-dimensional tomography of soft X-ray signal. It is shown that the growth rate of magnetic island of the mid-oscillation is smaller than that of the precursor oscillation, and the hot core in the mid-oscillation case does not move outward to the vicinity of the q=1q=1 surface. However, in the precursor oscillation case, the colder plasma develops a magnetic island on the former magnetic axis after the hot core expulsion, from the contour map of the soft X-ray emissivity.