| 摘要 |
PURPOSE: To keep a heat radiation shield at an almost fixed temperature by making a tank for cooling an external shield house a second liquid having a boiling point lower than normal temperature, and providing a transfer means for evaporating the second liquid, and a return means for returning a gas generated by evaporation to the tank. CONSTITUTION: The tank 52 of liquid nitrogen provided with an interval from the external shield 32 forms a part of a heat siphon and the external shield 34 is maintained at fixed temperature of 77.3 deg.K. The temperature is the boiling point of the liquid nitrogen under atmospheric pressure (15 psia). An output port 64 is provided on the base part of the tank 52 and the output port 64 supplies the liquid nitrogen to two tube lines. The respective tube lines are provided with a lower leg 66 and an upper leg 68 and return the gas generated by boiling to the tank by them. By the boiling of the liquid nitrogen in direct thermal contact with the shell body 34A of the external radiation shield 34, the shield is maintained at the fixed temperature and eddy current compensation required for the excitation of a gradient coil is made possible. |
