JPH04218998A - Magnetic shilding structure - Google Patents

Abstract

PURPOSE:To realize a magnetic field far lower than an outside magnetic field by arranging high-permeability cylindrical members, which have openings along the longitudinal direction of a cylindrical shield substance, inside that cylindrical shield substance, leaving space with the cylindrical inwall. CONSTITUTION:One high-permeability material FM each is arranged in the positions 800mm from the center of a superconductive cylinder SC, both whose ends are opened. The sizes of the superconductive cylinder SC are 100mm in inside diameter, 240mm in length, and 5mm in thickness. The high-permeability material cylinder FM is 10mm in length and 10000 in permeability, and the outside diameter Dmm is changed. As a result of measurement, it comes out that if the high-permeability material cylinder FM, which has an outside diameter 1/5 or more times as large as the superconductive cylinder SC, is arranged inside the superconductive cylinder SC, the shield effect more excellent than the superconductor cylinder simple can be gotten, and also the more the outside diameter of the high-permeability material cylinder FM approximates to the inside diameter of the superconductive cylinder SC, the more excellent shield effect can be obtained.

Description

Description: [0001] The present invention relates to a magnetic shield structure using a superconductor. [0002] A magnetic shield structure using a superconductor is a magnetic shield structure that utilizes the Meissner effect. For example, a material having the Meissner effect is formed into a cylindrical shape as a shield body, and this is used to By cooling the shield body to a temperature below TC to transform it into a superconducting state and making the shield body diamagnetic, the magnetic flux is pushed out to the outside of the shield and the internal space of the shield is magnetically shielded. On the other hand, in a commonly used shield structure using a high magnetic permeability material that does not use a superconductor, for example, when a cylindrical shield body is constructed of a high magnetic permeability material, this shield body is exposed to a magnetic field. When held, magnetic induction occurs along the shield body, resulting in a change in the direction of the magnetic field, thereby magnetically shielding the internal space. [0004] In a magnetic shield structure using such a superconductor, for example, the magnetic shielding efficiency of a cylindrical shield body with respect to a magnetic field parallel to the central axis of the cylinder (vertical magnetic field) is Although the shielding efficiency is good, the shielding efficiency against a magnetic field perpendicular to the central axis (transverse magnetic field) is not good, so there is a problem that the length must be longer than the inner diameter of the cylinder. On the other hand, with a cylindrical shield body made of a high magnetic permeability material, for example, the shielding efficiency of a vertical magnetic field is not better than that of a horizontal magnetic field, and due to its finite magnetic permeability, the shielding efficiency is not high with one layer. In order to obtain shielding efficiency, the cylinders had to be stacked in several layers, with the outer layer being longer than the inner layer. As a result, even with high magnetic permeability materials, the outer cylinder has a longer length, and the larger the usable volume, the longer the cylinder in both the radial and axial directions, resulting in an increase in cost. [0006] The object of the present invention has been made in view of the above various points, and is to improve magnetic shielding performance by combining magnetic shielding materials with different properties, increase usable high magnetic field shielding space, and Therefore, it is an object of the present invention to provide a magnetic shield structure that can efficiently realize a magnetic field much lower than an external magnetic field. [0007] Means for Solving the Problems In the magnetic shielding structure according to the invention as set forth in claim 1, a superconductor that transitions from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled below a critical temperature. In the magnetic shield structure of a cylindrical shield body made of a material, a cylindrical high magnetic permeability member having an opening along the longitudinal direction of the cylindrical shield body is spaced from the inner wall of the cylinder inside the cylindrical shield body. It was arranged as follows. In the magnetic shield structure according to the second aspect of the present invention, in the magnetic shield structure according to the first aspect, the plurality of cylindrical high magnetic permeability members are spaced apart in the radial direction and/or the longitudinal direction. They are opened and arranged in multiple and/or multiple layers. [Operation] A cylindrical shield made of a material exhibiting the Meissner effect causes a shielding current to flow in accordance with Lenz's law against a magnetic field from the outside, thereby forming a demagnetizing field. This demagnetizing field attenuates the magnetic field that enters the cylinder from the outside. For example, the theoretical formula for the internal magnetic field Hi of a superconducting cylinder can be expressed as follows with respect to the external magnetic field Ho in each direction. Transverse magnetic field; Hi=Ho・exp(-1.84(Z/r
)) …(1) Vertical magnetic field; Hi=Ho・ex
p(-3.83(Z/r))...(2) (However, Z is the distance from the open end, and r is the radius of the cylinder.) As is clear from these equations, the magnetic shielding of the superconductor cylinder The efficiency is high for magnetic fields parallel to the central axis of the cylinder (longitudinal magnetic field), but low for magnetic fields perpendicular to the central axis (transverse magnetic field). Therefore, if the transverse magnetic field is effectively attenuated, a very good magnetic field shielding space can be obtained. FIG. 17 shows a schematic diagram of magnetic vectors penetrating inside the superconducting cylinder when a transverse magnetic field is applied to the superconducting cylinder. As shown in the figure, on the cylindrical axis, only the horizontal magnetic field,
It can be seen that in the radial direction, the vertical component increases closer to the end. The internal penetrating magnetic field distributed in this way is magnetically short-circuited by changing the vertical component to the horizontal component by utilizing the property of magnetic induction of the high magnetic permeability member, thereby reducing the amount of penetrating into the interior. However, since the high magnetic permeability member has a residual magnetic field, it is necessary to arrange it at a position where the residual magnetic field does not affect it. In the present invention, in a magnetic shield structure of a cylindrical shield body made of a superconducting material that transitions from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled below a critical temperature, the cylindrical shield body Since a cylindrical high permeability member having an opening along the longitudinal direction of the cylindrical shield body is arranged at a distance from the inner wall of the cylinder, the longitudinal axis of the cylindrical shield body made of a material that exhibits the Meissner effect is Magnetic induction occurs in the cylindrical high-permeability member in response to an intruding magnetic field that exhibits an attenuation distribution toward the center of the top, and as a result, the intruding magnetic field is magnetically short-circuited, causing the magnetic field to intrude into the inside of the cylindrical shield. This will further reduce the amount. Specifically, the cylindrical high magnetic permeability member is arranged from the center of the superconducting cylinder toward the end, the cylindrical high permeability member is arranged near the end, and the cylindrical high permeability member is arranged in the vicinity of the end. There are two types: one in which a plurality of cylindrical high permeability members are laminated in the longitudinal direction near the end, and one in which a plurality of cylindrical high permeability members are laminated in the radial direction. In particular, when a plurality of cylindrical high magnetic permeability members are arranged in multiple layers and/or in multiple layers with intervals in the radial and/or longitudinal direction, the cylindrical high permeability member This further reduces the magnetic field penetrating into the inside of the shield body. The shape of the cylindrical high magnetic permeability member is such that it can be inserted into a cylindrical shield made of superconducting material, magnetic induction is generated in the cylindrical high permeability member, and the intruding magnetic field is magnetically short-circuited. Any shape can be used as long as it has any shape. Specifically, it is a cylinder that is open at both ends or at one end and has a length larger than the wall thickness of the constituent members, and the cross-sectional shape of the cylinder may be a circle, an ellipse, a polygon, or the like. Also,
Tapered types with an inner diameter that decreases along the longitudinal direction, types with unevenness on the inside and outside and different cross-sectional shapes on the inside and outside, types with internal openings that are wider than the openings at the ends, and types with bellows-shaped cylinders. It also includes L-shaped, T-shaped, H-shaped, +-shaped, U-shaped, and combinations thereof. [0015] Furthermore, the ratio of the outer diameter of the cylindrical high magnetic permeability member to the inner diameter of the cylindrical shield made of superconducting material is, as shown in the examples described later, when used alone. If a cylindrical high magnetic permeability member having an outer diameter of 1/5 or more of the inner diameter of the cylindrical shield body is placed inside the superconducting cylinder, a better shielding effect than the superconducting cylinder alone can be obtained. Now, in general, the shielding effect (Hi/Hs
c) is expressed as Hi/Hsc=2r/μ·t (3). Here, μ is magnetic permeability, t is wall thickness, and r is cylinder radius. Although it can be inferred from equation (3) that other shapes are used, it can be seen that, in general, the larger the magnetic permeability, the greater the shielding effect. Furthermore, it can be inferred from equation (3) that generally the larger the wall thickness, the greater the shielding effect. [Example] (Example 1: Effect of outer diameter) Figure 1 is a cross-sectional view of a cylinder made of a high magnetic permeability material for changing the size of the outer diameter D. One high permeability material cylinder was placed at a position 80 mm from the center of each superconductor cylinder (BiSrCaCuO) (hereinafter referred to as superconductor cylinder). The former size has an inner diameter of 100
mm, length 240mm, and wall thickness 5mm. The latter has a length of 10 mm, a wall thickness of 0.2 mm, a magnetic permeability of 10000, and an outer diameter Dmm. A uniform transverse magnetic field 1 [G
] was applied to measure the magnetic field distribution on the cylinder axis. Figure 2 shows the internal magnetic field distribution Hi(z) on the superconductor cylinder axis when the outer diameter Dmm of the high permeability material cylinder is changed (hereinafter, in all examples, z is the distance from the open end of the superconductor cylinder). FIG. In Figure 2, SC is the internal magnetic field distribution Hsc(z) in the case of a single superconducting cylinder without using a high permeability material cylinder.
, □ means outer diameter = 20mm, ● means outer diameter = 30mm, × means outer diameter = 40mm, ○ means outer diameter = 60mm, + means outer diameter = 80mm
are shown respectively. From FIG. 2, the penetrating magnetic field at the center of the superconducting cylinder is smaller when the high permeability material cylinder is inserted than when the superconducting cylinder is used alone. This is because the high permeability material cylinder changes the vertical component of the penetrating magnetic field into a horizontal component by magnetic induction, causing a magnetic short circuit. FIG. 3 is a diagram showing the relationship between the outer diameter D of the cylinder made of high magnetic permeability material and the shielding effect. That is, the shielding effect is defined as the magnetic field distribution Hi(z) shown in Fig. 2 normalized by the magnetic field Hsc(120) at the superconducting cylinder center position z=120, and is expressed as a function of the outer diameter of the high permeability material cylinder. This is a line diagram. Note that standardization was performed as follows according to the above-mentioned equation (3). Shielding effect = Hi(120)/Hsc(120) 00
21] As shown in FIG. 3, it can be seen that the shielding effect becomes better as the outer diameter of the high permeability cylinder approaches the inner diameter of the superconductor. This is achieved by increasing the outer diameter of the high permeability material cylinder to change the longitudinal component of the intruding magnetic field, which increases in the system direction inside the superconductor cylinder, into a lateral component, magnetically shorting it. This is because I let him do it. On the other hand, if the outer diameter is 20
In the case of mm, the shielding effect is 1, indicating that the high permeability material cylinder has no effect at all. In the radial direction within this range, the longitudinal component of the penetrating magnetic field is small, so that almost no magnetic short circuit effect can be obtained. From the above results, 1 of the inner diameter of the superconducting cylinder
When a high permeability material cylinder having an outer diameter of /5 or more is placed inside the superconductor cylinder, a better shielding effect can be obtained than with the superconductor cylinder alone. It has also been found that the closer the outer diameter of the high permeability cylinder is to the inner diameter of the superconductor cylinder, the better the shielding effect can be obtained. FIG. 4 is a sectional view of a superconducting cylinder with one end open and a cylinder made of a high magnetic permeability material. That is, one cylinder of high magnetic permeability material was placed at a position 80 mm from the bottom of the superconducting cylinder with one end open. The former has an inner diameter of 100 mm, a length of 120 mm, and a wall thickness of 5 mm. The latter is 10m long
m, wall thickness 0.2 mm, magnetic permeability 10000, outer diameter D
Changing mm. A uniform transverse magnetic field of 1 [G] was applied to the superconducting cylinder, and the magnetic field was measured at a position 30 mm from the bottom surface on the cylinder axis. According to equation (3) above, z
When expressed in terms of the shielding effect at =90, results almost consistent with those in FIG. 3 were obtained. The high permeability material cylinder exerts exactly the same shielding effect in the case of a superconductor cylinder with one end open as in the case of a superconductor cylinder with both ends open. FIG. 5 is a cross-sectional view of a superconducting cylinder with both ends open and a tapered cylinder of high magnetic permeability material arranged therein. That is, one high magnetic permeability material cylinder was placed at a position 80 mm from the center of each superconducting cylinder with both ends open. The former has an inner diameter of 100 mm, a length of 240 mm, and a wall thickness of 5 mm. The latter has a maximum outer diameter of 80 mm, a minimum outer diameter of 60 mm, a height of 10 mm, a wall thickness of 0.2 mm, and a magnetic permeability of 10,000. A uniform transverse magnetic field of 1 [G] was applied to the superconducting cylinder, and the magnetic field at the center position on the cylinder axis was measured. Similarly, according to equation (3), the shielding effect at z=120 is:
0.45 was obtained. From the above, it has been found that a good shielding effect can be obtained not only with a cylinder made of high magnetic permeability material whose opening is unchanged at both ends, but also with a cylinder made of high magnetic permeability material with a tapered shape in which the diameter of the opening is reduced. (Example 2: Effect of length 1, near the center)
FIG. 6 is a sectional view in which a high permeability material cylinder whose length 2P is changed is arranged. That is, a high magnetic permeability material cylinder was placed in a bismuth-based oxide superconductor cylinder (BiSrCaCuO) with both ends open. The former size has an inner diameter of 100 mm and a length of 15 mm.
0 mm, and the wall thickness is 5 mm. The latter has an inner diameter of 75 mm, a wall thickness of 2 mm, a magnetic permeability of 10,000, and a length of 2 P mm. As shown in FIG. 6, an experiment was conducted by arranging high magnetic permeability material cylinders with both ends open inside the superconducting cylinder so that the axes of each cylinder coincided with each other, and varying the length 2P. A uniform transverse magnetic field of 1 [G] was applied perpendicularly to each combined cylinder. FIG. 7 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when the length 2P of the high magnetic permeability cylinder is changed. SC75 in Fig. 7 represents the internal magnetic field distribution of a single superconducting cylinder (P = 75 mm), and SC+FM25 represents the superconducting cylinder, high magnetic permeability material cylinder, and high magnetic permeability material cylinder (P = 25 mm).
This shows the internal magnetic field distribution when combined. It is clearly seen from this figure that the combination of the superconductor cylinder and the high permeability material cylinder shows a lower magnetic field distribution than the case of the superconductor cylinder alone. In particular, as the length of the cylinder made of high magnetic permeability material increases, the magnetic field at the center position becomes lower. At the same time, for example, when looking at the shielded space of 0.1 [G], the shielded space becomes wider as the length of the cylinder made of high magnetic permeability material becomes longer. Looking at the case of a combination of high magnetic permeability material cylinders (P = 65 mm), the shielded space of 0.1 [G] extends to about 50 mm from the center of the cylinder. In order to obtain this with a single superconducting cylinder, a length of 225 mm or more is required when the inner diameter is 100 mm. FIG. 8 is a diagram showing the internal magnetic field when the length of the cylinder made of high magnetic permeability material is varied. In the figure, the internal magnetic field is the magnetic field at the center of the cylinder, ■ indicates the result when the superconducting cylinder and the high permeability cylinder are combined, and □ indicates the result when the high permeability cylinder is used alone. show. From FIG. 8, it can be seen that in the case of a single cylinder made of high magnetic permeability material, when the length P is longer than 60 mm, the magnetic field at the center position becomes constant. [0029] The longer the length, the more the equation (1)
Unlike superconducting cylinders, which improve shielding efficiency according to
It is obvious that a shielding efficiency higher than that obtained by equation (3) assuming an infinitely long cylinder of high magnetic permeability cannot be obtained with a single cylinder of high magnetic permeability of finite length. Similarly, even when a superconductor cylinder and a cylinder made of high magnetic permeability material are combined, the magnetic field at the center position becomes constant when the length P of the cylinder made of high magnetic permeability material exceeds 60 mm. Therefore, the shielding efficiency in the combination depends on the shielding effect of the cylinder of high magnetic permeability material. From the above results, it was found that when a high magnetic permeability material cylinder is disposed inside a superconducting cylinder, the lower magnetic field space becomes wider as the length of the high magnetic permeability material cylinder becomes longer. (Embodiment 3: Length Effect 2, Near End) FIG. 9 is a cross-sectional view of a cylinder of high magnetic permeability material whose length L is changed. That is, one cylinder of high magnetic permeability material was placed at a position 80 mm from the center of each bismuth-based oxide superconductor cylinder (BiSrCaCuO) (hereinafter referred to as superconductor cylinder) with both ends open. The former size has an inner diameter of 100mm
, length 240mm, wall thickness 5mm. The latter has an outer diameter of 7
0mm, wall thickness 0.2mm, magnetic permeability 10000, and length Lmm is changed. A uniform transverse magnetic field 1 [G
] was applied to measure the magnetic field at the center of the superconductor cylinder. FIG. 10 is a diagram showing the relationship between the length L of the cylinder made of high magnetic permeability material and the shielding effect. That is, the shielding effect shown in equation (3) above is expressed at the position of z=120, and is made a function of the length L of the cylinder of high magnetic permeability material. From this figure, it can be seen that the longer the length L of the cylinder made of high magnetic permeability material, the better the shielding effect becomes. It was also found that when the length exceeds 30 mm, the shielding effect becomes almost constant, and even if the length is longer than that, a better shielding effect cannot be obtained. This is achieved by placing a cylinder of high magnetic permeability material in the magnetic field gradient inside the superconducting cylinder.
Since the high magnetic permeability material has a finite magnetic permeability, it is thought that if it is made longer than a certain length, it will become magnetically saturated, and as a result, magnetic induction will be less likely to occur, and the shielding effect will be constant. (Example 4: Lamination Effect 1, Lamination in Longitudinal Direction) FIG. 11 is a cross-sectional view in which two cylinders made of high magnetic permeability material are laminated in the longitudinal direction of a superconducting cylinder. That is, a cylinder made of bismuth-based oxide superconductor (BiSrCaCuO) with both ends open (
80mm and 6mm from the center of the superconductor cylinder
It is a sectional view in which high magnetic permeability material cylinders are arranged at positions of 0 mm. The size of the superconductor cylinder is 100 mm in inner diameter.
It has a length of 240mm and a wall thickness of 5mm. The high magnetic permeability material cylinder is 70mm long, 0.2mm thick, and has a magnetic permeability of 10,000.
It is. A uniform transverse magnetic field 1 [G
] was applied to measure the magnetic field distribution on the cylinder axis. Figure 12 is 2
FIG. 3 is a diagram showing the internal magnetic field distribution Hi(z) on the superconductor cylinder axis when two high permeability material cylinders are stacked in the longitudinal direction. For comparison, L = 10 mm and 30 mm in Example 1.
The internal magnetic field distribution of is also shown. In Figure 12, SC is the internal magnetic field distribution Hsc (z) in the case of a single superconducting cylinder without using a high permeability material cylinder, □ is L = 10 mm, ● is L = 30 m
m and x each indicate L=10 mm×2 (see FIG. 11). From FIG. 12, L=3 which is longer than L=10 mm
The shielding effect was better when the thickness was 0 mm, and the best shielding effect was obtained when 2 layers of L=10 mm were stacked at the same positions as L=30 mm with an interval. This result shows that the shielding effect is better when the high magnetic permeability material cylinder is divided at intervals rather than by increasing its length. Furthermore, the above-mentioned Example 3
The results showed that the shielding effect did not improve beyond a certain level even if the length was increased, but when short high-permeability cylinders were stacked at intervals in the cross-sectional direction, each high-permeability cylinder became magnetically It was found that saturation did not occur because the layers were not connected to each other, and that the more layers were stacked, the better the shielding effect would be. [0036] Therefore, if a plurality of cylinders of high magnetic permeability members are laminated inside the superconducting cylinder at intervals in the longitudinal direction with a space between them and the inner wall of the cylinder, the desired magnetic field can be obtained efficiently and at low cost. . (Example 5: Lamination effect 2, radial overlapping) FIG. 13 is a cross-sectional view in which two cylinders made of high magnetic permeability material are arranged overlappingly in the radial direction of a superconducting cylinder. That is, a stack of two high-permeability material cylinders with different outer diameters was placed at a position 80 mm from the center of a bismuth-based oxide superconductor cylinder (BiSrCaCuO) (hereinafter referred to as the superconductor cylinder) with both ends open. did. The size of the superconductor cylinder is inner diameter 100
mm, length 240mm, and wall thickness 5mm. The high magnetic permeability material cylinder has a length of 10 mm, a wall thickness of 0.2 mm, and a magnetic permeability of 1.
0000, and the outer diameters are 80 mm and 60 mm, respectively. A uniform transverse magnetic field 1 [G
] was applied to measure the magnetic field distribution on the cylinder axis. Figure 14 is 2
FIG. 2 is a diagram showing the internal magnetic field distribution Hi(z) on the superconductor cylinder axis when two high permeability material cylinders are arranged in layers in the radial direction. For comparison, the outer diameter D of Example 1 is shown as 80 mm. In FIG. 14, SC is the internal magnetic field distribution Hsc in the case of a single superconducting cylinder without using a high permeability material cylinder.
(z), □ is D=80mm, ● is D=80mm+60m
m (see FIG. 13). From FIG. 14, D=
A better shielding effect was obtained with D = 80 mm + 60 mm, in which two cylinders made of high magnetic permeability material were layered in the radial direction, than with 80 mm. This is the same as the conventional magnetic shield made of a cylinder made of high magnetic permeability material, and shows that even in a uniform magnetic field or a gradient magnetic field, the shielding effect can be improved by stacking layers in the radial direction. However, from the results of Example 1, the high magnetic permeability member cylinder must have a maximum outer diameter that is 1/5 or more of the inner diameter of the superconductor cylinder. From the above results, the desired magnetic field can be obtained efficiently and inexpensively even if cylinders made of high magnetic permeability material are stacked at intervals in the radial direction as in Example 4. (Example 6: Lamination Effect 3, Lamination in Longitudinal and Radial Directions) FIG. 15 is a cross-sectional view of a plurality of high permeability material cylinders arranged in multiple layers in the radial and longitudinal directions. Figure A is a cross-sectional view of two long cylinders of high magnetic permeability material layered in the radial direction, and Figure B is a cross-sectional view of two long cylinders of high magnetic permeability material layered in the radial direction.
Figure C is a sectional view in which small-diameter high-magnetic-permeability cylinders and large-diameter high-permeability cylinders are alternately laminated. That is, a bismuth-based oxide long conductor cylinder (BiSrCSCuo) with both ends open (hereinafter referred to as
High magnetic permeability material cylinders having shapes as shown in Figures A to C were laminated inside the superconductor cylinder (referred to as a superconductor cylinder). The superconductor cylinder has an inner diameter of 100 mm, a length of 240 mm, and a wall thickness of 5 m. The magnetic permeability of the cylinders made of high magnetic permeability material is 10,000. Specifically, a uniform transverse magnetic field of 1 [G] was applied to the superconducting cylinder and the magnetic field distribution on the cylinder axis was measured. Figure A shows a structure in which cylinders of high magnetic permeability material having a length of 50 mm are laminated in the radial direction. In Figure B, high magnetic permeability cylinders each having a length of 10 mm are stacked at intervals in the radial and longitudinal directions, and the space occupied by the high magnetic permeability cylinders is the same as in Figure A. In Figure C, cylinders made of high magnetic permeability materials with different outer diameters are alternately stacked in the longitudinal direction. FIG. 16 is a diagram showing the internal magnetic field distribution Hi(z) on the superconductor cylinder axis when each of the high permeability material cylinders A, B, and C in FIG. 15 is arranged. In FIG. 16, SC
is the internal magnetic field distribution Hsc(z) in the case of a single superconducting cylinder without using a high permeability material cylinder, □ is diagram A, ● is diagram B, ×
shows what is shown in Figure C. As is clear from the figure, in each case, the intruding magnetic field is magnetically short-circuited by the high permeability material cylinder, and the reaching magnetic field is smaller than in the case of the superconducting cylindrical carrier. Comparing Diagram A and Diagram B, even though the space occupied by the high permeability cylinder is the same, Diagram B is much better in that it has shorter cylinders layered and laminated in the radial and longitudinal directions. This shows the shielding effect. Similar to the results of Example 3, Figure A shows that when there is a magnetic field gradient inside the superconducting cylinder, the high magnetic permeability material has a finite magnetic permeability and becomes magnetically saturated. It is predicted that even if the length is increased, the shielding effect will not improve any further. However, in the case of diagram B,
Because short high-permeability cylinders are stacked at intervals, each high-permeability cylinder is magnetically insulated, and if further stacked in the longitudinal direction, a better shielding effect can be obtained. It is. Further, Figure C is an example in which cylinders having different outer diameters are alternately stacked in the longitudinal direction. In this case as well, by stacking the layers at intervals, a better shielding effect than in Figure A is obtained. In this example, high permeability material cylinders with an outer diameter of 80 mm x 2 and 60 mm x 3 are used, but from the results of Example 1, the outer diameter is 80 mm.
It is easily inferred that the shielding effect will be better if 3 x 60 mm cylinders and 2 x 60 mm cylinders made of high magnetic permeability material are used. Similar to the results of Example 1 described above, for each model in FIG. 15, a superconducting cylinder with one end open having half the length of the superconducting cylinder with both ends open in FIG. Even if a cylinder of high magnetic permeability material is placed at the same position as shown in Fig. 15,
Exactly the same effect can be obtained as in the case of . From the above results, in the magnetic field gradient inside the superconducting cylinder, a plurality of high permeability material cylinders having an outer diameter of 1/5 or more of the inner diameter of the superconducting cylinder are spaced apart in the longitudinal and radial directions. By arranging them in multiple layers and in multiple layers, the intruding magnetic field can be attenuated inexpensively and efficiently. As a result, the space for shielding a high magnetic field increases, and a magnetic field that is extremely lower than the external magnetic field can be efficiently realized. [0047] As explained above, according to the present invention,
In a magnetic shield structure of a cylindrical shield body made of a superconducting material that transitions from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled below a critical temperature, the cylindrical shield is disposed inside the cylindrical shield body. Since the cylindrical high permeability member with an opening along the longitudinal direction of the body is spaced apart from the inner wall of the cylinder, the attenuation distribution is distributed toward the center on the longitudinal axis of the cylindrical shield made of a material that exhibits the Meissner effect. Magnetic induction occurs in the cylindrical high permeability member in response to an intruding magnetic field exhibiting . As a result, the intruding magnetic field is magnetically short-circuited, further reducing the magnetic field penetrating into the inside of the cylindrical shield. Specifically, cylindrical high magnetic permeability members are arranged from the center of the superconducting cylinder toward the ends, cylindrical high permeability members are arranged near the ends, and multiple cylindrical high permeability members are arranged at the ends. There are those in which a plurality of cylindrical high permeability members are laminated in the longitudinal direction, and those in which a plurality of cylindrical high permeability members are laminated in the radial direction. In particular, when a plurality of cylindrical high magnetic permeability members are arranged in multiple layers and/or in multiple layers with intervals in the radial direction and/or longitudinal direction, the cylindrical high permeability member This further reduces the magnetic field penetrating into the inside of the shield body. The shape mentioned above
By adopting this arrangement, a shielding effect that cannot be obtained with various cylinders alone can be obtained, and the usable low-magnetic field space is increased.
Since the length of the cylindrical shield required to obtain the desired magnetic field shielded space or low magnetic field space is short, costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view in which a cylinder made of high magnetic permeability material is arranged to change the size of the outer diameter D.

FIG. 2 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when the outer diameter D of the high permeability cylinder is changed.

FIG. 3 is a diagram showing the relationship between the outer diameter D of a cylinder made of high magnetic permeability material and the shielding effect.

FIG. 4 is a cross-sectional view of a superconducting cylinder with one end open and a cylinder of high magnetic permeability material arranged therein.

FIG. 5 is a cross-sectional view of a superconducting cylinder with both ends open and a tapered cylinder of high magnetic permeability material arranged therein.

FIG. 6 is a sectional view in which a high permeability material cylinder whose length 2P is changed is arranged.

FIG. 7 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when the length 2P of the high permeability cylinder is changed.

FIG. 8 is a diagram showing the relationship between the length 2P of a cylinder made of high magnetic permeability material and the internal magnetic field.

FIG. 9 is a cross-sectional view of a high permeability material cylinder whose length L is changed.

FIG. 10 is a diagram showing the relationship between the length L of a cylinder made of high magnetic permeability material and the shielding effect.

FIG. 11 is a cross-sectional view of two high permeability material cylinders stacked in the longitudinal direction of a superconducting cylinder.

FIG. 12 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when two cylinders made of high magnetic permeability material are stacked in the longitudinal direction.

FIG. 13 is a cross-sectional view in which two cylinders made of high magnetic permeability material are layered in the radial direction of a superconducting cylinder.

FIG. 14 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when two high permeability material cylinders are arranged in layers in the radial direction.

FIG. 15 is a sectional view of a plurality of high magnetic permeability material cylinders arranged in multiple layers in the radial and longitudinal directions, and Figure A is a cross section of two long high magnetic permeability material cylinders arranged in layers in the radial direction Figure, B
The figure is a cross-sectional view of three sets of two high magnetic permeability material cylinders stacked in the radial direction, and three sets of high magnetic permeability material cylinders with a small diameter and a high magnetic permeability material with a large diameter. FIG. 3 is a cross-sectional view of the cylinders arranged in a stacked manner alternately.

16 is a diagram showing the internal magnetic field distribution on the superconductor cylinder axis when each of the high magnetic permeability material cylinders A, B, and C in FIG. 15 is arranged; FIG.

FIG. 17 shows a schematic diagram of magnetic vectors penetrating inside the superconducting cylinder when a transverse magnetic field is applied to the superconducting cylinder.

Claims (2)

[Claims] Claim 1. In a magnetic shielding structure of a cylindrical shield body made of a superconducting material that transitions from a normal conductive state to a superconducting state and exhibits the Meissner effect when cooled below a critical temperature, a magnetic shield is provided inside the cylindrical shield body. A magnetic shielding structure characterized in that a cylindrical high magnetic permeability member having an opening along the longitudinal direction of the cylindrical shield body is disposed at a distance from an inner wall of the cylinder. 2. The magnetic shield structure according to claim 1, wherein the plurality of cylindrical high magnetic permeability members are arranged in multiple layers and/or in multiple layers with intervals in the radial direction and/or longitudinal direction. Features a magnetic shield structure.