JPH11197132A - Passive shield type superconducting magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a passive shield type superconducting magnet for generating the static magnetic field of a small leakage magnetic field and high magnetic field uniformity without enlarging the entire device by efficiently arranging a ferromagnetic body for a magnetic shield. SOLUTION: In this magnet, static magnetic field generation sources 2 are arranged in a vertical direction holding an uniform magnetic field area 1 there between and a magnetic shield plate 6 and a yoke 7 for constituting the magnetic shield are arranged around them. The magnetic shield plate 6 and the yoke 7 are magnetically coupled at a junction part 12. On the surface side facing the static magnetic field generation source 2 of the magnetic shield plate 6 near the junction part 12, the ferromagnetic body 10 provided with a bevel slope 11 is attached so as to be in contact with the magnetic shield plate 6 and the yoke 7. In the constitution, a magnetic flux line 14 is passed through a ferromagnetic body piece 10 and the magnetic flux line 14 is distributed at high density near the static magnetic field generation source 2 of the magnetic shield plate 6 as the whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive shield type superconducting magnet used for a magnetic resonance imaging (hereinafter, referred to as "MRI") apparatus, and more particularly to a magnetic shield of a magnetic shield arranged around a static magnetic field generating source. The present invention relates to a passive shield type superconducting magnet whose shape is improved and whose magnetic shield is made compact.

[0002]

2. Description of the Related Art Superconducting magnets are used in various fields, but the most practical use of general-purpose superconducting magnets is in the field of MRI apparatuses. In an MRI apparatus, a uniform magnetic field of a constant strength is created in a fixed space (imaging region), and various coils (gradient magnetic field coils—provide a gradient magnetic field to obtain spin position information in MRI; radio frequency (RF)
Coil—irradiates the subject with a high-frequency magnetic field to excite atomic nuclei and receive a nuclear magnetic resonance (NMR) signal generated in the subject; etc.) and perform NMR from the subject inserted into the imaging region. Collects information,
It is for reconstructing a sectional view in an arbitrary direction. In general,
The MRI apparatus is classified into a horizontal magnetic field type and a vertical magnetic field type according to the direction of the uniform magnetic field.

[0003] In a medical MRI apparatus, a horizontal magnetic field type is generally used as a conventional one using a superconducting magnet. However, in recent years, an open type permanent magnet type MRI apparatus using a permanent magnet and having a uniform magnetic field in a vertical direction has been put into practical use, and its openness has widely recognized its value worldwide. Therefore, at present, M using superconducting magnets
Open type (vertical magnetic field type) that can generate high magnetic field strength that cannot be achieved with permanent magnets even in RI equipment
A great deal of effort is being put into the development and commercialization of MRI equipment.

[0004] A superconducting magnet is usually provided in a uniform magnetic field region (MRI).
It comprises a static magnetic field generating source for generating a uniform magnetic field in an imaging region of the apparatus, and a magnetic shield disposed around the source to prevent leakage of the magnetic field to the outside of the apparatus. FIG. 9 shows an example of a vertical magnetic field type superconducting magnet. In FIG.
A static magnetic field generation source 2 is disposed above and below the uniform magnetic field region 1, and a uniform magnetic field Bo in the vertical direction is formed in the uniform magnetic field region 1 by the static magnetic field generation source 2. Static magnetic field source 2
Is composed of a superconducting coil 3 for generating a uniform magnetic field Bo, and a cooling container 4 for accommodating the superconducting coil 3 and cooling to a temperature exhibiting superconducting characteristics. The upper and lower cooling containers 4 are connected by a support 5.

The magnetic shield comprises a magnetic shield plate 6 disposed substantially horizontally above and below the static magnetic field generating source 2 and a yoke 7 for supporting and magnetically connecting the upper and lower magnetic shield plates 6.
Consisting of The materials of the magnetic shield plate 6 and the yoke 5 are both ferromagnetic materials such as iron. The static magnetic field generation source 2, the magnetic shield plate 6, and the yoke 7 constitute a magnetic circuit, and reduce the leakage of the magnetic field to the outside of the magnetic shield. As shown in FIG. 9, a superconducting magnet having a structure in which a magnetic shield is arranged around the static magnetic field generation source 2 is called a passive shield type superconducting magnet.

[0006] In the passive shield type superconducting magnet of the vertical magnetic field type, the direction of the uniform magnetic field B _O is up and down (vertical direction).
Therefore, the magnetic field strength of the leakage magnetic field is higher in the vertical direction. Furthermore, when this magnet is installed in a building for an MRI apparatus, since other rooms exist in the vertical direction,
The allowable value of the stray magnetic field in the vertical direction is limited to a strict value. On the other hand, in the horizontal magnetic field method, many parts with high leakage magnetic field strength are distributed in the horizontal direction, but since the horizontal direction (horizontal direction) is generally long in a room in a building, the allowable value of the leakage magnetic field in the horizontal direction is large. Are not as strict as those in the vertical direction. For this reason, in the passive shield type superconducting magnet of the vertical magnetic field type, in order to reduce the leakage magnetic field in the vertical direction, the thickness of the magnetic shield plate 6 is increased, or a stacked portion made of a ferromagnetic material is used in a portion where the leakage magnetic field is high. 8 are arranged.

[0007]

However, it is not preferable to stack a large amount of ferromagnetic material on the superconducting magnet from the viewpoint of the ceiling height in the room and the design of the apparatus. Therefore, as a superconducting magnet used in an MRI apparatus or the like, a magnet which makes the apparatus as compact as possible, has a small magnetic field leakage, and generates a highly uniform static magnetic field is required. Therefore, in the present invention, by efficiently arranging the ferromagnetic material for the magnetic shield plate and the yoke constituting the magnetic shield, the leakage magnetic field is small and the uniformity of the magnetic field is reduced without increasing the size of the entire device. An object of the present invention is to provide a passive shield type superconducting magnet which generates a high static magnetic field.

[0008]

In order to achieve the above object, a passive shield type superconducting magnet of the present invention accommodates a pair of superconducting coils arranged vertically facing each other, and accommodates each superconducting coil for cooling. A static magnetic field generating source comprising a cooling container having a magnetic field, and a magnetic shield plate made of a ferromagnetic material disposed above and below the static magnetic field generating source. In the passive shield type superconducting magnet which forms a magnetic circuit together with the static magnetic field generation source, the surface of the magnetic shield plate facing the cooling vessel is the magnetic shield plate and the yoke. In the vicinity of the junction, there is a hat-shaped inclined surface approaching the cooling vessel side (claim 1).

In this configuration, a shade-shaped inclined surface that covers the static magnetic field generation source is provided on the surface of the magnetic shield plate facing the static magnetic field generation source (cooling vessel), so that the magnetic shield plate and the yoke are provided. The magnetic path of the magnetic flux lines in the vicinity of the junction with the magnetic field becomes wider and the magnetic flux lines pass not only in the junction but also in the vicinity of the shaded inclined surface. As compared with, it is higher on the side closer to the static magnetic field generation source and lower on the far side. As a result, the strength of the leakage magnetic field at the upper and lower sides of the magnetic shield plate is reduced, so that it is not necessary to stack ferromagnetic substances on the upper and lower sides of the magnetic shield plate, and the height of the entire apparatus can be reduced.

[0010] The passive shield type superconducting magnet of the present invention comprises a static magnetic field generating source comprising a pair of superconducting coils arranged vertically facing each other, and a cooling container for accommodating and cooling each superconducting coil. Having a magnetic shield plate made of a ferromagnetic material above and below the static magnetic field source,
The upper and lower magnetic shield plates are coupled by a yoke made of one or more ferromagnetic materials to form a magnetic circuit together with the static magnetic field generating source. The magnetic shield plate has a shade-shaped inclined surface near the joint between the magnetic shield plate and the yoke on the opposing surface side so as to approach the cooling vessel near the joint. And a ferromagnetic piece in contact with the yoke (claim 2).

In this configuration, a shade-shaped inclined surface that covers the static magnetic field generation source is provided on the surface of the magnetic shield plate facing the static magnetic field generation source near the joint between the magnetic shield plate and the yoke. Due to the attachment of the ferromagnetic piece, the density of the magnetic flux lines passing through the magnetic shield plate is higher on the side closer to the static magnetic field generation source and lower on the far side as compared with the conventional product. As a result, an effect similar to that of the first aspect is obtained.

Further, in the passive shield type superconducting magnet of the present invention, at least one of the shaded inclined surfaces is provided for each of the joining portions between the magnetic shield plate and the yoke, and each inclined surface is provided. A start point is set on a surface of the magnetic shield plate facing the cooling container, and an end point is set on an inner surface of the yoke facing the cooling container (Claim 3).

In this configuration, one or more hat-shaped inclined surfaces are provided at each joint between the magnetic shield plate and the yoke.
Since the inclined surface covers the magnetic shield plate and the yoke near the joint, the magnetic path of the magnetic flux lines at each joint has been expanded from the joint to the portion of the hat-shaped inclined surface, The flow of the magnetic flux lines in this portion is shifted toward the inside, and the magnetic flux density outside is reduced.

[0014] In the passive shield type superconducting magnet of the present invention, the inclined surface of the shade shape includes at least one flat surface. In this configuration, since the hat-shaped inclined surface is formed by several planes, the shape of the hat-shaped inclined surface can be formed according to the flow of the magnetic flux lines flowing through the magnetic shield plate and the yoke. As a result, the flow of the magnetic flux lines near the junction is improved and the magnetic path expands, so the ferromagnetic material away from the static magnetic field source, such as the magnetic shield plate, where the magnetic flux lines hardly flow, can be removed. Since it can be deleted, it contributes to the reduction of the leakage magnetic field and the reduction in size and weight of the entire device.

In the passive shield type superconducting magnet of the present invention, the shaded inclined surface includes a curved surface. The magnetic flux lines passing through the magnetic shield plate and the yoke are
Since the flow is drawn in a curved line near the joint, the flow of the magnetic flux lines near the joint can be made smoother by forming the hat-shaped inclined surface using a curved surface, and at that portion, The magnetic path of the magnetic flux lines can be enlarged.
As a result, an effect similar to that of the fourth aspect is obtained.

In the passive shield type superconducting magnet of the present invention, an outer peripheral portion of the cooling container on a surface side facing the magnetic shield plate is formed with an inclined surface having substantially the same shape as the opposed hatched inclined surface. (Claim 6).

In this configuration, the cooling vessel (static magnetic field generating source)
Since the slope facing the hat-shaped inclined surface is provided with an inclined surface having substantially the same shape as the hat-shaped inclined surface, the cooling vessel has almost no loss of capacity at the inclined surface portion of the cooling vessel. It is possible to make the distance between the and the hat-shaped inclined surface extremely close. As a result, the height of the entire apparatus can be reduced, which contributes to the reduction in size and weight of the apparatus.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the passive shield type superconducting magnet of the present invention. FIG. 1 is a longitudinal sectional view of this embodiment. FIG. 2 is an enlarged view of the upper right part of FIG. In FIG. 1, in the passive shield type superconducting magnet of the present embodiment, a static magnetic field source 2 is disposed vertically across a uniform magnetic field region (which becomes an imaging region in an MRI apparatus) 1. A magnetic shield plate 6 and a yoke 7 which constitute a magnetic shield are arranged at the center.

The static magnetic field generating source 2 includes a superconducting coil 3 for generating a uniform vertical magnetic field in the uniform magnetic field region 1, a cooling container 4 for accommodating the superconducting coil 3, and cooling and maintaining the superconducting characteristic at a temperature showing superconducting characteristics. Consists of The superconducting coil 3 is usually a combination of a plurality of coils to enhance the uniformity of the magnetic field. Further, the cooling container 4 includes a refrigerant container that stores a refrigerant in which the superconducting coil 3 is immersed, a heat shield that includes the refrigerant container, and a vacuum container that includes the heat shield. The upper and lower cooling containers 4 are usually connected by a connecting pipe, and are cooled by one refrigerator. The static magnetic field generation source 2 is supported by the coupling body 13 on the upper and lower magnetic shield plates 6.

The magnetic shield plate 6 is a plate made of a ferromagnetic material such as iron. The magnetic shield plate 6 is disposed substantially parallel to the upper and lower sides of the static magnetic field generation source 2 and is supported by two yokes 7. The yoke 7 is a columnar body made of a ferromagnetic material such as iron. The yoke 7 supports the upper and lower magnetic shield plates 6 at predetermined intervals, and is magnetically coupled to the magnetic shield plate 6 at a joint 12. In the present invention, a ferromagnetic piece 10 having a hat-shaped inclined surface 11 on the surface of the magnetic shield plate 6 facing the cooling vessel 4 so as to be in contact with both the magnetic shield plate 6 and the yoke 7.
(The hat-shaped inclined surface 11 is arranged so as to cover the cooling vessel 4 with a hat). FIG. 2 is an enlarged view of a portion where the ferromagnetic piece 10 is attached. In FIG. 2, a ferromagnetic piece 10 is a magnetic shield plate 6.
The yoke 7 is made of a ferromagnetic material such as iron and has three surfaces. Of the three surfaces of the ferromagnetic piece 10, the surface facing the cooling container 4 is a hat-shaped inclined surface 11, and the other surface is the cooling container facing surface 6A of the magnetic shield plate 6 and the inner surface 7A of the yoke 7.
And are bonded to both sides thereof.

As shown in FIG. 2, by disposing the ferromagnetic piece 10 inside the joint 12 between the magnetic shield plate 6 and the yoke 7, the flow of the magnetic flux lines 14 in the magnetic shield plate 6 is improved. . The improvement of the flow of the magnetic flux lines will be described with reference to FIGS. FIG. 3 is an example of a magnetic flux line distribution of the superconducting magnet of the present embodiment, and FIG. 4 is an example of a magnetic flux line distribution of a conventional passive shield type superconducting magnet. In the case of the conventional example shown in FIG. 4, the magnetic flux lines 14 emitted from the upper superconducting coil 3 are divided into right and left parts at the center of the upper magnetic shield plate 6, and after passing through the upper magnetic shield plate 6, the upper joint 12 Go to yoke 7. The magnetic flux lines 14 passing through the yoke 7 return to the upper superconducting coil 3 via the lower joining portion 12, the lower magnetic shield plate 6, the lower superconducting coil 3, and the uniform magnetic field region 1. At this time, the magnetic flux lines 14 divided into right and left at the center of the magnetic shield plate 6 are concentrated on the left and right joints 12, so that the magnetic flux lines 14 traveling on the upper magnetic shield plate 6 are outside the magnetic shield plate 6. Tend to pass through the area close to. For this reason, the magnetic flux lines 14 easily leak to the upper side of the magnetic shield plate 4 and pass through the stacking portion 8 placed on the upper portion of the magnetic shield plate 6. As a result, it is necessary to increase the height of the superconducting magnet. was there.

On the other hand, in the case of the present embodiment shown in FIG.
By attaching the ferromagnetic piece 10 having the cap-shaped inclined surface 11 to the portion facing the cooling vessel 4 near the upper and lower joints 12, the upper superconducting coil 3 is emitted to the upper magnetic shield plate 6. The magnetic flux line 14 that has been directed to the yoke 7 is partially passed through the upper joint portion 12 and partially passed through the upper ferromagnetic piece 10. As a result, the magnetic flux lines 14 passing through the upper magnetic shield plate 6 have a distribution as if pressed down, the magnetic flux density of the upper portion of the upper magnetic shield plate 6 is lower than that of the conventional superconducting magnet, Magnetic field leakage outside the shield plate 6 is also reduced. Since the above description also occurs in the lower magnetic shield plate 6, the leakage magnetic field can be reduced without increasing the height of the superconducting magnet as in the conventional example.

The ferromagnetic piece 10 can be attached to the vicinity of the joint 12 by fixing it with a screw or welding it by welding. The ferromagnetic piece 10 may be attached to the magnetic shield plate 6 in advance, may be integrally processed with the magnetic shield plate 6, or may be attached after the magnetic shield plate 6 and the yoke 7 are assembled. You may.

FIG. 5 shows a second embodiment of the passive shield type superconducting magnet of the present invention. In the present embodiment, a shade-shaped inclined surface 11 is provided on the surface of the magnetic shield plate 6 facing the cooling container 4.
And a cooling container 4
An inclined surface 15 substantially parallel to the hat-shaped inclined surface 11 is also provided on the surface facing the magnetic shield plate 6.
As described above, since the inclined surface 15 is provided on the cooling container 4 and is substantially parallel to the hat-shaped inclined surface 11 of the ferromagnetic piece 10, the interval between the cooling container 4 and the magnetic shield plate 6 can be reduced. Therefore, the height of the superconducting magnet can be reduced. In addition, when the height of the superconducting magnet is the same, the size of the ferromagnetic material piece 10 can be increased.
It is possible to reduce the leakage of the magnetic field to the outside of the magnetic shield plate 6.

The shape of the magnetic shield plate 6 can be improved by attaching the ferromagnetic piece 10 to the magnetic shield plate 6. An example is shown in FIG. FIG. 6 is a top view of the second embodiment. The outer shape of the magnetic shield plate 6 includes a central circular top 20, an end face 21 narrower than the top 20, and an inclined section 1 connecting the top 20 and the end face 21.
6, the side surface portion 22, and the above-described cooling vessel facing surface 6A (the back side of the illustrated magnetic shield plate 6). The top 20 has a circular shape with a diameter larger than the diameter of the cooling container 4, covers the cooling container 4, and shields the magnetic field generated by the static magnetic field generation source 2. The end face portion 21 is a flat surface, and the width from the top portion 20 to the end face portion 21 is linearly narrowed, thereby forming a preferable shape in terms of design. The inclined portion 16 is a magnetic shield plate 6
Are formed as a result of removing the ferromagnetic material by diagonally cutting both outer end portions of the ferromagnetic material, thereby providing a preferable shape in design and also contributing to weight reduction of the ferromagnetic material. This is made possible by attaching the ferromagnetic piece 10 to the surface of the magnetic shield plate 6 facing the cooling container 4, thereby greatly reducing the magnetic flux density at both outer ends of the magnetic shield plate 6. It is.

FIG. 7 shows a third embodiment of the passive shield type superconducting magnet of the present invention. In this embodiment, the shapes of the hat-shaped inclined surface 11 of the ferromagnetic piece 10 and the inclined surface 15 of the cooling vessel 4 in the second embodiment are changed. In FIG. 7, the hat-shaped inclined surface 11A of the ferromagnetic piece 10 is constituted by two linear inclined surfaces. The hat-shaped inclined surface 11A is formed so as to be concave by two linear inclined surfaces, and the concave surface has a shape close to the flow of the magnetic flux lines 14 in this portion. You are using it. Further, the inclined surface 15A of the cooling container 4 is also constituted by two linear inclined surfaces. The inclined surface 15A forms a convex surface, and each of the two inclined surfaces is aligned with the two inclined surfaces of the opposing hat-shaped inclined surface 11A. Therefore, the distance between the cooling container 4 and the ferromagnetic piece 10 can be reduced. In addition, since the inclined surface 15A of the cooling container 4 is a convex surface, the internal volume of the cooling container 4 is increased, so that the positional restriction on the arrangement of the superconducting coils 3 is eased. Further, in the present embodiment, each inclined surface is constituted by two inclined surfaces, but it is needless to say that the number of inclined surfaces is not limited to two and may be three or more.

FIG. 8 shows a fourth embodiment of the passive shield type superconducting magnet of the present invention. In this embodiment, the shapes of the hat-shaped inclined surface 11 of the ferromagnetic piece 10 and the inclined surface 15 of the cooling vessel 4 in the second embodiment are curved. In FIG. 8, the cap-shaped inclined surface 11B of the ferromagnetic piece 10 is an arc-shaped inclined surface and is formed to be concave. The inclined surface 15B of the cooling container 4 is an arc-shaped inclined surface and is formed so as to be convex. In the case of this embodiment, the shade-shaped inclined surface 1
1B is formed as a concave surface, and the inclined surface 15B of the cooling container 4 is formed as a convex surface, so that the same effect as in the third embodiment can be obtained. Further, in the present embodiment, an arc-shaped surface is used as a curved surface, but the present invention is not limited to this, and another curved surface such as an elliptical surface or a parabolic surface may be used.

In the above embodiment, the case where the number of the yokes 7 is two has been described. However, when the number of the yokes 7 is other than two, for example, when the number of the yokes 7 is one or three or more, the same effect is obtained. Can be expected. In addition, the position of the joining portion 12 or the yoke 5 where the magnetic shield plate 6 and the yoke 7 are joined is illustrated on the case where the yoke 5 is located on the left and right sides of the static magnetic field generation source 2.
The present invention is not limited to this, and the same effect can be obtained in an open type superconducting magnet in which the yoke 5 and the like are disposed behind the uniform magnetic field region 1.

[0029]

As described above, according to the present invention, a shade-shaped inclined surface is provided on the surface of the magnetic shield plate facing the static magnetic field generation source near the joint between the magnetic shield plate and the yoke. Since the magnetic flux lines passing through the magnetic shield plate pass not only at the joint but also through the ferromagnetic pieces, the density of the magnetic flux lines passing through the magnetic shield plate is reduced by the generation of the static magnetic field. It is higher on the side facing the source. As a result, the magnetic field leakage above and below the magnetic shield plate is reduced, and it is not necessary to stack a ferromagnetic substance outside the magnetic shield plate, so that the height of the superconducting magnet can be reduced, and the entire device is compact. Can be

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the passive shield type superconducting magnet of the present invention.
Example.

FIG. 2 is an enlarged view of the upper right part of FIG.

FIG. 3 is an example of a magnetic flux line distribution according to the first embodiment of the present invention.

FIG. 4 is an example of a magnetic flux line distribution of a conventional passive shield type superconducting magnet.

FIG. 5 shows a second embodiment of the passive shield type superconducting magnet of the present invention.
Example.

FIG. 6 is a top view of the second embodiment.

FIG. 7 shows a third embodiment of the passive shield type superconducting magnet of the present invention.
Example.

FIG. 8 shows a fourth embodiment of the passive shield type superconducting magnet of the present invention.
Example.

FIG. 9 shows an example of a conventional vertical magnetic field type superconducting magnet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Uniform magnetic field area (imaging area) 2 Static magnetic field generation source 3 Superconducting coil 4 Cooling vessel 6 Magnetic shield plate 6A Cooling vessel facing surface 7 Yoke 7A Inner side face 8 Stacking part 10 Ferromagnetic piece 11, 11A, 11B Shaded slope DESCRIPTION OF SYMBOLS 12 Joining part 13 Coupling body 14 Magnetic flux line 15, 15A, 15B Cooling vessel inclined surface 16 Magnetic shield plate inclined surface 20 Top 21 End surface 22 Side surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Yao 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Medical Co., Ltd. (72) Inventor Takao Honma 1-1-1 Uchikanda, Chiyoda-ku, Tokyo No. Within Hitachi Medical Corporation

Claims (6)

[Claims] 1. A static magnetic field generating source comprising: a set of superconducting coils arranged to face each other in a vertical direction; and a cooling container for accommodating and cooling each superconducting coil. A magnetic shield plate made of a ferromagnetic material is disposed on the outside, and the upper and lower magnetic shield plates are connected by a yoke made of one or more ferromagnetic materials to form a magnetic circuit together with the static magnetic field source. In the superconducting magnet of the type, the surface of the magnetic shield plate facing the cooling vessel has a hat-shaped slope near the junction between the magnetic shield plate and the yoke so as to approach the cooling vessel side. A passively shielded superconducting magnet having a surface. 2. A static magnetic field generating source comprising a pair of superconducting coils disposed to face each other in a vertical direction, and a cooling container for accommodating and cooling each superconducting coil. A magnetic shield plate made of a ferromagnetic material is disposed on the outside, and the upper and lower magnetic shield plates are connected by a yoke made of one or more ferromagnetic materials to form a magnetic circuit together with the static magnetic field source. In the superconducting magnet of the type, the magnetic shield plate approaches the cooling container side near the joint between the magnetic shield plate and the yoke on the surface side facing the cooling container, near the joint. A passively-shielded superconducting magnet, having a hat-shaped inclined surface, and having a ferromagnetic piece in contact with the magnetic shield plate and the yoke. 3. The passive-shielding superconducting magnet according to claim 1, wherein at least one of the hat-shaped inclined surfaces is provided for each of the joint portions between the magnetic shield plate and the yoke. A passive shield type superconducting magnet, wherein each inclined surface has a starting point on a surface of the magnetic shield plate facing the cooling container and an ending point on an inner surface of the yoke facing the cooling container. 4. A superconducting magnet according to claim 1, wherein said hat-shaped inclined surface includes at least one flat surface. 5. The passive-shielded superconducting magnet according to claim 1, wherein the inclined surface of the shade shape includes a curved surface. 6. The passive shield type superconducting magnet according to claim 1, wherein an outer peripheral portion of the cooling container on a surface side facing the magnetic shield plate has substantially the same shape as the facing hatched inclined surface. A passive shield type superconducting magnet characterized by being formed on an inclined surface.