EAST cryogenic system
A large scale helium cryogenic system is one of the key components for the EAST tokamak device for the cooling of the cooling of poloidal field (PF) and toroidal field (TF) coils, structures, thermal shields, buslines, HTS current leads and cryopumps. The total cold mass is about 250 tons. The basic design capacity of the refrigerator is 1050 W/3.5 K + 200 W/4.5 K + 13 g/s LHe + 12–30 kW/80 K. It is approximately equivalent to a helium refrigerator with the capacity more than 2 kW at 4 K. EAST cryogenic system is composed of compressors, oil removal systems(ORS), cold box, distribution system, liquid helium Dewar, helium recovery and storage system, purifier, etc.
The helium compressor system was built and put into operation in 2001. Two large-capacity oil injected screw compressors from the MYCOM company were installed in 2012. Seven domestic compressors which were developed from the Freon compressors are retained as spare and recovery compressors. The discharge pressure of MYCOM compressors is 2.1 MPa with a 370 g/s mass flow.
The ORS reduces the oil-residuals down to 10 ppb(w). EAST cryogenic system finished ORS upgrade in 2020. It has two sets of ORS, one is from MYCOM, another one is domestic，which improve the reliability. Impurity content in the purified helium gas meet: H2O <1 ppm，N2 < 1 ppm，CxHy < 1 ppm，Oil < 10 ppb.
All of the heat exchangers, 80 and 20 K adsorbers, five turbines, are installed in a vacuum insulated vessel—cold box. There is another vacuum insulated valve box to install the cryogenic valves at the liquid helium temperature level. Heat exchangers are of the aluminum plate-fin type. The total weight of all the heat exchangers is about 2 tones. There are 80 and 20 K active charcoal adsorbers in the coldbox in order to further remove impurities, such as nitrogen, oxygen, hydrogen and neon. 5 Cezch centripetal turbines with an impeller of the radial-axis type are installed in the cold box. The rotor rotates in dynamic gas bearing turbines with eddy current brake.
The cryogenic distribution system is designed to distribute refrigeration to all of the cold components. The 4.5 K liquid helium (LHe) vessel, the 3.5 K LHe sub-cooler, a LN2 vessel are installed in the valve box. Four SHe circulators and all of the cryogenic valves are installed on the top plate of the valve box with a diameter of 2.6 m.
A 10,000 L Dewar is installed for the storage of liquid helium. It can reserve the refrigeration power when the tokamak is in the idle mode, increase the cooling capacity of the plant by adding LHe to the 4.5 K vessel in the cryogenic distribution valve box when the heat load increases, and supply other laboratories with liquid helium.