| 摘要 |
PURPOSE:To prevent a change in the intensity of a magnetic field and the uniformity of the magnetic field by providing the following: a pressure sensor used to detect a pressure inside a refrigerant container; and a pressure control means used to keep the inside of the refrigerant container at a prescribed pressure by applying an electric current to a heater attached to a cooling part by means of a signal from the pressure sensor. CONSTITUTION:When a pressure inside a liquid helium container 2 is lowered, a pressure sensor 8 detects the pressure. An electric current is applied to a heater 9 by using a pressure control means 10; and the cooling capacity of a very low temperature apparatus is lowered. The temperature of the liquid helium container 2 and a thermal shield 3 is raised. As a result, liquid helium 1 is evaporated. The pressure inside the liquid helium container 2 is raised. When it reaches a prescribed pressure, the electric current to the heater 9 is stopped by using the pressure control means 10. Consequently, the pressure inside the refrigerant container 2 is kept definite. Thereby, the refrigerant container 2 is not deformed by the pressure, and a superconducting coil 7 which has been wound on the refrigerant container 2 is not deformed. As a result, the intensity of a magnetic field and the uniformity of the magnetic field can be kept definite. |
