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EP-4502499-B1 - METHOD FOR OPERATING CRYOGENIC REFRIGERATOR

EP4502499B1EP 4502499 B1EP4502499 B1EP 4502499B1EP-4502499-B1

Inventors

  • YOKOYA, IZURU
  • YOKODO, TAKAYUKI

Dates

Publication Date
20260513
Application Date
20230320

Claims (6)

  1. A method for operating a cryocooler (10), in which the cryocooler (10) includes an expander (14) having an expander motor (42) that is connected to a power source by a power supply cable (48) and is capable of being driven at a power source frequency, the method comprising: releasing connection between the power source and the expander motor (42) by the power supply cable (48); connecting the power source and the expander motor (42) via an inverter (60); executing an accelerated cooling operation of the cryocooler (10) in which the power source frequency is converted into an operation frequency higher than the power source frequency by the inverter (60) and the expander motor (42) is driven at the converted operation frequency; and removing the inverter (60) and reconnecting the power source and the expander motor (42), after the accelerated cooling operation is stopped.
  2. The method according to claim 1, wherein the cryocooler (10) includes a compressor (12) for suctioning and discharging a working gas to and from the expander (14), and the compressor (12) is connected to the expander motor (42) by the power supply cable (48) as the power source.
  3. The method according to claim 2, wherein instead of the compressor (12), as the power source, another compressor (13) having a larger capacity than the compressor (12) is connected to the expander motor (42) via the inverter (60), and is used for the accelerated cooling operation.
  4. The method according to any one of claims 1 to 3, further comprising: temporarily increasing an amount of a working gas of the cryocooler (10) during the execution of the accelerated cooling operation.
  5. The method according to any one of claims 1 to 4, wherein the cryocooler (10) is used for cooling of a superconducting coil (102), and the superconducting coil (102) is cooled by using an additional cooling device that supplies a cooled gas to a periphery of the superconducting coil (102), in addition to the accelerated cooling operation.
  6. The method according to any one of claims 1 to 5, further comprising: executing a normal cooling operation of the cryocooler (10) that drives the expander motor (42) at the power source frequency, before releasing connection between the power source and the expander motor (42) by the power supply cable (48); and ending the normal cooling operation.

Description

Technical Field The present invention relates to a method for operating a cryocooler. Background Art One of the main uses of a cryocooler is to cool a superconducting magnet. For that purpose, so-called immersion cooling in which the entire superconducting magnet is immersed in liquid helium is often used in the related art. The cryocooler is used to re-condense the vaporized liquid helium. In PTL 1, the cryocooler may stop the cooling operation, for example, in order to receive regular maintenance, or suddenly due to a failure or some abnormality. In the immersion cooling, even when the cryocooler is stopped, the liquid helium can contribute to cooling and maintaining the temperature of an object to be cooled such as a superconducting magnet. PTL 2 discloses a cryopump and a cryocooler having a cryocooler motor that is connected to a power source. The input power to the cryocooler inverter is supplied from the power source, and the inverter outputs the converted power to the cryocooler motor . Accordingly, the cryocooler motor is driven by the operating frequency which is determined by a control unit and which is output from the cryocooler inverter. The control unit dynamically lowers the maximum operating frequency of the cryocooler motor during a cooldown operation. Citation List Patent Literature [PTL 1] PCT Japanese Translation Patent Publication No. 2020-515038[PTL 2] United States Patent Publication No. 2016/177934 Summary of Invention Technical Problem However, the immersion cooling system requires a large amount (for example, several hundred liters or more) of liquid helium. Therefore, against the background of the recent tight global helium supply and demand, research and development of a helium-saving cooling method in which the amount of liquid helium used is significantly reduced compared to the immersion cooling is being conducted. In the helium-saving cooling, a cryocooler serves as a main (or only) cooling source. Therefore, unlike the immersion cooling, the object to be cooled may be significantly heated due to input heat from the surrounding environment during the operation stop of the cryocooler. In that case, there is a concern that it may take a considerable time to re-cool to a desired cooling temperature after the operation of the cryocooler is resumed. The downtime in which the object to be cooled cannot be used is prolonged, which is undesirable. One exemplary object of an aspect of the present invention is to provide a method for operating a cryocooler that assists in re-cooling of an object to be cooled. Solution to Problem According to an aspect of the present invention, there is provided a method for operating a cryocooler as defined in claim 1. The cryocooler includes an expander having an expander motor that is connected to a power source by a power supply cable and is capable of being driven at a power source frequency. The method includes: releasing connection between the power source and the expander motor by the power supply cable; connecting the power source and the expander motor via an inverter; executing an accelerated cooling operation of the cryocooler in which the power source frequency is converted into an operation frequency higher than the power source frequency by the inverter and the expander motor is driven at the converted operation frequency; and removing the inverter and reconnecting the power source and the expander motor, after the accelerated cooling operation is stopped. Any combination of the above components or components or expressions of the present invention that are mutually replaced between methods, devices, systems, or the like are also effective as aspects , whereby the appended claims define the scope of the present invention. Advantageous Effects of Invention According to the present invention, it is possible to provide a method for operating a cryocooler that assists in re-cooling of an object to be cooled. Brief Description of Drawings Fig. 1 is a diagram schematically showing a superconducting device according to an embodiment of the present invention.Fig. 2 is a diagram schematically showing a cryocooler according to an embodiment of the present invention.Fig. 3 is a diagram schematically showing the cryocooler according to the embodiment.Fig. 4 is a flowchart illustrating a method for operating the cryocooler according to the embodiment.Fig. 5 is a diagram schematically showing an example of accelerated cooling operation of the cryocooler according to the embodiment.Fig. 6 is a diagram schematically showing another example of the accelerated cooling operation of the cryocooler according to the embodiment.Fig. 7 is a diagram schematically showing another example of the accelerated cooling operation of the cryocooler according to the embodiment.Fig. 8 is a diagram schematically showing another example of the accelerated cooling operation of the cryocooler according to the embodiment.Fig. 9 is a diagram schematically showing another example