JP2828895B2 - Cryogenic refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator.
Particularly, the present invention relates to a cryogenic refrigerator having excellent cooling temperature stability.

[0002]

2. Description of the Related Art A cryogenic refrigerator using a regenerator is known. As a cold storage material, copper (C
u), lead (Pb) and the like have been used.

However, these materials have a remarkably small heat capacity at a temperature of 20 K or less, especially at a temperature near liquid helium, and cannot perform a sufficient cold storage action. For this reason, in order to generate a cryogenic temperature of about the liquid helium temperature, a regenerator is insufficient and, for example, a cryogenic refrigerator or the like combining a Gifford McMahon refrigerator and a Joule-Thomson circuit has been used.

Some magnetic materials have a high magnetic specific heat at an extremely low temperature of 20 K or less. By using these magnetic materials, a regenerator material having a high heat capacity at an extremely low temperature can be realized.

For example, an Er—Ni alloy or Er _1-x Dy
_The magnetic material represented by xNi ₂ has a magnetic phase transition temperature Tc of 6
It changes within a range of up to 20K. Further, by substituting a part of Dy in the above composition with Yb or Tm, a more preferable magnetic regenerator material can be obtained.

FIG. 2 shows the configuration of a conventional refrigeration system.
Here is an example. FIG. 2A schematically shows the entire configuration of the refrigeration apparatus.
Is shown. The compressor 50 has valves on the high pressure side and the low pressure side.
V_H, V _LAnd is connected inside the cylinder 52.

In the cylinder 52, a displacer 51 is provided.
Are arranged, and are driven up and down in the figure. Cylinder 5
Reference numeral 2 denotes a two-stage configuration including an upper stage having a large diameter and a lower stage having a small diameter. The displacer 51 is also 2 according to the shape of the cylinder.
The first expansion space 53 and the second expansion space 54 are formed between the cylinder 52 and the first expansion space 53.

The inside of the displacer 51 also has a two-stage structure, and the upper stage is filled with a high-temperature regenerator material 57 such as copper, and the lower stage is filled with a low-temperature regenerator material 58 such as lead. When the high-temperature side valve _VH is opened, the high-pressure helium gas supplied from the compressor 50 is cooled by the regenerators 57 and 58 and reaches the second expansion space 54. In this step, the displacer 51 rises and the first expansion space 5
3. The second expansion space 54 has a maximum volume. Thereafter, the high-pressure side valve _VH is closed and the low-pressure side valve _VL is opened.

Then, the helium gas in the second expansion space 54 expands at a low temperature and is further cooled, and the cold storage material 58,
The refrigerant is recovered by the compressor 50 through the first expansion space 53 and the cold storage material 57. While performing this step, the first expansion space 53,
The second expansion space 54 changes to a minimum volume. By repeating such a cycle, an extremely low temperature is generated in the second expansion space 54.

FIG. 2B shows the structure of a refrigerator in which a magnetic material is used as the cold storage material and the refrigeration workability of the magnetic cold storage material is utilized in addition to the gas refrigeration shown in FIG. 2A. For simplicity, a configuration corresponding to only the second stage of the displacer is shown. The high temperature side of the cold storage material is filled with lead particles 58a conventionally used as a cold storage material, and the low temperature side is filled with magnetic material particles 58b.

Further, in order to selectively apply a magnetic field to the magnetic particles 58b, a superconducting magnet 59 may be arranged around the superconducting magnet 59. By the superconducting magnet 59, 3
A magnetic field of about T to 6T is applied. By exciting / demagnetizing the magnetic field, the magnetic body 58b undergoes a magnetic phase transition, and aggressive magnetic refrigeration by the magnetocaloric effect is performed.

As described above, by using the regenerative material formed of a magnetic material and utilizing the magnetocaloric effect, it is possible to more effectively generate an extremely low temperature of about the liquid helium temperature. Regarding such magnetic refrigeration, for example, JP-A-4-186802 can be referred to.

As described above, since it becomes possible to generate an extremely low temperature of about the liquid helium temperature in a refrigerator, a detection element of a measuring instrument conventionally cooled using liquid helium is cooled in the refrigerator. It became possible. Compared to liquid helium, handling of the refrigerator is extremely convenient.

[0014]

However, when cooling with a refrigerator, pulsation occurs in the cooling temperature. It is considered that this is because the refrigerant gas repeatedly expands and compresses in the expansion space adjacent to the cooling unit, and cold occurs during expansion.

The expansion space is defined by the closed end of the cylinder, which constitutes a cold head for cooling the object. By the way, the cylinder needs mechanical strength, and the cylinder is usually formed of metal such as copper or stainless steel (SUS).

These metals are 20K or less as described above,
In particular, the specific heat is extremely low at an extremely low temperature of 15 K or less.
Therefore, it is considered that the pulsating cold generated in the expansion space is given to the object to be cooled, causing the temperature to pulsate. Therefore, if the SIS element or the like of the radio telescope is cooled by the refrigerator, the detection sensitivity is reduced.

The present applicant has previously proposed a configuration in which a substance having a large heat capacity is interposed between a cooling stage of a refrigerator and an object to be cooled to form a thermal damper (Japanese Utility Model Application No. Hei 4-9876).
No. 5-69563). In this configuration, the refrigerator and the thermal damper are separate parts, even when a cooling circuit is provided outside the refrigerator, or when the cold storage material is externally attached to the refrigerator, which makes the device complicated and bulky. Also, handling is inconvenient.

Further, since the cold storage material is externally attached to the cylinder, if welding, soldering, or the like is performed, not only the process becomes complicated, but also the accuracy of the cylinder may be adversely affected. SUMMARY OF THE INVENTION An object of the present invention is to provide a cryogenic refrigerator having a relatively simple structure, convenient handling, and good cooling temperature stability.

Another object of the present invention is to provide a cryogenic refrigerator having good cooling efficiency and high temperature stability. Another object of the present invention is to provide a cryogenic refrigerator having a shape that is easy to handle and has high temperature stability.

[0020]

According to the present invention, there is provided a cryogenic refrigerator having a metal cylinder having a closed end constituting a cooling section, and a metal cylinder disposed in the closed end of the metal cylinder, the metal cylinder having a closed end. A cold insulator made of a material different from that of the cylinder; and a regenerator movably accommodated in the metal cylinder and forming an expansion space at the closed end.

Further, the cryogenic refrigerator according to the present invention has a metal container defining an expansion space for the refrigerant gas therein and having a cooling portion for cooling an object outside, and a metal container inside the metal container. It is provided in a portion corresponding to a cooling part and has a higher specific heat than the metal container at a cooling temperature.

[0022]

Since the cooling material is arranged inside the metal cylinder or the metal container, the dimensions of the metal cylinder or the metal container change, but the outer shape hardly changes. For this reason, handling becomes easy.

Since the cold insulator is disposed between the expansion space and the cooling section, pulsating cold generated in the expansion space is alleviated by the cold insulator, and the stability of the cooling temperature is increased.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of a study of the prior art conducted by the present inventors. The cylinder of the GM refrigerator is usually made of stainless steel or copper. Copper has a high thermal conductivity, but has a lower specific heat at cryogenic temperatures than stainless steel. Therefore, the cylinder 52 of the two-stage GM refrigerator as shown in FIG.
Was made in the same dimensions using copper and stainless steel.

Displacer 51 disposed in cylinder
The first stage displacer 57 and the second stage displacer 58 have the same configuration. Thus, two GM refrigerators differing only in the material of the cylinder 52 were operated, and the temperature of the stage in the cooling section adjacent to the second-stage expansion space 54 was measured. The displacer drives each 24 rp
m, 36 rpm and 60 rpm.

The experimental results are shown in FIG. FIG. 3 (B)
In the graph, the horizontal axis indicates the second stage temperature T ₂ in K,
The vertical axis indicates the variation width ΔT ₂ of the second stage temperature in K.
As is clear from the figure, 24 rpm, 36 rpm, 60 rpm
In all cases of rpm, the temperature fluctuation range in the cooling section was significantly larger when the cylinder was made of copper than when stainless steel was used.

Therefore, it has been found that when the heat capacity of the cold head is small, it is difficult to suppress the temperature fluctuation. FIG. 1 shows an embodiment of the present invention, FIG. 1 (A) schematically shows a configuration of a two-stage GM refrigerator, and FIG. 1 (B) shows a cooling material in the refrigerator of FIG. 1 (A). The following shows the specific heat of an example of a magnetic material that can be used as a magnetic material.

In FIG. 1A, a two-stage displacer 1 includes a first-stage regenerator 7 containing a regenerator material such as copper, a regenerator material such as lead, and a regenerator material for a magnetic material for cryogenic temperature. The second stage regenerator 8 is composed of a combination. The configuration of the displacer 1 is the same as that of the conventional displacer shown in FIG. Two-stage displacer 1
Are housed in a two-stage cylinder 2.

The displacer 1 is also basically the same as the displacer according to the prior art, except that the length of the second stage cylinder is increased only by the portion for accommodating the cold insulator 5. The cylinder 2 is made of, for example, stainless steel.

A cold insulator 5 having a high specific heat at a very low temperature is accommodated at the tip of the second stage of the cylinder 2 and is fixed with an adhesive such as a grease for a low temperature such as Apiezon or an epoxy resin for a low temperature. The cold insulator 5 is formed of, for example, an Er—Ni alloy or an Er—Ni—Co alloy as shown in FIG. These magnetic materials have significantly higher specific heats at very low temperatures (at least part of them) than the specific heats of Pb indicated by broken lines.

The distal end of the second stage of the cylinder 2 forms a cooling section (cold head), and holds the object 6 to be cooled outside. He, which is a refrigerant gas, is supplied to the first-stage expansion space 3 via the first-stage regenerator 7 and further supplied to the second-stage expansion space 4 through the second-stage regenerator 8. By expanding in the second-stage expansion space 4, the cooled He cools the second-stage regenerator 8 and returns to the first-stage expansion space 3, and further cools and recovers the first-stage regenerator 7.

Next, the first-stage regenerator 7, the first-stage expansion space 3,
He supplied to the second-stage regenerator 8 and the second-stage expansion space 4
Is cooled by regenerators 7 and 8, respectively. In addition,
The configuration other than the vicinity of the cooling unit is the same as that of the conventional refrigerator shown in FIG. The periodic cold generated in the expansion space 4 is provided to the cooling unit via the cold insulator 5. Since the cold insulator 5 has a large specific heat (heat capacity), the pulsation of the cooling portion temperature is reduced.

The cold insulator 5 is preferably formed of a porous material. The porous material has a significantly larger surface area than its volume, and can adsorb a large amount of He. He
Has a remarkably high specific heat at an extremely low temperature of 10 K or less, as shown in FIG. Therefore, when the porous magnetic material adsorbs He, it is possible to realize an extremely high heat capacity as a whole.

That is, a magnetic material having a high specific heat at an extremely low temperature is disposed between the second-stage expansion space 4 and the cooling portion, and not only high heat capacity is realized, but also the cold insulator 5 is made of a porous material. Thus, if He is adsorbed, the refrigerant gas He
By utilizing the high specific heat, a more effective high heat capacity can be realized.

The magnetic material used for the cold insulator 5 is not limited to the one shown in FIG. 1B, but can be widely selected from magnetic materials having a high specific heat at extremely low temperatures, such as Er-based alloys. . Of course, a non-magnetic material such as Pb can be used together.

Although the GM refrigerator has been described above as an example, the present invention is not limited to the case where a cooling material can be accommodated in a cylinder between an expansion space for generating cold and a cooling unit for cooling an object to be cooled. Can be widely applied.

By suppressing the fluctuation of the cooling temperature, it becomes possible to use the refrigerator for measuring equipment, experimental equipment and the like which require high temperature stability. Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0038]

As described above, high cooling temperature stability can be obtained even when a cooling object is cooled using a refrigerator.

[Brief description of the drawings]

FIG. 1 is a schematic diagram and a graph showing an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining a conventional technique.

FIG. 3 is a schematic cross-sectional view and a graph for explaining a study of a conventional technique performed by the present inventors.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 displacer 2 cylinder 3, 4 expansion space 5 cold insulator 6 cooling object 7, 8 regenerator

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F25B 9/00 F25B 9/14 510

Claims (5)

(57) [Claims] A metal cylinder having a closed end constituting a cooling unit; a cold insulator disposed in the closed end of the metal cylinder and formed of a different material from the metal cylinder; A cryogenic refrigerator having a regenerator movably housed in the metal cylinder and forming an expansion space at the closed end. 2. The cryogenic refrigerator according to claim 1, wherein the material of the cold insulator is a magnetic material having a specific heat peak at 20K or less. 3. The cryogenic refrigerator according to claim 1, wherein the cold insulator is porous, and He is used as a refrigerant gas. 4. The apparatus according to claim 1, further comprising a detection element mounted outside a closed end of said metal cylinder.
The cryogenic refrigerator according to any one of the above. 5. A metal container defining an expansion space for a refrigerant gas therein and having a cooling portion for cooling an object outside, and a portion corresponding to the cooling portion inside the metal container. A cold insulator having a specific heat higher than the metal container at a cooling temperature.