JP7131147B2 - Cooling device and sensor device - Google Patents

Description

The present invention relates to a cooling device and a sensor device using the same.

A highly sensitive magnetic sensor using a SQUID (Superconducting Quantum Interference Device) is used for geomagnetic observation, resource exploration, biomagnetic observation, and the like. Among superconductors, oxide-based superconductors can be used at a high temperature of 77K, which is the boiling point of liquid nitrogen.

The SQUID is cryogenically cooled to a suitable operating temperature. A SQUID is generally cooled by being immersed in a coolant. A high-temperature superconducting SQUID is immersed in liquid nitrogen in a vacuum vessel such as a cryostat. A SQUID using a niobium-based metal superconductor is immersed in liquid helium or liquid hydrogen. In the SQUID, it is difficult to install a refrigerator close to the SQUID due to the problem of noise, and when a refrigerator is used, it is currently limited to a large-sized device that circulates and re-liquefies the refrigerant.

However, depending on the type of superconducting device, the container may be provided with a refrigerator in order to maintain a low-temperature environment. The liquid refrigerant gradually evaporates by receiving heat from the object to be cooled. The refrigerator keeps the refrigerant at an extremely low temperature and re-condenses (or re-liquefies) the evaporated refrigerant, thereby suppressing the reduction of the refrigerant.

a tank containing a cryogen; a refrigerator for cooling the cryogen; A cryogenic cooling device is known that has a heat conducting member that extends toward a surface and conducts heat from the outside of the tank to the inside of the tank (see, for example, Patent Document 1).

JP 2014-173755 A

A SQUID is a device that detects weak magnetic fields with high sensitivity, and it is desirable to eliminate the influence of vibration noise and magnetic noise as much as possible. Therefore, the SQUID is indirectly cooled by filling a container such as a vacuum glass dewar or FRP (Fiber Reinforced Plastic) with a coolant such as liquid nitrogen or liquid helium.

When a coolant is used, the coolant gradually decreases due to evaporation due to heat exchange. There is a trade-off between system miniaturization and cooling medium retention time, and a compact cooling container that can maintain a cooling environment for a long period of time has not been realized. For example, it is difficult to maintain a cooling hold time of more than 150 hours with 1 liter of liquid nitrogen.

If noise is not a problem, a refrigerator and a heater mechanism for reliquefaction can be introduced into the container as in the known example, but the effect of noise increases when a weak magnetic field is detected with high sensitivity. configuration is undesirable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling device capable of suppressing the influence of noise and cooling for a long time, and a sensor device using the same.

In one aspect, a cooling device for cooling a superconducting magnetic sensor includes:
a container having an opening;
a heat insulating material that seals the opening;
a cooling head positioned outside the vessel;
connecting means for thermally connecting at least one of the insulating material and the inner wall of the container to the cooling head;
have

Suppresses the influence of noise and enables long-term cooling.

1 is a diagram showing a heat inflow path of a general SQUID cooling device; FIG. It is a figure which shows the shape and specification of the container for heat inflow measurement. FIG. 10 is a diagram showing a plot of the heat input flow rate of each inflow path as a function of the amount of decrease in refrigerant, and a diagram showing changes in the residual amount of refrigerant (calculated values and measured values) in the type A container. FIG. 10 is a diagram plotting the heat input flow rate of each inflow path as a function of the amount of decrease in refrigerant, and a diagram showing changes in the residual amount of refrigerant (calculated values and measured values) in the type B container. FIG. 10 is a diagram showing a plot of the heat input flow rate of each inflow path as a function of the amount of decrease in refrigerant, and a diagram showing changes in the residual amount of refrigerant (calculated values and measured values) in the type C container. 1 is a schematic diagram of a cooling device of a first embodiment; FIG. 7 is a schematic diagram of a sensor device using the cooling device of FIG. 6; FIG. It is the schematic of the cooling device of 2nd Embodiment. 9 is a schematic diagram of a sensor device using the cooling device of FIG. 8; FIG. It is the schematic of the cooling device of 3rd Embodiment. 11 is a schematic diagram of a sensor device using the cooling device of FIG. 10; FIG.

The inventors have found that when cooling an object to be cooled with a small calorific value such as a SQUID, the influx of heat from the outside greatly contributes to the evaporation of the refrigerant. The SQUID itself generates a few nanowatts of heat, but the heat input from the outside is a few watts. By cooling or blocking the heat inflow path itself, it should be possible to suppress the evaporation of the refrigerant and increase the retention time of the refrigerant.

FIG. 1 is a diagram showing a heat inflow path of a general SQUID cooling device. A coolant 21 such as liquid nitrogen is accommodated inside the container 11 . An upper end opening of the container 11 is sealed with a heat insulating material 13 . A rod 14 that penetrates the heat insulating material 13 extends inside the container 11 , and a SQUID 20 is fixed to the tip of the rod 14 and immersed in a coolant 21 . SQUID 20 is connected to an external electronic circuit by wiring 16 inserted in rod 14 .

Vessel 11 is, for example, a double vacuum glass dewar, with space 115 between inner wall 113 and outer wall 111 being evacuated. A radiation shield 112 such as silver plating is applied to the inside of the double wall.

The liquid coolant 21 is filled up to the upper end of the container 11, but evaporates over time and the liquid level drops. When the distance h from the upper end of the container 11 (or the lower end of the heat insulating material 13) to the liquid surface increases and the position of the liquid surface falls below a predetermined level, the refrigerant 21 is replenished. In the case of long-term resource exploration and geological survey, the longer the retention time of the refrigerant 21 is, the better.

The heat inflow path to the container 11 mainly includes the following four elements. Heat inflow through the container 11 (first element), heat inflow through the radiation shield 112 (second element), heat inflow through the evaporated refrigerant gas (third element), and radiant heat from the heat insulator 13 ( 4th element). The path and effects of heat influx into such cooling vessels have not been investigated.

If vacuum glass is used for container 11, the heat input through the glass container is denoted as _QG . If the radiation shield 112 is a silver (Ag) coating, the heat input through the Ag coating is denoted as Q _Ag . When liquid nitrogen is used as the coolant 21, the heat input flow rate through the nitrogen gas in the container 11 is expressed as _QN . Radiant heat from the heat insulating material 13 is written as _QR .

As will be described later, the total amount of heat inflow from the four inflow paths is much larger than the amount of heat generated by the SQUID 20 itself. On the other hand, the wiring 16 likely to be a heat inflow path is made of a material with low heat conductivity such as phosphor bronze or copper manganese wire for electric resistance, and is inserted into a rod 14 with low heat inflow such as glass epoxy. . Therefore, the heat inflow through the wiring 16 is smaller than the heat inflow through the Ag coating or nitrogen gas. However, the portion of the wiring 16 exposed from the rod 14 can serve as a heat inflow path.

<Preliminary measurement>
As a preliminary measurement, the shape of the vessel is varied and the heat input is calculated for each vessel. Specifically, for each container, the heat inflow amount for each inflow path (element) and the total heat inflow amount are calculated.

FIG. 2 is a diagram showing the shape and dimensions of the container DW for measurement. Three containers of type A, type B, and type C are prepared as containers DW for measurement. Both types are cylindrical Pyrex glass vacuum duplex dewars. Let φ be the inner diameter of the container, t be the thickness, and H be the height of the internal space. Let h be the reduction level of the refrigerant 21 .

Type A has an inner diameter φ of 115 mm, a thickness of 3.0 mm, and an internal space height H of 265 mm. The capacity of this container DW is about 2 L, and the aspect ratio (ratio of height H to inner diameter φ) is about 2.3.

Type B has an inner diameter φ of 70 mm, a thickness of 2.4 mm, and an internal space height H of 600 mm. The capacity of this container DW is about 2 L, which is the same as that of type A, but the thickness of the container is thinner than that of type A, and the aspect ratio is as large as about 8.57.

Type C has an inner diameter φ of 40 mm, a thickness of 2.4 mm, and an internal space height H of 700 mm. The capacity of this container DW is about 0.8L. The container is tall and has a small capacity, and the aspect ratio is 17.5.

For each of these three vessels, the heat inflow of the four inflow paths described above and the total heat inflow are calculated. The amount of heat inflow is calculated from the amount of evaporation of the refrigerant 21 or the decrease level h of the liquid surface. Common to types A to C, liquid nitrogen is used as the refrigerant 21 . Styrofoam (registered trademark) having a thickness of 50 mm is used as the heat insulating material 13 for sealing the opening of the container DW. All types of containers DW are plated with silver to a thickness of 1 μm as a radiation shield 112 .

FIG. 3A is a diagram plotting the heat input flow rate of each element (inflow path) in type A as a function of the liquid level drop amount of the refrigerant. FIG. 3B is a graph plotting calculated values and measured values of the remaining amount of refrigerant as a function of time. Curve a shows the total heat inflow. Curve b is heat inflow from the glass container, curve c is heat inflow from the Ag coating, curve d is heat inflow from nitrogen gas, and curve e is heat radiation from the heat insulating material 13 at the opening of the container.

The biggest cause of heat inflow is heat conduction through the glass of the container DW. evaporation of nitrogen) is reduced. On the other hand, the surface temperature of the heat insulating material at the opening of the container DW approaches the environmental temperature, and heat radiation increases.

With reference to FIG. 3(B), the residual amount of liquid nitrogen over time is almost the same as the calculated value calculated from the evaporation amount and the measured value, and the calculation result of FIG. 3(A) confirms that is correct.

FIG. 4A is a diagram plotting the heat input flow rate of each element (inflow path) in type B as a function of the amount of decrease in the liquid level of the refrigerant. (B) of FIG. 4 is a diagram plotting the calculated values and the measured values of the remaining amount of refrigerant as a function of time. The type B container has a capacity equivalent to that of the type A, but the thickness of the container DW is thinner than that of the type A, and the shape is elongated vertically.

Curve a shows the total heat inflow. Curve b is heat inflow from the glass container, curve c is heat inflow from the Ag coating, curve d is heat inflow from nitrogen gas, and curve e is heat radiation from the heat insulating material 13 at the opening of the container.

The trend of change in heat inflow with decreasing liquid nitrogen or increasing nitrogen vapor is the same as type A, but the amount of heat inflow from the outside is less than half that of the type A vessel. This is probably because the vertically elongated container lengthens the distance from the opening to the heat source (SQUID) near the bottom of the container, and reduces the amount of heat that reaches the vicinity of the heat source through the glass from the opening. In addition, by reducing the thickness of the container DW, the amount of heat accumulated in the glass per unit area is reduced.

From this, it can be seen that evaporation of liquid nitrogen can be effectively prevented by setting the aspect ratio of the container to 3 or more, more preferably 5 or more, and even more preferably 8 or more when the capacity is the same. Considering both the strength of the container and the suppression of heat inflow, the thickness of the container is 1.0 mm or more and less than 3.0 mm, more preferably in the range of 1.5 mm to 2.5 mm. can be maintained and heat influx can be reduced.

Also in FIG. 4B, the calculated value and the measured value of the remaining amount of liquid nitrogen with the lapse of time are almost the same, which confirms that the calculation result of FIG. 4A is correct.

FIG. 5A is a diagram plotting the heat input flow rate of each element (inflow path) in type C as a function of the amount of decrease in the liquid level of the refrigerant. FIG. 5B is a diagram plotting the calculated values and measured values of the remaining amount of refrigerant as a function of time. Type C containers have the same thickness as Type B, but have less than half the volume of Type B and have a higher aspect ratio.

Curve a shows the total heat inflow. Curve b is heat inflow from the glass container, curve c is heat inflow from the Ag coating, curve d is heat inflow from nitrogen gas, and curve e is heat radiation from the heat insulating material 13 at the opening of the container.

The trend of change in heat inflow with decreasing liquid nitrogen or increasing nitrogen vapor is the same as type A and type B, but the amount of heat inflow is smaller than type B.

In FIG. 5(B), the calculated value and the measured value of the remaining amount of liquid nitrogen with the lapse of time almost match, which confirms that the calculation result of FIG. 5(A) is correct. The retention time of liquid nitrogen is comparable to that of type B, even though the volume of the type C container is less than half that of the type B container. Both the miniaturization of the container and the ability to retain the refrigerant are satisfied.

The results of FIGS. 3 to 5 suggest that the evaporation of the refrigerant can be suppressed by cooling the heat flow path of at least one of the wall surface extending from the opening of the container 11 and the sealing material of the opening. By preventing at least one of heat inflow through the wall surface of the container (for example, the glass wall) and radiant heat from the heat insulating material 13, evaporation of the refrigerant can be suppressed, and heat inflow via refrigerant vapor (for example, nitrogen gas) can also be suppressed. can.

The results of FIGS. 3-5 also suggest that optimizing the shape and thickness of vessel 11 can reduce heat influx. Heat influx can be reduced by lengthening the heat conduction path from the opening or by reducing the thickness of the container.

Based on the result of the preliminary measurement described above, in the embodiment, at least one of the inner wall of the container 11 and the heat insulating material of the opening is cooled to prevent the refrigerant from evaporating. Instead of or in combination with this configuration, the container body may have an aspect ratio (ratio of height to diameter) of 3 or more. Alternatively, the thickness of the vacuum vessel may be 1.0 mm or more and less than 3.0 mm.

<First embodiment>
FIG. 6 is a schematic diagram of the cooling device 110A of the first embodiment. The cooling device 110A has a container 11A having an opening 116 at its upper end and a heat insulating material 13A sealing the opening 116, and is provided with a cooling mechanism for cooling at least one of the inner wall of the container 11A and the heat insulating material 13A. there is

In the example of FIG. 6, the cooling head 31 is arranged outside the opening 116, and the inner wall near the opening 116 of the container 11A and the heat insulating material 13A are cooled using a heat conductor, which will be described later. The cooling head 31 is connected to the refrigerator 30 . As for the capacity of the refrigerator 30, it is desirable to have a cooling output of 5 W or more at 77K.

The container 11A is, for example, a vacuum glass dewar of type A (see FIG. 2). This glass dewar is a double structure vacuum dewar, and the space 115 between the inner wall 113 and the outer wall 111 is evacuated. A radiation shield 112 such as silver plating is applied to the inside of the double wall.

In the cooling device 110A, in addition to the heat insulating material 13A that seals the opening 116, a heat insulating material 17 that covers the periphery of the opening 116 is also provided from the viewpoint of blocking heat inflow as much as possible. The cooling head 31 is arranged outside the opening 116 in a space surrounded by the heat insulating material 17 . By surrounding the upper end of the container 11A with the heat insulating material 17, the temperature outside the opening 116 can be brought close to 77 K and maintained in that state. For the heat insulating material 13A and the heat insulating material 17, suitable heat insulating materials such as plastic foam, carbon, glass wool, alumina (sapphire), and zirconia can be used. In this example, expanded polystyrene is used in this example.

A cooling member 18 is provided on the upper surface of the heat insulating material 13A, and a cooling member 19 is arranged on the inner wall near the opening 116. As shown in FIG. The cooling members 18 and 19 are cooling plates, cooling sheets, cooling bodies, etc. formed of Ag-plated copper (or Ag-plated copper alloy) with high thermal conductivity. The base material of the cooling members 18 and 19 can be made of various copper alloys, such as brass and phosphor bronze, in addition to pure copper.

A cooling member 18 for thermal insulation is connected to the cooling head 31 with a heat-conducting ribbon 23a. The cooling member 19 on the inner wall of the container is connected to the cooling head 31 with a heat-conducting ribbon 23b. Thermally conductive ribbons 23a and 23b are, for example, Ag-plated copper ribbons. The container 11A is cooled from the outside of the opening 116 by the cooling members 18 and 19 and the heat conducting ribbons 23a and 23b. By thermally connecting the cooling members 18 and 19 to the cooling head 31 using the heat-conducting ribbons 23a and 23b, direct transmission of the vibration of the refrigerator 30 to the cooling device 110A is suppressed.

By cooling the opening 116 of the container 11A and its vicinity, heat inflow (curve b) from the container wall (glass), which is the dominant factor in the heat inflow path in FIG. 3, and heat radiation from the heat insulating material 13A (curve e) can be suppressed. When the heat inflow through the glass is suppressed, the heat inflow (curve c) from the radiation shield 112 formed in the vacuum glass dewar of the container 11A is also suppressed. When the amount of heat generated by the object to be cooled is small, the evaporation amount of the refrigerant can be reduced by blocking the main factor of heat inflow from the outside. As a result, the heat inflow (curve d) due to the refrigerant vapor can also be reduced.

Another feature of the cooling device 110A is that the cooling head 31 is outside the opening 116 of the container 11A and the refrigerator 30 is positioned further away from the opening 116. As shown in FIG. The structure is such that the vibration of the refrigerator 30 is less likely to be transmitted to the inside of the container 11A, and is suitable for cooling a highly sensitive magnetic sensor such as a SQUID.

FIG. 7 is a schematic diagram of a sensor device 10A using the cooling device 110A of the first embodiment. The sensor device 10A has a cooling device 110A and a SQUID 20 arranged inside the cooling device 110A. The container 11A is filled with the coolant 21, and the SQUID 20 is immersed in the coolant 21 and cooled.

The SQUID 20 is an example of a sensor element to be cooled, and its type and configuration are not limited. In SQUID 20, an input coil and a pickup coil are magnetically connected to a SQUID loop having one or two Josephson junctions. The pickup coil and the SQUID coil may be arranged on the same plane, or may be stacked on one substrate. The SQUID loop and the pickup coil do not necessarily need to be integrally formed, and a pickup coil that is a separate body from the SQUID loop and wound three-dimensionally may be used.

From the viewpoint of canceling external noise, a gradiometer using a pair of coils wound in opposite phases is desirable as a pickup coil, but a single-phase pickup coil may also be used. SQUID 20 may be a multi-SQUID chip containing multiple SQUID loops.

SQUID 20 is fixed to the lower end of rod 14 and immersed in coolant 21 . The rod 14 is made of a material with low thermal conductivity, such as glass epoxy or sapphire. A signal (current) detected by SQUID 20 is supplied to an external electronic circuit by wiring 16 passing through rod 14 .

The SQUID 20 is arranged near the bottom surface of the container 11A. When measuring with the bottom surface of the container 11A facing the object to be measured, it is easier to detect the magnetic field if the SQUID 20 is arranged near the bottom surface of the container 11A. In the sensor device 10A of the embodiment, since evaporation of the coolant 21 due to external heat is suppressed, almost no vibration noise is generated due to collision of air bubbles with the SQUID 20 . Even if a minute amount of heat generated by the SQUID 20 can generate minute air bubbles, the air bubbles rise toward the liquid surface above the SQUID 20, so deterioration of the sensing sensitivity of the SQUID 20 is suppressed. Further, by placing a distance between the SQUID and the refrigerator, noise from the refrigerator to the SQUID can be suppressed.

As shown in FIGS. 6 and 7, a cooling head 31 may cool the wiring 16 drawn from the rod 14 in the vicinity of the opening 116 of the container 11A. This is because the portion of the wiring 16 exposed from the rod 14 can serve as a heat inflow path. By cooling the wiring 16, the inflow of heat from the outside can be further suppressed.

The cooling head 31 is arranged outside the container 11A, and the coolant 21 and the cooling head 31 are not in direct contact. In addition, the distance between the refrigerator 30 and the SQUID 20 at the tip of the rod 14 is set sufficiently long. Vibration of the refrigerator 30 is less likely to be transmitted to the inside of the cooling device 110A, and the influence of noise can be suppressed.

A cooling member 18 provided on the heat insulating material 13A and a cooling member 19 provided on the inner wall of the container are thermally connected to the cooling head 31 by heat-conducting ribbons 23a and 23b, and are main paths for heat inflow into the interior of the container 11A. is cooled. As a result, direct transmission of vibration from the refrigerator 30 can be suppressed, and the holding time of the refrigerant 21 can be lengthened.

When the inner diameter of the container 11A is 114 mm and the thickness is 3.0 mm, the total amount of heat inflow in the initial state is about 2 W by using the cooling device 110A configured as shown in FIG. While using a type A container 11A with a small aspect ratio, by cooling the heat insulating material 13A of the opening 116 of the container 11A and the heat inflow path itself through the glass wall, the total amount of heat inflow is halved or less. can be done. Since the amount of heat generated by the SQUID 20 itself is on the order of several nanowatts, evaporation of the refrigerant 21 is suppressed, and long-term cooling becomes possible.

When the container 11B is a type C container, that is, when the inner diameter of the glass dewar is 40 mm, the height of the internal space is 700 mm, and the thickness of the glass is 2.4 mm, the total heat inflow in the initial state is 0.4 mm. It can be reduced to 5W. In this case, the refrigerant 21 hardly evaporates or the amount of evaporation is very small. The sensor device 10A can be used over a long span without replenishment of the refrigerant 21. FIG.

When the type C container is used, the positions of the SQUID 20 and the refrigerator 30 are further separated, the influence of noise can be reduced, and heat transfer to the vicinity of the SQUID 20 can be suppressed. Instead of type C, a type B container may be used. The type B container is also more effective in preventing heat inflow and suppressing the influence of vibration than the type A container. However, by adopting the configurations shown in FIGS. 6 and 7, the influence of noise can be reduced and the cooling state can be maintained for a long time regardless of which type of container is used.

In the above example, Ag-plated copper or Ag-plated copper alloy was used as the cooling members 18, 19 and the heat conductive ribbons 23a, 23b. good too.

In particular, when a magnetic field is actively applied, such as in a TEM (Transient Electro-Magnetic) method for underground exploration, it is desirable to use a graphite sheet with anisotropic conductivity. By using a conductive anisotropic material as the thermal connection means, it is possible to prevent induced currents in the system from interfering with the measurement.

The cooling member 18 on the heat insulating material 13 side and the cooling member 19 on the inner wall of the container may be integrally formed. Also, as thermal connection means, one or more thermally conductive ribs extending from at least one of the cooling member 18 and the cooling member 19 toward the cooling head 31 may be provided instead of the thermally conductive ribbons 23a and 23b. .

As the material for the container 11A, besides heat-resistant glass, glass epoxy, FRP, and the like are also useful. The refrigerator 30 may be of any type, such as a Stirling refrigerator, a GM (Gifford-McMahon) refrigerator, or a pulse tube refrigerator.

<Second embodiment>
FIG. 8 is a schematic diagram of the cooling device 110B of the second embodiment. The cooling device 110B is based on the configuration of the first embodiment, and the same components as those of the first embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted.

A different point from the first embodiment is that a vacuum insulation structure is adopted for the heat insulating material 13B that seals the opening 116 of the container 11B. In this example, a hollow heat insulating material 13B is used.

The heat insulating material 13B has an annular main body 131 that matches the shape of the opening 116 of the container 11B. A hole 134 through which the rod 14 is passed is formed in the center of the main body 131 . A space 133 is formed inside the main body 131, and the inside of the space 133 is evacuated. A radiation shield 132 is formed on the wall surface of the internal space.

A main body 131 of the heat insulating material 13B is made of an appropriate heat insulating material such as Pyrex (registered trademark) glass, glass epoxy, FRP, or the like. The internal radiation shield 132 is Ag coating, for example.

As in the first embodiment, a cooling member 18 is provided on the surface of the heat insulating material 13B that seals the opening 116, and a cooling member 19 is provided on the inner wall of the container 11B. Cooling member 18 and cooling member 19 are thermally connected to cooling head 31, respectively, by thermally conductive ribbons 23a, 24b of graphite, Ag-plated copper, or the like. As a result, the heat radiation from the heat insulating material 13B and the heat inflow path through the wall surface of the container 11B are cooled, and direct transmission of vibration from the refrigerator can be prevented.

By applying the vacuum insulation structure to the heat insulating material 13B, the radiant heat from the heat insulating material 13B can be effectively reduced. Evaporation of the refrigerant 21 can be suppressed by reducing radiant heat, and heat conduction through the refrigerant vapor (for example, nitrogen gas) can also be reduced.

Any of types A to C may be used as the container 11B, but by combining the configuration of FIG.

FIG. 9 is a schematic diagram of a sensor device 10B using the cooling device 110B of the second embodiment. The sensor device 10B has a cooling device 110B and a SQUID 20 arranged inside the cooling device 110B. The container 11B of the cooling device 110B is filled with the coolant 21, and the SQUID 20 is immersed in the coolant 21 and cooled.

As in the first embodiment, the cooling head 31 is located outside the opening 116 of the container 11A, and the refrigerator 30 is arranged further away from the opening 116 . Vibration of the refrigerator 30 is less likely to be transmitted to the inside of the container 11B, and a highly sensitive sensor device using the SQUID 20 is realized.

When the cooling members 18, 19 and the heat conducting ribbons 23a, 23b are made of an anisotropic heat conducting material, the sensor device 10B can be effectively used for underground exploration by the TEM method or the like. In addition to being able to suppress the generation of an induced current that interferes with measurement, the retention time of the coolant 21 is extremely long, so the sensor device 10B can be installed underground for a long period of time.

<Third Embodiment>
FIG. 10 is a schematic diagram of a cooling device 110C of the third embodiment. 110 C of cooling devices are based on the structure of 1st Embodiment, attach the same code|symbol to the same component as 1st Embodiment, and abbreviate|omit the overlapping description.

A different point from the first embodiment is that the inner wall near the opening 116 of the container 11C is provided with a region 119 having a wavy surface. By undulating the surface, it is possible to increase the heat transfer distance from the ambient temperature to the surface of the coolant 21 .

The surface pattern for extending the heat conduction distance is not limited to the corrugated pattern, and a meander pattern, a sawtooth pattern, or the like may be used as the cross-sectional shape. By lengthening the heat transfer path from the opening 116 of the container 11C to the surface of the coolant 21, the inflow of heat to the coolant 21 is suppressed.

As in the first embodiment, a cooling member 18 is provided on the surface of the heat insulating material 13B that seals the opening 116, and the cooling member 18 is thermally connected to the cooling head 31 by a heat conducting ribbon 23a. As a result, the path of heat radiation from the heat insulating material 13B is cooled, and direct transmission of vibration from the refrigerator can be prevented.

In the third embodiment, the region 119 that extends the heat conduction distance suppresses heat inflow through the wall surface of the 11C container. Therefore, in the example of FIG. 10, no cooling member is provided on the inner wall of the container 11C. may be formed. As a thin film for cooling, a laminated film of copper alloy and silver, a graphite film, or other high thermal conductive films can be formed by spray coating or the like. A thermally conductive ribbon 23b may be used to thermally connect the cooling membrane to the cooling head 31 . The corrugated pattern can provide a large cooling area in the vicinity of the opening 116, thereby suppressing the influx of heat from the ambient temperature.

Any of types A to C may be used as the container 11C. By combining the configuration of FIG. 10 with the type B or type C container shape, the heat inflow prevention effect can be further enhanced.

FIG. 11 is a schematic diagram of a sensor device 10C using a cooling device 110C of the third embodiment. The sensor device 10C has a cooling device 110C and a SQUID 20 arranged inside the cooling device 110C. The container 11B of the cooling device 110B is filled with the coolant 21, and the SQUID 20 is immersed in the coolant 21 and cooled.

As in the first and second embodiments, the cooling head 31 is located outside the opening 116 of the container 11C, and the refrigerator 30 is arranged further away from the opening 116 . Vibration of the refrigerator 30 is less likely to be transmitted to the inside of the container 11C, and a highly sensitive sensor device using the SQUID 20 is realized.

When a thermally conductive material having anisotropic conductivity is used for the cooling member 18 and the thermally conductive ribbon 23a, the sensor device 10C can be applied to underground exploration by the TEM method. In addition to being able to suppress the generation of an induced current that interferes with measurement, the retention time of the coolant 21 is extremely long, so the sensor device 10C can be installed underground for a long period of time.

The configurations of the first to third embodiments described above can be appropriately combined. For example, the vacuum insulation configuration of the second embodiment may be combined with the extension configuration of the heat conduction path of the container 11C of the third embodiment. A cooling film may be provided in the region 119 of the inner wall of the container 11C of the third embodiment, and the upper end of the container 11C may be connected to the cooling head 31 by thermal connecting means (such as a heat conducting ribbon). Appropriate container shapes of type A to type C can be selected according to the usage environment, purpose of use, and the like.

The object to be cooled is not limited to a high-temperature superconducting SQUID, and may be a low-temperature superconducting SQUID. The coolant 21 is selected according to the operating temperature of the object to be cooled, and liquid nitrogen, liquid hydrogen, liquid helium, or the like is used.

A sensor system may be constructed using the sensor device 10 and the signal processing device of the embodiment. The SQUID 20 may be connected to an FLL (Flux-Locked Loop) circuit by wiring 16, for example. The FLL circuit is controlled by a personal computer or the like to control and drive the SQUID. The FLL circuit applies a bias current to SQUID 20 and outputs a voltage signal corresponding to changes in the magnetic field sensed by SQUID 20 . By moving the sensor device 10 to acquire signals at a plurality of different positions, or by collecting output signals from a plurality of sensor devices 10, the magnetic field distribution can be obtained with high sensitivity.

The sensor device 10 of the embodiment can be applied to a wide range of fields such as bridge deterioration diagnosis, resource exploration and production monitoring, geomagnetism observation, SQUID microscope, and biomagnetic measurement. The sensor device 10 of the embodiment can be operated continuously for a long time, and can contribute to the improvement of sensing technology.

To the above description, the following remarks are presented.
(Appendix 1)
A cooling device for cooling a superconducting magnetic sensor,
a container having an opening;
a heat insulating material that seals the opening;
a cooling head positioned outside the vessel;
connecting means for thermally connecting at least one of the insulating material and the inner wall of the container to the cooling head;
A cooling device comprising:
(Appendix 2)
2. The cooling device of claim 1, wherein said connecting means is a thermally conductive ribbon.
(Appendix 3)
The cooling device according to appendix 2, wherein the thermally conductive ribbon is a graphite sheet having anisotropic conductivity.
(Appendix 4)
The cooling device according to any one of appendices 1 to 3, wherein the heat insulating material has a vacuum heat insulating structure.
(Appendix 5)
5. A cooling device according to any one of claims 1 to 4, characterized in that the inner wall of the container has a region extending the heat transfer distance near the opening.
(Appendix 6)
The cooling device according to any one of appendices 1 to 5, wherein the aspect ratio of the height of the inner space of the container to the inner diameter is 3 or more.
(Appendix 7)
7. The cooling device according to claim 6, wherein the aspect ratio of the container is 5 or more.
(Appendix 8)
a first cooling member provided in the heat insulating material;
first connecting means for thermally connecting the first cooling member to the cooling head;
The cooling device according to appendix 1, characterized by comprising:
(Appendix 9)
a second cooling member provided on the inner wall of the container near the opening;
a second connection means for thermally connecting the second cooling member to the cooling head;
The cooling device according to appendix 1, characterized by comprising:
(Appendix 10)
a second insulation surrounding the opening;
further having
10. Cooling device according to any of claims 1 to 9, characterized in that the cooling head is arranged outside the container and in the space defined by the second insulating material.
(Appendix 11)
The cooling device according to any one of Appendices 1 to 10;
a refrigerant filled in the container;
a superconducting magnetic sensor immersed in the coolant in the container;
A sensor device comprising:
(Appendix 12)
12. The sensor device according to claim 11, wherein the cooling head cools wiring that connects the superconducting magnetic sensor to an external electronic circuit.
(Appendix 13)
13. The sensor device according to appendix 11 or 12, wherein the superconducting magnetic sensor is arranged in the vicinity of the bottom surface of the container.
(Appendix 14)
14. The sensor device according to any one of appendices 11 to 13, wherein the coolant is liquid nitrogen.

10, 10A to 10C sensor device 11, 11A to 11C container 13, 13A to 13C heat insulating material 17 heat insulating material 18, 19 cooling member 20 SQUID (superconducting magnetic sensor element)
21 Coolant 23a, 23b Heat-conducting ribbon (connecting means)
110, 110A to 110C Cooling device 112 Radiation shield 115 Space 116 Opening

Claims (8)

A cooling device for cooling a superconducting magnetic sensor,
a container having an opening;
a heat insulating material that seals the opening;
a cooling head positioned entirely outside the vessel;
connecting means for thermally connecting at least one of the insulating material and the inner wall of the vessel to the cooling head located entirely outside the vessel ;
A cooling device comprising: 2. The cooling device of claim 1, wherein said connecting means is a thermally conductive ribbon. 3. The cooling device according to claim 2, wherein the thermally conductive ribbon is a graphite sheet having anisotropic conductivity. The cooling device according to any one of claims 1 to 3, wherein the heat insulating material has a vacuum heat insulating structure. A cooling device as claimed in any preceding claim, wherein the inner wall of the container has an area extending the heat transfer distance near the opening. The cooling device according to any one of claims 1 to 5, wherein the aspect ratio of the height of the inner space of the container to the inner diameter is 3 or more. A cooling device according to any one of claims 1 to 6,
a refrigerant filled in the container;
a superconducting magnetic sensor immersed in the coolant in the container;
A sensor device comprising: 8. The sensor device according to claim 7, wherein the cooling head cools wiring connecting the superconducting magnetic sensor to an external electronic circuit.

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