JPWO2008066127A1 - refrigerator - Google Patents

Abstract

A cooling stage that cools the object to be cooled; a He condensing unit on which the object to be cooled is placed; a reservoir filled with He gas that communicates with the He condensing unit; and the cooling stage and the He condensing unit And a heat transfer buffer material made of a material having a lower thermal conductivity than the He condensing unit.

Description

  The present invention relates to a refrigerator.

  GM refrigerators are used for measuring sample physical properties in a cryogenic environment near 4K, measuring various physical quantities using sensors that utilize the cryogenic environment, and the like. This refrigerator cools an uncooled object to a very low temperature by repeating compression and expansion (refrigeration cycle) of refrigerant gas such as He gas. However, due to the pulsation of the heat flow caused by the above-described refrigeration cycle, a temperature amplitude is generated on the placement surface of the object to be cooled. In order to cool the object to be cooled stably, it is desired to reduce this temperature amplitude.

In Patent Document 1, a cold storage unit that stores helium gas or helium gas and liquid helium, a compressed helium gas supply unit, and the cold storage unit provided in a cooling unit to which an object to be cooled is attached is connected. A cryogenic refrigerator including helium gas introduction / exhaust means is disclosed.
Patent Document 2 discloses a cryogenic temperature damper having a helium gas introduction pipe for introducing a necessary amount of helium gas at room temperature, a capacitor chamber for liquefying helium gas, and a liquid helium chamber for storing liquefied liquid helium. Is disclosed.
Japanese Patent No. 2773793 JP 2004-79955 A

However, since the temperature amplitude in the cryogenic refrigerator of Patent Document 1 is about 30 mK, further reduction of the temperature amplitude is desired.
On the other hand, the cryogenic temperature damper of Patent Document 2 has a complicated structure, and the heat transfer flow path from the cooling object is long and non-axisymmetric, so that cooling may be uneven and unstable.

  The present invention has been made to solve the above-described problems, and is capable of reducing the temperature amplitude on the surface on which the object to be cooled is placed, and also capable of cooling the object to be cooled uniformly and stably. The purpose is to provide a machine.

In order to solve the above problems, the present invention employs the following means. That is, the refrigerator of the present invention includes a cooling stage that cools an object to be cooled; a He condensing unit on which the object to be cooled is placed; a reservoir filled with He gas that communicates with the He condensing unit; A heat transfer buffer material, which is disposed between the cooling stage and the He condensing unit and is made of a material having a lower thermal conductivity than the He condensing unit.
According to this configuration, the pulsation of the heat flow caused by the refrigeration cycle of the refrigerator is absorbed by the evaporation and condensation (phase transition) of He in the He condensation unit. At that time, since the heat transfer buffer acts as a heat flow restricting mechanism, transmission of temperature amplitude in the cooling stage is suppressed. As a result, the temperature amplitude on the placement surface of the object to be cooled can be reduced. Further, since the cooling stage, the heat transfer buffer material, the He condensing part, and the object to be cooled are continuously arranged coaxially, the object to be cooled can be uniformly and stably cooled.

The He condensing part may be made of a material having a thermal conductivity of 200 W / (m · K) or more at a temperature in the vicinity of 4K.
According to this configuration, the object to be cooled can be efficiently cooled by the liquid He condensed in the He condensing unit.

The heat transfer buffer material may be made of a material having a thermal conductivity of less than 100 W / (m · K) at a temperature in the vicinity of 4K.
According to this configuration, transmission of temperature amplitude in the cooling stage can be reliably prevented.

The volume of the He condensing part may be 10 cc or more and 100 cc or less.
According to this configuration, the He condensing unit can be made compact while securing the storage volume of the liquid He necessary for cooling the object to be cooled.

The volume of the reservoir may be not less than 5 times and not more than 100 times the volume of the He condensing unit.
According to this configuration, the reservoir can be made compact while ensuring the storage volume of the He gas necessary for cooling the object to be cooled.

The pressure of the He gas filled in the reservoir may be 0.1 MPa or more and 1.0 MPa or less at room temperature.
According to this configuration, even if the refrigerator is stopped and the liquid He in the He condensing part evaporates, it is possible to prevent the reservoir and the He condensing part from becoming high pressure.

A fin may be erected on the inner surface of the He condensing unit.
Further, a porous structure may be attached to the inner surface of the He condensing unit.
According to these structures, since the contact area of the inner surface of He condensation part and liquid He becomes large, the to-be-cooled object mounted in He condensation part can be cooled efficiently.

Irregularities may be formed on the contact surface between the heat transfer buffer material and the cooling stage or the He condensing unit.
According to this configuration, the contact area between the heat transfer buffer material and the cooling stage or the He condensing unit is reduced, so that transmission of temperature amplitude in the cooling stage is suppressed. As a result, the temperature amplitude on the placement surface of the object to be cooled can be reduced.

The apparatus may further comprise a temperature sensor and a heater attached to the He condensing unit; and a control unit that drives the heater based on a measurement result of the temperature sensor.
According to this configuration, when the temperature of the He condensing unit falls below a predetermined value, the heater can be driven to return the temperature of the He condensing unit to the predetermined value. Accordingly, it is possible to reduce the temperature amplitude on the placement surface of the object to be cooled.

  According to the present invention, by providing the heat transfer buffer material, the transmission of the temperature amplitude in the cooling stage is prevented, and as a result, the temperature amplitude on the placement surface of the object to be cooled can be reduced. Further, since the cooling stage, the heat transfer buffer material, the He condensing part, and the object to be cooled are continuously arranged coaxially, the object to be cooled can be uniformly and stably cooled.

FIG. 1 is a schematic configuration diagram of a refrigerator according to the first embodiment of the present invention. FIG. 2 is a graph showing the relationship between the temperature of the second cooling stage and the temperature amplitude. FIG. 3 is a graph showing the relationship between the volume ratio of the liquid He and the temperature amplitude in the He condensing unit. FIG. 4 is a graph showing the relationship between the temperature of the second cooling stage and the refrigerating capacity. FIG. 5 is a graph showing the relationship between the cooling time and the temperature of the second cooling stage. FIG. 6 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the second embodiment of the present invention. FIG. 7 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the third embodiment of the present invention. FIG. 8 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the fourth embodiment of the present invention. FIG. 9 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the fifth embodiment of the present invention.

Explanation of symbols

1 Refrigerator 14 Second cooling stage (cooling stage)
16 Heat transfer buffer 18 Concavity and convexity 20 He condensation unit 30 Reservoir 40 Object to be cooled 50 He gas 62 Control unit 64 Temperature sensor 66 Heater 222 First fin (fin)
224 2nd fin (fin)
322 Porous structure

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic configuration diagram of a refrigerator according to the first embodiment of the present invention. The refrigerator 1 according to the present embodiment includes a second cooling stage 14 that cools the object to be cooled 40, a He condensing unit 20 on which the object to be cooled 40 is placed, and a He gas 50 that communicates with the He condensing unit 20. And a heat transfer buffer 16 made of a material having a lower thermal conductivity than that of the He condensing unit 20, disposed between the second cooling stage 14 and the He condensing unit 20. It is.

  The refrigerator 1 mainly includes a compressor 4, a main body 2 and a cooling unit 15. The compressor 4 compresses low-pressure He gas supplied from the low-pressure pipe 8 into high-pressure He gas, and supplies the high-pressure pipe 6 to the high-pressure pipe 6. The main body 2 continuously switches the connection between the high-pressure pipe 6 and the low-pressure pipe 8 and the He gas flow path in the cooling unit 15 described below by the power of a motor or the like.

  A cooling unit 15 is provided continuously to the main body 2. The cooling part 15 is arrange | positioned inside the vacuum chamber 10 hold | maintained in the vacuum environment, and generates cold by expansion | swelling of He gas which distribute | circulates an inside. The cooling unit 15 includes a first cooling unit 11, a first cooling stage 12, a second cooling unit 13, and a second cooling stage 14 in order. The first cooling unit 11 and the second cooling unit 13 are formed in a columnar shape, and the first cooling stage 12 and the second cooling stage 14 are formed in a disk shape and are arranged coaxially. A He gas flow path (not shown) is formed inside the cooling unit 15. The high-pressure He gas supplied to the He gas flow path undergoes endothermic expansion in the second cooling stage 14 and changes to low-pressure He gas.

A heat transfer buffer 16 is provided between the lower surface of the second cooling stage 14 and the He condensing unit 20 described later. The heat transfer buffer 16 is formed in a plate shape having a diameter of about several tens mm and a thickness of about 2 mm, for example. The heat transfer buffer 16 is made of a stainless material or the like whose thermal conductivity at a temperature in the vicinity of 4K is lower than that of the He condensing unit 20 described later. In particular, if the heat transfer buffer 16 is made of a material having a thermal conductivity of less than 100 W / (m · K) at a temperature in the vicinity of 4K, the temperature amplitude of the second cooling stage 14 is transmitted to the He condensing unit 20. Can be suppressed.
In addition, In foil etc. are applied to both surfaces of the heat-transfer buffer material 16 in order to improve thermal contact property, the 2nd cooling stage 14, the heat-transfer buffer material 16, and the He condensation part 20 are fastened.

  A He condensing unit 20 on which the object to be cooled 40 is placed is provided on the lower surface of the heat transfer buffer 16. The He condensing unit 20 is made of a material such as Cu, Ag, or Al whose thermal conductivity at a temperature in the vicinity of 4K is higher than that of the heat transfer buffer 16 described above. In the present embodiment, the He condensing unit 20 is formed of oxygen-free copper. In particular, if the He condensing unit 20 is made of a material having a thermal conductivity of 200 W / (m · K) or more at a temperature in the vicinity of 4K, the liquid 40 condensed in the He condensing unit 20 efficiently causes the object 40 to be cooled. Can be cooled.

The He condensing unit 20 is formed in a cylindrical shape with both ends sealed, and can store liquid He therein. If the volume of the He condensing unit 20 is 10 cc or more and 100 cc or less, the He condensing unit 20 can be made compact while securing the storage volume of the liquid He necessary for cooling the object 40 to be cooled. In the present embodiment, the volume of the He condensing unit 20 is set to 40 cc.
A table 41 is disposed on the lower surface of the He condensing unit 20. The lower surface of the table 41 is a cooling position where the object to be cooled 40 is placed. The table 41 is made of a material having the same physical properties as the He condensing unit 20. In the present embodiment, In foil or the like is applied between the He condensing unit 20 and the table 41 and between the table 41 and the object to be cooled 40, and the He condensing unit 20 and the table 41 are fastened. . Note that the object 40 to be cooled may be applied to the He condensing unit 20 with good thermal contact without providing the table 41.

  The second cooling stage 14, the heat transfer buffer 16, the He condensing unit 20, and the object to be cooled 40 of the cooling unit 15 described above constitute a heat transfer channel from the object to be cooled. In this embodiment, it is possible to shorten the distance of the heat transfer flow path by continuously arranging them coaxially. Thereby, it becomes possible to reduce a cooling loss and to cool the to-be-cooled object 40 to the target temperature efficiently in a short time. Moreover, it becomes possible to make a heat-transfer flow path into an axisymmetric shape, and the whole to-be-cooled object 40 can be cooled uniformly and stably.

  A thin tube 32 extends from the He condensing unit 20 and is always connected to a reservoir 30 arranged outside the vacuum chamber 10. The volume of the reservoir 30 is desirably 5 to 100 times the volume of the He condensing unit 20. In this embodiment, the volume of the reservoir 30 is set to 3250 cc. As a result, the reservoir 30 can be made compact while ensuring the storage volume of the He gas necessary for cooling the object to be cooled 40.

  The interior of the reservoir 30 is filled with He gas. The pressure of the He gas is desirably 0.1 MPa or more and 1.0 MPa or less at room temperature. In the present embodiment, the reservoir 30 is filled with He gas 50 having a pressure of 0.4 MPa at room temperature. Thereby, even if the refrigerator 1 stops and the liquid He52 of the He condensing unit 20 evaporates, the reservoir 30 does not become a high pressure. A heat anchor 34 for heat exchange with the first cooling stage 12 is formed in the middle portion of the thin tube 32.

  Next, the operation of the refrigerator 1 according to this embodiment will be described. As described above, the high-pressure He gas supplied from the compressor 4 to the cooling unit 15 undergoes endothermic expansion in the second cooling stage 14 and changes to low-pressure He gas. The main body 2 continuously switches the connection between the high pressure pipe 6 and the low pressure pipe 8 and the He gas flow path of the cooling unit 15. Thereby, compression and expansion (refrigeration cycle) of He gas are repeated, and the temperature of the second cooling stage 14 becomes extremely low.

  A He condensing unit 20 is provided below the second cooling stage 14. When the He condensing unit 20 is cooled by the second cooling stage 14, the He gas inside the He condensing unit 20 is condensed and liquefied to generate liquid He52. In the present embodiment, the liquid He is generated so that the volume ratio with respect to the He condensing unit 20 is 30% or less (for example, about 20%).

  By the way, due to the pulsation of the heat flow caused by the above-described refrigeration cycle, a temperature amplitude is generated in the second cooling stage 14. However, in this embodiment, the pulsation of the heat flow caused by the refrigeration cycle is absorbed by the evaporation and condensation (phase transition) of He. Therefore, a temperature amplitude equivalent to that of the second cooling stage 14 does not occur in the He condensing unit 20, and the temperature amplitude of the He condensing unit 20 becomes small.

  Moreover, in the present embodiment, the heat transfer buffer 16 made of a material having a lower thermal conductivity than the He condenser 20 is provided between the second cooling stage 14 and the He condenser 20. Since the heat transfer buffer 16 acts as a heat flow restricting mechanism, it is possible to suppress the temperature amplitude in the second cooling stage 14 from being transmitted to the He condensing unit 20. Accordingly, it is possible to reduce the temperature amplitude on the placement surface of the object to be cooled.

  FIG. 2 is a graph showing the relationship between the temperature of the second cooling stage and the temperature amplitude. Here, the temperature amplitude was measured for three types of apparatus configurations. Specifically, (1) the temperature amplitude (diamond plot) of the He condensing unit 20 when the second cooling stage 14, the heat transfer buffer 16 and the He condensing unit 20 are provided as in the present embodiment, and (2 ) Temperature amplitude (triangle plot) of the He condensing unit 20 when the second cooling stage 14 and the He condensing unit 20 are provided without providing the heat transfer buffering material 16, and (3) the heat transfer buffering material 16 and the He condensing unit. The temperature amplitude (round plot) of the second cooling stage 14 when 20 was not provided was measured. The horizontal axis represents the temperature at the cooling position (temperature amplitude measurement position) where the object to be cooled is placed. The volume of the reservoir 30 was set to 3250 cc, the filling pressure of He gas into the reservoir 30 was set to 0.4 MPa, and the volume ratio of the liquid He inside the He condensing unit 20 was set to 20%.

  As a result, the magnitude of the temperature amplitude of each device configuration was in the order of (3)> (2)> (1). In addition, the difference of the temperature amplitude between each apparatus structure became large, so that the temperature of the cooling position was high. In the apparatus configuration (1), when the temperature at the cooling position is 4.2 K, the temperature amplitude of the He condensing unit 20 is suppressed to ± 9 mK. From the above measurement results, (3) Compared to the device configuration of only the second cooling stage 14, (2) The device configuration with the addition of the He condensing unit 20 significantly reduces the temperature amplitude, and (1) Heat transfer. It was confirmed that in the apparatus configuration in which the buffer material 16 and the He condensing unit 20 were added, the temperature amplitude was further reduced as compared with (2).

  FIG. 3 is a graph showing the relationship between the volume ratio of the liquid He and the temperature amplitude in the He condensing unit. Here, (1) the temperature amplitude when the heat transfer buffer material is provided (diamond plot) as in this embodiment, and (2) the temperature amplitude when the heat transfer buffer material is not provided (triangle plot) are measured. did. The volume of the reservoir 30 was set to 3250 cc, the maximum filling pressure of He gas into the reservoir 30 was set to 0.48 MPa, and the temperature at the cooling position was set to 4.2K.

  As a result, regardless of the volume ratio of the liquid He, the magnitude of the temperature amplitude was (2)> (1). In addition, the temperature amplitude increased when there was no liquid He, but the temperature amplitude decreased when liquid He existed even a little. Furthermore, in (1), when the volume ratio of the liquid He was 1% to 30%, the temperature amplitude of the He condensing unit 20 was suppressed to ± 9 mK in all cases. From the above, it was confirmed that even a small amount of liquid He has an effect of greatly reducing the temperature amplitude.

By the way, in this embodiment, since the heat-transfer buffer material 16 whose heat conductivity is lower than He condensation part 20 was provided, it is thought that the refrigerating capacity of a refrigerator falls. Therefore, the inventors of the present application investigated the difference in the refrigerating capacity depending on the presence or absence of the heat transfer buffer material 16.
FIG. 4 is a graph showing the relationship between the temperature at the cooling position and the refrigeration capacity at the cooling position. Here, (1) the refrigerating capacity (diamond plot) when the heat transfer buffer 16 is provided as in the present embodiment, and (2) the refrigerating capacity (square plot) when the heat transfer buffer is not provided. It was measured. The volume ratio of the liquid He inside the He condensing unit 20 was set to 20%.
As a result, regardless of the temperature at the cooling position, the reduction rate of the refrigerating capacity when the heat transfer buffer material 16 is present was about 25%. Therefore, it was confirmed that the loss of refrigeration capacity was suppressed to several tens of percent.

Moreover, in this embodiment, since the heat-transfer buffer material 16 whose heat conductivity is lower than He condensation part 20 was provided, it is thought that cooling time increases. Therefore, the inventors of the present application investigated the difference in cooling time depending on the presence or absence of the heat transfer buffer material 16.
FIG. 5 is a graph showing the relationship between the cooling time and the temperature at the cooling position. Here, (1) the temperature at the cooling position when the heat transfer buffer material is provided (solid line) as in the present embodiment, and (2) the temperature at the cooling position when the heat transfer buffer material is not provided (square plot) And measured. As a result, it was confirmed that there was almost no difference in cooling time depending on the presence or absence of the heat transfer buffer material 16.

  As described in detail above, the refrigerator according to the present embodiment (see FIG. 1) includes the He condensing unit 20 between the He condensing unit 20 on which the object to be cooled 40 is placed and the second cooling stage 14. It was set as the structure provided with the heat-transfer buffer material 16 which consists of material with lower heat conductivity. According to this configuration, the pulsation of the heat flow caused by the refrigeration cycle of the refrigerator 1 is absorbed by the evaporation and condensation (phase transition) of He in the He condensing unit 20. At that time, since the heat transfer buffer 16 acts as a heat flow restricting mechanism, the transmission of the temperature amplitude in the second cooling stage 14 is suppressed, and as a result, the temperature amplitude on the placement surface of the object 40 to be cooled is reduced. Can do. Moreover, since the 2nd cooling stage 14, the heat-transfer buffer material 16, He condensation part 20, and the to-be-cooled object 40 are continuously arrange | positioned coaxially, the heat-transfer flow path from a to-be-cooled object becomes an axisymmetric shape and a short distance. Therefore, the object 40 to be cooled can be uniformly and stably cooled.

  In the present embodiment, the volume ratio of the liquid He 52 in the He condensing unit 20 can be suppressed to 30% or less. Therefore, the reservoir 30 filled with the He gas 50 can be downsized. Further, the filling pressure of the He gas 50 at room temperature to the reservoir 30 can be lowered. As a result, even if the refrigerator 1 is stopped and the liquid He 52 in the He condensing unit 20 is vaporized, it is possible to prevent the reservoir 30 and the He condensing unit from becoming a high pressure.

(Second Embodiment)
Next, the refrigerator which concerns on 2nd Embodiment of this invention is demonstrated.
FIG. 6 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the present embodiment. In the refrigerator according to the present embodiment, fins 222 and 224 are erected on the inner surfaces 221 and 223 of the He condensing unit 220. Note that detailed description of portions having the same configuration as in the first embodiment is omitted.

A He condensing unit 220 is disposed between the second cooling stage 14 and the object to be cooled 40.
The He condensing unit 220 is a cylindrical hollow container made of a material such as Cu, Ag, Al, and the inside thereof is filled with He gas 50. When the He condensing unit 220 is cooled by the second cooling stage 14, the He gas is condensed and the liquid He52 is generated. The object to be cooled 40 is cooled by the liquid He52.

  A plurality of fins 222 and 224 are erected on the inner surface of the He condensing unit 220. Each of the fins 222 and 224 is preferably made of a material having high thermal conductivity, like the He condensing unit 220. The fins 222 and 224 may be formed integrally with the He condensing unit 220 or may be formed separately and fixed to the He condensing unit 220.

The first fins 222 are formed from the bottom surface 221 of the He condensing unit 220 toward the ceiling surface 223. This makes it possible to increase the contact area between the inner surface of the He condensing unit 220 and the liquid He52. Therefore, the object to be cooled 40 placed on the He condensing unit 220 can be efficiently cooled.
The second fins 224 are formed from the ceiling surface 223 of the He condensing unit 220 toward the bottom surface 221. As a result, the contact area between the inner surface of the He condensing unit 220 and the He gas 50 can be increased. Therefore, the He gas 50 inside the He condensing unit 220 can be efficiently cooled and condensed.

(Third embodiment)
Next, a refrigerator according to a third embodiment of the present invention will be described.
FIG. 7 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the present embodiment. In the refrigerator according to the present embodiment, a porous structure 322 is attached to the inner surface of the He condensing unit 320. Note that detailed description of portions having the same configuration as in the first embodiment is omitted.

A porous structure 322 is attached to the inner surface of the He condensing unit 320. The porous structure 322 is made of a mesh, a foamable metal, a sintered metal, or the like. The porous structure 322 may be filled in the entire inside of the He condensing unit 320, or may be filled only in a part.
The porous structure 322 is attached to the inner surface of the He condensing unit 320 with an adhesive or the like so as to keep good thermal contact with the inner surface of the He condensing unit 320.

  By providing the porous structure 322, it is possible to increase the contact area between the inner surface of the He condensing unit 320 and the liquid He52. Therefore, the object to be cooled 40 placed on the He condensing unit 320 can be efficiently cooled. Further, by providing the porous structure 322, the contact area between the inner surface of the He condensing unit 320 and the He gas 50 can be increased. Therefore, the He gas 50 inside the He condensing unit 320 can be efficiently cooled and condensed.

(Fourth embodiment)
Next, a refrigerator according to a fourth embodiment of the present invention will be described.
FIG. 8 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the present embodiment. In the refrigerator according to the present embodiment, unevenness 18 is formed on the contact surface of the heat transfer buffer 16 with the second cooling stage 14. Note that detailed description of portions having the same configuration as in the first embodiment is omitted.

  The heat transfer buffer 16 is made of a stainless material or the like having a low thermal conductivity. Concavities and convexities 18 are formed on the contact surface with the second cooling stage 14. The irregularities 18 may be formed regularly or irregularly (randomly). Further, the unevenness 18 may be formed in a pyramid shape so as to make point contact with the second cooling stage 14, and the unevenness 18 may be formed in a frustum shape so as to be in surface contact with the second cooling stage 14. Further, the projections and depressions 18 may be formed in a triangular projection so as to be in line contact with the second cooling stage 14, and the projections and depressions 18 may be formed in a trapezoidal section in such a manner as to be in surface contact with the second cooling stage 14.

  In this embodiment, since the unevenness | corrugation 18 was formed in the contact surface with the 2nd cooling stage 14 in the heat-transfer buffer material 16, the contact area of the heat-transfer buffer material 16 and the 2nd cooling stage 14 becomes small. Thereby, compared with the case where the heat transfer buffer 16 and the second cooling stage 14 are in full contact with each other, the heat flow throttling function is strengthened, so that the temperature amplitude in the second cooling stage 14 is increased in the He condensing unit 420. It is possible to suppress transmission. Accordingly, it is possible to reduce the temperature amplitude on the placement surface of the object to be cooled.

  In the present embodiment, the unevenness 18 is formed on the contact surface of the heat transfer buffer 16 with the second cooling stage 14. However, the unevenness may be formed on the contact surface of the second cooling stage 14 with the heat transfer buffer 16. . In addition, unevenness may be formed on the contact surface of the heat transfer buffer material 16 with the He condensing portion 420, and unevenness may be formed on the contact surface of the He condensation portion 420 with the heat transfer buffer material 16. That is, it is only necessary that irregularities be formed on the contact surface between the second cooling stage 14 or the He condensing unit 420 and the heat transfer buffer material 16. In any case, it is possible to suppress the temperature amplitude in the second cooling stage 14 from being transmitted to the He condensing unit 420. Accordingly, it is possible to reduce the temperature amplitude on the placement surface of the object to be cooled.

(Fifth embodiment)
Next, a refrigerator according to a fifth embodiment of the present invention will be described.
FIG. 9 is a schematic configuration diagram in the vicinity of the He condensing unit of the refrigerator according to the present embodiment. The refrigerator according to the present embodiment includes a temperature sensor 64 and a heater 66 attached to the He condensing unit 520, and a control unit 62 that drives the heater 66 based on the measurement result of the temperature sensor 64. . Note that detailed description of portions having the same configuration as in the first embodiment is omitted.

In the present embodiment, the temperature sensor 64 is mounted in the vicinity of the placement surface of the object to be cooled 40 in the He condensing unit 520. In addition, a heater 66 having a heating wire or the like is attached to the He condensing unit 520. The temperature sensor 64 and the heater 66 are connected to the control unit 62. The control unit 62 drives the heater 66 based on the measurement result of the temperature sensor 64. In other words, the output signal of the temperature sensor 64 is converted into a drive current for the heater 66, and a feedback current is passed through the heater 66 to control the temperature pulsation caused by the heat generation to be minimized.
Specifically, first, the set temperature of the mounting surface of the object to be cooled 40 is compared with the measured temperature of the temperature sensor 64. When the measured temperature falls below the set temperature, the heater is driven to heat the He condensing unit 520. Thereby, it becomes possible to raise the temperature of the mounting surface of the to-be-cooled object 40, and to return to setting temperature. Therefore, the temperature amplitude on the placement surface of the object to be cooled 40 can be reduced.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. That is, the specific materials and configurations described in the embodiments are merely examples, and can be changed as appropriate.

  It is possible to provide a refrigerator that can reduce the temperature amplitude on the surface on which the object to be cooled is placed and can cool the object to be cooled uniformly and stably.

Claims (10)

A cooling stage for cooling the object to be cooled;
A He condensing unit on which the object to be cooled is placed;
A reservoir filled with He gas that communicates with the He condensation section;
A heat transfer buffer material made of a material having a lower thermal conductivity than the He condensing unit, disposed between the cooling stage and the He condensing unit;
A freezer comprising the above.   The refrigerator according to claim 1, wherein the He condensing unit is made of a material having a thermal conductivity of 200 W / (m · K) or more at a temperature in the vicinity of 4K.   The refrigerator according to claim 1, wherein the heat transfer buffer material is made of a material having a thermal conductivity of less than 100 W / (m · K) at a temperature in the vicinity of 4K.   The refrigerator according to claim 1, wherein the volume of the He condensing unit is 10 cc or more and 100 cc or less.   The refrigerator according to claim 1, wherein the volume of the reservoir is 5 to 100 times the volume of the He condensing unit.   The refrigerator according to claim 1, wherein the pressure of the He gas filled in the reservoir is 0.1 MPa or more and 1.0 MPa or less at room temperature.   The refrigerator according to claim 1, wherein fins are erected on an inner surface of the He condensing unit.   The refrigerator according to claim 1, wherein a porous structure is attached to an inner surface of the He condensing unit.   The refrigerator according to claim 1, wherein unevenness is formed on a contact surface between the heat transfer buffer material and the cooling stage or the He condensing unit. A temperature sensor and a heater mounted on the He condensing unit;
A control unit that drives the heater based on the measurement result of the temperature sensor;
The refrigerator according to claim 1, further comprising:

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