JPH0285653A - Very low temperature refrigerator - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cryogenic refrigerator that cools objects to be cooled by generating cryogenic cold by adiabatic expansion of compressed refrigerant gas such as helium. In particular, the present invention relates to an improved technology for creating cooling grooves for objects to be cooled.

(Prior Art) Conventionally, as a cryogenic refrigerator for cooling low-temperature operating equipment that operates at a cryogenic level of about 4,000 yen to the same temperature level, a cryogenic refrigerator equipped with a pre-cooling refrigeration circuit and a J-7 circuit has been used.
The original circuit refrigerator is known.

This cryogenic refrigerator is disclosed in, for example, US Pat. No. 4,223,540.
As described in the above issue, helium gas (refrigerant gas) compressed by a compressor is adiabatically expanded by an expander, and the temperature of the gas is lowered to generate cryogenic level coldness, and the coldness causes the above-mentioned A pre-cooling refrigeration circuit such as a GM cycle (Gifford-McMahon cycle) or an improved Solvay cycle that keeps the heat station of the expander cool, and helium gas supplied from the compressor of the pre-cooling refrigeration circuit or another compressor. It is equipped with a precooler for precooling by exchanging heat with the heat station of the expander, and a J-7 circuit in which a J-T valve for Joule-Thomson expansion of helium gas is connected in a closed circuit. In the above J-7 circuit, the helium gas from the compressor is precooled by the precooler, and the precooled helium gas is Joule-Thompson expanded by the J-T valve to form a gas-liquid mixed state, and the latent heat of vaporization of the helium is It is designed to generate refrigeration at an even lower temperature level.

(Problems to be Solved by the Invention) By the way, when cooling objects including low-temperature operating equipment with the cryogenic level generated by the above-mentioned J-T circuit, (1) Storing liquid helium at an extremely low temperature in a cryostat, cooling the object by immersing it in the liquid helium, and maintaining the temperature at a low temperature. Generally, a method is adopted in which a cryogenic level generation part of the refrigerator is inserted into a container and the refrigerator is used to condense and liquefy the evaporated helium gas.

However, in method (2) above, due to the shape of the object, the properties of the material, etc., the cooling temperature of the object differs between the cooling part from the refrigerator and the other parts, resulting in local inconvenience. There is a problem that the cooling becomes stable and the time required to complete cooling of the object to be cooled increases.

Specifically, for example, it has a magnetic field gradiometer as the object to be cooled,
When trying to cool a superconducting m-son interferometer (SQUID), which is one of the superconducting devices that detect minute magnetic flux, to an extremely low temperature level (operating temperature level), a superconducting quantum interference device equipped with this magnetic field gradiometer is used. The meter is generally vertically long, and since the magnetic field gradiometer is wrapped around a material with low thermal conductivity such as resin, the shape and material may cause the local temperature instability and cooling completion time. cause an increase. In that case, since superconducting quantum interferometers have the characteristic of generating noise due to fluctuations in cooling temperature,
A problem arises in which the superconducting quantum interferometer cannot operate stably.

On the other hand, in the method (2) above, the object to be cooled is cooled by immersing it in liquid helium in the cryogenic container, so that the entire object to be cooled can be cooled stably and in a short time. However, on the other hand, since the object to be cooled is indirectly cooled through the helium in the cryogenic container, there is a problem in that the operability of the cooling system in the non-operating state deteriorates. In addition, the volume of helium gas that becomes a gas due to evaporation in the cryogenic container increases compared to that of a liquid state, so the large volume of helium gas must be cooled by a refrigerator, which causes a large cooling loss to the object to be cooled. A large capacity compressor is required.

The present invention has been made in view of the above points, and its purpose is to improve the cooling structure for the object to be cooled when the object to be cooled is cooled by a cryogenic refrigerator as described above. The object of the present invention is to enable cooling of the entire object to be cooled stably and in a short time, and to improve the operability of the cooling system.

(Means for Solving the Problem) In order to achieve the above object, the solving means of the present invention connects a refrigerant gas compression means and a fat expansion means to a closed circuit, and generates a cryogenic level in the closed circuit. A sealed cooling space is formed in the cooling space, and the object to be cooled is housed inside the cooling space.

That is, as shown in FIG. 1, in the present invention, a compression means for compressing refrigerant gas and an expansion means (16) for expanding the refrigerant gas compressed by the compression means are connected to a closed circuit. The premise is a cryogenic refrigerator that cools the object to be cooled (21) by lowering the temperature of the refrigerant gas to a cryogenic level by expanding the refrigerant gas by the fat expansion means (16) to generate cold. Its feature is that in the part of the closed circuit where the temperature of the refrigerant gas is lowered to an extremely low temperature level by the fat expansion means 06), there is a cooling space (20) whose shape approximately corresponds to the shape of the object to be cooled (21). to form the cooling space (20
) houses the object to be cooled (21).

Moreover, specifically, the refrigerator of the present invention has a pre-cooling refrigeration circuit (2
) and the J-7 circuit (8) are combined. That is, the pre-cooling refrigeration circuit (2) includes a compressor that compresses refrigerant gas and an expansion machine (3) that expands the compressed refrigerant gas, which are connected in a closed circuit, and the expansion machine (3) has a predetermined temperature. Heat station (8) held at level (
7) is formed, and the refrigerant gas compressed by the compressor is expanded in the expander (3) to generate cold, and the cold cools the heat stations (G) and (7).
) is kept cool. On the other hand, J-7 circuit (8)
The refrigerant gas supplied from the compressor of the pre-cooling refrigeration circuit (2) or another compressor is heat exchanged with the heat station (if), (7) of the expander (3). The precoolers (14) and (15) for precooling the refrigerant gas and the J-T valve (1G) for Joule-Thomson expansion of the refrigerant gas are connected in a closed circuit, and the refrigerant gas from the compressor is transferred to the precooler (15).
4) and (15), the precooled refrigerant gas is Joule-Thomson expanded in the J-T valve (16) to form a gas-liquid mixture state, and the latent heat of vaporization of the refrigerant cools the cryogenic temperature. It is something that generates.

In this refrigerator, a closed cooling space (20) approximately corresponding to the shape of the object to be cooled (21) is formed in the J-7 circuit (8) downstream of the J-T valve (16). Cooling space (
20) houses the object to be cooled (21).

In addition, the object to be cooled (21) is a superconducting quantum interferometer (21) having a magnetic field gradiometer (21a), which can obtain a remarkable effect by stably maintaining the whole at an extremely low temperature level. ).

Furthermore, in order to improve the cooling performance for the object to be cooled (21), the heat station (B) of the pre-cooling refrigeration circuit (2) is
), (7), J-T valve (1) of J-7 circuit (8)
B) and cooling space (20) are placed inside the vacuum container (1).

(Function) With the above configuration, in the present invention, during operation of the refrigerator, refrigerant gas circulates in a closed circuit between the compression means and the fat expansion means (16), and the refrigerant gas is compressed by the compression means. ,
This compressed refrigerant gas undergoes adiabatic expansion in the fat expansion means (16) and its temperature drops to a cryogenic level, and this drop in gas temperature generates cryogenic refrigeration. In a part of the closed circuit that connects the compression means and the fat expansion means (1B) and whose temperature drops due to gas expansion by the fat expansion means (16), there is a cooled object (21). A cooling space (20) having a shape approximately corresponding to the shape of The object (21) is directly cooled. In that case, the cooling space (20) forms part of a closed circuit (R), and the object to be cooled (21) is housed in the cooling space (20), so the cooling space (20) is kept at an extremely low temperature. The object to be cooled (21) will be cooled entirely by the refrigerant gas whose temperature has dropped to the level, and the temperature will not become locally unstable, and the temperature of the object to be cooled (21) will be reduced. It is possible to reach the cryogenic temperature level in a short time and shorten the cooling completion time.

In addition, the object to be cooled (21) is a compression means and an expansion means (1G).
A cooling space (20) forming part of a closed circuit connecting the
Since it is housed inside, the cooling operation for the object to be cooled (21) becomes a container, and the operability of the cooling system can be improved.

Furthermore, since the object to be cooled (21) is directly cooled in the closed circuit, the cooling opening space for the object to be cooled (21) is small, and a large-capacity compression means is not required.

It is equipped with a closed J-7 circuit (8) that includes a J-T valve (lO) as a component, and a pre-cooling refrigeration circuit (2) that pre-cools the refrigerant gas in the J and -T circuits (8). In the cryogenic refrigerator, the refrigerant gas from the compressor passes through the precooler (14),
(15), and the precooled refrigerant gas is
- The Joule-Thomson fat expands at the T valve (1B) and becomes a gas-liquid mixed state, and the latent heat of evaporation of the refrigerant in the gas-liquid mixed state generates freezing at an extremely low temperature level.

In that case, the J-7 circuit (
The object to be cooled (2) is placed in the closed cooling space (20) formed in (8).
1), the object to be cooled (21) is cooled by the cold generated by the latent heat of vaporization of the refrigerant in the gas-liquid mixed state. For this reason, the object to be cooled (21
) is directly and globally cooled, its temperature is not locally unstable, and the object to be cooled (21)
The cooling completion time can be shortened.

Further, when the object to be cooled (21) is a superconducting quantum interferometer (21) having a magnetic field gradiometer (21a), the superconducting quantum interferometer (21) is accommodated in the cooling space (20),
The entire structure is kept stably cooled to cryogenic levels.

This suppresses temperature fluctuations in the superconducting m-son interferometer (21) and reduces noise generation due to temperature fluctuations, resulting in a significant effect.

In addition, the heat station (
8), (7), J-T valve of J-7 circuit (8) (
16) and the cooling space (20) inside the vacuum container (1), they will be insulated from the normal temperature part by the vacuum, and the cooling performance for the object to be cooled (21) can be improved accordingly.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a binary circuit helium refrigerator according to an embodiment of the present invention, in which (1) is a hermetically sealed vacuum container, the interior of which is maintained in a vacuum state. This vacuum container (1) is equipped with an expander (3) of a pre-cooling refrigeration circuit (2) and a J-
An expansion unit (9) with 7 circuits (8) and a superconducting quantum interferometer (21) with a magnetic field gradiometer (2La) as a cooled object.
) is attached.

The pre-cooling refrigeration circuit (2) is G-M (Gifford).
It consists of a J-McMahon) cycle refrigerator.
7 Helium gas is compressed and expanded in order to pre-cool the helium gas in the circuit (8), and a pre-cooling compressor (not shown) and an expander (3) are connected in a closed circuit. The expander (3) is attached to the vacuum container (1) in a vibration-insulated manner. This expander (3) has a casing (4) arranged on the outer upper surface of the vacuum container (1), and a two-stage cylinder (5) connected to the lower part of the casing (4), A high-pressure gas inlet (4a) connected to the discharge side of the pre-cooling compressor and a low-pressure gas outlet (4b) connected to the suction side of the pre-cooling compressor are opened in the casing (4). Further, the cylinder (5) penetrates the earthen wall of the vacuum container (1) and hangs down inside the container (1), and has a large diameter portion (5a) on its outer periphery at a predetermined temperature level (55~
A first heat station (6) maintained at a temperature of 60 K) and a second heat station held at a predetermined temperature level (15 to 20 K) lower than the first heat station (6) at the lower end of the small diameter portion (5b). (7) are formed respectively.

Although not shown, the heat station (6) is installed inside the cylinder (5).

A displacer that partitions and forms an expansion chamber is fitted in a position corresponding to (7) so as to be reciprocally movable. On the other hand, in the casing (4), a valve is opened every time the casing rotates to supply 1% helium gas flowing from the high pressure gas population (4a) into the expansion chamber of the cylinder (5) or into the fat expansion chamber. A rotary valve that discharges the expanded helium gas from the low-pressure gas outlet (4b) and a valve motor that drives the rotary valve are installed, and when the rotary valve in the expander (3) is opened, high-pressure helium gas is discharged. Simon is inflated in the expansion chamber inside the cylinder (5) and its expansion is 1
This temperature drop generates a cryogenic level of cold, which is retained in the first and second heat stations (6), (7) in the cylinder (5). Therefore,
The high-pressure helium gas discharged from the pre-cooling compressor is supplied to the expander (3), and the temperature of the heat stations (G) and (7) is lowered by adiabatic expansion in the expander (3). - A closed precooling refrigeration circuit (2) that precools the precoolers (14) and (15) (described later) in the "l' circuit (8), and returns the expanded low-pressure helium gas to the compressor for recompression. is configured.

On the other hand, the above J-T circuit (8) operates at an extremely low temperature level (approximately 4K
) is a refrigeration circuit that compresses helium gas and expands it using a Joule-Thomson to generate cold air. It is equipped with an expansion unit (9) for inflating. The above expansion unit (
9) is a support part (
10), and the support part (lO) has a high pressure gas inlet (Ih) connected to the discharge side of the J-T compressor and a low pressure gas outlet (10b) connected to the suction side. It is opened.

In addition, at the lower part of the support part (lO), the first to the
-T heat exchange Ti (11) to (13) are connected.

Each of the J-T heat exchangers (11) to (13) exchanges heat with helium gas passing through the primary side and the secondary side, respectively, and the first J-T heat exchanger (11) 1
The next side is connected to the high pressure gas inlet (10a) of the support section (10). The primary sides of the first and second J-T heat exchangers (11) and (12) are connected to each other on the expansion a(3
> is connected via a first precooler (14) consisting of a heat exchanger disposed around the first heat station (0). In addition, the second and third J-T heat exchangers (12), (
13) are similarly connected to each other via a second precooler (15) consisting of a heat exchanger disposed around the second heat station (7) of the expander (3). moreover,
The primary side of the third J-T heat exchanger (13) is a J-T valve (1
6) via piping (17). The opening degree of this J-T valve (1B) is adjusted from outside the vacuum vessel (1) by an operating rod (lea). Above J-T valve (
16) is the third and second J-T heat exchanger (13),
(12) through each secondary side of the first J-T heat exchanger (11)
The secondary side of the first J-T heat exchanger (11) is connected to the low pressure gas outlet (IQb) of the support part (lO).
It is connected to the. Therefore, in the J-T circuit (8), J
- Helium gas is compressed to high pressure by a T compressor and supplied to the vacuum container (1) side, and then transferred to the first to third J-T heat exchangers (ll) to (13) of the vacuum container (1). At the same time, heat is exchanged with the low-temperature, low-pressure helium gas returning to the compressor side, and the first and second precoolers (14) and (15) are used to heat the first and second heat stations (3) of the expander (3), respectively.
After cooling by exchanging heat with θ) and (7), the J-T valve (
I6), the helium is expanded by Joule-Thomson to form helium in a gas-liquid mixed state of 1 atmosphere and about 4 degrees, and then the helium gas, which has become low pressure, is transferred to the first to third J-T heat exchangers (l[) to
It is configured so that it is sucked into the J-T compressor through each secondary side of ([3) and recompressed.

Furthermore, as a feature of the present invention, the above J-T valve (16)
An airtight container (19) is disposed in the middle of the pipe (16) connecting the secondary side of the third J-T heat exchanger (13). Inside this container (■9), there is a superconducting quantum interferometer (2) having the above-mentioned magnetic field gradiometer (21a).
1) Cooling space (with a shape corresponding to the shape of the object to be cooled)
20) is formed, and the cooling space (20) is the J-T
It communicates with the valve (lO) and the secondary side of the third J-T heat exchanger (13), and constitutes a part of the J-T circuit (8). In this cooling space (20), the magnetic field gradiometer (
A superconducting quantum interferometer (21) with 21a) is accommodated.

Next, the operation of the helium refrigerator of the above embodiment will be described in detail.

When the compressors of the pre-cooling refrigeration circuit (2) and the J-T circuit (8) are started and the refrigerator enters a steady operating state, the expander (3) in the pre-cooling refrigeration circuit (2) supplies air from the pre-cooling compressor. The high-pressure helium gas is expanded, and the temperature drop accompanying the expansion of the gas cools each heat station (0), (7) of the cylinder (5) to a cryogenic level.

On the other hand, at the same time, in the J-7 circuit (8), high pressure helium gas discharged from the compressor is supplied to the vacuum container (1) side, and high pressure helium gas supplied to the vacuum container (1) side. is the high pressure gas inlet (10a) of the support part (lO)
It enters the primary side of the first J-T heat exchanger (11), where it exchanges heat with the low-pressure helium gas on the secondary side that returns to the compressor side, and is cooled from room temperature 300 K to approximately 70 K, and then passes through the expander. (3) The first heat station (6), which is cooled to 55 to 60K, enters the first precooler (14) on the outer periphery and is cooled to about 55K. This cooled gas enters the primary side of the second J-T heat exchanger (12) and similarly
After being cooled down to about 20K by heat exchange with the low pressure helium gas on the next side, it is transferred to the second precooler (15) on the outer periphery of the second heat station (7) which is cooled to 15-20K in the expander (3). It is cooled down to about 15K. Further, the gas enters the primary side of the third J-T heat exchanger (13), is cooled to about 5K by heat exchange with the low-pressure helium gas on the secondary side, and reaches the J-T valve (16). This J-T valve (■6)
Then, the high-pressure helium gas is throttled and expanded by Joule-Thomson, becoming helium in a gas-liquid mixture state of 1 atm and 4.2%, which flows into the cooling space (19) in the storage container (19) downstream of the J-T valve (■0). 20).

Then, in the cooling space (20) within this storage container (19), the superconducting quantum interferometer (21) is cooled to an extremely low temperature level (operating temperature level) by the latent heat of vaporization of the acid part of the helium in the gas-liquid mixed state. be done.

Thereafter, the low pressure helium gas returning from the storage capacity W (19) to the secondary side of the third J-T heat exchanger (13) is approximately 4.
2 becomes a saturated gas, and the second and first J-T heat exchangers (
12), in (11), the high pressure helium gas on the primary side is cooled in order, and finally the temperature is raised to about 300K, and then it is passed from the low pressure gas outlet (10b) of the support part (10) to the suction side of the compressor. After that, the same cycle is repeated and the refrigeration operation is performed.

In the case of this embodiment, the cooling air 161 (20) in the storage container (19) is connected to the closed circuit J-7 circuit (
8), and the superconducting quantum interferometer (21) is accommodated in the cooling space (20). It will be directly cooled by helium in a gas-liquid state whose temperature has dropped to cryogenic levels. Moreover, the above cooling space (
20) is formed in a shape that roughly corresponds to the shape of the superconducting quantum interferometer 21), so even if the interferometer (21) is vertically long and the attached magnetic field gradiometer (21a) is Even if the interferometer (2 mm) is made of a material with a low
1) will be uniformly cooled throughout. Therefore,
The temperature of the interferometer (21) does not become locally unstable, and the entire interferometer (21) can be stably cooled to an extremely low temperature level.

As a result, the interferometer (21) m degree fluctuation is suppressed,
Noise from the interferometer (21) can be suppressed.

Furthermore, since the superconducting quantum interferometer (21) can be directly and totally cooled in this way, its temperature can be brought to an extremely low temperature level in a short time, and the time required to complete cooling can be shortened.

Furthermore, the superconducting quantum interferometer (21) is equipped with a J-7 circuit (8
), the cooling operation for the interferometer (21) is facilitated;
Improves the operability of the cooling system. Moreover, the interferometer (
Since the interferometer (21) is directly cooled in a closed circuit, the interferometer (2
The cooling loss for 1) is reduced, and the J-7 circuit (B
) The capacity of the compressor can be kept small.

In addition, the heat stations (Q), (7), J-7 of the expander (3) in the pre-cooling refrigeration circuit (2) are
Since the heat exchangers (11) to (13), J-T valve (16), and storage capacity a (19) of circuit (8) are housed in a vacuum container, they are separated from the normal temperature part by vacuum. It will be thermally insulated, and the superconducting quantum interferometer (2 [)
It is possible to improve the cooling performance for.

In addition, a superconducting quantum interferometer (21) inside the container (19)
) is located apart from the expander (3) of the pre-cooling refrigeration circuit (2), and the two are connected only by piping (17) and (+8), so the displacer in the cylinder (5) of the expander (3) The vibrations generated due to the reciprocating motion of the piping (1
7) and (16) and is less likely to be transmitted to the interferometer (21), thus making it possible to stably operate the interferometer (21).

In addition, some of the helium expanded by Joule-Thomson in the J-T valve (16) becomes liquid and accumulates in the cooling space (20), so the cool-down time when restarting the refrigerator after it has been stopped can be shortened. Can be done.

In the above embodiment, the object to be cooled is a superconducting quantum interferometer (2
1), but it goes without saying that it is not limited to this.

Moreover, although the pre-cooling refrigeration circuit (2) is configured with a GM cycle refrigerator, other types of refrigerators, such as an improved Solvay cycle, may be employed.

Furthermore, it goes without saying that the present invention is applicable not only to the helium refrigerator having a binary circuit as in the above embodiment, but also to other types of cryogenic refrigerators.

(Effects of the Invention) As described above, according to the present invention, the compression means for compressing refrigerant gas and the expansion means for expanding the same gas are connected in a closed circuit, and cold is generated by the expansion of refrigerant gas. In a cryogenic refrigerator designed to cool objects to be cooled, a sealed cooling space corresponding to the shape of the object to be cooled is formed in a part of the closed circuit where the temperature of the refrigerant gas drops due to expansion in the expansion machine. However, by storing the object to be cooled in this cooling space, the object to be cooled is directly cooled in the cooling space in the closed circuit, making the cooling operation easier and improving the operability of the cooling system. can be done. In addition, since the object to be cooled is cooled in the cooling space in the closed circuit, the entire object to be cooled can be cooled quickly, thereby maintaining a stable temperature of the object and shortening the cooling completion time. be able to.

Furthermore, for a dual-circuit cryogenic refrigerator equipped with a J-7 circuit having a J-T valve for Joule-Thomson expansion of refrigerant gas, and a pre-cooling refrigeration circuit for pre-cooling the refrigerant gas in the J-7 circuit, When a cooling space for accommodating the object to be cooled is formed in the J-7 circuit downstream of the J-T valve, the object to be cooled is heated by the refrigerant, which has become a gas-liquid mixture due to the temperature drop accompanying the Joule-Thomson expansion at the J-T valve. is directly cooled, and the above effects can be reliably obtained.

Furthermore, if the object to be cooled is a superconducting quantum interferometer with a magnetic field gradiometer, the entire superconducting quantum interferometer will be stably cooled and maintained at an extremely low temperature level, and the superconducting quantum interferometer will be Noise generation due to temperature fluctuations is reduced, resulting in a significant effect.

In addition, the heat station of the pre-cooling refrigeration circuit, J-7
When the J-T valve and cooling space of the circuit are housed in a vacuum container, they are insulated from the normal temperature part by the vacuum, so
It is possible to improve the cooling performance for the object to be cooled.

[Brief explanation of the drawing]

Figure T41 is a sectional view schematically showing a helium refrigerator according to an embodiment of the present invention. (1)...Vacuum container, (2)...Pre-cooling refrigeration circuit, (
3)...Expansion machine, (6), (7)...Heat station, (8)...J-7 circuit, (14),
(15)...Precooler, (16)...J-T valve (expansion means'), (19)...Accommodation container, (20)...
Cooling space, (21)...Superconducting quantum interferometer (object to be cooled), (21a)...Magnetic field gradiometer. Patent applicant Daikin Industries, Ltd.

Claims (4)

[Claims] (1) A compression means for compressing refrigerant gas and an expansion means (16) for expanding the refrigerant gas compressed by the compression means are connected in a closed circuit, and the refrigerant gas is expanded by the expansion means (16). In a cryogenic refrigerator that lowers the temperature of refrigerant gas to an extremely low temperature level to generate cold and cool an object to be cooled (21), the refrigerant gas is A cooling space (20) having a shape approximately corresponding to the shape of the object to be cooled (21) is formed in the part where the temperature drops to an extremely low temperature level, and the object to be cooled (21) is placed in the cooling space (20). A cryogenic refrigerator characterized by being housed. (2) A compressor that compresses refrigerant gas and an expander (3) that expands the compressed refrigerant gas are connected in a closed circuit, and the expander (3) is equipped with a heat station that is maintained at a predetermined temperature level. (6) and (7) are formed, and the refrigerant gas compressed by the compressor is expanded in the expander (3) to generate cold, and the cold cools the heat stations (6) and (7). A pre-cooling refrigeration circuit (2) for cooling and holding, and a refrigerant gas supplied from the compressor of the pre-cooling refrigeration circuit (2) or another compressor to the heat stations (6) and (7) of the expander (3). A precooler (14), (15) for precooling the refrigerant gas by exchanging heat between the two and a J-T valve (16) for Joule-Thomson expansion of the refrigerant gas are connected in a closed circuit, and the refrigerant gas from the compressor is Precooler (14),
(15), and the pre-cooled refrigerant gas is Joule-Thomson expanded in the J-T valve (16) to form a gas-liquid mixture, and the latent heat of vaporization of the refrigerant generates cryogenic cooling. -T circuit (8), and a closed cooling space (20) approximately corresponding to the shape of the object to be cooled (21) is formed in the J-T circuit (8) downstream of the J-T valve (16). The object to be cooled (21) is placed in the cooling space (20).
) is housed in a cryogenic refrigerator. (3) The cryogenic refrigerator according to claim (1) or (2), wherein the object to be cooled (21) is a superconducting quantum interferometer (21) having a magnetic field gradiometer (21a). (4) Heat station (6) of pre-cooling refrigeration circuit (2)
, (7), the pole according to claim (2) or (3), wherein the J-T valve (16) and the cooling space (20) of the J-T circuit (8) are housed in the vacuum container (1). Low temperature refrigerator.