Preliminary observations of hot spot for HT-7 long pulse discharges

Hot spot has been widely observed during long pulse discharge operation of tokamak devices. On HT-7, with the constant improvements on the plasma facing materials, in-vessel structure and plasma control technique in recent five years, the maximum pulse length has been extended to about 5 min. At the same time, it is more and more frequent to observe hot spot during HT-7 long pulse discharges. In addition, it has caused serious damages to the inner structure. Since one of the main missions of the HT-7 is the physics study of the steady state operation, hot spot becomes important not only because it is a research topic under this condition, but also because it should be understood to be avoided for extending the pulse duration. This paper introduces the preliminary observations of two typical kinds of hot spot in HT-7 by using visible camera, infra-red (IR) camera, etc.