JPH047806A - Low-temperature container for superconductive magnet - Google Patents

Abstract

PURPOSE:To aim at reducing the weight of a low-temperature container by mounting a magneto-shielding material between shielding coils and a superconductive magnet. CONSTITUTION:A cylindrical magneto-shielding plate 8 is mounted so that it may cover the peripheral part of each superconductive magnet 7. On the peripheral part of the magneto-shielding plate 8, two units of a shielding coil 9 are arranged in a row along the cylindrical axis of the magneto-shielding plate 8. These coils generate the magnetic filed of reverse direction against the static magnetic field. The external leakage magnetic field caused by the superconductive magnets 7 is at first reduced on the magneto-shielding plate 8, and then it is eliminated on the magnetic field by the shielding coil 9. In this way, the magneto-shielding plate is only arranged between the superconductive magnet and the shielding coil. Therefore, the total weight of the low-temperature container is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a cryogenic container for a superconducting magnet that houses a superconducting magnet used for generating a static magnetic field in, for example, a nuclear magnetic resonance tomography apparatus.

B. Conventional technology It is well known that the static magnetic field generated by superconducting magnets leaks to the outside of the low-temperature container and has an adverse effect on electronic devices placed around the low-temperature container. In order to suppress the magnetic field, the following measures have been taken in the cryogenic container.

■Passive shielding method This is a cylindrical magnetic shield plate made of ferromagnetic material such as iron or nickel that covers the periphery of the cryogenic container to suppress the magnetic field leaking outside the cryogenic container.

■Active shielding method In this method, a shielding coil that generates a magnetic field in the opposite direction to the static magnetic field generated by the superconducting magnet is placed around the superconducting magnet to cancel out the magnetic field leaking to the outside.

Problems to be Solved by the C0 Invention However, the cryogenic vessels for superconducting magnets employing the above-mentioned conventional methods have the following drawbacks.

In the passive shield method described in (2), the weight of the cylindrical magnetic shield plate is quite heavy.For example, the weight of the cylindrical magnetic shield plate is quite heavy. The weight ranges from 5 to 10 tons. For this reason, the total weight of the entire cryocontainer is quite heavy, and the building housing the cryocontainer must be reinforced to withstand the weight, which has the disadvantage of increasing the cost of the building. there were. Further, by disposing the magnetic shield plate, the outer dimensions of the cryogenic container become larger, and a considerable amount of space is required for housing the container, which requires a large room to be secured, which has the disadvantage of increasing the cost.

In the active shielding method described in ①, the magnetic field generated by the shielding coil is in the opposite direction to the static magnetic field formed by the superconducting magnet, so it has the effect of reducing not only the external leakage magnetic field but also the magnetic field strength of the static magnetic field. There is. Therefore, it is necessary to increase the current value flowing through the superconducting wire used in the superconducting magnet to reinforce the static magnetic field that is reduced by the shielding coil, which requires a large amount of expensive superconducting wire with a high critical value. There was a drawback.

This invention was made in view of the above circumstances, and aims to provide a cryogenic container for a superconducting magnet that can reduce the weight of the cryogenic container and reduce the cost of superconducting wire. .

01 Means for Solving the Problems The present invention has the following configuration to achieve the above object.

That is, the low temperature container for superconducting magnets according to the present invention is
A low-temperature superconducting magnet comprising: an inner container in which a superconducting magnet is immersed and stored in a cryogenic cryogen; a heat shield plate surrounding the inner container; and a vacuum container containing the inner container and the heat shield plate. In the container, a shielding coil that generates a magnetic field in the opposite direction to the static magnetic field formed by the superconducting magnet is arranged around the superconducting magnet, and a magnetic shielding material is arranged between the shielding coil and the superconducting magnet. It is characterized by what it did.

81 Effects According to this invention, the magnetic shielding material is not placed so as to cover the periphery of the low-temperature container as in the conventional case, but is simply placed between the superconducting magnet and the shielding coil, which is different from the conventional passive Compared to the shield method, the total weight of the cryogenic container is reduced.

In addition, by arranging magnetic shielding material, external leakage magnetic fields can be suppressed to some extent, so compared to the conventional active shield method, which only installs a shielding coil and cancels external leakage magnetic fields, the shielding coil The current value to be passed is small, so the magnetic field formed by the shielding coil is also small, and the intervention of the magnetic shielding material suppresses the magnetic field of the shielding coil from penetrating into the static magnetic field region. Therefore, the amount of current flowing through the superconducting magnet can be smaller than in the past.

F. Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a perspective view schematically showing the configuration of an embodiment of the present invention.

This figure shows a case where a cryogenic container for a superconducting magnet is used in a nuclear magnetic resonance tomography apparatus (hereinafter referred to as MRI).

In the figure, reference numeral 1 denotes a gantry into which a subject M is inserted when a tomographic image is taken by MRI. A superconducting magnet low-temperature container 2 (hereinafter simply referred to as low-temperature container 2) is inserted into the gantry 1. The low-temperature container 2 is formed as a cylindrical body, as shown by the dotted line in the figure, and its hollow portion serves as a through hole 3 into which the subject M is inserted.

A head 4 that moves forward and backward into the through hole 3 is installed on the floor surface on the end face side of the gantry 1 via a base 6.

A movement mechanism (not shown) for moving the bed 4 forward and backward is provided in the base 6, and the subject M placed on the bed 4 is guided into the through hole 3 by the movement of the head 4. and nuclear magnetic resonance tomography is performed.

In the figure, reference numeral 5 denotes legs for installing the gantry 1 on the floor.

FIG. 2 shows a longitudinal cross-sectional view of the cryogenic container 2. As shown in FIG.

Hereinafter, the internal structure of the low temperature container 2 will be explained with reference to this figure.

In the through hole 3 into which the subject M is inserted, a plurality of solenoid-shaped superconducting magnets 7 that generate a uniform static magnetic field in the body axis direction of the subject M are arranged in parallel along the sleeve of the cryogenic container 2. There is. A cylindrical magnetic shield plate 8 is provided so as to cover the outer peripheral surface of each superconducting magnet 7, and two shields that generate a magnetic field in the opposite direction to the static magnetic field are provided on the outer peripheral part of the magnetic shield plate 8. The magnetic shield plate 8
are arranged in parallel along the cylinder axis. These superconducting magnets 7, magnetic shielding plates 8, and shielding coils 9 are housed in an inner container 10 filled with a cryogenic cryogen (for example, liquid helium) for maintaining the superconducting state of the superconducting magnets 7. .

The inner container 10 is surrounded by a second heat shield 11 made of a highly thermally conductive material such as aluminum, and the second heat shield 11 is surrounded by a first heat shield 12 made of a similar material. covered by. The second heat shield 11 is maintained at about 20K by the cooling action of Refrigeration II (not shown), and the first heat shield 12 is maintained at about 80K.
is maintained. The inner container 10, the second heat shield 11, and the first heat shield 12 are housed in a vacuum container 13 at room temperature.

The operation of the low temperature container 2 having such a configuration is as follows.

In order to perform nuclear magnetic resonance tomography, the bed 4 is inserted into the through hole 3.
The subject M lying supine on the bed 4 is set in the through hole 3.

A current is passed through a superconducting wire (not shown) constituting the superconducting magnet 7 to form a uniform static magnetic field in the space around the subject M (inside the through hole 3).

This static magnetic field is formed not only within the through hole 3 but also spreads toward the periphery of the superconducting magnet 7, so it extends to the outside of the cryogenic vessel 2, and becomes an external leakage magnetic field that spreads around the cryogenic vessel 2. It has a negative impact on various electronic devices etc.

The magnetic shield plate 8 and the shielding coil 9 have the function of suppressing this external leakage magnetic field. At the same time as a static magnetic field is generated by the superconducting magnet 7,
A current is also passed through the shielding coil 9 to generate a magnetic field in the opposite direction to the static magnetic field (hereinafter, this magnetic field will be referred to as a canceling magnetic field).

The external leakage magnetic field caused by the superconducting magnet 7 is first reduced by the magnetic shield plate 8, and then canceled by the canceling magnetic field. Further, by interposing the magnetic shield plate 8, the cancellation magnetic field is prevented from entering into the static magnetic field region (inside the through hole 3).

In this way, the external leakage magnetic field is reduced to some extent by the magnetic shield plate 8 before being canceled by the canceling magnetic field, so the magnitude of the canceling magnetic field is smaller than when only the shielding coil 9 is arranged (conventional active shield method). Since the magnetic shield plate 8 suppresses the cancellation magnetic field from entering the static magnetic field region, the amount of reinforcement of the static magnetic field by the superconducting magnet 7 is significantly reduced. In addition, since the magnetic shield plate 8 is only provided to cover the outer periphery of the ultra-conducting magnet 7, it is better than the case where the magnetic shield plate is attached all around the cryogenic container 2 (conventional passive shield method). , the weight of the cryocontainer 2 is reduced.

In the above-described embodiment, the cylindrical magnetic shield plate 8 was used as an example of the magnetic shield material, but various materials can be used without being limited to this shape.

Two examples are shown in FIGS. 3 and 4. In these figures, the superconducting magnet 7 is shown as an integrated cylindrical body for simplicity.

(a) As shown in FIG. 3, rod-shaped magnetic shielding materials 14 extending in the axial direction of the superconducting magnet 7 are arranged around the entire circumference of the superconducting magnet 7 at predetermined intervals in the circumferential direction. It may also be a configuration.

(b) As shown in FIG. 4, annular magnetic shielding members 15 concentric with the superconducting magnet 7 may be arranged at predetermined intervals in the cylindrical axis direction of the superconducting magnet 7.

Moreover, it goes without saying that a magnetic shielding material may be further placed outside the shielding coil 9 in order to further reduce the external leakage magnetic field.

Effects of the G0 Invention As is clear from the above explanation, the cryogenic container for superconducting magnets according to the present invention has a shielding coil that generates a magnetic field in the opposite direction to the static magnetic field formed by the superconducting magnet, which is placed around the superconducting magnet. Since the magnetic shielding material is placed between the shielding coil and the superconducting magnet, the following effects can be obtained.

(a) Since the external leakage magnetic field caused by the superconducting magnet is reduced to some extent by the magnetic shielding material, the magnetic field that should be formed by the shielding coil can be reduced, and the current passing through the shielding coil can also be small, so the shielding The cost of superconducting wire for the coil can be reduced.

(D) In addition to reducing the current flowing through the shielding coil, the interposition of the magnetic shielding material suppresses the magnetic field formed by the shielding coil from entering the static magnetic field region, so the static magnetic field is supplemented by the superconducting magnet. Since the amount of reinforcement can be reduced and the current flowing through the superconducting magnet can be significantly reduced, the cost of the superconducting wire can be reduced.

(c) Since the magnetic shield material is only provided to cover the outer periphery of the superconducting magnet, it is easier to protect the cryo-container than when the magnetic shield material is attached all the way around the cryo-container (conventional passive shielding method). The weight can be reduced, the strength of the building housing the cryogenic container can be reduced, the space required to house the device can be reduced, and the cost of the building can be reduced.

[Brief explanation of drawings]

1 to 4 relate to an embodiment of the present invention, in which FIG. 1 is a perspective view showing a schematic configuration of a nuclear magnetic resonance tomography apparatus in which a cryogenic container for a superconducting magnet is housed, and FIG. 3 is a vertical cross-sectional view of a low-temperature vessel for a superconducting magnet, and FIGS. 3 and 4 are perspective views showing a part of a low-temperature vessel for a superconducting magnet as a modified example. 7... Superconducting magnet 8.14.15... Magnetic shielding plate (magnetic shielding material) 9... Shielding coil 10... Inner container 11
．． 12... Heat shield 13... Vacuum container patent applicant Shimadzu Corporation

Claims (1)

[Claims] (1) A superconductor comprising an inner container in which a superconducting magnet is immersed and stored in a cryogenic cryogen, a heat shield plate surrounding the inner container, and a vacuum container containing the inner container and the heat shield plate. In the low-temperature container for magnets, a shielding coil that generates a magnetic field in the opposite direction to the static magnetic field formed by the superconducting magnet is arranged around the superconducting magnet, and a magnetic shield is placed between the shielding coil and the superconducting magnet. A low-temperature container for superconducting magnets, characterized by the arrangement of materials.