Internal collapse of the plasma during the long pulse plasma discharge and its influence on the plasma performance

The main mission of the HT-7 machine is to explore high-performance plasma operation under steady-state conditions and relevant physics. The key issues for pursuing such study are wall recycling, high impurity radiation, and MHD instability. During the operation scenario of long pulse discharge, internal collapse of the plasma, apparently exhibited on the radiation signals of the soft X-ray (SXR), was observed. Following the event, the plasma was cooled down, accompanying strong plasma and wall interaction, finally the plasma thermal quench occurred. There is no apparent precursor except the peaking of the SXR radiation. Another type of internal collapse was also observed in the other operation scenario of synergy discharge of LHCD and IBW. In this paper, the relative phenomena are analyzed and discussed in detail.