| The EAST is a fully superconducting fusion experimental device, and it has been funded as a National Meg-science Engineering Project. The toroidal field (TF) magnets is one of the most important parts of EAST. It is made of NbTi/Cu cable in conduit conductor (CICC). They are cooled with forced flow supercritical helium and the windings should operate at the temperature from 3.8K to 4.5K.Conduction ,convection and radiation can bring heat load. When the TF magnets work at the temperature of 3.8K～4.5K, the heat load is 3928W in which the heat load from nitrogen screen, rarefactive gas and nuclear heat are the mainly compos ion., about ninety-six percent of it.The transient thermal analysis is to calculate the Alternating Current (AC Mosses during plasma discharge and after plasma disruption. The calculations show the average losses is almost 18J/m and the total quantity of heat can reach to 4375W.The process of the low temperature system is to take away heat load of TF and provide some wet helium to cool the current lead. Then the superconducting magnets can work steadily in the natural or disturbed state. A recommendation of the toroidal field's cooled fashion is stated in detail in the paper. The paper also calculated the necessary helium mass flow rate for TF coil during cooling the magnet from 300K to 80K . The mass flow also should keep 196g/s at the temperature of 3.8K and 218g/s after plasma disruption.A good performance of magnet is achieved successfully during the cool experiment on toroidal field. Some important parameters of magnet, such as the pressure, temperature, the helium flux are measured. The resistance of joint is less than 2×10-9O, and the pressure in the machine always maintain 10-4～10-3pa. The velocity in the process of cool-down from 300K to 80K is 1.02K/h. But from 80K TO 4.0K the velocity is slower , it's just only 0.45 K/h. the deference between them is because of the shrinkage of stainless steel. These data are very significant for the first operation of EAST. |
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