JPH0638008B2 - Cryogenic cooling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to, for example, a superconducting magnet immersed in liquid helium as an object to be cooled, and this object to be cooled is vacuumed together with a heat shield surrounding the object to be cooled. Collected in a container all at once,
And by cooling the heat shield by a refrigerator to remove the radiant heat entering from the outside of the vacuum container, the cooled object placed in the center of the vacuum container is maintained in a cryogenic cooling state. Of the cryogenic cooling device for the cryostat with a refrigerator described above.

[Conventional technology]

First, the conventional structure of the cryogenic cooling device described above is shown in FIG. In the figure, reference numeral 1 denotes a cooled object which is a superconducting magnet of a medical device which operates at a very low temperature and which utilizes magnetic resonance,
Reference numeral 2 denotes an internal container in which the object to be cooled is immersed in liquid helium 3 and accommodated therein, 4 is a vacuum container in which the internal container 2 is placed in the center, and the interior container 3 is provided inside the vacuum container 4. Surrounding the outer periphery of the heat shields 5, 6
Has been deployed. Reference numeral 7 denotes a high vacuum space in the vacuum container, and the inner container 2 and the heat shields 5 and 6 are supported by the vacuum container 4 via a heat insulating support (not shown).

On the other hand, a refrigerator installation window is opened at the center of the top of the vacuum container 4, and an expander 8 of a closed-cycle refrigerator based on a heat cycle such as Gifford-McMahon cycle, Solvay cycle, Stirling reverse cycle, etc. is opened in this portion. Cylinder of the upper and lower two-stage structure which is detachably bolted and installed through the fixing bolt 8b so as to hermetically seal the opening window by the mounting flange 8a, and which projects from the expander body into the vacuum container. A flange-shaped heat transfer terminal 10 made of a good heat-conducting metal on the peripheral surface of the tips of the generators 9A and 9B.
A and 10B are fixed.

Further, in order to enable the expander 8 to be removed from the vacuum container 4 without breaking the vacuum of the high vacuum space 7 in the vacuum container 4 during maintenance work of the refrigerator described later,
Inside the vacuum container 4, the cold generating parts 9A and 9B of the expander 8 are provided.
A bottomed airtight inner cylinder 11 is installed so as to surround the space and isolate the vacuum space 7 of the vacuum container 4 from the expander 8.
The inside of this airtight inner cylinder 11 is open to the expansion machine installation surface of the vacuum container 4 described above, and the structure is such that the bottom plate flange 12 made of a good heat conductive metal, the ring-shaped intermediate flange 13, and the flange 12 are formed. A bellows 14 made of a material having a large heat transfer resistance, which is airtightly coupled with the bellows 13, and a bellows 15 which is airtightly coupled with the flange 13 at one end and the open end of the vacuum container 4 at the other end. Further, the outer peripheral ends of the flanges 12 and 13 are thermally connected to the above-mentioned heat shields 5 and 6 through flexible heat transfer members 16, respectively, and the airtight inner cylinder 11
A movable heat transfer terminal plate 18A which is in intimate contact with the surfaces of the heat transfer terminals 10A and 10B on the expander 8 side described above on the upper surfaces of the flanges 12 and 13 on the inner side of the heat transfer terminals. , 18B is a flexible heat transfer member
19, is attached and supported via a compression biasing spring 20. Reference numeral 21 allows the bellows 14 and 15 to expand and contract, and the flange 1
These are heat-insulating support legs that loosely support 2 and 13.

Further, a gas conduit 21 is drawn from the outside through the top flange portion of the vacuum container 4 toward the inner space of the airtight inner cylinder 11, and the gas conduit 21 has a valve 21 and valves 22, 23.
It is connected to the vacuum pump 24 and a source of inert gas such as helium gas via. Here, the vacuum pump 24 is for vacuuming the inner space of the airtight inner cylinder 11 during operation of the refrigerator to eliminate air, and to prevent icing from occurring in the cold generating part and its peripheral members. Further, as will be described later, when the expander 8 of the refrigerator is taken out from the vacuum container 4 during maintenance, an inert gas is sent through the gas conduit 21 so as to suppress the outside air from entering the inside of the airtight inner cylinder 11. Perform gas replacement.

With this structure, the heat transfer terminals 10A and 10B are provided between the cold generating portions 9A and 9B of the expander 8 and the heat shields 5 and 6 → the heat transfer terminal plates 18A and 1B.
8B-> flexible heat transfer member 19-> flange 12,13-> flexible heat transfer member 16-> heat shield 5 and 6 is formed. Here, by operating the refrigerator to cool the heat shields 5 and 6 to an extremely low temperature in a state where the inner space of the airtight inner cylinder 11 is evacuated, the radiant heat that has entered from the outside through the vacuum container 4 is cooled. The heat is removed from the heat shields 5 and 6 before reaching the inner container 3 accommodating the superconducting magnet 1 and the liquid helium 2, and the superconducting magnet 1 can be stably maintained in a cryogenic cooling state. Become.

On the other hand, the expander 8 of the refrigerating machine needs to perform maintenance such as replacement of the seal ring at the time when the specified operation time has elapsed. For this purpose, the expander 8 is once removed from the vacuum container 4, After the maintenance, it is necessary to install the vacuum container 4 again. In this case, an inert gas such as helium that does not condense from the outside at the cooling temperature of the cold generation portion is blown from the outside into the inner space of the airtight inner cylinder 11 through the gas conduit 21 described above so as to suppress the invasion of the outside air. At the same time, the expander 8 is pulled out from the vacuum container 4, and then the top opening surface of the vacuum container 4 is temporarily sealed with a blind lid. As a result, the invasion of outside air is suppressed during the removal process of the expander 8 to prevent the formation of ice on the cold generation part and its surroundings, and the heat intrusion from the outside is further suppressed during the period when the refrigerator is removed. To maintain the cryogenic temperature of the superconducting magnet 1. When the expander 8 of the refrigerator is installed again after the maintenance work is completed, the blind lid is removed and the expander 8 is installed while the inert gas is blown into the airtight inner cylinder 11 to prevent outside air from entering. After installation, heat transfer terminals 10A, 10B on the side of the cold generating parts 9A, 9B are heat-transfer-bonded to the heat transfer terminal plates 18A, 18B on the other side, and in this state, the inside of the airtight inner cylinder 11 is evacuated again. Then restart the refrigerator.

[Problems to be solved by the invention]

By the way, in the above-described conventional configuration, the heat transfer terminals 10A and 10B fixed to the cold generating portion of the expander 8 in the installed state of the expander 8 and the heat transfer terminal plates 18A and 18B on the other side in contact therewith are the compression spring 20. They are pressed against each other by the spring force of. However, in this case, the spring load remains as it is and the cold generating part 9 of the expander 8
Since it is applied to the A and 9B, the spring force of the biasing spring 20, and therefore the contact pressure between the heat transfer terminals 10A and 10B on the expander side and the heat transfer terminal plates 18A and 18B on the heat shield side, is the cold generating portion 9A. However, due to the mechanical strength of the 9B, the load is limited to the allowable load or less, and as a result, it becomes difficult to sufficiently reduce the heat transfer resistance between the heat transfer terminals. Moreover, if the heat transfer resistance of the heat transfer terminal contact part is high, a temperature drop occurs in this part during the cooling operation, and high heat conductivity cannot be obtained, so that the heat shields 5 and 6 can be efficiently cooled to an extremely low temperature. It will be difficult.

An object of the present invention is to firmly join the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side connected to the heat shield without being restricted by the mechanical strength of the expander, and to provide the contact portion. By providing a low-temperature cooling device having a low heat transfer resistance, a heat transfer path having a high heat transfer property is secured between the expander and the heat shield to enable efficient cooling operation. is there.

[Means for solving problems]

In order to solve the above-mentioned problems, according to the present invention, a bottomed air-tightness is provided by being isolated from a high-vacuum space inside a vacuum container accommodating a body to be cooled and a heat shield surrounding the body to be cooled. A fixed side provided with an inner cylinder and accommodating the cold-generating part of the expander of the refrigerator, which is detachably installed in the opening of the vacuum container, and which is pulled out from the heat shield and exposed and arranged in the airtight inner cylinder. A heat transfer path is formed between the cold-generating part of the expander and the heat shield by contacting the heat-transfer terminal of the other side, which is fixed to the cold-generating part of the expander, on the plate surface of the heat-transfer terminal plate, and freezing In a cryogenic cooling device that cools the heat shield by operating the machine, tighten the bolts between the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side in contact with each other. With the heat transfer coupling, the expander is installed in the vacuum vessel through the mounting flange. Ri, and the flange is assumed to provide a sealing plug for sealing the tool insertion hole for bolt operation from Utsuwagai the fastening bolt of the heat transfer terminal side, and this hole.

[Action]

With the above configuration, when the expander is installed, the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side that abuts against the heat transfer terminal are firmly bolted together, so that the contact heat transfer resistance between them is increased. The value is suppressed to a low value, which makes it possible to secure a heat transfer path having a higher heat transfer property between the expander and the heat shield as compared with the conventional contact method using spring pressure.

〔Example〕

FIGS. 1 and 2 show the structure of the main parts according to the embodiment of the present invention, and the same members corresponding to those in FIG. 3 are designated by the same reference numerals. That is, in the illustrated embodiment, the movable heat transfer terminal plates 18A and 18B shown in FIG. 3 and the flexible heat transfer member 19 and the biasing spring 20 attached thereto are omitted, and the expander 8 is installed in the installed state. The heat transfer terminals 10A and 10B fixed to the peripheral surfaces of the cold generating portions 9A and 9B of 8 directly contact the plate surfaces of the heat transfer terminal plates 12 and 13 on the fixed side which also serve as the flanges of the airtight inner cylinder 11, respectively. Here, the both are firmly fastened and coupled by fastening bolts 25 and 26. The heat transfer terminal plates 12 and 13 are heat transfer coupled to the heat shields 5 and 6 via the flexible heat transfer member 16 as in FIG.

Here, the outer shape of the expander 8 including the heat transfer terminals 10A and 10B is shown in FIG. 2. First, the heat transfer terminals 10A fixed to the cold generation part 9A on the lower side are projected to both sides of the cold generation part. It becomes a square plate, and bolt holes 25A corresponding to the fastening bolts 25 are drilled on the plate surface. On the other hand, the cold generating part 9B on the upper side
The heat transfer terminal 10B fixed to is a disc, and a tool insertion hole 25B for inserting a tightening tool of the bolt 25 from above from the upper side by aligning the axis with the bolt hole 25A on the plate surface, and the hole 25B. And 90
Bolt holes 26A corresponding to the fastening bolts 26 at offset positions
Is perforated. Further, the mounting flange 8a for the expander 8
In addition to the bolt holes 8c corresponding to the fixing bolts 8b for fixing the expander 8 to the vacuum container 4 on the peripheral surface of the tool insertion holes 25C, 26B by aligning the axes with the bolt holes 25A, 26A.
Is perforated. That is, the heat transfer terminals 10A and 10B and the mounting flange 8a corresponding to the fastening bolts 25 and 26, respectively.
Bolt holes 25A, tool insertion holes 25B and 25C on the same axis,
A bolt hole 26A and a tool insertion hole 26A are drilled side by side. Further, in the tool insertion holes 25C and 26B drilled in the mounting flange 8a of the expander 8, the airtight sealing plug 27 shown in FIG.
Is detachably attached.

Next, the installation method of the expander 8 having the above structure will be described. First, the fastening bolts are respectively attached to the bolt holes 25A and 25B of the heat transfer terminals 10A and 10B at the upper and lower stages fixed to the cold generating portion of the expander.
With the 25 and 26 set, the expander 8 cold generators 9A and 9B are hung from above the vacuum container 4 into the airtight inner cylinder 11,
In the middle of this process, the lower heat transfer terminal 10A is cut out in the center of the fixed heat transfer terminal plate 13 shown in FIG.
And the direction of the entire expander is changed by 90 degrees to land on the heat transfer terminal plate 12 on the fixed side. In this state, next, the fixing bolt 8c is passed through the bolt hole 8a formed in the mounting flange 8a of the expander 8 and fixed on the upper surface of the vacuum container 4.
Next, insert a bolt tightening tool from the outside through the tool insertion holes 25C and 25B drilled in the mounting flange 8a and the upper heat transfer terminal 10B, and tighten the fastening bolt 25 to heat transfer terminal 10A and the heat transfer terminal on the other side. The plate 12 is firmly fastened. Further, a fastening tool is inserted into the tool insertion hole 26B drilled at another position and the fastening bolt 26 is tightened to firmly fasten the heat transfer terminal 10B and the mating heat transfer terminal plate 13. Finally, plug the tool insertion holes 25C and 26B opened in the mounting flange 8a.
27 is attached and hermetically sealed. Note that the displacement of the fixed side terminal plates 12 and 13 due to the tightening operation of the fastening bolts described above is
Since it is absorbed by the bellows 14 and 15 of the expander 8, the heat transfer terminals of the expander 8 can be firmly fastened between the heat transfer terminals without applying any mechanical load, and thus the heat transfer resistance of the contact parts is low. Will be able to be suppressed.

When the expander 8 is removed from the vacuum container 4 during maintenance of the expander, the fastening bolts 25 and 26 between the heat transfer terminals and the fixing bolt 8c are removed by performing the above operations in the reverse order to remove the expander 8. It can be taken out of the vacuum container.

〔The invention's effect〕

As described above, according to the present invention, as a result of adopting the above configuration, the expander of the refrigerator is installed in the vacuum container, without adding any mechanical load to the cold generating part of the expander. The contact heat transfer resistance between the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side connected to the heat shield can be suppressed to be low, and thus the expander of the refrigerator and the heat shield can be connected. It is possible to improve the cooling performance of the cryogenic cooling device by securing a heat transfer path having high heat conductivity between the two.

[Brief description of drawings]

FIG. 1 is a sectional view showing the construction of an essential part of an embodiment of the present invention,
1 is an external perspective view of the expander in FIG. 1, and FIG. 3 is a cross-sectional view of the entire structure of a conventional cryogenic cooling device. In each drawing, 1: cooled object, 4: vacuum container, 5, 6: heat shield, 7:
High vacuum space, 8: expander of refrigerator, 8a: mounting flange of expander, 8b: fixing bolt, 9A, 9B: cold generating part, 10
A, 10B: Heat transfer terminals, 11: Airtight inner cylinder, 12, 13: Heat transfer terminal plate on the fixed side that also functions as a flange for the airtight inner cylinder, 14, 15: Bellows, 25, 26: Fastening bolts, 25A, 26A : Bolt hole, 25B, 25
C, 26B: tightening tool insertion hole, 27: plug.

Claims (2)

[Claims] 1. A vacuum container accommodating a cooled body and a heat shield surrounding the cooled body is provided with a bottomed airtight inner cylinder, which is isolated from a high vacuum space, and a vacuum vessel is installed therein. The cold generation part of the expander of the refrigerator, which is removably installed in the opening, is housed and expanded on the plate surface of the fixed-side heat transfer terminal plate that is drawn out from the heat shield and exposed in the airtight inner cylinder. A heat transfer terminal is fixed between the cold generator of the expander and the heat shield by contacting the heat transfer terminal on the other side that is fixed to the cold generator of the machine, and the heat shield is cooled by the operation of the refrigerator. In the cryogenic cooling device, the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side are brought into contact with each other by bolting them together for heat transfer coupling, and also for mounting the expander. It is installed in the vacuum vessel via a flange, and the flange has heat transfer terminals. The tool insertion hole for bolt operation from Utsuwagai the fastening bolt, and cryogenic cooling apparatus characterized in that a sealing plug for sealing the hole. 2. The cryogenic cooling device according to claim 1, wherein the airtight inner cylinder is a combination of a heat transfer terminal plate connected to the heat shield side and a bellows. Cooling system.