JPS6290910A - Cryogenic device - Google Patents

Abstract

PURPOSE:To raise temperature only in a refrigerating machine without rising the temperatures of a radiation shielding plate and a medium to be cooled by providing thermal switches for turning ON, OFF thermal transfer media between the plate and the machine and between a container and the machine. CONSTITUTION:A superconductive coil 11 is dipped in liquid helium 12 filled in an inner tank vessel 13. The vessel 13 is contained in a vacuum container 16, and two stages of radiation shielding plates 14, 15 are disposed between the container 16 and the vessel 13. The plates 14, 15 are connected through thermal switches 17, 18 to a refrigerating machine 19. With the construction, when the switches 17, 18 are normally turned ON, the plates 14, 15 can be sufficiently cooled. Since the machine 19 and the plates 14, 15 are insulated by turning OFF the switches 17, 18, only the machine 19 can be raised at its temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a cryogenic device such as a cryostat for a superconducting coil immersed in liquid helium used in a superconducting magnetic resonance imaging apparatus or the like.

(Prior art) In recent years, as superconducting magnetic resonance imaging devices have been put into practical use, in order to reduce the amount of evaporation of liquid helium, which is a coolant used in superconducting magnets, from the perspective of device maintenance, etc. A configuration in which a radiation shield plate surrounding a superconducting coil, which is a cooling body, is cooled by a refrigerator has been considered.

Such a conventional configuration has the following problems. That is, the freezing temperature by the refrigerator is extremely low, and is a temperature at which even air solidifies. For this reason, impurities contained in the working fluid (generally helium gas) of the refrigerator solidify at low temperatures, which may cause various troubles. Additionally, refrigerators are generally equipped with a sealing member, and when this sealing member is regularly replaced, impurities enter the system and reach the low-temperature section, where they solidify. There was a problem. In this case, it is necessary to raise the temperature of the refrigerator in order to thaw the solidified impurities, but it is difficult to thaw the solidified impurities by applying heat only to the solidified impurities without raising the temperature of the superconducting coil or the width side shield plate. It is. In particular, when the impurity is water, it is necessary to raise the temperature of the refrigerator to B), which also raises the temperature of the superconducting coils, etc. to near room temperature. The coil must be recooled, and recooling causes various problems in practical use, including the time required and the consumption of refrigerant.

(Problems to be Solved by the Invention) In this cryogenic equipment configured to use a refrigerator to cool the radiation shield plate that surrounds the object to be cooled, the amount of evaporation of the refrigerant can be reduced; As a result, impurities enter and are assimilated, and in order to unsolidify the impurities, it is necessary to raise the temperature, and on the other hand, the object to be cooled must be recooled for equipment operation, making it impractical. There wasn't.

Therefore, an object of the present invention is to provide a cryogenic device that can raise the temperature of only the refrigerator without raising the temperature of the radiation shield plate or the object to be cooled, and that allows repair and maintenance of the refrigerator to be performed easily and inexpensively. It is about providing.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized by taking the following measures in order to solve the above problems and achieve the object. That is, an object to be cooled, a container in which the object to be cooled is accommodated together with a refrigerant, a vacuum container in which this container is accommodated, a radiation shield plate disposed between the container and the vacuum container, and this radiation shield plate. and a refrigerator that cools at least one of the containers, and a refrigerator that is connected to at least one of the radiation shield plate and the refrigerator and between the container and the refrigerator to turn on heat transfer therebetween.・It is characterized by being equipped with a heat switch that turns off.

(Function) By taking such measures, it is possible to sufficiently cool at least one of the radiation shield plate and the container, usually by turning on the heat switch, and to release the assimilation of impurities. If it is necessary to raise the temperature of the refrigerator, turn off the temperature switch and the refrigerator and at least one of the radiation shield plate and container will be insulated, so the temperature of the radiation shield plate and container will be lowered. It is possible to raise the temperature of only the refrigerator without raising the temperature.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a schematic configuration of a superconducting magnet according to an embodiment of the present invention. In the figure, reference numeral 11 denotes a superconducting coil (object to be cooled), and this coil 11 is immersed in liquid helium 12 filled in an inner tank 13. Inner tank container 1
3 is housed in a vacuum container 16 that is evacuated. Two stages of radiation shield plates 14 and 15 are arranged between the vacuum container 16 and the inner tank 13 so as to surround the inner tank 13. The radiation shield plates 14 and 15 are connected to a refrigerator 19 via thermal switches 17 and 18, respectively.

The thermal switch 17,18 is connected to the end plate 21, as shown in FIG.
22, cylindrical body 23 (23a, ~.

23d), 24 (24a, ~, 24d>, bellows 25, FRP (II! fiber-reinforced plastic) cylindrical body 26
．． 27, piping 28, etc. That is, end plate 2
1 is attached to the refrigerator 9, and the end plate 22 is attached to the N radiation shield plate 14 (or 15). A plurality of cylindrical bodies (first plate bodies) 23 having different diameters are coaxially attached to the side surface of the end plate 22 of the end plate 21 by brazing or the like. Further, a plurality of cylindrical bodies (second plate bodies) 24 having different diameters are coaxially attached to the side surface of the end plate 21 of the end plate 22, respectively. Note that the cylindrical body 24d is actually a cylinder. The cylindrical bodies 23 and 24 are arranged coaxially and alternately, with each cylindrical body 23.2
The interval between 4 is a gap of about 0.5 [s+].

A bellows 25 is connected between the end plates 21 and 22, and the space in which the cylindrical bodies 23 and 24 are arranged is thereby kept airtight. A suction/exhaust pipe 28 for evacuating the space or introducing helium gas into the space is introduced into the space. Also, the end plate 21.2
Between the two, an FRP cylindrical body 26 surrounds the bellows 25.
．． 27 is fixed.

This FRP circular/cylindrical body 26.27 has an end plate 21 and an end plate 22.
The positional relationship, and ultimately the positional relationship between the cylindrical bodies 23 and 24, is maintained while being insulated, thereby maintaining the gap between the cylindrical bodies 23 and 24.

Here, the principle of the thermal switch will be explained.

In other words, heat transfer includes convection, conduction, and radiation; radiation is approximately constant regardless of the distance between the objects to be heat transferred; conduction is inversely proportional to the distance; and heat transfer through narrow gaps is WAII.
It is an order of magnitude larger than . By utilizing this, the following principles A, B, and C can be considered as a thermal switch.

Principle A is to arrange plates with good thermal conductivity to face each other with a small gap between them, and to introduce helium gas as a working medium into this gap or to evacuate the gap to improve heat transfer between the plates. Can be turned on-off. This principle A
1. : The thermal switch based on this is of the configuration shown in FIG.

Principle B is that in a gas atmosphere, contact heat transfer is relatively large, so with vacuum insulation using only radiation, heat transfer is extremely small. It is also possible to construct a thermal switch using this @principle B, which has the construction shown in FIG. 3, which will be described later.

As principle C, heat transfer by convection can obtain a large amount of heat transfer compared to conduction, so it can be used as a mechanism for turning on a thermal switch. In particular, convection is directional, so if the temperature relationship between the two objects to which heat is transferred is reversed (the higher temperature side is on the upper side and the lower temperature side is on the lower side), temperature stratification will occur, and convection will stop and heat will be transferred only by conduction. becomes. Since conduction transfers much less heat than convection, a thermal switch can also be constructed by utilizing the relationship in which convection occurs and convection stops.

This principle C has a structure shown in FIGS. 4 and 5, which will be described later.

Here, if you choose an appropriate boiling point for the refrigerant, you can use condensation and boiling heat transfer, which has the same directionality and can be used in the same way as convection heat transfer, and is also more effective than convection. In the veon state, heat transfer is much worse, and an excellent thermal switch can be constructed.

In addition, if the radiation shield plate is provided with a liquid refrigerant container and a flow path for the refrigerant, as in normal cryogenic equipment, it will be possible to continue cooling the radiation shield plate even when the thermal switch is off. During the initial cooling of the radiation shield plate, the time required can be shortened by filling the container with refrigerant or flowing the refrigerant through the flow path.

Based on the above-mentioned principle A of the thermal switch and configured as shown in FIG. By filling helium or evacuating the space, the thermal switch 17 (or 18
) can be turned on and off. That is, by introducing helium gas into the space, heat is transferred between the cylindrical bodies 23 and 24 by the heat conduction of the helium gas, thereby turning on the thermal switch 17. Also, if the above space is evacuated,
Only a small amount of heat is transferred between the cylindrical bodies 23 and 24 due to radiation, which turns off the thermal switch 17.

Therefore, if the thermal switch 17.18 is normally kept in the ON state, the radiation shield plate 14.15 can be sufficiently cooled. If it is necessary to raise the temperature of the refrigerator 19 for some reason, such as to thaw the solidification of impurities in the refrigerator 19, the heat switches 17 and 18 are turned off. In this case, the refrigerator 19 and the radiation shield plate 14.1
5 is insulated, the temperature of the radiation shield plate 14, 15 and the superconducting coil 11 can be increased without increasing the temperature
9 can be easily repaired and maintained.

FIG. 3 is a cross-sectional view showing the main structure of another embodiment.

This embodiment differs from the previously described embodiments in the configuration of the thermal switch. That is, the thermal switch of this embodiment is
As shown in FIG. 3, the end plate 31, container 32, plate body 33,
, rod 34, bellows 35, guide 37 and piping 38
It is composed of etc. The upper surface of the end plate 31 is
The lower surface of the container 32 is attached to the radiation shield plate 14 (or 15). A first plate 33 is fixed to the lower surface of the end plate 31 via a rod 34. The rod 34 is introduced into the container 32 through the central opening of the second plate 36 forming the upper wall of the container 32, and
The plate body 33 is arranged inside the container 32. A guide 37 is fixed to the central opening of the second plate 36, and the rod 34 can move forward and backward along this guide 37.

A bellows 35 is attached between the lower surface of the end plate 31 and the upper surface of the second plate 36, and the space in which the first plate 33 is arranged is kept airtight by the bellows 35. It has become a thing. In this space, piping 38
is to be introduced. In addition, 368 in the figure is
This is a through hole provided in the second plate 36.

Based on the thermal switch principle B described above and configured as shown in FIG. 3, when helium gas is introduced into the space, the bellows 35 expands due to the pressure of helium, and the first and second plates 33.36 touch. Therefore, heat is transferred between the plates 33 and 36 by surface contact heat transfer in the gas, and the heat switch is turned on. On the other hand, when the space is evacuated, the bellows 35 contracts and the plates 33 and 36 are separated, and these spaces become evacuated.

Therefore, only a small amount of heat is transferred between the plates 33 and 36 due to radiation, which turns off the thermal switch.

Therefore, according to this embodiment, the refrigerator 19 and the radiation shield plate 14 are controlled by the thermal switches 17 and 18 as in the previous embodiment.
．． 15, and the same effects as in the previous embodiment can be obtained.

FIG. 4 is a cross-sectional view showing the main structure of another embodiment. This embodiment differs from the previous embodiment in the configuration of the thermal switch. That is, the thermal switch of this embodiment is composed of an end plate 41, a cylinder 42, an end plate (plate) 43, a plate 44, and a pipe 45, as shown in FIG. The end plate 41 is attached to the refrigerator 19, and the end plate (
The radiation shield plate 14 (or 15)
) is installed. The end plate 41 is located above the end plate 43. The plate body 44 is fixed to the end plate 41 by brazing or the like.

Based on the above-described thermal switch principle C and configured as shown in FIG. 4, when the working medium is fed through the pipe 45, it condenses on the plate 44, becomes liquid, boils on the plate 43, and becomes a gas. becomes. Due to this boiling and condensation, heat is transferred from the plate 43 with a high temperature to the plate 44 with a low temperature. In addition, since the end plate 41 is arranged above the end plate 43, the steam boiling on the plate 43 rises and reaches the plate 44, and the liquid condensed on the plate 44 falls downward. , the natural convection occurs in such a way that it reaches the plate 43.

Note that the working medium needs to be in a gas-liquid two-phase state in the temperature range determined by the plates 43 and 44. Therefore, -200
It is necessary to select an appropriate working medium depending on the temperature level, such as using nitrogen when used at temperatures around 0.degree. C. and hydrogen when used at around -250.degree.

In this state, when the temperature of the plate 44 is increased to become higher than the temperature of the plate 43, the natural convection stops, and the gas in the space between the plates 44 and 43 forms temperature stratification, resulting in heat generation. Transmits only by conduction. By providing a sufficient distance between the plates 44 and 43, heat transfer due to thermal conduction can be sufficiently reduced. In other words, a thermal switch can be configured that is turned on when the temperature of the plate 44 is lower than that of the plate 43 and turned off when the humidity of the plate 44 is higher than that of the plate 43. Moreover, if the working medium is evacuated from the pipe 45, the thermal switch will be turned off regardless of the temperature relationship between the plates 44 and 43.

FIG. 5 shows a modification of the embodiment shown in FIG.

A container 51 provided with a plate 54 and a container 52 provided with a plate 53 are constructed separately, and both are connected by piping 5.6.57.

Based on the above-described thermal switch principle C and configured as shown in FIG. 5, slight fluctuations in the relative positions of the containers 51 and 52 can be absorbed by deformation of the pipes 56 and 57. Even if the container 51 is firmly attached to the refrigerator 19 and the plate 53 is firmly attached to the radiation shield plate 14 (or 15), the refrigerator 19 and the radiation shield plate 14 (or 15)
It is possible to absorb the relative positional deviation of Furthermore, since the containers 51 and 52 are connected by thin pipes 56 and 57, the heat transfer during off-time can be reduced.

Note that the present invention is not limited to the embodiments described above.

For example, the plate in the embodiment shown in FIG. 2 is not limited to a cylindrical body, but may be any plate having a sufficiently large facing area between the first and second plates.

For example, as the first and second plates, parallel plates are used and they are arranged alternately with small gaps between them, or plates arranged radially are arranged alternately with small gaps between them. It may be arranged in a configuration.

Furthermore, the gap between the plates is not limited to 0.5 mm, but can be changed as appropriate according to specifications. Furthermore, the means for adhering and separating the plates in the embodiment shown in FIG. 3 is not necessarily limited to gas pressure;
It may also be mechanically driven.

Furthermore, although the configurations shown in FIGS. 4 and 5 are both based on Principle C, their shapes are not limited to those shown.

Note that the working medium is not limited to helium.
Nitrogen, argon, neon according to specifications.

Alternatively, hydrogen or the like may be used, and its forms include gas, liquid, two-phase gas-liquid, two-phase gas-solid, two-phase liquid-solid, and three-phase gas-liquid-solid.

Or, if it has fluidity, such as a supercritical pressure state without a clear phase change, its specifications are not specified. Further, materials that are solid at the steady operating temperature but become fluid when the temperature is slightly raised can also be used as the working medium. In particular, in the embodiment shown in Fig. 4, a two-phase gas-liquid phase is illustrated, but basically it is sufficient if the natural convection can be utilized, and it goes without saying that a single phase of only gas can be used, as well as all the above-mentioned forms. Flowable working media are available.

FIG. 6 is a diagram showing an example of how the working medium is used, and is a sectional view of a cryostat for a superconducting coil immersed in liquid helium used in a superconducting magnetic resonance imaging apparatus, etc., in which the object to be cooled is a superconducting coil. Here, the liquid helium 12 cooling the superconducting coil 11 evaporates and exits from the inner tank 3 and vent pipe 60. Piping 61. It is discharged to the atmosphere through valve 62. This piping 61 is branched, and the valve 63. Piping 64. Helium gas, which serves as a working medium, is supplied to the thermal switches 17.18 through valves 65a and 65b.

According to this configuration, there is no need to separately prepare a working medium, and the switch can be operated easily. Valve 6
6 is a line for exhausting air when the switch is turned off. In this way, if the switch operating medium is supplied from the refrigerant used in the cryogenic apparatus, handling becomes easier. It should be noted that it is rather preferable to add a refrigerant reservoir or cooling piping for shield cooling to the radiation shield plate, as used in conventional devices, as this increases redundancy and increases the options for use.

Furthermore, as shown in FIG. 7, the present invention may have a configuration in which the inner tank container 13 and the refrigerator 19 are thermally connected via a thermal switch 71 in addition to the radiation shield plates 14 and 15.

In this case, either one of the radiation shield plates 14, 15 and the refrigerator 19 may be thermally connected via the thermal switch 17 or 18.

Furthermore, the object to be cooled is not limited to superconducting coils, but can be applied to objects that need to be cooled to extremely low temperatures. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, the cryogenic apparatus according to the present invention includes an object to be cooled, a container in which the object to be cooled is accommodated together with a refrigerant, a vacuum container in which the container is accommodated, and a vacuum a radiation shield plate disposed between the container and the refrigerator; a refrigerator that cools at least one of the radiation shield plate and the container; and a refrigerator that cools at least one of the radiation shield plate and the refrigerator; The structure includes a thermal switch connected to at least one of the two, which turns on/off heat transfer between the two.

According to this configuration, normally, by turning on the heat switch, at least one of the radiation shield plate and the container can be sufficiently cooled, and the temperature of the refrigerator can be raised to thaw the solidification of impurities. If it is necessary to do so, turning off the heat switch will insulate the freezing chamber and at least one of the radiation shield plate and container. can be heated.

Therefore, according to the present invention, it is possible to easily repair and maintain the refrigerator, and it is possible to significantly reduce the cost required for recooling the object to be cooled, which is extremely useful in practice.
t low temperature equipment can be provided.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the general structure of a superconducting magnet according to one embodiment of the present invention, FIG. 2 is a cross-sectional view showing the main structure of the above device, and FIG. 3 is a cross-sectional view showing the main structure of another embodiment. FIG. FIG. 4 is a cross-sectional view showing the main part structure of still another embodiment of the present invention, FIG. 5 is a cross-sectional view showing the main part structure of a modification thereof,
FIG. 6 is a sectional view showing a specific usage example of the present invention, and FIG. 7 is a sectional view showing a modification of the configuration shown in FIG. 1 as another embodiment of the invention. 11... Superconducting coil (cooled body), 12... Liquid helium, 13... Inner tank container, 14.15... Radiation shield plate, 16... Vacuum container, 17.18.71.
...Heat switch, 19... Refrigerator, 21.22...
End plate, 23.24... Cylindrical body (plate body), 25.35.
...Bellows, 28.38...Piping, 33...1st
plate body, 36... second plate body, 41... end plate, 42
... tube, 43 ... end plate (plate body), 44 ... plate body,
45... Piping, 51° 52... Container, 53.54.
...Plate, 55.56°57...Piping, 60...Bent pipe, 61.64...Piping, 62.63.65.6
6... Valve. Applicant's agent Patent attorney Takehiko Suzue Figure 1 23a 23b Z3c 23d 21 No. 2
Figure 3 Chrysanthemum Figure 4 Figure 5 Figure 6 Figure 7

Claims (9)

[Claims] (1) An object to be cooled, a container containing the object to be cooled together with a refrigerant, a vacuum container containing the container, a radiation shield plate disposed between the container and the vacuum container, and the radiation shield. A refrigerator that cools at least one of the plate and the container, and a refrigerator that is connected to at least one of the radiation shield plate and the refrigerator and between the container and the refrigerator to facilitate heat transfer therebetween. A cryogenic device characterized by comprising a heat switch that turns on and off. (2) The thermal switch connects a first plate with good thermal conductivity connected to the refrigerator side and a second plate with good thermal conductivity connected to the radiation shield plate side with a small gap between them. By placing the working medium in the gap between the first and second plates, heat is transferred between each plate by heat conduction of the working medium.
The cryogenic apparatus according to claim 1, characterized in that, by evacuating the gap, only a small amount of heat transfer between the plates is caused by radiation (off). (3) The first and second plates include a plurality of cylindrical bodies having different diameters, these cylindrical bodies are arranged coaxially, and the cylindrical body serving as the first plate body and the second plate The cryogenic apparatus according to claim 2, characterized in that the cryogenic apparatus is constructed by alternately arranging cylindrical bodies as bodies. (4) The first and second plates are constructed by using plates arranged in parallel and alternately arranged with slight gaps between them. Cryogenic equipment as described. (5) The first or second plate body is constructed by using plate materials arranged radially, and these plates are arranged alternately with small gaps between them. Cryogenic equipment as described. (6) The thermal switch includes a first plate with good thermal conductivity connected to the refrigerator side and a second plate with good thermal conductivity connected to the radiation shield plate side, which are arranged opposite to each other. By bringing the first and second plates into close contact with each other and filling a working medium between the plates, heat is transferred (turned on) between each plate by surface contact heat transfer in the working medium, and the first and second plates are brought into contact with each other. Claim 1, characterized in that by separating the second plate and evacuating the space between the plates, only a small amount of heat is transferred between each plate due to radiation (off). Cryogenic equipment as described. (7) The thermal switch has a first thermally conductive plate connected to the refrigerator side that is relatively above or equal to a second thermally conductive plate connected to the radiation shield plate. By placing the working medium between them, heat is transferred from the second plate to the first plate by natural convection and transferred (on), and by evacuating the space between them, only radiation is generated. The cryogenic device according to claim 1, characterized in that the cryogenic device is configured such that only a small amount of heat transfer (off) occurs due to the heat transfer. (8) The thermal switch arranges a first thermally conductive plate connected to the refrigerator side relatively above a second thermally conductive plate connected to the radiation shield plate. By inserting a working medium between them, heat transfer (turns on) by natural convection occurs when the temperature of the refrigerator is lower than the temperature of the radiation shield, and only conduction (turns on) when the temperature of the refrigerator is higher than the temperature of the radiation shield. The cryogenic device according to claim 1, characterized in that the cryogenic device is configured to be turned off). (9) The working medium for operating the thermal switch is the same as the refrigerant that cools the object to be cooled,
The cryogenic apparatus according to claim 1, characterized in that the cryogen is supplied from a refrigerant supply system to the container.