Cryostat including gas phase volume-varying unit

A cryostat comprising:

• a coolant tank housing a liquid coolant,
• a refrigerator provided above the coolant tank, which recondenses the liquid coolant evaporated in the coolant tank,
• a cylindrical member housing a lower part of the refrigerator and forming a recondensing chamber that communicates with the coolant tank, and
• a variable volume container assembly communicating with a gas-phase space above a liquid surface of the liquid coolant in the coolant tank and varying a gas phase volume in the gas-phase space to cancel out a pressure fluctuation in the coolant tank,
• wherein the variable volume container assembly comprises:
• a variable volume container capable of varying the gas phase volume in the gas-phase space, and
• a waveform generator which produces a drive waveform in a substantially opposite phase to a waveform of the pressure fluctuation in the coolant tank by using a phase of a liquefaction cycle of the refrigerator;
• and
• wherein
• a volume of the variable volume container is controlled with the drive waveform produced by the waveform generator,
• a valve is rotated by a motor in the refrigerator,
• the variable volume container assembly further comprises a rotation angle detector which detects a rotation angle of the motor, and
• the waveform generator produces the drive waveform by using a phase of a rotation of the motor, which has been detected by the rotation angle detector as the phase of the liquefaction cycle of the refrigerator.

A cryostat comprising:

• a coolant tank housing a liquid coolant,
• a refrigerator provided above the coolant tank, which recondenses the liquid coolant evaporated in the coolant tank,
• a cylindrical member housing a lower part of the refrigerator and forming a recondensing chamber that communicates with the coolant tank, and
• a variable volume container assembly communicating with a gas-phase space above a liquid surface of the liquid coolant in the coolant tank and varying a gas phase volume in the gas-phase space to cancel out a pressure fluctuation in the coolant tank,
• wherein the variable volume container assembly comprises:
• a variable volume container capable of varying the gas phase volume in the gas-phase space, and
• a waveform generator which produces a drive waveform in a substantially opposite phase to a waveform of the pressure fluctuation in the coolant tank by using a phase of a liquefaction cycle of the refrigerator;
• and
• wherein
• a volume of the variable volume container is controlled with the drive waveform produced by the waveform generator,
• a valve is rotated by a motor in the refrigerator, and
• the waveform generator produces the drive waveform by using a phase of a drive signal of the motor as the phase of the liquefaction cycle of the refrigerator.