Pre-cooling device, cryogenic device and pre-cooling method

Abstract

To provide a pre-cooling device that suppresses heat input to an object to be cooled.SOLUTION: A pre-cooling device 100 pre-cools an object to be cooled by a cryogenic refrigeration device 20. The pre-cooling device 100 includes a liquid refrigerant reservoir 110 that cools the object to be cooled by liquid refrigerant stored inside. The liquid refrigerant reservoir 110 is movable between a cooling position and a standby position. When in the cooling position, the object to be cooled is cooled by the liquid refrigerant. When in the standby position, the liquid refrigerant reservoir 110 is arranged physically away from a heat transfer path from the cryogenic refrigeration device 20 to the object to be cooled.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pre-cooling device, a cryogenic device, and a pre-cooling method. [Background technology]

[0002] Conventionally, cryogenic cooling devices are known in which a cryostat is provided with a main cooling system that uses a cryogenic refrigerator to cool the object to be cooled with a refrigerant gas, and a sub-cooling system that uses a cryogenic liquid to cool the object to be cooled. When the cryogenic cooling device is in a normal operating state, such as when the object to be cooled is cooled to a cryogenic temperature, the object to be cooled is cooled by the main cooling system. When the temperature of the object to be cooled has risen and it is necessary to cool it to a cryogenic temperature, such as when the cryogenic cooling device starts operating, the object to be cooled is cooled by the main cooling system and the sub-cooling system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-172813 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned cryogenic cooling device, the sub-cooling system does not operate under normal operating conditions, so the pipes of the cryogenic liquid constituting the sub-cooling system act as a heat transfer path connecting the surrounding environment to the object to be cooled, and the heat input to the object through these pipes can raise the temperature of the object to be cooled, which should be kept at a cryogenic temperature. This heat input also becomes a thermal load for the main cooling system, and in order to suppress the temperature rise of the object to be cooled, the main cooling system is required to have a higher cooling capacity.

[0005] An exemplary object of an embodiment of the present invention is to provide a pre-cooling device that suppresses heat input to an object to be cooled. [Means for solving the problem]

[0006] According to one aspect of the present invention, a pre-cooling device that pre-cools an object to be cooled by a cryogenic refrigerator includes a liquid refrigerant storage section that cools the object to be cooled by a liquid refrigerant stored therein, the liquid refrigerant storage section being movable between a cooling position and a standby position, and when in the cooling position, the liquid refrigerant storage section cools the object to be cooled by the liquid refrigerant, and when in the standby position, the liquid refrigerant storage section is positioned physically separated from the heat transfer path from the cryogenic refrigerator to the object to be cooled.

[0007] According to one aspect of the present invention, a cryogenic device includes a pre-cooling device of the above aspect and a cryogenic refrigerator, the cryogenic refrigerator being thermally coupled to an object to be cooled so as to cool the object by conductive cooling.

[0008] According to one aspect of the present invention, a method of pre-cooling an object to be cooled by a cryogenic refrigerator comprises moving a liquid refrigerant storage section to a cooling position where the object to be cooled is cooled, supplying liquid refrigerant to the liquid refrigerant storage section, cooling the object to be cooled by storing the liquid refrigerant in the liquid refrigerant storage section, discharging the liquid refrigerant from the liquid refrigerant storage section after the object to be cooled has been cooled, and moving the liquid refrigerant storage section to a standby position physically separated from a heat transfer path from the cryogenic refrigerator to the object to be cooled after the object to be cooled has been cooled. Effect of the Invention

[0009] According to the present invention, a pre-cooling device that suppresses heat input to an object to be cooled can be provided. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a schematic diagram of a cryogenic device according to an embodiment; [Diagram 2] 1A to 1C are diagrams illustrating a pre-cooling method according to an embodiment of the present invention. [Diagram 3] 1A to 1C are diagrams illustrating a pre-cooling method according to an embodiment of the present invention. [Figure 4] 1A to 1C are diagrams illustrating a pre-cooling method according to an embodiment of the present invention. [Diagram 5] 1A to 1C are diagrams illustrating a pre-cooling method according to an embodiment of the present invention. [Figure 6] FIG. 13 is a diagram illustrating a schematic diagram of another example of a pre-cooling device according to an embodiment. [Figure 7] FIG. 13 is a diagram illustrating a schematic diagram of another example of a pre-cooling device according to an embodiment. [Figure 8] FIG. 13 is a diagram illustrating a schematic diagram of another example of a pre-cooling device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiments are merely examples, and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] 1 is a schematic diagram of a cryogenic device 10 according to an embodiment. The cryogenic device 10 is configured to cool a superconducting coil 12, which is an example of an object to be cooled, from room temperature to a cryogenic temperature, and to maintain the superconducting coil 12 at a cryogenic temperature during use of the superconducting coil 12. The cryogenic device 10 also includes a pre-cooling device 100 that pre-cools the superconducting coil 12.

[0013] The superconducting coil 12 is mounted in high magnetic field equipment as a magnetic field source for, for example, an NMR system, an MRI system, an accelerator such as a cyclotron, a high energy physics system such as a nuclear fusion system, or other high magnetic field equipment (not shown), and can generate a high magnetic field required by the equipment. The superconducting coil 12 is configured to generate a strong magnetic field by passing electricity through the superconducting coil 12 in a state where it is cooled to an extremely low temperature below the superconducting transition temperature.

[0014] The cryogenic device 10 includes a cryogenic refrigerator 20, a vacuum vessel 30, and a radiation heat shield 40. In this embodiment, the cryogenic device 10 is configured as a conduction cooling type in which the superconducting coil 12 is directly cooled by the cryogenic refrigerator 20, rather than an immersion cooling type in which the superconducting coil 12 is immersed in a cryogenic liquid refrigerant such as liquid helium. The cryogenic refrigerator 20 is thermally coupled to the superconducting coil 12 so as to cool the superconducting coil 12 by conduction cooling. Note that, although one cryogenic refrigerator 20 is shown as an example in FIG. 1, the cryogenic device 10 may include multiple cryogenic refrigerators 20 for cooling one and the same object to be cooled, as necessary, for example, when the superconducting coil 12 is large.

[0015] The cryogenic refrigerator 20 includes a cooling stage 22 that cools an object by conduction cooling, more specifically, a first cooling stage 22a and a second cooling stage 22b. The cryogenic refrigerator 20 is installed in a vacuum vessel 30, and the first cooling stage 22a and the second cooling stage 22b are disposed inside the vacuum vessel 30.

[0016] The cryogenic refrigerator 20 includes a compressor (not shown) for a working gas (e.g., helium gas) and an expander also called a cold head. The compressor and the expander form a refrigeration cycle of the cryogenic refrigerator 20, whereby the first cooling stage 22a and the second cooling stage 22b are cooled to a desired cryogenic temperature. The first cooling stage 22a is cooled to a first cooling temperature, for example, 30K to 80K, and the second cooling stage 22b is cooled to a second cooling temperature, for example, 3K to 20K, which is lower than the first cooling temperature. The second cooling temperature is a temperature lower than the superconducting transition temperature of the superconducting coil 12. The first cooling stage 22a and the second cooling stage 22b are formed of a metal material such as copper or other material having high thermal conductivity.

[0017] Cryocooler 20 is, by way of example, a two-stage Gifford-McMahon (GM) refrigerator, but may also be a pulse tube refrigerator, a Stirling refrigerator, or any other type of cryocooler. Cryocooler 20 may also be a single-stage GM refrigerator or any other type of cryocooler that can provide the desired cooling temperature.

[0018] The vacuum vessel 30 is configured to separate the vacuum region 32 from the external environment 14. The vacuum region 32 is defined within the vacuum vessel 30. The vacuum vessel 30 may be, for example, a cryostat. The superconducting coil 12, the cooling stage 22 of the cryocooler 20, and the radiant heat shield 40 are disposed in the vacuum region 32 and are vacuum insulated from the external environment 14.

[0019] As an exemplary configuration, the vacuum vessel 30 has an upper wall 30a, a side wall 30b, and a lower wall 30c. The vacuum vessel 30 may be placed on the floor surface 16. For example, the lower wall 30c of the vacuum vessel 30 may be placed on the floor surface 16 via an appropriate support member 34.

[0020] The radiant heat shield 40 is thermally coupled to the first cooling stage 22a and is cooled to a first cooling temperature. The radiant heat shield 40 is disposed to surround the superconducting coil 12, which is cooled to a second cooling temperature, the second cooling stage 22b of the cryogenic refrigerator 20, and other low-temperature parts, and can thermally protect these low-temperature parts from external radiant heat. The radiant heat shield 40 is formed of a metal material such as copper or other material having high thermal conductivity.

[0021] The radiant heat shield 40 is directly attached to the first cooling stage 22a and thermally coupled to the first cooling stage 22a, or may be attached to the first cooling stage 22a via a flexible or rigid heat transfer member.

[0022] The superconducting coil 12 is thermally coupled to the second cooling stage 22b via the heat transfer member 24. As an example, the heat transfer member 24 is attached to the bottom surface of the superconducting coil 12 as shown in FIG. 1, but may be attached to other portions such as the side or top surface of the superconducting coil 12. The heat transfer member 24 may be formed, for example, as a bundle of thin wires or a laminate of foils so as to be flexible, and may be formed of a highly thermally conductive material such as copper. The heat transfer member 24 may be a rigid heat transfer member, for example, in the shape of a rod or plate. Alternatively, the superconducting coil 12 may be directly attached to the second cooling stage 22b without the heat transfer member 24.

[0023] An additional heat transfer member may be attached to the surface of the superconducting coil 12. For example, as shown in Fig. 1, a coil upper surface heat transfer plate 26a attached to the upper surface of the superconducting coil 12 and a coil side surface heat transfer plate 26b attached to the outer circumferential surface of the superconducting coil 12 may be provided. A heat transfer plate may be provided on the inner circumferential surface of the superconducting coil 12. Such an additional heat transfer member may be thermally coupled to the second cooling stage 22b via the heat transfer member 24 or directly.

[0024] Next, a description will be given of the pre-cooling device 100. The pre-cooling device 100 includes a movable liquid refrigerant storage unit 110 disposed within the vacuum container 30, a movement mechanism 120 for moving the liquid refrigerant storage unit 110 within the vacuum container 30 by operation from outside the vacuum container 30, and a liquid refrigerant pipe 130 and a gas pipe 140 connected to the liquid refrigerant storage unit 110 and drawn out to the outside of the vacuum container 30.

[0025] As will be described in more detail below, the liquid refrigerant storage section 110 is movable between a cooling position and a standby position within the vacuum vessel 30, and when in the cooling position it cools the superconducting coil 12 with liquid refrigerant, and when in the standby position it is positioned physically separated from the heat transfer path from the cryogenic refrigerator 20 to the superconducting coil 12.

[0026] 1, the liquid refrigerant reservoir 110 is in the standby position. As shown in the figure, in this embodiment, when in the standby position, the liquid refrigerant reservoir 110 is in physical contact with the radiant heat shield 40, more specifically, in physical contact with the radiant heat shield 40 so as to block the opening 42 provided in the radiant heat shield 40. When in the standby position, the liquid refrigerant reservoir 110 is positioned so as not to contact the second cooling stage 22b of the cryogenic refrigerator 20, the heat transfer member 24, the superconducting coil 12, or any other member cooled to the second cooling temperature.

[0027] When in the cooling position, the liquid refrigerant reservoir 110 is in physical contact with a heat transfer path from the second cooling stage 22b to the superconducting coil 12. This heat transfer path may include the second cooling stage 22b, the superconducting coil 12, the heat transfer member 24 connecting them, and a portion thermally coupled to any of these members and cooled to a second cooling temperature.

[0028] As an example, the liquid refrigerant storage unit 110 is configured as a liquid refrigerant tank capable of storing a liquid refrigerant (e.g., liquid nitrogen) therein, and has a tank upper wall 110a, a tank side wall 110b, and a tank bottom wall 110c. In the standby position, the liquid refrigerant storage unit 110 contacts the radiant heat shield 40, for example, with the outer periphery of the tank upper wall 110a (and / or the upper part of the tank side wall 110b) closing the opening 42. In the cooling position, the liquid refrigerant storage unit 110 contacts the heat transfer member 24 with the tank bottom wall 110c. This liquid refrigerant tank is formed of, for example, stainless steel or other appropriate metal material.

[0029] At least a part of the outer surface of the liquid refrigerant storage portion 110 may be covered with a heat transfer layer 112 in order to reduce contact thermal resistance with another member when the liquid refrigerant storage portion 110 comes into contact with the other member. The heat transfer layer 112 may be provided on the outer surface of the liquid refrigerant storage portion 110 that comes into contact with a member that is cooled to the second cooling temperature, such as the heat transfer member 24, for example, on the tank bottom wall 110c in this embodiment. The heat transfer layer 112 may be a sheet or plate formed of a material with a higher thermal conductivity than the material forming the liquid refrigerant storage portion 110 (for example, a metal material with high thermal conductivity such as copper). Alternatively, the heat transfer layer 112 may be a sheet or plate formed of a soft metal with a higher thermal conductivity than the material forming the liquid refrigerant storage portion 110, such as indium.

[0030] The liquid refrigerant storage unit 110 can receive liquid refrigerant from a liquid refrigerant source outside the vacuum vessel 30 (e.g., the dewar 150 shown in FIG. 2) and can discharge liquid refrigerant through the liquid refrigerant piping 130. The liquid refrigerant storage unit 110 can also discharge the liquid refrigerant vaporized in the liquid refrigerant storage unit 110 to the external environment 14 through the gas piping 140. As will be described later, the liquid refrigerant storage unit 110 can receive purge gas for discharging the liquid refrigerant from the liquid refrigerant storage unit 110 through the gas piping 140.

[0031] The movement mechanism 120 includes an operating member 121 and a support structure 122. The operating member 121 penetrates the radiant heat shield 40 in the vacuum vessel 30. The opening 42 of the radiant heat shield 40 is provided to allow the operating member 121 to pass through. The liquid refrigerant storage portion 110 is fixed to one end (the lower end in this embodiment) of the operating member 121, while the support structure 122 is provided to the other end (e.g., the upper end) of the operating member 121. One end of the operating member 121 is fixed to, for example, the tank upper wall 110a. The operating member 121 is supported by the support structure 122 on a wall (e.g., the upper wall 30a) of the vacuum vessel 30, and can be operated from outside the vacuum vessel 30 to move the liquid refrigerant storage portion 110.

[0032] The operation member 121 is formed of a heat insulating material such as fiber reinforced plastic (FRP). Alternatively, the operation member 121 may be formed of a material having a lower thermal conductivity than the highly thermally conductive material forming the heat transfer path in the cryogenic device 10, such as stainless steel. The operation member 121 is, for example, a rod extending linearly. The operation member 121 may be a solid rod. Alternatively, the operation member 121 may have a hollow structure. In this case, the cross-sectional area of ​​the operation member 121 is smaller than when the operation member 121 is a solid rod, and it is possible to reduce the intrusion of heat from the external environment of the vacuum vessel 30 to the low-temperature part in the vacuum vessel 30 due to thermal conduction through the operation member 121.

[0033] The support structure 122 has a bellows 123 and a support flange 124. The bellows 123 connects a wall (e.g., the upper wall 30a) of the vacuum vessel 30 to the support flange 124. In the bellows 123, the operating member 121 is fixed to the support flange 124. The operating member 121 extends from the support flange 124 into the vacuum vessel 30 through an insertion hole formed in the wall of the vacuum vessel 30. The support flange 124 may be considered to be a part of the operating member 121 provided for operating the operating member 121 from outside the vacuum vessel 30.

[0034] The support structure 122 may be provided with a pressure device 125 configured to move the support flange 124. The pressure device 125 can be used to operate the operating member 121 from outside the vacuum vessel 30. The pressure device 125 may have a movable mechanism, such as a push screw type, and the movable mechanism may be manually operated to move the support flange 124. To operate the movable mechanism, the pressure device 125 may have an appropriate drive source, such as hydraulic pressure, air pressure, an electric motor, or an electromagnet.

[0035] The liquid refrigerant line 130 has a liquid refrigerant port 131 in the liquid refrigerant reservoir 110. The liquid refrigerant port 131 may be a tube end of the liquid refrigerant line 130 disposed in the liquid refrigerant reservoir 110. The liquid refrigerant line 130 is connectable to a liquid refrigerant source such that liquid refrigerant is supplied to the liquid refrigerant reservoir 110 through the liquid refrigerant port 131.

[0036] The liquid refrigerant piping 130 extends from the liquid refrigerant port 131 into the liquid refrigerant reservoir 110, and then passes through the liquid refrigerant reservoir 110 in an airtight manner, for example, at the top of the tank top wall 110a or the tank side wall 110b, and continues to the outside of the liquid refrigerant reservoir 110. The liquid refrigerant piping 130 extending from the liquid refrigerant reservoir 110 to the outside of the radiant heat shield 40 through the opening 42 of the radiant heat shield 40, and then passes through the vacuum vessel 30 (for example, the top wall 30a) to the external environment 14. The liquid refrigerant piping 130 may be a vacuum feed-through piping. The liquid refrigerant piping 130 can be connected to a liquid refrigerant source outside the vacuum vessel 30.

[0037] In this embodiment, liquid refrigerant piping 130 is used not only to supply liquid refrigerant to liquid refrigerant storage portion 110, but also to recover liquid refrigerant from liquid refrigerant storage portion 110. Liquid refrigerant piping 130 is connected to liquid refrigerant storage portion 110 so that liquid refrigerant is discharged from liquid refrigerant storage portion 110 through liquid refrigerant port 131.

[0038] By using one liquid refrigerant pipe 130 for both supplying and recovering the liquid refrigerant, the structure of the pre-cooling device 100 can be simplified compared to a case in which a supply pipe and a recovery pipe are separately provided. In addition, such a pipe can be a path for heat input from the external environment 14 to the inside of the vacuum vessel 30 when the pre-cooling device 100 is not in use, but by using one liquid refrigerant pipe 130, the amount of heat input through the pipe can be reduced.

[0039] The gas pipe 140 has a gas port 141 in the liquid refrigerant storage section 110. The gas port 141 may be a gas inlet / outlet opening into the liquid refrigerant storage section 110, and may be disposed in the upper portion of the liquid refrigerant storage section 110, for example, in the upper portion of the tank upper wall 110a or the tank side wall 110b. The gas pipe 140 is provided as a discharge path from the liquid refrigerant storage section 110 for the liquid refrigerant vaporized in the liquid refrigerant storage section 110. The gas pipe 140 extending out from the liquid refrigerant storage section 110 is drawn out of the radiant heat shield 40 through the opening 42 of the radiant heat shield 40, and is further drawn out to the external environment 14 through the vacuum vessel 30 (for example, the upper wall 30a). The gas pipe 140 may be a vacuum feed-through pipe.

[0040] In addition, a first vacuum valve 132 and a second vacuum valve 142 are connected to the liquid refrigerant storage section 110. The first vacuum valve 132 is provided on the liquid refrigerant pipe 130 outside the vacuum vessel 30, and the second vacuum valve 142 is provided on the gas pipe 140 outside the vacuum vessel 30. When the first vacuum valve 132 and the second vacuum valve 142 are closed, they each block the inflow of fluid into the liquid refrigerant storage section 110, and can maintain the liquid refrigerant storage section 110 in a vacuum state when the inside of the liquid refrigerant storage section 110 is in a vacuum. When the first vacuum valve 132 is opened, the liquid refrigerant is allowed to flow in the liquid refrigerant pipe 130, and when the second vacuum valve 142 is opened, the gas is allowed to flow in the gas pipe 140.

[0041] 2 to 5 are diagrams that show a schematic diagram of a pre-cooling method according to an embodiment. The pre-cooling method according to the embodiment includes moving the liquid refrigerant storage unit 110 to a cooling position for cooling the superconducting coil 12, supplying the liquid refrigerant 190 to the liquid refrigerant storage unit 110, cooling the superconducting coil 12 by storing the liquid refrigerant 190 in the liquid refrigerant storage unit 110, discharging the liquid refrigerant 190 from the liquid refrigerant storage unit 110 after cooling the superconducting coil 12, and moving the liquid refrigerant storage unit 110 to a standby position that is physically separated from the heat transfer path from the cryogenic refrigerator 20 to the superconducting coil 12 after cooling the superconducting coil 12.

[0042] Prior to commencing this pre-cooling method, the accessories of the pre-cooling apparatus 100 to be used in the pre-cooling method, such as the dewar 150, vacuum pump 160, and purge gas source 180, are attached to the pre-cooling apparatus 100 as shown in FIG.

[0043] The dewar 150 is connected to the liquid refrigerant pipe 130. The dewar 150 stores, for example, liquid nitrogen as a liquid refrigerant. The dewar 150 is connected to the first vacuum valve 132 via the first on-off valve 151. By opening the first on-off valve 151 (and the first vacuum valve 132), the liquid refrigerant can be supplied from the dewar 150 to the liquid refrigerant storage unit 110 through the liquid refrigerant pipe 130, or the liquid refrigerant can be recovered from the liquid refrigerant storage unit 110 to the dewar 150 through the liquid refrigerant pipe 130. When the liquid refrigerant is not supplied or recovered between the dewar 150 and the liquid refrigerant storage unit 110, the first on-off valve 151 is closed.

[0044] The vacuum pump 160 is also connected to the liquid refrigerant pipe 130. The vacuum pump 160 is connected to the first vacuum valve 132 via the second on-off valve 152. The vacuum pump 160 and the second on-off valve 152 are connected to the liquid refrigerant pipe 130 between the first on-off valve 151 and the first vacuum valve 132. The liquid refrigerant reservoir 110 can be evacuated by opening the second on-off valve 152 (and the first vacuum valve 132) and operating the vacuum pump 160. The first on-off valve 151 and the second on-off valve 152 are configured or operable to close one when opening the other, thereby allowing only one of the Dewar 150 or the vacuum pump 160 to act on the liquid refrigerant reservoir 110. It should be noted that the vacuum pump 160 and the second on-off valve 152 may be connected to the gas pipe 140 instead of the liquid refrigerant pipe 130.

[0045] The end of the gas pipe 140 drawn out from the vacuum vessel 30 to the external environment 14 is provided as a gas outlet 170 to the external environment 14. A third on-off valve 153 is provided at the gas outlet 170. By opening the third on-off valve 153 (and the second vacuum valve 142), the liquid refrigerant vaporized in the liquid refrigerant storage section 110 can be discharged from the gas outlet 170 through the gas pipe 140 to the external environment 14.

[0046] Moreover, the gas pipe 140 can be connected to a purge gas source 180 so that a purge gas for discharging the liquid refrigerant from the liquid refrigerant storage section 110 is supplied to the liquid refrigerant storage section 110. For example, nitrogen gas, air, or other purge gas is stored in the purge gas source 180. The purge gas source 180 is connected to the second vacuum valve 142 via a fourth on-off valve 154. By opening the fourth on-off valve 154 (and the second vacuum valve 142), a purge gas can be supplied from the purge gas source 180 to the liquid refrigerant storage section 110 through the gas pipe 140. When no purge gas is supplied, the fourth on-off valve 154 is closed.

[0047] The purge gas source 180 and the fourth on-off valve 154 are connected between the third on-off valve 153 and the second vacuum valve 142. The third on-off valve 153 and the fourth on-off valve 154 are configured or operable to close one of them when opening the other, thereby allowing switching between supplying purge gas to the liquid refrigerant reservoir 110 and discharging vaporized liquid refrigerant from the liquid refrigerant reservoir 110.

[0048] By using one gas pipe 140 for both gas exhaust and purge gas supply, the structure of the pre-cooling device 100 can be simplified compared to a case in which an exhaust pipe and a supply pipe are separately provided. In addition, such a pipe can be a path for heat input from the external environment 14 to the inside of the vacuum vessel 30 when the pre-cooling device 100 is not in use, but by using one gas pipe 140, the amount of heat input through the pipe can be reduced.

[0049] It is not essential to provide the purge gas source 180 in the pre-cooling device 100. When the purge gas source 180 and the fourth on-off valve 154 are not connected to the gas pipe 140, the third on-off valve 153 does not need to be provided in the gas pipe 140 either.

[0050] A pressure gauge 143 may be provided in the gas pipe 140 or the gas outlet 170. When liquid refrigerant is present in the liquid refrigerant storage unit 110, the measured pressure becomes relatively high due to the refrigerant vaporized and discharged therefrom. By monitoring the pressure measured by this pressure gauge 143, it is possible to know whether or not there is liquid refrigerant in the liquid refrigerant storage unit 110. Alternatively, a liquid level gauge for measuring the liquid level of the liquid refrigerant may be provided in the liquid refrigerant storage unit 110. Alternatively, a thermometer may be provided in the liquid refrigerant storage unit 110. Even in this manner, it is possible to know whether or not there is liquid refrigerant in the liquid refrigerant storage unit 110.

[0051] In the pre-cooling method according to the embodiment, first, the liquid refrigerant storage section 110 is moved from the standby position shown in Fig. 1 to the cooling position shown in Fig. 2. Specifically, when the support flange 124 is brought close to the vacuum vessel 30 manually or by operating the pressurizing device 125, the bellows 123 contracts and the operating member 121 is pushed into the vacuum vessel 30. The liquid refrigerant storage section 110 moves away from the radiant heat shield 40 and toward the heat transfer member 24, and the heat transfer layer 112 of the tank bottom wall 110c comes into contact with the heat transfer member 24. In this way, the liquid refrigerant storage section 110 is moved from the standby position to the cooling position.

[0052] When the liquid refrigerant storage section 110 is moved to the cooling position, as shown in FIG. 3, the liquid refrigerant 190 is supplied to the liquid refrigerant storage section 110. The first on-off valve 151 (and the first vacuum valve 132) is opened, and the liquid refrigerant 190 is supplied from the Dewar 150 to the liquid refrigerant storage section 110 through the liquid refrigerant piping 130. The liquid refrigerant 190 flows into the liquid refrigerant storage section 110 from the liquid refrigerant port 131. At this time, the liquid refrigerant 190 vaporized in the liquid refrigerant storage section 110 flows into the gas piping 140 from the gas port 141. By opening the third on-off valve 153 (and the second vacuum valve 142), the vaporized liquid refrigerant is discharged from the gas outlet 170 through the gas piping 140 to the external environment 14. The second on-off valve 152 and the fourth on-off valve 154 are closed. Alternatively, liquid refrigerant 190 may be supplied when liquid refrigerant reservoir 110 is in the standby position, and then liquid refrigerant reservoir 110 may be moved to the cooling position.

[0053] In this manner, the superconducting coil 12 is cooled by storing the liquid refrigerant 190 in the liquid refrigerant storage portion 110. During cooling, the liquid refrigerant 190 gradually decreases from the liquid refrigerant storage portion 110 due to evaporation of the liquid refrigerant 190. Therefore, the liquid refrigerant 190 may be replenished from the Dewar 150 to the liquid refrigerant storage portion 110 during cooling.

[0054] When the superconducting coil 12 is pre-cooled to a target temperature (for example, when cooled to the temperature of the liquid refrigerant 190), the liquid refrigerant 190 is discharged from the liquid refrigerant storage section 110 as shown in FIG. 4. The fourth on-off valve 154 (and the second vacuum valve 142) is opened, and purge gas is supplied from the purge gas source 180 to the liquid refrigerant storage section 110 through the gas piping 140. At this time, the third on-off valve 153 is closed. By supplying the purge gas to the liquid refrigerant storage section 110, the inside of the liquid refrigerant storage section 110 is pressurized. The liquid refrigerant 190 remaining in the liquid refrigerant storage section 110 flows from the liquid refrigerant port 131 into the liquid refrigerant piping 130 as if being pushed out by the purge gas, and is collected in the Dewar 150 through the liquid refrigerant piping 130. By pressurizing the liquid refrigerant reservoir 110 using a purge gas, the liquid refrigerant 190 remaining in the liquid refrigerant reservoir 110 can be quickly expelled from the liquid refrigerant reservoir 110 .

[0055] The liquid refrigerant port 131 is disposed at the bottom of the liquid refrigerant storage portion 110, and is provided, for example, close to or adjacent to the tank bottom wall 110c. The height at which the liquid refrigerant port 131 is located is lower than the height at which the gas port 141 is located. In this way, even when the liquid level of the liquid refrigerant 190 in the liquid refrigerant storage portion 110 drops and approaches the tank bottom wall 110c, the liquid refrigerant port 131 is immersed in the liquid refrigerant 190. Therefore, compared to when the liquid refrigerant port 131 is located at the top of the liquid refrigerant storage portion 110, more liquid refrigerant 190 can flow from the liquid refrigerant storage portion 110 into the liquid refrigerant piping 130 and be collected in the Dewar 150.

[0056] When the liquid refrigerant 190 is discharged from the liquid refrigerant storage portion 110 in this manner, the second on-off valve 152 may be opened, and the liquid refrigerant storage portion 110 may be evacuated by the vacuum pump 160, as shown in Fig. 5. At this time, the second vacuum valve 142 is closed. When the liquid refrigerant storage portion 110 is evacuated, the first vacuum valve 132 is also closed. In this manner, a vacuum is maintained inside the liquid refrigerant storage portion 110.

[0057] Then, the liquid refrigerant storage portion 110 is moved from the cooling position to the standby position. When the support flange 124 is lifted from the vacuum vessel 30 manually or by operating the pressurizing device 125, the bellows 123 is expanded, and the liquid refrigerant storage portion 110 is lifted together with the operating member 121. The liquid refrigerant storage portion 110 is separated from the heat transfer member 24 and comes into contact with the radiant heat shield 40. Since the liquid refrigerant storage portion 110 and the heat transfer member 24 are disposed in the vacuum region 32, even a small gap between them will block heat conduction. In this manner, the liquid refrigerant storage portion 110 is moved from the cooling position to the standby position. Note that the liquid refrigerant storage portion 110 may be first moved from the cooling position to the standby position, and then the liquid refrigerant 190 may be discharged from the liquid refrigerant storage portion 110.

[0058] The pre-cooling apparatus 100 accessories such as the dewar 150, vacuum pump 160, purge gas source 180, etc. are then removed and returned to the state shown in Figure 1. The pre-cooling method is now complete.

[0059] When the pre-cooling of the superconducting coil 12 is completed, the cryogenic refrigerator 20 is started. The first cooling stage 22a of the cryogenic refrigerator 20 is cooled to a first cooling temperature, and the second cooling stage 22b is cooled to a second cooling temperature. The superconducting coil 12 is cooled from the pre-cooling temperature by the liquid refrigerant 190 to the second cooling temperature by the second cooling stage 22b. By passing electricity through the superconducting coil 12 from a power source (not shown), the superconducting coil 12 can generate a strong magnetic field. In this manner, the steady operation of the cryogenic device 10 can be started.

[0060] The cryogenic refrigerator 20 may be operating during pre-cooling of the superconducting coil 12. The superconducting coil 12 may be cooled by both the pre-cooling device 100 and the cryogenic refrigerator 20. However, in this case, there is a concern that the liquid refrigerant reservoir 110 may be excessively cooled by the second cooling stage 22b of the cryogenic refrigerator 20 when the liquid refrigerant reservoir 110 is in the cooling position, and the liquid refrigerant 190 in the liquid refrigerant reservoir 110 may be frozen. To avoid this, a thermometer may be used to monitor the temperature of the liquid refrigerant reservoir 110, and the pre-cooling by the pre-cooling device 100 may be terminated before the measured temperature falls below the freezing point of the liquid refrigerant. The thermometer may be installed in the liquid refrigerant reservoir 110, or may be installed in a portion to be cooled to the second cooling temperature, such as the second cooling stage 22b or the heat transfer member 24.

[0061] Incidentally, in a superconducting system, initial cooling is performed when starting up the system, in which the superconducting equipment is cooled from room temperature or a high temperature, for example, 200 K or higher, to a target cooling temperature (for example, 10 K or lower in most cases). Steady-state operation of the superconducting system becomes possible after the initial cooling is completed. In order to make superconducting equipment available for use as soon as possible, it is desirable to shorten the time required for initial cooling as much as possible.

[0062] However, in existing superconducting systems, the initial cooling of superconducting equipment, especially large superconducting coils, often requires a long time. One reason for this is that the cryocoolers that cool superconducting equipment are usually designed to provide a cooling capacity during steady-state operation, but in this case, the cooling capacity of the cryocooler is often insufficient compared to the cooling capacity desired for the initial cooling. Another reason is that the specific heat of the materials that make up the system increases as the temperature increases. In some cases, the initial cooling can take several days or even a week.

[0063] According to the embodiment, the pre-cooling device 100 can be used to pre-cool the superconducting coil 12. Therefore, the time required for initial cooling of the cryogenic device 10 can be shortened compared to the case where the superconducting coil 12 is pre-cooled using only the cryogenic refrigerator 20.

[0064] Also, there is less need to increase the refrigeration capacity of the cryogenic refrigerator 20 in preparation for initial cooling or to increase the number of cryogenic refrigerators 20. Therefore, the cryogenic device 10 according to the embodiment can be designed to optimize the cryogenic refrigerator 20 for steady operation, and for example, it is possible to mount a cryogenic refrigerator 20 with a lower refrigeration capacity in the cryogenic device 10 or reduce the number of cryogenic refrigerators 20 mounted in the cryogenic device 10.

[0065] As mentioned at the beginning of this document, when a sub-cooling system is provided in a cryogenic cooling device to cool the object to be cooled using a cryogenic liquid, and this system is not operated under normal operating conditions of the cryogenic cooling device, the pipe of the cryogenic liquid acts as a heat transfer path connecting the surrounding environment to the object to be cooled. The heat input to the object to be cooled through this pipe can heat the object to be cooled. This heat input also becomes a thermal load for the main cooling system, i.e., the cryogenic refrigerator, so that the main cooling system is required to have a higher cooling capacity to suppress the temperature rise of the object to be cooled. In addition, when the sub-cooling system is operating, the cryogenic cooling device must continue to adjust the flow of the cryogenic liquid to properly adjust the temperature of the object to be cooled. This can be cumbersome or can require a control mechanism for adjustment, making the device configuration complicated.

[0066] However, in the pre-cooling device 100 according to the embodiment, the liquid refrigerant storage section 110 is movable between a cooling position and a standby position in the vacuum vessel 30, and when in the cooling position, the liquid refrigerant storage section 110 cools the superconducting coil 12 with the liquid refrigerant, and when in the standby position, the liquid refrigerant storage section 110 is physically located away from the heat transfer path from the cryogenic refrigerator 20 to the superconducting coil 12. Therefore, the pre-cooling device 100 can suppress the heat input to the superconducting coil 12 during the steady operation of the cryogenic device 10 after the completion of pre-cooling. In addition, the liquid refrigerant storage section 110 is simple because it cools the superconducting coil 12 with the liquid refrigerant stored therein. When the liquid refrigerant is liquid nitrogen, the vaporized refrigerant is allowed to be released into the external environment 14, making it easy to handle. Liquid nitrogen is also inexpensive.

[0067] Furthermore, in the pre-cooling device 100 according to the embodiment, when in the standby position, the liquid refrigerant storage section 110 is in physical contact with the radiant heat shield 40. Therefore, during normal operation of the cryogenic device 10, the liquid refrigerant storage section 110 is cooled by the radiant heat shield 40 and maintained at the first cooling temperature. The liquid refrigerant storage section 110 can be utilized as a part of the radiant heat shield 40, and heat input to the superconducting coil 12 and other parts cooled to the second cooling temperature can be suppressed.

[0068] Furthermore, in the embodiment, the liquid refrigerant reservoir 110 is in physical contact with the radiant heat shield 40 so as to block the opening 42 provided in the radiant heat shield 40. In this manner, the liquid refrigerant reservoir 110 can block radiant heat that may enter through the opening 42 from the vacuum vessel 30 or the external environment 14. This makes it possible to suppress heat input to the superconducting coil 12 and other parts cooled to the second cooling temperature.

[0069] In addition, in the embodiment, when the liquid refrigerant storage section 110 is in the standby position, a vacuum is maintained by the first vacuum valve 132 and the second vacuum valve 142 connected to the liquid refrigerant storage section 110. By virtue of the vacuum insulation, heat input through the liquid refrigerant storage section 110 can be suppressed.

[0070] Various other configurations may be used for the pre-cooling device 100, and in particular the liquid refrigerant reservoir 110. Several other examples of the pre-cooling device 100 according to the embodiment will be described with reference to Figs.

[0071] As shown in FIG. 6, the liquid refrigerant reservoir 110 may be thermally coupled to the first cooling stage 22a of the cryogenic refrigerator 20 via a flexible heat transfer element 50. The flexible heat transfer element 50 may be made of a highly thermally conductive material such as copper and may be formed, for example, as a bundle of thin wires or a laminate of foils to have flexibility. Alternatively, the flexible heat transfer element 50 may be formed in a spring shape. The liquid refrigerant reservoir 110 is attached to a portion to be cooled to the first cooling temperature by the first cooling stage 22a, such as the radiant heat shield 40, by the flexible heat transfer element 50. In this way, the liquid refrigerant reservoir 110 can be made movable relative to the portion. In addition, when the liquid refrigerant reservoir 110 is in the cooling position, the liquid refrigerant 190 stored therein can be used to pre-cool not only the superconducting coil 12 and the second cooling stage 22b, but also the portion to be cooled to the first cooling temperature, such as the radiant heat shield 40, via the flexible heat transfer element 50.

[0072] Conversely, when the liquid refrigerant reservoir 110 is in the standby position, the liquid refrigerant reservoir 110 can also be cooled by the first cooling stage 22a via the flexible heat transfer element 50. Therefore, when the liquid refrigerant reservoir 110 is in the standby position, it does not need to be in physical contact with the portion that is cooled to the first cooling temperature by the first cooling stage 22a, such as the radiant heat shield 40.

[0073] As shown in FIG. 7, the liquid refrigerant storage 110 may include a flange portion 52 that is thermally coupled to the second cooling stage 22b of the cryogenic refrigerator 20 when in the cooling position and is thermally coupled to the first cooling stage 22a when in the standby position. The flange portion 52 may be formed around the entire circumference of the liquid refrigerant storage 110, for example, on the outside of the tank side wall 110b. The flange portion 52 may be provided at the same height as the tank bottom wall 110c. When the liquid refrigerant storage 110 is in the standby position, the flange portion 52 physically contacts the radiation heat shield 40 so as to close the opening 42. As shown by the dashed line in FIG. 7, when in the cooling position, the liquid refrigerant storage 110 contacts the heat transfer member 24 at the flange portion 52 and the tank bottom wall 110c. In this way, when pre-cooling is completed and the liquid refrigerant storage section 110 is in the standby position, at least a portion or most of the liquid refrigerant storage section 110 can be stored outside the radiant heat shield 40, thereby avoiding protrusion toward the second cooling stage 22b.

[0074] 8, the liquid refrigerant storage section 110 may protrude toward the vacuum vessel 30 through the opening 42 of the radiant heat shield 40. In this way, the capacity of the liquid refrigerant 190 in the liquid refrigerant storage section 110 can be increased, and the number of times that the liquid refrigerant 190 needs to be replenished into the liquid refrigerant storage section 110 during pre-cooling can be reduced.

[0075] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination has the combined effects of each of the combined embodiments.

[0076] In the above-described embodiment, the liquid refrigerant reservoir 110 is in physical contact with the heat transfer member 24 when in the cooling position, but is not limited to this. The liquid refrigerant reservoir 110 may be configured to be in physical contact with the second cooling stage 22b of the cryogenic refrigerator 20, the superconducting coil 12, or any other member that is thermally coupled with the second cooling stage 22b and is cooled to the second cooling temperature when in the cooling position.

[0077] In the above embodiment, the liquid refrigerant reservoir 110 is in physical contact with the radiant heat shield 40 when in the standby position, but this is not limited thereto. The liquid refrigerant reservoir 110 may be configured to be in physical contact with the first cooling stage 22a of the cryogenic refrigerator 20 or another member that is thermally coupled with the first cooling stage 22a and cooled to the first cooling temperature when in the standby position.

[0078] In the embodiment described above, the opening 42 is a through hole formed in the radiant heat shield 40. However, the opening 42 may be formed in the first cooling stage 22a of the cryogenic refrigerator 20, or in another member that is thermally coupled to the first cooling stage 22a and cooled to the first cooling temperature. The opening 42 may be provided between multiple such members, for example, between the radiant heat shield 40 and the first cooling stage 22a.

[0079] In the above-described embodiment, the moving mechanism 120 of the pre-cooling device 100 is provided on the upper wall 30a of the vacuum vessel 30, and the liquid refrigerant storage unit 110 is movable in the vertical direction by the moving mechanism 120, but this is not limited thereto. For example, the moving mechanism 120 may be provided on the side wall 30b of the vacuum vessel 30, and the liquid refrigerant storage unit 110 may be movable in the horizontal direction by the moving mechanism 120.

[0080] In the above embodiment, one liquid refrigerant pipe 130 is used for both supplying and recovering the liquid refrigerant, but the pre-cooling device 100 may have separate liquid refrigerant pipes for supplying and recovering the liquid refrigerant. Also, in the above embodiment, one gas pipe 140 is used for both discharging gas and supplying purge gas, but the pre-cooling device 100 may have separate gas pipes for discharging and for supplying purge gas.

[0081] The shape and structure of the liquid refrigerant storage unit 110 are not limited to the specific form described above. For example, it is not essential that the liquid refrigerant storage unit 110 is configured as a liquid refrigerant tank. The liquid refrigerant storage unit 110 may be configured in the form of a movable liquid refrigerant pipe within the vacuum vessel 30, and may be movable between a cooling position and a standby position within the vacuum vessel 30, and may cool the superconducting coil 12 with the liquid refrigerant when in the cooling position, and may be physically separated from the heat transfer path from the cryogenic refrigerator 20 to the superconducting coil 12 when in the standby position.

[0082] In the above embodiment, the object to be cooled is described by taking the superconducting coil 12 as an example, but the present invention is not limited thereto. The cryogenic device 10 may be configured to cool the object to be cooled, such as a superconducting device, a sensor, or other cryogenic device, from room temperature to a cryogenic temperature and to maintain the object at a cryogenic temperature during use of the object. Thus, the cryogenic refrigerator 20 may be configured to cool the object to be cooled, and the pre-cooling device 100 may be configured to pre-cool the object to be cooled.

[0083] The cryogenic device 10 may also employ a cooling method in which a relatively small amount of cryogenic refrigerant (e.g., liquid helium) is circulated through the object to be cooled by a refrigerant pipe to cool the object to a cryogenic temperature. The refrigerant pipe is provided on the surface of or inside the object to be cooled. The cryogenic refrigerator 20 may be thermally coupled to the refrigerant pipe so as to recool the cryogenic refrigerant that has been heated by heat exchange with the object to be cooled. The pre-cooling device 100 according to the embodiment may be incorporated in the cryogenic device 10 in order to pre-cool the object to be cooled by the cryogenic refrigerator 20 in this manner.

[0084] The present invention has been described using specific terms based on the embodiments, but the embodiments merely show one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0085] 10 cryogenic device, 20 cryogenic refrigerator, 22 cooling stage, 22a first cooling stage, 22b second cooling stage, 42 opening, 100 pre-cooling device, 110 liquid refrigerant reservoir, 130 liquid refrigerant piping, 131 liquid refrigerant port, 140 gas piping, 180 purge gas source, 190 liquid refrigerant.

Claims

1. A pre-cooling device that pre-cools an object to be cooled by a cryogenic refrigerator, the cryogenic refrigerator comprising a first cooling stage that is cooled to a first cooling temperature, and a second cooling stage that is thermally coupled to the object to be cooled and is cooled to a second cooling temperature that is lower than the first cooling temperature, the pre-cooling device comprising: a liquid refrigerant storage section that cools the object to be cooled by a liquid refrigerant stored therein; the liquid refrigerant reservoir is movable between a cooling position and a standby position, and when in the cooling position, the liquid refrigerant reservoir cools the object to be cooled with the liquid refrigerant, and when in the standby position, the liquid refrigerant reservoir is disposed physically separated from a heat transfer path from the cryogenic refrigerator to the object to be cooled; A pre-cooling device, characterized in that the liquid refrigerant reservoir is in physical contact with the heat transfer path from the second cooling stage to the object to be cooled when in the cooling position.

2. The pre-cooling device of claim 1 , wherein the liquid refrigerant reservoir is in physical contact with the first cooling stage or a member thermally coupled to the first cooling stage when in the standby position.

3. an opening is provided in the first cooling stage or the member; 3. The pre-cooling device according to claim 2, wherein the liquid refrigerant reservoir is in physical contact with the first cooling stage or the member so as to block the opening when in the standby position.

4. 4. The pre-cooling device of claim 1, wherein the liquid refrigerant reservoir is thermally coupled to the first cooling stage via a flexible heat transfer element.

5. A pre-cooling device for pre-cooling an object to be cooled by a cryogenic refrigerator, comprising: a liquid refrigerant storage section that cools the object to be cooled by a liquid refrigerant stored therein; the liquid refrigerant reservoir is movable between a cooling position and a standby position, and when in the cooling position, the liquid refrigerant reservoir cools the object to be cooled with the liquid refrigerant, and when in the standby position, the liquid refrigerant reservoir is disposed physically separated from a heat transfer path from the cryogenic refrigerator to the object to be cooled; a liquid refrigerant pipe having a liquid refrigerant port at a lower portion of the liquid refrigerant reservoir and connected to the liquid refrigerant reservoir so that the liquid refrigerant is discharged from the liquid refrigerant reservoir through the liquid refrigerant port; a gas piping connected to the liquid refrigerant reservoir, the gas piping being connectable to a purge gas source so that a purge gas for discharging the liquid refrigerant from the liquid refrigerant reservoir is supplied to the liquid refrigerant reservoir.

6. the liquid refrigerant line is connectable to a liquid refrigerant source such that the liquid refrigerant is supplied to the liquid refrigerant reservoir through the liquid refrigerant port; 6. The pre-cooling device according to claim 5, wherein the gas pipe is provided as a path for discharging the liquid refrigerant vaporized in the liquid refrigerant reservoir from the liquid refrigerant reservoir.

7. 7. A pre-cooling device according to claim 1, further comprising a vacuum valve connected to said liquid refrigerant reservoir, the vacuum valve being adapted to close and block the inflow of fluid into said liquid refrigerant reservoir.

8. A pre-cooling device according to any one of claims 1 to 7 and the cryogenic refrigerator, The cryogenic device is characterized in that the cryogenic refrigerator is thermally coupled to an object to be cooled so as to cool the object by conductive cooling.

9. A method for pre-cooling an object to be cooled by a cryogenic refrigerator, the cryogenic refrigerator comprising a first cooling stage cooled to a first cooling temperature, and a second cooling stage thermally coupled to the object to be cooled and cooled to a second cooling temperature lower than the first cooling temperature, the method comprising: moving a liquid refrigerant reservoir to a cooling position where the object to be cooled is cooled; supplying a liquid refrigerant to the liquid refrigerant reservoir; cooling the object to be cooled by storing the liquid refrigerant in the liquid refrigerant storage section; Discharging the liquid refrigerant from the liquid refrigerant reservoir after cooling the object to be cooled; and after cooling the object to be cooled, moving the liquid refrigerant reservoir to a standby position physically separated from a heat transfer path from the cryogenic refrigerator to the object to be cooled, the liquid refrigerant reservoir being in physical contact with the heat transfer path from the second cooling stage to the object to be cooled when in the cooling position.

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