JP6975015B2 - Cryogenic system - Google Patents

Description

The present invention relates to cryogenic systems.

A very low temperature system equipped with a Joule-Thomson (JT) refrigerator to cool a highly sensitive electromagnetic wave detection element or other object to be cooled, which is conventionally used for astronomical observation, to a desired extremely low temperature. Is being used. Cryogenic systems are usually equipped with a precooler that precools the JT refrigerator. As the precooler, a two-stage mechanical refrigerator such as a two-stage Stirling refrigerator or a two-stage Gifford-McMahon (GM) refrigerator can be typically used. Such a cryogenic system can cool the object to be cooled to, for example, a temperature range of 1K to 4K.

Japanese Unexamined Patent Publication No. 4-444202

One exemplary object of an aspect of the invention is to improve the efficiency of a cryogenic system.

According to an aspect of the present invention, the cryogenic system includes a single-stage precooler including a one-stage cooling stage, a two-stage precooler including a one-stage cooling stage and a two-stage cooling stage, and a one-stage cooling stage of the single-stage precooler. A JT refrigerator including a one-stage precooling unit cooled by the two-stage precooling unit and a two-stage precooling unit cooled by the two-stage cooling stage. The single-stage precooler is a single-stage Stirling refrigerator or a single-stage Stirling type pulse tube refrigerator, and is operated at the first operating frequency. The two-stage precooler is a two-stage Stirling refrigerator or a two-stage Stirling type pulse tube refrigerator, and is operated at a second operating frequency lower than the first operating frequency. The one-stage precooling unit is thermally coupled to the one-stage cooling stage of the single-stage precooler and thermally separated from the one-stage cooling stage of the two-stage precooler.

It should be noted that any combination of the above components or components or expressions of the present invention that are mutually replaced between methods, devices, systems, etc. are also effective as aspects of the present invention.

According to the present invention, the efficiency of the cryogenic system can be improved.

It is a figure which shows schematically the cryogenic system which concerns on embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are designated by the same reference numerals, and duplicate description will be omitted as appropriate. The scales and shapes of the illustrated parts are set for convenience of explanation and are not limitedly interpreted unless otherwise specified. The embodiments are exemplary and do not limit the scope of the invention in any way. Not all features and combinations thereof described in the embodiments are essential to the invention.

FIG. 1 is a diagram schematically showing a cryogenic system 10 according to an embodiment. The cryogenic system 10 is a cryogenic cooling that cools the single-stage precooler 12, the two-stage precooler 14, the JT refrigerator 16, the vacuum vessel 18, the one-stage radiation shield 20, the two-stage radiation shield 22, and the object to be cooled 24. A unit 26 is provided.

The normal temperature part of each of the single-stage precooler 12, the two-stage precooler 14, and the JT refrigerator 16 is arranged outside the vacuum vessel 18, and the single-stage precooler 12, the two-stage precooler 14, and the JT refrigerator 16 are each arranged. The single-stage precooler 12, the two-stage precooler 14, and the JT refrigerator 16 are installed in the vacuum container 18 so that the low temperature portion is arranged in the vacuum container 18. An exemplary configuration of the single-stage precooler 12, the two-stage precooler 14, and the JT refrigerator 16 will be described later.

The vacuum vessel 18 is an ultra-low temperature vacuum vessel such as a cryostat, and accommodates a one-stage radiation shield 20 and a two-stage radiation shield 22. A heat insulating material such as a multi-layer heat insulating material may be arranged between the vacuum container 18 and the one-stage radiation shield 20. The one-stage radiant shield 20 is arranged in the vacuum vessel 18 so as to surround the two-stage radiant shield 22, the object to be cooled 24, and the ultra-low temperature cooling unit 26, and the two-stage radiant shield 22, the object to be cooled 24, and the ultra-low temperature cooling are cooled. Suppresses the incident of radiant heat on the unit 26. The two-stage radiant shield 22 is arranged in the vacuum vessel 18 (specifically, in the one-stage radiant shield 20) so as to surround the object to be cooled 24 and the ultra-low temperature cooling unit 26, and the object to be cooled 24 and the ultra-low temperature cooling unit 26 are arranged. Suppresses the incident of radiant heat on.

As an example, the object to be cooled 24 is a detection element that detects infrared rays, submillimeter waves, X-rays, or other electromagnetic waves, and such a detection element is a component of an observation device used for astronomical observation. The vacuum vessel 18, the one-stage radiation shield 20, and the two-stage radiation shield 22 are provided with an observation window 28 through which an electromagnetic wave to be detected by a detection element is transmitted. Therefore, electromagnetic waves can be incident on the detection element from outside the cryogenic system 10 through the observation window 28.

The cryogenic cooling unit 26 is cooled by the JT refrigerator 16. The cryogenic cooling unit 26 is also called a cooling stage of the JT refrigerator 16. The object to be cooled 24 is physically in contact with the ultra-low temperature cooling unit 26 and thermally coupled, or is thermally coupled to the ultra-low temperature cooling unit 26 via a heat transfer member. The ultra-low temperature cooling unit 26 can be cooled in a temperature range of, for example, less than 4K (for example, 1K to 4K), and thus the object to be cooled 24 can be cooled in the temperature range.

The cryogenic system 10 can be mounted on a spacecraft such as an artificial satellite together with an observation device having the above-mentioned electromagnetic wave detecting element. The cryogenic system 10 may be mounted on a ground facility equipped with such an observation device. The cryogenic system 10 may be mounted on a spacecraft or ground equipment together with, for example, a superconducting device or other device for which a cryogenic environment is desired.

The single-stage precooler 12 is a single-stage Stirling refrigerator. The single-stage precooler 12 includes a first compressor 30, a single-stage cold head 32 as an expander, and a first connection pipe 34 for connecting the first compressor 30 to the single-stage cold head 32. The first connecting pipe 34 provides a gas flow path for passing a refrigerant gas (for example, helium gas) between the first compressor 30 and the single-stage cold head 32. The single-stage cold head 32 includes a single-stage cooling stage 32a. The room temperature portion of the single-stage precooler 12 includes the first compressor 30 and the first connecting pipe 34, and the low temperature portion of the single-stage precooler 12 includes the one-stage cooling stage 32a.

The first compressor 30 is configured to generate pressure vibration of the refrigerant gas. The generated pressure vibration is transmitted to the single-stage cold head 32 through the first connecting pipe 34. The single-stage cold head 32 is configured such that the pressure vibration transmitted from the first compressor 30 induces a pressure vibration having a phase difference in the single-stage cold head 32 at the same frequency as the pressure vibration. As a result, a refrigeration cycle (specifically, a reverse Stirling cycle) is formed between the first compressor 30 and the single-stage cold head 32.

In this way, the one-stage cooling stage 32a of the single-stage precooler 12 is cooled to the one-stage cooling temperature. The one-stage cooling temperature of the single-stage precooler 12 is selected from, for example, a temperature range of 50K or more and 150K or less. The one-stage cooling temperature may be, for example, in the temperature range of 80K or more and 120K or less, and may be, for example, about 100K.

The two-stage precooler 14 is a two-stage Stirling refrigerator. The two-stage precooler 14 includes a second compressor 36, a two-stage cold head 38 as an expander, and a second connection pipe 40 for connecting the second compressor 36 to the two-stage cold head 38. The second connecting pipe 40 provides a gas flow path for passing a refrigerant gas (for example, helium gas) between the second compressor 36 and the two-stage cold head 38. The two-stage cold head 38 includes a one-stage cooling stage 38a and a two-stage cooling stage 38b. The room temperature portion of the two-stage precooler 14 includes the second compressor 36 and the second connecting pipe 40, and the low temperature portion of the two-stage precooler 14 includes the one-stage cooling stage 38a and the two-stage cooling stage 38b. The two-stage cooling stage 38b is arranged in the one-stage radiation shield 20.

The second compressor 36 is configured to generate pressure vibration of the refrigerant gas. The generated pressure vibration is transmitted to the two-stage cold head 38 through the second connecting pipe 40. The two-stage cold head 38 is configured such that the pressure vibration transmitted from the second compressor 36 induces a pressure vibration having a phase difference in the two-stage cold head 38 at the same frequency as the pressure vibration. As a result, a refrigeration cycle (specifically, a reverse Stirling cycle) is formed between the second compressor 36 and the two-stage cold head 38.

In this way, the one-stage cooling stage 38a of the two-stage precooler 14 is cooled to the one-stage cooling temperature, and the two-stage cooling stage 38b is cooled to the two-stage cooling temperature. The one-stage cooling temperature of the two-stage precooler 14 is selected from, for example, a temperature range of 50K or more and 150K or less. The one-stage cooling temperature may be, for example, in the temperature range of 80K or more and 120K or less, and may be, for example, about 100K. The two-stage cooling temperature is lower than the one-stage cooling temperature. The two-stage cooling temperature is selected from, for example, a temperature range of 10 K or more and 25 K or less. The two-stage cooling temperature may be, for example, in the temperature range of 15K or more and 20K or less, and may be, for example, about 15K.

The one-stage cooling temperature of the two-stage precooler 14 may be equal to the one-stage cooling temperature of the single-stage precooler 12. Alternatively, the one-stage cooling temperature of the two-stage precooler 14 may be different from the one-stage cooling temperature of the single-stage precooler 12. For example, the one-stage cooling temperature of the two-stage precooler 14 may be lower than the one-stage cooling temperature of the single-stage precooler 12. In this case, the one-stage cooling stage 38a of the two-stage precooler 14 may be arranged in the one-stage radiation shield 20.

The one-stage radiation shield 20 is thermally coupled to the one-stage cooling stage 32a of the single-stage precooler 12 and thermally separated from the one-stage cooling stage 38a of the two-stage precooler 14. The one-stage radiation shield 20 is physically in contact with the one-stage cooling stage 32a of the single-stage precooler 12 and thermally coupled, or is thermally coupled to the one-stage cooling stage 32a via a heat transfer member. The one-stage radiation shield 20 is arranged away from the one-stage cooling stage 38a of the two-stage precooler 14, and is not in physical contact with the one-stage cooling stage 38a. The one-stage radiation shield 20 may be supported by the one-stage cooling stage 38a via a heat insulating member. In this way, the one-stage radiation shield 20 is cooled to the one-stage cooling temperature of the single-stage precooler 12 by the one-stage cooling stage 32a of the single-stage precooler 12.

The two-stage radiation shield 22 is thermally coupled to the two-stage cooling stage 38b of the two-stage precooler 14. The two-stage radiation shield 22 is physically in contact with the two-stage cooling stage 38b and thermally coupled to the two-stage cooling stage 38b, or is thermally coupled to the two-stage cooling stage 38b via a heat transfer member. In this way, the two-stage radiation shield 22 is cooled to the two-stage cooling temperature of the two-stage precooler 14 by the two-stage cooling stage 38b.

The JT refrigerator 16 includes a JT compression system 46, a heat exchanger group 48, a one-stage precooling unit 50, a two-stage precooling unit 52, a JT valve 54, and a refrigerant circulation line 56 connecting these components. The refrigerant circulating in the JT refrigerator 16 is, for example, helium (helium 3 or helium 4). The heat exchanger group 48 includes a series of countercurrent heat exchangers (48a to 48c). The refrigerant circulation line 56 connects the discharge side of the JT compression system 46 to the supply side of the ultra-low temperature cooling unit 26 and the recovery side of the ultra-low temperature cooling unit 26 to the suction side of the JT compression system 46. A refrigerant recovery line 56b is provided. The refrigerant circulation line 56 is fluidly isolated from both the single-stage precooler 12 and the two-stage precooler 14.

The JT compression system 46 is configured to increase the pressure of the refrigerant gas recovered from the refrigerant recovery line 56b and send it to the refrigerant supply line 56a. The JT compression system 46 acts as a refrigerant source for circulating the refrigerant in the refrigerant circulation line 56. The JT compression system 46 is located outside the vacuum vessel 18.

As an example, the JT compression system 46 comprises a two-stage compression configuration having a one-stage JT compressor 46a and a two-stage JT compressor 46b connected in series. A low-pressure refrigerant gas of, for example, about atmospheric pressure is recovered from the refrigerant supply line 56a to the JT compression system 46. The one-stage JT compressor 46a can boost the recovered refrigerant gas to, for example, about several atmospheres. The two-stage JT compressor 46b can boost the refrigerant gas boosted by the one-stage JT compressor 46a to, for example, about several tens of atmospheres. The high-pressure refrigerant gas thus obtained is sent from the JT compression system 46 to the refrigerant supply line 56a. The JT compression system 46 may have other multi-stage compression configurations or may have a single-stage compression configuration.

In the refrigerant circulation line 56, the heat exchanger group 48 is arranged between the JT compression system 46 and the ultra-low temperature cooling unit 26. The heat exchanger group 48 includes a three-stage configuration including a first heat exchanger 48a, a second heat exchanger 48b, and a third heat exchanger 48c. The first heat exchanger 48a cools the high-temperature (for example, normal temperature, for example, about 300 K) refrigerant gas flowing into the vacuum vessel 18 from the outside of the vacuum vessel 18. The second heat exchanger 48b further cools the refrigerant cooled by the first heat exchanger 48a and the one-stage precooling unit 50. The third heat exchanger 48c further cools the refrigerant cooled by the second heat exchanger 48b and the two-stage precooling unit 52. The heat exchanger group 48 may have other multi-stage configurations.

The refrigerant supply line 56a has high-pressure side channels for each of the first heat exchanger 48a, the second heat exchanger 48b, and the third heat exchanger 48c, and the refrigerant recovery line 56b is the first heat exchanger 48a, Each of the second heat exchanger 48b and the third heat exchanger 48c has a low pressure side flow path. In each heat exchanger, the refrigerant flowing in the high pressure side flow path can be cooled by heat exchange between the high pressure side flow path and the low pressure side flow path. The high-pressure side flow path and the low-pressure side flow path can also be referred to as a high-temperature side flow path and a low-temperature side flow path, respectively.

The first heat exchanger 48a is arranged between the vacuum vessel 18 and the one-stage radiation shield 20, that is, in the space inside the vacuum vessel 18 and outside the one-stage radiation shield 20. The second heat exchanger 48b is arranged between the one-stage radiation shield 20 and the two-stage radiation shield 22, that is, in the space inside the one-stage radiation shield 20 and outside the two-stage radiation shield 22. The third heat exchanger 48c is arranged inside the two-stage radiation shield 22.

The one-stage precooling unit 50 is thermally coupled to the one-stage cooling stage 32a of the single-stage precooler 12, and is thermally separated from the one-stage cooling stage 38a of the two-stage precooler 14. The refrigerant flowing through the one-stage precooling unit 50 is cooled by heat exchange with the one-stage cooling stage 32a of the single-stage precooler 12. In the refrigerant supply line 56a, the one-stage precooling unit 50 is arranged between the first heat exchanger 48a and the second heat exchanger 48b.

The two-stage precooling unit 52 is thermally coupled to the two-stage cooling stage 38b of the two-stage precooler 14. The refrigerant flowing through the two-stage precooling unit 52 is cooled by the two-stage cooling stage 38b. In the refrigerant supply line 56a, the two-stage precooling unit 52 is arranged between the second heat exchanger 48b and the third heat exchanger 48c.

In the refrigerant supply line 56a, the JT valve 54 is arranged between the heat exchanger (third heat exchanger 48c in this example) at the final stage of the heat exchanger group 48 and the ultra-low temperature cooling unit 26. The JT valve 54 is, for example, a fixed orifice.

Further, the JT refrigerator 16 includes a bypass path 58 that bypasses the JT valve 54, and the bypass path 58 includes a bypass valve 60. As an example, the bypass path 58 branches from the refrigerant supply line 56a between the two-stage precooling unit 52 and the third heat exchanger 48c, and becomes the refrigerant supply line 56a between the JT valve 54 and the ultra-low temperature cooling unit 26. Meet again. The bypass valve 60 is, for example, a gas pressure driven open / close valve. The bypass valve 60 may be an electromagnetic, mechanical, manual or other drive open / close valve.

When the bypass valve 60 is open, the refrigerant flows through the bypass path 58, and when the bypass valve 60 is closed, the refrigerant flows through the JT valve 54. The bypass valve 60 is opened to precool the JT refrigerator 16 using the single-stage precooler 12 and the two-stage precooler 14 when the JT refrigerator 16 is started. During steady operation of the JT refrigerator 16, the bypass valve 60 is closed.

In the steady operation of the JT refrigerator 16, the refrigerant flows through the refrigerant circulation line 56 as follows. The high-pressure refrigerant compressed by the JT compression system 46 is first supplied to the high-pressure side flow path of the first heat exchanger 48a. The high-pressure refrigerant flowing through the high-pressure side flow path of the first heat exchanger 48a exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the first heat exchanger 48a to be cooled. The high-pressure refrigerant cooled by the first heat exchanger 48a flows into the one-stage precooling unit 50 through the refrigerant supply line 56a.

The high-pressure refrigerant is cooled by the one-stage cooling stage 32a of the single-stage precooler 12 in the one-stage precooling unit 50, and is sent to the high-pressure side flow path of the second heat exchanger 48b. The high-pressure refrigerant flowing through the high-pressure side flow path of the second heat exchanger 48b exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the second heat exchanger 48b to be cooled. The high-pressure refrigerant cooled by the second heat exchanger 48b flows into the two-stage precooling unit 52 through the refrigerant supply line 56a.

The high-pressure refrigerant is cooled by the two-stage cooling stage 38b of the two-stage precooler 14 in the two-stage precooling unit 52, and is sent to the high-pressure side flow path of the third heat exchanger 48c. The high-pressure refrigerant flowing through the high-pressure side flow path of the third heat exchanger 48c exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the third heat exchanger 48c to be cooled. In this way, the high-pressure refrigerant is cooled to a temperature below the temperature at which the Joule-Thomson effect is expected, and is sent to the JT valve 54.

When the cooled high-pressure refrigerant passes through the JT valve 54, it becomes a low-pressure refrigerant in a mist-like gas-liquid mixed state due to the Joule-Thomson effect, and generates a cooling capacity in the temperature range of the liquefied refrigerant. The mist-like low-pressure refrigerant is sent to the ultra-low temperature cooling unit 26. When the refrigerant is helium as described above, the cryogenic cooling unit 26 can be cooled to the liquid helium temperature range, whereby the object to be cooled 24 can be cooled to the temperature.

When the ultra-low temperature cooling unit 26 is cooled, the mist-like low-pressure refrigerant evaporates and vaporizes again. The liquefied refrigerant and the refrigerant vaporized by evaporation in the JT valve 54 are returned to the low pressure side flow path of the third heat exchanger 48c. The low-pressure refrigerant flows through the refrigerant recovery line 56b in the order of the second heat exchanger 48b and the first heat exchanger 48a. At this time, as described above, the low-pressure refrigerant is heated while cooling the high-pressure refrigerant in each heat exchanger (48c, 48b, 48a). The low-pressure refrigerant that has returned to room temperature in this way exits the vacuum vessel 18, is recovered by the JT compression system 46, and is compressed again.

The JT refrigerator 16 is not limited to the above-mentioned specific configuration, and various typical configurations can be appropriately adopted.

In this way, the cryogenic system 10 sets the cryogenic cooling unit 26 and the object to be cooled 24 to a temperature lower than the two-stage cooling temperature of the two-stage precooler 14, for example, a desired temperature of less than 4K (for example, 1K to 4K). Can be cooled.

The number of refrigeration cycles per unit time in the single-stage precooler 12, that is, the frequency of the pressure vibration of the refrigerant gas in the single-stage cold head 32 (or the first compressor 30) is referred to as the "first operating frequency" in this document. .. The first operating frequency is based on the mechanical characteristics of the single-stage precooler 12. Therefore, when the single-stage precooler 12 has a specific design, the first operating frequency takes a fixed value based on the design.

Further, the number of refrigeration cycles in the two-stage precooler 14 per unit time, that is, the frequency of the pressure vibration of the refrigerant gas in the two-stage cold head 38 (or the second compressor 36) is referred to as the “second operating frequency” in this document. It is called. The second operating frequency is based on the mechanical characteristics of the two-stage precooler 14. Therefore, when the two-stage precooler 14 has a specific design, the second operating frequency takes a fixed value based on the design.

By the way, in the cold head of the two-stage cold storage type refrigerator such as the two-stage cold head 38 of the two-stage precooler 14, different cold storage materials are filled in the first stage and the second stage. Optimal cold storage materials can be used for each of the one-stage cooling temperature and the two-stage cooling temperature. The heat exchange efficiency and pressure loss with the refrigerant gas differ between the first stage and the second stage due to the difference in the cooling temperature and the cold storage material. Therefore, the optimum operating frequency for improving the refrigerating efficiency (for example, the refrigerating capacity per unit power consumption) is originally different between the first stage and the second stage. However, since the two-stage refrigerator is configured to drive the first stage and the second stage in synchronization, it is structurally difficult to make the operating frequencies of the first stage and the second stage different. Therefore, it is difficult to individually optimize the operating frequencies of the first stage and the second stage in one two-stage refrigerator. For example, when the optimum operating frequency is selected for the first stage, the operating frequency is not the optimum operating frequency for the second stage.

A high operating frequency is desirable to improve the refrigerating efficiency of the first stage, and a low operating frequency is desirable to improve the refrigerating efficiency of the second stage. The main reason for this is that the time constant of heat conduction of the cold storage material, that is, the thermal responsiveness, differs between the first-stage cold storage material and the second-stage cold storage material. The second-stage cold storage material suitable for lower temperature generally has a larger time constant of heat conduction and a slower thermal response than the first-stage cold storage material. Therefore, even if the two-stage refrigerator is operated at an excessively high operating frequency, the second-stage cooling stage is difficult to cool.

The single-stage precooler 12 and the two-stage precooler 14 are configured as separate cryogenic refrigerators and can be operated independently of each other. The refrigerant gas circuits of the single-stage precooler 12 and the two-stage precooler 14 are fluidly isolated from each other, and the refrigerant gas pressure vibration in the single-stage precooler 12 and the refrigerant gas pressure vibration in the two-stage precooler 14 Does not affect each other. Therefore, the first operating frequency of the single-stage precooler 12 and the second operating frequency of the two-stage precooler 14 can be set to different values from each other.

Therefore, in the present embodiment, the second operating frequency of the two-stage precooler 14 is lower than the first operating frequency of the single-stage precooler 12. By doing so, the refrigerating efficiency in the two-stage cooling stage 38b of the two-stage precooler 14 can be improved, and the refrigerating efficiency of the one-stage cooling stage 32a of the single-stage precooler 12 can also be improved. By using the single-stage precooler 12 and the two-stage precooler 14 in combination, the first operating frequency and the second operating frequency can be individually optimized.

When the single-stage precooler 12 is a single-stage Stirling refrigerator, the first operating frequency is selected from, for example, a frequency range of 35 Hz or more and 100 Hz or less. By setting the lower limit of the first operating frequency to 35 Hz, it is easy to secure the refrigerating capacity at the desired one-stage cooling temperature by the single-stage precooler 12. The larger the first operating frequency, the easier it is to secure the refrigerating capacity, but it becomes difficult to guarantee the mechanical reliability of the single-stage precooler 12. For example, there is a concern that the mechanical strength of the moving parts in the single-stage precooler 12 and its peripheral structures tends to decrease due to fatigue. Therefore, it is desirable that the upper limit of the first operating frequency is 100 Hz.

The first operating frequency may be, for example, in the frequency range of 45 Hz or more and 65 Hz or less, or in the frequency range of, for example, 50 Hz or more and 60 Hz or less, or may be, for example, about 50 Hz. In this way, the single-stage precooler 12 can be operated at an optimum operating frequency in consideration of ensuring refrigerating capacity and mechanical reliability.

When the two-stage precooler 14 is a two-stage Stirling refrigerator, the second operating frequency is selected from, for example, a frequency range of 1 Hz or more and 30 Hz or less. By setting the possible range of the second operating frequency to 1 Hz or more and 30 Hz or less, it is easy to secure the refrigerating capacity at a desired two-stage cooling temperature by the two-stage precooler 14.

The second operating frequency may be, for example, in the frequency range of 10 Hz or more and 20 Hz or less, and may be, for example, about 15 Hz. By doing so, the refrigerating efficiency in the two-stage cooling stage 38b of the two-stage precooler 14 can be further increased.

Since the second operating frequency is relatively low, the refrigerating capacity of the one-stage cooling stage 38a of the two-stage precooler 14 can be suppressed. However, the one-stage cooling stage 38a is thermally separated from the one-stage radiation shield 20 and the one-stage precooling unit 50. The one-stage cooling stage 38a is used only for cooling the two-stage cooling stage 38b. Therefore, the heat load of the one-stage cooling stage 38a is small, and it is possible to cover the relatively small refrigerating capacity of the one-stage cooling stage 38a.

Since the two-stage precooler 14 can be operated independently of the single-stage precooler 12, even if the refrigerating capacity of the single-stage precooler 12 deteriorates over time, the performance of the single-stage precooler 12 deteriorates. The effect on the performance of the two-stage precooler 14 is minor. Further, since the second operating frequency is lower than the first operating frequency, there is an advantage that the one-stage refrigerating capacity of the two-stage precooler 14 is less likely to deteriorate over time than the refrigerating capacity of the single-stage precooler 12.

Finally, the trial calculation of efficiency improvement by the present inventor is introduced. First, as a comparative example, consider the case where only the two-stage Stirling refrigerator is used as the precooler of the JT refrigerator. A typical two-stage Stirling refrigerator has a one-stage refrigerating capacity of 1W @ 100K and a two-stage refrigerating capacity of 0.2W @ 20K, for example, at a power consumption of 80W at an operating frequency of 15Hz. Assuming that the normal temperature part is 300K, the Carnot efficiency η1 and η2 of the first and second stages are η1 = 100K / (300K-100K) = 0.5 and η2 = 20K / (300K-20K) = 0.0714. be. The ideal work at this time is W1 = 1W / 0.5 = 2W and W2 = 0.2W / 0.0714 = 2.8W, respectively. Therefore, the ratio of refrigerating capacity per unit power consumption is (2W + 2.8W) / 80W = 0.06.

On the other hand, in the case of the embodiment, for example, it is as follows. The single-stage Stirling refrigerator as the single-stage precooler 12 has a one-stage refrigerating capacity of 2W @ 100K, for example, when the operating frequency is 52 Hz and the power consumption is 30 W. In this case, since the Carnot efficiency is η1 = 100K / (300K-100K) = 0.5 as described above, the ideal work is W1 = 2W / 0.5 = 4W. Assuming that one stage of the two-stage Stirling refrigerator as the two-stage precooler 14 is simply replaced with this single-stage Stirling refrigerator, the ratio of the freezing capacity per unit power consumption is (4W + 2.8W) /80=0. It becomes 085. Therefore, the ratio of refrigerating capacity per unit power consumption in the examples is improved by about 41.7% compared to the ratio in the comparative example (0.085 / 0.06 = 1.417).

As described above, according to the cryogenic system 10 according to the present embodiment, a more efficient cooling system can be constructed. Under a given power consumption, refrigeration efficiency can be improved, for example, in a temperature range of less than 4K (eg 1K-4K).

The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above embodiment, various design changes are possible, various modifications are possible, and such modifications are also within the scope of the present invention. By the way.

The single-stage precooler 12 is not limited to the single-stage Stirling refrigerator. The single-stage precooler 12 may be a single-stage sterling type pulse tube refrigerator. The two-stage precooler 14 is not limited to the two-stage Stirling refrigerator. The two-stage precooler 14 may be a two-stage sterling type pulse tube refrigerator. In this case, the optimum values of the first operating frequency and the second operating frequency may be different from the case where the single-stage precooler 12 and the two-stage precooler 14 are the single-stage sterling refrigerator and the two-stage sterling refrigerator. However, even when the single-stage precooler 12 and the two-stage precooler 14 are the single-stage sterling type pulse tube refrigerator and the two-stage sterling type pulse tube refrigerator, the second operating frequency should be lower than the first operating frequency. It is expected that the refrigeration efficiency will be improved.

Even when the single-stage precooler 12 and the two-stage precooler 14 are the single-stage sterling type pulse tube refrigerator and the two-stage sterling type pulse tube refrigerator, the optimum operating frequency is that these two precoolers are the sterling refrigerators. There is a possibility that it may be the same as the case of. Therefore, when the single-stage precooler 12 is a single-stage sterling type pulse tube refrigerator, the first operating frequency may be selected from, for example, a frequency range of 35 Hz or more and 100 Hz or less. The first operating frequency may be, for example, in the frequency range of 45 Hz or more and 65 Hz or less, or in the frequency range of, for example, 50 Hz or more and 60 Hz or less, or may be, for example, about 50 Hz. When the two-stage precooler 14 is a two-stage sterling type pulse tube refrigerator, the second operating frequency may be selected from, for example, a frequency range of 1 Hz or more and 30 Hz or less. The second operating frequency may be, for example, in the frequency range of 10 Hz or more and 20 Hz or less, and may be, for example, about 15 Hz.

Further, if the cooling capacity of the one-stage cooling stage 38a of the two-stage precooler 14 is sufficient, the one-stage cooling stage 38a may be used for cooling either the one-stage precooling unit 50 or the one-stage radiation shield 20. For example, the one-stage precooling unit 50 is thermally coupled to the one-stage cooling stage 32a of the single-stage precooler 12, and is thermally separated from the one-stage cooling stage 38a of the two-stage precooler 14, and the one-stage radiation shield 20 is the single-stage precooler 12. It may be thermally separated from the one-stage cooling stage 32a and thermally coupled to the one-stage cooling stage 38a of the two-stage precooler 14. Alternatively, the one-stage radiation shield 20 is thermally coupled to the one-stage cooling stage 32a of the single-stage precooler 12 and thermally separated from the one-stage cooling stage 38a of the two-stage precooler 14, and the one-stage precooling unit 50 is the single-stage precooler 12. It may be thermally separated from the one-stage cooling stage 32a and thermally coupled to the one-stage cooling stage 38a of the two-stage precooler 14. Thus, in one embodiment, the one-stage precooling unit 50, the one-stage radiation shield 20, or both are thermally coupled to the one-stage cooling stage 32a of the single-stage precooler 12, and the two-stage precooler 14 has. It may be thermally separated from the one-stage cooling stage 38a.

10 Cryogenic system, 12 Single-stage precooler, 14 Two-stage precooler, 16 JT refrigerator, 18 Vacuum container, 20 One-stage radiation shield, 22 Two-stage radiation shield, 24 To be cooled, 26 Extremely low temperature cooling unit, 32a One-stage Cooling stage, 38a one-stage cooling stage, 38b two-stage cooling stage, 50 one-stage precooling section, 52 two-stage precooling section.

Claims (5)

A single-stage precooler equipped with a one-stage cooling stage,
A two-stage precooler equipped with a one-stage cooling stage and a two-stage cooling stage,
A JT refrigerator provided with a one-stage precooling unit cooled by the one-stage cooling stage of the single-stage precooling machine and a two-stage precooling unit cooled by the two-stage cooling stage.
A one-stage radiation shield that surrounds the two-stage cooling stage and the two-stage precooling unit and is cooled by the one-stage cooling stage of the single-stage precooler .
The single-stage precooler is a single-stage Stirling refrigerator or a single-stage Stirling type pulse tube refrigerator, and is operated at the first operating frequency.
The two-stage precooler is a two-stage Stirling refrigerator or a two-stage Stirling type pulse tube refrigerator, and is operated at a second operating frequency lower than the first operating frequency.
The one-stage precooling unit and the one-stage radiation shield are thermally coupled to the one-stage cooling stage of the single-stage precooler.
Cryogenic system stage cooling stage of the two-stage pre-cooling machine, wherein is thermally decoupled from JT refrigerator and the single-stage radiation shield, characterized by Rukoto is used only for cooling of the two-stage cooling stage. The single-stage precooler includes a single-stage cold head provided with the one-stage cooling stage of the single-stage precooler, and a first compressor that causes pressure vibration of a refrigerant gas in the single-stage cold head.
The two-stage precooler includes a two-stage cold head including the one-stage cooling stage and the two-stage cooling stage of the two-stage precooler, and the first compression that causes pressure vibration of a refrigerant gas in the two-stage cold head. Equipped with a second compressor separate from the machine,
The ultra-low temperature system according to claim 1, wherein the single-stage precooler and the two-stage precooler can be operated independently of each other. The ultra-low temperature system according to claim 1 or 2, wherein the first operating frequency is selected from a range of 35 Hz or more and 100 Hz or less, and the second operating frequency is selected from a range of 1 Hz or more and 30 Hz or less. .. The ultra-low temperature system according to claim 3, wherein the first operating frequency is selected from a range of 50 Hz or more and 60 Hz or less, and the second operating frequency is selected from a range of 10 Hz or more and 20 Hz or less. The ultra-low temperature system according to any one of claims 1 to 4, further comprising a two-stage radiation shield surrounded by the one-stage radiation shield and cooled by the two-stage cooling stage.

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