JP3133481B2 - Superconducting magnetic shield - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield using a superconductor for forming and using a magnetic shield space in a strong magnetic field such as near a superconducting magnet in an ultra-low temperature range.

[0002]

2. Description of the Related Art When a superconductor is cooled to a temperature below a critical temperature and is in a superconducting state, a superconducting current which cancels an external magnetic field flows due to the Meissner effect, and the property of blocking the penetration of an external magnetic field is known. Used as a magnetic shield.

[0003] The ability of a superconductor to shield an external magnetic field, that is, the amount of magnetic shielding, generally depends on the type of superconductor and the thickness of the plate-like superconductor. The larger the plate thickness, the greater the amount of magnetic shielding. Can shield strong magnetic fields,
Part of the external magnetic field exceeding the magnetic shielding amount is transmitted through the superconductor.

However, when a superconductor is used in the form of a thick plate in order to shield a strong magnetic field, an abrupt phenomenon called a flux jump occurs.
The phase transition from the superconductor to the normal conductor is accompanied by heat generation, and the unstable phenomenon that most of the external magnetic field permeates easily occurs.

In order to cope with this, the present inventors have avoided the instability phenomenon by using a superconductor as a thin layer, and at the same time, using a single thin layer reduces the amount of magnetic shielding. Japanese Patent Laid-Open No. 61-183979 has proposed a shield having a multilayer structure having a multilayer structure in which a normal-conducting metal layer is interposed between superconducting layers.

[0006] By forming a thin multilayer of superconductor layers, the laminate has a better magnetic shielding ability than a single superconductor of the same thickness, and the superconductivity of the superconductor with which the normal metal layer is in contact. It cuts off current and conducts heat from the superconductor layer to the outside of the laminate, and further forms a branch of the induced current locally generated in the superconductor in the normal conductor to reduce the current density and reduce the strong magnetic field. This is to eliminate the unstable phenomenon that occurs when shielding. It has also been disclosed that it is effective to provide a large number of small through holes in the superconductor layer to suppress the flow of magnetic flux and to prevent the occurrence of a flux jump (Japanese Patent Application Laid-Open No. Sho 63/1988).
-233577).

[0007] A magnetic shield using a laminate including a superconductor layer includes, in addition to a flat or curved shield, an annular superconductor layer and a normal metal layer which are alternately laminated. A cylindrical body (Japanese Patent Application Laid-Open No. 2-97098) or a cylindrical body formed by winding or attaching a laminated sheet formed of a superconductor layer and a metal layer and concentrically stacking them. Kaihei 1-3027
No. 99) is known, and all use a hollow portion opened at both ends or one end of a cylindrical body as a magnetically shielded space.

[0008]

Although the above-mentioned magnetic shield of a laminate comprising a superconductor layer and a normal-conducting metal layer is extremely effective for shielding a strong magnetic field, it is possible to reduce the weight of the magnetic shield. If the normal conductive metal layer, for example, a Cu layer is made thinner for downsizing, the above-mentioned instability phenomenon is likely to occur, and there is a limit to weight reduction. On the other hand, if the Cu layer is made extremely thick for stabilization, the magnetic field penetrates and the magnetic shielding amount itself decreases.

When the magnetic field strength is adjusted by changing the external magnetic field during use of the magnetic shield, an unstable phenomenon is likely to occur if the excitation speed is relatively high. In addition, fluctuations in the position and time of the external magnetic field and movement of the magnetic shield itself cause a flux jump, and in such a case, an unstable phenomenon is likely to occur. Such an unstable phenomenon is likely to occur when used in a strong magnetic field lower than the maximum shielding magnetic field of the magnetic shield, and the magnetic shielding ability of the magnetic shield that can be safely used due to the unstable phenomenon is remarkable. Will drop.

Therefore, in practice, the magnetic shield is used for shielding an external magnetic field that is much lower than the maximum magnetic shield amount of the laminate including the superconductor layer. On the other hand, the magnetic shield had to be formed with an unnecessarily large number of superconductors, and the total thickness had to be increased.

The present invention addresses these problems,
The superconducting magnetic shield stably shields the fluctuating magnetic field,
Without reducing the amount of magnetic shielding, weight reduction,
The purpose is to increase the reliability as a magnetic shield.

[0012]

SUMMARY OF THE INVENTION A superconducting magnetic shield according to the present invention comprises a superconducting layer, a normal conductive metal layer having high electrical and thermal conductivity, and a resistor layer having a lower electrical conductivity than the normal conductive metal layer. Are laminated.

The superconducting magnetic shield of the present invention is formed by laminating a superconducting layer, a normal conducting metal layer and a resistor layer in this order. Preferably, the superconducting magnetic layer is provided on both sides of the superconducting layer. The unit laminate is further laminated as a unit laminate having a three-layer structure or a superconductor and a normal-conducting metal layer laminated on each other, and the above-described resistance is placed between adjacent unit laminates. A superconducting magnetic shield having at least one body layer interposed therebetween is included.

As the superconductor layer, a thin layer of a second type superconductor is used, for example, NbTi, Nb ₃ Sn, Nb ₃ A.
1, metal-based superconductors such as Nb ₃ (Al, Ge) and V ₃ Ga, compound superconductors such as NbN, NbC and NbN / TiN, and Y—Ba—Cu—O, Bi—Sr—C
Thin or film-like oxide superconductors such as a-Cu-O, Bi-Pb-Sr-Ca-Cu-O and Sr-X-Cu-O (X = Ba, Ca and lanthanide metals) Is used. On the other hand, metal Cu or metal Al, or an alloy such as brass or duralumin is used for the normal conductive metal layer having good electrical conductivity and thermal conductivity.

The resistor layer, which is a feature of the present invention, is a thin layer of a material having a lower electrical conductivity than the above-mentioned normal conductive metal layer at a use temperature, and the electrical resistivity of the resistor of the resistor layer is as described above. than the electrical resistivity of the metal of normal conduction metal layer, 10 ¹ times or more, preferably selected is greater 10 ³ times or more. Such a resistor layer is formed of an alloy having an electric resistivity of 1 × 10 ⁻⁷ Ωm or more, for example, when a metal Cu or Al or the like is used for the normal conductive metal layer in a range of liquid helium temperature to liquid nitrogen temperature. Cu-Al alloys (composition alloys of constantan and monel metal), Fe-Ni alloys (invar and other FCC alloys) or Ni-Cr austenitic steels can be used. -Zn alloy is also used.

Further, the concept of the resistor layer naturally includes a high-resistance layer and an insulator layer having an electric resistivity higher than that of the above alloy. Such a high-resistance layer / insulator layer is, for example, aluminum nitride, copper oxide, inorganic materials such as alumina, low-temperature vacuum grease such as Apiezon grease and silicon grease, epoxy-based, polyimide-based, phenol-based and Polyurethane-based adhesive cured product, Mylar (polyethylene terephthalate), Nylon (polyamide-based plastic), Teflon (polytetrafluoroethylene), Kapton (polyimide), silicon resin, etc., and fiber reinforced material (FRP) of these resins Examples include film-like or plate-like resin, insulating paper such as mica paper and kraft paper.

These resistors preferably have high thermal conductivity. From this viewpoint, aluminum nitride (AlN),
A thin film of carbon having a diamond structure or a graphite structure is excellent. Further, the resistor layer may be a fluid layer. A space layer through which a fluid for cooling the magnetic shield itself, such as liquid helium or liquid hydrogen, flows is also used.

In the superconducting magnetic shield of the present invention, in forming a laminate, the superconducting layer and the normal-conducting metal layer are adhered and integrated, and the resistor layer is adhered and integral with the adjoining normal-conducting metal layer. Is preferred. A laminated body in which these layers are closely adhered and integrated is a laminated body in which thin plates and foils are stacked and pressed with a press or a roller, and a superconductor material and a normal conductor metal are alternately vacuum-deposited and laminated on a substrate. And the like.

The three-layer structure constituting the magnetic shield of the present invention is disclosed in Japanese Patent Application Laid-Open No. 3-283475.
No.), superconductor foil, for example, on both sides of Nb-Ti alloy foil,
A three-layer foil material formed by joining a high-conductivity normal conducting metal, for example, a metal Al foil by rolling, can be used. When a large number of three-layer foil materials are further stacked, if they are bonded with the synthetic resin adhesive, a cured layer of the adhesive can also serve as a resistor layer.

[0020]

The resistor layer increases the electrical resistance in the thickness direction of the laminate to prevent the occurrence of a flux jump. As described above, in order to increase the maximum shielding magnetic field, it is effective to make the superconducting layer a thin layer and increase the distribution density of the superconductor. For this purpose, it is better to make the normal conducting metal thinner. Stability decreases. On the other hand, for stabilization, it is effective to increase the thickness of the normal conducting metal layer. However, since the distribution density of the superconductor is reduced and the critical current density of the laminate is also reduced, the maximum shielding magnetic field is reduced. By interposing the resistor layer, the normal conductive metal layer can be made thin, and the distribution density in the thickness direction of the superconductor layer can be increased, resulting in a magnetic shield with good stability and a large maximum shielding magnetic field. .

The laminate of the superconductor layer and the normal metal layer is
When excited by an external magnetic field, a loop of the shielding current is formed in each superconductor layer, so that the larger the number of layers in a strong magnetic field, the greater the interaction between the shielding current magnetism and the normal metal layer. The interaction of eddy currents flowing on the surface also increases, and the shielding current of some superconductor layers fluctuates due to slight fluctuations in the external magnetic field, and the magnetic effect adversely affects the shielding current of other adjacent superconductors. Giving a rapid magnetic flux, leading to a flux jump. The resistor layer cuts off such interaction of the shielding current to localize it and contributes to stabilization.

The laminate of the magnetic shield of the present invention is shown in FIG.
As shown in (B), the normal conductive metal layer 12, the superconductor layer 1
1. It is preferable that the normal conductive metal layer 12 and the resistor layer 13 are repeatedly laminated in this order. The metal layers 12, 1 are cooled in a conductive state on both surfaces of the superconductor layer 11, and
2 is practically insulated by the resistor layer 13,
This regulates the generation and propagation of the flux jump. Therefore, even if the normal conductive metal layer 12 is thinned, it is unlikely to be unstable, so that the entire laminated body can be thinned, and the magnetic shield can be reduced in weight by using a synthetic resin layer or a ceramic layer. Such a magnetic shield has a resistor layer 13 interposed in a three-layer structure 1a in which normal conductive metal layers 12, 12 are sandwiched on both surfaces of a superconductor layer 11 as shown in FIG. hand,
It is easily formed by alternately stacking.

FIG. 1C shows a structure in which a resistor layer 13 is appropriately interposed in the course of alternate lamination of the normal-conducting metal layer 12 and the superconductor layer 11. In this case, the alternate laminated body is used as a unit laminated body. , And are easily formed by alternately laminating the unit laminated body 1a and the resistor layer 13.

As described above, since the strong magnetic field near the maximum shielding magnetic field can be stably shielded by interposing the resistor layer, the magnetic shield can be made thinner.
Since the normal conducting metal layer can also be formed as a thin layer, it can be reduced in thickness and weight as a magnetic shield.

[0025]

EXAMPLE A test for examining the magnetic shielding ability of the magnetic shielding of the present invention was carried out as follows. (Example 1) First, Nb-T
Rolled and soft annealed i-alloy, 10 μm thick Nb
-Sputtering Cu on both sides of Ti foil to a thickness of 2μ
m to form a disk-shaped three-layer structure having a diameter of 45 mm.

Eight three-layered structures and eight 5 μm-thick polyethylene terephthalate films are alternately stacked, and both sides thereof are sandwiched between glass fiber reinforced synthetic resin (FRP) plates to form a disc-shaped disk according to the present invention. Magnetic shield.

As a comparative example, eight sheets of the three-layer structure were simply stacked without interposing the above-mentioned polyethylene terephthalate film, and similarly, both surfaces thereof were sandwiched between glass fiber reinforced synthetic resin (FRP) plates. Thus, a magnetic shield on the disk was obtained.

In the test apparatus for magnetic shielding, a superconducting magnet fixed inside a low-temperature container is immersed and cooled in liquid helium, and the disk-shaped magnetic shield is laminated in a hollow portion of a coil of the superconducting magnet. The surface is fixed so as to be perpendicular to the line of magnetic force, and a Hall element for detecting a magnetic field intensity is arranged near the center of the surface of the laminate. Both the magnetic shield and the Hall element are under 4.2K liquid helium cooling.

In the test, the magnetic field strength was measured by the detection output of the Hall element while increasing the coil current of the superconducting magnet in a state where the magnetic shield was arranged. In addition, the magnetic field strength was measured at the same position without disposing the magnetic shield, and an external magnetic field was obtained.

FIG. 2 shows test results at an excitation speed of 0.2 T / min. FIG. 2A shows the magnetic properties of the magnetic shield of the laminated body provided with the resistor layer according to the embodiment of the present invention. It shows a shielding curve, and the magnetic field behind the magnetic shield is zero even when the external magnetic field is excited up to about 0.23 T (a region in the figure).
From the magnetic field strength exceeding 0.23 T, the magnetic shield penetrates the magnetic shield (region b in the drawing), and has a magnetic shielding amount of about 0.23 T (point e in the drawing) in this example. No flux jump occurred.

On the other hand, as shown in FIG.
In Comparative Example 1 having no resistor layer, 0.2 T / mi
When the external magnetic field exceeds 0.1 T during the increase in the external magnetic field at the excitation speed of n, a flux jump occurs (region c in the figure), and the internal magnetic field rapidly increases from zero and becomes equal to the external magnetic field.
The function of the magnetic shield has been lost. In this case, the maximum external magnetic field that can maintain the internal magnetic field at zero, that is, the amount of magnetic shielding was 0.1 T of the external magnetic field when the flux jump occurred.

(Embodiment 2) Next, an embodiment using a cylindrical magnetic shield will be described. The magnetic shield is made of an NbTi alloy having a thickness of 0.4 μm and metal Cu on an annular Al film substrate surface having an outer diameter of 60 mm, an inner diameter of 35 mm, and a thickness of 50 μm.
Was alternately deposited by sputtering at a thickness of 0.8 μm to form an annular unit laminate having 25 layers.

This annular unit laminated body and a CuNi alloy film having the same inner and outer diameters and having a thickness of 10 μm are alternately laminated as resistors, and clamped and fixed by FRP flanges 32 and 33 as shown in FIG. A cylindrical magnetic shield 1 having a length of 60 mm was obtained.

As Comparative Example 2, a cylindrical magnetic shield having a length of 60 mm similar to that shown in FIG. 3 was formed by laminating a large number of the above annular unit laminates without using a CuNi alloy film. did.

In the magnetic shielding test, the cylindrical magnetic shield 1 was coaxially arranged and fixed in the hollow portion of the coil of the superconducting magnet, and the magnetic field detecting Hall element sensor was fixed in the cylindrical hollow portion 10. Excitation speed was set at 0.4 T / min in the same manner as in Example 1 above.

FIG. 4A shows the magnetic field inside the shield when the magnetic field of the second embodiment is excited to about 4 T. The magnetic shield amount is 2.5 T without flux jump.
(Point e in the figure). On the other hand, Comparative Example 2
The flux jump occurs at the time of excitation of about 2.2 T, and the internal magnetic field rapidly increases to the external magnetic field.

(Embodiment 3) Each of the cylindrical magnetic shields is formed by laminating an annular film having an outer diameter of 60 mm and an inner diameter of 35 mm, and has a thickness of 20 μm Al foil and a thickness of 10 μm Nb.
Ti alloy film, Al foil of 20 μm and 10 μm
CuNi alloy films are sequentially laminated to a length of 100 m.
m of a cylindrical magnetic shield.

As Comparative Example 3, an Al foil having a thickness of 30 μm was used instead of the Al foil having a thickness of 20 μm used in the above embodiment, and the Cu—Ni alloy film was omitted.
A 0 mm cylindrical magnetic shield was used.

The same magnetic shielding test as in Example 2 was performed, and the results are shown in FIG.

FIG. 5A shows a maximum magnetic shielding amount of about 2 T without any flux jump as shown in the behavior of the internal magnetic field of the present embodiment.
As shown in (B), a flux jump occurs at point e in the figure, and the maximum magnetic shield is reduced to about 1.4T.

As described above, when a flux jump occurs in the magnetic shield exposed to the strong magnetic field, the maximum magnetic shield amount decreases, and almost all the magnetic flux of the external magnetic field passes through the magnetic shield. Although the function of the magnetic shield is not achieved, the magnetic shield including the resistor layer of the present invention can reliably prevent the occurrence of the flux jump, and can increase the reliability of the magnetic shield.

(Example 4) Next, the stabilization of the magnetic shield in a fluctuating magnetic field from a zero magnetic field to a strong magnetic field was investigated using a cylindrical magnetic shield. The superconducting layer is made of an Nb-Ti alloy, the normal conducting metal layer is made of metal Cu, a 60 μm thick metal aluminum foil is used as a substrate, and the Nb—Ti alloy layer 0.4 μm and the metallic copper layer 0 are formed by sputtering. 0.8 μm
Are alternately deposited over all 50 layers to a total thickness of 90 μm
, A unit laminated plate having an inner diameter of 10 mm and an outer diameter of 20 mm
A ring of mm was cut out to obtain a unit laminated ring.

Next, a polyethylene terephthalate film having a thickness of 10 μm as an edge layer is formed into a ring having the same shape, and the edge ring and the unit lamination ring are alternately laminated to form a cylinder having a length of 300 m. A magnetic shield having a structure as shown in FIG.

In the test of the magnetic shielding ability, the cylindrical magnetic shield was fixed inside a hollow part having an inner diameter of 65 mm of a superconducting coil immersed and cooled in liquid helium, and was placed in the hollow part of the magnetic shield. Is 10 mm from the end on its central axis.
Starting from the point at which mm was entered, five Hall element sensors for measurement were further arranged at intervals of 70 mm. During the measurement,
Both the magnetic shield and the Hall element are under 4.2K liquid helium cooling.

FIG. 6 shows the test results.
Shows the relationship between the external magnetic field at the base point of the measurement and the magnetic field inside the magnetic shield. Even when the external magnetic field is 3T, a zero magnetic field is obtained in the hollow portion of the magnetic shield. When the external magnetic field exceeds 3T, magnetic penetration into the inside of the magnetic shield occurs. This tendency hardly differs between the inner base point 10 mm from the end of the magnetic shield cylinder and the center.

FIG. 8 shows the change in the magnetic field inside the magnetic shield when excitation and demagnetization are repeated 10 times at a magnetic field speed of 0.6 T / min in the range of the strong field strength of 0 to 3 T. Even with a magnetic field, it has the ability to completely shield a strong magnetic field up to 3T, and was stable without generating a flux jump even in such a fluctuating magnetic field.

The change in magnetic flux penetration with time when the external magnetic field was kept constant at 3T for a long time was examined. The magnetic field inside the magnetic shield was always 0T for 10 hours. This indicates that the magnetic shield of the present invention is extremely stable.

[0048]

According to the present invention, there is provided a superconducting magnetic shield comprising a laminated body of a superconducting layer and a normal-conducting metal layer. Since the occurrence of the phenomenon is prevented, it is possible to effectively and stably shield a strong magnetic field near the maximum magnetic shielding amount of the laminate. Further, the magnetic shield of the present invention also effectively exhibits magnetic shielding ability against magnetic field fluctuation due to disturbance / fluctuation of an external magnetic field.

Since a strong magnetic field close to the maximum magnetic shielding amount can be stably shielded, the total thickness of the magnetic shield can be reduced, and the thickness of the normal conducting metal layer which contributes to stabilization of the strong magnetic field shielding can be reduced. Therefore, the weight and size of the magnetic shield can be easily reduced. In particular, if the resistor layer is made of an inorganic compound or a synthetic resin having a small specific gravity, it is effective for weight reduction.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram (A, B, C) showing a laminated structure of a superconducting magnetic shield.

FIG. 2 is a magnetic shield curve diagram of a plate-shaped superconducting magnetic shield.
(A) shows an embodiment having a resistor layer of CuNi alloy,
(B) shows a comparative example.

FIG. 3 is a sectional view of a cylindrical superconducting magnetic shield.

FIG. 4 is a view similar to FIG. 2, showing a cylindrical superconducting magnetic shield.

FIG. 5 is a view similar to FIG. 2 of a cylindrical superconducting magnetic shield.

FIG. 6A is a magnetic shielding curve diagram in a cylindrical superconducting magnetic shield hollow portion according to an example, and FIG. 6B is a diagram showing a change in an internal magnetic field with respect to a fluctuating external magnetic field.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Superconducting magnetic shield 11 Superconducting layer 12 Normal conducting metal layer 13 Resistor layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuo Takagi 1-5 Doyamacho, Kita-ku, Osaka City Inside High-Pressure Gas Industry Co., Ltd. (72) Inventor Masaru Inoue 1-5 Doyamacho, Kita-ku, Osaka High-pressure gas Inside Kogyo Co., Ltd. (72) Kohei Otani 1-5 Doyamacho, Kita-ku, Osaka City High Pressure Gas Kogyo Co., Ltd. (72) Inventor Manabu Sato 1-5 Doyamacho, Kita-ku, Osaka City High-Pressure Gas Industry (56) References JP-A-2-97098 (JP, A) JP-A-61-58299 (JP, A) JP-A-62-105497 (JP, A) JP-A-3-273700 (JP, A) A) JP-A-63-233577 (JP, A) JP-A-3-283475 (JP, A) JP-A-63-245823 (JP, A) Japanese Utility Model Showa 60-18512 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H05K 9/00 ZAA

Claims (10)

(57) [Claims] 1. A superconducting magnetic shield comprising a superconducting layer, a normal conducting metal layer having high electric conductivity and thermal conductivity, and a resistor layer having a lower electric conductivity than the metal layer. , the resistance layer, under operating temperature, superconducting magnetic shield, characterized in that an alloy layer having a high electrical resistivity 10 ¹ times or more than the electric resistivity of the normal-conducting metal layer. 2. A three-layer structure in which a superconducting metal layer having high electrical conductivity and thermal conductivity is sandwiched on both surfaces of a superconductor layer, or a superconducting layer and a normal conductive metal material having high electrical conductivity and thermal conductivity The unit laminate is formed by laminating a layer and a unit laminate, and the unit laminate is further laminated, and any of the adjacent unit laminates is more conductive than the normal conductive metal layer. every a small resistor layer superconducting magnetic shield which is interposed, the resistance layer, under operating temperature, the alloy layer having 10 ¹ times or more greater electrical resistivity than the electrical resistivity of the normal-conducting metal layer A superconducting magnetic shield, characterized in that: 3. The method according to claim 1, wherein the alloy layer is made of a Cu—Al alloy,
The superconducting magnetic shield according to claim 1, which is a Ni-based alloy or a Cr—Ni-based austenitic steel. 4. A superconducting magnetic shield comprising a superconducting layer, a normal conducting metal layer having high electric conductivity and thermal conductivity, and a resistor layer having a lower electric conductivity than the metal layer. A superconducting magnetic shield, wherein the resistor layer is a hardened synthetic resin adhesive or a thin synthetic resin film. 5. A three-layer structure in which a superconducting metal layer having high electrical conductivity and thermal conductivity is sandwiched on both surfaces of a superconductor layer, or a superconducting layer and a normal conducting metal material having high electrical conductivity and thermal conductivity. The unit laminate is formed by laminating a layer and a unit laminate, and the unit laminate is further laminated, and any of the adjacent unit laminates is more conductive than the normal conductive metal layer. What is claimed is: 1. A superconducting magnetic shield comprising a resistor layer having a small degree of resistance, wherein said resistor layer is a cured synthetic resin adhesive or a synthetic resin thin film. 6. The superconducting magnetic shield according to claim 1, wherein the superconducting layer and the normal conducting metal layer are laminated in close contact with each other. 7. The superconducting magnetic shield according to claim 2, wherein the unit laminates are in close contact with each other, and the unit laminate and the resistor layer are in close contact with each other and are integrally laminated. 8. The superconducting magnetic shield according to claim 1, wherein at least one or a plurality of small holes penetrating the superconducting layer is provided on both sides thereof. 9. The superconducting magnetic shield according to claim 1, wherein said superconducting layer, normal conducting metal layer and resistor layer are formed in a ring shape and laminated in a cylindrical shape. 10. The superconducting magnetic shield according to claim 1, wherein the resistor layer is sandwiched between the normal conducting metal layers.