Identification of m=2 competent mode of complex magneto-hydro-dynamics activities during internal soft disruption based on singular value decomposition and tomography of soft-X-ray emission on the HT-7 tokamak

In this paper, the singular value decomposition (SVD) method as a filter is applied before the tomographic inversion of soft-X-ray emission. Series of 'filtered' signals including specific chronos and topos are obtained. (Here, chronos and topos are the decomposed spatial vectors and the decomposed temporal vectors, respectively). Given specific magnetic flux function with coupling m=1 and m=2 modes, the line-integrated soft-X-ray signals at all chords have been obtained. Then m=1 and m=2 modes have been identified by tomography of simulated 'filtered' signals extracted by the SVD method. Finaly, using the experimental line-integrated soft-X-ray signals,m=2 competent mode of complex magnetohydrodynamics(MHD) activities during internal soft disruption is observed. This result demonstrates that m=2 mode plays an important role in internal disruption (Here, m is the poloidal mode number).