A refrigerator (180) for cooling the interior of the superconducting coil (140), the coolant container (130), the radiation shield (120), the vacuum container (110), the coolant container (130) and the radiation shield (120) A tubular current lead (not shown) electrically connected to the superconducting coil (140), constituting a flow path of the refrigerant (151) which has penetrated from the outside of the vacuum container (110) to the inside of the refrigerant container (130) A pressure gauge (198) disposed outside the vacuum container (110) and electrically connected to the current lead (190), a pressure gauge (198) for measuring the pressure inside the refrigerant container (130), a vacuum A thermometer (122) disposed in the container (110) for measuring the temperature of the current lead (190), a control unit (122) connected to each of a power supply (193), a pressure gauge (198) and a thermometer (199). The control unit (199) increases the output of the power supply (193) only when the measured value of the pressure gauge (198) is equal to or greater than the set value and the measured value of the thermometer (122) is equal to or less than the set value, and the superconducting coil Thereby changing the value of the current flowing through the current path (140).超電導コイル(140)と、冷媒容器(130)と、輻射シールド(120)と、真空容器(110)と、冷媒容器(130)の内部および輻射シールド(120)を冷却する冷凍機(180)と、真空容器(110)の外側から冷媒容器(130)の内側まで貫通して気化した冷媒(151)の流路を構成し、超電導コイル(140)に電気的に接続された管状の電流リード(190)と、真空容器(110)の外側に配置され、電流リード(190)と電気的に接続された電源と、冷媒容器(130)の内部の圧力を測定する圧力計(198)と、真空容器(110)内に配置されて電流リード(190)の温度を測定する温度計(122)と、電源(193)、圧力計(198)および温度計(122)の各々に接続された制御部(199)とを備える。制御部(199)は、圧力計(198)の測定値が設定値以上、かつ、温度計(122)の測定値が設定値以下である場合のみ電源(193)の出力を上昇させて超電導コイル(140)に流れる電流値を変化させる。
