JPH0545016A - Cryogenic freezer device - Google Patents

Abstract

PURPOSE:To simplify a configuration of a magnetic shield against a cooled item, facilitate a handling of a cryogenic freezer device and improve a portable characteristic of the freezer device. CONSTITUTION:A shield case 62 formed by high temperature superconductive material for use in enclosing the second stage heat station 12 of a cryogenic freezer including the second stage heat station 12 for getting a cryogenic temperature and the second stage heat station 12 of the cryogenic freezer device is thermally coupled with the first stage heat station 11.

Description

Detailed Description of the Invention

[0001]

This invention relates to a cryogenic refrigerator,
More specifically, the present invention relates to a cryogenic refrigerator in which a displacer is reciprocated by gas pressure in a cylinder of an expander, and adiabatic expansion of a refrigerant gas accompanying the reciprocating motion of the displacer generates cryogenic refrigeration. ..

[0002]

2. Description of the Related Art Conventionally, a gas pressure drive type GM refrigerator having a GM (Gifford-McMahon) cycle refrigerant cycle has been known as a cryogenic refrigerator of this type. The expander of this refrigerator comprises a cylinder and a displacer and a slack piston that are reciprocally arranged in the cylinder. The displacer defines an expansion chamber at the tip of the cylinder. Through the regenerator of the cylinder. The slack piston is arranged on the base end side of the cylinder so as to divide the base end side space into a gas supply / discharge chamber and an intermediate pressure chamber, and is engaged with the displacer at a predetermined stroke interval. The intermediate pressure chamber communicates with the surge volume, while the gas supply / discharge chamber communicates with a high pressure gas inlet and a low pressure gas outlet connected to the discharge side and the suction side of the compressor, respectively. By periodically switching the supply / discharge of the refrigerant gas to / from the gas supply / discharge chamber or the expansion chamber, the differential pressure between the gas supply / discharge chamber and the intermediate pressure chamber moves the slack piston to reciprocate the displacer. The refrigerant gas expands in the expansion chamber due to the reciprocal movement of the cylinders, whereby cold is generated in the cylinder around the expansion chamber.

By the way, in recent years, as one of the superconducting devices, a superconducting quantum interference device (hereinafter referred to as SQUID) utilizing the Josephson effect has attracted attention. This S
By connecting a magnetic flux input circuit consisting of a superconducting coil to a QUID, it is possible to obtain a gradiometer capable of measuring an extremely weak magnetic flux such as a magnetic field associated with a minute current flowing in a living body or a magnetic field from a minute magnet in the body. You can

However, when the gas pressure drive type GM refrigerator having the above-mentioned electric actuator is used to cool the SQUID to the operating temperature level, a magnetic flux is generated in the refrigerator such as a motor and a solenoid valve. Since the actuator is provided, the magnetic flux from this actuator is detected as harmful noise, which causes a problem that the measurement accuracy is reduced.

When measuring a very low level magnetic field such as a biomagnetic field, not only the magnetic flux from the actuator but also the magnetic flux due to the earth magnetism and the commercial AC power supply cannot be ignored. Since it acts as noise, a magnetic shield capable of accommodating at least the SQUID and the measurement object is indispensable.
The magnetic flux is measured inside a magnetically shielded room that can block the earth's magnetism, or the magnetic flux is measured using a magnetically shielded case that cools the superconducting material case with a cryogen such as liquid helium. ..

[0006]

When magnetic flux measurement is performed using a magnetically shielded room, noise magnetic flux can be blocked with high precision, so that the measurement precision can be improved. However, the magnetic shield is provided in the room itself. Therefore, there is a disadvantage that not only the structure becomes large as a whole but also complicated, but there is a disadvantage that the place where magnetic flux measurement can be performed is limited.

Further, when a magnetic shield case cooled by a cryogen is used, the size can be made to be the minimum necessary, so that it can be transported to a desired place relatively easily and the restriction on the place where the magnetic flux can be measured is eliminated. However, since a cryogen such as liquid helium is indispensable, there is a disadvantage that a qualified person who is skilled in handling the cryogen is required in addition to an engineer for measuring magnetic flux. Further, in addition to the refrigerator for cooling the SQUID, a device for cooling the shield case is also required, which not only makes the overall size larger but also complicates the configuration.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a cryogenic refrigerator having a simple structure, easy handling, and excellent portability. There is.

[0009]

To achieve the above object, a cryogenic refrigerator according to claim 1 is a compressor for compressing a refrigerant gas to generate a high pressure gas, and a high pressure supplied from the compressor. An expander that adiabatically expands the gas to generate a cryogenic level of refrigeration, and the expander includes a final expansion stage that obtains a desired cryogenic temperature and a pre-expansion stage that obtains a low temperature higher than the desired cryogenic temperature. A cryogenic refrigerator, which includes a shield case made of high temperature superconducting material that is thermally coupled to the pre-expansion stage and surrounds the final expansion stage.

Examples of the high temperature superconducting material include oxide superconducting materials such as chemical formula 1 and chemical formula 2.

[Chemical 1]

[Chemical 2] In the cryogenic refrigerator of claim 2, the inner surface of the shield case is a mirror surface.

[0011]

According to the cryogenic refrigerator of claim 1, the compressor compresses the refrigerant gas to generate high-pressure gas, and the high-pressure gas supplied from the compressor is adiabatically expanded by the expander to achieve a cryogenic level. In generating cold, a low temperature higher than the target cryogenic temperature can be obtained in the pre-expansion stage of the expander, and a target cryogenic temperature can be obtained in the final expansion stage. And SQU by the final expansion stage
When cooling a superconducting device such as an ID and causing the superconducting device to perform a predetermined operation, the shield case made of a high-temperature superconducting material that is thermally coupled to the preceding expansion stage becomes a superconducting state, and the Meissner effect This prevents the external magnetic flux from entering the inside, so that the superconducting device can be operated without being affected by the external magnetic flux. As a result, it is possible to improve the measurement accuracy when measuring the biomagnetic field.

Further, as is clear from the above description, since the shield case is only thermally coupled to the front expansion stage, it is excellent in portability, and since no cryogen is required, the structure can be simplified and the cryogen can be used. It does not require a qualified person to handle it. According to the cryogenic refrigerator of claim 2, since the mirror case is formed by forming an aluminum vapor deposition layer or the like on the inner surface of the shield case, the radiation shield efficiency can be improved and the cryogenic temperature of the superconducting device can be maintained. Can be facilitated.

[0013]

Embodiments will now be described in detail with reference to the accompanying drawings showing embodiments. FIG. 1 is a schematic vertical cross-sectional view showing an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view showing the overall structure of a gas pressure drive type GM type cryogenic refrigerator, which is a helium gas (refrigerant). It is used as a pre-cooling refrigerator for a JT refrigerator utilizing Joule-Thomson expansion of gas), and the SQUID (not shown) is cooled to a cryogenic level by this JT refrigerator. In FIG. 2, 1 is a compressor that compresses helium gas as a refrigerant gas to generate high-pressure gas, and 2 is an expansion that adiabatically expands the high-pressure gas supplied from the compressor 1 to generate cryogenic cold. It is a machine.
The expander 2 is composed of a cylinder assembly 3 and a valve motor assembly 40.

The cylinder assembly 3 has a cylinder 10 having a bottomed cylindrical shape that is opened upward, and a valve stem 4 that hermetically closes an opening on the upper end side (base end side) of the cylinder 10. The valve stem 4 has, in the cylinder 10, a columnar protrusion 4a that concentrically protrudes from the inner wall of the cylinder 10 with a predetermined gap. In addition, the valve stem 4 has
Gas supply / discharge port 5 opening on the cylinder center line on the upper surface
And a surge volume 7 having a relatively small capacity, and a gas flow path 8 that connects the gas supply / discharge port 5 to the inside of the cylinder 10. Further, the gas flow passage 8 is always in communication with the surge volume 7 via a communication passage 9 having a small passage cross-sectional area, and the communication passage 9 sets the intermediate pressure in the surge volume 7 to an appropriate value.

The cylinder 10 is formed in a two-stage structure with a large diameter portion 10a on the upper end side (base end side) and a small diameter portion 10b continuous with the lower end (tip) of the large diameter portion 10a. 1
At the lower end of 0a is a first-stage heat station 11, which is maintained at a temperature level of 55 to 60K, and at the lower end of the small diameter portion 10b, which is at a lower temperature level than that of the first-stage heat station 11, such as 15 to 20K. The second stage heat station 12 is provided for holding the helium gas in the JT refrigerator (not shown) by heat transfer from the two stage heat stations 11 and 12.

Inside the upper end of the large diameter portion 10a of the cylinder 10, a slack piston 15 for partitioning and forming an intermediate pressure chamber 13 is disposed inside the large diameter portion 10a, and the intermediate pressure chamber 13 has a surge volume inside the valve stem 4. 7 through the orifice 14 at all times. The slack piston 15 is of a substantially cup shape having a bottom wall, the inner peripheral upper end of which is the outer periphery of the protruding portion 4a of the valve stem 4, and the outer peripheral lower end of which is the cylinder 1.
The inner diameter of the large diameter portion 10a of 0 is slidably contacted with each other. Further, a center hole 15a is formed at the center of the bottom wall of the slack piston 15, and a plurality of communication holes 15b, 15b, ... Which communicate the inside and outside of the piston 15 are formed at the corners of the bottom wall.

A displacer 16 is reciprocally fitted in the cylinder 10. The displacer 16 is continuous with a large-diameter portion 16a arranged so as to be airtightly slidable in the large-diameter portion 10a of the cylinder 10, a lower end (tip) of the large-diameter portion 16a, and air-tight with a small-diameter portion 10b of the cylinder 10. It has a two-stage structure composed of a slidably arranged small-diameter portion 16b, and a closed space is formed inside each of the large-diameter portion 16a and the small-diameter portion 16b. The space is surrounded by the gas supply / discharge chamber 17 surrounded by the upper end of the displacer 16 and the slack piston 15, the large diameter portion 16a of the displacer 16 and the large diameter portion 10a of the cylinder 10, and corresponds to the first-stage heat station 11. The second stage heat station is surrounded by the first stage expansion chamber 18, the small diameter portion 16b of the displacer 16 and the small diameter portion 10b of the cylinder 10. Is partitioned into a second stage expansion chamber 19 that corresponds to 2. ． Further, communication holes 20, 20 are formed at the lower end of the large diameter portion 16a of the displacer 16 so that the closed space inside the large diameter portion 16a is always communicated with the first stage expansion chamber 18. In addition, a space within the small diameter portion 16b is provided at the upper end of the small diameter portion 16b.
Communication holes 21 and 21 that are always in communication with the stage expansion chamber 18 are formed, and communication holes 22 and 22 that constantly communicate the closed space with the second stage expansion chamber 19 are formed at the lower ends thereof.

Further, at the upper end of the large-diameter portion 16a of the displacer 16, a tubular locking piece 23 for communicating the space inside the large-diameter portion 16a with the gas supply / discharge chamber 17 is integrally projected, and the locking piece 23 is formed. Is the central hole 15 in the bottom wall of the slack piston 15
A flange-shaped engaging portion 23a that engages with the bottom wall of the piston 15 is integrally formed at the upper end of the slack piston 15 when the slack piston 15 moves upward. When the piston 15 rises by a predetermined stroke, the displacer 16 is driven by the piston 15 to start rising by the engagement between the bottom wall of the piston 15 and the locking portion 23a of the locking piece 23, that is, the displacer 16 moves by a predetermined stroke. With a delay of 15
It is designed to follow.

A first-stage regenerator 24 (regenerator) is placed in the closed space inside the large-diameter portion 16a of the displacer 16, and a second-stage regenerator 25 is placed in the closed space inside the small-diameter portion 16b. It has been inserted. Each of these regenerators 24 and 25 is composed of a cold storage type heat exchanger. Specifically, the first stage regenerator 24
Is a stack of a large number of disk-shaped copper meshes as a cold storage material in a closed space, while in the second stage regenerator 25, a large number of lead balls (lead Shot) is filled and enclosed, and the mesh between these meshes and the gap between the lead balls serves as a gas passage. The cold heat of the helium gas flowing through this gas passage is stored in the mesh and each lead ball. That is, when the displacer 16 is in the intake stroke in which it rises in the cylinder 10, the mesh and the lead balls that have been cooled to the cryogenic temperature level in the previous exhaust stroke are transferred from the gas supply / discharge chamber 17 to the first and second expansion chambers 18, 19. By contacting with helium gas at room temperature,
The heat exchange between the two cools the gas to near cryogenic levels. On the other hand, when the displacer 16 is in the descending exhaust stroke, the helium gas whose temperature has dropped to a cryogenic level due to expansion in the expansion chambers 18 and 19 is used in the cylinder 10.
The mesh and the lead ball are brought into contact with each other during discharging to the outside, and the mesh and the lead ball are cooled again to near the cryogenic level by heat exchange between them.

On the other hand, the valve motor assembly 40 is a closed cylinder having a bottomed cylindrical valve housing 41 whose upper end is closed, and a valve stem 42 which airtightly closes the lower end opening of the housing 41. In the side wall of the valve housing 41, a high pressure gas inlet 43 connected to the discharge side of the compressor 1 and a low pressure gas outlet 44 connected to the suction side thereof are opened. A gas supply / discharge port 45 having the same diameter as the gas supply / discharge port 5 of the cylinder assembly 3 is opened at the lower end of the valve stem 42.
Inside the valve housing 41, a valve chamber 46 communicating with the high pressure gas inlet 43 is formed, and the valve chamber 46 faces the upper surface of the valve stem 42.

The valve stem 42 has a first gas passage 48 whose upper half is branched into two and communicates the valve chamber 46 with the gas supply / discharge port 45, and one end of which is described later in the first gas passage 48. A second gas flow path 49, which communicates with the low pressure port 53 of the valve disk 51 and has the other end communicating with the low pressure gas outlet 44 through a communication passage 50 formed in the valve housing 41, is formed. .. Both gas channels 48,
As shown in FIG. 3, the reference numeral 49 designates a valve chamber 46 on the upper surface of the valve stem 42, a central portion of the valve stem 42 in the second gas passage 49, and two branch portions of the first gas passage 48. In that case, the second gas passages 49 are opened at symmetrical positions with respect to the opening.

Further, in the valve chamber 46, the valve motor 5
4 is provided with a valve disc 51 as a switching valve that is rotationally driven in a predetermined cycle.
By this switching operation, the valve chamber 46 communicating with the high pressure gas inlet 43 and the communication passage 50 communicating with the low pressure gas outlet 44 are alternately communicated with the gas supply / discharge port 45.

More specifically, the valve disc 51 is slidably connected to the output shaft 54a of the valve motor 54. A spring 55 is contracted between the upper surface of the valve disk 51 and the motor 54. The spring force of the spring 55 and the pressure of the high-pressure helium gas introduced into the valve chamber 46 cause the lower surface of the valve disk 51 to move toward the valve stem. The upper surface of 42 is pressed with a constant pressing force. Further, as shown in FIG. 4, a pair of high-pressure ports 52, 5 are formed on the lower surface of the valve disc 51 by cutting a predetermined length in the center direction from the outer peripheral edges facing each other in the radial direction.
2 and the valve disk 51 for the high pressure ports 52, 52
Are arranged at angular intervals of about 90 ° in the rotation direction of
A low pressure port 53 is formed by cutting out in the diameter direction from the center of the lower surface of the valve disk 51 toward the vicinity of the outer peripheral edge. When the valve disk 51 is rotated by the drive of the valve motor 54 while the lower surface thereof is pressed against the upper surface of the valve stem 42 to perform the switching operation, the high pressure gas inlet 43 or the low pressure gas outlet 44 is operated according to the switching operation of the valve disk 51. Are alternately communicated with the gas supply / discharge port 45 at a predetermined timing.

Further, as a feature of the present invention, as shown in FIG. 1, a vacuum chamber 61 surrounding the entire cylinder assembly 3 is provided, and a shield case 62 made of a high temperature superconducting material is housed inside the vacuum chamber 61. Is the first
It is provided in a state where it is tightly thermally coupled to the stage heat station 11. The shield case 62 is set to have a shape and size that surrounds not only the second-stage heat station 12 but also the measurement space in which the magnetic flux measurement target by the SQUID 65, which is kept at a critical temperature or lower by the second-stage heat station 12, is accommodated. Has been done. Then, a predetermined position of the vacuum chamber 61 is recessed into the inner depth of the shield case 62 (a portion close to the SQUID) to form a measurement space 63, and the radiant heat is shielded on the inner surface of almost the entire recessed portion. A super insulation layer 64 is provided. The gas supply / discharge port 5 of the cylinder assembly 3 and the gas supply / discharge port 45 of the valve motor assembly 40 are connected to each other directly or via a refrigerant pipe 60 of a predetermined length. Further, the shield case 62 may be formed of a high temperature superconducting material having a critical temperature higher than the temperature obtained by the first stage heat station 11, for example,
It is formed of a YBa2Cu3O7-δ-based oxide superconducting material. Furthermore, the length and diameter of the shield case 62 are set to a ratio that can effectively prevent the magnetic flux from entering the measurement space 63. Then, by switching the valve disc 51 in the valve motor assembly 40, the high pressure gas from the high pressure gas inlet 43 or the low pressure gas from the low pressure gas outlet 44 is alternately acted on the gas supply / discharge port 5 of the cylinder assembly 3 to slack piston. 15 and displacer 1
6 is reciprocated in the cylinder 10, and as shown in FIG. 3A, the high pressure ports 52, 52 on the lower surface of the valve disk 51 are
Of the high pressure port 5 when the inner ends of the valve chamber 46 and the first gas flow passage 48 on the upper surface of the valve stem 42 respectively match.
2, 52, the first gas flow path 48 and the refrigerant pipe 60 to communicate with the gas supply / discharge chamber 17, the first and second expansion chambers 18 and 19 in the cylinder 10, and these chambers 17 to 19 are connected.
By introducing and filling high-pressure helium gas into, the slack piston 15 and the displacer 16 driven by this piston 15 are raised.

On the other hand, as shown in FIG. 3B, the outer end of the low-pressure port 53, which is always in communication with the second gas passage 49 opening on the upper surface of the valve stem 42 in the central portion, is the first gas passage 48.
If the chambers in the cylinder 10 to 19
Is communicated with the low pressure gas outlet 44 through the refrigerant pipe 60, the first gas flow passages 48, 48, the low pressure port 53, the second gas flow passage 49 and the communication passage 50, and is filled in each of the chambers 17 to 19. By discharging the helium gas to the low pressure gas outlet 44, the slack piston 15 and the displacer 1
6 is lowered, and cold is generated in each of the heat stations 11 and 12 by the expansion of the helium gas in the expansion chambers 18 and 19 accompanying the downward movement of the displacer 16.

The operation of the cryogenic refrigerator having the above structure is as follows. During cool-down, the SQUID65 is gradually cooled to a low temperature level with the operation of the GM refrigerator and the JT refrigerator, and after the temperature of the SQUID65 drops to an extremely low temperature level (about 4K), the refrigerator enters a steady operation state. Then, the SQUID 65 operates in that state.

More specifically, the operation of the GM refrigerator will be described in detail. First, during the cool-down operation, the gas supply / discharge port 5 of the cylinder assembly 3 and the gas supply / discharge port 45 of the valve motor assembly 40 are connected by the refrigerant pipe 60. To be done. When the pressure in the cylinder 10 of the cylinder assembly 3 of the expander 2 is low and the slack piston 15 and the displacer 16 are at the lower end position, the valve motor 54 of the valve motor assembly 40 is
The valve disc 51 is rotated by the drive of FIG.
As shown in FIG.
The valve disc 51 opens to the high pressure side in conformity with the first gas passages 48, 48 on the upper surface of the second side. Accordingly, the high-pressure helium gas at room temperature supplied from the compressor 1 to the valve chamber 46 of the valve motor assembly 40 via the high-pressure gas inlet 43 is supplied to the high-pressure ports 52 and 52 of the valve disk 51 and the first gas flow. Gas is supplied to a gas supply / discharge port 45 via a passage 48, and from this gas supply / discharge port 45, a refrigerant pipe 60, a gas supply / discharge port 5 of the cylinder assembly 3 and a gas flow passage 8 are provided below the slack piston 15. Introduced into chamber 17. Further, this gas is purely charged into the expansion chambers 18 and 19 from the gas supply / discharge chamber 17 through the regenerators 24 and 25 of the displacer 16.
It is cooled by heat exchange with the copper mesh and the lead spheres which were cooled in the previous exhaust stroke while passing through 4, 25.

Further, since the intermediate pressure chamber 13 on the upper side of the slack piston 15 communicates with the surge volume 7 through the orifice 14, the pressure thereof is kept at a constant proper value. Therefore, when the high-pressure helium gas is introduced into the gas supply / discharge chamber 17, the internal pressure becomes higher than that in the intermediate pressure chamber 13, and the piston 15 rises due to the pressure difference between the chambers 13 and 17. Then, when the piston 15 moves upward by a predetermined stroke, the bottom wall of the piston 15 and the locking piece 23 at the upper end of the displacer 16 are engaged with each other, and the displacer 16 is delayed with respect to the pressure change.
By the upward movement of the displacer 16, the expansion chambers 18 and 19 below the displacer 16 are further filled with high-pressure gas (intake stroke).

After that, the valve disc 51 is rotated by 90 ° and closed, but the displacer 16 is also raised by the quiet force thereafter, and along with this, the helium gas in the gas supply / discharge chamber 17 above the displacer 16 becomes the first. And it moves to the second stage expansion chambers 18, 19. After the displacer 16 reaches the rising end position, the valve disc 51 is
Rotate 0 °, and as shown in FIG. 3 (B), the low pressure port 53
Corresponds to the first gas flow path 48 and the valve disc 51 opens to the low pressure side. With this valve opening, the helium gas in the expansion chambers 18 and 19 below the displacer 16 expands by Simon, and the helium gas Chilling occurs due to expansion (expansion stroke).

The helium gas in this cryogenic state is
Contrary to the above-described gas introduction, the gas passes through the regenerators 24 and 25 in the displacer 16 and returns into the gas supply / discharge chamber 17, while cooling the copper mesh and the lead balls in the regenerators 24 and 25 at room temperature. Can be warmed up to. The helium gas at room temperature, together with the gas in the gas supply / discharge chamber 17, is the reverse of the above, and is the gas flow path 8, the gas supply / discharge port 5, the refrigerant pipe 60, the gas supply / discharge port 45 of the valve motor assembly 40. , First gas passage 48, valve disc 51
Through the low pressure port 53 and the communication passage 50 to the low pressure gas outlet 44, and is sucked into the compressor 1 from there. This gas pressure decreases and becomes lower than the intermediate pressure chamber 13.
The slack piston 15 descends due to the pressure difference between 3 and 17, and after the bottom wall of this piston 15 contacts the upper surface of the displacer 16, the displacer 16 is pressed and descends. 1
The gas in 8 and 19 is further discharged out of the expander 2 (exhaust stroke).

Then, the valve disc 51 is rotated by 90 ° and closed, and after that, the displacer 16 is lowered to the lower end position, the gas in the expansion chambers 18 and 19 is discharged, and the initial state is restored. With the above, one cycle of the operation of the expander 2 is completed, and thereafter, the same operation as described above is repeated. By repeating this, the two-stage heat stations 11 and 12 of the cylinder 10 are gradually cooled, the helium gas of the JT refrigerator that has received the cold from the two-stage heat stations 11 and 12 is pre-cooled, and the SQUID 65 is cooled by this JT refrigerator.
Are cooled to cryogenic levels.

In this way, after a lapse of a predetermined time from the start of the refrigerator or after the temperature of the SQUID 65 has dropped to the predetermined temperature, the cool down operation is completed and the refrigerator enters a steady operation state. In this state, due to the Meissner effect of the shield case 62 cooled to the critical temperature or lower by the first stage heat station 11, the external magnetic flux including the noise magnetic flux due to the valve motor assembly 40 is effectively invaded into the measurement space 63. Can be prevented. Therefore, by accommodating the measurement target, such as the head of the human body, in the measurement space 63, the magnetic flux measurement of the measurement target can be achieved with high sensitivity and high accuracy. Further, the cooling heat radiation from the second-stage heat station 12 in the state where the human head or the like is accommodated in the measurement space 63 is effectively blocked by the super insulation layer 64, and the abnormal temperature drop of the human body or the like can be prevented, and the SQUID 65 It becomes easy to keep the temperature of 1 at an extremely low temperature.

[0033]

[Embodiment 2] FIG. 5 is a schematic vertical sectional view showing another embodiment of the cryogenic refrigerator of the present invention. The difference from the embodiment of FIG. 1 is that a vapor deposition layer of aluminum or the like is formed on the inner surface of the shield case 62. Only the point that 62a is formed, other configurations are the same as the embodiment of FIG. Therefore, in the case of this embodiment, the effect of preventing cold heat radiation from the second stage heat station 12 can be enhanced as compared with the case of only the shield case 62, and it is easier to keep the SQUID at an extremely low temperature. become.

The present invention is not limited to the above embodiment, and for example, a vapor deposition layer of aluminum or the like can be formed on the inner surface of the vacuum chamber 61, and the gist of the present invention is changed. It is possible to make various design changes in the range not to do.

[0035]

As described above, the invention of claim 1 is excellent in portability because the shield case is only thermally coupled to the pre-expansion stage, and applicable positional restrictions can be greatly relaxed. In addition, since a cryogen is not required, the structure can be simplified, and a unique effect that a qualified person for handling the cryogen can be eliminated.

In addition to the effect of claim 1, the invention of claim 2 has a unique effect that it is possible to easily maintain the cryogenic temperature of the object to be cooled by enhancing the effect of preventing cold heat radiation.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing an overall configuration of a gas pressure drive type GM type cryogenic refrigerator in a cool down operation state.

FIG. 3 is a plan view of an upper surface of a valve stem facing a valve chamber.

FIG. 4 is a plan view of the lower surface of the valve disc.

FIG. 5 is a schematic vertical sectional view showing another embodiment of the present invention.

[Explanation of symbols]

1 Compressor 2 Expander 3 Cylinder assembly 5 Gas supply / discharge port 10 Cylinder 16 Displacer 18, 19 Expansion chamber 40 Valve motor assembly 43 High pressure gas inlet 44 Low pressure gas outlet 45
Gas supply / discharge port 62 Shield case 62a Deposition layer

Claims (2)

[Claims] 1. A compressor (1) for compressing a refrigerant gas to generate a high-pressure gas, and an expander (a) for adiabatically expanding the high-pressure gas supplied from the compressor (1) to generate a cryogenic level of cold. 2) and a cryogenic refrigerator including a final expansion stage (19) in which the expander (2) obtains a desired cryogenic temperature and a pre-expansion stage (18) obtaining a low temperature higher than the desired cryogenic temperature. And a cryogenic refrigerator characterized by including a shield case (62) made of a high temperature superconducting material that is thermally coupled to the preceding expansion stage (18) and surrounds the final expansion stage (19). .. 2. The cryogenic refrigerator according to claim 1, wherein the inner surface of the shield case (62) is a mirror surface (62a).