The MHD instabilities in the plasma centre can be observed with pinhole cameras to record soft X-ray (SXR) emission along many chords with high speatial resolution. The soft X-ray system in the HL-1M tokamak consists of three pinhole cameras with 60 chords. The method of singular value decomposition(SVD) can split such signals into orthogonal spatial and temporal vectors. By this means,
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