JPH0639983B2 - Cryogenic cooling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a superconducting magnet immersed in liquid helium as an object to be cooled, and this object to be cooled together with a heat shield surrounding the object to be cooled. It was placed in the center of the vacuum container by collectively storing it in a vacuum container and cooling the heat shield by a refrigerator installed in the vacuum container to remove radiant heat that entered from the outside of the vacuum container. The present invention relates to a configuration of a cryogenic cooling device for a cryostat with a refrigerator, which is designed to maintain a cooled object in a cryogenic cooling state.

[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. Flange-shaped heat transfer terminals 10A, 10 made of a good heat conductive metal are provided on the tip peripheral surface of the generators 9A, 9B.
B is stuck.

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 portions 9A and 9B of the expander 8 are provided.
A bottomed airtight inner cylinder 11 is installed so as to surround the space between the high vacuum space 7 of the vacuum container 4 and the expander 8. The inner space of the airtight inner cylinder 11 is open to the expander installation surface of the vacuum container 4 described above, and its structure is a bottom plate flange 12 made of a good heat conductive metal, and a ring-shaped intermediate flange 1
3, a bellows 14 made of a material having a large heat transfer resistance in which the flanges 12 and 13 are airtightly connected, and a bellows 15 having one end connected to the flange 13 and the other end airtightly connected to the open end of the vacuum container 4. Composed as a combination. Also, the flanges 12, 1
The outer peripheral ends of 3 are heat-conductively connected to the aforementioned heat shields 5 and 6 through flexible heat transfer conductors 16, respectively,
Further, the flanges 12 and 13 are provided on the inner space side of the airtight inner cylinder 11.
On the upper surface of the movable heat transfer terminal plate 18 which is in close contact with the plate surfaces of the heat transfer terminals 10A and 10B on the expander 8 side described above and is in heat transfer contact therewith.
A and 18B are mounted and supported via a flexible heat transfer conductor 19 and a compression biasing spring 20. 21 is bellows 14,15
Is a heat insulating support leg that supports the flanges 12 and 13 by allowing expansion and contraction of the.

A gas conduit 21 is drawn from the outside into the vacuum container 4 toward the inner space of the airtight inner cylinder 11, and the gas conduit 21 is connected via valves 22 and 23 to a vacuum pump 24 and helium. It is connected to a source of inert gas such as gas. 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 such a structure, the cold generating portions 9A and 9B of the expander 8 Is made. 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. Install and heat-bond the heat transfer terminals 10A, 10B on the cold generating parts 9A, 9B to the heat transfer terminal plates 18A, 18B on the mating side, and then evacuate the inside of the airtight inner cylinder 11 again in this state. Then restart the refrigerator.

[Problems to be solved by the invention]

By the way, in the above-mentioned conventional structure, the heat transfer terminals 10A and 10B fixed to the cold generating part 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 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. The mechanical strength of 9B limits the load to below the allowable load, 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 provide a bolt between the heat transfer terminal on the expander side and the heat transfer terminal plate on the fixed side connected to the heat shield without applying any mechanical load to the cold generating part of the expander. The heat transfer resistance of the contact part is suppressed to be low by fastening firmly and the heat transfer path having a high heat transfer property is secured between the cold generating part of the expander and the heat shield, whereby the cooling operation can be efficiently performed. An object of the present invention is to provide a configuration of such a cryogenic cooling device.

[Means for solving problems]

In order to solve the above problems, according to the present invention, a heat transfer terminal plate is relatively displaceably coupled to a cold generation part of an expander via a flexible heat transfer conductor, and the expander is installed at the installation position. The heat transfer terminal plate on the expander side is brought into contact with the heat transfer terminal plate on the fixed side that faces the expander side, and in this state, the heat transfer terminals are bolted together and the expander vacuums via the mounting flange. The flange is provided with a tool insertion hole that is installed in the container and that allows the fastening bolts that fasten the heat transfer terminals to be bolted from outside the vessel, and a sealing plug that seals this hole.

[Action]

With the above structure, when the expander is installed, the heat transfer terminal plate on the expander cold generator side and the heat transfer terminal plate on the fixed side opposite to the heat transfer terminal plate are firmly bolted to each other for contact transfer between them. The thermal resistance 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. . Moreover, since the heat transfer terminal plate on the expander side is connected to the cold generation part via the flexible heat transfer conductor so as to be displaceable relative to each other, the bolts between the heat transfer terminal plates are fastened to the cold generation part. The heat transfer terminal plates can be bolted to each other with proper contact between the heat transfer terminal plates without being applied with a general interference force and without being hindered by the displacement of the installation position of the expander.

The structural part that constitutes the cold-generating part of the expander has a low mechanical strength because it reduces heat transfer and intrusion heat from the outside. Therefore, it is desirable that the external force is not applied to the cold generating portion as much as possible. According to the above configuration of the present invention, the load of the heat transfer terminal plate on the fixed side is not applied to the expander. Therefore, it is possible to prevent an excessive external force from being applied to the expander, and normal operation is maintained.

〔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, 18B shown in FIG. 3 and the heat transfer conductor 19 and the biasing spring 20 attached thereto are omitted, and instead the cold generating portion 9A of the expander 8, Flexible heat transfer conductors 2 for 9B
The ring-shaped heat transfer terminal plates 26 and 27 are connected to the expander via the 5 so as to be relatively displaceable, and the heat transfer terminal plates 26 and 27 are hermetically sealed in the installed state of the expander 8. Tube 1
The heat transfer terminal plates 12 and 13 on the fixed side, which also serve as the flange of 1, are brought into contact with the plate surfaces of the heat transfer terminal plates 12 and 13, and are fastened and coupled together by fastening bolts 28 and 29. The heat transfer terminal plates 12 and 13 are heat transfer-coupled to the heat shields 5 and 6 via the flexible heat transfer conductor 16 as in FIG.

Here, an external perspective view of the expander 8 equipped with the heat transfer terminal plates 26, 27 is shown in FIG. 2. First, the heat transfer unit which is connected to the cold generating section 9A on the lower stage side through the flexible heat transfer conductor 25 is used. Bolt holes 30A corresponding to the fastening bolts 28 are formed in both sides of the hot terminal plate 26 with the cold generating portion 9A interposed therebetween. On the other hand, the flexible heat transfer conductor 25
The heat transfer terminal plate 27 coupled via the, the plate surface on the plate hole is aligned with the bolt hole 30A tool insertion hole 30B for inserting the tightening tool of the bolt 28 from above, and the hole 30B. Phase
Bolt holes 31 corresponding to the fastening bolts 29 at positions shifted by 90 degrees
A is perforated. Furthermore, the mounting flange 8 for the expander 8
On the peripheral surface of a, in addition to the bolt holes 8c corresponding to the fixing bolts 8b (Fig. 1) for installing and fixing the expander 8 in the vacuum container 4, align the axes with the bolt holes 30A and 31A. Tool insertion holes 30C and 31B are drilled. Ie each fastening bolt 2
Corresponding to 8 and 29, heat transfer terminal plates 26 and 27 and mounting flange 8a have bolt hole 30A and tool insertion hole 3 on the same axis.
0B, 30C, a bolt hole 31A, and a tool insertion hole 31B are drilled side by side. Further, the tool insertion holes 30C and 31B formed in the mounting flange 8a of the expander 8 are removably attached with the sealing plugs 32 for airtight sealing shown in FIG. It should be noted that bolt holes are bored at predetermined positions on the fixed heat transfer terminal plates 12 and 13 facing the fastening bolts 28 and 29 described above.

Next, the installation method of the expander 8 having the above structure will be described. First, in the bolt holes 30A and 31A of the heat transfer terminal plates 26 and 27 of the upper and lower stages, which are connected to the cold generating portions 9A and 9B of the expander, respectively. With the fastening bolts 28, 29 temporarily fixed, the cold generating portions 9A, 9B of the expander 8 are hung from above the vacuum container 4 into the airtight inner cylinder 11, and during this process, the cold generating portions 9A and the heat transfer are conducted. Terminal board 26
Through the elongated slit hole 13a cut out in the center of the fixed side heat transfer terminal plate 13 shown in FIG. Land. 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. Then, insert a bolt tightening tool from the outside through the tool insertion holes 30C and 30B drilled in the mounting flange 8a and the upper heat transfer terminal plate 27, and tighten the fastening bolts 28 to transfer heat to the heat transfer terminal plate 26 and the mating side. The heat terminal board 12 is firmly fastened. Tool insertion hole drilled in another position
A fastening tool is inserted into 31B and a fastening bolt 29 is tightened to firmly fasten the heat transfer terminal plate 27 and the mating heat transfer terminal plate 13. Finally, a sealing plug 32 is attached to the tool insertion holes 30C and 31B opened in the mounting flange 8a to hermetically seal. Moreover, in this installed state, since the cold heat generating portions 9A and 9B of the expander 8 and the heat transfer terminal plates 26 and 27 are connected by the flexible heat transfer conductor 25, no mechanical operation is performed on the cold heat generating portion. It is possible to firmly fasten the heat transfer terminal plates to each other by bolts without adding any interference, and it is possible to suppress the heat transfer resistance of the contact portion to a low value.

When the expander 8 is removed from the vacuum container 4 during maintenance of the expander, the fastening bolts 28 and 29 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, 8c: bolt hole, 9A, 9B: cold generating part, 11: airtight inner cylinder, 12, 13: airtight Fixed side heat transfer terminal plate that doubles as a cylinder flange, 14, 15: Bellows, 25:
Flexible heat transfer conductor, 26,27: Heat transfer terminal board, 28,29: Fastening bolt, 30A, 31A: Bolt hole, 30B, 30C, 31B: Fastening tool insertion hole, 32: Sealing plug.

Claims (2)

[Claims] 1. A bottomed airtight inner cylinder is installed inside a vacuum container accommodating an object to be cooled and a heat shield surrounding the object to be cooled so as to be isolated from a high vacuum space, and the inside of the airtight inside is sealed. The cold generation part of the expander of the refrigerator installed in the vacuum container is housed in the cylinder, and the heat transfer terminal plate on the fixed side and the expander of the expander connected to the heat shield are connected to the heat shield. A pole configured to form a heat transfer path between the cold generation part of the expander and the heat shield by heat transfer coupling with the heat shield part, and cool the heat shield by operating the refrigerator in this assembled state. In the low temperature cooling device,
A heat transfer terminal plate is relatively displaceably coupled to the cold-generating part of the expander via a flexible heat transfer conductor, and the heat transfer terminal plate on the expander side is fixed so as to face it at the installation position of the expander. Side heat contact terminal plate, and in this state, the heat transfer terminals are bolted together, and the expander is installed in the vacuum container via the mounting flange, and heat transfer is performed on the flange. A cryogenic cooling device comprising a tool insertion hole for operating a fastening bolt for fastening terminals to each other from outside the device and a 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.