Cryogenic cooling system and cryogenic cooling method

Abstract

According to an embodiment, provided is a cryogenic cooling system (10) for cooling a first cooled object (1) having a cryogenic operation temperature and a second cooled object (2) having an operation temperature higher than the first cooled object (1); the cryogenic cooling system (10) comprising a refrigerant flow path (11) along which a first refrigerant (A) is circulated by a circulation unit (14) of the refrigerant flow path (11); along the refrigerant flow path (11), a cryogenic cooling source (12), the first cooled object (1), a preheating heat exchanger (13), the second cooled object (2), the preheating heat exchanger (13), and the cryogenic cooling source (12) being sequentially disposed; the first refrigerant (A) cooled to a cryogenic temperature by the cryogenic cooling source (12) cooling the first cooled object (1) to a cryogenic temperature; after cooling the first cooled object (1), the first refrigerant (A) being preheated to the operation temperature of the second cooled object (2) by the preheating heat exchanger (13) and then cooling the second cooled object (2); after cooling the second cooled object (2), the first refrigerant (A) being cooled by the preheating heat exchanger (13) and then returned to the cryogenic cooling source (12).

Description

Cryogenic cooling system and cryogenic cooling method

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to cryogenic cooling 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. Methods for transferring heat between the superconducting coil and the cooling source include conduction cooling, refrigerant circulation, and cryogen immersion cooling. Conduction cooling is used in many superconducting devices due to its simple configuration, but in high-magnetic-field devices or large devices, the distance between the cooling source and the superconducting coil becomes long, which creates a problem of a large temperature difference between the two. For such superconducting devices, a refrigerant circulation method is used.

[0003] U.S. Patent No. 11,152,844

[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 coil could be used to cool room-temperature equipment, it would have the advantage of making the cooling system more compact. However, if an extremely low-temperature refrigerant is used to cool room-temperature equipment, problems arise, such as damage to the room-temperature equipment due to excessive cooling below the operating temperature, or malfunction due to freezing of oxygen or nitrogen in the atmosphere.

[0006] In the prior art, there is an example of using low-temperature gas after cooling a rotor having a superconducting coil to cool a stator. However, the rotor and stator are cooled to an extremely low temperature, and this cannot be used when there is a large difference in the operating temperature between room temperature and the extremely low temperature.

[0007] In another example, a cryogenic liquid refrigerant is used as a cooling source to cool a rotor to a cryogenic temperature, and then 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] An embodiment of the present invention has been made taking these circumstances into consideration, and aims to provide a cryogenic cooling technology 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.

[0009] 1. A system diagram showing the configuration of a cryogenic cooling system according to a first embodiment. 2. A system diagram showing the configuration of a cryogenic cooling system according to a second embodiment. 3. A system diagram showing the configuration of a cryogenic cooling system according to a third embodiment. 4. A system diagram showing the configuration of a cryogenic cooling system according to a fourth embodiment. 5. A system diagram showing the configuration of a cryogenic cooling system according to a fifth embodiment. 6. A system diagram showing the configuration of a conventional cryogenic cooling system.

[0010] 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 configured such 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 sequentially arranged in a refrigerant flow path through which a first refrigerant is circulated by a circulation section provided in the refrigerant flow path, and the first cooled object is cooled to a cryogenic temperature by the first refrigerant cooled to a cryogenic temperature by the cryogenic cooling source, the first 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 first refrigerant that has cooled the second cooled object is cooled by the preheating heat exchanger and then returned to the cryogenic cooling source.

[0011] A cryogenic cooling method in an embodiment of the present invention is a cryogenic cooling method for cooling a first cooled object having an operating temperature of a cryogenically low temperature and a second cooled object having an operating temperature higher than that of the first cooled object, in which a first refrigerant cooled to a cryogenically low temperature by a cryogenic cooling source is introduced into the first cooled object to cool the first cooled object to a cryogenically low temperature, the first refrigerant that has cooled the first cooled object is preheated in a preheating heat exchanger to the operating temperature of the second cooled object, and then introduced into the second cooled object to cool the second cooled object, and the first refrigerant that has cooled the second cooled object is cooled by the preheating heat exchanger, and then returned to the cryogenic cooling source to be cooled to a cryogenically low temperature and circulated.

[0012] According to the embodiment of the present invention, it is possible to effectively cool a first object to be cooled that has an extremely low operating temperature and a second object to be cooled that has a higher operating temperature than the first object, and to simplify the cooling system, although this effect does not limit the present invention.

[0013] First Embodiment Hereinafter, embodiments of a cryogenic cooling system and a cryogenic cooling method will be described in detail with reference to the drawings. First, a cryogenic cooling system 10 according to a first embodiment will be described with reference to FIG. 1. The cryogenic cooling 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 the stator coil 2 constitute a superconducting rotating electric machine 6.

[0014] In the cryogenic cooling system 10, a cryogenic cooling source 12, a rotor 1, a preheating heat exchanger 13, a stator coil 2, another preheating heat exchanger 13, and a cryogenic cooling source 12 are arranged in this order as a refrigerant flow path 11 through which a refrigerant A serving as a first refrigerant flows. Furthermore, a pump 14 serving as a circulation unit is arranged in this refrigerant flow path 11. When this pump 14 is operated, the refrigerant A circulates within the refrigerant flow path 11. Here, the refrigerant A is preferably a gas refrigerant such as helium gas.

[0015] The cryogenic cooling source 12 uses a cryogenic refrigerator or a cryogenic refrigerant such as liquid hydrogen, liquid helium, or liquid nitrogen. The cryogenic cooling source 12 cools the introduced refrigerant A to a cryogenic temperature (e.g., 20 K) below the superconducting transition temperature.

[0016] The preheating heat exchanger 13 heats up 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 down the refrigerant A, which has been heated (for example, 320 K) by cooling the stator coil 2, to a lower temperature (for example, 45 K) by heat exchange. In other words, the preheating heat exchanger 13 exchanges heat on the outward and return paths of the refrigerant A to and from the stator coil 2.

[0017] When the pump 14 is operated, the rotor 1 is cooled to a cryogenic temperature (e.g., 20 K) by the refrigerant A cooled to a cryogenic temperature by the cryogenic cooling source 12. The refrigerant A that has cooled the rotor 1 is then preheated by the preheating heat exchanger 13 to the operating temperature of the stator coil 2 (e.g., 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 has cooled the stator coil 2 is then cooled to a cryogenic temperature (e.g., 45 K) by the preheating heat exchanger 13, returned to the cryogenic cooling source 12, cooled to a cryogenic temperature (e.g., 20 K), and circulated.

[0018] The first embodiment has the following advantages. The refrigerant A cooled to a cryogenic temperature by the cryogenic cooling source 12 cools the rotor 1 to a cryogenic temperature. The refrigerant A that cooled the rotor 1 is preheated to the operating temperature of the stator coil 2 by the preheating heat exchanger 13, and then cools the stator coil 2. The refrigerant A that cooled the stator coil 2 is cooled by 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. In this manner, 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, can be appropriately cooled without overcooling the stator coil 2.

[0019] Furthermore, the refrigerant A that has cooled the rotor 1 to a cryogenic temperature is preheated by the preheating heat exchanger 13. This preheated refrigerant A cools the stator coil 2. This refrigerant A is further cooled by the preheating heat exchanger 13 and returned to the cryogenic cooling source 12, resulting in the circulation of a single refrigerant A. In this way, the cryogenic cooling system 10 can be simplified.

[0020] Second Embodiment Next, a cryogenic cooling system 20 according to a second embodiment will be described with reference to Fig. 2. In this second embodiment, parts similar to those in the first embodiment are designated by the same reference numerals as in the first embodiment, and description thereof will be simplified or omitted.

[0021] The second embodiment differs from the first embodiment in that the second object to be cooled in the first embodiment is another refrigerant B as a second refrigerant. This refrigerant B is cooled by heat exchange with refrigerant A (first refrigerant) via refrigerant-to-refrigerant heat exchanger 21, and circulates within refrigerant flow path 22 to cool stator coil 2 as a third object to be cooled.

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

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

[0024] The second embodiment has the following advantages. 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. In other words, the second embodiment does not dissipate heat by exchanging heat with the atmosphere using the cooling device 106 (FIG. 6) as in the conventional system. 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] Third Embodiment Next, a cryogenic cooling system 30 according to a third embodiment will be described with reference to Fig. 3. In this third embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and description thereof will be simplified or omitted.

[0026] The third embodiment differs from the first embodiment in that the cryogenic cooling system 30 has a heater 31 as a heating unit, a first branch flow path 32 and a second branch flow path 33, and a first valve 34 and a second valve 35 as flow rate adjustment units.

[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 the refrigerant A (first refrigerant) flowing out of the preheating heat exchanger 13 to the operating temperature of the stator coil 2 (e.g., 300 K).

[0028] The first branch flow path 32 and the second branch flow path 33 are refrigerant flow paths 11 on the outlet side of the rotor 1, and are formed by branching off the refrigerant flow path 11 between the rotor 1 and the preheating heat exchanger 13. One of the first branch flow paths 32 is connected to the preheating heat exchanger 13. The other, the second 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 first branch flow path 32 and the second branch flow path 33 make it possible to prevent the entire amount of refrigerant A flowing out of the rotor 1 from being introduced into the preheating heat exchanger 13.

[0029] The first valve 34 is disposed in the first branch flow path 32 and adjusts the flow rate of the refrigerant A flowing through the first branch flow path 32. The second valve 35 is disposed in the second branch flow path 33 and adjusts the flow rate of the refrigerant A flowing through the second branch flow path 33. By changing the opening degrees of the first valve 34 and the second valve 35, it is possible to adjust the flow rate of the refrigerant A that has cooled the rotor 1 and is introduced into the preheating heat exchanger 13.

[0030] The third embodiment has the same effects as the first embodiment, and also has the following effects.

[0031] 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. For example, due to fluctuations in the amount of heat required for cooling the rotor 1 when the superconducting rotating electric machine 6 is started or stopped, the temperature of the refrigerant A supplied to the stator coil 2, whose operating temperature is room temperature, may become too low. In such cases, the refrigerant A introduced into the stator coil 2 can be heated to reliably adjust the temperature of this refrigerant A to the operating temperature of the stator coil 2.

[0032] Furthermore, the refrigerant flow path 11 between the rotor 1 and the preheating heat exchanger 13 is branched into a first branch flow path 32 connected to the preheating heat exchanger 13 and a second branch flow path 33 bypassing the preheating heat exchanger 13 and 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 improving the cooling efficiency of the stator coil 2.

[0033] Furthermore, a first valve 34 and a second valve 35 for adjusting the flow rate are disposed in the first branch flow path 32 and the second branch flow path 33, respectively, between the rotor 1 and the preheating heat exchanger 13. Therefore, the opening degree of the first valve 34 is changed according to the required cooling heat amount of the stator coil 2, which is used at room temperature, and the flow rate of the refrigerant A introduced into the preheating heat exchanger 13 is adjusted (e.g., reduced), thereby suppressing the heating amount of the heater 31. This improves the cooling efficiency of the stator coil 2. Furthermore, during initial cooling of the rotor 1, the first valve 34 is fully closed and the second valve 35 is fully opened, thereby cutting off the supply of the refrigerant A to the stator coil 2. All of the refrigerant A that has cooled the rotor 1 is returned to the cryogenic cooling source 12 and quickly cooled to a cryogenic temperature. This shortens the initial cooling time of the rotor 1.

[0034] Fourth Embodiment Next, a cryogenic cooling system 40 according to a fourth embodiment will be described with reference to Fig. 4. In this fourth embodiment, parts similar to those in the first embodiment are designated by the same reference numerals as in the first embodiment, and description thereof will be simplified or omitted.

[0035] 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 Fig. 4 does not show the stator coil 2 that constitutes the superconducting rotating electric machine 6.

[0036] The connection portion 41C connecting the rotating portion 41A and the stationary portion 41B of the current lead 41 generates heat due to friction and connection resistance. Because the connection portion 41C is located outside the vacuum vessel 4, its operating temperature is room temperature (e.g., 300 K). The cryogenic cooling system 40 preheats the refrigerant A (first refrigerant) used to cool the rotor 1 to room temperature using the preheating heat exchanger 13, and then cools the connection portion 41C of the current lead 41 with this refrigerant A.

[0037] In the fourth embodiment, the second cooled object is the connection portion 41C of the current lead 41 instead of the stator coil 2, and in addition to achieving the same effect as the first embodiment with regard to cooling of this connection portion 41C and the rotor 1, the fourth embodiment also achieves the following effect.

[0038] A 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 that has cooled the rotor 1 and that has been preheated by the preheating heat exchanger 13. In this way, a cooling device dedicated to cooling the connection portion 41C of the current lead 41 can be omitted.

[0039] The stator coil 2 as the third object to be cooled in the second embodiment (FIG. 2) may be replaced by the connection portion 41C between the rotating portion 41A and the stationary portion 41B of the current lead 41. This connection portion 41C may be cooled by another refrigerant B (second refrigerant) that has been cooled by the refrigerant A after cooling the rotor 1 using the preheating heat exchanger 13 and the refrigerant-to-refrigerant heat exchanger 21. In other words, the second object to be cooled may be the other refrigerant B, and the third object to be cooled may be the connection portion 41C.

[0040] Fifth Embodiment Next, a cryogenic cooling system 50 according to a fifth embodiment will be described with reference to Fig. 5. In this fifth embodiment, parts similar to those in the first embodiment are designated by the same reference numerals as in the first embodiment, and description thereof will be simplified or omitted.

[0041] The fifth embodiment differs from the first embodiment in that the second cooled object is a seal 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 (first refrigerant) into the rotor 1. Note that the stator coil 2 that constitutes the superconducting rotating electric machine 6 is omitted from Fig. 5.

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

[0043] In the fifth embodiment, the second cooled object is the sealed portion 51C of the refrigerant flow path 11 instead of the stator coil 2, and in addition to achieving the same effects as the first embodiment with regard to cooling of this sealed portion 51C and the rotor 1, the fifth embodiment also achieves the following effects.

[0044] The seal area 51C between the rotating part 51A and the stationary part 51B in the refrigerant flow path 11 is cooled by the refrigerant A that has cooled the rotor 1 and that has been preheated by the preheating heat exchanger 13. In this way, a cooling device dedicated to cooling the seal area 51C of the refrigerant flow path 11 can be omitted.

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

[0046] 2, a heater 31 is disposed 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. The heater 31 may heat 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.

[0047] The present invention has been described above based on the first to fifth embodiments, but the configuration applied in any of the embodiments may be applied to other embodiments, and the configurations applied in each embodiment may be combined.

[0048] Although several 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, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and variations thereof are within the scope and spirit of the invention, as well as the scope of the invention described in the claims and their equivalents. Note that the singular does not exclude the plural unless the context clearly dictates otherwise. Furthermore, conjunctions such as "and" and "or" are inclusive unless the context clearly dictates otherwise.

Claims

1. A cryogenic refrigeration system for cooling a first cooled object having a cryogenic operating temperature and a second cooled object having a higher operating temperature than the first cooled object, wherein 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 sequentially arranged in a refrigerant flow path through which a first refrigerant is circulated by a circulation section provided in the refrigerant flow path, the first cooled object is cooled to a cryogenic temperature by the cryogenic cooling source, the first refrigerant that has cooled the first cooled object is preheated in the preheating heat exchanger to the operating temperature of the second cooled object and then cools the second cooled object, and the first refrigerant that has cooled the second cooled object is cooled in the preheating heat exchanger and then returned to the cryogenic refrigeration source.

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

3. A cryogenic cooling system according to claim 1 or claim 2, wherein a heating unit capable of adjusting the temperature of the first refrigerant is provided between the preheating heat exchanger and the second object to be cooled.

4. A cryogenic cooling system as described in any one of claims 1 to 3, wherein the refrigerant flow path between the first cooled object and the preheating heat exchanger branches to provide a first branch flow path and a second branch flow path, the first branch flow path is connected to the preheating heat exchanger, and the second branch flow path bypasses the preheating heat exchanger and is connected to the refrigerant flow path between the preheating heat exchanger and the cryogenic cooling source.

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

6. A cryogenic cooling system according to any one of claims 1 to 5, wherein the operating temperature of the second object to be cooled is atmospheric temperature.

7. A cryogenic cooling system according to any one of claims 1 to 6, wherein the first object to be cooled is a rotor having a superconducting coil, and the second object to be cooled or another third object to be cooled is a stator coil.

8. A cryogenic cooling system as claimed in any one of claims 1 to 6, wherein the first cooled object is a rotor having a superconducting coil, and the second cooled object or another third cooled object is a connection part 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 6, wherein the first cooled object is a rotor having a superconducting coil, and the second cooled object or another third cooled object is a sealed portion between a rotating part and a stationary part that rotates integrally with the rotor in the refrigerant flow path.

10. 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, comprising the steps of: introducing a first refrigerant cooled to a cryogenic temperature by a cryogenic cooling source into the first object to cool the first object to a cryogenic temperature; preheating the first refrigerant that has cooled the first object to the operating temperature of the second object in a preheating heat exchanger, and then introducing the first refrigerant into the second object to cool the second object; and cooling the first refrigerant that has cooled the second object in the preheating heat exchanger, returning it to the cryogenic cooling source to be cooled to a cryogenic temperature and circulating it.

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