阅读说明：本技术 超低温冷却系统 (Ultra-low temperature cooling system ) 是由 江原悠太 森江孝明 吉田润 于 2018-11-09 设计创作，主要内容包括：超低温冷却系统(10)具备：气体循环源(12)；超低温制冷机(22),冷却冷却气体；冷却气体流路(14),使冷却气体从气体循环源(12)流向被冷却物(11)；及控制装置(40),控制气体循环源(12)以按照规定的流量模式执行被冷却物(11)的从室温冷却至目标冷却温度的初始冷却。规定的流量模式预先设定成使冷却气体从初始冷却开始至过渡时刻为止以第1平均流量流过冷却气体流路(14),使冷却气体从过渡时刻至初始冷却完成为止以第2平均流量流过冷却气体流路(14)。第2平均流量设为小于第1平均流量,使得超低温冷却系统(10)的冷却能力相比从过渡时刻至初始冷却完成为止维持第1平均流量的情况增加。(The cryogenic cooling system (10) is provided with: a gas circulation source (12); a cryogenic refrigerator (22) that cools the cooling gas; a cooling gas flow path (14) for allowing cooling gas to flow from the gas circulation source (12) to the object (11) to be cooled; and a control device (40) for controlling the gas circulation source (12) to perform initial cooling of the object (11) to be cooled from room temperature to a target cooling temperature in a predetermined flow rate pattern. The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path (14) at a 1 st average flow rate from the start of initial cooling to the time of transition, and the cooling gas flows through the cooling gas flow path (14) at a 2 nd average flow rate from the time of transition to the time of completion of initial cooling. The 2 nd average flow rate is set to be smaller than the 1 st average flow rate so that the cooling capacity of the ultra-low-temperature cooling system (10) is increased as compared with a case where the 1 st average flow rate is maintained from the transition time to the completion of the initial cooling.)

1. An ultra-low-temperature cooling system is characterized by comprising:

a gas circulation source for circulating cooling gas;

a cryogenic refrigerator having a refrigerator cooling stage that cools the cooling gas;

a cooling gas flow path for flowing the cooling gas from the gas circulation source to the gas circulation source via the refrigerator cooling stage and the object to be cooled; and

a control device that controls the gas circulation source to perform initial cooling of the object to be cooled from room temperature to a target cooling temperature in a prescribed flow rate pattern,

the predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path at a 1 st average flow rate from the start of the initial cooling to a transition point, and the cooling gas flows through the cooling gas flow path at a 2 nd average flow rate from the transition point to the completion of the initial cooling,

the 2 nd average flow rate is set to be smaller than the 1 st average flow rate so that the cooling capacity of the ultra-low-temperature cooling system is increased as compared with a case where the 1 st average flow rate is maintained from the transition time to the completion of the initial cooling.

2. The ultra-low temperature cooling system of claim 1,

the control device starts the initial cooling in synchronization with the start-up of the gas circulation source or the start-up of the gas circulation source and the cryogenic refrigerator.

3. The ultra-low-temperature cooling system according to claim 1 or 2,

the predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path at an upper limit cooling gas flow rate of the ultra-low-temperature cooling system for at least a period of time during which the initial cooling is started until the transition time.

4. The ultra-low-temperature cooling system as set forth in any one of claims 1 to 3,

the predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path at a cooling gas flow rate that maximizes the cooling capacity of the ultra-low-temperature cooling system at the target cooling temperature for at least a period of time during the period from the transition time to completion of the initial cooling.

5. The ultra-low-temperature cooling system according to any one of claims 1 to 4,

the transition time is preset after the 1 st reference time and before the 2 nd reference time,

the 1 st reference time is expressed as a ratio of an amount of heat that should be removed from the object to be cooled by the initial cooling to a cooling capacity of the ultra-low-temperature cooling system at a 1 st representative temperature, the 2 nd reference time is expressed as a ratio of an amount of heat that should be removed from the object to be cooled by the initial cooling to a cooling capacity of the ultra-low-temperature cooling system at a 2 nd representative temperature,

the 1 st representative temperature and the 2 nd representative temperature are selected from a temperature range from the room temperature to the target cooling temperature, and the 2 nd representative temperature is lower than the 1 st representative temperature.

6. The ultra-low-temperature cooling system according to any one of claims 1 to 5,

the control device is provided with:

an initial cooling setting that sets in advance a target cooling gas flow rate at each time point from the start to the completion of the initial cooling according to the predetermined flow rate pattern; and

a gas flow rate control unit that determines the target cooling gas flow rate from the initial cooling setting and an elapsed time from the start of the initial cooling, and controls the gas circulation source so that the cooling gas flows through the cooling gas flow path at the target cooling gas flow rate.

Technical Field

The invention relates to an ultra-low temperature cooling system.

Background

Conventionally, there has been known a circulation cooling system for cooling an object to be cooled, such as a superconducting electromagnet, by using a gas cooled to an extremely low temperature. For cooling the cooling gas, a cryogenic refrigerator such as a GM (Gifford-McMahon ) refrigerator is generally used.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 1-14559

Disclosure of Invention

Technical problem to be solved by the invention

In the ultra-low-temperature cooling system, initial cooling for cooling the object to be cooled from room temperature to a target cooling temperature is performed at the time of starting the system. The cooled object is available after the initial cooling is completed. Therefore, it is desirable to shorten the time required for initial cooling as much as possible.

One of exemplary objects of an embodiment of the present invention is to shorten an initial cooling time of an ultra-low-temperature cooling system.

Means for solving the technical problem

According to one embodiment of the present invention, an ultra-low-temperature cooling system includes: a gas circulation source for circulating cooling gas; a cryogenic refrigerator having a refrigerator cooling stage that cools the cooling gas; a cooling gas flow path for flowing the cooling gas from the gas circulation source to the gas circulation source via the refrigerator cooling stage and the object to be cooled; and a control device for controlling the gas circulation source to perform initial cooling of the object to be cooled from room temperature to a target cooling temperature in a predetermined flow rate pattern. The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path at a 1 st average flow rate from the start of the initial cooling to a transition point, and the cooling gas flows through the cooling gas flow path at a 2 nd average flow rate from the transition point to the completion of the initial cooling. The 2 nd average flow rate is set to be smaller than the 1 st average flow rate so that the cooling capacity of the ultra-low-temperature cooling system is increased as compared with a case where the 1 st average flow rate is maintained from the transition time to the completion of the initial cooling.

In addition, any combination of the above-described constituent elements or substitution of the constituent elements and the embodiments described above for each other among methods, apparatuses, systems and the like is also effective as an embodiment of the present invention.

Effects of the invention

According to the present invention, a practical ultralow temperature cooling system can be provided.

Drawings

Fig. 1 is a diagram schematically showing an ultra-low-temperature cooling system according to an embodiment.

Fig. 2 (a) and (b) are diagrams illustrating flow rate patterns of the cooling gas that can be used for initial cooling according to the comparative example.

Fig. 3 (a) to (d) are diagrams illustrating flow rate patterns of the cooling gas that can be used for the initial cooling according to the embodiment.

Fig. 4 (a) and (b) are graphs showing cooling capacity curves of the ultra-low-temperature cooling system 10 at a plurality of cooling temperatures.

Fig. 5 is a flowchart illustrating a method of controlling initial cooling of the ultra-low-temperature cooling system according to the embodiment.

Fig. 6 (a) shows a temperature change in initial cooling of the ultra-low-temperature cooling system, and fig. 6 (b) shows a flow rate pattern used for the initial cooling.

Fig. 7 is a diagram schematically showing another example of the ultra-low-temperature cooling system according to the embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description and the drawings, the same or equivalent constituent elements, components, and processes are denoted by the same reference numerals, and overlapping description is appropriately omitted. For convenience of explanation, the scale and shape of each part are appropriately set in each drawing, and are not to be construed as limiting unless otherwise specified. The embodiments are examples and do not limit the scope of the invention in any way. All the features or combinations thereof described in the embodiments are not necessarily essential contents of the invention.

Fig. 1 is a diagram schematically showing an ultra-low-temperature cooling system 10 according to an embodiment. The cryogenic cooling system 10 is a circulating cooling system configured to cool the object 11 to be cooled to a target temperature by circulating a cooling gas. Helium is generally used as the cooling gas, for example, but other suitable gases corresponding to the cooling temperature may be used.

The object to be cooled 11 is, for example, a superconducting electromagnet. The superconducting electromagnet is mounted on, for example, a particle accelerator or other superconducting device used in a particle beam therapy device or other devices. In addition, the object to be cooled 11 is not limited to a superconducting electromagnet, as a matter of course. The object to be cooled 11 may be other devices or fluids requiring ultra-low temperature cooling.

The target cooling temperature is a desired ultra-low temperature selected from a temperature range from a predetermined lower limit temperature to a predetermined upper limit temperature. The lower limit temperature is, for example, the lowest temperature that can be cooled by the ultra-low-temperature cooling system 10, and may be, for example, 4K. The upper limit temperature is, for example, a desired ultralow temperature selected from a temperature range below the superconducting critical temperature. The superconducting critical temperature depends on the superconducting material used, but is, for example, ultralow temperature of not higher than liquid nitrogen temperature, not higher than 30K, not higher than 20K, or not higher than 10K. Thus, the target cooling temperature is selected from a temperature range of e.g. 4K to 30K or a temperature range of e.g. 10K to 20K.

The cryogenic cooling system 10 includes a gas circulation source 12 for circulating cooling gas and a cooling gas flow path 14 for flowing the cooling gas to cool the object 11 to be cooled. The gas circulation source 12 is configured to control the flow rate of the supplied cooling gas in accordance with the gas circulation source control signal S1. For example, the gas circulation source 12 includes a compressor that pressurizes and conveys the recovered cooling gas. The cooling gas channel 14 includes a gas supply line 16, a cooled object gas channel 18, and a gas recovery line 20. The circulation circuit of the cooling gas is constituted by the gas circulation source 12 and the cooling gas flow path 14. In fig. 1, several arrows drawn along the cooling gas flow path 14 indicate the flow direction of the cooling gas.

The gas circulation source 12 is connected to the gas recovery line 20 to recover the cooling gas from the gas recovery line 20, and the gas circulation source 12 is connected to the gas supply line 16 to supply the gas supply line 16 with the pressurized cooling gas. The gas supply line 16 is connected to the object gas flow path 18 to supply the cooling gas to the object gas flow path 18, and the gas recovery line 20 is connected to the object gas flow path 18 to recover the cooling gas from the object gas flow path 18.

The gas supply line 16, the object gas flow path 18, and/or the gas recovery line 20 may be flexible pipes or rigid pipes.

The cryogenic cooling system 10 includes a cryogenic refrigerator 22 that cools the cooling gas of the cryogenic cooling system 10. The cryogenic refrigerator 22 includes a compressor 24 and a cold head 26 having a refrigerator cooling stage 28.

The compressor 24 of the cryogenic refrigerator 22 is configured to recover the working gas of the cryogenic refrigerator 22 from the cold head 26, pressurize the recovered working gas, and supply the working gas to the cold head 26 again. The circulation circuit of the working gas (i.e., the refrigeration cycle of the cryogenic refrigerator 22) is constituted by the compressor 24 and the cold head 26, thereby cooling the refrigerator cold stage 28. The working gas is typically helium, but other suitable gases may be used. For example, the cryogenic refrigerator 22 is a Gifford-mcmahon (GM) refrigerator, but may be a pulse tube refrigerator, a stirling refrigerator, or another cryogenic refrigerator.

The compressor 24 of the cryogenic refrigerator 22 is provided separately from the gas circulation source 12. The working gas circulation circuit of the cryogenic refrigerator 22 and the cooling gas circulation circuit of the cryogenic cooling system 10 are fluidly isolated from each other.

The object gas flow path 18 is provided around or inside the object 11 to allow the cooling gas to flow therethrough. The object gas flow path 18 includes an inlet 18a, an outlet 18b, and a gas pipe 18c extending from the inlet 18a to the outlet 18 b. The gas supply line 16 is connected to an inlet 18a of the object gas flow path 18, and the gas recovery line 20 is connected to an outlet 18b of the object gas flow path 18. Therefore, the cooling gas flows from the gas supply line 16 into the gas pipe 18c through the inlet 18a, and flows from the gas pipe 18c to the gas recovery line 20 through the outlet 18 b.

The gas pipe 18c is in physical contact with the object 11 to be cooled and is thermally connected to the object 11 to cool the object 11 to be cooled by heat exchange between the cooling gas flowing through the inside of the gas pipe 18c and the object 11 to be cooled. For example, the gas pipe 18c is a coiled cooling gas pipe disposed in contact with the outer surface of the object 11 to be cooled so as to be wound around the object 11.

In the case where the object gas passage 18 is formed as a separate piping member from the gas supply passage 16, the inlet 18a may be a pipe joint provided at one end of the gas pipe 18c for connecting the gas supply passage 16 to the object gas passage 18. In the case where the object gas flow path 18 is formed as an integral pipe member continuous with the gas supply line 16, the inlet 18a may be a portion where the gas pipe 18c starts to come into physical contact with the object 11, and the contact start point may be regarded as the inlet 18a of the object gas flow path 18. When the object gas flow path 18 passes through the inside of the object 11, the inlet 18a may be a portion where the object gas flow path 18 enters the object 11 as literally shown.

Similarly, in the case where the object gas flow passage 18 is configured as another piping member different from the gas recovery passage 20, the outlet 18b may be a pipe joint provided at the other end of the gas pipe 18c for connecting the gas recovery passage 20 to the object gas flow passage 18. When the object gas flow path 18 is configured as an integral pipe member continuous with the gas recovery conduit 20, the outlet 18b may be a portion where physical contact between the gas pipe 18c and the object to be cooled 11 is completed, and this contact termination point may be regarded as the outlet 18b of the object gas flow path 18. When the object gas flow path 18 passes through the inside of the object 11, the outlet 18b may be a portion of the object gas flow path 18 that comes out of the object 11, as literally shown.

In other words, neither the gas supply line 16 nor the gas recovery line 20 is in physical contact with the object 11 to be cooled. The gas supply line 16 extends from the inlet 18a of the object gas flow path 18 in a direction away from the object 11, and the gas recovery line 20 extends from the outlet 18b of the object gas flow path 18 in a direction away from the object 11. The cryogenic refrigerator 22 and the refrigerator cooling stage 28 thereof are also disposed at a position distant from the object 11 to be cooled.

The gas supply line 16 connects the gas circulation source 12 to the inlet 18a of the object gas flow path 18 so that the cooling gas is supplied from the gas circulation source 12 to the object gas flow path 18 via the refrigerator cooling stage 28. Gas supply line 16 is in physical contact with refrigerator cold stage 28 and is thermally connected to refrigerator cold stage 28 so as to cool the cooling gas by heat exchange between the cooling gas flowing through gas supply line 16 and refrigerator cold stage 28. Therefore, the cooling gas flows from the gas circulation source 12 into the gas supply line 16, is cooled by the refrigerator cooling table 28, and then flows from the gas supply line 16 to the object gas flow path 18.

Hereinafter, for convenience of explanation, a portion of the gas supply line 16 between the gas circulation source 12 and the refrigerator cooling stage 28 may be referred to as an upstream portion 16a of the gas supply line 16, and a portion of the gas supply line 16 between the refrigerator cooling stage 28 and the inlet 18a of the object gas flow path 18 may be referred to as a downstream portion 16b of the gas supply line 16. That is, the gas supply line 16 includes an upstream portion 16a and a downstream portion 16 b.

The portion of the gas supply line 16 disposed on the refrigerator cooling stage 28 may be referred to as an intermediate portion 16c of the gas supply line 16. For example, the intermediate portion 16c of the gas supply line 16 is a coiled cooling gas pipe disposed on the outer surface of the refrigerator cooling table 28 so as to be wound around the refrigerator cooling table 28.

Therefore, the cooling gas reaches the lowest reaching temperature in the cooling gas flow field 14 at the outlet 16d of the intermediate portion 16c of the gas supply line 16 (i.e., the inlet of the downstream portion 16 b).

The gas recovery line 20 connects the outlet 18b of the object gas flow path 18 to the gas circulation source 12 so that the cooling gas is recovered from the object gas flow path 18 to the gas circulation source 12. Therefore, the cooling gas flows from the object gas flow path 18 into the gas recovery line 20, and flows from the gas recovery line 20 to the gas circulation source 12.

The ultra-low-temperature cooling system 10 is provided with a heat exchanger 30. The heat exchanger 30 is configured to exchange heat between the cooling gases flowing through the gas supply line 16 and the gas recovery line 20, respectively, between the two lines. The heat exchanger 30 contributes to the improvement of the cooling efficiency of the ultra-low-temperature cooling system 10.

The heat exchanger 30 includes a high-temperature inlet 30a and a low-temperature outlet 30b in the gas supply line 16 (more specifically, the upstream portion 16a), and a low-temperature inlet 30c and a high-temperature outlet 30d in the gas recovery line 20. The cooling gas on the supply side (i.e., the high-temperature cooling gas flowing from the gas circulation source 12 into the heat exchanger 30 through the high-temperature inlet 30 a) is cooled in the heat exchanger 30 by the gas recovery line 20, and flows toward the refrigerator cooling table 28 through the low-temperature outlet 30 b. Accordingly, the cooling gas on the recovery side (i.e., the low-temperature cooling gas flowing from the cooled gas passage 18 into the heat exchanger 30 through the low-temperature inlet 30 c) is heated by the gas supply line 16 in the heat exchanger 30, and flows to the gas circulation source 12 through the high-temperature outlet 30 d.

The ultra-low-temperature cooling system 10 includes a vacuum chamber 32 defining a vacuum environment 34. The vacuum vessel 32 is configured to isolate the vacuum environment 34 from an ambient environment 36. The vacuum vessel 32 is an ultra-low temperature vacuum vessel such as a cryostat. The vacuum environment 34 is, for example, an ultra-low temperature vacuum environment, and the ambient environment 36 is, for example, a room temperature and atmospheric pressure environment.

The object to be cooled 11 is disposed in the vacuum chamber 32 (i.e., in the vacuum atmosphere 34). Among the main components of the cryogenic cooling system 10, the cooled object gas flow path 18, the refrigerator cooling stage 28 of the cryogenic refrigerator 22, and the heat exchanger 30 are disposed in a vacuum environment 34. On the other hand, the gas circulation source 12 and the compressor 24 of the cryogenic refrigerator 22 are disposed outside the vacuum vessel 32 (i.e., in the ambient environment 36). Therefore, one end of the gas supply line 16 and the gas recovery line 20 connected to the gas circulation source 12 is disposed in the ambient environment 36, and the remaining portion is disposed in the vacuum environment 34.

The cryogenic cooling system 10 includes a temperature sensor 38 provided on the refrigerator cooling stage 28. Only 1 temperature sensor 38 is provided in the cooling gas flow path 14 (specifically, in the gas supply line 16) of the ultra-low-temperature cooling system 10. Therefore, the temperature sensor 38 is not provided on the object to be cooled gas passage 18 nor on the object to be cooled 11. The temperature sensor 38 is also not provided on the gas recovery line 20.

The location of the temperature sensor 38 is not limited to the refrigerator cooling stage 28. The temperature sensor 38 may be provided at any position on the cooling gas flow path 14 including the object gas flow path 18. Further, a plurality of temperature sensors 38 may be provided at different positions on the cooling gas flow path 14.

The cryogenic cooling system 10 includes a controller 40 that controls the cryogenic cooling system 10. The control device 40 includes a gas flow rate control unit 42. The gas flow rate control unit 42 includes a timer 44 and an initial cooling setting 46. The control device 40 is disposed in the ambient environment 36. The control device 40 may be located on the gas circulation source 12 (e.g., a compressor).

The control device 40 of the ultra-low-temperature cooling system 10 is implemented by elements or circuits including a CPU and a memory of a computer in terms of a hardware configuration, and is implemented by a computer program or the like in terms of a software configuration, but the control device 40 is appropriately depicted as a functional block realized by cooperation of these in fig. 1. Those skilled in the art will appreciate that these functional blocks can be implemented in various forms through a combination of hardware and software.

Here, the initial cooling of the ultra-low-temperature cooling system 10 is a control process of the ultra-low-temperature cooling system 10 that quickly cools the object 11 to be cooled from the room temperature to the target cooling temperature, which is performed when the ultra-low-temperature cooling system 10 is started. By the initial cooling, the object to be cooled 11 is cooled from room temperature to the target cooling temperature. After the initial cooling is completed, the ultra-low-temperature cooling system 10 transitions to stable cooling for maintaining the object to be cooled 11 at the target cooling temperature. The temperature decrease rate in the initial cooling (for example, the average temperature decrease rate of the object 11 in the initial cooling) is larger than the temperature decrease rate in the steady cooling.

The controller 40 is configured to start initial cooling of the object 11 to be cooled in synchronization with the start-up of the ultra-low-temperature cooling system 10. For example, the control device 40 starts the initial cooling of the object 11 to be cooled at the same time as the start of the ultra-low-temperature cooling system 10 or when a predetermined delay time elapses after the start of the ultra-low-temperature cooling system 10.

Typically, the start-up of the ultra-low-temperature cooling system 10 means the start-up of the gas circulation source 12 or the start-up of the gas circulation source 12 and the ultra-low-temperature refrigerator 22. Therefore, the control device 40 may be configured to start the initial cooling of the object 11 to be cooled in synchronization with the activation of the gas circulation source 12. Alternatively, the controller 40 may be configured to start the initial cooling in synchronization with the start-up of the gas circulation source 12 and the cryogenic refrigerator 22.

The ultra-low-temperature cooling system 10 includes a main switch 48. The main switch 48 includes a manually operable operation tool such as an operation button or a switch, and is configured to output a system start instruction signal S2 to the control device 40 when operated. When the operator operates the main switch 48, the ultra-low-temperature cooling system 10 is started to start operation. The main switch 48 can function not only as a start switch of the cryogenic cooling system 10 but also as a stop switch of the cryogenic cooling system 10.

The main switch 48 is disposed in the ambient environment 36. The main switch 48 may be provided on the control device 40 or its housing. Alternatively, the main switch 48 may be provided in a compressor provided in the gas circulation source 12 to serve as a start switch for the compressor. The main switch 48 may also be provided on the cryogenic refrigerator 22 (e.g., the compressor 24) to serve as a start switch for the cryogenic refrigerator 22.

Alternatively, when a host control device is provided in addition to the control device 40, the host control device may be configured to output the system activation instruction signal S2 to the control device 40. The object to be cooled 11 is usually a particle accelerator or another host device or a part of a system including a host control device.

The control device 40 is configured to start the initial cooling in response to the received system activation instruction signal S2. The control device 40 is configured to control the gas circulation source 12 to perform initial cooling of the object 11 to be cooled. During the initial cooling, the control device 40 controls the gas circulation source 12 to cause the cooling gas to flow through the cooling gas flow path 14 in a prescribed flow rate pattern. The control device 40 may control the gas circulation source 12 to perform stable cooling of the object 11 to be cooled after the initial cooling or at other appropriate timing.

The gas flow rate control unit 42 is configured to determine the target cooling gas flow rate based on the initial cooling setting 46 and the elapsed time from the start of initial cooling. The gas flow rate control unit 42 is configured to control the gas circulation source 12 so that the cooling gas flows through the cooling gas flow path 14 at the determined target cooling gas flow rate. The gas flow rate control unit 42 is configured to generate a gas circulation source control signal S1 for causing the gas circulation source 12 to supply the cooling gas at the target cooling gas flow rate to the cooling gas flow path 14, and to output the gas circulation source control signal S1 to the gas circulation source 12.

The timer 44 is configured to be able to measure an elapsed time from any time. The timer 44 is configured to measure an elapsed time in response to the system start instruction signal S2. The timer 44 can calculate the elapsed time from the start of the initial cooling.

The initial cooling setting 46 sets in advance a target cooling gas flow rate at each time point from the start of initial cooling to the completion thereof in accordance with a predetermined flow rate pattern. The initial cooling setting 46 may have a function, lookup table, map, or other form that represents a correspondence between elapsed time and target cooling gas flow rate. The initial cooling setting 46 is created in advance (e.g., by the manufacturer of the ultra-low temperature cooling system 10) and stored in the control apparatus 40 or in a storage device attached to the control apparatus 40.

The target cooling gas flow rate is set, for example, to provide a cooling capacity of the ultra-low-temperature cooling system 10 sufficient to cool the object 11 to be cooled to the target temperature. The target cooling gas flow rate may be set as appropriate in accordance with the experience of the designer, or experiments or simulation tests performed by the designer.

It is convenient to express the cooling gas flow as mass flow. As is well known, the mass flow rate is constant at each portion of the cooling gas flow path 14, and therefore the flow rate of the cooling gas supplied from the gas circulation source 12 is equal to the flow rate of the cooling gas flowing through the object gas flow path 18. However, when applicable, the flow rate pattern may be described as a volume flow rate or other relationship between the flow rate and time.

Fig. 2 (a) and (b) are diagrams illustrating flow rate patterns of the cooling gas that can be used for initial cooling according to the comparative example. Fig. 3 (a) to (d) are diagrams illustrating flow rate patterns of the cooling gas that can be used for the initial cooling according to the embodiment. These flow patterns represent the relationship between the target mass flow rate of the cooling gas and the elapsed time from the start of the initial cooling. In each figure, the initial cooling start time and the completion time are denoted as T0, Tc, respectively.

The flow pattern shown in fig. 2 (a) is fixed at the upper limit cooling gas flow rate of the ultra-low-temperature cooling system 10. Here, the upper limit cooling gas flow rate may be, for example, the maximum rated flow rate m _ max of the super low temperature cooling system 10.

The flow pattern shown in fig. 2 (b) fixes the flow rate of the cooling gas used in the stable cooling of the ultra-low-temperature cooling system 10. The fixed flow rate may be a flow rate of the cooling gas that maximizes the cooling capacity of the ultra-low-temperature cooling system 10 at a target cooling temperature in steady cooling (hereinafter, also referred to as a steady operation cooling temperature Tf), which may be referred to as an optimum flow rate m _ opt. The steady operation cooling temperature Tf generally coincides with the target cooling temperature of the initial cooling. The optimum flow rate m _ opt is smaller than the maximum rated flow rate m _ max.

As described later, the optimum flow rate m _ opt is a value different depending on the cooling temperature. Thus, the optimum flow for cooling at temperature Ta (K) can be expressed as a function of temperature Ta, i.e., m _ opt (Ta). The optimum flow at the steady operation cooling temperature Tf can be expressed as m _ opt (Tf).

In the flow rate pattern according to the comparative example, the mass flow rate of the cooling gas flowing through the cooling gas flow path 14 does not change with the passage of time. In contrast, in the initial cooling according to the embodiment, the mass flow rate of the cooling gas flowing through the cooling gas flow path 14 changes with the passage of time in accordance with a predetermined flow rate pattern. The predetermined flow rate pattern is set such that the mass flow rate of the cooling gas decreases with the passage of time.

The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path 14 at the 1 st average flow rate m1 from the initial cooling start time T0 to the transition time T, and the cooling gas flows through the cooling gas flow path 14 at the 2 nd average flow rate m2 from the transition time T to the initial cooling completion time Tc. The 2 nd average flow rate m2 is set smaller than the 1 st average flow rate m1 so that the cooling capacity of the ultra-low-temperature cooling system 10 is increased as compared with the case where the 1 st average flow rate m1 is maintained from the transition time T to the initial cooling completion time Tc.

The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path 14 at the upper limit cooling gas flow rate of the ultra-low-temperature cooling system 10 at least for a certain period of time from the initial cooling start time T0 to the transition time T. Here, the upper limit cooling gas flow rate corresponds to, for example, the maximum rated flow rate m _ max of the ultra-low-temperature cooling system 10, but is not limited thereto.

The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path 14 at a cooling gas flow rate (i.e., the optimum flow rate m _ opt (tf)) at which the cooling capacity of the ultra-low-temperature cooling system 10 is maximized at the target cooling temperature for at least a certain period of time from the transition time T to the initial cooling completion time Tc.

For convenience of explanation, hereinafter, the period from the initial cooling start time T0 to the transition time T may be referred to as the first half of the initial cooling, and the period from the transition time T to the initial cooling completion time Tc may be referred to as the second half of the initial cooling.

The transition time T is set in advance after the 1 st reference time T1 and before the 2 nd reference time T2. The transition time T is selected from a period from the 1 st reference time T1 to the 2 nd reference time T2. It can be said that the period of transition from the first half to the second half of the initial cooling is determined by the 1 st reference time T1 and the 2 nd reference time T2. The 1 st reference time T1 and the 2 nd reference time T2 provide reference for setting the transition time T, which will be described later.

The predetermined flow rate pattern shown in fig. 3 (a) is set such that the mass flow rate of the cooling gas decreases with a constant gradient from the initial cooling start time T0 to the completion time Tc. That is, the predetermined flow rate pattern has a constant mass flow rate decrease rate from the initial cooling start time T0 to the completion time Tc. The predetermined flow rate pattern has the maximum rated flow rate m _ max at the initial cooling start time T0 and the optimum flow rate m _ opt at the initial cooling completion time Tc. However, the initial value and the final value of the flow rate in the flow rate pattern are not limited to these. For example, the flow rate initial value may be smaller than the maximum rated flow rate m _ max.

Therefore, the flow pattern shown in fig. 3 (a) has the 1 st average flow rate m1 in the first half of the initial cooling and the 2 nd average flow rate m2 in the second half of the initial cooling. The 2 nd average flow rate m2 is smaller than the 1 st average flow rate m 1. The 1 st average flow rate m1 is smaller than the maximum rated flow rate m _ max. The 2 nd average flow rate m2 is larger than the optimum flow rate m _ opt at the target cooling temperature for the initial cooling.

The prescribed flow rate pattern shown in fig. 3 (b) is set such that the mass flow rate of the cooling gas decreases with a non-constant gradient at least for a period of time during the initial cooling. The predetermined flow rate pattern is set such that the mass flow rate of the cooling gas is fixed at a constant value in the first half of the initial cooling and decreases with a gradient that decreases with the passage of time in the second half of the initial cooling. The prescribed flow rate pattern has the maximum rated flow rate m _ max in the first half of the initial cooling and the optimum flow rate m _ opt at the target cooling temperature of the initial cooling at the initial cooling completion time Tc.

The predetermined flow rate pattern may be set in advance such that the cooling gas flows through the cooling gas flow path 14 at least for a certain period of time during the initial cooling period at a flow rate of the cooling gas that maximizes the cooling capacity of the ultra-low-temperature cooling system 10 at the predicted cooling temperature at each time. The predetermined flow rate pattern shown in fig. 3 (b) is set so that the cooling gas flow rate becomes the optimum cooling gas flow rate at the predicted cooling temperature at each time in the latter half of the initial cooling.

Therefore, the flow pattern shown in (b) of fig. 3 also has the 1 st average flow rate m1 in the first half of the initial cooling and the 2 nd average flow rate m2 in the latter half of the initial cooling, and the 2 nd average flow rate m2 is smaller than the 1 st average flow rate m 1. The 1 st average flow rate m1 is equal to the maximum rated flow rate m _ max. The 2 nd average flow rate m2 is larger than the optimum flow rate m _ opt at the target cooling temperature.

Similarly to the flow rate pattern, the predetermined flow rate pattern shown in fig. 3 (c) is set such that the mass flow rate of the cooling gas decreases with time. The predetermined flow rate pattern is fixed to a 1 st constant value for a first half of the initial cooling and to a 2 nd constant value for a second half of the initial cooling. The 2 nd constant value is less than the 1 st constant value. More specifically, the predetermined flow rate pattern uses the maximum rated flow rate m _ max as the 1 st constant value from the initial cooling start time T0 to the 1 st reference time T1, and uses the optimum flow rate m _ opt as the 2 nd constant value from the 2 nd reference time T2 to the initial cooling completion time Tc. The predetermined flow rate pattern is set such that the mass flow rate of the cooling gas decreases with a constant (or non-constant) gradient from the 1 st reference time T1 to the 2 nd reference time T2.

Therefore, the flow pattern shown in (c) of fig. 3 also has the 1 st average flow rate m1 in the first half of the initial cooling and the 2 nd average flow rate m2 in the latter half of the initial cooling, and the 2 nd average flow rate m2 is smaller than the 1 st average flow rate m 1.

As shown in fig. 3 (d), the predetermined flow rate pattern may be set such that the mass flow rate of the cooling gas is fixed at an intermediate constant value from the 1 st reference time T1 to the 2 nd reference time T2. The intermediate constant value m3 is less than the 1 st constant value (e.g., the maximum rated flow m _ max) and greater than the 2 nd constant value (e.g., the optimal flow m _ opt). Similarly, the flow pattern shown in fig. 3 (d) also has the 1 st average flow rate m1 in the first half of the initial cooling and the 2 nd average flow rate m2 in the second half of the initial cooling, and the 2 nd average flow rate m2 is smaller than the 1 st average flow rate m 1.

In the illustrated prescribed flow rate pattern, the cooling gas flow rate monotonically decreases with the passage of time, but this is not essential. The prescribed flow rate pattern may also be a pattern in which the flow rate of the cooling gas is increased over a period of time.

Fig. 4 (a) and (b) are graphs showing cooling capacity curves of the ultra-low-temperature cooling system 10 at a plurality of cooling temperatures. Fig. 4 (a) and (b) show changes in the cooling capacity of the ultra-low-temperature cooling system 10 with respect to the mass flow rate of the cooling gas flowing through the cooling gas flow path 14. These cooling capacity curves are calculated by the present inventors. In fig. 4 (a), the cooling capacity of the ultra-low-temperature cooling system 10 at several representative temperatures selected from the entire temperature range from room temperature to the target cooling temperature of the initial cooling is plotted. Fig. 4 (b) is an enlarged view of a temperature range of 100K or less of fig. 4 (a), and plots the cooling capacity of the ultra-low-temperature cooling system 10 at several representative temperatures.

As can be seen from fig. 4, the cooling capacity curve becomes maximum at a certain mass flow rate. The optimum mass flow rate for maximizing the cooling capacity differs depending on the cooling temperature, and specifically, the lower the cooling temperature, the smaller the optimum mass flow rate. In addition, in the cooling capacity curve at a certain cooling temperature, the cooling capacity is decreased at a mass flow rate smaller than the optimum mass flow rate because the amount of heat that the cooling gas can take away from the object to be cooled 11 by heat exchange between the cooling gas and the object to be cooled 11 is reduced at such a small flow rate. And, the cooling capacity is decreased at a mass flow rate greater than the optimum mass flow rate because of being restricted by the cooling capacity of the cryogenic refrigerator 22. As the flow rate of the cooling gas increases, the heat exchange between the cooling gas and the refrigerator cooling stage 28 becomes insufficient, and the temperature of the cooling gas flowing to the object 11 to be cooled may increase.

Fig. 4 (a) illustrates an upper limit cooling gas flow rate (e.g., the maximum rated flow rate m _ max) of the ultra-low-temperature cooling system 10. At room temperature or in a relatively high temperature range (the range of 290K to 110K in fig. 4 (a)), the upper flow rate of the cooling system is smaller than the mass flow rate that provides the maximum value of the cooling capacity. Therefore, in this high temperature range, the ultra-low-temperature cooling system 10 can achieve the maximum cooling capacity by flowing the cooling gas through the cooling gas flow path 14 at the upper limit cooling gas flow rate.

On the other hand, in a relatively low temperature range (about 100K or less in fig. 4 (b)) including the target cooling temperature of the initial cooling, the optimum mass flow rate that provides the maximum value of the cooling capacity is smaller than the upper limit flow rate of the ultra-low-temperature cooling system 10. For example, the optimum mass flow rates (m _ opt (70K), m _ opt (50K), m _ opt (30K), and m _ opt (20K)) at cooling temperatures of 70K, 50K, 30K, and 20K are all less than the maximum rated flow rate m _ max.

Therefore, in this low temperature range, the ultra-low-temperature cooling system 10 can achieve the maximum cooling capacity by reducing the cooling gas flow rate from the upper limit cooling gas flow rate to the optimum flow rate. In fig. 4 (b), the broken line indicates a line connecting the maximum values of the plurality of cooling capacity curves. By reducing the mass flow of the cooling gas in accordance with the temperature drop caused by cooling and the dotted line, the ultra-low-temperature cooling system 10 can achieve the maximum cooling capacity for each cooling temperature.

In the ultra-low-temperature cooling system 10, a temperature change when initial cooling is performed in a certain flow rate pattern is predictable. For example, by performing a simulation test using an appropriate thermodynamic model, the temperature of the object 11 to be cooled at each time point in the initial cooling can be calculated. In particular, since the object 11 is not in use or in an idling state during the initial cooling, the amount of heat generation of the object 11 can be regarded as constant, and calculation can be performed relatively easily. Various known methods can be used for such thermodynamic calculations, and therefore, they will not be described in detail here.

As a result of the calculation, the temporal change in the predicted cooling temperature can be obtained. By referring to the cooling capacity curve, the optimum flow rate of the cooling gas can be found from the predicted cooling temperature. Therefore, the flow rate pattern that provides the flow rate of the cooling gas that maximizes the cooling capacity of the ultra-low-temperature cooling system 10 at each time can be determined from the predicted cooling temperature at each time. In this way, the flow rate pattern illustrated in fig. 3 (b) can be set in advance.

Another important point that can be seen from fig. 4 (a) is that, in the ultra-low-temperature range around the target cooling temperature of the initial cooling (about 40K or less in fig. 4 (a) and (b)), even if the cooling gas is made to flow at the upper limit flow rate of the ultra-low-temperature cooling system 10, no cooling capacity is generated (i.e., heating is generated). Therefore, even if the cooling gas is continuously passed by the restricted flow amount or more as in the flow rate pattern according to the comparative example shown in fig. 2 (a), the object 11 cannot be cooled to the target cooling temperature (for example, 30K or less as described above). As a result, the initial cooling of the ultra-low-temperature cooling system 10 cannot be completed.

Fig. 5 is a flowchart illustrating a method of controlling initial cooling of the ultra-low-temperature cooling system 10 according to the embodiment. The control routine shown in fig. 5 is executed by the control device 40 at the time of starting the ultra-low-temperature cooling system 10.

First, it is determined whether the main switch 48 is operated (S10). The gas flow rate control unit 42 of the control device 40 determines whether or not the system activation instruction signal S2 is input from the main switch 48 to the gas flow rate control unit 42. If the system activation instruction signal S2 is not input (no in S10), the process ends because initial cooling is not necessary.

If the system start instruction signal S2 is input (yes at S10), the initial cooling of the ultra-low-temperature cooling system 10 is started. At this time, the timer 44 is used to measure the elapsed time from the start of the initial cooling (S12). Next, the target cooling gas flow rate is determined from the elapsed time using the flow rate pattern defined in the initial cooling setting 46 (S14). The gas flow rate control unit 42 determines a target cooling gas flow rate corresponding to the elapsed time from the flow rate pattern of the initial cooling setting 46.

The gas flow rate control unit 42 controls the gas circulation source 12 so that the cooling gas flows through the object gas flow path 18 at the determined target cooling gas flow rate (S16). The gas flow rate control unit 42 generates a gas circulation source control signal S1 to achieve the determined target cooling gas flow rate. The gas circulation source control signal S1 indicates an operation parameter of the gas circulation source 12 that determines the flow rate of the cooling gas supplied from the gas circulation source 12 to the cooling gas flow path 14. The gas circulation source control signal S1 may also indicate, for example, the rotational speed of a motor driving the gas circulation source 12. Alternatively, the gas circulation source control signal S1 may be a gas flow rate indicating signal indicative of the determined target cooling gas flow rate. In this case, the gas circulation source 12 may be configured to control the flow rate of the supplied cooling gas in accordance with the gas flow rate instruction signal.

The gas flow rate control unit 42 determines whether or not the elapsed time from the start of the initial cooling has reached the initial cooling completion time (Tc) (S18). If the initial cooling completion time is not reached (no in S18), the gas flow rate control unit 42 continues the initial cooling. That is, the gas flow rate control portion 42 re-executes the above-described S12 to S18. When the initial cooling completion time is reached (yes at S18), the gas flow rate control unit 42 ends the initial cooling.

Thereby, initial cooling can be automatically performed when the ultra-low-temperature cooling system 10 is started. The gas flow rate control unit 42 starts the initial cooling of the ultra-low-temperature cooling system 10 based on the system start instruction signal S2, generates the gas circulation source control signal S1 based on a predetermined flow rate pattern, and outputs the gas circulation source control signal S1 to the gas circulation source 12. The gas circulation source 12 is operated in accordance with the gas circulation source control signal S1, and thereby the target cooling gas flow rate can be made to flow through the object gas flow path 18. If the initial cooling is completed, the stable cooling of the object to be cooled 11 can be started.

The initial cooling setting 46 may have a plurality of flow rate patterns corresponding to a plurality of target cooling temperatures that can be used. The target cooling temperature for the initial cooling is set by, for example, a user of the ultra-low-temperature cooling system 10. The gas flow rate control unit 42 can select a flow rate pattern corresponding to the set target cooling temperature. The gas flow rate control portion 42 may determine the target cooling gas flow rate according to the selected flow rate pattern.

Also, in the above-described control process, the initial cooling of the ultra-low-temperature cooling system 10 is automatically started while the main switch 48 is operated, but this is not necessarily required. For example, the initial cooling may be started separately from the operation of the main switch 48 by manual setting by the user of the ultra-low-temperature cooling system 10. Alternatively, the initial cooling may be automatically started based on the control of the host control device.

Fig. 6 (a) shows a temperature change in the initial cooling of the ultra-low-temperature cooling system 10, and fig. 6 (b) shows a flow rate pattern used in the initial cooling. Fig. 6 (a) and (b) show changes in temperature in the two comparative examples and changes in temperature in the initial cooling in the example. These temperature change charts are calculation results obtained by the present inventors through calculation. In order to reduce the calculation load and to satisfactorily simulate the actually occurring temperature change, the result is obtained under several assumptions (for example, the heat capacity of the material of the object to be cooled 11 is constant regardless of the temperature).

As in the flow rate pattern shown in fig. 3 (b), in the flow rate pattern used in the embodiment, the cooling gas flow rate is fixed to the maximum rated flow rate m _ max in the first half of the initial cooling, and the cooling gas flow rate is set to the optimum flow rate m _ opt based on the predicted cooling temperature in the second half of the initial cooling. In the flow rate pattern used in comparative example 1, the cooling gas flow rate was always fixed to the maximum rated flow rate m _ max, as in the flow rate pattern shown in fig. 2 (a). In the flow rate pattern used in comparative example 2, the cooling gas flow rate is always fixed to the optimum flow rate m _ opt (Tf) at the steady operation cooling temperature Tf, as in the flow rate pattern shown in fig. 2 (b).

In comparative example 1, since the cooling gas flows at a large flow rate, the temperature decrease rate in the high temperature range is relatively high. However, as described above, the cooling gas of a large flow rate cannot generate cooling capacity in the low temperature range, and therefore, in comparative example 1, the temperature cannot be lowered to the steady operation cooling temperature Tf. Initial cooling cannot be accomplished.

In comparative example 2, since the cooling gas was flowed at a small flow rate, the temperature decrease rate in the high temperature range was also slow. Unlike comparative example 1, the temperature can be lowered to the steady operation cooling temperature Tf, and the initial cooling can be completed. However, the cooling rate in the high temperature range is slow, and thus it takes a relatively long time to complete the initial cooling.

According to the embodiment, the cooling gas is caused to flow at a large flow rate in the first half of the initial cooling, and therefore the temperature decrease speed in the high temperature range can be increased. In particular, the maximum cooling capacity available to the cryogenic cooling system 10 can be exhibited by flowing the cooling gas at the maximum rated flow rate m _ max. In the latter half of the initial cooling, the cooling gas flow rate is changed at an optimum flow rate with the passage of time. Therefore, a large cooling capacity can be utilized also in the latter half of the initial cooling. Therefore, the time required for initial cooling can be shortened. As shown in fig. 6, the time required for initial cooling in the example was shortened by Δ T as compared with comparative example 2.

As described above, according to the ultra-low-temperature cooling system 10 of the embodiment, the initial cooling is performed in the predetermined flow rate pattern. The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path 14 at the 1 st average flow rate m1 from the initial cooling start time T0 to the transition time T, and the cooling gas flows through the cooling gas flow path 14 at the 2 nd average flow rate m2 from the transition time T to the initial cooling completion time Tc. The 2 nd average flow rate m2 is set smaller than the 1 st average flow rate m1 so that the cooling capacity of the ultra-low-temperature cooling system 10 is increased as compared with the case where the 1 st average flow rate m1 is maintained from the transition time T to the initial cooling completion time Tc.

This can increase the cooling capacity of the ultra-low-temperature cooling system 10 in both the first half and the second half of the initial cooling, and effectively cool the object 11 to be cooled, thereby shortening the time required for the initial cooling.

Further, for example, in another method of feedback-controlling the flow rate of the cooling gas using the measured temperature, a temperature measurement sensor and a feedback control system are required, and thus the configuration becomes complicated. In contrast, according to the embodiment, the flow rate of the cooling gas is controlled by the open-loop control method without using the feedback control, so that a relatively simple control system can be adopted, and there are advantages in that the risk of failure is reduced and the cost is reduced.

Then, the controller 40 starts the initial cooling in synchronization with the start-up of the gas circulation source 12 or the start-up of the gas circulation source 12 and the cryogenic refrigerator 22. Thus, since the starting and initial cooling of the components of the ultra-low-temperature cooling system 10 such as the gas circulation source 12 are automatically performed in a unified manner, the operability of the ultra-low-temperature cooling system 10 is improved for the worker as compared with the case where these processes are performed individually.

The predetermined flow rate pattern is set in advance such that the cooling gas flows through the cooling gas flow path 14 at the upper limit cooling gas flow rate of the ultra-low-temperature cooling system 10 for at least a period of time in the first half of the initial cooling. As a result, as described above, the cooling capacity in the first half of the initial cooling (i.e., in a state where the temperature of the ultra-low-temperature cooling system 10 is relatively high) can be increased, and the object 11 to be cooled can be cooled efficiently.

The prescribed flow rate pattern is preset such that the cooling gas flows through the cooling gas flow path 14 at least for a certain period of time in the latter half of the initial cooling so as to maximize the cooling capacity of the ultra-low-temperature cooling system 10 at the target cooling temperature. As a result, as described above, the cooling capacity in the latter half of the initial cooling can be improved, and the object 11 to be cooled can be cooled efficiently.

If the transition time T is too late, cooling in the ultra-low temperature range is hindered as in comparative example 1, and initial cooling may take a long time. If the transition time T is too early, the cooling rate in the high temperature range becomes faster as in comparative example 2, and it may be necessary to lengthen the time required for initial cooling. Therefore, it is desirable to appropriately set the transition time T. The transition time T may be set as appropriate according to experience knowledge of the designer, experiments or simulation tests performed by the designer, or the like. The reference for the transition time T may also be provided as follows.

The transition time T is set in advance after the 1 st reference time T1 and before the 2 nd reference time T2. The 1 st reference time T1 may be expressed as a ratio of the amount of heat that should be removed from the object to be cooled 11 by the initial cooling to the cooling capacity of the ultra-low-temperature cooling system 10 at the 1 st representative temperature Tr 1. The 2 nd reference time T2 may be expressed as a ratio of the amount of heat that should be removed from the object to be cooled 11 by the initial cooling to the cooling capacity of the ultra-low-temperature cooling system 10 at the 2 nd representative temperature Tr 2. The 1 st representative temperature Tr1 and the 2 nd representative temperature Tr2 may be selected from a temperature range from room temperature to a target cooling temperature, and the 2 nd representative temperature Tr2 may be lower than the 1 st representative temperature Tr 1.

That is, the transition time T is set to "1 st reference time T1 ≦ transition time T ≦ 2 nd reference time T2", and the inequality may be described as follows.

[ numerical formula 1]

Here, T_RTAt room temperature, T_LMi is the mass of the member to be cooled (e.g., the object to be cooled 11), c_piIs the (constant pressure) specific heat of the member to be cooled. i represents the kind of the member. Q_cryocooler(Tr1) represents the refrigerating capacity of the cryogenic refrigerator 22 at the 1 st representative temperature Tr1, Q_cryocooler(Tr2) represents the refrigerating capacity of the cryogenic refrigerator 22 at the 2 nd representative temperature Tr 2. In the case where the 2 nd representative temperature Tr2 is lower than the 1 st representative temperature Tr1, usually Q_cryocooler(Tr1)＞Q_cryocooler(Tr2)。

In short, the 1 st reference time T1 provides a reference of the time until the object 11 is cooled to the 1 st representative temperature Tr 1. The 2 nd reference time T2 provides a reference of the time until the object 11 is cooled to the 2 nd representative temperature Tr 2. For example, the 1 st representative temperature Tr1 may be a temperature at or near the temperature of liquid nitrogen. The 2 nd representative temperature Tr2 may be a temperature at or near the upper limit temperature of the temperature range to be maintained by the object to be cooled 11 in the steady cooling. This makes it easy to accurately set the transition time T. The refrigerating capacity of the cryogenic refrigerator 22 in the above inequality need not be a value at a certain representative temperature, but may be an average value of refrigerating capacities in a certain temperature range.

Fig. 7 is a diagram schematically showing another example of the ultra-low-temperature cooling system 10 according to the embodiment. The flow path structure of the cooling gas in the illustrated ultra-low-temperature cooling system 10 is different from that of the ultra-low-temperature cooling system 10 shown in fig. 1, and the rest is substantially the same. Hereinafter, different configurations will be mainly described, and the same configurations will be briefly described or omitted.

The cryogenic cooling system 10 includes a gas circulation source 12 and a cooling gas flow path 14. The cooling gas channel 14 includes a gas supply line 16, a cooled object gas channel 18, and a gas recovery line 20. The cryogenic cooling system 10 further includes a cryogenic refrigerator 22, a heat exchanger 30, and a vacuum vessel 32 defining a vacuum environment 34. The cryogenic refrigerator 22 includes a cold head 26 having a refrigerator cooling stage 28. The gas circulation source 12 is disposed in an ambient environment 36.

As described above, both the cooling gas and the working gas of the cryogenic refrigerator 22 may be helium gas. In this way, in the case where the cooling gas and the working gas are the same gas, 1 common compressor can be provided in the ultra-low-temperature cooling system 10. That is, the gas circulation source 12 not only flows the cooling gas through the cooling gas flow path 14, but also functions as a compressor that circulates the working gas through the cryogenic refrigerator 22.

In this case, the gas circulation source 12 may include a flow control valve 50 for controlling the flow rate of the cooling gas flowing through the object gas passage 18, and the flow control valve 50 may be configured to control the flow rate of the cooling gas. The flow control valve 50 is configured to control the flow rate of the supplied cooling gas in accordance with the gas circulation source control signal S1.

The cryogenic cooling system 10 is provided with a refrigerator supply line 52 for supplying the working gas from the gas circulation source 12 to the cryogenic refrigerator 22, and the cryogenic cooling system 10 is provided with a refrigerator recovery line 54 for recovering the working gas from the cryogenic refrigerator 22 to the gas circulation source 12. A refrigerator supply line 52 branches from gas supply line 16 and connects to cold head 26 in ambient environment 36, and a refrigerator recovery line 54 branches from gas recovery line 20 and connects to cold head 26 in ambient environment 36.

A flow control valve 50 is disposed on the gas supply line 16 in the ambient environment 36. Alternatively, the flow control valve 50 may be disposed on the gas recovery line 20 in the ambient environment 36. This enables a general flow control valve to be used as the flow control valve 50, and is more advantageous in terms of manufacturing cost than when the flow control valve 50 is disposed in the vacuum atmosphere 34. However, the flow control valve 50 may also be disposed in the vacuum environment 34.

The ultra-low-temperature cooling system 10 further includes a control device 40 having a gas flow rate control unit 42, a timer 44, and an initial cooling setting 46, and a main switch 48.

As in the above-described embodiment, the cooling capacity of the ultra-low-temperature cooling system 10 can be increased, and the object 11 can be cooled efficiently, so that the time required for initial cooling can be shortened. Since the flow rate of the cooling gas is controlled in an open-loop control manner without using feedback control, a relatively simple control system can be employed, which has the advantages of reducing the risk of failure and reducing the cost.

In the case where the gas circulation source 12 and the compressor 24 of the cryogenic refrigerator 22 are provided separately as in the cryogenic cooling system 10 shown in fig. 1, the cryogenic cooling system 10 may be provided with the flow rate control valve 50 in the cooling gas flow path 14. The flow control valve 50 may be disposed on the gas supply line 16 in the ambient environment 36, for example.

The present invention has been described above with reference to the embodiments. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and various design changes and modifications are possible and are within the scope of the present invention.

Various features illustrated in one embodiment may be applicable to other embodiments as well. The new embodiment which is produced by the combination has the effects of the combined embodiments.

Description of the symbols

10-cryogenic cooling system, 11-object to be cooled, 12-gas circulation source, 14-cooling gas flow path, 22-cryogenic refrigerator, 28-refrigerator cooling stage, 40-control device, 42-gas flow rate control section, 46-initial cooling setting, m 1-1 st average flow rate, m 2-2 nd average flow rate, T-transition time, T1-1 st reference time, T2-2 nd reference time.

Industrial applicability

The present invention can be used in the field of ultra-low temperature cooling systems.