Cryogenic cooling system, superconducting device, and method for operating a cryogenic cooling system

Abstract

To improve the refrigerating capacity of a cooling source by reducing a temperature difference between a cooling source and an object to be cooled.SOLUTION: Provided is a cryogenic cooling system that includes: a vacuum vessel 14 for housing a first-stage cooling stage 15, second-stage cooling stages 16A, 16B, a superconductive coil 1, and a cryogenic fan 22 of a cryogenic refrigerator 13; a first circulation system 11 in which main parts except for a compressor 17 are arranged in the vacuum vessel and gas compressed by the compressor is circulated to cool the superconducting coils by the first-stage cooling stage 15 and the second-stage cooling stage 16A of the cryogenic refrigerator; and a second circulation system 12 which is located in the vacuum vessel, and in which the gas pumped by the cryogenic fan 22 is circulated to cool the superconducting coils by the two-stage cooling stage 16B of the cryogenic refrigerator 13, wherein the first circulation system 11 and the second circulation system 12 are joined at a joining point M on the upstream side of the superconducting coil 1, and are branched and connected at a branching point N on the downstream side of the superconductive coil.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a cryogenic cooling system, a superconducting device including the cryogenic cooling system in which the object to be cooled is a superconducting coil, and an operation method of the cryogenic cooling system.

Background Art

[0002] A superconducting magnet (superconducting coil) needs to be cooled to cryogenic temperatures. Initially, a method of cooling with liquid helium was common. Subsequently, with the development of a small cryogenic refrigerator capable of cooling to liquid helium temperatures, a method of cooling a superconducting coil by conduction cooling using this cryogenic refrigerator has been developed. This method is becoming increasingly widespread because it does not require handling liquid helium, which requires specialized knowledge, and due to the difficulty of obtaining liquid helium due to the depletion of helium resources in recent years. Conduction cooling using this cryogenic refrigerator has already become widespread in small superconducting devices, and it is expected that in the future, the cooling method using a cryogenic refrigerator will also become the mainstream for large superconducting devices.

[0003] In the cooling of small superconducting devices by a cryogenic refrigerator, a conduction cooling method using a good heat conductor between the cryogenic refrigerator and the superconducting coil is common. However, in large superconducting devices, the heat load is large and the heat transfer distance is long, so there is a problem that the temperature difference between the cryogenic refrigerator and the superconducting device becomes large in the conduction cooling method. Therefore, a gas circulation cooling method in which a gas cooled by a cryogenic refrigerator is circulated to cool the superconducting coil of a superconducting device is advantageous. In this gas circulation cooling method, there is an advantage that the temperature difference between the cryogenic refrigerator and the superconducting device does not change even if they are separated.

Prior Art Documents

Patent Documents

[0004] [[ID=2​​​​​​​[Patent Document 3] Japanese Patent Publication No. 2010-196909 [Patent Document 4] Japanese Patent Publication No. 2009-246231 [Patent Document 5] Japanese Patent Application Publication No. 6-123506 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, cryogenic cooling systems using a gas circulation cooling method include the cryogenic cooling system 100 shown in Figure 6(A) and the cryogenic cooling system 110 shown in Figure 6(B). These cryogenic cooling systems 100 and 110 have a cryogenic refrigerator 103 equipped with a single-stage cooling stage 101 and a double-stage cooling stage 102 as a cooling source, and cool the superconducting coil 105, which is the object to be cooled, housed in a vacuum vessel 104.

[0006] In the cryogenic cooling system 100, a compressor 107, a first heat exchanger 108, a first-stage cooling stage 101, a second heat exchanger 109, a second-stage cooling stage 102, a superconducting coil 105, a second heat exchanger 109, a first heat exchanger 108, and a compressor 107 are sequentially arranged in a loop-shaped cooling pipe 106. Of these, the compressor 107 is located outside the vacuum vessel 104, while the first-stage cooling stage 101 and second-stage cooling stage 102 of the cryogenic refrigerator 103, the first heat exchanger 108, and the second heat exchanger 109 are located inside the vacuum vessel 104 along with the superconducting coil 105. The refrigerant gas, compressed and discharged by the compressor 107, is sequentially cooled in the first heat exchanger 108, the first-stage cooling stage 101, the second heat exchanger 109, and the second-stage cooling stage 102, and is then guided to the superconducting coil 105, which is cooled to an extremely low temperature (for example, around 4K).

[0007] In the cryogenic cooling system 110, a cryogenic fan 112, a two-stage cooling stage 102, a superconducting coil 105, and another cryogenic fan 112 are sequentially arranged in a loop-shaped cooling pipe 111. These cryogenic fans 112, the two-stage cooling stage 102, and the superconducting coil 105 are placed inside a vacuum vessel 104. The refrigerant gas, pressurized by the cryogenic fan 112, is cooled by the two-stage cooling stage 102 and guided to the superconducting coil 105, which is then cooled to an extremely low temperature (for example, around 4K).

[0008] In the gas circulation cooling method described above, there is a problem in that the temperature of the gas rises as it absorbs heat from the object being cooled (superconducting coil 105). The difference between the inlet temperature and outlet temperature of the superconducting coil 105 in the gas is proportional to the amount of heat transferred and inversely proportional to the gas flow rate. Therefore, the more the gas flow rate is increased, the smaller the temperature rise of the gas due to the superconducting coil 105 becomes, and consequently the smaller the temperature difference between the cryogenic refrigerator 103 and the superconducting coil 105 becomes, so it seems that a higher gas flow rate would be better. However, there are also problems when the gas flow rate is too high.

[0009] In the cryogenic cooling system 100 (Figure 6(A)) which uses a compressor 107 at room temperature outside the vacuum vessel 104, it is necessary to circulate the gas between the outside (room temperature section) and the inside (low temperature section) of the vacuum vessel 104, and high-temperature gas is sent from the compressor 107 to the low temperature section. If the efficiency of the first heat exchanger 108 is 100%, the gas from the room temperature section can be cooled by the return gas from the low temperature section. However, in reality, the efficiency of the first heat exchanger 108 is, for example, around 96%, and 4% of the heat enters the low temperature section. This is called heat exchanger loss. Since this heat exchanger loss is proportional to the gas flow rate, increasing the gas flow rate increases the heat exchanger loss, which becomes a heat load on the cryogenic refrigerator 103 and reduces its effective cooling capacity.

[0010] On the other hand, the cryogenic cooling system 110 (Figure 6(B)) using the cryogenic fan 112 appears to be problem-free at first glance because there are no heat exchanger losses. However, looking at the characteristics of the cryogenic fan 112, there is a problem in that the pressure difference between the inlet and outlet of the cryogenic fan 112 cannot be set to a large size. The gas flow rate is determined by the condition that the pressure loss in the cooling pipe 111 is equal to the pressure difference between the inlet and outlet of the cryogenic fan 112, so there is an upper limit to the gas flow rate that can be flowed. Of course, it is possible to increase the flow rate by increasing the rotation speed of the cryogenic fan 112 or by making the cryogenic fan 112 larger, but in that case the heat load on the cryogenic refrigerator 103 increases due to the amount of heat ingress from the cryogenic fan 112 and the heat generated during gas pumping, and the effective cooling capacity is reduced.

[0011] As described above, when comparing cryogenic cooling systems 100 and 110, cryogenic cooling system 110, which has no heat exchanger losses, is considered to be of higher performance. However, in cryogenic cooling system 110, there is an upper limit to the gas flow rate due to the small pressure difference between the inlet and outlet of the cryogenic fan 112, and in cryogenic cooling system 100, there is a problem in that the temperature difference between the cryogenic refrigerator 103 and the superconducting coil 105 is limited due to the increase in heat exchanger losses as the gas flow rate increases.

[0012] Embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a cryogenic cooling system, a superconducting device, and a method for operating a cryogenic cooling system that can reduce the temperature difference between the cooling source and the object to be cooled and improve the cooling capacity of the cooling source. [Means for solving the problem]

[0013] The cryogenic cooling system in an embodiment of the present invention comprises a vacuum vessel housing a cooling section of a cooling source, an object to be cooled, and a fan; a first circulation system, the main components excluding the compressor, arranged within the vacuum vessel, which circulates the gas compressed by the compressor to be cooled in the cooling section of the cooling source in order to cool the object to be cooled; and a second circulation system, arranged within the vacuum vessel, which circulates the gas pressurized by the fan to be cooled in the cooling section of the cooling source in order to cool the object to be cooled, wherein the first circulation system and the second circulation system merge upstream of the object to be cooled and branch off and connect downstream of the object to be cooled. The first circulation system is operated in a pre-cooling mode to cool the object to be cooled from room temperature to a predetermined temperature, or in an excitation / demagnetization mode to change the magnetic field of the superconducting coil as the object to be cooled, and the second circulation system is operated in a steady-state cooling mode to maintain the temperature of the object to be cooled to a predetermined temperature, or in a steady-state mode to maintain a constant magnetic field of the superconducting coil. It is characterized by its structure.

[0014] The superconducting device in the embodiment of the present invention is characterized by having a cryogenic cooling system as described in the above embodiment, wherein the object to be cooled is a superconducting coil.

[0015] The method for operating the cryogenic cooling system in an embodiment of the present invention includes: a vacuum vessel housing a cooling unit of a cooling source, an object to be cooled, and a fan; a first circulation system in which the main parts excluding the compressor are arranged inside the vacuum vessel and the gas compressed by the compressor is cooled in the cooling unit of the cooling source and circulated to cool the object to be cooled; and a second circulation system arranged inside the vacuum vessel and the gas pumped by the fan is cooled in the cooling unit of the cooling source and circulated to cool the object to be cooled; and the first circulation system and the second circulation system are switched selectively according to the operating mode of the object to be cooled. In a pre-cooling mode to cool the object to be cooled from room temperature to a predetermined temperature, or in an excitation / demagnetization mode to change the magnetic field of the superconducting coil as the object to be cooled, the first circulation system is operated. In a steady-state cooling mode to maintain the temperature of the object to be cooled after it has been cooled to a predetermined temperature, or in a steady-state mode to maintain a constant magnetic field of the superconducting coil, the second circulation system is operated. It is characterized by the following: [Effects of the Invention]

[0016] According to embodiments of the present invention, the cooling capacity of the cooling source can be improved by reducing the temperature difference between the cooling source and the object to be cooled. [Brief explanation of the drawing]

[0017] [Figure 1] A piping diagram showing a cryogenic cooling system according to the first embodiment. [Figure 2] A piping diagram showing a cryogenic cooling system according to the second embodiment. [Figure 3] A piping diagram showing a cryogenic cooling system according to the third embodiment. [Figure 4] A piping diagram showing a cryogenic cooling system according to the fourth embodiment. [Figure 5] A piping diagram showing a cryogenic cooling system according to the fifth embodiment. [Figure 6] A piping diagram showing a conventional cryogenic cooling system, where (A) shows an example and (B) shows another example.

Mode for Carrying Out the Invention

[0018] Hereinafter, modes for carrying out the present invention will be described based on the drawings. [A] First Embodiment (Fig. 1) Fig. 1 is a piping diagram showing a cryogenic cooling system according to the first embodiment. The cryogenic cooling system 10 shown in Fig. 1 uses a superconducting coil 1 that constitutes a superconducting device such as an MRI (Magnetic Resonance Imaging apparatus) as an object to be cooled, and cools this superconducting coil 1 to a cryogenic temperature (for example, about 4K) by a gas circulation cooling method. It includes a first circulation system 11 including a cryogenic refrigerator 13 as a cooling source, a second circulation system 12 including the cryogenic refrigerator 13, and a vacuum vessel 14.

[0019] The cryogenic refrigerator 13 is, for example, a GM (Gifford-McMahon) refrigerator and has a single-stage cooling stage 15 and two-stage cooling stages 16A and 16B as cooling units. This cryogenic refrigerator 13 is installed in a vacuum vessel 14, and the single-stage cooling stage 15 and the two-stage cooling stages 16A and 16B are housed inside the vacuum vessel 14. The cryogenic refrigerator 13 is not limited to a GM refrigerator, but may also be a pulse tube refrigerator or a Stirling refrigerator. Furthermore, the two-stage cooling stages 16A and 16B of the cryogenic refrigerator 13 may be arranged in series with the second-stage cooling stage 16A positioned on the side of the first-stage cooling stage 15, or with the second-stage cooling stage 16B positioned on the side of the first-stage cooling stage 15, or both of the two-stage cooling stages 16A and 16B may be arranged in parallel. Moreover, the two-stage cooling stages 16A and 16B may be integrated.

[0020] The first circulation system 11 comprises a compressor 17, cooling piping 18, a cryogenic refrigerator 13, a first heat exchanger 19, a second heat exchanger 20, and a room temperature valve 21 as the first valve.

[0021] The cooling pipe 18 is formed in a loop shape, and the compressor 17, room temperature valve 21, first heat exchanger 19, first stage cooling stage 15 of the cryogenic refrigerator 13, second heat exchanger 20, second stage cooling stage 16A of the cryogenic refrigerator 13, superconducting coil 1, second heat exchanger 20, first heat exchanger 19, and compressor 17 are sequentially arranged in this cooling pipe 18. Of these, the compressor 17 and room temperature valve 21 are located outside the vacuum vessel 14, while the other main parts of the first circulation system 11, namely the first stage cooling stage 15 and second stage cooling stage 16A of the cryogenic refrigerator 13, the first heat exchanger 19, and the second heat exchanger 20, are located inside the vacuum vessel 14 together with the superconducting coil 1.

[0022] The compressor 17 compresses and discharges a refrigerant gas such as helium gas, and circulates it within the cooling pipe 18. The gas discharged from the compressor 17 is sequentially supplied to the first heat exchanger 19, the first cooling stage 15 of the cryogenic refrigerator 13, the second heat exchanger 20, and the second cooling stage 16A of the cryogenic refrigerator 13, where it is cooled in stages. After being guided to the superconducting coil 1 to cool the superconducting coil 1, the gas is returned to the compressor 17 via the second heat exchanger 20 and the first heat exchanger 19 in sequence, and circulated back into the system.

[0023] The first heat exchanger 19 and the second heat exchanger 20 each cool the gas before it flows into the first-stage cooling stage 15 and the second-stage cooling stage 16A of the cryogenic refrigerator 13, respectively, by heat exchange using the gas after it has cooled the superconducting coil 1. In other words, the second heat exchanger 20 cools the gas before it flows out of the first-stage cooling stage 15 of the cryogenic refrigerator 13 and into the second-stage cooling stage 16A by heat exchange using the gas after it has cooled the superconducting coil 1. The first heat exchanger 19 cools the gas discharged from the compressor 17 before it flows into the first-stage cooling stage 15 of the cryogenic refrigerator 13 by heat exchange using the gas after it has cooled the superconducting coil 1 and has undergone further heat exchange by the second heat exchanger 20.

[0024] The room temperature valve 21 is located downstream of the compressor 17 and upstream of the first heat exchanger 19, in the cooling pipe 18 outside the vacuum vessel 14 in the room temperature range, and adjusts the flow rate of gas flowing through the cooling pipe 18. Furthermore, when the cryogenic cooling system 10 is in operation, this room temperature valve 21 opens and closes in conjunction with the cryogenic valve 24 in the second circulation system 12 (described later), and only one of the valves opens at a time.

[0025] The second circulation system 12 comprises a cryogenic fan 22, cooling piping 23, a cryogenic refrigerator 13, and a cryogenic valve 24 as a second valve. The cooling piping 23 is formed in a loop shape, and the cryogenic fan 22, cryogenic valve 24, the two-stage cooling stage 16B of the cryogenic refrigerator 13, the superconducting coil 1, and the cryogenic fan 22 are sequentially arranged in this cooling piping 23. The cryogenic fan 22, cooling piping 23, the two-stage cooling stage 16B of the cryogenic refrigerator 13, and the cryogenic valve 24 that constitute this second circulation system 12 are arranged together with the superconducting coil 1 inside the vacuum vessel 14.

[0026] The low-temperature fan 22 pumps a refrigerant gas, such as helium, under pressure and circulates it within the cooling pipe 23. The gas pumped from the low-temperature fan 22 passes through the low-temperature valve 24 and is supplied to the second-stage cooling stage 16B of the cryogenic refrigerator 13, where it is cooled. It is then guided to the superconducting coil 1, which is cooled to an extremely low temperature (approximately 4K), before being returned to the low-temperature fan 22 and circulated.

[0027] The cryogenic valve 24 is located downstream of the cryogenic fan 22 and upstream of the two-stage cooling stage 16B of the cryogenic chiller 13 in the cooling pipe 23, and is, for example, an on-off valve that controls the flow of gas through this cooling pipe 23. Alternatively, the cryogenic valve 24 may also be a check valve that prevents gas flowing through the first circulation system 11 from unnecessarily flowing into the second circulation system 12 when the second circulation system 12 is not in operation and the first circulation system 11 is in operation.

[0028] In the first circulation system 11 and the second circulation system 12 configured as described above, the cooling pipe 18 of the first circulation system 11 and the cooling pipe 23 of the second circulation system 12 merge at the upstream confluence point M of the superconducting coil 1, and then branch off and connect at the downstream branching point N of the superconducting coil 1. Note that the cooling pipes 18 and 23 may be connected independently to the superconducting coil 1.

[0029] Incidentally, in the cryogenic cooling system 10, the first circulation system 11 and the second circulation system 12 are switched selectively depending on the operating mode of the superconducting coil 1, for example, a pre-cooling mode in which the superconducting coil 1 is cooled from room temperature to a predetermined cryogenic temperature (for example, around 4K), and a steady-state cooling mode in which the temperature of the superconducting coil 1 cooled to the predetermined cryogenic temperature is maintained.

[0030] In other words, in the pre-cooling mode of the superconducting coil 1, the room temperature valve 21 of the first circulation system 11 is opened and the low-temperature valve 24 of the second circulation system 12 is closed, so that only the first circulation system 11 is operated. Also, in the steady-state cooling mode of the superconducting coil 1, the room temperature valve 21 of the first circulation system 11 is closed and the low-temperature valve 24 of the second circulation system 12 is opened, so that only the second circulation system 12 is operated.

[0031] In the pre-cooling mode of the superconducting coil 1, the temperature of the superconducting coil 1 is close to room temperature. If the second circulation system 12 is operated, the temperature of the gas flowing through the second circulation system 12 is high, resulting in a large pressure loss in the cooling pipe 23 and a reduced gas flow rate in the second circulation system 12. In contrast, in the first circulation system 11, the temperature of the superconducting coil 1 is close to room temperature in the pre-cooling mode, so the heat exchanger losses of the first heat exchanger 19 and the second heat exchanger 20 are reduced. Therefore, it becomes possible to increase the gas flow rate through the cooling pipe 18, and thus, operation of the first circulation system 11 is selected in the pre-cooling mode.

[0032] In the steady-state cooling mode of the superconducting coil 1, the temperature difference between the superconducting coil 1 and the room temperature becomes large. Therefore, if the first circulation system 11 is operated, the heat exchanger losses of the first heat exchanger 19 and the second heat exchanger 20 increase, making it impossible to increase the gas flow rate in the first circulation system 11. In contrast, in the second circulation system 12, the superconducting coil 1 is in an extremely low temperature state in the steady-state cooling mode, and the temperature of the gas flowing through the cooling pipe 23 is low, resulting in small pressure losses in the cooling pipe 23. For this reason, it becomes possible to increase the gas flow rate in the second circulation system 12, and since there are no heat exchanger losses, operation of the second circulation system 12 is selected in the steady-state cooling mode.

[0033] As configured as described above, this first embodiment provides the following effect (1). (1) The first circulation system 11 and the second circulation system 12 are used selectively depending on whether the superconducting coil 1 is in pre-cooling mode or steady-state cooling mode. The first circulation system 11 is operated in pre-cooling mode, and the second circulation system 12 is operated in steady-state cooling mode. This maximizes the gas flow rate through each circulation system (first circulation system 11, second circulation system 12) in each operating mode (pre-cooling mode, steady-state cooling mode, etc.) of the superconducting coil 1, thereby reducing the temperature difference between the cryogenic refrigerator 13 and the superconducting coil 1. This improves the cooling capacity of the cryogenic refrigerator 13 and enhances the cooling performance of the superconducting coil 1.

[0034] [B] Second embodiment (Figure 2) Figure 2 is a piping diagram showing a cryogenic cooling system according to the second embodiment. In this second embodiment, parts that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their descriptions are simplified or omitted.

[0035] The difference between the cryogenic cooling system 25 of this second embodiment and the first embodiment is that the first circulation system 26 is configured to guide the gas flowing out from the first cooling stage 15 of the cryogenic refrigerator 13 to the second cooling stage 16A of the cryogenic refrigerator 13, bypassing the second heat exchanger 20, and also includes a bypass line 27 equipped with a bypass valve 28.

[0036] Generally, the temperatures of the two-stage cooling stages 16A and 16B of the cryogenic refrigerator 13 are lower than the temperature of the single-stage cooling stage 15. Therefore, in the steady-state cooling mode of the superconducting coil 1, the superconducting coil 1 is cooled by the cooling capacity of the two-stage cooling stage 16B of the cryogenic refrigerator 13 when the second circulation system 12 is in operation. In contrast, in the pre-cooling mode of the superconducting coil 1, the temperature of the superconducting coil 1 is close to room temperature, so the single-stage cooling stage 15 of the cryogenic refrigerator 13 is sufficient, and moreover, the cooling capacity of the single-stage cooling stage 15 is several times higher than that of the two-stage cooling stages 16A and 16B. Accordingly, in the pre-cooling mode of the superconducting coil 1, the first circulation system 11 is in operation, and the superconducting coil 1 is cooled by the single-stage cooling stage 15 and the second-stage cooling stage 16A of the cryogenic refrigerator 13.

[0037] In particular, during the initial stages of the pre-cooling mode, the superconducting coil 1 is at room temperature, so the temperature of the gas flowing from this superconducting coil 1 into the second heat exchanger 20 becomes high, causing the bypass valve 28 to open. As a result, the gas flowing out from the first-stage cooling stage 15 of the cryogenic refrigerator 13 flows through the bypass line 27, bypassing the second heat exchanger 20, and flows directly into the second-stage cooling stage 16A of the cryogenic refrigerator 13. Therefore, the temperature rise of the gas flowing into the second-stage cooling stage 16A due to heat exchange in the second heat exchanger 20 is prevented.

[0038] As configured as described above, this second embodiment also provides the same effects as the first embodiment (1), as well as the following effect (2).

[0039] (2) In the cooling mode of the superconducting coil 1 operating the first circulation system 11, the temperature of the superconducting coil 1 is at room temperature in the initial stages, so the bypass valve 28 is opened, and the gas flowing out from the first stage cooling stage 15 of the cryogenic refrigerator 13 bypasses the second heat exchanger 20 and flows directly into the second stage cooling stage 16A of the cryogenic refrigerator 13 via the bypass line 27. As a result, the gas flowing into the second stage cooling stage 16A is cooled efficiently without the temperature rise caused by the second heat exchanger 20, and as a result, the superconducting coil 1 can be effectively cooled by the gas flowing in the first circulation system 11.

[0040] [C] Third embodiment (Figure 3) Figure 3 is a piping diagram showing a cryogenic cooling system according to the third embodiment. In this third embodiment, parts that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their explanation is simplified or omitted.

[0041] The difference between the cryogenic cooling system 30 of this third embodiment and the first embodiment is that the first circulation system 31 further comprises a JT cooling system 34, which includes a third heat exchanger 33 and a JT valve (JT: Joule-Thomson) 32 that expands and liquefies the gas. As a result, the first circulation system 31 has the same configuration as the GM / JT refrigerator. The aforementioned third heat exchanger 33 and JT valve 32 are sequentially installed from upstream to downstream in the cooling piping 18, which is downstream of the two-stage cooling stage 16A of the cryogenic refrigerator 13 and upstream of the confluence point M.

[0042] Here, we compare the GM / JT refrigerator as the first circulation system 31 with the GM refrigerator of the cryogenic refrigerator 13. The GM / JT refrigerator expands and liquefies the gas using the JT valve 32, increasing its cooling capacity to more than three times that of the GM refrigerator (cryogenic refrigerator 13). Furthermore, the power required for the compressor 17 of the JT cooling system 34 in the GM / JT refrigerator is significantly greater than that required for the low-temperature fan 22 of the second circulation system 12, which includes the GM refrigerator (cryogenic refrigerator 13). In other words, the first circulation system 31 as the GM / JT refrigerator has high cooling capacity and power requirements, while the second circulation system 12, which includes the GM refrigerator (cryogenic refrigerator 13), has low cooling capacity and power requirements.

[0043] On the other hand, let's consider the operating modes of the superconducting coil 1. In addition to the pre-cooling mode and steady-state cooling mode mentioned above, the operating modes of the superconducting coil 1 include an excitation / demagnetization mode in which the magnetic field is changed, and a steady-state mode in which the magnetic field is kept constant. In the excitation / demagnetization mode, a large amount of heat is generated in the superconducting coil 1 compared to the steady-state mode.

[0044] Therefore, in excitation-demagnetization mode or pre-cooling mode, the cryogenic cooling system 30 closes the cryogenic valve 24 and opens the room temperature valve 21 and JT valve 32 to operate the first circulation system 31 (GM / JT chiller), which has a large cooling capacity, and cools the superconducting coil 1. In addition, in steady-state mode or steady-state cooling mode, the cryogenic cooling system 30 closes the room temperature valve 21 and JT valve 32 and opens the cryogenic valve 24 to operate the second circulation system 12, which requires less power (i.e., consumes less power), and cools the superconducting coil 1.

[0045] As configured as described above, this third embodiment also provides the same effects as the first embodiment (1), as well as the following effect (3).

[0046] (3) In the cryogenic cooling system 30, the first circulation system (GM / JT chiller) with a large cooling capacity is operated in the excitation / demagnetization mode or pre-cooling mode, and the second circulation system 12 with a small power requirement is operated in the steady-state mode or steady-state cooling mode. As a result, the cryogenic cooling system 30 can reduce the overall power requirement (i.e., power consumption) while ensuring the necessary cooling capacity in each operating mode of the superconducting coil 1.

[0047] [D] Fourth embodiment (Figure 4) Figure 4 is a piping diagram showing the cryogenic cooling system according to the fourth embodiment. In this fourth embodiment, parts that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their description is simplified or omitted.

[0048] The difference between the cryogenic cooling system 40 of this fourth embodiment and the first embodiment is that the cryogenic refrigerator 13 has a single two-stage cooling stage 16, and the cooling pipes 18 of the first circulation system 11 and the cooling pipes 23 of the second circulation system 12 merge at the upstream confluence point M of the two-stage cooling stage 16 located upstream of the superconducting coil 1, and then branch off and connect at the downstream branching point N of the superconducting coil 1.

[0049] As described above, this fourth embodiment provides the same effect as the first embodiment (1), as well as the following effect (4).

[0050] (4) Since the cooling pipe 18 of the first circulation system 11 and the cooling pipe 23 of the second circulation system 12 are joined and connected at the confluence point M upstream of the two-stage cooling stage 16 of the cryogenic refrigerator 13, the two-stage cooling stage 16 of the cryogenic refrigerator 13 can be made common, and the cryogenic refrigerator 13 can be configured with a compact structure.

[0051] [E] Fifth embodiment (Figure 5) Figure 5 is a piping diagram showing the cryogenic cooling system according to the fifth embodiment. In this fifth embodiment, parts that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their explanation is simplified or omitted.

[0052] The difference between the cryogenic cooling system 50 of this fifth embodiment and the first embodiment is that there are multiple cooling sources (for example, cryogenic refrigerator 13 and cryogenic refrigerator 53), and at least one of these cooling sources, for example, cryogenic refrigerator 53, is configured as a component of only the first circulation system 51.

[0053] In other words, the second-stage cooling stage 52 of the cryogenic refrigerator 53 is located between the downstream side of the second-stage cooling stage 16A of the cryogenic refrigerator 13 and the confluence point M in the cooling piping 18 of the first circulation system 51, further cooling the gas cooled by the second-stage cooling stage 16A and guiding it to the superconducting coil 1, which in turn cools the superconducting coil 1. Alternatively, instead of the cryogenic refrigerator 53, a storage tank for liquid helium, for example, may be installed in the cooling piping 18.

[0054] As configured as described above, this fifth embodiment also provides the same effects as the first embodiment (1), as well as the following effect (5).

[0055] (5) In addition to the cryogenic refrigerator 13 which is a component of the first circulation system 51 and the second circulation system 12, the cryogenic refrigerator 53 which is a component of only the first circulation system 51 is also included.Therefore, in the cryogenic cooling system 50, the cooling capacity is improved by, for example, the two cryogenic refrigerators 13 and 53 in the pre-cooling mode or excitation-demagnetization mode of the superconducting coil 1, and the superconducting coil 1 can be cooled rapidly.

[0056] 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 carried out in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention, and such substitutions, modifications, and combinations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0057] 1…Superconducting coil (object to be cooled), 10…Cryogenic cooling system, 11…First circulation system, 12…Second circulation system, 13…Cryogenic refrigerator (cooling source), 14…Vacuum vessel, 15…Single-stage cooling stage, 16, 16A, 16B…Two-stage cooling stage, 17…Compressor, 19…First heat exchanger, 20…Second heat exchanger, 21…Room temperature valve (first valve), 22…Cryogenic fan (fan), 24…Cryogenic valve (second valve), 25…Cryogenic cooling system, 26…First circulation system, 27…Bypass line, 28…Bypass valve, 30…Cryogenic cooling system, 31…First circulation system, 32…JT valve, 34…JT cooling system, 40…Cryogenic cooling system, 50…Cryogenic cooling system, 51…First circulation system, 53…Cryogenic refrigerator (cooling source), M…Confluence point, N…Branch point

Claims

1. A vacuum container housing the cooling section of the cooling source, the object to be cooled, and the fan, The main components, excluding the compressor, are arranged within the vacuum vessel, and a first circulation system circulates the gas compressed by the compressor to cool the object to be cooled by cooling it in the cooling section of the cooling source, It has a second circulation system, which is arranged inside the vacuum container and circulates the gas pumped by the fan to cool the object to be cooled by cooling it in the cooling section of the cooling source, The first circulation system and the second circulation system merge upstream of the object to be cooled and branch off and connect downstream of the object to be cooled. In the pre-cooling mode, which cools the object to be cooled from room temperature to a predetermined temperature, or in the excitation / demagnetization mode, which changes the magnetic field of the superconducting coil as the object to be cooled, the first circulation system is operated. A cryogenic cooling system characterized in that the second circulation system is operated in a steady-state cooling mode that maintains the temperature of the object to be cooled to a predetermined temperature, or in a steady-state mode that maintains a constant magnetic field of the superconducting coil.

2. The cryogenic cooling system according to claim 1, characterized in that the first circulation system comprises a compressor located outside the vacuum vessel, a cryogenic refrigerator as a cooling source equipped with a cooling stage as a cooling unit, a heat exchanger that cools the gas before it flows into the cooling stage by heat exchange with the gas that has cooled the object to be cooled, and a first valve located outside the vacuum vessel and provided downstream of the compressor for adjusting the gas flow rate.

3. The cryogenic cooling system according to claim 1 or 2, characterized in that the second circulation system comprises a fan, a cryogenic refrigerator as a cooling source equipped with a cooling stage as a cooling unit, and a second valve disposed together with the fan in a vacuum vessel and provided downstream of the fan to control the flow of gas.

4. The cryogenic cooling system according to claim 3, characterized in that the second valve is a check valve that prevents gas flowing through the first circulation system from flowing into the second circulation system when the second circulation system is not in operation and the first circulation system is in operation.

5. The cryogenic refrigerator comprises a first-stage cooling stage and a second-stage cooling stage, and the heat exchanger comprises a first heat exchanger that cools the gas by exchanging heat before it flows into the first-stage cooling stage, and a second heat exchanger that cools the gas that flows out of the first-stage cooling stage before it flows into the second-stage cooling stage. The cryogenic cooling system according to claim 2, characterized in that the first circulation system guides the gas flowing out of the first-stage cooling stage to the second-stage cooling stage by bypassing the second heat exchanger and further includes a bypass line equipped with a bypass valve.

6. The cryogenic cooling system according to claim 2, characterized in that the first circulation system further comprises a JT cooling system equipped with a JT valve for expanding and liquefying gas.

7. The cryogenic cooling system according to claim 1, characterized in that the first circulation system and the second circulation system are connected by merging on the upstream side of the cooling section of a cooling source located upstream of the object to be cooled, and by branching off on the downstream side of the object to be cooled.

8. The cryogenic cooling system according to claim 1, characterized in that there are multiple cooling sources, and at least one of the cooling sources is configured as a component of only the first circulation system.

9. A superconducting device characterized by having a cryogenic cooling system according to claim 1, wherein the object to be cooled is a superconducting coil.

10. A vacuum container housing the cooling section of the cooling source, the object to be cooled, and the fan, The main components, excluding the compressor, are arranged within the vacuum vessel, and a first circulation system circulates the gas compressed by the compressor to cool the object to be cooled by cooling it in the cooling section of the cooling source, A second circulation system is prepared, which is placed inside the vacuum container and circulates the gas pumped by the fan to cool the object to be cooled by cooling it in the cooling section of the cooling source. The first circulation system and the second circulation system are operated by selectively switching between them according to the operating mode of the object to be cooled. In the pre-cooling mode, which cools the object to be cooled from room temperature to a predetermined temperature, or in the excitation / demagnetization mode, which changes the magnetic field of the superconducting coil as the object to be cooled, the first circulation system is operated. A method for operating a cryogenic cooling system, characterized in that the second circulation system is operated in a steady-state cooling mode that maintains the temperature of the object to be cooled to a predetermined temperature, or in a steady-state mode that maintains a constant magnetic field of the superconducting coil.

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