Dilution freezer and control method therefor

Abstract

To provide a dilution freezer capable of easily adjusting an amount of circulating helium, and a control method therefor.SOLUTION: A dilution freezer comprises a mechanical freezer 20 having a cold generation unit, and a helium gas circulation path 30 having at least a compressor 31 for compressing helium gas, a purifier 50 for removing impurities from the helium gas, a heat exchanger 33 for exchanging heat with the cold generation unit, and a mixing chamber (38) serving as a low-temperature output unit, all of which are arranged in this order. In the dilution freezer, the purifier has a heater 70 for adjusting a temperature of the purifier. A control method for the dilution freezer causes the cold generation unit and the purifier to come into thermal contact with each other, to control the heater, thereby adjusting the temperature of the purifier, adjusting an amount of helium gas adsorbed onto the purifier, and adjusting an amount of helium gas circulating through the circulation path.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dilution refrigerator that uses helium gas and a control method thereof. [Background technology]

[0002] It is an isotope of helium gas 3 He and 4 Dilution refrigerators that utilize the physical properties of He are known (see, for example, Patent Document 1). He is pre-cooled to a few degrees Kelvin using a mechanical refrigerator, and then liquefied by the Joule-Thomson effect. 3 He is supplied to the mixing chamber, and 3 He 4 By successive dilutions in He, it is possible to achieve extremely low temperatures of around 0.1 K. 3 He gas is expensive, so it is repeatedly used in the circulation path of the dilution refrigerator.

[0003] The helium gas circulation line should be set at a voltage of, for example, 10 to obtain the Joule-Thomson effect. 10 cm -3 A high impedance (for example, a pipe with an inner diameter of 0.05 mm) is attached to this part. Because this part of the impedance is at a low temperature of 4 K or less, it can easily become clogged if there is even a small amount of impurity gas such as air or hydrogen in addition to helium. Therefore, the dilution refrigerator described in Patent Document 1 discloses a structure in which a container filled with an adsorbent such as activated carbon is cooled using the cold heat of a mechanical refrigerator, and this container functions as a purifier in order to remove impurity gases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6432087 Summary of the Invention [Problem to be solved by the invention]

[0005] In a helium-circulating dilution refrigerator, the circulating gas is used to optimize the ability to achieve extremely low temperatures. 3 He and 4 It is sometimes necessary to adjust the He gas ratio or the total amount of circulating helium gas. One method for making these adjustments is to install a buffer tank at any point in the helium circulation path and release or store helium from the buffer tank as needed. However, while buffer tanks are good for large-scale adjustments, they are not necessarily suitable for fine adjustments. In addition, installing a buffer tank can complicate the system configuration, and there are concerns about impurities being introduced when helium gas is taken in and out of the buffer tank. Therefore, there is a need for a method that can easily adjust the amount of circulating helium gas without relying on a buffer tank.

[0006] The present invention has been made in view of the above circumstances, and provides a dilution refrigerator that can easily adjust the amount of circulating helium, and a control method thereof. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration. [1] A method for controlling a dilution refrigerator comprising: a helium gas circulation path including at least a mechanical refrigerator having a cold region generating unit, a compressor that compresses helium gas, a purifier that removes impurities from the helium gas, a heat exchanger that exchanges heat with the cold region generating unit, and a mixing chamber that serves as a low-temperature output unit, these being arranged in this order; and a cold-insulated outer tank that stores the cold region generating unit, the purifier, the heat exchanger, and the mixing chamber in a vacuum-insulated inner space, wherein the purifier has a heater for adjusting the temperature of the purifier, the cold region generating unit and the purifier are in thermal contact with each other, and the heater is located at a position away from the contact point between the purifier and the cold region generating unit, and the method comprises controlling the heater to adjust the temperature of the purifier and adjust the amount of helium gas adsorbed onto the purifier, thereby adjusting the amount of helium gas circulating through the circulation path. [2] The method for controlling a dilution refrigerator according to [1], wherein the purifier has a plurality of purifiers including a first purifier and a second purifier. [3] The method for controlling a dilution refrigerator according to claim 2, wherein the first refiner and the second refiner are each independently in thermal contact with the cold region generating unit, the heater has a first heater and a second heater, the first heater is provided in the first refiner at a position spaced apart from a contact portion between the first refiner and the cold region generating unit, and the second heater is provided in the second refiner at a position spaced apart from a contact portion between the second refiner and the cold region generating unit, and the method comprises adjusting a temperature of the first refiner to be substantially constant and increasing or decreasing a temperature of the second refiner to increase or decrease an amount of helium gas adsorbed in the second refiner, thereby adjusting an amount of helium gas circulating through the circulation path. [4] The method for controlling a dilution refrigerator described in [2], wherein the cold region generating unit has a first cold region generating unit and a second cold region generating unit that generates cold region at a temperature lower than that of the first cold region generating unit, the first purifier is in thermal contact with the first cold region generating unit, and the second purifier is in thermal contact with the second cold region generating unit, the heater has a first heater and a second heater, the first heater is provided in the first purifier at a position spaced apart from a contact portion between the first purifier and the first cold region generating unit, and the second heater is provided in the second purifier at a position spaced apart from a contact portion between the second purifier and the second cold region generating unit, and the method includes adjusting a temperature of the first purifier to be substantially constant and increasing or decreasing a temperature of the second purifier to increase or decrease an amount of helium gas adsorbed in the second purifier, thereby adjusting an amount of helium gas circulating through the circulation path. [5] The method for controlling a dilution refrigerator according to any one of [2] to [4], further comprising adjusting a temperature of the first purifier to a temperature at which the first purifier can adsorb impurities in the circulation path and at which the first purifier is less likely to adsorb helium gas than the second purifier. [6] A dilution refrigerator comprising at least a mechanical refrigerator having a cold region generating unit, a compressor for compressing helium gas, a purifier for removing impurities from the helium gas, a heat exchanger for exchanging heat with the cold region generating unit, and a mixing chamber serving as a low-temperature output unit, these being arranged in this order; and a cold-insulated outer tank containing the cold region generating unit, the purifier, the heat exchanger, and the mixing chamber in a vacuum-insulated inner space, wherein the purifiers are a plurality of purifiers, each having a heater for adjusting the temperature of the purifier, and the cold region generating unit and the plurality of purifiers are in thermal contact with each other independently, and the heater is located at a position separated from the contact point between the purifier and the cold region generating unit. [Effects of the Invention]

[0008] The dilution refrigerator and its control method of the present invention can adjust the amount of circulating helium without relying on a buffer tank, enabling long-term continuous operation to meet the demands of analytical instruments, etc. at the installation site. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a system diagram showing an example of the configuration of a dilution refrigerator. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the configuration of a purifier included in a dilution refrigerator. [Figure 3] FIG. 10 is a partial schematic view showing an example of a configuration in which two refiners are provided. [Figure 4] FIG. 10 is a partial schematic view showing another example of a configuration in which two refiners are provided. [Figure 5] 1 is a graph showing the results of a test example. [Figure 6] 1 is a graph showing the results of a test example. DETAILED DESCRIPTION OF THE INVENTION

[0010] An example of an embodiment of a dilution refrigerator according to the present invention will be described below with reference to the drawings. For the sake of convenience, the drawings may show characteristic parts enlarged, and the dimensional proportions of the components may not necessarily be the same as those of the actual components.

[0011] <Structure of a dilution refrigerator> The dilution refrigerator 10 of the first embodiment shown in Figure 1 includes a mechanical refrigerator 20, a helium circulation path 30, and a cold-insulated outer tank 40. The dilution refrigerator 10 can be used, for example, in an analytical device that detects signals with high sensitivity and high resolution by cooling a detector.

[0012] Mechanical refrigerator 20 has a two-stage cold generation section: a first cooling stage (first cold generation section) 21 that cools the helium circulating in circulation path 30 to about 50 K, and a second cooling stage (second cold generation section) 22 that further cools the same helium to about 4.2 K. First and second cooling stages 21, 22 are each stored in the space inside cold insulation outer tank 40.

[0013] The circulation path 30 is a flow path made up of piping or the like through which helium can flow. The circulation path 30 includes a compressor 31 that compresses helium gas, a first heat exchanger (inlet side) 32, a purifier 50, a second heat exchanger (heat exchanger) 33 that exchanges heat with the first cooling stage 21, a condenser 34 that exchanges heat with the second cooling stage 22, an impedance 35 that decompresses the helium gas, a fractionator (inlet side) 36, a third heat exchanger (inlet side) 37, a c phase 38A, and a d phase 38B. The circulation path 30 also includes a mixing chamber 38 that serves as a low-temperature output section, the third heat exchanger (return side) 37, the fractionator (return side) 36, and the first heat exchanger (return side) 32, which are arranged in this order. The helium gas can be circulated from the first heat exchanger (return side) 32 back to the compressor 31.

[0014] The cold insulation outer tank 40 houses, in its vacuum-insulated inner space, first and second cooling stages (cold generation units) 21, 22, a first heat exchanger 32, a purifier 50, a second heat exchanger (heat exchanger) 33, an impedance 35, a fractionator 36, a third heat exchanger 37, and a mixing chamber 38. The housed equipment can be isolated from outside air to create a vacuum-insulated state. A compressor 31, which constitutes part of the circulation path 30, is provided outside the cold insulation outer tank 40.

[0015] The refiner 50 is a heat exchanger between the first cooling stage 21, which is a cold generating part, and the second heat exchanger 33. The purifier 50 is a low-temperature purifier provided to remove impurities from helium gas before the helium gas is cooled. In the dilution refrigerator 10 of this embodiment, the purifier 50 is provided in the space inside the cold-insulated outer tank 40, on the primary side (upstream side) of the second heat exchanger 33. Because the purifier 50 and the first cooling stage 21, which is the cold generating section, are in thermal contact, part of the cold generated in the first cooling stage 21 can be used as a cold source for the purifier 50.

[0016] 2 includes a cylindrical main body (body) 51A that is open at both ends, a first flange surface 51B that closes one of the open faces, and a second flange surface 51C that closes the other open face. The first and second flange surfaces 51B and 51C are fixed to the open faces of the main body 51A by brazing, welding, or the like, so that the refiner 50 is a sealed cylindrical container.

[0017] A plurality of partition plates 52 are provided inside the main body 51A at intervals in the axial direction of the main body 51A, dividing the interior of the main body 51A into a plurality of spaces. Each of the divided spaces is filled with activated carbon (not shown) as an adsorbent. A seal member 52A is provided in the center of each partition plate 52 to seal between the helium supply pipe 53A and the partition plate 52.

[0018] The main body 51A, the first flange surface 51B, the second flange surface 51C, and the multiple partition plates 52 can be made of metal materials such as copper, aluminum, cupronickel, brass, and stainless steel, but copper, which has excellent thermal conductivity, is preferred.

[0019] A helium supply pipe 53A and a helium discharge pipe 53B are provided on the first flange surface 51B, each penetrating the first flange surface 51B. The base end of the helium supply pipe 53A is connected to the inlet side 30A of the circulation path 30. The tip 53a of the helium supply pipe 53A penetrates the multiple partition plates 52 and opens into the space facing the second flange surface 51C. The helium supply pipe 53A also functions as a support for each partition plate 52. The base end of the helium discharge pipe 53B is connected to the return side 30B of the circulation path 30. The tip 53b of the helium discharge pipe 53B opens into the space facing the first flange surface 51B.

[0020] By providing the tip of helium supply pipe 53A and the tip of helium discharge pipe 53B at opposite ends of the space inside main body 51A, the contact area with the activated carbon is increased by the siphon effect, enabling impurities in the helium gas to be efficiently removed. Gasket-type filters 54 are provided at the base ends of helium supply pipe 53A and helium discharge pipe 53B to prevent the activated carbon filled in main body 51A from flowing out into circulation path 30.

[0021] By providing the base ends of the helium supply pipe 53A and the helium discharge pipe 53B on the first flange surface 51B side, the second flange surface 51C can be used as the mounting surface for the connecting member 60 for thermally contacting the first cooling stage 21, which is the cold generation part.

[0022] In the dilution refrigerator 10, the first cooling stage (first cold generation unit) 21 and the purifier 50 are in thermal contact. This thermal contact is achieved via a thermally conductive connecting member 60, as shown in Figures 1 and 2. Specifically, the first cooling stage 21 and the purifier 50 are connected (fixed) by the thermally conductive connecting member 60.

[0023] The connecting member 60 may be composed of a single member, but is preferably composed of two or more members as shown in the drawing. The connecting member 60 is composed of a flange-shaped first member 61 attached so as to contact the first cooling stage 21, and a second member 62, which is a fixture for fixing the refiner 50 to the first member 61 and for adjusting the heat transfer from the first cooling stage 21 to the refiner 50.

[0024] The material of the connection member 60 is not particularly limited as long as it has thermal conductivity, and may be, for example, metal. As a specific example, it is preferable that the connection member 60 is composed of a first member (member made of a first metal) 61 made of a metal with excellent thermal conductivity (e.g., copper), and a second member (member made of a second metal) 62 made of a metal with lower thermal conductivity than the first metal (e.g., stainless steel).

[0025] The second member 62 of the dilution refrigerator 10 is a bolt that connects the flange-shaped first member 61 connected to the first cooling stage 21 to the second flange surface 51C of the refiner 50. In anticipation of contraction / expansion due to temperature changes and from the perspective of preventing rattles between the respective members, it is desirable that the thermal expansion coefficients of the materials of the first member 61, the second member 62, and the refiner 50 are similar.

[0026] The refiner 50 is equipped with a heater 70 and a thermometer 71, so that the operating temperature of the refiner 50 can be monitored and controlled as desired. The temperature of the heater 70 is adjusted by known means such as a variable current source or a temperature controller (not shown). From the viewpoint of facilitating temperature control, the heater 70 is preferably provided at a position separated from the contact portion between the refiner 50 and the connecting member 60.

[0027] Although the dilution refrigerator 10 of the first embodiment has been described above as having one purifier 50, the number of purifiers provided in the dilution refrigerator according to the present invention is not limited, and may be multiple.

[0028] 3 is a partial schematic diagram of a dilution refrigerator 10 equipped with a first purifier 50A and a second purifier 50B. The first purifier 50A and the second purifier 50B are each in thermal contact with the first cooling stage 21 via a first member 61 made of a first metal and second members 62A and 62B made of a second metal having lower thermal conductivity than the first metal. Here, the second members 62A and 62B may be made of the same material or different materials.

[0029] The first refiner 50A and the second refiner 50B are each equipped with independent heaters 70A and 70B. The temperatures of the heaters 70A and 70B are independently adjusted by variable current sources and temperature controllers (not shown). The first heater 70A is provided in the first refiner 50A at a position spaced apart from the contact area between the first refiner 50A and the first cooling stage 21 (i.e., the first member 61 and the second member 62A). Similarly, the second heater 70B is provided in the second refiner 50B at a position spaced apart from the contact area between the second refiner 50B and the first cooling stage 21 (i.e., the first member 61 and the second member 62B).

[0030] In the configuration of Fig. 3, the detailed structure of each of the refiners 50A, 50B is similar to that of the refiner 50 illustrated in Fig. 2. Thermometers 71A, 71B are provided in the helium discharge pipes installed in each of the refiners 50A, 50B, respectively, to monitor the operating temperature inside each refiner.

[0031] In the configuration of FIG. 3, the first refiner 50A and the second refiner 50B may be connected in series or in parallel.

[0032] In the case of a series arrangement, in the circulation path 30, helium is supplied to the first purifier 50A via a helium supply pipe 53A connected to the first heat exchanger 32, and then the helium discharged from the helium discharge pipe 53B of the first purifier 50A is supplied to the second purifier 50B via piping, and the helium discharged from the helium discharge pipe 53B of the second purifier 50B is supplied to the second heat exchanger 33 via piping.

[0033] In the case of parallel connections, helium is supplied to the first purifier 50A and the second purifier 50B via individual helium supply pipes 53A connected to the first heat exchanger 32 in the circulation path 30, and then the helium discharged from the helium discharge pipes 53B of each purifier 50A, 50B is supplied to the second heat exchanger 33 via piping.

[0034] 3, the sizes of the first purifier 50A and the second purifier 50B (i.e., the volumes of the adsorbents such as activated carbon provided in the purifiers) may be the same or different. As will be described later, if one purifier's main role is to adsorb impurities and the other purifier's main role is to control the amount of helium circulated by adsorbing helium, the size of the other purifier can be adjusted according to the amount of helium adsorbed by the other purifier; for example, the size of the other purifier can be made smaller than the first purifier.

[0035] 4 is a partial schematic diagram of another configuration of the dilution refrigerator 10 equipped with a first purifier 50A and a second purifier 50B. The first purifier 50A is in thermal contact with the first cooling stage 21 via a first member 61 made of a first metal and a second member 62A made of a second metal having a lower thermal conductivity than the first metal. The second purifier 50B is in thermal contact with the second cooling stage 22 via a first member 63 made of the first metal and a second member 62B made of the second metal having a lower thermal conductivity than the first metal. Here, the first member 61 in thermal contact with the first cooling stage 21 and the first member 63 in thermal contact with the second cooling stage 22 may be made of the same material or different materials. Furthermore, the second member 62A that is in thermal contact with the first cooling stage 21 and the second member 62B that is in thermal contact with the second cooling stage 22 may be formed from the same material or from different materials.

[0036] The first refiner 50A and the second refiner 50B are each equipped with independent heaters 70A and 70B. The temperatures of the heaters 70A and 70B are independently adjusted by variable current sources and temperature controllers (not shown). The first heater 70A is provided in the first refiner 50A at a position spaced apart from the contact area between the first refiner 50A and the first cooling stage 21. Similarly, the second heater 70B is provided in the second refiner 50B at a position spaced apart from the contact area between the second refiner 50B and the second cooling stage 22.

[0037] In the configuration of Fig. 4, the detailed structure of each of the refiners 50A, 50B is similar to that of the refiner 50 illustrated in Fig. 2. Thermometers 71A, 71B are provided in the helium discharge pipes installed in each of the refiners 50A, 50B, respectively, to monitor the operating temperature inside each refiner.

[0038] In the configuration of FIG. 4, the first refiner 50A and the second refiner 50B may be connected in series or in parallel.

[0039] In the case of a series arrangement, in the circulation path 30, helium is supplied to the first purifier 50A via a helium supply pipe 53A connected to the first heat exchanger 32, and then the helium discharged from the helium discharge pipe 53B of the first purifier 50A is supplied to the second purifier 50B via piping, and the helium discharged from the helium discharge pipe 53B of the second purifier 50B is supplied to the second heat exchanger 33 via piping.

[0040] In the case of parallel connections, helium is supplied to the first purifier 50A and the second purifier 50B via individual helium supply pipes 53A connected to the first heat exchanger 32 in the circulation path 30, and then the helium discharged from the helium discharge pipes 53B of each purifier 50A, 50B is supplied to the second heat exchanger 33 via piping.

[0041] The sizes of the first refiner 50A and the second refiner 50B may be the same or different. As will be described later, if one refiner's main role is to adsorb impurities and the other refiner's main role is to control the amount of helium circulated by adsorbing helium, the size of the other refiner may be adjusted according to the amount of helium adsorbed by the other refiner. For example, the size of the other refiner may be smaller than the first refiner.

[0042] Although the dilution refrigerator 10 described above has a configuration including one or two purifiers, the dilution refrigerator according to the present invention may also include three or more purifiers. For example, a configuration may be possible in which two or more purifiers are in thermal contact with the first cooling stage 21 and two or more purifiers are in thermal contact with the second cooling stage 22, resulting in a total of four or more purifiers. The piping connecting the purifiers can be connected in series or parallel as desired within a path that starts at the first heat exchanger 32 and ends at the second heat exchanger 33.

[0043] <<Control method of dilution refrigerator>> The dilution refrigerator 10 uses the first cooling stage 21 (example temperature: 40 to 50 K) or the second cooling stage 22 (example temperature: 4.2 to 10 K) as the cold source for the purifier 50, and independently of the adjustment of thermal conductivity by the connecting member 60, the heater 70 and the thermometer 71 are used to prevent the purifier 50 from being overcooled and to arbitrarily control the temperature inside the purifier 50.

[0044] In order to increase the adsorption capacity of the adsorbent, such as activated carbon, packed inside the purifier 50 and to adequately adsorb impurities (air, nitrogen, hydrogen, moisture, etc.), the temperature inside the purifier 50 is cooled to 77 K or less. If the temperature inside the purifier 50 is further cooled below 60 K, not only the impurities but also the circulating 3 He gas adsorption begins.

[0045] In the present invention, the amount of circulating helium is adjusted by utilizing the above-mentioned adsorption phenomenon. 3 When the circulation amount of He gas is reduced, the temperature of the purifier 50 is lowered to below 60 K. 3A part of the He gas is adsorbed and retained. 3 When increasing the circulation amount of He gas, the temperature of the purifier 50 is increased to 60 K or more to remove the adsorbed gas in the purifier 50. 3 The He gas is released into the circulation path 30 and circulated. By controlling the temperature of the purifier 50 in this way, the He gas in the circulation path 30 3 The amount of He gas circulated can be controlled. 3 By controlling the increase or decrease in the circulation amount of He gas, the amount of He gas circulated in the circulation path 30 is increased or decreased. 3 He gas / 4 The ratio of He gas can also be controlled.

[0046] The material of the connecting member 60 is preferably selected from the following viewpoints: Specifically, a material with excellent thermal conductivity is used for the first member 61 connected to the first cooling stage 21, and a second member 62, which is a fixture made of a material with poor thermal conductivity, is sandwiched between the refiner 50 and the first cooling stage 21 as a spacer to create a temperature difference and prevent the temperature of the refiner 50 from dropping too much. In addition to the selection of material, the thermal conductivity can also be adjusted by the thickness, volume, and shape of the first member 61 and the second member 62. The first member 63 and the second member 62B connected to the second cooling stage 22 can also be selected based on the same considerations.

[0047] An example of the operation method of dilution refrigerator 10 will be described with reference to Figure 1. First, helium gas circulating within circulation path 30 is pressurized to approximately 400 kPa by room-temperature compressor 31. The pressurized helium gas, which is close to room temperature, is introduced via circulation path 30 into first heat exchanger 32, where it is cooled to a temperature suitable for adsorbing impurities by heat exchange with low-temperature return helium gas, which will be described later.

[0048] Next, the cooled helium gas is introduced into the purifier 50. In the purifier 50, impurities such as air are removed from the helium gas. Here, the temperature inside the purifier 50 is measured by a thermometer 71, and the temperature is adjusted by the heater 70 as necessary so that it is kept approximately constant at a temperature (for example, 60 to 77 K) suitable for the amount of impurities adsorbed. Furthermore, when the amount of helium circulated is reduced, the heat input by the heater 70 is reduced, and the temperature inside the purifier 50 is lowered to below 60 K for circulation. 3 A portion of the He gas is adsorbed. This reduces the amount of helium gas circulating in the circulation path 30. When increasing the amount of helium circulated, the amount of heat input by the heater 70 is increased, and the temperature in the purifier 50 is raised to 60 K or higher to remove the previously adsorbed He gas. 3 The He gas is released, and the amount of helium gas circulating in the circulation path 30 increases.

[0049] The helium gas discharged from the purifier 50 is then introduced into the second heat exchanger 33. The circulating helium passes through the second heat exchanger 33, is cooled to about 50 K by the first cooling stage 21, and is further cooled to about 4.2 K by the second cooling stage 22 through the condenser 34. The pressure is then reduced by the impedance 35, and the helium is introduced into the fractionator 36, the third heat exchanger (inlet side) 37, and the mixing chamber 38.

[0050] The helium gas is mixed in the mixing chamber 38. 4 He 3 d-phase 38B with He dissolved in it, 3 The phase d 38B is separated into two phases, the phase c 38A of He and the phase d 38B of He. 4 It contains a lot of He, and c-phase 38A 3 Contains a large amount of He. 3 The specific gravity of He (phase c 38A) is 4 Since the c-phase 38A is smaller than the d-phase 38B, the c-phase 38A is floating on the d-phase 38B. 3 He is d-phase 38B 4 The mixture is further cooled by dissolving in He, so that the mixing chamber 38 functions as a low-temperature output.

[0051] Dissolved in d-phase 38B 3 The He passes through the third heat exchanger (return side) 37 and the fractionator 36 (return side) to exchange heat with the inlet helium gas. Then, in the first heat exchanger 32, the He is heated to near room temperature by heat exchange with the helium gas supplied from the compressor 31 outside the outer cold-insulation vessel 40, and is circulated to the compressor 31 again.

[0052] As described above, when helium gas repeatedly circulates within circulation path 30, the amount of circulating helium gas can be controlled by controlling the temperature of purifier 50, adsorbing a portion of the helium gas into purifier 50, or discharging the helium gas adsorbed into purifier 50.

[0053] When the dilution refrigerator according to the present invention is equipped with multiple purifiers, the temperature of one or a group of purifiers may be maintained in the range of 60 to 77 K to be dedicated to adsorbing impurities, while the temperature of another or a group of purifiers may be adjusted relatively frequently within an arbitrary temperature range centered around a temperature suitable for adsorbing / releasing helium gas (for example, 60 K) to control the increase or decrease of the circulation amount of helium gas. With this configuration, even if impurities adsorbed together with helium gas are released from a purifier whose temperature has risen during the release of helium gas, the impurities can be adsorbed by another purifier dedicated to purification, making it easier to maintain the cleanliness of the inside of circulation path 30.

[0054] The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiments, the purifier is connected to the first cold region generating unit or the second cold region generating unit through thermal contact via a member made of a first metal and a member made of a second metal having a lower thermal conductivity than the first metal. However, as long as temperature control by the heater is sufficient, the connection is not necessarily limited to these connecting members, and the thermal conductivity relationship between each member may be different from that described above. Furthermore, although activated carbon is described as an example of the adsorbent filled in the purifier, it is not limited to activated carbon, and other adsorbents can be used depending on the type of impurities. [Example]

[0055] The following cooling experiment was carried out using the dilution refrigerator shown in Figures 1 and 2. In the test, the dilution refrigerator was set to its lowest temperature, and then the temperature of the low-temperature purifier 50 (cold trap) was changed using the heater 70, and the lowest temperature reached in the mixer 38 (mixing chamber) and the refrigerant gas circulation gas pressure were measured. The measurement results are shown in Figure 5. Data interpretation (steady state): The lower the mixing chamber (MC) temperature, the higher the refrigeration capacity. The amount of circulating gas is proportional to the pressure and amount of circulating gas. Pressure fluctuations can occur when the gas volume is large - Temperature rises if gas volume conditions are poor Figure 6 shows the data from another test conducted under different fill gas conditions, plotted with circles. The data shows the low-temperature purifier (cold trap) temperature, the minimum temperature reached by the mixer, and stability (standard deviation). Under these conditions, the optimum purifier temperature is 60 to 65 K. The star plot in Figure 6 shows the data at 68 K in Figure 5. In Figure 6, when the low-temperature purification temperature is changed from 71.3 K to 65 K, the circulation gas pressure decreases (a decrease in the amount of gas due to adsorption is observed) and the mixer temperature increases slightly, but there is no oscillation compared to 71.3 K. Furthermore, when the temperature of the low-temperature purifier was increased from 65 K to 68 K, the circulating gas pressure increased (gas release) and the mixer temperature decreased (refrigeration capacity increased). The fluctuation at 71.3 K is thought to be due to a slightly larger amount of gas. This result shows that the amount of gas can be changed by adjusting the temperature of the low-temperature purifier, and that the refrigeration capacity can be optimized. The amount of gas fluctuation is very small, and it is difficult to deal with by adding or recovering gas from outside. [Explanation of symbols]

[0056] 10 Dilution refrigerator 20 Mechanical Refrigeration Unit 21 First cooling stage (first cold generation part) 22 Second cooling stage (second cold generation part) 30 Circulation Route 30A entrance side 30B Return side 31 Compressor 32 1st heat exchanger 33 Second heat exchanger (heat exchanger) 34 Condenser 35 Impedance 36 Flow divider 37 Third heat exchanger 38 Mixing chamber 38A c phase 38B d phase 40 Cold storage outer tank 50 Purifier 51A Main body (body) 51B First flange surface 51C Second flange surface 52 Partition 52A Sealing material 53A Helium supply pipe 53B Helium exhaust pipe 54 filters 60 Connecting member 61 First member 62 Second member 70 Heater 71 Thermometer

Claims

1. a helium gas circulation path including at least a mechanical refrigerator having a cold temperature generating unit, a compressor for compressing helium gas, a purifier for removing impurities from the helium gas, a heat exchanger for exchanging heat with the cold temperature generating unit, and a mixing chamber serving as a low-temperature output unit, all of which are arranged in this order; A method for controlling a dilution refrigerator comprising: an outer cold-insulated tank that stores the cold generation unit, the purifier, the heat exchanger, and the mixing chamber in a vacuum-insulated inner space, the method comprising: the purifier has a heater for adjusting the temperature of the purifier; the cold generating unit and the purifier are in thermal contact with each other, The heater is provided at a position spaced apart from a contact portion between the purifier and the cold generating portion, a control method for a dilution refrigerator, the method comprising: controlling the heater to adjust a temperature of the purifier; and adjusting an amount of the helium gas circulating through the circulation path by adjusting an adsorption amount of the helium gas adsorbed in the purifier.

2. The method for controlling a dilution refrigerator according to claim 1 , wherein the purifier comprises a plurality of purifiers including a first purifier and a second purifier.

3. the first refiner and the second refiner are each independently in thermal contact with the cold generating unit, the heater includes a first heater and a second heater; the first heater is provided in the first refiner at a position spaced apart from a contact portion between the first refiner and the cold region generating portion, the second heater is provided in the second refiner at a position spaced apart from a contact portion between the second refiner and the cold region generating portion, adjusting the temperature of the first refiner to be substantially constant; 3. The method for controlling a dilution refrigerator according to claim 2, wherein the amount of helium gas circulating through the circulation path is adjusted by increasing or decreasing the temperature of the second purifier to increase or decrease the amount of helium gas adsorbed in the second purifier.

4. The cold region generating unit has a first cold region generating unit and a second cold region generating unit that generates cold at a temperature lower than that of the first cold region generating unit, the first refiner is in thermal contact with the first cold generating unit, the second refiner is in thermal contact with the second cold generating unit, the heater includes a first heater and a second heater; the first heater is provided in the first purifier at a position spaced apart from a contact portion between the first purifier and the first cold generation portion, the second heater is provided in the second refiner at a position spaced apart from a contact portion between the second refiner and the second cold region generating portion, adjusting the temperature of the first refiner to be substantially constant; 3. The method for controlling a dilution refrigerator according to claim 2, wherein the amount of helium gas circulating through the circulation path is adjusted by increasing or decreasing the temperature of the second purifier to increase or decrease the amount of helium gas adsorbed in the second purifier.

5. 5. The method for controlling a dilution refrigerator according to claim 2, wherein a temperature of the first purifier is adjusted to a temperature at which the first purifier can adsorb impurities in the circulation path and at which the first purifier is less likely to adsorb helium gas than the second purifier.

6. a helium gas circulation path including at least a mechanical refrigerator having a cold temperature generating unit, a compressor for compressing helium gas, a purifier for removing impurities from the helium gas, a heat exchanger for exchanging heat with the cold temperature generating unit, and a mixing chamber serving as a low-temperature output unit, all of which are arranged in this order; a cold-insulating outer tank that stores the cold generating unit, the purifier, the heat exchanger, and the mixing chamber in a vacuum-insulated inner space; The refiner includes a plurality of refiners, each of which has a heater for adjusting the temperature of the refiner; The cold generating unit and the plurality of purifiers are in thermal contact with each other independently, and a dilution refrigerator, wherein the heater is provided at a position spaced apart from a contact portion between the purifier and the cold generating portion.

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