Cryogenic temperature cooling system and cryogenic temperature cooling method

Abstract

To improve energy efficiency when cooling a cooled object by circulating a heat medium which is cooled by a cooling source.SOLUTION: A cryogenic temperature cooling system comprises: a storage container 12 in which a coolant 12A of a cryogenic temperature liquid and a coolant 12B of a gas are stored; a liquid phase heat exchanger 13 which is in contact with the coolant of the liquid inside of the storage container; a gas phase heat exchanger 14 which is in contact with the coolant of the gas inside of the storage container and connected to the liquid phase heat exchanger; and a circulation system 15 which includes a supply side pipe 16 guiding a heat medium 15H from the liquid phase heat exchanger to a superconducting coil 1 and a return side pipe 17 guiding the heat medium from the superconducting coil to the gas phase heat exchanger and circulates the heat medium. A heat shield 2 at a higher temperature than that of the superconducting coil is thermally in contact with the return side pipe of the circulation system. The heat medium which is successively cooled by heat exchange with the coolants by the gas phase heat exchanger and the liquid phase heat exchanger is supplied to the supply side pipe to cool the superconducting coil into a cryogenic temperature and guided to the return side pipe to cool the heat shield into a cryogenic temperature.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a cryogenic cooling system and a cryogenic cooling method.

Background Art

[0002] Generally, a superconducting coil is used after being cooled to a cryogenic temperature by a cryogenic agent such as liquid helium or a cooling source such as a cryogenic refrigerator. Here, as a method of transferring heat between the superconducting coil and the cooling source, there are a conduction cooling method and a refrigerant circulation method. The conduction cooling method is used in many superconducting devices because of its simple configuration. However, this conduction cooling method has a problem that in a high magnetic field device or a large device, the distance between the cooling source and the superconducting coil becomes long and the temperature difference between the two becomes large. In such superconducting devices, the refrigerant circulation method is used.

[0003] On the other hand, in recent years, development of devices using hydrogen energy as a countermeasure against global warming has been actively carried out, and development of liquid hydrogen and high-temperature superconducting devices using the same has been promoted. Liquid hydrogen has an advantage in automobiles, aircraft, etc. because its volume can be made smaller than that of gaseous hydrogen. Further, by using a high-temperature superconducting motor cooled with this liquid hydrogen, it becomes possible to realize miniaturization and weight reduction of the motor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Examples of cryogenic cooling systems such as described above include those shown in Patent Documents 1, 2, and 3, and FIG. 4. In FIG. 4, the cryogenic cooling system 100 includes a first vacuum vessel 111 that houses a superconducting coil 101 as an object to be cooled, a second vacuum vessel 112 that houses a storage vessel 113 in which liquid hydrogen 113H as a refrigerant is stored, and a circulation system 117 that includes a supply-side pipe 114, a return-side pipe 115, and a cryogenic fan 116. This circulation system 117 supplies and circulates a heat medium 118 cooled by the liquid hydrogen 113H in the storage vessel 113 to the superconducting coil 101 through the supply-side pipe 114 by the operation of the cryogenic fan 116 disposed in the return-side pipe 115.

[0006] One of the problems of the cryogenic cooling system 100 described above is to reduce the consumption of liquid hydrogen 113H. For this purpose, it is particularly necessary to reduce the amount of heat intrusion into the superconducting coil 101. As a method for reducing this amount of heat intrusion, a method of providing a heat shield is known. However, in order to cool the heat shield, an additional cooling source is required, so it is not necessarily effective in consideration of the overall energy efficiency.

[0007] Embodiments of the present invention have been made in consideration of the above circumstances, and an object thereof is to provide a cryogenic cooling system and a cryogenic cooling method capable of improving energy efficiency when cooling an object to be cooled by circulating a heat medium cooled by a cooling source.

Means for Solving the Problem

[0008] The cryogenic cooling system in the embodiment of the present invention is a cryogenic cooling system for cooling a first object to be cooled and a second object to be cooled to cryogenic temperatures, comprising: a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant obtained by evaporation of this refrigerant; a liquid-phase heat exchanger provided in the storage container and in contact with the liquid refrigerant; a gas-phase heat exchanger provided in the storage container and in contact with the gaseous refrigerant, and connected to the liquid-phase heat exchanger; a supply-side pipe for guiding a heat medium from the liquid-phase heat exchanger to the first object to be cooled, and a return-side pipe for guiding the heat medium from the first object to be cooled to the gas-phase heat exchanger, and having a circulation system for circulating the heat medium; wherein the second object to be cooled set at a temperature higher than that of the first object to be cooled is provided in thermal contact with the return-side pipe of the circulation system; and the heat medium sequentially cooled by heat exchange with the refrigerant by the gas-phase heat exchanger and the liquid-phase heat exchanger is supplied to the supply-side pipe to cool the first object to be cooled to cryogenic temperatures and is guided to the return-side pipe to cool the second object to be cooled to cryogenic temperatures.

[0009] The cryogenic cooling method in the embodiment of the present invention is a cryogenic cooling method for cooling a first object to be cooled and a second object to be cooled to cryogenic temperatures, comprising: preparing a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant obtained by evaporation of this refrigerant; a liquid-phase heat exchanger provided in the storage container and in contact with the liquid refrigerant; a gas-phase heat exchanger provided in the storage container and in contact with the gaseous refrigerant, and connected to the liquid-phase heat exchanger; a supply-side pipe for guiding a heat medium from the liquid-phase heat exchanger to the first object to be cooled, and a return-side pipe for guiding the heat medium from the first object to be cooled to the gas-phase heat exchanger, and having a circulation system for circulating the heat medium; providing the second object to be cooled set at a temperature higher than that of the first object to be cooled in thermal contact with the return-side pipe of the circulation system; supplying the heat medium sequentially cooled by heat exchange with the refrigerant by the gas-phase heat exchanger and the liquid-phase heat exchanger to the supply-side pipe to cool the first object to be cooled to cryogenic temperatures, and then guiding it to the return-side pipe to cool the second object to be cooled to cryogenic temperatures.

Advantages of the Invention

[0010] According to an embodiment of the present invention, energy efficiency can be improved when cooling an object to be cooled by circulating a heat medium cooled by a cooling source.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. [A] First Embodiment (FIG. 1) FIG. 1 is a schematic pipeline diagram showing the configuration of a cryogenic cooling system according to the first embodiment. The cryogenic cooling system 10 shown in FIG. 1 cools a superconducting coil 1 as a first object to be cooled and a cooling stage 11 to a cryogenic temperature (for example, 20 K), and a heat shield 2 as a second object to be cooled to a cryogenic temperature (for example, 50 K to 40 K). This cryogenic cooling system 10 includes, in addition to the cooling stage 11 and the heat shield 2, a storage container 12 for storing refrigerants 12A and 12B as a cooling source, a liquid-phase heat exchanger 13, a gas-phase heat exchanger 14, a supply-side pipe 16, a return-side pipe 17, and a low-temperature fan 18, and a circulation system 15 for circulating a heat medium 15H, and a first vacuum container 21 and a second vacuum container 22.

[0013] The cooling stage 11 is thermally in contact with the superconducting coil 1 using, for example, a high-purity aluminum sheet, and the superconducting coil 1 is placed thereon. Further, the cooling stage 11 is fixed to the supply-side pipe 16 of the circulation system 15 using, for example, silver wax, and is thermally in contact with the supply-side pipe 16.

[0014] The storage container 12 stores both the cryogenic liquid refrigerant 12A and the gaseous refrigerant 12B obtained by evaporation of this liquid refrigerant 12A. Liquid hydrogen is used as the liquid refrigerant 12A, but liquid neon, liquid nitrogen, liquid argon, etc. may also be used.

[0015] The liquid-phase heat exchanger 13 is installed in the storage container 12 and contacts the liquid refrigerant 12A, and cools the heat medium 15H of the circulation system 15 to a cryogenic temperature by heat exchange with this liquid refrigerant 12A. The gas-phase heat exchanger 14 is installed in the storage container 12, contacts the gaseous refrigerant 12B, and is connected to the liquid-phase heat exchanger 13. By this gas-phase heat exchanger 14, the gaseous refrigerant 12B and the heat medium 15H of the circulation system 15 are heat-exchanged, and the heat medium 15H is cooled to a cryogenic temperature.

[0016] Helium gas is used as the heat medium 15H circulating in the circulation system 15, but any gas such as hydrogen gas, nitrogen gas, neon gas, argon gas, etc. whose melting point is lower than the boiling point of the refrigerant 12A may be used. The supply-side pipe 16 guides the heat medium 15H from the liquid-phase heat exchanger 13 to the cooling stage 11. The return-side pipe 17 guides the heat medium 15H from the cooling stage 11 to the gas-phase heat exchanger 14. The cryogenic fan 18 is disposed in the return-side pipe 17 to pressurize the heat medium 15H and circulate this heat medium 15H among the supply-side pipe 16, the return-side pipe 17, the gas-phase heat exchanger 14, and the liquid-phase heat exchanger 13.

[0017] The first vacuum container 21 houses the superconducting coil 1 and the cooling stage 11, and reduces the amount of heat intrusion into the superconducting coil 1 and the cooling stage 11 by vacuum insulation. The second vacuum container 22 houses the storage container 12 and the cryogenic fan 18, and reduces the amount of heat intrusion into the storage container 12 and the cryogenic fan 18 by vacuum insulation. These first vacuum container 21 and second vacuum container 22 are connected and joined by the heat-insulating pipe portion 23, and the supply-side pipe 16 and the return-side pipe 17 are housed in this heat-insulating pipe portion 23.

[0018] The thermal shield 2 includes a coil-side thermal shield 2X that covers and encloses the superconducting coil 1 and the cooling stage 11, a container-side thermal shield 2Y that covers and encloses the storage region of the mainly liquid refrigerant 12A in the storage container 12, and a pipe-side thermal shield 2Z that covers and encloses the supply-side pipe 16 within the heat-insulating pipe section 23. The coil-side thermal shield 2X is provided within the first vacuum container 21 to reduce the amount of heat intrusion into the superconducting coil 1 and the cooling stage 11. The container-side thermal shield 2Y is provided within the second vacuum container 22 to reduce the amount of heat intrusion into the storage container 12. The pipe-side thermal shield 2Z is provided within the heat-insulating pipe section 23 to reduce the amount of heat intrusion into the supply-side pipe 16. Among these, the coil-side thermal shield 2X and the container-side thermal shield 2Y are thermally connected by the pipe-side thermal shield 2Z. Note that at least one of the coil-side thermal shield 2X, the container-side thermal shield 2Y, and the pipe-side thermal shield 2Z may be provided as appropriate.

[0019] These coil-side thermal shield 2X, container-side thermal shield 2Y, and pipe-side thermal shield 2Z are in thermal contact with the return-side pipe 17 of the circulation system 15 and are cooled to an extremely low temperature (for example, 50K to 40K) by the heat medium 15H flowing within this return-side pipe 17. On the other hand, the superconducting coil 1 is cooled to an extremely low temperature (for example, 20K) by the cooling stage 11 being in thermal contact with the supply-side pipe 16 of the circulation system 15 and being cooled to an extremely low temperature by the heat medium 15H flowing through the supply-side pipe 16. Therefore, the coil-side thermal shield 2X, the container-side thermal shield 2Y, and the pipe-side thermal shield 2Z are set to a higher temperature than the superconducting coil 1.

[0020] That is, by the operation of the low-temperature fan 18 in the circulation system 15, the heat medium 15H exchanges heat with the gaseous refrigerant 12B through the gas-phase heat exchanger 14 and is cooled, and then exchanges heat with the liquid refrigerant 13H through the liquid-phase heat exchanger 13 and is further cooled. The heat medium 15H sequentially cooled by the gas-phase heat exchanger 14 and the liquid-phase heat exchanger 13 is guided to the supply-side pipe 16 and supplied to the cooling stage 11 to cool the superconducting coil 1 to an extremely low temperature (for example, 20K). After cooling the superconducting coil 1, the heat medium 15H is guided to the return-side pipe 17, and the coil-side heat shield 2X, the pipe-side heat shield 2Z, and the container-side heat shield 2Y thermally contacting the return-side pipe 17 are sequentially cooled to an extremely low temperature (for example, 50K to 40K) and then returned to the low-temperature fan 18.

[0021] Here, a support member 24 for supporting the cooling stage 11 by the first vacuum vessel 21 penetrates the coil-side heat shield 2X. The support member 24 is thermally connected to the coil-side heat shield 2X and the thermal anchor 25, and thus is cooled to an extremely low temperature (for example, 50K to 40K) in the same manner as the coil-side heat shield 2X. Therefore, the support member 24 is also a second object to be cooled that is cooled by the heat medium 15H flowing in the return-side pipe 17 via the thermal anchor 25 and the coil-side heat shield 2X. By cooling the support member 24 to an extremely low temperature as described above, the amount of heat intrusion from the support member 24 into the superconducting coil 1 and the cooling stage 11 is reduced.

[0022] In addition, by cooling the heat shield 2 (coil-side heat shield 2X, container-side heat shield 2Y, pipe-side heat shield 2Z) to an extremely low temperature in addition to the superconducting coil 1 by the heat medium 15H circulating in the circulation system 15, the temperature of the gaseous refrigerant 12B discharged from the storage container 12 will rise compared to the case where the heat medium 15H cools only the superconducting coil 1. However, when the liquid refrigerant 12A is liquid hydrogen, the gaseous refrigerant 12B discharged from the storage container 12 is further heated to room temperature and used for a fuel cell or the like. Therefore, as described above, even if the temperature of the gaseous refrigerant 12B discharged from the storage container 12 rises, there is no problem.

[0023] Due to the configuration as described above, according to the first embodiment, the following effects (1) and (2) are achieved. (1) The superconducting coil 1 is covered by the coil-side thermal shield 2X, and the storage container 12 is covered by the container-side thermal shield 2Y. Thus, the coil-side thermal shield 2X can reduce the amount of heat intrusion from the outside into the superconducting coil 1 and the cooling stage 11. Also, the container-side thermal shield 2Y can reduce the amount of heat intrusion from the outside into the storage container 12. Furthermore, the support member 24 is thermally connected to the coil-side thermal shield 2X by the thermal anchor 25 and is cooled in the same manner as the coil-side thermal shield 2X. Therefore, the thermal anchor 25 can reduce the amount of heat intrusion from the outside through the support member 24 into the superconducting coil 1 and the cooling stage 11. By reducing the amount of heat intrusion into the superconducting coil 1, the cooling stage 11, and the storage container 12 as described above, the consumption amount (evaporation amount) of the liquid refrigerant 12A in the storage container 12 for cooling the heat medium 15H of the circulation system 15 can be reduced.

[0024] (2) Not only the liquid refrigerant 12A but also the gaseous refrigerant 12B obtained by evaporation of this liquid refrigerant 12A cools the heat medium 15H of the circulation system 15 through heat exchange by the liquid-phase heat exchanger 13 and the gas-phase heat exchanger 14 respectively. The heat medium 15H cools the superconducting coil 1 to an extremely low temperature (for example, 20K) through the cooling stage 11. After cooling the superconducting coil 1, the heat medium 15H cools the thermal shield 2 (coil-side thermal shield 2X, container-side thermal shield 2Y, pipe-side thermal shield 2Z) set at a higher temperature than the superconducting coil 1 to an extremely low temperature (for example, 50K - 40K).

[0025] In particular, in order to cool the heat shield 2 (coil-side heat shield 2X, container-side heat shield 2Y, pipe-side heat shield 2Z) to an extremely low temperature, the gas-phase heat exchanger 14 cools the heat medium 15H in the circulation system 15 by heat exchange with the gaseous refrigerant 12B. Therefore, no additional cooling source (refrigerant) is required to cool the heat medium 15H in order to cool the heat shield 2 to an extremely low temperature. Moreover, compared with the case where the heat medium 15H is cooled only by heat exchange with the liquid refrigerant 12A by the liquid-phase heat exchanger 13 to cool the superconducting coil 1 and the heat shield 2 (coil-side heat shield 2X, container-side heat shield 2Y, pipe-side heat shield 2Z) to an extremely low temperature, an increase in the evaporation amount of the liquid refrigerant 12A can be suppressed. As a result, the energy efficiency of the cryogenic cooling system 10 can be improved.

[0026] [B]Second Embodiment (FIG. 2) FIG. 2 is a schematic piping diagram showing the configuration of the cryogenic cooling system according to the second embodiment. Regarding the parts similar to those in the first embodiment in this second embodiment, the description is simplified or omitted by attaching the same reference numerals as those in the first embodiment.

[0027] The difference between the cryogenic cooling system 27 of this second embodiment and the first embodiment is that the second object to be cooled, which is set at a higher temperature than the superconducting coil 1, is the current lead 3 that energizes the superconducting coil 1, and this current lead 3 is provided in thermal contact with the return-side pipe 17 of the circulation system 15 and is cooled to an extremely low temperature (for example, to an extremely low temperature of 25K near the superconducting coil 1 and with a temperature gradient up to 300K as it moves away from this superconducting coil 1) by the heat medium 15H flowing in the return-side pipe 17.

[0028] In this cryogenic cooling system 27, most of the piping portion of the return piping 17 of the circulation system 15, except for the portion in thermal contact with the current lead 3, is arranged in the room temperature region outside the first vacuum vessel 21 and the second vacuum vessel 22. And a compressor 28 in a room temperature state is disposed in the piping portion arranged in the room temperature region in the return piping 17, that is, the piping portion through which the heat medium 15H flows after cooling the current lead 3. The heat medium 15H in the supply piping 16 and the return piping 17 of the circulation system 15 is circulated in the circulation system 15 by being pressurized by the compressor 28.

[0029] Due to being configured as described above, according to the second embodiment, the following effects (3) to (5) can be achieved. (3) The current lead 3 is provided in thermal contact with the return piping 17 of the circulation system 15 and is cooled to, for example, 300K to 25K by the heat medium 15H flowing in the return piping 17. Therefore, the amount of heat intrusion entering from the outside from the current lead 3 into the superconducting coil 1 can be reduced.

[0030] (4) Not only the liquid refrigerant 12A but also the gaseous refrigerant 12B obtained by evaporation of the liquid refrigerant 12A cools the heat medium 15H of the circulation system 15 by heat exchange through the liquid-phase heat exchanger 13 and the gas-phase heat exchanger 14 respectively. The superconducting coil 1 is cooled to a cryogenic temperature (for example, 20K) through the cooling stage 11 by the heat medium 15H, and the current lead 3 set at a temperature higher than that of the superconducting coil 1 is cooled to, for example, 300K to 25K by the heat medium 15H after cooling the superconducting coil 1.

[0031] In particular, in order to cool the current lead 3, since the gas-phase heat exchanger 14 cools the heat medium 15H of the circulation system 15 by heat exchange with the gaseous refrigerant 12B, no additional cooling source (refrigerant) is required to cool the heat medium 15H in order to cool the current lead 3. Moreover, compared with the case where the heat medium 15H is cooled by heat exchange only with the liquid refrigerant 12A by the liquid-phase heat exchanger 13 to cool the superconducting coil 1 and the current lead 3, an increase in the evaporation amount of the liquid refrigerant 12A can be suppressed. As a result, the energy efficiency of the cryogenic cooling system 27 can be improved.

[0032] (5) Most of the piping portions in the return-side piping 17 of the circulation system 15 are arranged in the room-temperature region outside the first vacuum vessel 21 and the second vacuum vessel 22, and a compressor 28 in the room-temperature state is disposed in the piping portion of this room-temperature region to circulate the heat medium 15H in the circulation system 15. Since this compressor 28 is low-cost and highly reliable as compared with the cryogenic fan 18, the equipment cost of the cryogenic cooling system 27 can be reduced and the reliability can be improved.

[0033] [C] Third Embodiment (FIG. 3) FIG. 3 is a schematic piping diagram showing the configuration of the cryogenic cooling system according to the third embodiment. Regarding the parts similar to those in the first and second embodiments in this third embodiment, the description is simplified or omitted by attaching the same reference numerals as those in the first and second embodiments.

[0034] The difference between the cryogenic cooling system 30 of this third embodiment and the first and second embodiments is that the second object to be cooled is the thermal shield 2 (coil-side thermal shield 2X, container-side thermal shield 2Y, piping-side thermal shield 2Z) and the support member 24 in the first embodiment, and the current lead 3 in the second embodiment, and these thermal shield 2, support member 24, and current lead 3 are cooled by the heat medium 15H flowing through the branch pipes 31 and 32 (both will be described later) in the return-side piping 17 of the circulation system 15. Further, the gas-phase heat exchanger 14 includes a first-stage gas-phase heat exchanger 14M and a second-stage gas-phase heat exchanger 14N, and the second-stage gas-phase heat exchanger 14N is connected to the liquid-phase heat exchanger 13.

[0035] The return-side pipe 17 branches near the downstream side of the cooling stage 11, and one of the branch pipes 31 is installed in the first vacuum vessel 21, the heat-insulating pipe section 23, and the second vacuum vessel 22 and is connected to the second-stage gas-phase heat exchanger 14N. A cryogenic fan 18 is disposed on this branch pipe 31, and the coil-side heat shield 2X, the pipe-side heat shield 2Z, and the vessel-side heat shield 2Y are provided in thermal contact. Due to the operation of the cryogenic fan 18, the heat medium 15H flowing in the branch pipe 31 cools the heat shield 2 (coil-side heat shield 2X, vessel-side heat shield 2Y, pipe-side heat shield 2Z) to an extremely low temperature (50K to 40K) and then flows into the second-stage gas-phase heat exchanger 14N.

[0036] Also, the other branch pipe 32 extends from inside the first vacuum vessel 21 to outside the first vacuum vessel 21 and is connected to the first-stage gas-phase heat exchanger 14M. On this branch pipe 32, the current lead 3 is provided in thermal contact inside the first vacuum vessel 21, and a compressor 28 at room temperature is disposed outside the first vacuum vessel 21. Due to the operation of this compressor 28, the heat medium 15H flowing in the branch pipe 32 cools the current lead 3 to 300K to 25K and then flows into the first-stage gas-phase heat exchanger 14M.

[0037] Since it is configured as described above, according to the third embodiment, the effects (1) to (5) of the first and second embodiments are achieved.

[0038] As described above, some embodiments of the present invention have been described. These embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. Also, those replacements, changes, and combinations are included in the scope and gist of the invention and are included in the invention described in the claims and its equivalent scope.

[0039] For example, the second object to be cooled that is thermally in contact with the return pipe 17 of the circulation system 15 may be not limited to the heat shields 2 (coil-side heat shield 2X, container-side heat shield 2Y, pipe-side heat shield 2Z) and the support member 24 of the first and third embodiments, and the current leads 3 of the second and third embodiments, but may be, for example, an electronic circuit or the like in a control device that controls the superconducting coil 1. The cryogenic cooling systems 10, 27, and 30 may be configured by combining a cooling system that cools this electronic circuit or the like.

Explanation of Reference Numerals

[0040] 1... superconducting coil (first object to be cooled), 2... heat shield (second object to be cooled), 2X... coil-side heat shield, 2Y... container-side heat shield, 2Z... pipe-side heat shield, 3... current lead (second object to be cooled), 10... cryogenic cooling system, 11... cooling stage, 12... storage container, 12A... liquid refrigerant, 12B... gaseous refrigerant, 13... liquid-phase heat exchanger, 14... gas-phase heat exchanger, 15... circulation system, 15H... heat medium, 16... supply-side pipe, 17... return pipe, 24... support member (second object to be cooled), 27... cryogenic cooling system, 28... compressor, 30... cryogenic cooling system, 31, 32... branch pipes

Claims

1. A cryogenic cooling system for cooling a first object to be cooled and a second object to be cooled to cryogenic temperatures, comprising: a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant obtained by evaporation of this refrigerant; a liquid-phase heat exchanger provided in the storage container and in contact with the liquid refrigerant; a gas-phase heat exchanger provided in the storage container and in contact with the gaseous refrigerant and connected to the liquid-phase heat exchanger; a circulation system for circulating a heat medium, comprising a supply-side pipe for guiding the heat medium from the liquid-phase heat exchanger to the first object to be cooled and a return-side pipe for guiding the heat medium from the first object to be cooled to the gas-phase heat exchanger; the second object to be cooled, which is set at a higher temperature than the first object to be cooled, is provided in thermal contact with the return-side pipe of the circulation system; the heat medium sequentially cooled by heat exchange with the refrigerant by the gas-phase heat exchanger and the liquid-phase heat exchanger is supplied to the supply-side pipe to cool the first object to be cooled to cryogenic temperatures and is guided to the return-side pipe to cool the second object to be cooled to cryogenic temperatures, characterized in that the cryogenic cooling system is configured as such.

2. The cryogenic cooling system according to claim 1, characterized in that the second object to be cooled is a heat shield enclosing at least one of the storage container and the first object to be cooled.

3. The cryogenic cooling system according to claim 1, characterized in that the second object to be cooled is a current lead for energizing a superconducting coil that is the first object to be cooled.

4. The second object to be cooled is a heat shield enclosing at least one of the storage container and a superconducting coil that is the first object to be cooled, and a current lead for energizing the superconducting coil, the return-side pipe is branched near the superconducting coil, and one branch pipe is in thermal contact with the heat shield and the other branch pipe is in thermal contact with the current lead, respectively, characterized in that the cryogenic cooling system according to claim 1 is configured as such.

5. The cryogenic cooling system according to claim 3 or 4, characterized in that a room-temperature compressor is provided in a pipe portion through which the heat medium flows after cooling the current lead in the return pipe.

6. The cryogenic cooling system according to claim 1, characterized in that the refrigerant is hydrogen, neon, nitrogen, or argon.

7. A cryogenic cooling method for cooling a first object to be cooled and a second object to be cooled to cryogenic temperatures, comprising: a storage container for storing both a cryogenic liquid refrigerant and the gaseous refrigerant obtained by evaporation of this refrigerant; A liquid-phase heat exchanger provided in the storage container and in contact with the liquid refrigerant; A gas-phase heat exchanger provided in the storage container and in contact with the gaseous refrigerant and connected to the liquid-phase heat exchanger; A circulation system for circulating the heat medium, comprising a supply-side pipe for guiding the heat medium from the liquid-phase heat exchanger to the first object to be cooled and a return-side pipe for guiding the heat medium from the first object to be cooled to the gas-phase heat exchanger; A second object to be cooled, which is set at a temperature higher than that of the first object to be cooled, is provided in thermal contact with the return-side pipe of the circulation system; The heat medium sequentially cooled by heat exchange with the refrigerant by the gas-phase heat exchanger and the liquid-phase heat exchanger is supplied to the supply-side pipe to cool the first object to be cooled to an extremely low temperature, and then guided to the return-side pipe to cool the second object to be cooled to an extremely low temperature. An extremely low temperature cooling method characterized by this.

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