Ultra-low temperature system and control method of ultra-low temperature system

Abstract

A cryogenic system (100) is provided with a cryogenic refrigerator (10) and a controller (60). A cryogenic refrigerator (10) is provided with: a first cylinder (16a); a second cylinder (16b) provided with a heat absorption part (46) thermally connected to a heat source in an axial middle part; a first temperature sensor (51) that measures the temperature at one axial end of the second cylinder (16b); a second temperature sensor (52) that measures the temperature at the other axial end of the second cylinder (16b); and a third temperature sensor (53) that measures the temperature in the heat absorbing part (46). The controller (60) is configured to acquire a first measured temperature from the first temperature sensor (51), acquire a second measured temperature from the second temperature sensor (52), and acquire a third measured temperature from the third temperature sensor (53), set an upper limit temperature of the heat absorbing part (46) according to the first measured temperature, the second measured temperature, and an axial position of the heat absorbing part (46), and control the heat source. Therefore, the third measured temperature is lower than the upper limit temperature of the heat absorption part (46).

Description

Technical Field

[0001] The invention relates to an ultra-low temperature system and a control method of the ultra-low temperature system. Background Art

[0002] Conventionally, there is known a cryogenic refrigerator represented by a Gifford-McMahon (GM) refrigerator, which is used for cooling various cryogenic systems.

[0003] Previous technical literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2001-116379 Summary of the invention

[0006] Technical issues to be solved by the invention

[0007] One of the exemplary purposes of an embodiment of the present invention is to efficiently cool a cryogenic system.

[0008] Means for solving technical problems

[0009] According to one embodiment of the present invention, a cryogenic system includes a cryogenic refrigerator and a controller. The cryogenic refrigerator includes: a first cylinder; a second cylinder, which is axially arranged in series with the first cylinder and has a heat absorbing part thermally connected to a heat source in its axial middle part; a first temperature sensor, which measures a first measured temperature at an axial end of the second cylinder on one side close to the first cylinder; a second temperature sensor, which measures a second measured temperature at an axial end of the second cylinder on the other side away from the first cylinder; and a third temperature sensor, which measures a third measured temperature at the heat absorbing part. The controller is configured to obtain the first measured temperature from the first temperature sensor, the second measured temperature from the second temperature sensor, and the third measured temperature from the third temperature sensor, and to set an upper limit temperature of the heat absorbing part according to the first measured temperature, the second measured temperature and the axial position of the heat absorbing part, and to control the heat source so that the third measured temperature becomes below the upper limit temperature of the heat absorbing part.

[0010] According to one embodiment of the present invention, a control method for a cryogenic system is provided. The cryogenic system includes a cryogenic refrigerator, which includes a first cylinder and a second cylinder arranged in series along the axial direction, and the second cylinder includes a heat absorbing part thermally connected to a heat source in its axial middle part. The method includes the following steps: measuring a first measured temperature at an axial end of the second cylinder on one side close to the first cylinder; measuring a second measured temperature at an axial end of the second cylinder on the other side away from the first cylinder; measuring a third measured temperature at the heat absorbing part; setting an upper limit temperature of the heat absorbing part according to the first measured temperature, the second measured temperature and the axial position of the heat absorbing part; and controlling the heat source so that the third measured temperature becomes below the upper limit temperature of the heat absorbing part.

[0011] In addition, any combination of the above-mentioned constituent elements or any form in which constituent elements and expressions of the present invention are mutually replaced in the form of methods, apparatuses, systems, etc. may also be practiced as additional embodiments of the present invention.

[0012] Effects of the Invention

[0013] According to the present invention, a cryogenic system can be cooled efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram schematically showing a cryogenic system according to an embodiment.

[0015] Figure 2 It is a rough representation of what can be applied to Figure 1 A diagram of a cryogenic refrigerator of a cryogenic system is shown.

[0016] Figure 3 (a) and (b) are graphs showing the results of experiments conducted by the present inventors according to the embodiments.

[0017] Figure 4 (a) and (b) are graphs showing the results of experiments conducted by the present inventors according to the embodiments.

[0018] Figure 5 This is a flowchart showing a control method of a cryogenic system according to an embodiment.

[0019] Figure 6 Yes means Figure 5 FIG. 1 is a flowchart of an example of the control process ( S30 ) of the refrigerant gas pipeline shown in FIG.

[0020] Figure 7 This is a diagram schematically showing a cryogenic system according to another embodiment. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, the same or equivalent components, parts and processes are marked with the same symbols, and repeated descriptions are appropriately omitted. For the convenience of explanation, in each of the drawings, the scale or shape of each part is appropriately set, and unless otherwise specifically stated, it is not interpreted as a limitative. The embodiments are examples and do not limit the scope of the present invention in any way. All the features or combinations thereof described in the embodiments are not necessarily the essence of the invention.

[0022] Figure 1 It is a diagram schematically showing a cryogenic system 100 according to an embodiment. Figure 2 It is a rough representation of what can be applied to Figure 1 FIG. 1 is a diagram of a cryogenic refrigerator 10 of a cryogenic system 100. The appearance of the cryogenic refrigerator 10 is as follows: Figure 1 As shown, the internal structure of the ultra-low temperature refrigerator 10 is as follows Figure 2 As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator.

[0023] In this embodiment, the ultra-low temperature system 100 can be used as an ultra-low temperature liquid storage device. Therefore, in addition to the ultra-low temperature refrigerator 10, the ultra-low temperature system 100 also has a vacuum container 110 for storing liquid helium or other ultra-low temperature liquids 102. Through the ultra-low temperature refrigerator 10, the stored ultra-low temperature liquid 102 is cooled to an ultra-low temperature below its liquefaction temperature (when it is liquid helium, about 4K).

[0024] The vacuum container 110 includes an outer tank 112 and an inner tank 114. A vacuum insulation layer 116 is formed between the outer tank 112 and the inner tank 114, and the outer tank 112 is configured to separate the vacuum insulation layer 116 from the surrounding environment of the ultra-low temperature system 100 (for example, the room temperature atmospheric pressure environment). The vacuum insulation layer 116 may be provided with an insulating structure such as a multilayer insulation (MLI). In addition, the inner tank 114 is configured to accommodate the ultra-low temperature liquid 102 therein and separate the ultra-low temperature liquid 102 from the vacuum insulation layer 116. The outer tank 112 and the inner tank 114 are formed of metal materials such as stainless steel or other suitable high-strength materials to withstand the pressure difference between the inside and the outside.

[0025] The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, increase the pressure of the recovered working gas, and then supply the working gas to the expander 14 again. The working gas is also called a refrigerant gas, and is usually helium, but other suitable gases may also be used.

[0026] The expander 14 includes a refrigerator cylinder 16, a displacer assembly 18, and a refrigerator housing 20. The refrigerator housing 20 is combined with the refrigerator cylinder 16 to form an airtight container for accommodating the displacer assembly 18. The refrigerator cylinder 16 and the refrigerator housing 20 are formed of, for example, a metal material such as stainless steel or other suitable high-strength materials.

[0027] The expander 14 is arranged in the vacuum container 110 in a state where the refrigerator cylinder 16 is inserted into the inner groove 114 of the vacuum container 110 and the refrigerator housing 20 is installed on the outside of the vacuum container 110. As an example, the expander 14 is arranged in the upper part of the vacuum container 110 in a manner that its central axis is consistent with the vertical direction. However, the installation position and installation posture of the expander 14 are not limited to this. For example, the expander 14 can also be arranged in the lower part of the vacuum container 110. In addition, the expander 14 can be arranged in a desired posture, and can also be arranged in the vacuum container 110 in a manner that its central axis is consistent with the inclined direction or the horizontal direction.

[0028] The refrigerator cylinder 16 has a Figure 1 and Figure 2 The first cylinder body 16a and the second cylinder body 16b are provided in series with the first cylinder body 16a in the axial direction. As an example, the first cylinder body 16a and the second cylinder body 16b are cylindrical components, and the diameter of the second cylinder body 16b is smaller than the diameter of the first cylinder body 16a. The first cylinder body 16a and the second cylinder body 16b are coaxially arranged, and the lower end of the first cylinder body 16a and the upper end of the second cylinder body 16b are rigidly connected together.

[0029] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b. As an example, the first displacer 18a and the second displacer 18b are cylindrical members, and the diameter of the second displacer 18b is smaller than that of the first displacer 18a. The first displacer 18a and the second displacer 18b are coaxially arranged.

[0030] The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a can reciprocate in the axial direction along the first cylinder 16a, and the second displacer 18b can reciprocate in the axial direction along the second cylinder 16b. The first displacer 18a and the second displacer 18b are connected to each other so as to move integrally.

[0031] In this specification, in order to explain the positional relationship between the components of the ultra-low temperature refrigerator 10, for the sake of convenience, the side close to the upper dead point of the axial reciprocating movement of the displacer is marked as "up", and the side close to the lower dead point is marked as "down". The upper dead point is the position of the displacer when the volume of the expansion space becomes the maximum, and the lower dead point is the position of the displacer when the volume of the expansion space becomes the minimum. When the ultra-low temperature refrigerator 10 is running, a temperature gradient is generated in which the temperature decreases from the upper axial side to the lower axial side, so the upper side can also be called the high temperature side, and the lower side can be called the low temperature side.

[0032] The first displacer 18a accommodates the first cold storage device 26. The first cold storage device 26 is formed by filling a metal wire mesh such as copper or other appropriate first cold storage material in the cylindrical main body of the first displacer 18a. The upper cover and the lower cover of the first displacer 18a can be provided as components different from the main body of the first displacer 18a, and the upper cover and the lower cover of the first displacer 18a can be fixed to the main body by an appropriate method such as fastening and welding, so that the first cold storage material is accommodated in the first displacer 18a.

[0033] Similarly, the second displacer 18b accommodates the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacer 18b with a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other appropriate second cold storage material. The second cold storage material may also be formed into a granular form. The upper cover and the lower cover of the second displacer 18b may be provided as components different from the main body of the second displacer 18b, and the upper cover and the lower cover of the second displacer 18b may be fixed to the main body by an appropriate method such as fastening or welding, whereby the second cold storage material is accommodated in the second displacer 18b.

[0034] The displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. In order to perform heat exchange with a desired object or medium to be cooled by the ultra-low temperature refrigerator 10, the expander 14 is provided with a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper cover portion of the first displacer 18a and the upper portion of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover portion of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower cover portion of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower portion of the first cylinder 16a in a manner surrounding the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower portion of the second cylinder 16b in a manner surrounding the second expansion chamber 34. The first cooling stage 33 and the second cooling stage 35 are made of, for example, pure copper (eg, oxygen-free copper, tough pitch copper, etc.) or other high thermal conductivity metals.

[0035] The first regenerator 26 is communicated with the upper chamber 30 through a working gas flow path 36a formed on the upper cover portion of the first displacer 18a, and is communicated with the first expansion chamber 32 through a working gas flow path 36b formed on the lower cover portion of the first displacer 18a. The second regenerator 28 is communicated with the first regenerator 26 through a working gas flow path 36c formed from the lower cover portion of the first displacer 18a to the upper cover portion of the second displacer 18b. Furthermore, the second regenerator 28 is communicated with the second expansion chamber 34 through a working gas flow path 36d formed on the lower cover portion of the second displacer 18b.

[0036] In order to prevent the working air flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 from being introduced into the gap between the refrigerator cylinder 16 and the displacer assembly 18 and being introduced into the first cold storage device 26 and the second cold storage device 28, a first seal 38a and a second seal 38b may be provided. The first seal 38a may be installed on the upper cover of the first displacer 18a in a manner arranged between the first displacer 18a and the first cylinder 16a. The second seal 38b may also be installed on the upper cover of the second displacer 18b in a manner arranged between the second displacer 18b and the second cylinder 16b.

[0037] Furthermore, the expander 14 includes a pressure switching valve 40 and a drive motor 42. The pressure switching valve 40 is accommodated in the refrigerator casing 20, and the drive motor 42 is attached to the refrigerator casing 20.

[0038] like Figure 2 As shown, the pressure switching valve 40 is constructed to include a high-pressure valve 40a and a low-pressure valve 40b and to generate periodic pressure fluctuations in the refrigeration machine cylinder 16. The working gas outlet of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the working gas intake of the compressor 12 is connected to the upper chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are constructed to selectively open and close alternately (that is, while one valve is open, the other valve is closed). High-pressure (for example, 2 to 3 MPa) working gas is supplied from the compressor 12 to the expander 14 through the high-pressure valve 40a, and low-pressure (for example, 0.5 to 1.5 MPa) working gas is recovered from the expander 14 to the compressor 12 through the low-pressure valve 40b. For ease of understanding, in Figure 2 The arrows in the figure indicate the flow direction of the working gas.

[0039] The drive motor 42 is provided to drive the displacer assembly 18 to reciprocate. The drive motor 42 is connected to the displacer drive shaft 44 via a motion conversion mechanism 43 such as a scotch yoke mechanism. Similar to the pressure switching valve 40, the motion conversion mechanism 43 is also accommodated in the refrigerator housing 20. The displacer drive shaft 44 extends toward the upper chamber 30 after passing through the refrigerator housing 20 from the motion conversion mechanism 43, and is fixed to the upper cover portion of the first displacer 18a. In order to prevent leakage of the working gas from the upper chamber 30 to the refrigerator housing 20 (sometimes maintained at a low pressure as described above), a third seal 38c is provided. The third seal 38c can be installed in the refrigerator housing 20 in a manner arranged between the refrigerator housing 20 and the displacer drive shaft 44.

[0040] When the drive motor 42 is driven, the rotation output of the drive motor 42 is converted by the motion conversion mechanism 43 into axial reciprocating movement of the displacer drive shaft 44, and the displacer assembly 18 reciprocates in the axial direction in the refrigerator cylinder 16. In addition, the drive motor 42 is connected to the high-pressure valve 40a and the low-pressure valve 40b in a manner that selectively opens and closes these valves alternately.

[0041] When the compressor 12 and the drive motor 42 are running, the ultra-low temperature refrigerator 10 generates periodic volume changes and pressure changes of the working gas synchronized therewith in the first expansion chamber 32 and the second expansion chamber 34, thereby forming a refrigeration cycle, and the first cooling stage 33 and the second cooling stage 35 are cooled to the desired ultra-low temperature. The first cooling stage 33 can be cooled to a first cooling temperature in the range of, for example, about 20K to about 40K. The second cooling stage 35 can be cooled to a second cooling temperature (for example, about 1K to about 4K) lower than the first cooling temperature.

[0042] It is known that in addition to the first cooling stage 33 and the second cooling stage 35 being able to absorb heat, the expander 14 can also absorb heat on the refrigerator cylinder 16 (for example, the axial middle part of the second cylinder 16b). This heat absorbing portion 46 is cooled to a cooling temperature based on the axial temperature distribution on the refrigerator cylinder 16 (for example, the second cylinder 16b) and the axial position of the heat absorbing portion 46, and a certain refrigeration capacity can be provided by the cooling temperature. The cooling temperature of the heat absorbing portion 46 becomes a temperature between the first cooling temperature of the first cooling stage 33 and the second cooling temperature of the second cooling stage 35. The heat absorbing portion 46 can be located in the range of, for example, 1 / 4 to 3 / 4 of the normalized axial position on the second cylinder 16b (that is, the axial position with a dimension of 1 with the positions of the first cooling stage 33 and the second cooling stage 35 being set to 0 and 1 respectively).

[0043] In a common use scenario of the cryogenic refrigerator 10, the object to be cooled is thermally connected to either the first cooling stage 33 or the second cooling stage 35 for cooling according to the desired cooling temperature. The heat absorbing portion 46 on the second cylinder 16b is not connected to anything, so the cooling capacity of the heat absorbing portion 46 is not utilized.

[0044] If the refrigeration capacity of the heat absorbing part 46 can be utilized in addition to the refrigeration capacity of the two cooling stages, more effective cooling of the ultra-low temperature system 100 can be achieved. However, the heat input to the heat absorbing part 46 may affect the cooling temperature of the cooling stage (for example, the second cooling stage 35) (a large amount of heat input to the heat absorbing part 46 may cause the temperature of the second cooling stage 35 to rise). Generally, in the ultra-low temperature system 100, in order to maintain the object to be cooled at the desired cooling temperature, it is necessary to operate the ultra-low temperature refrigerator 10 in such a way that the temperature of the cooling stage does not exceed a preset limit temperature. The reason why cooling using the heat absorbing part 46 has not been used so far is that there is a risk of heating the cooling stage due to the heat input to the heat absorbing part 46.

[0045] As described in detail below, the present inventors have found that by keeping the temperature of the heat absorbing portion 46 below a certain upper limit temperature, the temperature rise of the second cooling stage 35 can be prevented or minimized. From this point of view, in this embodiment, the ultra-low temperature system 100 is configured to control the heat source so as to optimize the amount of heat input from the heat source (i.e., the object to be cooled) to the heat absorbing portion 46. The optimization of the amount of heat is achieved by keeping the temperature of the heat absorbing portion 46 below the upper limit temperature.

[0046] Figure 3 (a) and (b) are graphs showing the experimental results conducted by the inventors involved in the embodiment. In this experiment, a heater for simulating the heat input to the heat absorption part 46 is provided on the heat absorption part 46. The position of the heater (in other words, the position of the heat absorption part 46) is located slightly on the low temperature side relative to the axial center, specifically, at a position of about 0.54 of the normalized axial position on the second cylinder 16b (as described above, the first cooling stage 33 is set to 0 and the second cooling stage 35 is set to 1). In addition, in order to apply a heat load (for example, a rated heat load of 1.5W), a heater is also provided on the second cooling stage 35. The ultra-low temperature refrigerator 10 operates in a manner that maintains the first cooling stage 33 at a constant temperature (for example, 43K) while applying a rated heat load to the second cooling stage 35.

[0047] exist Figure 3(a) shows the relationship between the normalized heater output representing the amount of heat input to the heat absorbing portion 46 and the temperature rise of the second cooling stage 35. The temperature rise of the second cooling stage 35 represents the temperature rise relative to the target cooling temperature (for example, 4K) of the second cooling stage 35. Figure 3 (b) shows the relationship between the normalized axial position and temperature on the second cylinder 16b, that is, how the axial temperature distribution on the second cylinder 16b changes according to the normalized heater output. Figure 3 In (a) and (b), the temperature measurement results when the normalized heater output is zero (i.e., no heat is input to the heat absorption portion 46) are indicated by circular marks, and the temperature measurement results when the normalized heater output is 0.085, 0.31, and 0.45, respectively, are indicated by square marks, triangle marks, and diamond marks.

[0048] refer to Figure 3 As shown in (a), when the normalized heater output is zero, the temperature of the second cooling stage 35 rises to 0K (circle mark), and as the normalized heater output increases to 0.085, 0.31, and 0.45, the temperature rise of the second cooling stage 35 also increases (square, triangle, and diamond mark). Specifically, when the normalized heater output is 0.085, the temperature rise is about 0.04K (square mark), when the normalized heater output is 0.31, the temperature rise is about 0.09K (triangle mark), and when the normalized heater output is 0.45, the temperature rise is about 0.17K (diamond mark).

[0049] According to the knowledge and experience of the present inventors, in some applications of the ultra-low temperature refrigerator 10 in which the target cooling temperature of the second cooling stage 35 is set to about 4K (for example, liquid helium cooling, etc.), in many cases, it is preferred to set the allowable value of the temperature rise of the second cooling stage 35 to not more than about 0.1K and not more than about 0.2K at most.

[0050] from Figure 3 From (a), we can see that Figure 3 The normalized heater output threshold value Th1 indicated by the dotted line in (a) represents an important boundary. If the amount of heat input to the heat absorbing portion 46 is lower than the threshold value Th1, the temperature rise of the second cooling stage 35 is suppressed to a relatively small value within about 0.1 K. On the other hand, if the amount of heat input to the heat absorbing portion 46 exceeds the threshold value Th1, the temperature rise state of the second cooling stage 35 changes, and becomes larger in proportion to the increase in the normalized heater output, and easily exceeds 0.2 K.

[0051] refer to Figure 3In (b), the relationship between the normalized heater output and the temperature of the heat absorbing portion 46 (the temperature at the normalized axial position of about 0.54) can be understood. It can be seen that when the normalized heater output is zero, the temperature of the heat absorbing portion 46 is about 8K (circular mark), and as the normalized heater output increases to 0.085, 0.31 and 0.45, the temperature of the heat absorbing portion 46 also increases (square mark, triangle mark, diamond mark). More specifically, when the normalized heater output is 0.085, the temperature of the heat absorbing portion 46 is about 13K (square mark), when the normalized heater output is 0.31, the temperature of the heat absorbing portion 46 is about 20K (triangle mark), and when the normalized heater output is 0.45, the temperature of the heat absorbing portion 46 is about 24K (diamond mark).

[0052] Figure 3 The dotted line L1 shown in (b) is a straight line connecting the measured temperature of the first cooling stage 33 and the measured temperature of the second cooling stage 35. Figure 3 As can be seen from (a) and (b), it is important that the temperature of the heat absorbing portion 46 at the normalized heater output threshold Th1 is located on or near the straight line L1 ( Figure 3 between the diamond mark and the triangle mark in (b).

[0053] Therefore, if the amount of heat input to the heat absorbing portion 46 is large (i.e., exceeds the threshold value Th1) and causes the temperature of the heat absorbing portion 46 to exceed the upper limit temperature of the straight line L1 or its vicinity, the second cooling stage 35 may experience a significant temperature rise due to the heat input to the heat absorbing portion 46. Furthermore, if the amount of heat input to the heat absorbing portion 46 is such that the temperature of the heat absorbing portion 46 does not exceed the upper limit temperature, the temperature rise of the second cooling stage 35 caused by the heat input to the heat absorbing portion 46 does not substantially occur or can be controlled within an allowable range (e.g., within 0.2K or preferably within 0.1K).

[0054] Figure 4 (a) and (b) are graphs showing the experimental results performed by the inventors according to the embodiments. Figure 3 Compared with the experimental results of (a) and (b), Figure 4 The experimental results shown in (a) and (b) are obtained after changing the axial position of the heat absorbing portion 46, and the other experimental conditions are the same. Figure 4 In (a) and (b), Figure 3 (a) and Figure 3 Compared with (b), the heat absorbing portion 46 is located on the high temperature side, specifically, at a position of about 0.35 of the normalized axial position on the second cylinder block 16 b.

[0055] and Figure 3 (a) Similarly, in Figure 4 (a) shows the relationship between the normalized heater output representing the amount of heat input to the heat absorbing portion 46 and the temperature rise of the second cooling stage 35. Figure 3 (b) Similarly, in Figure 4 (b) shows the relationship between the normalized axial position and temperature on the second cylinder 16b. Figure 4 In (a) and (b), the temperature measurement results when the normalized heater output is zero (i.e., no heat is input to the heat absorption portion 46) are indicated by circular marks, and the temperature measurement results when the normalized heater output is 0.31, 0.55, and 0.72, respectively, are indicated by square marks, triangle marks, and diamond marks.

[0056] refer to Figure 4 It can be seen from (a) that when the normalized heater output is zero, there is no temperature rise of the second cooling stage 35 (circular mark), and as the normalized heater output increases, the temperature rise of the second cooling stage 35 also increases. Specifically, when the normalized heater output is 0.31, the temperature rise is about 0.02K (square mark), when the normalized heater output is 0.55, the temperature rise is about 0.07K (triangle mark), and when the normalized heater output is 0.72, the temperature rise is about 0.09K (diamond mark). Figure 4 In (a), Figure 3 Compared with (a), since the heat absorbing portion 46 is located on the high temperature side, the temperature rise of the second cooling stage 35 caused by the increase in the amount of heat input to the heat absorbing portion 46 is weakened.

[0057] exist Figure 4 In (a), the normalized heater output threshold value Th2 indicated by the dotted line becomes an important boundary. If the amount of heat input to the heat absorbing portion 46 is lower than the threshold value Th2, the temperature rise of the second cooling stage 35 is suppressed to a very small value within about 0.02 K. On the other hand, if the amount of heat input to the heat absorbing portion 46 exceeds the threshold value Th2, the temperature rise state of the second cooling stage 35 changes and becomes larger in proportion to the normalized heater output.

[0058] refer to Figure 4In (b), the relationship between the normalized heater output and the temperature of the heat absorbing portion 46 (the temperature at the normalized axial position of about 0.35) can be grasped. When the normalized heater output is zero, the temperature of the heat absorbing portion 46 is about 16K (circular mark), and as the normalized heater output increases, the temperature of the heat absorbing portion 46 also rises. Specifically, when the normalized heater output is 0.31, the temperature of the heat absorbing portion 46 is about 27K (square mark), when the normalized heater output is 0.55, the temperature of the heat absorbing portion 46 is about 33K (triangle mark), and when the normalized heater output is 0.72, the temperature of the heat absorbing portion 46 is about 38K (diamond mark).

[0059] Figure 4 The dotted line L2 shown in (b) is a straight line connecting the measured temperature of the first cooling stage 33 and the measured temperature of the second cooling stage 35. Figure 4 As can be seen from (a) and (b), the temperature of the heat absorbing portion 46 at the normalized heater output threshold Th2 is located on or near the straight line L2 ( Figure 4 between the square mark and the triangle mark in (b).

[0060] Therefore, if the amount of heat input to the heat absorbing portion 46 is large (i.e., exceeds the threshold value Th2) and causes the temperature of the heat absorbing portion 46 to exceed the upper limit temperature of the straight line L2 or its vicinity, the second cooling stage 35 may experience a significant temperature rise due to the heat input to the heat absorbing portion 46. Furthermore, it can be considered that if the amount of heat input to the heat absorbing portion 46 is such that the temperature of the heat absorbing portion 46 does not exceed the upper limit temperature, the temperature rise of the second cooling stage 35 caused by the heat input to the heat absorbing portion 46 will not substantially occur or can be controlled within an allowable range.

[0061] Apart from Figure 3 Medium (a) to Figure 4 In addition to the experimental results shown in (b) above, the inventors conducted the same experiment by changing the axial position of the heat absorbing portion 46 and the temperature of the first cooling stage 33 to various conditions. As a result, the inventors confirmed that the same trend as the above results was observed in both the relationship between the amount of heat input to the heat absorbing portion 46 and the temperature rise of the second cooling stage 35 and the relationship between the normalized axial position and the temperature on the second cylinder 16b.

[0062] Therefore, in order to prevent or minimize the temperature increase of the second cooling stage 35 caused by the heat input to the heat absorption part 46, the upper limit temperature of the heat absorption part 46 can be set according to the measured temperatures at both ends of the second cylinder 16b and the axial position of the heat absorption part 46.

[0063] In an exemplary method, the upper limit temperature of the heat absorbing portion 46 may be set based on the reference temperature distribution of the second cylinder 16b and the axial position of the heat absorbing portion 46. Here, the reference temperature distribution of the second cylinder 16b may be a temperature distribution having a first measured temperature at an axial end portion on one side of the second cylinder 16b (e.g., the first cooling stage 33) and a second measured temperature at an axial end portion on the other side of the second cylinder 16b (e.g., the second cooling stage 35), and linearly changing according to the axial position in the second cylinder 16b.

[0064] An exemplary structure for optimizing the amount of heat input to the heat absorbing portion 46 will be described below. Figure 1 It can be seen that the cryogenic refrigerator 10 includes a first temperature sensor 51 , a second temperature sensor 52 , a third temperature sensor 53 , and a controller 60 .

[0065] The first temperature sensor 51 measures the first measured temperature T1 at the axial end of the second cylinder 16b on the side close to the first cylinder 16a. The first temperature sensor 51 can be provided on the first cooling stage 33, so that the first measured temperature T1 can be measured at the first cooling stage 33. The second temperature sensor 52 measures the second measured temperature T2 at the axial end of the other side of the second cylinder 16b away from the first cylinder 16a. The second temperature sensor 52 can be provided on the second cooling stage 35, so that the second measured temperature T2 can be measured at the second cooling stage 35. The third temperature sensor 53 is provided on the heat absorbing portion 46, so that the third measured temperature T3 can be measured at the heat absorbing portion 46.

[0066] The controller 60 is communicatively connected to the first temperature sensor 51 , the second temperature sensor 52 , and the third temperature sensor 53 , and can receive the first measured temperature T1 , the second measured temperature T2 , and the third measured temperature T3 from these temperature sensors, respectively.

[0067] The internal structure of the controller 60 is realized in terms of hardware structure by components or circuits represented by a CPU (Central Processing Unit) or a memory of a computer, and in terms of software structure by computer programs, etc. However, in the figure, the functional blocks realized by their cooperation are appropriately depicted. It should be understood by those skilled in the art that these functional blocks can be realized in various forms by a combination of hardware and software.

[0068] The ultra-low temperature system 100 is provided with a refrigerant gas pipeline 118 cooled by the ultra-low temperature refrigerator 10. The refrigerant gas in the refrigerant gas pipeline 118 is condensed by cooling, thereby generating an ultra-low temperature liquid 102. The refrigerant gas pipeline 118 is provided with a supply pipeline 120 for supplying the ultra-low temperature liquid 102 to the inner tank 114 of the vacuum container 110 and a return pipeline 122 for the ultra-low temperature liquid 102 (i.e., refrigerant gas) gasified in the inner tank 114. The supply pipeline 120 and the return pipeline 122 can be rigid or flexible pipes for the refrigerant gas to flow through, respectively.

[0069] The supply line 120 includes a first heat exchanger 124 , a second heat exchanger 126 , and a recondensing unit 128 . In the supply line 120 , the refrigerant gas flows through the first heat exchanger 124 , the second heat exchanger 126 , and the recondensing unit 128 in this order.

[0070] The first heat exchanger 124 is configured to be disposed outside the first cooling stage 33 in the inner tank 114, and precool the refrigerant gas to the first cooling temperature by heat exchange between the first cooling stage 33 and the refrigerant gas. The second heat exchanger 126 is configured to be disposed outside the second cylinder 16b in the inner tank 114, and precool the refrigerant gas to the cooling temperature of the heat absorbing portion 46 by heat exchange between the heat absorbing portion 46 of the second cylinder 16b and the refrigerant gas.

[0071] The recondensation part 128 becomes the outlet of the supply pipeline 120 leading to the inner tank 114. The recondensation part 128 is configured to be arranged on the outer side of the second cooling stage 35 in the inner tank 114, and the refrigerant gas is cooled to the second cooling temperature by the heat exchange between the second cooling stage 35 and the refrigerant gas, so that the refrigerant gas is recondensed into the ultra-low temperature liquid 102. As described above, the ultra-low temperature liquid 102 after recondensation is stored in the inner tank 114. As shown in the figure, the recondensation part 128 can be formed as one body with the second cooling stage 35, and in order to increase the surface area in contact with the refrigerant gas or the ultra-low temperature liquid 102, it can also have a convex protrusion or concave-convex. Similar to the second cooling stage 35, the recondensation part 128 is, for example, made of pure copper (for example, oxygen-free copper, tough copper, etc.) or other high thermal conductivity metals.

[0072] Furthermore, the refrigerant gas pipeline 118 is provided with a flow regulator 130, which is configured to regulate the refrigerant gas flow rate of the refrigerant gas pipeline 118. In the illustrated example, the flow regulator 130 is provided on the refrigerant gas pipeline 118, and connects the return pipeline 122 to the supply pipeline 120. The flow regulator 130 receives the refrigerant gas from the return pipeline 122, regulates the refrigerant gas flow rate, and delivers the refrigerant gas to the supply pipeline 120 at the regulated flow rate. The flow regulator 130 may be a circulating flow generator (e.g., a pump, a compressor, etc.) or a mechanism for regulating the gas flow rate (e.g., a flow regulating valve, a variable throttle, etc.).

[0073] The flow regulator 130 may be disposed outside the vacuum container 110 as shown, or may be disposed inside the vacuum container 110. Furthermore, the flow regulator 130 may be disposed at any position on the refrigerant gas pipeline 118, may be disposed on the supply pipeline 120, or may be disposed on the return pipeline 122.

[0074] As described later, the flow rate regulator 130 can regulate the flow rate of the refrigerant gas circulating in the refrigerant gas pipeline 118 under the control of the controller 60. The amount of heat input from the refrigerant gas pipeline 118 to the heat absorption unit 46 is controlled by the flow rate regulation.

[0075] The refrigerant gas pipeline 118 is used as a heat source of the ultra-low temperature refrigerator 10. The heat source includes a first portion (e.g., a first heat exchanger 124), a second portion (e.g., a recondensing portion 128), and a third portion (e.g., a second heat exchanger 126) connecting the first portion and the second portion. An axial end portion of one side of the second cylinder 16b (e.g., the first cooling stage 33) is thermally connected to the first portion of the heat source, and an axial end portion of the other side of the second cylinder 16b (e.g., the second cooling stage 35) is thermally connected to the second portion of the heat source. The heat absorbing portion 46 is thermally connected to the third portion of the heat source. The refrigerant gas pipeline 118 passes through the first portion, the third portion, and the second portion of the heat source in sequence.

[0076] Figure 5 1 is a flow chart showing a control method of the ultra-low temperature system 100 according to the embodiment. The method includes the following steps: obtaining a first measured temperature T1 from a first temperature sensor 51, obtaining a second measured temperature T2 from a second temperature sensor 52, and obtaining a third measured temperature T3 from a third temperature sensor 53 (S10); setting an upper limit temperature of the heat absorbing part 46 according to the first measured temperature T1, the second measured temperature T2, and the axial position of the heat absorbing part 46 (S20); and controlling a heat source (i.e., a refrigerant gas pipeline 118) so that the third measured temperature T3 becomes lower than the upper limit temperature of the heat absorbing part 46 (S30).

[0077] In S10, at the axial end portion (for example, the first cooling stage 33) on one side of the second cylinder 16b close to the first cylinder 16a, the first temperature T1 is measured by the first temperature sensor 51. A signal indicating the first measured temperature T1 is input from the first temperature sensor 51 to the controller 60. Furthermore, at the axial end portion on the other side of the second cylinder 16b away from the first cylinder 16a, the second measured temperature T2 is measured by the second temperature sensor 52. A signal indicating the second measured temperature T2 is input from the second temperature sensor 52 to the controller 60. At the heat absorbing portion 46, the third measured temperature T3 is measured by the third temperature sensor 53. A signal indicating the third measured temperature T3 is input from the third temperature sensor 53 to the controller 60.

[0078] In S20, first, the controller 60 determines the reference temperature distribution of the second cylinder 16b based on the first measured temperature T1 and the second measured temperature T2. The reference temperature distribution is a temperature distribution that has the first measured temperature T1 at the axial end of one side of the second cylinder 16b and the second measured temperature T2 at the axial end of the other side of the second cylinder 16b and changes linearly according to the axial position in the second cylinder 16b. On the XY plane where the normalized axial position on the second cylinder 16b is set as the X axis and the temperature is set as the Y axis, the reference temperature distribution becomes a straight line passing through the two points (0, T1) and (1, T2) (Y = (T2-T1)X+T1).

[0079] The controller 60 sets the upper limit temperature of the heat absorbing portion 46 based on the reference temperature distribution and the axial position of the heat absorbing portion 46. By substituting the normalized position in the axial direction of the heat absorbing portion 46 into the above formula representing the reference temperature distribution, a candidate value of the upper limit temperature of the heat absorbing portion 46 is obtained. The controller 60 can adopt the candidate value as the upper limit temperature.

[0080] Alternatively, when emphasis is placed on reliably preventing a temperature increase of the second cooling stage 35 due to heat input into the heat absorption section 46, the controller 60 may adopt a value slightly smaller than the candidate value (for example, a value selected from a range of 70 to 100% or 80 to 100% or 90 to 100% of the candidate value) as the upper limit temperature of the heat absorption section 46.

[0081] Alternatively, while allowing a certain degree of temperature increase of the second cooling stage 35 due to the heat input to the heat absorption section 46, the controller 60 may adopt a value slightly larger than the candidate value (for example, a value selected from the range of 100 to 130% or 100 to 120% or 100 to 110% of the candidate value) as the upper limit temperature of the heat absorption section 46.

[0082] In S30, the controller 60 controls the refrigerant gas flow rate of the refrigerant gas pipeline 118 so that the third measured temperature T3 becomes equal to or lower than the upper limit temperature of the heat absorbing portion 46. An example of this control will be described later. Figure 6 Give a narrative.

[0083] The controller 60 may periodically repeat Figure 5 The processing shown in the figure is performed to update the upper limit temperature of the heat absorbing part 46 according to the first measured temperature T1 and the second measured temperature T2. Furthermore, when the cryogenic refrigerator 10 is operated in a manner that the cooling temperature of the first cooling stage 33 (and / or the second cooling stage 35) is maintained at a certain target temperature, the reference temperature distribution remains substantially unchanged unless the target temperature is changed. In this case, once the upper limit temperature of the heat absorbing part 46 is set, it can be continuously used thereafter.

[0084] Figure 6 Yes means Figure 5 1 is a flowchart of an example of a control process (S30) of the refrigerant gas pipeline 118 shown in FIG. In this process, the controller 60 controls the flow regulator 130 of the refrigerant gas pipeline 118 based on the comparison between the third measured temperature T3 and the upper limit temperature of the heat absorption part 46, thereby controlling the refrigerant gas flow rate of the refrigerant gas pipeline 118. During the operation of the cryogenic refrigerator 10, the controller 60 repeatedly executes this process at a predetermined cycle.

[0085] Therefore, if Figure 6 As shown, first, the controller 60 compares the third measured temperature T3 with the upper limit temperature T of the heat absorbing portion 46. lim As described above, the third temperature sensor 53 measures the third measured temperature T3 ( Figure 5 The upper limit temperature of the heat absorbing portion 46 is set according to the measured temperatures at both ends of the second cylinder 16b and the axial position of the heat absorbing portion 46 ( Figure 5 S20).

[0086] The controller 60 compares the third measured temperature T3 with the upper limit temperature T lim The controller 60 compares the temperature T3 and the upper limit temperature T4 to determine the relative magnitude of the temperature. lim (ii) The third measured temperature T3 is lower than the upper limit temperature T lim ; and (iii) the third measured temperature T3 and the upper limit temperature T lim equal.

[0087] The controller 60 controls the flow rate regulator 130 based on the comparison result. Specifically, (i) when the third measured temperature T3 is higher than the upper limit temperature T limWhen the third measured temperature T3 is lower than the upper limit temperature T3, the controller 60 controls the flow regulator 130 to reduce the refrigerant gas flow rate (S32). As a result, the amount of heat input from the second heat exchanger 126 to the heat absorbing portion 46 can be reduced, thereby lowering the third measured temperature T3. lim When the third measured temperature T3 is equal to the upper limit temperature T4, the controller 60 controls the flow regulator 130 to increase the refrigerant gas flow rate (S33). As a result, the heat input from the second heat exchanger 126 to the heat absorption part 46 can be increased, so that the refrigerant gas pipeline 118 can be cooled more efficiently. lim When the refrigerant gas flow rate is equal, there is no need to increase or decrease the refrigerant gas flow rate, so the controller 60 controls the flow regulator 130 to maintain the current refrigerant gas flow rate. In addition, the situation (iii) can be included in any one of (i) or (ii).

[0088] As described above, according to the embodiment, in addition to using the first cooling stage 33 and the second cooling stage 35 to cool the refrigerant gas pipeline 118, the refrigeration capacity of the heat absorbing portion 46 on the second cylinder 16b can also be used to cool the refrigerant gas pipeline 118. Compared with a typical cooling structure that does not use the heat absorbing portion 46, the ultra-low temperature system 100 can be cooled more efficiently.

[0089] Furthermore, in the embodiment, the upper limit temperature T of the heat absorbing portion 46 is set based on the first measured temperature T1, the second measured temperature T2, and the axial position of the heat absorbing portion 46. lim , and controls the heat source (e.g., the refrigerant gas pipeline 118) of the cryogenic refrigerator 10 in the cryogenic system 100 so that the third measured temperature T3 becomes the upper limit temperature T lim In this way, by keeping the temperature of the heat absorbing portion 46 at the upper limit temperature T lim Thereby, the temperature increase of the second cooling stage 35 can be prevented or minimized.

[0090] Furthermore, in the embodiment, the upper limit temperature T lim Based on the above-mentioned linear reference temperature distribution and the axial position of the heat absorbing portion 46, even if the temperatures of the first cooling stage 33 and the second cooling stage 35 vary according to various operating conditions of the cryogenic refrigerator 10, or the heat absorbing portion 46 is set at various axial positions, the upper limit temperature T can be clearly and easily determined. lim .

[0091] Figure 7 This is a diagram schematically showing a cryogenic system 100 according to another embodiment. Figure 7 The ultra-low temperature system 100 shown is Figure 1The difference of the ultra-low temperature system 100 shown is the object to be cooled, and the rest of the parts are substantially the same. Hereinafter, the different structures will be described with emphasis, and the same structures will be described briefly or omitted.

[0092] In the above embodiment, the case where the cryogenic system 100 is a storage device for the cryogenic liquid 102 is described as an example, but other structures may be adopted. For example, the cryogenic system 100 may also be applied to superconducting equipment, and the cryogenic refrigerator 10 may be used to cool the superconducting coil 150 disposed in the vacuum container 110 and the current lead 152 for supplying power to the superconducting coil 150. The superconducting coil 150 is cooled by the second cooling stage 35, and the current lead 152 is cooled by the first cooling stage 33, the heat absorbing portion 46, and the second cooling stage 35.

[0093] The current lead 152 electrically connects the power source 154 disposed outside the vacuum container 110 to the superconducting coil 150, and forms a current path from the power source 154 to the superconducting coil 150. Therefore, the current lead 152 can generate heat when energized, and thus serves as a heat source for the cryogenic refrigerator 10. The current lead 152 includes a first portion 152a, a second portion 152b, and a third portion 152c connecting the first portion 152a and the second portion 152b.

[0094] The axial end portion on one side of the second cylinder 16b (e.g., the first cooling stage 33) is thermally connected to the first portion 152a of the current lead 152, and the axial end portion on the other side of the second cylinder 16b (e.g., the second cooling stage 35) is thermally connected to the second portion 152b of the current lead 152. The heat absorbing portion 46 is thermally connected to the third portion 152c of the current lead 152.

[0095] As an example of thermal connection, the first cooling stage 33 may be connected to the first portion 152a of the current lead 152 via the first heat transfer member 156, and the second cooling stage 35 may be connected to the second portion 152b of the current lead 152 via the second heat transfer member 158. Furthermore, the second cooling stage 35 may be connected to the superconducting coil 150 via the second heat transfer member 158. The heat absorbing portion 46 of the second cylinder 16b may be connected to the third portion 152c of the current lead 152 via the thermal bridge 160.

[0096] Controller 60 is configured to control the current of current lead 152 so that third measured temperature T3 is equal to or lower than the upper limit temperature. Controller 60 may control power supply 154 based on comparison between third measured temperature T3 and the upper limit temperature of heat absorbing portion 46 to control the current of current lead 152 .

[0097] As an example, (i) when the third measured temperature T3 is higher than the upper limit temperature T lim, the controller 60 controls the power supply 154 to reduce the current of the current lead 152. As a result, the amount of heat input from the second heat exchanger 126 to the heat absorbing portion 46 can be reduced, thereby lowering the third measured temperature T3. (ii) When the third measured temperature T3 is lower than the upper limit temperature T lim , the controller 60 controls the power supply 154 to increase the current of the current lead 152. As a result, the amount of heat input from the second heat exchanger 126 to the heat absorbing portion 46 can be increased, thereby cooling the current lead 152 more efficiently. (iii) When the third measured temperature T3 is equal to the upper limit temperature T lim When they are equal, there is no need to increase or decrease the current of the current lead 152, so the controller 60 controls the power supply 154 to maintain the current.

[0098] In this way, in addition to using the first cooling stage 33 and the second cooling stage 35 to cool the current lead 152, the cooling capacity of the heat absorbing portion 46 on the second cylinder 16b can also be used to cool the current lead 152. Compared with a typical cooling structure that does not use the heat absorbing portion 46, the cryogenic system 100 can be cooled more efficiently. By keeping the temperature of the heat absorbing portion 46 at the upper limit temperature T lim Thereby, the temperature increase of the second cooling stage 35 can be prevented or minimized.

[0099] The present invention has been described above based on the embodiments. The present invention is not limited to the above-mentioned embodiments. It should be understood by those skilled in the art that the present invention can be subjected to various design changes, and various modifications can exist, and these modifications are also included in the scope of the present invention. Various features described in one embodiment can also be applied to other embodiments. The new embodiment generated by the combination has the effects of each of the combined embodiments.

[0100] In the above embodiment, one temperature sensor (third temperature sensor 53) is provided to measure the temperature of the heat absorbing portion 46, but other structures may be adopted. In one embodiment, the temperature of the heat absorbing portion 46 may be measured at a plurality of temperature measurement positions. Therefore, a plurality of temperature sensors (for example, two third temperature sensors 53) may be provided on the heat absorbing portion 46. These temperature sensors are provided at different axial positions on the second cylinder 16b. As an example, one third temperature sensor 53 is arranged on the high temperature side relative to the other third temperature sensor 53.

[0101] At this time, the controller 60 can set the upper limit temperature for each temperature measurement position (temperature sensor) according to the measured temperatures at both ends of the second cylinder 16b and the temperature measurement position. The controller 60 can control the heat source so that any of the multiple measured temperatures becomes below the corresponding upper limit temperature.

[0102] In the above embodiment, the ultra-low temperature refrigerator 10 is illustrated as a two-stage GM refrigerator, but other structures may also be used. For example, the ultra-low temperature refrigerator 10 may also be a single-stage GM refrigerator. Alternatively, the ultra-low temperature refrigerator 10 may also be a Solvay refrigerator, a Stirling refrigerator, a pulse tube refrigerator, or other ultra-low temperature refrigerators.

[0103] The present invention has been described above based on the implementation mode and using specific terms, but the implementation mode merely illustrates one aspect of the principle and application of the present invention. The implementation mode allows for a variety of variations or configuration changes without departing from the scope of the idea of ​​the present invention specified in the technical solution.

[0104] Industrial Applicability

[0105] The present invention can be used in the field of ultra-low temperature systems and ultra-low temperature system control methods.

[0106] Explanation of symbols

[0107] 10-ultra-low temperature refrigerator, 16a-first cylinder, 16b-second cylinder, 46-heat absorption part, 51-first temperature sensor, 52-second temperature sensor, 53-third temperature sensor, 60-controller, 100-ultra-low temperature system, 118-refrigerant gas pipeline, 152-current lead.

Claims

1. A cryogenic system, characterized in that: Equipped with ultra-low temperature refrigerator and controller, The ultra-low temperature refrigerator has: Cylinder No. 1; The second cylinder is axially arranged in series with the first cylinder and has a heat absorbing portion in its axial middle portion which is thermally connected to the heat source; a first temperature sensor for measuring a first measured temperature at an axial end portion of the second cylinder body on a side close to the first cylinder body; a second temperature sensor for measuring a second measured temperature at an axial end portion of the second cylinder body on the other side away from the first cylinder body; and a third temperature sensor for measuring a third temperature at the heat absorbing portion; The controller is configured as follows: acquiring the first measured temperature from the first temperature sensor, acquiring the second measured temperature from the second temperature sensor, and acquiring the third measured temperature from the third temperature sensor, The upper limit temperature of the heat absorbing portion is set according to the first measured temperature, the second measured temperature and the axial position of the heat absorbing portion. The heat source is controlled so that the third measurement temperature becomes equal to or lower than an upper limit temperature of the heat absorbing portion.

2. The ultra-low temperature system according to claim 1, characterized in that: The controller is configured as follows: determining a reference temperature distribution of the second cylinder, the reference temperature distribution of the second cylinder having the first measured temperature at the axial end of the one side of the second cylinder and the second measured temperature at the axial end of the other side of the second cylinder, and linearly changing according to the axial position in the second cylinder, An upper limit temperature of the heat absorbing portion is set according to the reference temperature distribution and the axial position of the heat absorbing portion.

3. The ultra-low temperature system according to claim 1 or 2, characterized in that: The axial end portion of the second cylinder on the one side is thermally connected to the first portion of the heat source. The other axial end of the second cylinder is thermally connected to the second portion of the heat source. The heat absorbing portion is thermally connected to a third portion of the heat source connecting the first portion and the second portion.

4. The ultra-low temperature system according to claim 3, characterized in that: The heat source includes a refrigerant gas pipeline that passes through the first portion, the third portion, and the second portion in sequence. The controller is configured to control the refrigerant gas flow rate of the refrigerant gas pipeline so that the third measured temperature becomes equal to or lower than the upper limit temperature.

5. The ultra-low temperature system according to claim 3, characterized in that: The heat source includes a current lead that passes through the first portion, the third portion, and the second portion in sequence. The controller is configured to control the current of the current lead so that the third measurement temperature becomes equal to or lower than the upper limit temperature.

6. A control method for a cryogenic system, characterized in that: The ultra-low temperature system comprises an ultra-low temperature refrigerator, wherein the ultra-low temperature refrigerator comprises a first cylinder and a second cylinder which are arranged in series in the axial direction, wherein the second cylinder comprises a heat absorbing portion which is thermally connected to a heat source in the middle part in the axial direction, The method comprises the following steps: measuring a first measured temperature at an axial end portion of the second cylinder body on a side close to the first cylinder body; measuring a second measured temperature at an axial end portion of the second cylinder body on the other side away from the first cylinder body; measuring a third measurement temperature at the heat absorbing portion; setting an upper limit temperature of the heat absorbing portion according to the first measured temperature, the second measured temperature, and the axial position of the heat absorbing portion; and The heat source is controlled so that the third measurement temperature becomes equal to or lower than an upper limit temperature of the heat absorbing portion.

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