JP4519363B2 - Cryogenic containment vessel and biomagnetic measuring device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel cryogenic storage container and a biomagnetic measurement device using the same, and more particularly to a heat insulating container for measuring a weak magnetic field that cools a magnetometer using a refrigerant such as liquid helium, and a refrigerant such as liquid helium. It is related with the structure of the heat insulation container which reduces the consumption of gas and reduces operating cost.
[0002]
[Prior art]
In a biomagnetism measuring apparatus that measures magnetism generated from a living body, a high-sensitivity magnetic flux sensor using a SQUID (Superconducting Quantum Interference Device) is used to measure extremely small magnetism. Since this SQUID uses superconductivity, it is necessary to cool the SQUID magnetic flux sensor to below the superconducting critical temperature. When using a SQUID magnetic flux sensor using an Nb-based superconductor that has been generally used so far, the boiling point is required. Is cooled with liquid helium, which is 4.2K. This liquid helium has a very small latent heat of vaporization, and liquid helium evaporates due to slight heat penetration, so regular replenishment is required, which not only raises the running cost of the biomagnetic measurement device, but is also a serious problem in maintainability. It was.
[0003]
In order to reduce the evaporation amount of liquid helium, a high level of heat insulation technology is required, and a cryogenic storage container called a dewar or cryostat is used as a container for storing a sensor in a biomagnetic measuring device and storing liquid helium. It is used. Especially in biomagnetism measuring devices, it is necessary to suppress the generation of magnetism from the container itself, and since low heat conductivity and sufficient strength at low temperatures are necessary, glass fibers that clear these problems Reinforced plastic is used.
[0004]
FIG. 1 is a cross-sectional view showing the structure of a cryostat in a conventional biomagnetic measuring apparatus. In the cryostat, a SQUID magnetic flux sensor 3 can be arranged at the bottom, an inner container 1 for storing liquid helium 2, an outer container 4 that forms a vacuum tank 5 between the inner container 1, and a vacuum tank 5 A radiation shield 6 installed on the inner container 1, a heat insulating material 7 inserted into the opening of the inner container 1, and a lid (upper flange) 12 for closing the opening.
[0005]
Since the heat intrusion into the dewar is the sum of the heat conduction component from the wall of the inner container 1 and the radiation component from the surroundings, a heat insulation technique for reducing each component is used. In order to reduce the heat conduction component, not only the heat conduction area is reduced, but also heat exchange is performed using the sensible heat of the evaporated helium gas. In order to reduce the radiation component, a radiation shield 6 is provided in the vacuum chamber 5 between the inner container 1 and the outer container 4. Moreover, in the vacuum chamber 5 between the radiation shield 6 and the outer container 4, what is called mylar in which aluminum is vapor-deposited on the surface of the polyester thin film, and what is called emboss in which the surface has irregularities and vapor-deposited aluminum on both sides A laminated heat insulating material 10 in which several layers are alternately stacked is installed.
[0006]
It is known that the radiant heat flux depends on the number of laminated heat insulating materials 10 and the gaps (lamination intervals) between the thin films, and the larger the number of layers, the smaller the radiant heat flux becomes. It has become clear.
[0007]
This laminated heat insulating material 10 is an indispensable technique in the field where extremely low temperature is required, for example, when using superconductivity. For example, in MRI, multilayer heat insulating material is wound around a radiation shield surrounding the superconducting magnet in multiple layers. As a result, the amount of radiant heat applied to the superconducting magnet is reduced. Here, in the case of MRI, since the magnet is ring-shaped and has a structure in which a magnetic field is generated at the center of the ring, the distance between the magnet and the outer wall of the container does not affect the sensitivity. Therefore, since a space in which the multilayer heat insulating material can be installed in multiple layers can be secured around the magnet, the method of winding the laminated heat insulating material has not been a problem.
[0008]
In the case of a superconducting magnet, the ring is installed mainly with the horizontal axis as the central axis, so the radiation shield installed around the ring also has the horizontal axis as the central axis. The laminated heat insulating material wound around the structure has a structure that is supported in the vertical direction by the radiation shield, and dropping of the laminated heat insulating material did not cause a problem.
[0009]
On the other hand, in the biomagnetic measuring device, the distance between the sensor arranged at the bottom of the inner container 1 and the object to be inspected greatly depends on the sensor sensitivity, and therefore exists between the bottom of the inner container 1 and the bottom of the outer container 4 at the bottom. The thickness of the vacuum chamber 5 to be reduced is narrow, and it is difficult to install multiple layers of the laminated heat insulating material 10 at the bottom. Therefore, the influence of heat intrusion from the bottom is increasing, and it is necessary to reduce heat intrusion from the bottom surface.
[0010]
In addition, since the laminated heat insulating material 10 is wound around the side surface portion in the biomagnetic measuring device, the laminated heat insulating material 10 itself can freely move in the vertical direction. For example, the laminated heat insulating material 10 can be moved by the vibration during transportation. It is conceivable that it will fall to the bottom of the. When the laminated heat insulating material 10 falls to the bottom of the outer container 4, the outer container 4 at room temperature and the laminated heat insulating material 10 come into contact with each other, and this laminated heat insulating material 10 has the same temperature as the outer container 4. The heat insulation capability of the material 10 is deteriorated. Especially on the bottom surface, since only a few layers of the heat insulating material 10 can be installed, the effect of deterioration of the heat insulation performance is great, the amount of heat entering from the bottom increases, and the consumption of liquid helium 2 stored in the inner container 1 Will increase.
[0011]
In biomagnetism measuring devices developed so far, the consumption of liquid helium is as large as about 10 L per day, so that the amount of heat intrusion from the bottom surface has not been a big problem. However, if the liquid helium consumption is further reduced in the future, it is thought that the final heat insulation of the bottom layer will affect the liquid helium consumption. This is an important issue in promoting low consumption.
[0012]
Japanese Patent Laid-Open No. 3-218079 discloses that a specific material is used as a support member for supporting the radiation shield and the liquid nitrogen tank, and Japanese Patent Publication No. 7-507878 discloses that the liquid nitrogen container is an upper colorizer of the vacuum container. A structure supported by a rod is shown.
[0013]
[Problems to be solved by the invention]
In the conventional biomagnetic measuring device, the reduction of the amount of heat entering the storage container, particularly the inner container, is a big problem. The amount of heat entering the inner container evaporates the refrigerant stored inside the inner container, which necessitates frequent replenishment of the refrigerant, which not only increases the running cost, but also has a problem in maintainability.
[0014]
In particular, in the biomagnetic measuring device, since the vacuum chamber at the bottom has an extremely thin structure, ensuring heat insulation at the bottom directly leads to a reduction in the total amount of intrusion heat. The present invention was born from the need to have a structure in which the laminated heat insulating material does not contact the outer container in order to stabilize the heat insulating performance at the bottom.
[0015]
Even when looking at the prior art, the laminated heat insulating material is described on the assumption that usually several to several tens of layers are installed, and a structure in which only one or two layers of heat insulating material can be installed is mentioned. There is nothing. In a biomagnetic measuring device with reduced consumption of liquid helium, whether or not this one-layer or two-layer heat insulating material is in contact with the outer container has a large influence on the refrigerant consumption, and the performance of the storage container In order to stabilize, it is necessary to have a structure in which the laminated heat insulating material does not contact the outer container.
[0016]
In order to suppress the vertical displacement of the laminated heat insulating material, for example, a method of providing a protrusion on the container side and supporting the laminated heat insulating material with this protrusion can be considered, but since the laminated heat insulating material has a multilayer structure, several layers on the inside Can be influenced by protrusions, but the outer laminated heat insulating material is not affected by the protrusions, so that the outer heat insulating material can be translated in the vertical direction.
[0017]
In addition, for example, a method of increasing the frictional force by strongly winding the laminated heat insulating material and preventing the laminated heat insulating material from falling can be considered, but the ability of the laminated heat insulating material depends on the stacking interval of each thin film, so By winding, the lamination | stacking space | interval of a laminated heat insulating material becomes narrow, and as a result, heat insulation performance deteriorates.
[0018]
In addition, a method of supporting the laminated heat insulating material with the flange surface of the radiation shield by making the laminated heat insulating material into a bag shape is conceivable, but when some of the heat insulating material breaks in order to support the self weight of the laminated heat insulating material The laminated heat insulating material falls and also deteriorates the heat insulating performance at the bottom surface.
[0019]
Further, none of the above-mentioned publications show a structure for directly supporting the heat insulating material in the vacuum chamber.
[0020]
An object of the present invention is to provide a cryogenic storage container having a structure in which a laminated heat insulating material does not come into contact with an outer container, and preventing the laminated heat insulating material from falling to prevent deterioration of heat insulating performance, and a biomagnetic measuring device using the same Is to provide.
[0021]
[Means for Solving the Problems]
The present invention includes an inner container for storing a refrigerant and storing an object to be cooled,
The inner container is disposed within the outer container connected with the upper part of the inner container,
Disposed between the inner container and the outer container, a radiation shield that is placed so as to cover at least the bottom of the inner container and the side surface portion,
Heat insulating means disposed on the bottom and side portions of the radiation shield ;
In a cryogenic containment vessel having
A first support that supports the heat insulating means is disposed between the heat insulating means and the outer container disposed at the bottom of the radiation shield ;
A cryogenic containment vessel comprising a second support that supports the first support and is connected to the upper portion of the outer container , preferably a second comprising a support thread or a support bar . It is characterized by having a structure which is supported by the support body and supports the heat insulating means from below.
[0022]
Further, according to the present invention, in the above-described cryogenic storage container, a neck portion that communicates from the inner container to the outer container and is formed on the upper portion of the inner container and has a smaller diameter than the inner container, and the neck portion is filled. And a second heat insulating means .
[0023]
At least hand of the first support and the second support is made of a nonmagnetic material, it is preferred second support is a support yarn or support rods.
[0024]
Furthermore, the present invention is a superconducting quantum interference device arranged at the bottom of the inner container as the object to be cooled, wherein the cryogenic storage container for storing and cooling the superconducting quantum interference device comprises the above-mentioned cryogenic storage container. The biomagnetic measuring device is characterized by the following.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 2 is a cross-sectional view of the biomagnetic measurement apparatus according to the present invention. The inner container 1 has an area for storing the SQUID magnetic flux sensor 3 at the bottom, and has a structure capable of storing liquid helium 2 therein. Further, by adopting a narrow neck type structure that is coupled to the inner container 1 and has a neck portion 11 in which the size of the opening is smaller than the size of the bottom surface of the inner container 1, the liquid helium temperature is controlled from the open room temperature end. The heat conduction area of the connecting portion is reduced, and the heat conduction component from the upper end of the opening is reduced. Here, the neck portion 11 smaller than the size of the bottom surface of the inner container 1 is a container having a diameter smaller than the diameter of the inner container 1. Further, the heat conduction component is reduced by reducing the thickness of the wall of the neck portion 11 as much as possible within a range in which sufficient reliability can be ensured in terms of strength.
[0026]
By laminating a heat insulating material 7 as a second heat insulating means made of polyurethane foam having a low thermal conductivity inside the neck portion 11, the amount of intrusion heat due to heat conduction from the upper surface at room temperature is reduced. ing. A plurality of polyurethane foam heat insulating materials 7 are stacked and laminated, and a material having high thermal conductivity is arranged between the heat insulating materials 7 to make the temperature uniform. In this embodiment, a thin aluminum plate is used. I use it. Bubbles existing inside the polyurethane foam are liquefied in a cryogenic state and thus serve as a vacuum insulation, and have a high insulation performance in a cryogenic temperature range.
[0027]
The outer container 4 has a vacuum exhaust port (not shown) in order to form a vacuum chamber 5 between the outer container 4 and the inner container 1. Here, the vacuum exhaust port is disposed at the side surface position of the neck portion 11 to prevent the heat insulating material from being sucked from the vacuum exhaust port during vacuum exhaust.
[0028]
The inner container 1, the neck part 11 , and the outer container 4 are made of glass fiber reinforced plastic (GFRP) having a low thermal conductivity and high strength in a cryogenic temperature range, and are formed using a polymer adhesive, It is manufactured as a single unit. The outer diameter of the heat insulating material 7 to be inserted inside of the neck portion 1 1 is smaller than the inner diameter of the neck portion 1 1, evaporated helium gas a structure through the gap between the heat insulating material 7 and the neck portion 1 1 ing. Also, the cable for taking out the detection signal is taken out using this gap. The evaporated helium gas flows through the gap between the heat insulating material 7 and the neck portion 11 and is released into the atmosphere from a gas vent port (not shown) attached to the upper flange. At this time, the space between the heat insulating material 7 and the neck portion 11 is released. By exchanging heat, the heat conduction component transmitted through the neck portion 11 is reduced.
[0029]
The surface of the inner container 1 on the vacuum side and the surface of the radiation shield 6 are affixed with a tape having aluminum deposited on the entire surface. By reducing the emissivity of the radiation surface, the inner container 1 is protected from the radiation shield. The amount of radiant heat received from 6 and the amount of radiant heat received by the radiation shield 6 from the outer container 4 are reduced.
[0030]
A laminated heat insulating material 10 is applied to the vacuum chamber 5 between the radiation shield 6 and the outer container 4 to reduce the amount of radiant heat. Here, the gap between the radiation shield 6 and the outer container 4 can be secured about 10 mm on the side surface, but it is necessary to make the distance between the non-inspection object and the SQUID magnetic flux sensor 3 close to the bottom, so that the vacuum chamber 5 has only about 2 mm. I can't take the thickness.
[0031]
The laminated heat insulating material 10 is applied around the side surface between the radiation shield 6 and the outer container 4. Moreover, it has also given on the flange surface 13 which couple | bonds the radiation shield 6 and the inner container 1. FIG. Between the bottom surface of the radiation shield 6 and the outer container 4, one layer of laminated heat insulating material (one embossed and one-sided aluminum vapor deposited mylar) is installed.
[0032]
Between the outermost layer of the laminated heat insulating material 10 on the bottom surface of the radiation shield 6 and the outer container 4 , a support plate 8 that is a first support body having a thickness of 0.5 mm is installed. Here, on both surfaces of the support plate 8, tape having aluminum deposited on the surface is attached, so that the amount of radiant heat received by the support plate 8 is reduced. Since the support plate 8 is mounted between the SUQID magnetic flux sensor 3 and the non-inspection object, it needs to be non-magnetic and uses GFRP. The support plate 8 is suspended by a support thread or a support rod 9 that is on the upper surface of the support plate 8 and has one end fixed to the vacuum chamber side, and supports the laminated heat insulating material 10 from the bottom. The support plate 8 is suspended by a support thread or a support rod 9 as a second support, and has a structure that floats so as not to contact the outer container 4. Therefore, high heat insulation is obtained.
[0033]
Further, the support yarn or support rod 9 is provided suspended above or on the upper surface of the outer container 4, and a laminated heat insulating material 10 is provided on the inner container 1 side, and the laminated heat insulating material 10 is formed by the support yarn or support rod 9. Since the laminated heat insulating material 10 does not come into contact with the outer container 4, a high heat insulating property can be obtained.
[0034]
When liquid helium 2 is injected into the inner container 1, the inner container 1 contracts due to thermal contraction, but the inner container 1 that is suspended from the upper surface contracts toward the upper surface that is the fixed end. The fixed radiation shield 6 and laminated heat insulating material 10 itself move upward. On the other hand, since the support plate 8 itself supporting the laminated heat insulating material 10 is not affected by heat shrinkage, a gap is generated between the laminated heat insulating material 10 and the support plate 8, and the heat insulating performance is improved.
[0035]
Since the laminated heat insulating material 10 is wound around the side surface of the radiation shield 6 and the load received by the support plate 8 acts on the edge side of the support plate 8, even if a thin material having a thickness of about 0.5 mm is used for the support plate 8. It is possible to support the load of the laminated heat insulating material 10 sufficiently.
[0036]
When the laminated heat insulating material falls by experiment and the bottom surface of the laminated heat insulating material contacts the outer container, the liquid helium consumption is about 0.4 L compared to the case where the bottom surface of the laminated heat insulating material does not contact the outer container. The use of this structure makes it possible to prevent an increase in liquid helium consumption due to the fall of the laminated heat insulating material.
[0037]
(Example 2)
FIG. 3 is a cross-sectional view of a biomagnetic measuring apparatus showing another embodiment of the present invention. This embodiment is characterized in that the supporting thread or the supporting rod 9 is fixed to the protruding portion 14 provided on the side surface of the outer container 4. The support yarn or support bar 9 can support the weight of the laminated heat insulating material 10 if it is above the support plate 8, but if the distance between the support plate 10 and the fixed end is short, the support yarn or support rod The amount of intrusion heat due to heat conduction through 9 is a problem. Therefore, it is desirable that the protrusion 14 provided on the outer container 4 be installed at a position away from the support plate 8. Other structures are the same as those in the first embodiment.
[0038]
【The invention's effect】
According to the present invention, it is possible to prevent the laminated heat insulating material from falling, stabilize the heat insulation performance of the biomagnetic measuring device, reduce the consumption of liquid helium, and provide a highly stable biomagnetic measuring device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cryostat in a conventional biomagnetic measurement apparatus.
FIG. 2 is a cross-sectional view of the cryostat according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view of a cryostat in Embodiment 2 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Inner container, 2 ... Liquid helium, 3 ... SQUID magnetic flux sensor, 4 ... Outer container, 5 ... Vacuum tank, 6 ... Radiation shield, 7 ... Heat insulation material, 8 ... Support plate, 9 ... Support thread or support rod, 10 ... laminated heat insulating material, 11 ... neck, 12 ... cover, 13 ... radiation shield flange.

Claims (6)

An inner container for storing the refrigerant and storing the object to be cooled;
An inner container disposed inside and connected to an upper part of the inner container ;
Disposed between the inner container and the outer container, a radiation shield that is placed so as to cover at least the bottom of the inner container and the side surface portion,
And insulation means disposed on the bottom and side portions of the radiation shield,
In a cryogenic containment vessel having
A first support supporting the thermal insulation means between said heat-insulating means and the outer container, which is located at the bottom of the radiation shield is disposed,
Cryogenic storage vessel supporting the first support, characterized by comprising a second support connected to the upper portion of the outer container. In claim 1 ,
The cryogenic storage container, wherein the inner container is connected to the outer container by a neck portion formed to have a diameter smaller than that of the inner container , and has a second heat insulating means inside the neck portion. Oite to claim 1,
A cryogenic storage container, wherein at least one of the first support and the second support is made of a nonmagnetic material. An inner container for storing the refrigerant and storing the object to be cooled;
An inner container disposed inside and connected to an upper part of the inner container ;
A radiation shield disposed between the inner container and the outer container, and disposed so as to cover at least a bottom portion and a side surface portion of the inner container ;
Heat insulating means disposed on the bottom and side portions of the radiation shield;
A superconducting quantum interference device disposed at the bottom of the inner container ;
In a biomagnetic measuring device having
A first support that supports the heat insulating means is disposed between the heat insulating means and an outer container disposed at the bottom of the radiation shield ;
Supporting the first support, the biomagnetic measurement apparatus characterized by comprising a second support connected to the upper portion of the outer container. )
In claim 4 ,
The inner container is connected to the outer container by a neck portion having a diameter smaller than that of the inner container, and has a second heat insulating means inside the neck portion. Oite to claim 4,
A biomagnetic measuring apparatus, wherein at least one of the first support and the second support is made of a nonmagnetic material.

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