JPH02303077A - Radiation shielding structure of refrigerator - Google Patents

Abstract

PURPOSE:To restrain the generation of eddy current harmful to magnetic flux measurement with a gradiometer by using material wherein the heat dissipating ratio of a radiation shield to cut off the input of radiation heat into the gradiometer is low, and the thermal conductivity is high, and forming slits at some parts of the material. CONSTITUTION:Since a radiation shield 28 is provided with slits 29, 30, the inside and the outside of the radiation shield 28 are linked by them. Vacuum exhaust for discharging air from a vacuum vessel 1 is enabled in a matter of minutes. Since the shield 28 is made of material of high thermal conductivity, the inside can be cooled in a matter of minutes. The cooling time of a gradiometer can be reduced. Since the shield 28 is made of mateiral of low heat dissipating ratio, the shielding effect of radiation heat input to the gradiometer can be effectively secured. Even in the case where the shield 28 is made of electrically conductive material, the generation of eddy current loop of the radiation shield 28 caused by magnetic induction is restrained by the slits 29, 30. Thereby noise caused by the eddy current can be reduced, and the magnetic flux mesuring sensitivity of the gradiometer can be kept high.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to a superconducting quantum interference device (S Q U I D ;
duelve Quantum Interfere
The present invention relates to an improvement in a radiation shield structure for shielding radiant heat input to the gradiometer in a refrigerator that cools a gradiometer consisting of a magnetic flux input circuit connected to the gradiometer in a vacuum container.

(Prior Art) A superconducting quantum interference element that utilizes the Josephson effect has been known as one of the superconducting devices. And 1. By connecting a magnetic flux input circuit consisting of a superconducting coil to this superconducting quantum interference element, extremely weak magnetic flux, such as the magnetism associated with a minute current flowing inside a living body, can be transmitted to n1.
gradiometer can be obtained.

When this gradiometer is cooled to an extremely low temperature level, that is, a temperature level at which the superconducting quantum interference element and the superconducting coil become superconducting, liquid helium at an extremely low temperature level is stored in a cryostat (cryostat). There is a method of cooling the gradiometer by immersing it. In this case, a cooler for a refrigerator for generating cold is usually inserted into the low temperature holding container, and the helium gas evaporated in the container is condensed and liquefied by the refrigerator.

In this method, the gradiometer is immersed in liquid helium, so the entire gradiometer can be cooled stably and in a short time. However, on the other hand, since the helium in the cryogenic container is used to cool the gradiometer, the operability of the cooling system in the non-operating state deteriorates. Moreover, since the volume of helium gas that becomes a gas due to evaporation in the cryostat is larger than that of a liquid state, this large volume of helium gas must be cooled with a refrigerator, which causes a large cooling loss to the gradiometer. There is. For this reason, a method of cooling the gradiometer by bringing it into direct contact with a cooler of a refrigerator to allow heat transfer is attracting attention.

(Problem to be Solved by the Invention) By the way, when the gradiometer is directly cooled by a refrigerator, the gradiometer and the cooler that cools it are usually placed in a vacuum container, and
A radiation shield with a cross-sectional structure made of fiber-reinforced resin (FRP) laminated with super insulation is placed around them, and the -radiant heat that is input from the room temperature area outside the container to the gradiometer etc. is removed by vacuum and radiation. A shield is used to block it. Although this radiation shield structure can improve the insulation effect for the gradiometer, it cannot reliably prevent the generation of eddy current loops in the radiation shield that are harmful to the gradiometer's magnetic flux measurement. In addition, the vacuum layer inside the container is divided into two parts (inside and outside) with the radiation shield as negative, and gas is released from the super insulation resin when the container is evacuated, resulting in a vacuum state inside the container. The problem was that it took a long time to do so.

In addition, since the super insulation resin that is placed on the side of the radiation shield cannot be fixedly supported by itself, it is supported by being laminated on the outer surface of the fiber reinforced resin, but since the thermal conductivity of this fiber reinforced resin is low, the radiation There is a problem in that it takes time to cool down the inside of the shield.

Furthermore, when attaching and detaching the gradiometer, it is troublesome to remove and wrap the super insulation around the radiation shield, and there is also the problem that it takes a lot of work to disassemble and assemble the refrigerator.

The present invention has been made in view of the above-mentioned points, and its purpose is to dispose the gradiometer in a vacuum container and cool it to an extremely low temperature level with a refrigerator as described above. By improving the structure of the radiation shield, we can suppress the generation of eddy currents in the radiation shield that are harmful to gradiometer magnetic flux measurement, and reduce the evacuation time of the vacuum chamber without reducing the gradiometer's sensitivity. The purpose of this invention is to shorten the time required to cool down the inside of the radiation shield, and to facilitate the disassembly and assembly of the refrigerator.

(Means for Solving the Problem) In order to achieve the above object, the solving means of the invention according to claim (1) provides a radiation shield that has a low heat radiation rate and a low thermal conductivity. Constructed from high-quality materials,
A slit is formed in a part of it.

That is, in the invention according to claim (1), FIGS.
As shown in the figure, a vacuum container (1
), and a cooler (25) disposed within the vacuum container (1).
In the refrigerating machine, the refrigerant compressed by the compressor is expanded to generate cryogenic cold in the cooler (25). The cooler (25
), and a radiation shield (28) is provided to shield the gradiometer (CB) from inputting radiant heat.

The radiation shield (28) is made of a material with a low heat dissipation rate and high thermal conductivity, and slits (29) to (31) are formed by partially cutting out a portion of the radiation shield (28).

Further, in the invention according to claim (2), the slit (2
It is desirable to form slits 9) to (31) on the entire radiation shield (28), but if it is difficult to form them on the top plate or bottom plate (28b), as shown in FIG. (28), the top plate or bottom plate (28b) of the radiation shield (28) is made of fiber-reinforced resin, and the vacuum container (1) is formed on the outer surface of the top plate or bottom plate (28b). Super insulation that reaches the inner wall surface (
32) are laminated.

(Function) With the above configuration, in the invention according to claim (1), super insulation is not used in the radiation shield (28), so compared to a radiation shield in which super insulation is wrapped around fiber reinforced resin. , there is no gas release, and the inside and outside of the radiation shield (28) are communicated through the slits (29) to (31), so that evacuation can be performed in a short time. Also,
Since the radiation shield (28) has a high thermal conductivity, its interior is efficiently cooled, and the cooling time of the gradiometer (B) can be shortened. Moreover, the radiation shield (
Since the emissivity of 28) is low, the radiant heat input to the gradiometer (B) inside it can be effectively blocked.

In addition, the radiation shield (28) has slits (29) to (
31) is formed, so the radiation shield (28)
Even if the material is electrically conductive, its radiation shield (2
The current generated by magnetic induction in 8) is passed through the slit (29
) to (31), so that no eddy current loop is formed, and therefore the magnetic flux i'llJ constant sensitivity of the gradiometer (B) can be maintained with high sensitivity. It becomes possible to form the refrigerator using a material having a low thermal conductivity and a high thermal conductivity, such as a single plate, and the work involved in disassembling and assembling the refrigerator becomes easier, thereby simplifying the work.

In the invention according to claim (a), the slit (29) is formed only on the outer periphery of the radiation shield (28), and the top plate or bottom plate (28b) of the radiation shield (28) is made of fiber reinforced resin. Super insulation on the outside (3
2) are stacked, so the slit (aO).

Even if it is difficult to form (30), ... on the top plate or bottom plate (28b) of the radiation shield (28), the top plate or the bottom plate has a radiation shield structure, thereby effectively shielding the radiant heat. can do.

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

FIG. 2 shows the overall configuration of the first embodiment of the present invention, (A
) is a two-circuit helium refrigerator, and this refrigerator (A) has a vacuum container (1) that is hermetically sealed, and the inside of the vacuum container (1) is kept in a vacuum state. (1) A gradiometer (B) as an object to be cooled is housed inside.

In addition, in the vacuum container (1), an expansion unit (3) of the pre-cooling refrigeration circuit (2) and an expansion unit (16) of the J-T circuit (16) are added.
17) is attached. The above pre-cooling refrigeration circuit (2)
is composed of a G-M (Gifford φ McMahon) cycle refrigerator, which compresses and expands helium gas in order to pre-cool the helium gas in the J-T circuit (1B). Compressor and the above 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) is
A casing (4) placed on the outer upper surface of the vacuum container (1)
) and a two-stage cylinder (13) connected to the lower part of the casing (4), and the casing (4) has a high-pressure gas inlet ( 4
a) and a low pressure gas outlet (4b) connected to the suction side. Further, the cylinder (13) penetrates the earth wall of the vacuum container (1) and hangs down inside the container (1), and the lower end of its large diameter part (13a) has a temperature level of 55 to 60 degrees. The first heat station (14
), and a second heat station (15) which is maintained at a temperature level of 15 to 20 degrees lower than that of the first heat station (14) is formed at the lower end of the small diameter portion (13b).

Although not shown here, the cylinder (13)
A displacer is reciprocatably fitted inside the cylinder (13) to define expansion chambers at positions corresponding to the heat stations (14) and (15). On the other hand, inside the casing (4), a valve is opened every time the casing rotates to supply helium gas flowing from the high-pressure gas inlet (4a) to the expansion chamber in the cylinder (13) or to expand the helium gas inside the expansion chamber. A rotary valve that switches to discharge helium gas from the low-pressure gas outlet (4b) and a valve motor that drives the rotary valve are fitted. Then, by opening the rotary valve in the expander (3), high pressure helium gas is pumped into the cylinder (13).
Simon is expanded in the expansion chamber inside the cylinder, and the temperature drop associated with the expansion generates cryogenic cold, which is then transferred to the first and second heat stations (14) and (15) in the cylinder (13). Hold. 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 (14) and (15) is lowered by adiabatic expansion in the expander (3). , the below-mentioned precooler (2) in the J-7 circuit (1B)
A closed precooling refrigeration circuit (2) is configured to precool the gases 2) and (23) and return the expanded low-pressure helium gas to the compressor for recompression.

On the other hand, the above J-T circuit (16) operates at an extremely low temperature level (approximately 4
K) A refrigeration circuit that compresses helium gas and expands it by Joule-Thomson in order to generate cold air. The expansion unit (17) for Thomson expansion is provided. This expansion unit (17) has a support part (18) arranged on the outer upper surface of the vacuum container (1), and the support part (18) is connected to the discharge side of the J-T compressor. High pressure gas inlet (
18a) and a low pressure gas outlet (18a) connected to the same suction side.
b) is open. In addition, at the lower part of the support part (18), there are provided first to third J-T heat exchangers (19) that penetrate the earthen wall of the vacuum container and the container (1) and hang down into the container (1). (2
1) are connected. Each of the above J-T heat exchangers (19)
- (21) are for exchanging heat between the helium gases passing through the primary side and the secondary side, respectively, and the primary side of the first J-T heat exchanger (19) is connected to the high pressure of the support part (18). It is connected to the gas inlet (18a). Further, the primary sides of the first and second J-T heat exchangers (19) and (20) are connected to the first heat station (
14) The first precooler (2
2). Similarly, the 2nd and 33rd
- The primary sides of the heat exchangers (20) and (21) are
The second heat station (15) of the expander (3) is connected via a second precooler (23) consisting of a heat exchanger disposed around the outer periphery of the second heat station (15). Furthermore, the third J-T heat exchanger (2
The primary side of 1) is connected to a cooler (25) via a J-T valve (24) that expands high-pressure helium gas.
It is connected to the. The opening degree of the J-T valve (24) is adjusted from outside the vacuum vessel (1) by an operating rod (not shown). The cooler (25) also has a cylindrical cooling member (26).
) consists of a coil-shaped pipe wound along the outer periphery of the cooler (25) and the cooling member (26).
) are in contact for heat transfer. In addition, the cooling member (26)
A cold receiving plate (27) is integrally formed at the lower end of the cooling plate (27), and the gradiometer (B) is integrally attached to the lower surface of the plate (27) so that heat can be transferred thereto.

Further, the cooler (25) is connected to the third and second J-T.
1J via each secondary side of heat exchangers (21) and (20)
- Connected to the secondary side of the T heat exchanger (19), and the first J-
The secondary side of the T heat exchanger (19) is connected to the low pressure gas outlet (18b) of the support section (18). Therefore, J-
In the 7th circuit (1B), helium gas is compressed to high pressure by a J-T compressor and supplied to the vacuum vessel (1) side, and it is transferred to the first to third J-T heat exchangers of the vacuum vessel (1). Vessel (19)
~(21) J:l: and exchanges heat with the low temperature, low pressure helium gas returning to the compressor side, and the first and second precoolers (22) and (23) respectively cool the expander (3). First and second heat stations (14), (15)
After cooling by heat exchange with J-T valve (24), it is expanded by Joule-Thomson in the cooler (25) to form helium in a gas-liquid mixed state at 1 atm and about 4. Inspection part (26), inspection plate (27
) and the gradiometer (B) in contact with it are cooled to an extremely low temperature level (approximately 4K), and then the helium gas, which has become low pressure due to the expansion, is transferred to the first to third J-T heat exchangers (19) to ( 21) is configured to be sucked into the J-T compressor through each secondary side and recompressed.

The above-mentioned gradiometer (B) is a well-known device, not shown, and includes a superconducting quantum interference element that becomes superconducting at an extremely low temperature level, and a magnetic flux input circuit connected to the superconducting quantum interference element, and the above-mentioned magnetic flux The input circuit is of a differential type, in which a plurality of superconducting coils arranged on the same straight line are connected in series so that current flows in opposite directions.

As shown in FIGS. 1 and 2, a cylindrical radiation shield (28) is disposed inside the vacuum container (1), and inside the radiation shield (28), the expansion machine (3
) of the cylinder (13) in the small diameter part (13b) (second
Heat station (15)), 2nd and 3rd J-
T heat exchanger (20), (21), J-T valve (24),
Cooler (25), inspection member (28), inspection plate (2)
7) as well as a gradiometer (B). This radiation shield (28) is the first radiation shield (28) of the expander (3).
It is in heat transferable contact with the heat station (14) and is maintained at a temperature level of 55 to 60°C, and the radiation shield (28) shields the radiant heat input to the gradiometer (B). There is.

As shown in FIG. 3, the radiation shield (28) is composed of a side plate (28a), a top plate (not shown) that closes the upper and lower openings of the side plate (28a), and a bottom plate (28b). Both are made of materials with low heat dissipation and high thermal conductivity. The side plate (28a) is formed by bending a single plate or the like of the above-mentioned material into a cylindrical shape, and includes a single strip extending in the direction of the center line of the radiation shield, which is formed by partially cutting out the side plate (28a). A slit (29) is formed. On the other hand, the top plate or bottom plate (28b) is disk-shaped, and a large number of slits (30), (to), . . . are formed in this top plate or bottom plate (28b). ), (30), ... are the side plates (28a
) extend parallel to each other in a direction perpendicular to the vertical plane passing through the slit (29) and the center line of the radiation shield.

In addition, the side plate (28a) and the top plate or bottom plate (21ib)
and are connected through Zetsusha-yo no Gakusaku (28c).

Next, the operation of the above embodiment will be explained.

The gradiometer (
Once B) is cooled and the temperature of the gradiometer (B) drops to cryogenic levels (approximately 4K), the gradiometer (B) becomes operational.

That is, first, the compressors of the pre-cooling refrigeration circuit (2) and the J-7 circuit (1B) are started, and the helium refrigerator (A) is activated.
When the is in steady operation, the high pressure helium gas supplied from the precooling compressor expands in the expander (3) in the precooling refrigeration circuit (2), and the temperature drop accompanying the expansion of this gas causes the cylinder (13) to cool down. 1st heat station (14)
is cooled to a temperature level of 55-60°C, and the second heat station (15) to a temperature level of 15-20°C.

Meanwhile, at the same time, in the J-7 circuit (1B), high pressure IJ and ram gas discharged from the compressor are pumped into the vacuum container (1B).
) side, and the high pressure helium gas supplied to this vacuum container (1) side is supplied to the high pressure gas inlet (1) of the support part (18).
8a) enters the primary side of the first J-T heat exchanger (L9), 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 300K to approximately 70K, and then the above-mentioned The first precooler (
22) and is cooled to about 55K. This cooled gas enters the primary side of the second J-T heat exchanger (20) and is similarly cooled down to about 20K by heat exchange with the low pressure helium gas on the secondary side, and then is cooled down to about 20K. ) of 15-20K
The heat enters the second precooler (23) on the outer periphery of the second heat station (15), which is cooled to approximately 15K.

Furthermore, the gas enters the primary side of the third J-T heat exchanger (21) and is cooled down to approximately 5K by heat exchange with the low pressure hem ram gas on the secondary side, and then flows into the J-T valve (24). reach. In this J-T valve (24), the high-pressure helium gas is throttled and expanded by Joule-Thomson, becoming helium in a gas-liquid mixture state of 1 atm and approximately 400 ml. ). And this cooler (25
), the testing member (28) and testing plate (27) are cooled by the latent heat of vaporization of the liquid portion of helium in the gas-liquid mixed state. When this inspection plate (27) is cooled, the gradiometer (B) which is in contact with the inspection plate (27) in a heat transferable manner is also cooled.

Then, the evaporated low-pressure helium gas is transferred to a cooler (25
) returns to the secondary side of the third J-T heat exchanger (21), during which time it becomes a saturated gas of about 4 ml, and this helium gas flows into the second and first J-T heat exchangers (20), (19). The high pressure helium gas on the primary side is sequentially cooled down to about 300K (room temperature) through the secondary side of the compressor. Return to the suction side. The above completes the pre-cooling refrigeration circuit (2) and J-
One cycle of the T circuit (18) is completed, and thereafter, the same cycle is repeated to perform the refrigeration operation of the refrigerator (A). Due to the continuation of such refrigeration operation, the gradiometer (
The temperature of B) falls towards a cryogenic level (operating temperature level), after reaching which cryogenic level the gradiometer (B) becomes operational.

Also, the first heat station (1) of the expander (3)
Since the radiation shield (28) is in heat transferable contact with 4), this radiation shield (28) is maintained at a temperature level of 55-60°C by cooling from the same heat station (14). As a result, this cryogenic radiation shield (
28), the gradiometer (B
) etc., and thus the gradiometer (B) can be maintained at an extremely low temperature level.

In that case, since no super insulation is used in the radiation shield (28), no gas is released from the super insulation. Moreover, the radiation shield (28) has a slit (29).

(30) is formed, so the slit (29)
.

(30) allows communication between the inside and outside of the radiation shield (28).

Due to these synergistic effects, vacuum evacuation for discharging air from the inside of the vacuum container (1) can be performed in a short time.

Moreover, since the radiation shield (28) is made of a material with high thermal conductivity, it takes only a short time to cool the inside thereof, and the cooling time of the gradiometer (B) can be shortened. Furthermore, since the radiation shield (28) is made of a material with low emissivity, it is possible to ensure a good shielding effect against the radiant heat input to the gradiometer (B). In addition, the radiation shield (28) has a slit (29).
), (30) are formed, so even if the radiation shield (28) is made of an electrically conductive material, the slit (29) prevents a high current loop from being generated in the radiation shield (28) due to magnetic induction. ), suppressed by (30),
Noise due to eddy currents can be reduced, and therefore the magnetic flux measurement sensitivity of the gradiometer (B) can be maintained at high sensitivity.

Furthermore, since the radiation shield (28) is formed of a veneer or the like made of a material with low heat dissipation rate and high thermal conductivity, when disassembling or assembling the vacuum container (1) of the refrigerator (A), etc. These tasks can be made easier without requiring much effort.

FIG. 4 shows a second embodiment of the present invention, in which the same parts as in FIG. 3 are given the same reference numerals and detailed explanation thereof is omitted), in which the structure of the radiation shield (28) is changed. It is.

That is, in this embodiment, the insulating groove (28e) in the radiation shield (28) is omitted, and instead, the slit (30) is formed in the top or bottom plate (28b).

In addition to (aO), ..., the slit (30), (3
One slit (31
) is formed. This embodiment can also provide the same effects as the first embodiment.

Further, FIG. 5 shows a third embodiment of the present invention, in which the slit (29) is formed only in the side plate (28a) on the outer periphery of the radiation shield (28). On the other hand, the top plate or bottom plate (28b) of the radiation shield (28) is composed of a disk-shaped fiber-reinforced resin plate, and the outer surface of the top plate or bottom plate (2gb) reaches the inner wall surface of the vacuum container (lo). Super insulation resin (32) is laminated.

Therefore, in this example, the slit (aO).

Even if it is difficult to form (30), ... on the top plate or bottom plate (28b) of the radiation shield (28), that part can be made into a radiation shield structure, thereby shielding the gradiometer (8) from radiant heat. can.

(Effects of the Invention) As explained above, according to the invention according to claim (1), the gradiometer is disposed in the vacuum container of the refrigerator, and the gradiometer is heated to a cryogenic level by the cooler of the refrigerator. When cooling the radiation shield to It is possible to improve gradiometer sensitivity by suppressing the generation of eddy currents that are harmful to magnetic flux measurements, while also shortening the evacuation time from the vacuum container and shortening the cooling time inside the radiation shield. At the same time, disassembling and assembling the refrigerator can be facilitated.

Further, according to the invention according to claim (a), the slit is formed only on the outer periphery of the radiation shield, and the top plate or the bottom plate that is a part of the radiation shield is made of fiber reinforced resin, and the outer surface of the top plate or the bottom plate is made of fiber reinforced resin. By laminating super insulation that reaches the inner wall surface of the vacuum container, even if it is difficult to form slits on the top or bottom plate of the radiation shield, the top or bottom plate can shield radiant heat with a radiation shield structure. I can do it.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, FIG. 1 is a sectional view showing main parts of a vacuum container and a radiation shield, FIG. 2 is a sectional view schematically showing a refrigerator, and FIG. FIG. 3 is a perspective view of the radiation shield. FIG. 4 is a diagram corresponding to FIG. 3 showing the second embodiment. FIG. 5 is a diagram corresponding to FIG. 1 showing the third embodiment. (A)... Helium refrigerator (1)... Vacuum container (2)... Pre-cooling refrigeration circuit (3)... Expansion machine (14), (15)... Heat station (1B
)...J-T circuit (24)...J-T valve (25)...Cooler (28)...Radiation shield (28b)...Bottom plate (29) to (31)...・Slit (32)...Super insulation (B)...
・Gradiometer Diagram 2

Claims (2)

[Claims] (1) Comprising a vacuum container (1) whose interior is evacuated and a cooler (25) disposed within the vacuum container (1),
The refrigerant compressed by the compressor is expanded to connect the cooler (25
), in which the vacuum container (1) has a superconducting quantum interference element that becomes superconducting at an extremely low temperature level and a magnetic flux input circuit connected to the element. The gradiometer (B) is cooled by the cooler (25), and the radiation shield (B) shields the gradiometer (B) from inputting radiant heat.
28) is arranged, and the radiation shield (28) is made of a material with low heat dissipation rate and high thermal conductivity, and slits (29) to (31) formed by partially cutting out a part of the radiation shield (28) are arranged. A radiation shield structure for a refrigerator, which is characterized by: (2) The slit (29) is formed only on the outer periphery of the radiation shield (28), and the top plate or bottom plate (28b) of the radiation shield (28) is made of fiber reinforced resin, and the top plate or bottom plate (28b) A radiation shield structure for a refrigerator according to claim 1, characterized in that super insulation (32) is laminated on the outer surface of the vacuum container (1) to reach the inner wall surface of the vacuum container (1).