JPH0738278A - Superconducting magnetic shield container - Google Patents

Abstract

PURPOSE:To reduce leakage magnetic field entering from the open edge part of a superconducting magnetic shield container by laying out a superconductive lid consisting of a superconductor at the open edge part of a magnetic shield body consisting of, for example, cylindrical superconductor whose both edges are open and then laying out ferromagnetic bodies at the clearance. CONSTITUTION:Ferromagnetic body 3 is laid out outside or inside a superconductive side wall part 4 constituting a superconductive lid 2 and then the superconductive lid 2 is inserted into a superconducting magnetic shield body 1, thus forming a combined structure of superconductor, ferromagnetic body, and superconductor from the outside. Then, wen a spacing (x) between the superconductive lid 2 and the superconductive magnetic shield body 1 and a height (h) of a side wall part 4 of the superconductive lid 2 are set so that they satisfy 2x<=h, the leaked magnetic field from an open edge part is equal to or less than 1/1000, thus securing an attenuation ratio of 1/10000 even if the depth/aperture of the container is reduced drastically. For example, when a superconductive magnetic shield is applied to the device experiment such as an superconducting element using Josephson elements, an ideal non-magnetic field space can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield container utilizing the superconducting phenomenon (excluding magnetic flux), and particularly, the superconductor comprises a sintered body of a high temperature oxide superconductor, a thick film and a thin film, The present invention relates to a superconducting magnetic shield container capable of reducing the leakage magnetic field penetrating from the opening end of the above.

[0002]

2. Description of the Related Art Recently, studies have been conducted to apply an oxide superconductor to a magnetic shield container by utilizing the superconducting phenomenon of eliminating its magnetic flux. In this case, the superconducting shield does not take an external magnetic field into the superconductor and eliminates it toward the outside to prevent the magnetic field from penetrating into the internal space, and the magnetic shield effect is orders of magnitude greater than that of a ferromagnetic material. That is, the ferromagnetic shield has a limit due to the presence of remanent magnetization, and the magnetic shield in a region exceeding this limit must wait for the superconducting magnetic shield. However, for example, in Nb-based metal superconductors, liquid helium needs to be used as a coolant, so there is a cost barrier in magnetic shield construction, and superconducting shields have been put to practical use except for a small part. The reality is that there is none.

Recently, studies have been activated to measure the magnetic field emitted from the brain to elucidate the mechanism of the brain, elucidate headache, and examine the brain. Conventionally, MRI and positron C
Although the search for the inside of the brain such as T is practiced clinically,
There are restrictions on the resolution, time resolution, spatial resolution, radiation used, and the like. Especially, in order to clarify the function of the brain, it is necessary to measure the EEG and the magnetic field of the brain. The strength of the brain magnetic field is an extremely weak magnetic field of 10 to the 9th power (1/10 ⁹ ) gauss, and the geomagnetism is 0.3 gauss. To detect this signal, SQUID (superconducting quantum interference device) Called a magnetometer and a superconducting magnetic shield are essential.

The present inventors have previously clarified that the oxide high-temperature superconductor has an order of magnitude better magnetic shield effect than the conventional ferromagnet (Japanese Patent Application No. 1-25471).
No. 1). This magnetic shield container has depth / caliber (L / D)
It is an essential requirement that the ratio be 1 or more.
When measuring a human brain magnetic field using such a superconducting magnetic shield, it must be clinically applicable to the target patient without fear. In particular, it is desirable for the clinician to measure the SQUID magnetometer while looking at the patient's face, resulting in the need for a large superconducting magnetically shielded container. In particular, when the superconducting container is cooled and the room is provided with an insulating space at room temperature, for example,
The diameter of the superconducting container reaches 2m. In this case, if L / D is 1 or more, preferably 2 to 3, the length of the container is 5 to 6
m, etc. Although it is technically possible to produce such a superconductor, it is too costly and requires a very large installation place, which is not practical.

As a method for reducing the leakage magnetic field from the opening end of the superconducting magnetic shield container, a ferromagnetic material is arranged inside or outside the superconductor to attenuate the magnetic field in the radial direction perpendicular to the superconducting cylinder axis. There has already been proposed a method of providing the same and a method of arranging a lid of a ferromagnetic material at the opening end (Japanese Patent Application Nos. 3-21869 and 3-218696). However, these methods are all incomplete in preventing the leakage magnetic field from the opening end, and especially the magnetic field in the axial direction cannot be sufficiently attenuated. Therefore, it is necessary to take a large L / D and measure at a deep portion inside the container. As described above, when the diameter of the superconducting container is as large as 2 m, the length of the container becomes as large as 5 to 6 m, which is extremely disadvantageous in practical use, and the attenuation rate of the external magnetic field is limited.

The present invention has been made under such a technical background, and L of a superconducting magnetic shield container body is formed.
It is an object of the present invention to provide a superconducting magnetic shield container capable of extremely reducing the leakage magnetic field penetrating from the opening end even if / D is set to 1 or 1 or less.

[0007]

A superconducting magnetic shield container according to the present invention is provided with at least one opening end portion of a magnetic shield body made of a cylindrical or rectangular tube-shaped superconductor with both ends open or one end closed / one end open. A superconducting lid made of a superconductor is arranged, and a ferromagnetic material is arranged in a gap between the magnetic shield body and the superconducting lid. The superconducting lid arranged in this superconducting magnetic shield container has a side wall portion parallel or inclined to the side wall of the superconducting magnetic shield main body at the peripheral portion of a circular or rectangular plate or a plate having a curvature, and preferably the superconducting lid At least 2x ≦ h, where h is the height of the side wall and x is the gap between the magnetic shield body and the superconducting lid.

As the superconducting container body and the lid in the present invention, a sintered body, a thick film formed on a substrate, a thin film or the like can be used. Further, as the ferromagnetic material arranged in the gap between the superconducting body and the superconducting lid, permalloy, Ni-Fe
Alloys and the like can be used.

In general, even if both ends of a monolithic superconducting magnetic shield container are open, when a magnetic field tries to enter the openings, a shield current flows in the circumferential direction of the cylinder to prevent the magnetic field from entering. In this case, the leakage magnetic field penetrating from the opening end is exponentially attenuated as the above L / D increases. However, practically, it is necessary to reduce the cost of the magnetic shield container and the cryostat for cooling it by setting L / D to 1 or 1 or less and to make the magnetic shield device compact. From such a viewpoint, in the present invention,
The superconducting magnetic shield body is provided with a superconductor lid at at least one opening end, and a ferromagnetic material is inserted into a gap between the body and the lid, thereby making it possible to dramatically prevent a leakage magnetic field. . That is, the present invention has been found as a result of various studies conducted by disposing lids of various shapes at the open end of the superconducting magnetic shield container.

The mechanism of the present invention configured as described above will be described for better understanding of the present invention. Therefore, the following description does not limit the scope of the invention. Now, when considering two components in the axial direction and the radial direction of the cylinder or the square cylinder as the components of the external magnetic field, the axial component of the leakage magnetic field from the opening end is the superconducting lid 2 shown in FIG. 1 and its sidewall. By setting the height h of the portion 4 to a predetermined size, it is possible to remarkably reduce the damping. As shown in FIG. 1, by disposing a ferromagnetic material on the outside or inside of the superconducting side wall portion 4 constituting the superconducting lid 2, and inserting the superconducting lid 2 into the superconducting magnetic shield body 1, the superconductor from the outside can be The structure is a combination of a ferromagnetic material and a superconductor, and the gap x between the superconducting lid 2 and the superconducting magnetic shield body 1 and the side wall portion 4 of the superconducting lid 2 are formed.
When the height h is 2x ≦ h, the leakage magnetic field from the opening end is 1/1000 or less, and the attenuation rate of 1/1000 can be secured no matter how small the L / D of the container is. Further, preferably by setting h / x> 3 to 5, both the axial magnetic field and the radial magnetic field can be remarkably attenuated, and the practical value of the superconducting lid is exhibited. In this way, the axial and radial magnetic field leakage from the open end can be attenuated to, for example, 1 / 10,000,000 or less. For example, by arranging the superconducting lid 2 and the ferromagnetic body 3 of the present invention at both ends of a double-sided open cylindrical container, the superconducting closed space is equivalent to that of an integrated body, that is, L / D is about 1 in principle. However, it is possible to make the external magnetic field infinitely small.

FIG. 1 shows the relationship among the superconducting magnetic shield body 1, the superconducting lid 2 and the ferromagnetic body 3, and FIGS.
Shows an example of the positional relationship among the superconducting magnetic shield body 1, the superconducting lid 2 and the ferromagnetic body 3. Superconducting lid 2 of FIG.
A high damping rate can be obtained by appropriately taking the height h of the side wall portion 4 and the ratio h / x of the gap x between the main body 1 and the superconducting lid 2. x is usually sufficiently smaller than the inner diameter of the superconducting cylinder (square tube) (in the case of a square tube, the diagonal length, for example), and is, for example, about 1/5 to 1/10. For example, 100 cm diameter
In the case of the cylindrical container of, x is about 5 to 10 cm. Further, the ferromagnetic material 3 to be inserted in the gap may have a length equal to the length h of the side wall portion 4 of the superconducting lid 2, and the thickness of the ferromagnetic material is 1 as well.
-10 mm can be appropriately selected. The larger the initial relative permeability μ of the ferromagnetic material 3 is, the better, usually 10,000 to 10,000.
It is 0. When the superconducting lid 2 is fitted into the opening end of the superconducting magnetic shield body 1 as shown in FIG. 1, the side wall portion 4 of the superconducting lid 2 can be omitted if the thickness of the superconducting lid 2 is h. is there.

By a computer simulation using the finite element method, the shield effect S and h / x of the leakage magnetic field at the end of the superconducting cylindrical opening with one end opening / one end closing shown in FIG.
The result of calculation of the relationship is shown in FIG. S is a shield effect defined by the ratio of external magnetic field strength / internal magnetic field strength, and S (axial direction) and S (radial direction) when an external magnetic field is applied from the axial direction and the radial direction of the cylindrical container, respectively. . When the superconducting magnetic shield body 1, the superconducting lid 2 and the ferromagnetic body 3 are arranged as shown in FIG. 1, the shield effect is determined from the magnetic field strengths at points P and Q in these figures. Note that it was calculated that μ of the inserted ferromagnetic material 3 was infinitely large.

From FIG. 3, in the case where the superconducting lid and the ferromagnetic material are arranged, when h / x exceeds 4, the attenuation factor of the leakage magnetic field becomes 1 / million or less, and when h / x further increases, the opening becomes larger. The leakage magnetic field from the edge is extremely reduced, and shows the same shielding effect as when a closed space is created by a superconducting magnetic shield. The ferromagnetic material is preferably arranged so as to be positioned in the center of the gap between the superconducting magnetic shield body and the superconducting lid, but the superconducting magnetic shield body or the superconducting lid 2 may be provided in separate cryostats in consideration of the arrangement process. In the case of cooling with, the ferromagnetic material may be attached in a state of being bonded to one of the cryostats.

As shown in FIG. 2, according to the present invention, there are several methods for combining the superconducting magnetic shield body 1 and the superconducting lid 2, but any combination satisfies the ratio of h and x. If so, the leakage magnetic field at the opening end can be shielded almost completely, and the present invention is not limited to FIG.

By applying the superconducting magnetic shield container of the present invention to the superconducting magnetic shield chamber, a space having a very weak magnetic field can be created. For example, the length of one side is 2m,
A two-sided open-ended rectangular tube shield body having a height of 2 m is provided with a door at the open end portion by using the method of the present invention.
It is possible to produce a high-performance superconducting magnetically shielded room. If this is applied to biomagnetic measurement, the patient and the doctor can simultaneously enter the superconducting magnetic shield room and perform measurement in a magnetic field environment with an extremely low noise and an attenuation factor of 1,000,000 or less.

The present invention is particularly suitable for biomagnetic measurement, but is not limited to this and can be applied to various fields such as physical experiments and device experiments requiring magnetic shielding.

[0017]

According to the present invention as described above, the following effects can be obtained. (1) Since the leakage magnetic field from the open end of the superconducting magnetic shield can be reduced to the limit, even if L / D is 1 or less, 1
An extremely weak magnetic field space of 1,000,000 or less can be created. For example, when applying a superconducting magnetic shield to a device experiment such as a superconducting element using a Josephson element, it is ideal to install the superconducting shield lid of the present invention at both ends of a short cylinder (L / D to 1). It is possible to create a space without a magnetic field. (2) When a large space such as a magnetically shielded room is to be secured by using a superconductor, a shielding door is installed according to the present invention, so that a long superconductor is conventionally used in a very long method. What you needed is more compact, and you can significantly reduce manufacturing costs.

[0018]

Example 1 Bi: Pb: Sr: Ca: Cu = 1.7:
Using an oxide superconductor powder having a composition of 0.3: 2: 2: 3, an inner diameter 15 cm, a length 35 cm, a thickness 5 mm both-ends opening container, and an outer diameter 14 cm, the height h of the side wall 4 = 5c.
A superconducting lid 3 having a thickness of 5 mm and a thickness of 5 mm was molded by cold isostatic pressing and fired to produce a superconducting magnetic shield container.
The critical temperature Tc of this superconductor was 105K. The superconducting magnetic shield body 1 and the superconducting lid 2 which are open at both ends are shown in FIG.
As shown in FIG. 5, the ferromagnetic body 3 has a length of 5 cm,
Permalloy with thickness t = 1 mm (initial relative permeability at room temperature μ =
50000) ring was used to insert it in the middle of the gap of the superconductor. The distance between the magnetic shield body 1 and the superconducting lid 2 was 5 mm, and h / x = 10. The superconducting magnetic shield body 1, the superconducting lid 2 and the ferromagnetic body 3 are cooled to the temperature of liquid nitrogen, and two channels of the axial direction and the radial direction SQU are used.
The ID was inserted from the opening end, and the magnetic shield effect was measured at point Q in FIG. Here, as the external magnetic field, a Helmholtz coil with a diameter of 1 m was used, and a magnetic field of about 0.3 Gauss was applied in the axial direction and the radial direction of the cylindrical container. The magnetic shield effect S was defined by the ratio of external magnetic field / internal magnetic field. The measurement position was right above the superconducting lid, and the distance from the SQUID insertion opening had an L / D ratio of about 2. The obtained magnetic shield effect S (axial direction) is about 10 ⁶ , and S (radial direction) is 1 × 1.
0 ³ and was almost identical to the magnetic shielding effect of the one open end / end closed container. As described above, by using the superconducting magnetic shield container of the present invention, the leakage magnetic field at the opening end can be reduced to the limit.

[0019]

Example 2 The composition ratio of superconductivity is Bi: Pb: Sr: C.
a: Cu = 1.5: 0.5: 1.9: 1.9: 2.8 using powder, inner diameter 10 cm, length 10 cm, thickness 1.
On the outer surface of a Ni-cylindrical pipe of 5 mm, Ag was 50 μm, and a superconducting layer was 500 μm on the surface thereof by plasma spraying to prepare a thick film superconducting magnetic shield both-end opening cylindrical container. Similarly, a superconducting lid having a diameter of 9 cm and an outer wall height h = 3 cm was produced. The Tc of the thick film was 106K. The containers were assembled as shown in FIG. The gap x between the superconducting magnetic shield body 1 and the superconducting lid 2 is about 5 mm. As a result, the test was conducted at h / x = 6. As the ferromagnetic material 3, a permalloy ring having a length of 5 cm and a thickness of t = 1 mm was used as in the first embodiment, and was placed in the gap between the superconducting lid 2 and the main body 1. In order to measure the magnetic shield effect, after installing the fluxgate meter at the center position (point Q in FIG. 5) at the same distance from the openings at both ends of the magnetic shield body 1, the superconducting lids and the gaps between them are strong at both ends. The magnetic body 3 was arranged. The signal line of the fluxgate meter was led out through the gap between the lid 2 and the magnetic shield body 1. In the same manner as in Example 1, an external magnetic field of 3 Gauss (10 times that in Example 1) was applied in consideration of the sensitivity of the fluxgate meter, and the shield effect was measured. The magnetic field strength inside was 0.01 milligauss or less in both the axial direction and the radial direction (10 ⁵ or more as the shield effect), and below the detection sensitivity of the measuring instrument. When the superconducting lid 2 of the present invention is not installed, the shielding effect S of only the superconducting magnetic shield body 1 is obtained.
Was about 40 in the axial direction and about 6 in the radial direction. As a result, it was found that the magnetic shield container having the superconducting lid 2 of the present invention can shield the leakage magnetic field at the opening end to the utmost limit.

[0020]

[Embodiment 3] FIG. 6 shows a schematic view in the case of producing a superconducting magnetic shield chamber by using the shielding lid 2 of the present invention. The superconducting magnetic shield body 1 and the shielding lid 2 are separately housed in a cryostat 8 for cooling liquid nitrogen, and the ferromagnetic material 3 inserted between the superconductors is attached to either the magnetic shield body 1 or the cryostat 8 of the superconducting lid 2. Can be made. The size of the main body 1 is, for example, a rectangle having a side length of 2 m and a length of 2.5 m, the superconducting lid 2 has a side length of 1.7 m, the side wall 4 has a height of 60 cm, and h / x = 4. . In such a superconducting magnetically shielded room, a SQUID magnetometer 9 for multi-channel brain magnetic field measurement, a bed 11 for the person to be measured 10 and the like are housed inside the main body 1, and a door composed of a shielding lid 2 and a cryostat 8 is provided. By installing at both open ends of the main body, a superconducting magnetic shielded chamber having an extremely simple structure can be produced, and the attenuation rate of the magnetic field is reduced to one millionth or less.

[0021]

Comparative Example 1 Instead of the superconducting lid of Example 1, Example 1 was used.
Ferromagnetic lid of the same size as (μ is 50,000, thickness 1
mm) was used, and the magnetic shield effect was measured under the same conditions as in Example 1. S (axial direction) was about 100, and S (radial direction) was also about 100. As a result, S of the ferromagnetic lid was significantly lower than that of the superconducting lid.

[0022]

COMPARATIVE EXAMPLE 2 As in Comparative Example 1, using a ferromagnetic lid having a diameter of 17 cm and a side wall height of 5 cm, the outer surface of the superconducting magnetic shield body of Example 1 was covered (the ferromagnetic ring was removed). The same experiment as in Example 1 was performed. S (axial direction) was about 100, and S (radial direction) was also about 100. As a result, as in Comparative Example 1, the S of the ferromagnetic lid was significantly lower than that of the superconductor lid.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a superconducting magnetic shield container of the present invention.

FIG. 2 is a schematic cross-sectional view showing an arrangement example of a magnetic shield body, a superconducting lid and a ferromagnetic material in a superconducting magnetic shield container according to the present invention.

FIG. 3 is a diagram showing the relationship between h / x and the magnetic shield effect S in the example of the present invention.

FIG. 4 is an explanatory diagram of Embodiment 1 of the present invention.

FIG. 5 is an explanatory diagram of a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of Embodiment 3 of the present invention.

[Explanation of symbols]

 1 Superconducting Magnetic Shield Main Body 2 Superconducting Lid 3 Ferromagnetic Material 4 Sidewall of Lid 5 SQUID Dewar 6 Liquid Nitrogen Container 7 Liquid Nitrogen 8 Cryostat 9 SQUID Fluxmeter 10 Measured Person 11 Bed

Claims (3)

[Claims] 1. A superconducting lid made of a superconductor is disposed at at least one opening end of a magnetic shield body made of a cylindrical or rectangular tube-shaped superconductor having both ends open or one end closed / one end open. A superconducting magnetic shield container characterized in that a ferromagnetic material is arranged in a gap between the superconducting lid and the superconducting lid. 2. The superconducting magnetic shield container according to claim 1, wherein the superconducting lid has a side wall portion parallel or inclined to a side wall of the superconducting magnetic shield body side wall at a peripheral portion of a circular or rectangular plate or a plate having a curvature. 3. When the height of the side wall portion of the superconducting lid is h and the gap between the magnetic shield body and the superconducting lid is x,
The superconducting magnetic shield container according to claim 1, wherein at least 2x ≦ h.