Design of actively cooled flat toroidal limiter with CuCr heat sink for the HT-7 superconducting tokamak

Long plasma discharges require in-vessel integration of actively cooled plasma facing components (PFC) in order to operate the HT-7 tokamak at the steady state. To promote power removing capacity, two flat toroidal limiters with high heat removal capability have been designed and installed in the HT-7 tokamak. The high performance toroidal limiters, 1.7 m² area, were located at top and bottom of the HT-7 vessel, covering 265° and 285°, respectively, in the toroidal direction. The bolted structure for the graphite tile has been adopted. Employing flexible graphite sheet interlayer between the graphite tile and copper alloy heat sink has been demonstrated to be an effective way to improve heat transfer. The water cooling in the heat sink has been specially designed with large channel. The geometry of the array bars in the water cooling channel accelerates the turbulent flow of the cooling water and provided higher heat removing capacity. The experiences accumulated in the process of design of the HT-7 toroidal limiter will be helpful to design high thermal conductive plasma facing components with easy maintenance. Its heat removal capacity has been increased by a factor of 5 compared with the previous the HT-7 poloidal limiter with stainless steel heat sink, which were served as the main limiter.