JPH04276669A - Superconducting magnetic shielding body - Google Patents

Abstract

PURPOSE:To obtain a superconducting magnetic shielding body which is excellent in the stability of a superconducting state even in a fluctuating magnetic field having a fairly large exciting and demagnetizing speed and whose magnetic shielding characteristic is high. CONSTITUTION:The title shielding body is formed by laminating superconducting layers 2 and normal conducting metal layers alternately in their thickness direction and are formed as a cylindrical shape in which no connecting part exists in the peripheral direction and in the axial direction. The normal conducting metal layers are all composed of high-resistance metal layers 3 or are formed by laminating the high-resistance metal layers 3 and highly conductive metal layers alternately. The highly conductive metal layers may be divided into a plurality of stripes by using stripe-shaped high-resistance metal belts. An eddy current generated by a fluctuating magnetic field or a coupling electric current between the superconducting layers can be suppressed, and the stability of a superconducting state a is enhanced. The title shielding body displays an effect as a magnetic shielding cylinder for fluctuating magnetic-field use.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical superconducting magnetic shield that exhibits excellent stability in a superconducting state even in a fluctuating magnetic field with high excitation and demagnetization rates and has high magnetic shielding properties.

0002

2. Description of the Related Art Hitherto, type 1 superconductors and type 2 superconductors have been used as magnetic shielding materials that utilize superconductivity. Both are used depending on the strength of the magnetic field, and the first
Seed superconductors can be completely magnetically shielded by the Meissner effect, albeit down to fairly low magnetic fields. Second
The seed superconductor has a lower critical magnetic field Bc1 and an upper critical magnetic field Bc2
Although the magnetic field is quite low up to Bc1, complete magnetic shielding can be achieved due to the Meissner effect. B
Between c1 and Bc2, it becomes a mixed state of superconducting state and normal conducting state, and magnetic shielding can be performed, but Bc2
If a material with a high magnetic field is used, magnetic shielding of a high magnetic field is also possible.

If a type 2 superconductor having a cylindrical shape, for example, is used, when a magnetic field is applied from the outside, a superconducting shielding current flows annularly through the cylindrical material in a direction that cancels the magnetic field. If the strength of the external magnetic field is below a certain value and the length of the cylinder in the axial direction is infinite, the magnetic field in the internal space of the cylinder is maintained at completely zero. The same thing can be applied when there is an internal magnetic source. In other words, when the strength of the internal magnetic field is below a certain value,
If the length of the cylinder in the axial direction is infinite, magnetic leakage from the inside of the cylinder into the external space can be completely eliminated. Although the length in the axial direction is, of course, limited, the above two types of superconducting magnetic shields using a cylindrical shape are currently being technologically developed as being most suitable for practical use.

0004

[Problems to be Solved by the Invention] It is desirable to bond a highly conductive metal such as Cu or Al to the superconducting material in order to stabilize the superconducting properties. This is because heat is generated due to the rapid penetration of magnetic flux into the superconducting layer, but because the highly conductive metal layers are bonded to both sides of the superconducting layer, this heat can be quickly dissipated into the external liquid He. Depends on what you can do. In addition, even if the superconducting state is partially destroyed and a high-resistance region occurs, the highly conductive metal acts as a highly conductive bypass for the superconducting current, making it possible to restore the superconducting state again. . Furthermore, it is necessary to minimize the hysteresis loss during excitation and demagnetization, which is characteristic of type 2 superconductors, and to minimize the thickness of each superconducting layer in order to increase the stability of the superconducting state. Therefore, in view of these circumstances, one of the effective methods is to create a multilayer structure of highly conductive metal layers and superconducting layers alternating in the thickness direction of the cylindrical shape.

[0005] As a technique based on this idea, for example, Cu/Nb-T in Japanese Patent Application No. 2-71863
Examples include a cylinder having a multilayer composite structure of an i-based alloy.

However, in this multilayer composite cylinder, in a fluctuating magnetic field with a large excitation/demagnetization rate, eddy currents occur in the highly conductive metal, and depending on the direction of the magnetic flux lines, coupling currents occur between the superconducting layers. It occurs to such an extent that it cannot be ignored. Since both of these currents are generated in materials having resistance, they cause heat generation, and even lead to destruction of the superconducting state, contributing to superconducting instability.

[0007]

[Means for Solving the Problems] The gist of the present invention is that at least one superconducting layer and one normal-conducting metal layer are alternately laminated in the thickness direction, there are no connecting parts in the circumferential direction and the axial direction, and the entire or one part It has a cylindrical shape with a bottom at the bottom or a bottomless cylindrical shape, and the normal conductive metal layer is made of a high resistance metal, or at least one high resistance metal layer and one high conductivity metal layer are each alternately laminated in the thickness direction. This is a superconducting magnetic shield body characterized by the following.

Preferably, the highly conductive metal layer is divided into a plurality of stripes by striped high-resistance metal bands. Here, it is sufficient that one striped high-resistance metal strip is arranged so as not to be connected to another adjacent striped high-conductivity metal strip. Therefore, the striped high-resistance metal strips may have no points where they intersect with each other, and may be in one row each, or they may have intersection points at various locations, that is, the walls of the high-resistance metal strips allow the highly conductive metal to form a cellular shape ( It may be a structure surrounded by cells (cell-like).

[0009] The above-mentioned high-resistance metal is a Cu-Ni alloy, a Cu-
It is preferable that the highly conductive metal is either Mn alloy or Cu-Co alloy, and the highly conductive metal is Cu, Cu alloy, Al, Al alloy, Ag, or Ag alloy. Among these high-resistance metals, in order for each Cu alloy to have sufficiently high resistance, it is desirable that each second element be contained in an amount of 3 wt % or more. In addition, Cu or Al is most suitable as a highly conductive metal in consideration of conductivity and cost, but it is also possible to add small amounts of other elements to the extent that the conductivity is not significantly reduced.

[0010] As the superconducting material of the superconducting layer, Nb,
In addition to Nb-Ti alloy, Nb-Zr alloy, Nb3
Sn, V3 Ga, Nb3Al, Nb3 Ga, Nb3
Examples include A15 type intermetallic compounds such as Ge and Nb3 (AlGe). In addition, La-Sr-Cu-O system, Y-
Ba-Ca-O system, Bi-Sr-Ca-O system, Tl-B
Ceramic superconducting materials such as a-Ca-Cu-O-based materials may also be mentioned.

When the superconducting layer is an Nb-Ti alloy or a Nb-Zr alloy, a barrier layer for preventing diffusion made of Nb or Ta or an alloy of both is provided at the interface with the normal conducting metal layer. I don't have any problem with it. In these superconducting alloys, heat is sometimes applied to improve their superconducting properties or during processing, and this barrier layer is formed by the diffusion of Ti and Zr in the superconducting alloy and normal conductive metal elements into hard and brittle intermetallic compounds. It has the role of preventing the formation of This intermetallic compound may cause problems in subsequent processing, change the component ratio of the superconducting alloy, and ultimately deteriorate the superconducting properties.

[0012] The cross-sectional shape of the cylinder can be freely selected from circular, polygonal, etc. depending on its use.

[0013]

[Operation] A cylindrical superconductor with no connections in the circumferential and axial directions has a closed loop in which a superconducting shielding current perpendicular to an external magnetic field parallel to the axial direction creates a magnetic field in the opposite direction to the external magnetic field. Create and flow. If there is a connection or normally conducting part in the middle of this closed loop, the superconducting shielding current will attenuate over time and the superconducting magnetic shielding properties will also be lost. Therefore, according to the present invention, the superconducting shielding current can flow in a closed loop over the entire circumference of the cylinder without attenuation, and high magnetic shielding characteristics can be obtained semi-permanently.

[0014] The same is basically true when one end of the cylindrical shape is closed with a plate made of the same material, that is, when the cylindrical shape has a bottom. In a cylindrical shape with both ends open, a certain amount of magnetic field penetrates into the internal space from the open ends. On the other hand, in the case of a cylindrical shape with a bottom, no magnetic field penetrates into the inner space of the bottom, depending on the magnetic field strength. Therefore, if a cylindrical shape with a relatively short axial length is desired for more efficient magnetic shielding, a cylindrical shape with a bottom is suitable. However, there are many cases where it is necessary to pass an object or living body from the outside to the inside of the cylinder, or in the opposite direction. That is, it is convenient for maintaining uniformity. In this case, it has a cylindrical shape with a partial bottom.

[0015] When all the normal conducting metal layers are made of high resistance metal, although the effectiveness as a heat dissipation medium or a bypass for superconducting current is reduced, it is possible to considerably suppress eddy currents caused by a fluctuating magnetic field and coupling current between superconducting layers. It can be used effectively as a magnetic shield for fluctuating magnetic fields.

[0016] In the case where the normal conductive metal layer is made up of at least one high resistance metal layer and one high conductivity metal layer each alternately laminated in the thickness direction, both of them are highly conductive, especially on the side bonded to the superconducting layer. If the metal layers have a sandwich structure with a high-resistance metal layer sandwiched between them, if the cross-sectional area ratio of the normal-conducting metal layers is the same, the area where large eddy currents flow will be reduced, and the coupling current between the superconducting layers will be reduced. A high resistance metal layer allows for a significant reduction. In addition, the effect as a heat dissipation medium or a superconducting current bypass is maintained to some extent. A sandwich structure in which a high-resistance metal and a high-conductivity metal are swapped is also effective for the same reason.

[0017] Considerable effects can be obtained even with two layers instead of the three-layer sandwich structure described above. Of course, it is also possible to increase the number of layers to four or five layers, and since the highly conductive metal layer is further divided, this is particularly effective in suppressing eddy currents, although it depends on the direction of magnetic flux.

In addition, when the highly conductive metal layer in the normal conductive metal layer is divided into a plurality of streak-like high-conductivity metal bands by streak-like high-resistance metal bands, not only the thickness direction of the cylindrical shape but also the By dividing also in the plane direction, there is a greater effect particularly on suppressing eddy currents. Since there is a high-resistance metal layer in the thickness direction, it also has the effect of suppressing the coupling current.

[0019] Also, for higher magnetic field shielding,
It is also possible to increase the thickness of the cylinder by preparing multiple cylinders with similar shapes but slightly different sizes and stacking them concentrically.

So far, we have discussed the case where the internal space of a cylindrical shape is shielded from a magnetic field from outside, but there is an object that generates a magnetic field such as a superconducting coil inside the cylindrical shape, and Of course, it is also possible to shield the space.

[0021]Also, so far we have discussed an arrangement in which the cylindrical axis is parallel to the direction of the external magnetic field or the internal magnetic field, but magnetic shielding is also possible when the axis is perpendicular or tilted between the two. .

[0022]

[Example] Example 1 As shown in Figure 1, 11 layers of high-resistance metal layers 3 made of Cu-Ni alloy with a thickness of 30 μm and 10 layers of superconducting layers 2 made of Nb-Ti alloy with a thickness of 30 μm are alternately arranged. Laminated to a thickness of 0.63
A bottomless cylindrical superconducting magnetic shield 1 having an inner diameter of 50 mm and a length of 100 mm was manufactured by a pipe cladding method and a subsequent rolling method. Also, for comparison with this, C
A bottomless cylinder of the same size and structure was also manufactured using the same process, only by replacing all the u-Ni alloys with Cu.

When these cylinders were placed as samples in a fluctuating magnetic field and their magnetic shielding characteristics were evaluated, it was found that the product of the present invention maintains superconductivity up to an excitation-demagnetization rate that is more than five times greater than that of the comparative product, which loses its superconducting state due to flux jumps. It was possible to maintain the state and exert a magnetic shielding effect. When a cylinder with the same size and structure and bottom was evaluated, there was a slight improvement in the maximum values of the leakage magnetic field and the shielding magnetic field, but the excitation and demagnetization speeds showed almost the same characteristics.

[0024] Also, Cu-M instead of Cu-Ni alloy
Almost similar results could be obtained using n alloy or Cu-Co alloy.

Even when Nb or Nb-Zr alloys were used as the superconducting layer, the maximum magnetic field capable of magnetic shielding was different, but the effects on the excitation/demagnetization rate were almost the same.

When the superconducting layer is an Nb-Ti alloy or a Nb-Zr alloy, a barrier layer for preventing diffusion made of Nb or Ta or an alloy of both is provided at the interface with the normal conducting metal layer. However, the effect on excitation speed was almost the same.

[0027] Nb3 Sn, V3 Ga, Nb3 Al
, Nb3 Ga, Nb3 Ge, Nb3 (AlGe)
In the A15 type intermetallic compound such as, a 5 μm thick Nb or V layer is placed at the center of the superconducting layer, and a 12.5 μm thick Cu alloy layer containing Sn is placed on both sides of the layer, for example, in the case of Nb3Sn. After disposing and molding, heat treatment was performed to obtain an A15 type intermetallic compound layer approximately several μm thick. In this case, very good magnetic shielding properties were obtained, but the effect on excitation and demagnetization speed was almost the same as when using the Nb-Ti alloy.

[0028] La-Sr-Cu-O system, Y-Ba-Ca
-O system, Bi-Sr-Ca-Cu-O system, Tl-Ba-
In the case of ceramic superconducting materials such as Ca-Cu-O type, the thickness of one layer was set to 30 μm, and after molding, heat treatment etc. were performed to obtain superconducting properties. In this case as well, the effect on the excitation/demagnetization rate was almost the same as in the case of using the Nb-Ti alloy.

[0029]

[Example 2] As shown in Fig. 2, Cu-
The thickness of the two layers sandwiching the Ni alloy high resistance metal layer 3 is 10 μm.
Nine normal conductive metal layers in a sandwich structure consisting of a highly conductive metal layer 4 of Cu with a thickness of m and 10 superconducting layers 2 of a Nb-Ti alloy with a thickness of 30 μm are laminated alternately, and the outermost surface is thick on both sides. A high-resistance metal layer 3 made of a Cu-Ni alloy with a thickness of 20 μm and a highly conductive metal layer 4 made of Cu with a thickness of 10 μm are laminated to have a thickness of 0.0 μm.
A bottomless cylindrical superconducting magnetic shield 1 having a diameter of 63 mm, an inner diameter of 50 mm, and a length of 100 mm was manufactured by a pipe cladding method and a subsequent rolling method. In addition, for comparison, a bottomless cylinder of the same size and structure was also manufactured using the same process, except that all the Cu-Ni alloys were replaced with Cu.

When these cylinders were placed as samples in a fluctuating magnetic field and their magnetic shielding properties were evaluated, it was found that the product of the present invention maintains superconductivity at an excitation-demagnetization rate that is more than twice as fast as the comparative product, which loses its superconducting state due to flux jumps. It was possible to maintain the state and exert a magnetic shielding effect.

[0031] Also, Cu-M instead of Cu-Ni alloy
Almost similar results could be obtained using n alloy or Cu-Co alloy.

Almost the same results could be obtained using Al or Ag instead of Cu. When a dilute Cu alloy, Al alloy, or Ag alloy was used instead of Cu, an improvement of 10% or more was observed in the excitation speed, but the maximum magnetic field value capable of magnetic shielding was slightly lowered.

Even when Nb or Nb-Zr alloys were used as the superconducting layer, the maximum magnetic field capable of magnetic shielding was different, but the effect on excitation/demagnetization speed was almost the same.

When the superconducting layer is an Nb-Ti alloy or a Nb-Zr alloy, a barrier layer for preventing diffusion made of Nb or Ta or an alloy of both is provided at the interface with the normal conducting metal layer. However, the effect on excitation speed was almost the same.

[0035] Nb3 Sn, V3 Ga, Nb3 Al
, Nb3 Ga, Nb3 Ge, Nb3 (AlGe)
In the A15 type intermetallic compound such as, a 5 μm thick Nb or V layer is placed at the center of the superconducting layer, and a 12.5 μm thick Cu alloy layer containing Sn is placed on both sides of the layer, for example, in the case of Nb3Sn. After disposing and molding, heat treatment was performed to obtain an A15 type intermetallic compound layer approximately several μm thick. In this case, very good magnetic shielding properties were obtained, but the effect on excitation and demagnetization speed was almost the same as when using the Nb-Ti alloy.

[0036] La-Sr-Cu-O system, Y-Ba-Ca
-O system, Bi-Sr-Ca-Cu-O system, Tl-Ba-
In the case of ceramic superconducting materials such as Ca-Cu-O type, the thickness of one layer was set to 30 μm, and after molding, heat treatment etc. were performed to obtain superconducting properties. In this case as well, the effect on the excitation/demagnetization rate was almost the same as in the case of using the Nb-Ti alloy.

[0037]

[Example 3] As shown in Fig. 3, Cu-
A high-resistance metal band 3a made of a Cu-Ni alloy is sandwiched between a high-resistance metal layer 3 made of a Ni alloy and has a thickness of 10 μm and a width of 1 mm.
9 normal conducting metal layers in a sandwich structure consisting of highly conductive metal strips 4a of Cu having a width of 1 mm and finely divided into stripes, and a superconducting layer 2 of Nb-Ti alloy having a thickness of 30 μm.
10 layers are laminated alternately, and the outermost surface is 20 μm thick on both sides.
High resistance metal layer 3 of Cu-Ni alloy and 10 μm thick C
0 thickness laminated mixed layer of u-Ni alloy band and Cu band
．． A bottomless cylindrical superconducting magnetic shield 1 having a diameter of 63 mm, an inner diameter of 50 mm, and a length of 100 mm was manufactured by a pipe cladding method and a subsequent rolling method. In addition, for comparison, a bottomless cylinder of the same size and structure was also manufactured using the same process, except that all the Cu-Ni alloys were replaced with Cu.

When these cylinders were placed as samples in a fluctuating magnetic field and their magnetic shielding characteristics were evaluated, it was found that the product of the present invention maintains superconductivity up to an excitation-demagnetization rate that is more than three times greater than that of the comparative product, which loses its superconducting state due to flux jumps. It was possible to maintain the state and exert a magnetic shielding effect.

[0039] Also, Cu-M instead of Cu-Ni alloy
Almost similar results could be obtained using n alloy or Cu-Co alloy.

Almost the same results could be obtained using Al or Ag instead of Cu. C instead of Cu
When u alloy, Al alloy, and Ag alloy were used, the excitation speed was improved by 10% or more, but the maximum magnetic field value capable of magnetic shielding was slightly lowered.

When Nb or Nb-Zr alloys were used as the superconducting layer, the maximum magnetic field capable of magnetic shielding was different, but the effect on excitation/demagnetization speed was almost the same.

When the superconducting layer is an Nb-Ti alloy or a Nb-Zr alloy, a barrier layer for preventing diffusion made of Nb or Ta or an alloy of both is provided at the interface with the normal conducting metal layer. However, the effect on excitation speed was almost the same.

[0043] Nb3 Sn, V3 Ga, Nb3 Al
, Nb3 Ga, Nb3 Ge, Nb3 (AlGe)
In the A15 type intermetallic compound such as, a 5 μm thick Nb or V layer is placed at the center of the superconducting layer, and a 12.5 μm thick Cu alloy layer containing Sn is placed on both sides of the layer, for example, in the case of Nb3Sn. After disposing and molding, heat treatment was performed to obtain an A15 type intermetallic compound layer approximately several μm thick. In this case, very good magnetic shielding properties were obtained, but the effect on excitation and demagnetization speed was almost the same as when using the Nb-Ti alloy.

[0044] La-Sr-Cu-O system, Y-Ba-Ca
-O system, Bi-Sr-Ca-Cu-O system, Tl-Ba-
In the case of ceramic superconducting materials such as Ca-Cu-O type, the thickness of one layer was set to 30 μm, and after molding, heat treatment etc. were performed to obtain superconducting properties. In this case as well, the effect on the excitation/demagnetization rate was almost the same as in the case of using the Nb-Ti alloy.

[0045]

[Effects of the Invention] As explained above, according to the superconducting magnetic shield of the present invention, the rate of excitation and demagnetization is high, which could not be handled by the conventional superconducting composite cylindrical shape that was bonded only to a highly conductive metal layer. A superconducting cylindrical shape with excellent stability of the superconducting state and high magnetic shielding properties even in a fluctuating magnetic field can be obtained, and its industrial utility value is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a bottomless cylindrical superconducting magnetic shield body in which superconducting layers and high-resistance metal layers are alternately laminated in the thickness direction.

[Fig. 2] A bottomless cylindrical superconducting magnetic shield body that has a sandwich structure in which both sides that are bonded to the superconducting layer are high conductive metal layers, and high resistance metal layers are sandwiched between them. FIG.

[Figure 3] A bottomless cylindrical superconducting magnetic shield having a structure in which the highly conductive metal layer in the normal conductive metal layer in Figure 2 is divided into a plurality of streak-like high-conductivity metal bands by streak-like high-resistance metal bands. FIG.

[Explanation of symbols]

1 Superconducting magnetic shield 2 Superconducting layer 3 High resistance metal layer 3a High resistance metal band 4 Highly conductive metal layer 4a Highly conductive metal strip

Claims (3)

[Claims] Claim 1: A cylindrical or bottomless cylinder in which at least one superconducting layer and one normal-conducting metal layer are alternately laminated in the thickness direction, there are no connecting parts in the circumferential direction and the axial direction, and the whole or part has a bottom. A superconducting magnetic shield body characterized in that the normal conductive metal layer is made of a high resistance metal, or at least one high resistance metal layer and one high conductivity metal layer are each alternately laminated in the thickness direction. . 2. The superconducting magnetic shield according to claim 1, wherein the highly conductive metal layer is divided into a plurality of stripes by striped high-resistance metal bands. 3. The high resistance metal is a Cu-Ni alloy, a Cu-
3. The highly conductive metal is either Mn alloy or Cu-Co alloy, and the highly conductive metal is Cu, Cu alloy, Al, Al alloy, Ag or Ag alloy. Superconducting magnetic shield.