Cryogenic cooling system and cryogenic cooling method

Abstract

To suitably cool a first cooled object having an extremely low working temperature and a second cooled object having a working temperature higher than that of the first cooled object, and to simplify a cooling system.SOLUTION: A cryogenic cooling system 10 for cooling a rotor 1 having an extremely low operating temperature and a stator coil 2 having an operating temperature higher than that of the rotor includes a cryogenic cooling source 12, a rotor 1, a preheating heat exchanger 13, a stator coil 2, and a refrigerant flow path in which a refrigerant circulates by a pump 14 provided in the refrigerant flow path. The refrigerant which has cooled the rotor is preheated to the working temperature of the stator coil 2 by the preheating heat exchanger 13 and then cools the stator coil, and the refrigerant which has cooled the stator coil is cooled by the preheating heat exchanger and then returned to the cryogenic cooling source and circulated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to cryogenic cooling systems and methods. [Background technology]

[0002] Generally, superconducting coils are used after being cooled to extremely low temperatures using a cryogen such as liquid helium or a cooling source such as a cryogenic refrigerator. There are three methods for transferring heat between the superconducting coil and the cooling source: conduction cooling, refrigerant circulation, and immersion cooling in a cryogen. Conduction cooling is used in many superconducting devices due to its simple configuration, but in high-magnetic-field devices or large equipment, the distance between the cooling source and the superconducting coil becomes long, which poses a problem of a large temperature difference between the two. For such superconducting devices, a refrigerant circulation method is used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 1,152,844 [Patent Document 2] Patent No. 4622458 Summary of the Invention [Problem to be solved by the invention]

[0004] In the superconducting rotating electric machine 100 shown in Fig. 6, a rotor 102 equipped with a superconducting coil 101 is placed in a vacuum vessel 104 and is cooled to a cryogenic temperature by a refrigerant α cooled to a cryogenic temperature by a cryogenic cooling source 105. A stator coil 103 in the room temperature section is cooled to room temperature by a refrigerant β, such as cooling oil, cooled by a cooling device 106 that dissipates heat into the atmosphere. However, a cooling system equipped with such a cryogenic cooling source 105 and a cooling device 106 would be complicated and large in size.

[0005] If the refrigerant used to cool the superconducting coils could be used to cool devices at room temperature, this would have the advantage of making the cooling system more compact. However, if an extremely low-temperature refrigerant is used to cool devices at room temperature, problems arise, such as damage to the devices due to excessive cooling below the operating temperature, or malfunction due to freezing of oxygen and nitrogen in the atmosphere.

[0006] Prior art includes an example in which low-temperature gas used to cool a rotor having a superconducting coil is used to cool a stator, as shown in Patent Document 1. However, both the rotor and the stator are cooled to extremely low temperatures, and this method cannot be applied when there is a large difference in the operating temperatures between the two (rotor and stator), such as between room temperature and extremely low temperatures.

[0007] In Patent Document 2, a cryogenic liquid refrigerant is used as a cooling source, and after the rotor is cooled to a cryogenic temperature by the liquid refrigerant, a heat exchanger is used to cool equipment at room temperature. However, the liquid refrigerant is consumed as fuel after leaving the heat exchanger, and is not circulated for use.

[0008] The embodiments of the present invention have been made in consideration of the above-mentioned circumstances, and aim to provide a cryogenic cooling system and a cryogenic cooling method that can suitably cool a first cooled object having an extremely low operating temperature and a second cooled object having a higher operating temperature than the first cooled object, while also simplifying the cooling system. [Means for solving the problem]

[0009] In an embodiment of the present invention, the cryogenic cooling system is a cryogenic cooling system that cools a first cooled object having a cryogenic operating temperature and a second cooled object having a higher operating temperature than the first cooled object, and is characterized in that a cryogenic cooling source, the first cooled object, a preheating heat exchanger, the second cooled object, the preheating heat exchanger, and the cryogenic cooling source are arranged in sequence in the refrigerant flow path through which the refrigerant is circulated by a circulation means provided in the refrigerant flow path, and the first cooled object is cooled to a cryogenic temperature by the refrigerant cooled to a cryogenic temperature by the cryogenic cooling source, the refrigerant that has cooled the first cooled object is preheated to the operating temperature of the second cooled object in the preheating heat exchanger and then cools the second cooled object, and the refrigerant that has cooled the second cooled object is cooled by the preheating heat exchanger and then returned to the cryogenic cooling source.

[0010] A cryogenic cooling method in an embodiment of the present invention is a cryogenic cooling method for cooling a first object to be cooled, the operating temperature of which is cryogenic, and a second object to be cooled, the operating temperature of which is higher than that of the first object, and is characterized in that a refrigerant cooled to a cryogenic temperature by a cryogenic cooling source is introduced into the first object to cool the first object to a cryogenic temperature, the refrigerant that has cooled the first object to a cryogenic temperature is preheated in a preheating heat exchanger to the operating temperature of the second object to be cooled, and then introduced into the second object to cool the second object, and the refrigerant that has cooled the second object to be cooled is cooled by the preheating heat exchanger, and then returned to the cryogenic cooling source to be cooled to a cryogenic temperature and circulated. [Effects of the Invention]

[0011] According to an embodiment of the present invention, it is possible to preferably cool a first object to be cooled, which has an extremely low operating temperature, and a second object to be cooled, which has a higher operating temperature than the first object, while also simplifying the cooling system. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a system diagram showing the configuration of a cryogenic cooling system according to a first embodiment. [Figure 2] FIG. 10 is a system diagram showing the configuration of a cryogenic cooling system according to a second embodiment. [Figure 3] FIG. 10 is a system diagram showing the configuration of a cryogenic cooling system according to a third embodiment. [Figure 4] FIG. 10 is a system diagram showing the configuration of a cryogenic cooling system according to a fourth embodiment. [Figure 5] FIG. 10 is a system diagram showing the configuration of a cryogenic cooling system according to a fifth embodiment. [Figure 6] FIG. 1 is a system diagram showing the configuration of a conventional cryogenic cooling system. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [A] First embodiment (Fig. 1) Fig. 1 is a system diagram showing the configuration of a cryogenic refrigeration system according to a first embodiment. The cryogenic refrigeration system 10 shown in Fig. 1 uses a refrigerant circulation system to cool a rotor 1 as a first object to be cooled whose operating temperature is cryogenic, and a stator coil 2 as a second object to be cooled whose operating temperature is higher than that of the rotor 1. Here, the rotor 1 has a superconducting coil 3 and is rotatably mounted within a vacuum vessel 4 around a rotating shaft 5. The operating temperature of the stator coil 2 is higher than that of the rotor 1, for example, atmospheric temperature (room temperature). The rotor 1 and stator coil 2 constitute a superconducting rotating electric machine 6.

[0014] The cryogenic cooling system 10 is configured by sequentially arranging a cryogenic cooling source 12, a rotor 1, a preheating heat exchanger 13, a stator coil 2, a preheating heat exchanger 13, and a cryogenic cooling source 12 in a refrigerant flow path 11, and by arranging a pump 14 as a circulation means in the refrigerant flow path 11. Operation of the pump 14 causes a refrigerant A to circulate within the refrigerant flow path 11. Here, the refrigerant A is preferably a gas refrigerant such as helium gas.

[0015] A cryogenic refrigerator or a cryogenic refrigerant such as liquid hydrogen, liquid helium, or liquid nitrogen is used as the cryogenic cooling source 12. This cryogenic cooling source 12 cools the introduced refrigerant A to a cryogenic temperature (for example, 20 K) below the superconducting transition temperature.

[0016] The preheating heat exchanger 13 heat-exchanges the refrigerant A, which has been heated (for example, 40 K) by cooling the rotor 1, to room temperature (300 K), which is the operating temperature of the stator coil 2. Furthermore, the preheating heat exchanger 13 cools the refrigerant A, which has been heated (for example, 320 K) by cooling the stator coil 2, to lower its temperature (for example, 45 K) by heat exchange.

[0017] By operating the pump 14, the rotor 1 is cooled to a cryogenic temperature (for example, 20 K) by the refrigerant A cooled to a cryogenic temperature by the cryogenic cooling source 12. The refrigerant A that cooled the rotor 1 is then preheated by the preheating heat exchanger 13 to the operating temperature of the stator coil 2 (for example, 300 K) and then introduced into the stator coil 2 to cool the stator coil 2 that has generated heat due to losses such as electrical resistance. The refrigerant A that cooled the stator coil 2 is then cooled to a cryogenic temperature (for example, 45 K) by the preheating heat exchanger 13, returned to the cryogenic cooling source 12, cooled to a cryogenic temperature (for example, 20 K), and circulated.

[0018] As configured as above, the first embodiment provides the following effects (1) and (2). (1) The rotor 1 is cooled to a cryogenic temperature by the refrigerant A cooled to a cryogenic temperature by the cryogenic cooling source 12, and the refrigerant A that cooled the rotor 1 is preheated in the preheating heat exchanger 13 to the operating temperature of the stator coil 2 before cooling the stator coil 2. The refrigerant A that cooled the stator coil 2 is then cooled in the preheating heat exchanger 13, returned to the cryogenic cooling source 12, cooled to a cryogenic temperature, and circulated within the refrigerant flow path 11. This makes it possible to appropriately cool the rotor 1, whose operating temperature is a cryogenic temperature, and the stator coil 2, whose operating temperature is higher than that of the rotor 1, without, for example, overcooling the stator coil 2.

[0019] (2) The refrigerant A that has cooled the rotor 1 to a cryogenic temperature is preheated by the preheating heat exchanger 13, and this preheated refrigerant A is used to cool the stator coil 2. This refrigerant A is then cooled by the preheating heat exchanger 13 and returned to the cryogenic cooling source 12, thereby circulating a single refrigerant A. This simplifies the cryogenic cooling system 10.

[0020] [B] Second embodiment (Fig. 2) 2 is a system diagram showing the configuration of a cryogenic cooling system according to a second embodiment. In this second embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be simplified or omitted.

[0021] The second embodiment of the cryogenic cooling system 20 differs from the first embodiment in that the second cooled object in the first embodiment is another refrigerant B that is cooled by heat exchange with refrigerant A via refrigerant-to-refrigerant heat exchanger 21 and circulates within refrigerant flow path 22 to cool the stator coil 2 as the third cooled object.

[0022] The coolant B has an operating temperature of room temperature (e.g., 300 K) and is made of oil, water, etc. A pump 23 is disposed in the coolant flow path 22, and operation of the pump 23 causes the coolant B to circulate within the coolant flow path 22 as described above.

[0023] By operating pumps 14 and 23, rotor 1 is cooled to a cryogenic temperature by refrigerant A cooled to a cryogenic temperature by cryogenic cooling source 12, and the refrigerant A that has cooled rotor 1 is preheated to the operating temperature of refrigerant B by preheating heat exchanger 13, after which refrigerant B is cooled by refrigerant-to-refrigerant heat exchanger 21, and stator coil 2 is cooled by refrigerant B circulating in refrigerant flow path 22. Then, refrigerant A that has cooled refrigerant B by refrigerant-to-refrigerant heat exchanger 21 is cooled by preheating heat exchanger 13, returned to cryogenic cooling source 12, and cooled to a cryogenic temperature, and circulated in refrigerant flow path 11.

[0024] As configured as above, the second embodiment provides the following effect (3). (3) The refrigerant B for cooling the stator coil 2 is cooled by the refrigerant A that has cooled the rotor 1 using the preheating heat exchanger 13 and the refrigerant-to-refrigerant heat exchanger 21, and is not dissipated by heat exchange with the atmosphere using the cooling device 106 (FIG. 6) as in the past. In this case, the heat exchange area of ​​the refrigerant-to-refrigerant heat exchanger 21 can be made smaller than that of the cooling device 106, and therefore the cryogenic cooling system 20 can be made smaller.

[0025] [C] Third embodiment (Fig. 3) 3 is a system diagram showing the configuration of a cryogenic cooling system according to a third embodiment. In this third embodiment, the same parts as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the description thereof will be simplified or omitted.

[0026] The cryogenic cooling system 30 of the third embodiment differs from the first embodiment in that it has a heater 31 as heating means, branch flow paths 32 and 33, and valves 34 and 35 as flow rate adjusting means.

[0027] The heater 31 is disposed in the refrigerant flow path 11 between the preheating heat exchanger 13 and the stator coil 2, and on the outlet side of the preheating heat exchanger 13. The heater 31 heats and adjusts the temperature of the refrigerant A flowing out from the preheating heat exchanger 13 to the operating temperature of the stator coil 2 (e.g., 300 K).

[0028] The branch flow paths 32 and 33 are formed by branching the refrigerant flow path 11 between the rotor 1 and the preheating heat exchanger 13, which is the refrigerant flow path 11 on the outlet side of the rotor 1, and one branch flow path 32 is connected to the preheating heat exchanger 13. The other branch flow path 33 bypasses the preheating heat exchanger 13 and is connected to the refrigerant flow path 11 before returning from the preheating heat exchanger 13 to the cryogenic cooling source 12, i.e., the refrigerant flow path 11 between the preheating heat exchanger 13 and the cryogenic cooling source 12. The branch flow paths 32 and 33 are provided so as to prevent the entire amount of refrigerant A flowing out from the rotor 1 from being introduced into the preheating heat exchanger 13.

[0029] Valve 34 is disposed in branch flow path 32 to adjust the flow rate of refrigerant A flowing through branch flow path 32. Valve 35 is disposed in branch flow path 33 to adjust the flow rate of refrigerant A flowing through branch flow path 33. By changing the opening degrees of these valves 34 and 35, it is possible to adjust the flow rate of refrigerant A introduced into preheating heat exchanger 13 after cooling rotor 1.

[0030] As configured as above, the third embodiment provides the following effects (4) to (6) in addition to the effects (1) and (2) of the first embodiment.

[0031] (4) A heater 31 is provided in the refrigerant flow path 11 between the preheating heat exchanger 13 and the stator coil 2 and on the outlet side of the preheating heat exchanger 13. Therefore, when the temperature of the refrigerant A supplied to the stator coil 2, whose operating temperature is room temperature, becomes too low due to fluctuations in the amount of cooling heat required by the rotor 1 when the superconducting rotating electric machine 6 is started or stopped, the refrigerant A introduced into the stator coil 2 can be heated, and the temperature of this refrigerant A can be reliably adjusted to the operating temperature of the stator coil 2.

[0032] (5) The refrigerant flow path 11 between the rotor 1 and the preheating heat exchanger 13 is branched into a branch flow path 32 connected to the preheating heat exchanger 13 and a branch flow path 33 that bypasses the preheating heat exchanger 13 and is connected to the refrigerant flow path 11 between the preheating heat exchanger 13 and the cryogenic cooling source 12. This allows a portion of the refrigerant A flowing out of the rotor 1 to be returned directly to the cryogenic cooling source 12, bypassing the stator coil 2 whose operating temperature is room temperature. As a result, the flow rate of the refrigerant A flowing from the preheating heat exchanger 13 to the heater 31 can be reduced, thereby suppressing the amount of heat generated by the heater 31 and thereby improving the cooling efficiency of the stator coil 2.

[0033] (6) Flow rate adjusting valves 34, 35 are provided in the branch flow paths 32, 33 between the rotor 1 and the preheating heat exchanger 13, respectively. Therefore, by changing the opening of the valve 34 in accordance with the required cooling heat amount of the stator coil 2, which is operating at room temperature, and adjusting (e.g., reducing) the flow rate of the refrigerant A introduced into the preheating heat exchanger 13, the amount of heat generated by the heater 31 can be suppressed, thereby improving the cooling efficiency of the stator coil 2. Furthermore, during initial cooling of the rotor 1, the valve 34 is fully closed and the valve 35 is fully opened, thereby cutting off the supply of the refrigerant A to the stator coil 2 and returning all of the refrigerant A that has cooled the rotor 1 to the cryogenic cooling source 12, thereby quickly cooling it to a cryogenic temperature, thereby shortening the initial cooling time of the rotor 1.

[0034] [D] Fourth embodiment (Fig. 4) 4 is a system diagram showing the configuration of a cryogenic cooling system according to a fourth embodiment. In this fourth embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0035] The cryogenic cooling system 40 of the fourth embodiment differs from the first embodiment in that the second cooled object is a connection portion 41C between a rotating portion 41A that rotates integrally with the rotor 1 and a stationary portion 41B of a current lead 41 that supplies current to the rotor 1. Note that the stator coil 2 that constitutes the superconducting rotating electric machine 6 is omitted from Fig. 4.

[0036] Connection portion 41C, which connects rotating portion 41A and stationary portion 41B of current lead 41, generates heat due to friction, connection resistance, etc. Since connection portion 41C is located outside vacuum vessel 4, its operating temperature is room temperature (e.g., 300 K). In cryogenic cooling system 40, refrigerant A, which has cooled rotor 1, is preheated to room temperature by preheating heat exchanger 13, and then this refrigerant A cools connection portion 41C of the current lead.

[0037] As configured as described above, according to the fourth embodiment, by using the connection portion 41C of the current lead 41 instead of the stator coil 2 as the second cooled object, effects similar to those (1) and (2) of the first embodiment are achieved with regard to cooling of this connection portion 41C and the rotor 1, as well as the following effect (7).

[0038] (7) Since the connection portion 41C between the rotating portion 41A and the stationary portion 41B of the current lead 41 of the rotor 1 is cooled by the refrigerant A after cooling the rotor 1 and by the refrigerant A preheated by the preheating heat exchanger 13, a cooling device dedicated to cooling the connection portion 41C of the current lead 41 can be omitted.

[0039] In addition, the stator coil 2 as the third cooled object in the second embodiment (Figure 2) may be replaced with the connection part 41C between the rotating part 41A and the stationary part 41B in the current lead 41, and this connection part 41C may be cooled by the refrigerant B that has been cooled using the preheating heat exchanger 13 and the refrigerant-to-refrigerant heat exchanger 21 by the refrigerant A after cooling the rotor 1.

[0040] [E] Fifth embodiment (Fig. 5) 5 is a system diagram showing the configuration of a cryogenic cooling system according to a fifth embodiment. In this fifth embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0041] The cryogenic cooling system 50 of the fifth embodiment differs from the first embodiment in that the second object to be cooled is a sealed portion 51C between a rotating portion 51A and a stationary portion 51B that rotate integrally with the rotor 1 in a refrigerant flow path 11 that introduces refrigerant A into the rotor 1. Note that the stator coil 2 that constitutes the superconducting rotating electric machine 6 is omitted from Fig. 5.

[0042] Sealed portion 51C, which seals refrigerant A between rotating portion 51A and stationary portion 51B of refrigerant flow path 11, is, for example, a magnetic fluid sealing member, and generates heat due to the viscosity of refrigerant A. Since sealed portion 51C of refrigerant flow path 11 is located outside vacuum vessel 4, its operating temperature is room temperature (for example, 300 K). In cryogenic cooling system 50, refrigerant A, which has cooled rotor 1, is preheated to room temperature by preheating heat exchanger 13, and then seal portion 51C of refrigerant flow path 11 is cooled by this refrigerant A.

[0043] As configured as described above, according to the fifth embodiment, by using the sealed portion 51C of the refrigerant flow path 11 instead of the stator coil 2 as the second cooled object, effects similar to those (1) and (2) of the first embodiment are achieved with regard to cooling of this sealed portion 51C and the rotor 1, as well as the following effect (8).

[0044] (8) Since the sealing portion 51C between the rotating portion 51A and the stationary portion 51B in the refrigerant flow path 11 is cooled by the refrigerant A after cooling the rotor 1 and preheated by the preheating heat exchanger 13, a cooling device dedicated to cooling the sealing portion 51C of the refrigerant flow path 11 can be omitted.

[0045] In addition, the stator coil 2 as the third cooled object in the second embodiment (Figure 2) may be replaced with the sealing portion 51C between the rotating portion 51A and the stationary portion 51B in the refrigerant flow path 11, and this sealing portion 51C may be cooled by the refrigerant B that has been cooled using the preheating heat exchanger 13 and the refrigerant-to-refrigerant heat exchanger 21 by the refrigerant A after cooling the rotor 1.

[0046] Although several embodiments of the present invention have been described above, 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, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, such substitutions, changes, and combinations are included in the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims.

[0047] For example, as shown by the two-dot chain line in Figure 2, a heater 31 may be arranged in the refrigerant flow path 11 between the preheating heat exchanger 13 and the refrigerant-to-refrigerant heat exchanger 21, on the outlet side of the preheating heat exchanger 13, and this heater 31 may be used to heat and adjust the temperature of the refrigerant A flowing out from the preheating heat exchanger 13 to the operating temperature (e.g., 300 K) of the stator coil 2 and the refrigerant B. [Explanation of symbols]

[0048] 1...rotor (first cooled object), 2...stator coil (second cooled object, third cooled object), 3...superconducting coil, 10...cryogenic cooling system, 11...refrigerant flow path, 12...cryogenic cooling source, 13...preheating heat exchanger, 14...pump (circulation means), 20...cryogenic cooling system, 21...refrigerant-to-refrigerant heat exchanger, 22...refrigerant flow path, 30...cryogenic cooling system, 31...heater (heating means), 32, 33...branch flow path, 34, 35...valve (flow rate adjustment means), 40...cryogenic cooling system, 41...current lead, 41A...rotating part, 41B...stationary part, 41C...connection part, 50...cryogenic cooling system, 51A...rotating part, 51B...stationary part, 51C...sealing part, A...refrigerant, B...refrigerant (second cooled object).

Claims

1. A cryogenic refrigeration system that cools a first object to be cooled having an extremely low operating temperature and a second object to be cooled having a higher operating temperature than the first object, a cryogenic cooling source, the first object to be cooled, a preheating heat exchanger, the second object to be cooled, the preheating heat exchanger, and the cryogenic cooling source are sequentially arranged in the refrigerant flow path through which the refrigerant is circulated by a circulation means provided in the refrigerant flow path; A cryogenic cooling system characterized in that the first cooled object is cooled to a cryogenic temperature by a refrigerant cooled to a cryogenic temperature in the cryogenic cooling source, the refrigerant that cooled the first cooled object is preheated to the operating temperature of the second cooled object in the preheating heat exchanger and then cools the second cooled object, and the refrigerant that cooled the second cooled object is cooled by the preheating heat exchanger and then returned to the cryogenic cooling source.

2. the second object to be cooled is another refrigerant, 2. The cryogenic cooling system of claim 1, wherein the other refrigerant is cooled by the refrigerant via a refrigerant-to-refrigerant heat exchanger and is circulated to cool the third object to be cooled.

3. 2. The cryogenic cooling system according to claim 1, further comprising a heating means for adjusting the temperature of the refrigerant provided between the preheating heat exchanger and the second object to be cooled.

4. a refrigerant flow path between the first object to be cooled and the preheating heat exchanger is branched; 2. The cryogenic cooling system of claim 1, wherein one branch flow path is connected to the preheating heat exchanger, and the other branch flow path bypasses the preheating heat exchanger and is connected to a refrigerant flow path between the preheating heat exchanger and a cryogenic cooling source.

5. 5. The cryogenic cooling system according to claim 4, wherein the one branch flow path and the other branch flow path are provided with flow rate adjusting means capable of adjusting the flow rate of the refrigerant.

6. 6. The cryogenic cooling system according to claim 1, wherein the temperature of the second object to be cooled is atmospheric temperature.

7. 6. The cryogenic cooling system according to claim 1, wherein the first object to be cooled is a rotor having a superconducting coil, and the second object to be cooled or the third object to be cooled is a stator coil.

8. A cryogenic cooling system as described in any one of claims 1 to 5, characterized in that the first cooled object is a rotor having a superconducting coil, and the second cooled object or the third cooled object is a connection point between a rotating part and a stationary part in a current lead that rotates integrally with the rotor.

9. A cryogenic cooling system as described in any one of claims 1 to 5, characterized in that the first cooled object is a rotor having a superconducting coil, and the second cooled object or the third cooled object is a sealed portion between a rotating part and a stationary part that rotates integrally with the rotor in a refrigerant flow path.

10. A cryogenic cooling method for cooling a first object to be cooled having an extremely low operating temperature and a second object to be cooled having a higher operating temperature than the first object, comprising: a refrigerant cooled to a cryogenic temperature by a cryogenic cooling source is introduced into the first object to be cooled, thereby cooling the first object to a cryogenic temperature; the refrigerant that has cooled the first object to be cooled is preheated in a preheating heat exchanger to a temperature at which the second object to be cooled is used, and then introduced into the second object to cool the second object to be cooled; The cryogenic cooling method is characterized in that the refrigerant that has cooled the second object to be cooled is cooled by the preheating heat exchanger, and then returned to the cryogenic cooling source to be cooled to a cryogenic temperature and circulated.

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