JPH06224036A - Superconducting magnetic shielding body for magnetic leakage prevention to outside - Google Patents

Abstract

PURPOSE:To shield effectively a magnetic field to leak to the outside by a method wherein a cylindrical superconduction magnetic shielding body is constituted into a structure, wherein annular superconducting shielding bodies are respectively fixed annularly only on both end parts of the cylindrical superconducting magnetic shielding body and a superconducting layer, which is not formed into a shielding current loop about the axial center, is applied and formed on the peripheral surface of the drum part of the cylindrical superconducting magnetic shielding body. CONSTITUTION:A cylindrical superconducting magnetic shielding body is constituted into a structure, wherein a superconducting magnet 90 is internally provided in the hollow part of the shielding body to reduce a magnetic leakage to the outside. The superconducting magnetic shielding body 4 consists of one pair of end part shielding bodies 42, on which superconducting sheets 3 closed annularly on both end parts of the shielding body 4 are respectively fixed annularly, and a peripheral surface shielding body 41 with a piece-shaped superconducting sheet 1, which is provided on the peripheral surface of the center, part of the shielding body 4 closely at the region of the peripheral surface and so as to be unable to close annularly a superconductor. This shielding body 41 involves the magnet 90 roughly coaxially and an internal magnetic field space is formed between the shielding body 41 and the magnet 90. Thereby, a magnetic field to leak to the outside can be effectively shielded and at the same time, it can be easily done to design and manufacture freely the cylindrical superconducting magnetic shielding body having a large diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnetic shield for surrounding a magnetic source such as a superconducting magnet to prevent the generated magnetic field from leaking out of the apparatus.

[0002]

2. Description of the Related Art In recent years, a device utilizing a superconducting magnet as a strong magnetic field source has been put into practical use. In such a device, the magnetic field generated by the superconducting magnet may leak to the periphery of the device and adversely affect peripheral instruments and precision electronic devices, and it is necessary to reduce and shield the magnetic field to the outside.

As a magnetic shield for this purpose, there is conventionally known a superconducting magnetic shield in which a superconducting magnet is coaxially surrounded and enclosed by a cylinder of a superconductor, and a slit-like cutout is formed on the side surface of the cylinder. Superconducting magnetic shields have been proposed.

As a device using a superconducting magnet,
Single crystal pulling equipment such as semiconductor silicon, magnetic refrigerator, SQ
UID system and MRI (Nuclear Magnetic Resonance Tomography)
and so on.

[0005]

A magnetic shield by a conventional superconductor cylinder shields a magnetic field in the radial direction of a solenoid by diamagnetism of a solenoid cylinder surface, but at the same time, a cylindrical superconductor has a magnetic field around a solenoid axis. Through the shielding current,
Shields the magnetic field in the solenoid axis direction. In this case, there is a problem in that the magnetic field formed by the shielding current also reduces the central magnetic field in the bore of the solenoid magnet. In a device that requires a large-diameter cylindrical body to be placed in a magnetic field and uses a large-sized superconducting magnet, the device becomes larger.

Further, in the cylindrical superconductor having the slit-shaped cutout portion on the side surface, the induced shielding current around the solenoid shaft is blocked by the cutout portion and does not flow, so that the central magnetic field at the bore portion of the solenoid does not flow. It is said that the leakage magnetic field in the radial direction can be effectively blocked without reducing it.

However, the cylindrical surface of the superconductor whose side surface is cut off reduces the central magnetic field and, at the same time, strengthens the magnetic field in the axial direction of the cylindrical body, that is, in the axial direction of the solenoid, as will be described later. He was powerless to shield.

Since many devices using the superconducting magnet utilize the strong magnetic field in the hollow of the superconducting magnet, the superconducting magnetic shield for surrounding the magnet also has an opening communicating with the hollow portion of the magnet. Or it must be provided at both ends. In this case, further, outside the device, the outside of the opening of the solenoid forming the magnet, that is, the axial direction, needs to be magnetically shielded so that the magnetic field is as low as the radial direction.

Further, if a shield for a large-scale device is formed by a superconductor having an integral cylinder or a side cutout cylinder, a wide superconductor plate is required, which makes roll forming difficult, resulting in high processing cost. There was a problem such as becoming.

In view of the above problems, the present invention encloses a magnetic generation source such as a superconducting magnet in a cylindrical hollow portion,
It is intended to provide a superconducting magnetic shield capable of effectively shielding an external leakage magnetic field.

[0011]

A superconducting magnetic shield of the present invention is a cylindrical superconducting magnetic shield in which a superconducting magnet is housed in a hollow portion to reduce magnetic leakage to the outside, and both ends of the superconducting magnetic shield. A pair of end shields, each of which has a closed superconducting sheet, and a peripheral shield in which a piece-shaped superconducting sheet is provided on the peripheral surface of the central portion without a gap in the peripheral surface region and so that the superconductor cannot be closed. It is characterized by consisting of and.

In the above superconducting magnetic shield, the peripheral shield encloses the superconducting magnet substantially coaxially, and a considerable internal magnetic field space is formed between the peripheral shield and the superconducting magnet. An arrangement is preferably adopted in which the end shield is positioned ahead of the opening of the hollow portion of the superconducting magnet.

More specifically, the superconducting magnetic shield of the present invention has the end shield at the end of the tubular support of the desired shape and the peripheral shield at the peripheral surface of the body. The attached one is adopted. The strip-shaped superconducting sheet forming the peripheral surface shield does not have to be a single sheet, and in the case of a plurality of or a large number of the sheets, the edge portions of the strip-shaped superconducting sheets which are adjacent to each other in the circumferential surface region without a gap. , Superconductors are superposed so that they cannot contact each other, and are attached to each other.

The present invention will be described with reference to the conceptual diagram of FIG.
First, the peripheral surface shield 41 uses a rolled body formed by winding the single wide strip-shaped superconducting sheet 1 twice around the central peripheral surface of the cylindrical magnetic shield 4. Since the strip-shaped superconducting sheet 1 is arranged in the peripheral surface region without any gap, the magnetic generation source 90 of the superconducting magnet housed in the hollow portion is formed.
In the magnetic field 9 of FIG. 1 (B), in the direction perpendicular to the axis,
That is, the radial magnetic field component 9r is effectively shielded by the diamagnetism of the superconductor of the sheet 1.

However, in the rolled body 61 of the wide strip-shaped superconducting sheet 1, since the superconductors are arranged in an open ring, the superconducting flow passages flowing through the superconductor are open around the axis,
Therefore, with respect to the magnetic field component 9z in the axial direction, the superconducting current loop (Lenz's shielding current) around the axis does not flow in the superconductor, and this magnetic field component 9z is the cylindrical surface of the superconductor surface of the sheet 1. Parallel to and does not produce a diamagnetic effect,
Therefore, there is no magnetic shielding effect. That is, the peripheral surface shield 41 (6
Since the shield current loop is not formed in the superconductor of the strip-shaped superconductor sheet 1 which constitutes 1), the magnetic field reduction of the axial component is small.

On the other hand, in the peripheral body of the end shields 42, 42 at both ends of the cylindrical magnetic shield 4, the superconductor forms a closed ring with respect to the axial magnetic field 9z, so the Lenz shield current loop 9 is formed.
1 flows into the circumferential bodies 42, 42 of the superconductor, cancels the magnetic field from the openings of the circumferential bodies 42, 42 of the superconductor to the outside, and reduces the magnetic leakage. However, the surrounding bodies 42, 42 of the superconductor
Is limited to both ends and is not provided in the central portion, so that the magnetic field strength formed in the hollow portion of the superconducting magnet 90 is not significantly reduced.

In the present invention, the strip-shaped superconducting sheet 1 forming the peripheral surface shield 41 includes a strip-shaped, rectangular or circular sheet. However, the strip-shaped superconducting sheet 10 having a long end is used. On the peripheral surface of the central portion of the magnetic shield 4,
The above-mentioned superconducting sheet stack 61 (FIG. 1 (A)) in which the wide superconducting sheet 1 is wound one or more times to form a tubular shape,
A wound body 62 (FIG. 2 (A)), which is a cylindrical body in which the long and narrow superconducting sheet 10 is spirally wound from one end to the other end, can be adopted. In the latter spiral wound body 62, it is desirable that the side edge portion of the superconducting sheet overlaps the side edge portion of the adjacent superconducting sheet, and there is no surface area where the superconductor does not exist in the normal direction of the cylindrical surface. .

The piece-shaped superconducting sheet 1 is attached to the peripheral surface of the tubular support 40 having a desired shape with an adhesive or the like, and the peripheral surface shield 4 is formed.
1 and end shields 42, 42 are formed on both ends thereof. The superconducting magnetic shield 4 is used by being immersed in a refrigerant (for example, a liquid helium bath) in order to maintain superconductivity. In this case, the inner surface of the refrigerant container may also serve as the peripheral surface of the cylindrical support. Of. Such a support 40 is effective for supporting the thin superconducting sheet 1 (10) having high flexibility and forming the superconducting shield 4 having a desired shape.
It has an important function of preventing an instability phenomenon of the superconductor due to vibration of the superconducting sheet 1 (10) in a strong magnetic field.

The wound body 6 of the strip-shaped superconducting sheet 10
2 is that it is important that the superconductors of the stacked sheets 10 are not in contact with each other to the extent that a shield current loop cannot be formed around the cylinder. In this case, an insulating material (which may also serve as an adhesive curing layer) or a normal-conducting metal layer (Al or Cu, stainless steel) is interposed and stacked.

In the case of the rectangular superconducting sheet 19 as shown in FIG. 2 (B), a large number of rectangular superconducting sheets 19 are laid on the peripheral surface of the support 40 by superimposing the peripheral edges of the sheets 19 on each other, and , So that the superconductors of each sheet 19 do not come into contact with each other.

On the other hand, both end shields 42 of the magnetic shield 4,
As for the closed annular superconducting sheet 3 of 42, a seamless annular sheet of a superconductor is arranged coaxially with the central axis of the cylindrical body. As such a closed annular sheet 3, an annular disk whose inner side is punched out and a cylindrical sheet whose height is smaller than its diameter can be used.

The closed annular superconducting sheet 3 may be formed by brazing with a superconducting solder alloy into an annular shape so that both ends of the band-shaped superconducting sheet 10 are joined to each other. As shown, the superconducting strip-shaped sheet 10 is incised on the incision line 16 in parallel with the longitudinal direction of the sheet 10, leaving both end portions 21 and 22.
3 is expanded to obtain a closed annular sheet 3 (see FIG. 3 (B,
C)). Since the annular sheet 3 is seamless, a loop 91 of superconducting current is formed, and since the superconductor along the loop path does not have a connecting portion such as a joint by brazing, the shield current is attenuated. In addition, the stability of the magnetic shielding ability against the leakage magnetic field is good. By stacking the closed annular sheet 3 in multiple layers in the radial direction of the cylinder, the magnetic shielding ability can be enhanced.

The closed ring-shaped superconducting sheet 3 formed by cutting the band-shaped superconducting sheet 10 into a ring having a desired diameter by appropriately adjusting the cut length, and hence the length of the band-shaped sheet 1. There is an advantage that it can be done, and this is appropriately attached to the outer circumference or the inner circumference of the end of the cylindrical support 40 to form the end shield 42.

The most preferable superconducting sheet 1 (1) of the present invention for forming the end shield 42 and the peripheral shield 41.
0) is a laminated body of a thin layer of a superconductor and a thin layer of a normal conducting metal, especially a multilayer laminated body. Such a superconducting sheet 1 (10) is used, for example, for a magnetic shield used at a liquid helium temperature and an Nb-Ti alloy layer 51 and a metal A.
The rolled sheet 1 in which the 1-layers 52 and 52 are laminated in three layers (see FIG.
(D)) or a multilayer laminated vapor deposition sheet in which Nb-Ti alloy and metal Al are alternately sputter vapor-deposited on a suitable base material sheet (for example, metal Al foil). Rolled sheets and vapor-deposited sheets made of Nb-Ti alloy and metal such as Al are
Since it is flexible and can be slightly plastically deformed, the end shield 42 and the peripheral shield 41 can be formed by cutting, bending, or adhering.
Is easy to mold.

The superconducting sheets 1, 10 and 19 of the laminated body forming the peripheral surface shield 41 are, in particular, both surfaces of the metal Al layer 5.
Since the superconducting layers such as 2, 52, which are covered with the normal conducting metal layer do not come into contact with each other due to the presence of the normal conducting metal layer at the peripheral portion of each sheet stacked on the peripheral surface of the support 40, It is possible to prevent the formation of ring closure around the peripheral surface of the superconductor.

[0026]

EXAMPLE FIG. 4 is a partial sectional view of a large-diameter superconducting magnetic shield 4 having a diameter of about 2 m, which is formed by using a narrow band-shaped superconducting sheet 10 having a width of about 25 cm. On the outer peripheral surface of the cylindrical support 40 made of stainless steel, the above-mentioned Al layer / N
Three-layered strip-shaped sheet 10 composed of b-Ti layer / Al layer
Is spirally wound so that the side edge portions overlap with each other, and is adhered by a low temperature adhesive 44 to form a peripheral surface shield 41. As shown in FIGS. 5A and 5B, a strip-shaped sheet 1 having a three-layer lamination is cut and formed at an end portion on the peripheral surface shield 41, and a closed annular superconducting sheet 3 is coaxially laminated. The end shield 42 is attached by being attached by a low temperature adhesive 44. In this example,
The closed loop superconducting sheets 3 are arranged in three rows in the axial direction on the peripheral surface of the end portion. As described above, according to the present invention, since the narrow band-shaped superconducting sheet 10 can be used, the superconducting magnetic shield having an arbitrary diameter can be easily formed.

Next, a magnetic shield for shielding the leakage of the magnetism formed by the superconducting magnet to the outside was prepared and tested in the following manner.

First, the superconducting sheet has a width of 50 mm and a thickness of 4
An Nb-Ti layer of 0.4 μm and a Cu layer of 0.8 μm are alternately deposited on the upper surface of a 0 μm long Al foil by sputter deposition to form 2 layers each.
It is made by stacking five layers. In this superconducting sheet, the maximum shielding magnetic field at the sample center with respect to the magnetic field in the surface normal direction was 0.12 T per unit sheet.

As shown in FIG. 5 (C), a length of 80 m is provided on the outer peripheral surface of an aluminum cylindrical support 40 having an outer diameter of 50 mm.
A strip-shaped superconducting sheet 1 was spirally wound and adhered over m to obtain a peripheral surface shield 41.

The peripheral surface shield 41 is obtained by cutting the superconducting sheet into a width of 20 mm, and spirally adhering it to the surface of the support 40 with a low-temperature adhesive so that the side edges 5 mm overlap each other. A wound body was formed, and the wound body was stacked in four layers.

The end shield 42 has a width of 50 mm and a length of 17 mm.
The superconducting sheet 1 of 0 mm is cut in the longitudinal direction on the center line to form a closed ring having a diameter of 50 mm and a height of 25 mm,
Four layers of this closed annular sheet 3 are stacked (see FIG. 5 (A,
B)), a peripheral surface interval of 50 mm is provided on both ends of the peripheral surface shield 41 so as to cover the peripheral surface shield 41 with a pair of end shields 42, 4
It was set to 2.

As a comparative example, the peripheral surface shield by the spirally wound superconducting sheet 1 in the magnetic shield of the above-mentioned embodiment is the same, but instead of both end shields 42, 42,
The band-shaped superconducting sheet having a width of 25 mm was wound around the same position four times to form an open-ring shield.

Therefore, the superconducting magnetic shield of the comparative example has almost the same magnetic shield ability with respect to the radial magnetic field of the shield,
The end shield is different from that of the embodiment in that the shield current loop around the axial direction is not formed, and thus it is considered that the end shield does not have the magnetic shielding ability against the axial magnetic field.

FIG. 6 is a waist cross-sectional view of a test apparatus in which the cylindrical superconducting magnetic shield 4 is arranged in order to shield the external magnetic field of the small superconducting magnet 90. Solide of superconducting magnet 90 and each shield 41, 4 of magnetic shield
2, 42 are arranged coaxially with each other and vertically symmetrically, and are immersed in liquid helium, and the measurement positions a, b, c, e,
The Hall element was fixed to g to k, and the magnetic field strength in the solenoid axis direction at each position was measured.

The magnetic field measuring position a is the center position of the solenoid hollow portion 93 of the superconducting magnet 90, and the positions b and c are the ends of the end shield 42 outside the hollow portion of the solenoid on the central axis of the solenoid. The outside of the hollow portion of the partial shield 42 is shown.

The measurement positions e, g, and h are at the same height as the same a and show the magnetic field distribution in the radial direction.
The symbols k to k are for investigating the magnetic field distribution near the outside of the end shield 42.

In the test, first, without arranging the superconducting magnetic shield 4, the magnetic field at the central position a of the solenoid was 0.5 T,
The magnetic field is measured to be 1.0 T and 1.5 T to determine the solenoid current value, and then the superconducting magnetic shield 4 according to the embodiment is arranged and adjusted to the solenoid current value, and the magnetic field is adjusted. The measurement was performed. Similarly, the measurement was performed on the magnetic shield of Comparative Example. The results are summarized in Tables 1-3.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

The following can be seen from Tables 1 to 3 and FIG. First, the superconducting magnetic shield of the comparative example is a wound body of a superconducting sheet having shields at both ends in the form of strips, but the leakage magnetic field at the measurement positions g and h outside the magnetic shield in the radial direction from the solenoid center position. The magnetic field is slightly reduced at the solenoid center position a, but the magnetic field tends to increase at the measurement positions b and c in the solenoid axial direction, and the magnetic field between the solenoid and the superconducting magnetic shield is The magnetic field increases at position e. From this result, when the superconducting magnet is coaxially enclosed by the cylindrical superconductor in which the superconducting current loop is not formed in the circumferential direction on the circumferential surface, the magnetic flux is shielded in the radial direction, but on the other hand, on the opening side. On the contrary, it can be seen that the behavior is such that the leakage magnetic flux extends.

On the other hand, in comparison with the comparative example, the superconducting magnetic shield 4 of the example has magnetic fields at the measurement positions c, g, h, i, j, k outside the superconducting magnetic shield 4. It is effectively reduced, and it is clear that not only the magnetic field on the outer side in the axial direction can be reduced but also the leakage magnetic field in the radial direction can be effectively reduced by making only the both end shields 42, 42 into a closed ring shape. became.

On the other hand, the closed annular end shield 42 slightly reduces the central magnetic field of the hollow portion of the superconducting magnet as compared with the comparative example, but such a magnetic field change is caused by adjusting the magnet exciting current. , It is easy to set a predetermined magnetic field.

[0044]

In the cylindrical superconducting magnetic shield of the present invention, the annular superconducting shield is attached only to both ends, and the body peripheral surface is covered with a superconductor layer which does not form a shield current loop around the axis. Since it is formed, the reduction of the central magnetic field is made as small as possible,
Since it can effectively shield an external leakage magnetic field, it is extremely useful as a shield for a magnetic device using a superconducting magnet.

Since the tubular superconducting magnetic shield of the present invention can be constructed by forming the end shield and the peripheral shield from a band-shaped superconducting sheet, it is possible to use a strip-shaped superconducting sheet which is easy to manufacture. By sticking and arranging it on a shaped support, it is possible to easily design and manufacture a large-diameter cylindrical superconducting magnetic shield that can be used for a large magnetic device.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a cylindrical superconducting magnetic shield of the present invention,
(A) is a perspective view and (B) is a sectional view.

FIG. 2 is a perspective view (A, B) according to an embodiment of a cylindrical superconducting magnetic shield.

FIG. 3 shows an end shield for use in a superconducting magnetic shield, which includes a band-shaped superconducting sheet (A) to an annular superconducting sheet (B).
The figure which shows the process of forming (C), and sectional drawing (D) of a strip | belt-shaped superconducting sheet as an example.

FIG. 4 is a partially cutaway sectional view of a cylindrical superconducting magnetic shield (A,
B).

FIG. 5 is an external view (A, B) of an end shield in which the annular bodies are stacked as shown in FIG. 3B, and an external view of a superconducting magnetic shield for a magnetic shield test formed by using the end shield (A, B). Including partially cutaway section) (C).

FIG. 6 is a layout view of a cylindrical superconducting magnetic shield and a superconducting magnet in a magnetic shielding test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flake-shaped superconducting sheet 10 Band-shaped superconducting sheet 19 Square-shaped superconducting sheet 3 Closed annular superconducting sheet 4 Cylindrical superconducting magnetic shield 40 Support 41 Peripheral shield 42 End shield 51 Superconducting layer 52 Normal conducting metal layer 90 Superconducting Magnet 9 Magnetic line 91 Superconducting current loop

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Sato 1-5 Doyamacho, Kita-ku, Osaka City High Pressure Gas Industry Co., Ltd.

Claims (8)

[Claims] 1. A superconducting magnet is provided inside the hollow portion,
In a cylindrical superconducting magnetic shield for preventing the magnetic field of the magnet from leaking to the outside, the cylindrical superconducting magnetic shield comprises a pair of end shields each having a closed annular superconducting sheet mounted at both ends thereof. A superconducting magnetic shield, comprising: a peripheral surface shield provided with a piece-shaped superconducting sheet on the peripheral surface of the central portion without a gap in the peripheral surface region and incapable of ring closure of the superconductor. 2. A pair of end shields are formed on both ends of a tubular support, and a peripheral shield is formed on the peripheral surface of the support between the end shields, whereby the flaky superconducting material is formed. The superconducting magnetic shield according to claim 1, wherein the sheets are attached so that the superconductors of the adjacent sheets cannot contact each other. 3. The closed-loop strip-shaped superconducting sheet is a laminate of a superconductor thin layer and a normal-conducting metal thin layer, and at least the superconductor thin layer of the laminate has a seamless closed ring shape. 1. The superconducting magnetic shield according to 1. 4. A closed ring-shaped sheet, wherein the closed-loop strip-shaped superconducting sheet is formed by cutting a strip-shaped sheet of a laminate of a superconducting thin layer and a normal-conducting metal thin layer in the longitudinal direction with both ends left uncut. The superconducting magnetic shield according to claim 1 or 2. 5. The strip-shaped superconducting sheet is an endless strip-shaped sheet of a laminate of a superconducting thin layer and a normal-conducting metal thin layer, and the strip-shaped sheets are adjacent to each other. As the edges are superposed so that the superconductor layers on the side edges cannot contact each other,
The superconducting magnetic shield according to claim 1 or 2, wherein the superconducting magnetic shield is spirally wound around the peripheral surface of the support. 6. The strip-shaped superconducting sheet is an endless wide strip sheet of a laminate of a superconducting thin layer and a normal conducting metal thin layer, the wide strip sheet being provided at least once on the peripheral surface of the support. The superconducting magnetic shield according to claim 1, which is wound as described above. 7. The piece-shaped superconducting sheet is a plurality of piece-shaped sheets of a laminate of a superconducting thin layer and a normal-conducting metal thin layer, wherein a side edge portion of the sheet is a superconducting layer of the side edge portion. 2. The superconducting magnetic shield according to claim 1, wherein the superconducting magnetic shield is formed by superimposing the particles so that they cannot come into contact with each other and adhering in a cylindrical shape. 8. The superconducting magnetic shield according to claim 3, wherein the thin superconducting layer is an Nb—Ti alloy, and the normal conducting thin metal layer is a metal Al or Cu.