JPH0498899A - Magnetic shielding device - Google Patents

Abstract

PURPOSE:To realize a practical shielding device taking the material of the cooling case of an oxide superconductor into consideration by a method wherein a space magnetically shielded as surrounded with the oxide superconductor is surrounded with material whose residual magnetic field is 10<-2> Gauss or below. CONSTITUTION:In a magnetic shielding device provided with an oxide superconductor 1, a space surrounded with the oxide superconductor 1 is magnetically shielded owing to the Meissner effect or the diammagnetism of the superconductor 1, but practically the space concerned is surrounded with the inner wall of a cooling case 2 which puts the superconductor 1 in a superconductive state. If the inner wall of the cooling case, a fixing device located in the space concerned, and the like are formed of ferromagnetic material prominent in residual magnetic field or material whose residual magnetic field is 10<-2> Gauss or above, they function as magnetic sources of a very small magnetic field and generate magnetic noises in a space of very weak magnetic field. Therefore, that taking the material of the cooling case of an oxide superconductor into consideration as above is important to make a magnetic shielding device provided with the oxide superconductor 1 excellent in practical use, in result the measurement of very weak magnetism such as biomagnetism can be improved in accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic shielding device, and more particularly to a magnetic shielding device comprising at least an oxide superconductor and a cooling container.

[Conventional technology]

Conventionally, a space surrounded by a ferromagnetic material such as permalloy or ferrite has been used for magnetic shielding. Furthermore, in recent years, many magnetic shielding devices have been proposed that utilize the diamagnetic properties of superconductors, which have been actively researched and developed. For example, in Japanese Patent Application Laid-Open No. 1-134998, it was proposed to place a superconductor at the innermost side of a space to be magnetically shielded, and in Japanese Patent Application No. 1-97197, the applicant proposed On the other hand, we proposed a magnetic shield cylinder having at least two layers in the order of substrate and superconducting layer from the magnetic source side.

On the other hand, although oxide superconductors, which are attracting attention for use in a wide range of fields, have a high critical temperature, they require cooling with liquid nitrogen, etc. in order to develop superconducting properties, and when applied to magnetic shielding devices. However, a cooling container is required.

[The problem that the invention attempts to solve! ! ] However, the current situation is that no development has been made regarding a practical magnetic shielding device, and consideration including cooling containers has not been made.

The present invention aims to provide a practical magnetic shielding device by considering a cooling container for the oxide superconductor in order to perform magnetic shielding using an oxide superconductor.

[Means for Solving the Problems] According to the present invention, in a magnetic shielding device consisting of at least an oxide superconductor and a cooling container, a space surrounded by the oxide superconductor and magnetically shielded has a residual magnetic field of IO) Gauss or less. A magnetic shielding device is provided, characterized in that it is surrounded by a material.

In the present invention, a space surrounded by an oxide superconductor and magnetically shielded usually refers to a space surrounded by an inner wall of a cooling container. That is, the oxide superconductor is generally placed in a cooling container, and the magnetically shielded space is a space surrounded by the inner wall of the cooling container.

For example, if a bottomed double-layer cylinder is used as a cooling container, the cylindrical oxide superconductor will have a space formed by an outer annular part and an inner annular part in which a cooling medium such as liquid nitrogen of the cooling container is held. The magnetically shielded space corresponds to a portion surrounded by the inner wall of the inner annular portion.

Furthermore, in the present invention, the inspection equipment installed in the magnetically shielded space and various devices for carrying in, holding and fixing the object to be inspected, etc. are made of materials with a residual magnetic field of 10-2 Gauss or less. It means something.

In a magnetic shielding device using an oxide superconductor, the space surrounded by the oxide superconductor is basically magnetically shielded due to the diamagnetic property of the Meissner effect of the oxide superconductor, but in reality, as described above, The space surrounded by the inner wall of the cooling container for developing superconducting properties is magnetically shielded.

In the present invention, the inner wall of the cooling container and the fixing device within the space are made of iron, which has a significant residual magnetic field, a ferromagnetic material at room temperature such as 5US430, or a ferromagnetic material at liquid nitrogen temperature such as Inconel 600. Of course, furthermore, for example, 5US310 5US304. inconel 625
Even materials that are normally considered non-magnetic, such as Incoloy 825 and Hastelloy, are magnetized by the earth's magnetism and have a magnetic field of 10-'~
If the inner wall of the cooling container or the fixing device in the space is made of a material with a residual magnetic field of 10-2 Gauss, it will become a magnetic source of a minute magnetic field, This finding has revealed that magnetic noise is generated in a magnetic field space, making magnetic shielding devices using oxide superconductors more practical and improving the accuracy of measuring weak magnetism such as biomagnetism.

In the present invention, materials having a residual magnetic field of 10 −2 Gauss or less include glass, resin, carbon, ceramics, plastics, and metals other than iron-based or nickel-based.

The cooling container that develops the superconducting properties of oxide superconductors is
In general, it is preferable to use a vacuum insulated container in terms of insulation efficiency, and in addition to maintaining a vacuum state as an insulating space, the part that holds a refrigerant such as liquid nitrogen must have sufficient strength at extremely low temperatures in the presence of a refrigerant. Must not be. Therefore, the materials constituting the inner wall of the cooling container include Cu, AI, brass, A1 alloy, Ti, and fiber reinforced plastic (FRP).
) is preferred, and it is also preferred to use a combination of other resins and foam materials known as heat insulating materials such as expanded polystyrene. In this case, not only the inner wall but the entire cooling container is made of FRP.
Constructed of Cu or brass, and further made of foamed steel.
A super insufflation such as a 1 itr film may be provided inside. In addition, the outer wall portion, etc. corresponding to the magnetic source side is not limited to the above-mentioned material (it may be made of ferromagnetic material, and only the inner wall portion is made of a material with the above-mentioned residual magnetic field of 10-” Gauss or less). In addition, two or more types of materials with a diameter of 10-'' Gauss or less may be used in combination, and can be appropriately selected depending on the application conditions.

The cooling container of a magnetic shielding device used in small-scale or research laboratories is a simple structure in which the cooling container is formed of AI or A1 alloy without providing a vacuum insulation space, and the outer periphery of the cooling container is covered with a heat insulating material. It can also be a mold.

In addition, the materials for the fixing devices in the magnetically shielded space need to be strong enough to withstand the fixing and holding of measuring instruments and the transportation and fixing of living bodies and other test objects, such as Cu, A, etc.
I, brass, A1 alloy, Ti, wood, glass, carbon, and plastics are preferred, and wood can also be used for measurements at room temperature.

Moreover, optical fibers such as glass can also be used as materials for signal processing from the measuring instrument and illumination.

In particular, the device in the magnetic shield close to the object to be inspected is preferably constructed of Cu, AI, wood, glass, and plastics with a residual magnetic field of 1O-5 Gauss or less, and more preferably wood, glass, and plastics. It is better to configure the

In the present invention, the oxide superconductor is placed in the cooling medium holding part of the cooling container described above, but a bulk body of the oxide superconductor may be used as the oxide superconductor, or a metal or the like may be used as the oxide superconductor. An oxide superconducting laminate in which oxide superconducting layers are stacked on a substrate can also be used.

When using an oxide superconducting laminate as the oxide superconductor, it is preferable to use 8g, Cu, brass, or Ti as the substrate and glass as the bonding material. For example, it is preferable that the layer arrangement of the laminate is oxide superconducting layer-Ag layer or oxide superconducting layer-Ag layer-glass layer-Cu/or brass layer from the magnetic source side. Further, when the oxide superconducting layer is arranged as the innermost layer on the side opposite to the magnetic source, that is, on the inner wall side of the cooling container, the material of the substrate etc. is not particularly limited.

In the present invention, when a material with a thickness of 1O-2 Gauss or less is used for the cooling container and the oxide superconducting laminate adopts a stacked arrangement form in which it is not the innermost layer on the inner wall side of the cooling container as described above, the oxide superconducting By using a material with lo-2 Gauss or less for the superconductor substrate as well, magnetic noise within the magnetic shielding device can be made extremely small. Whether or not to use materials with lo-2 Gauss or less for both the cooling container material and the oxide superconducting laminated substrate material can be appropriately selected depending on the usage conditions such as the application of the magnetic shield.

The oxide superconductor in the present invention is not particularly limited, and is, for example, an M-Ba-Cu-0 based compound in which H is Sc, Y, La, Eu, Gd, Er,
A rare earth oxide superconductor having a multilayer perovskite structure containing one or more rare earth elements selected from rank nitrides such as Yb and Lu, and also, for example, BizSrzCalCu.
Any oxide superconductor may be used, such as a bismuth-based (Bi-based) superconductor having a composition represented by zOX, Bi, or 5rzCazCu-JOX.

〔Example] Hereinafter, the present invention will be explained in detail with reference to Examples.

However, the present invention is not limited to the following examples.

[Production of oxide superconductor A 1 BizSrzCa, Cu20 was applied to the outer surface of an Ag cylinder with an outer diameter of 1100aφ, a height of 450mm, and a thickness of 500μm.
1 was spray-coated to form a Bi-based superconducting layer, partially melted at 890°C for 30 minutes in an oxygen atmosphere, and then gradually cooled to 850°C at a cooling rate of 1'c/min.
Crystallization was performed at 850°C for 15 hours. Thereafter, the atmosphere was changed to nitrogen, and oxide superconductor A was obtained by heat treatment at 400° C. for 10 hours. The layered superconducting layer of the obtained oxide superconductor A was 300 μm.

[Manufacture of oxide superconductor B] YBa2Cu3O7 calcined powder was granulated to an average particle size of 50 μm using a spray dryer, preformed into a cylindrical shape using a mold press, and then hydrostatically pressed at a pressure of 2.5 t/cd. Molded. The obtained molded body was heated at 960°C in an oxygen atmosphere.
After baking for 6 hours at 500'C, cooling rate 1
It was slowly cooled for 67 minutes and heat-treated at 500° C. for 10 hours to obtain an oxide superconductor B in the form of a cylindrical fired body with an inner diameter of 100 mmφ, a height of 450 mm, and a thickness of 8 m.

[Production of oxide superconductor C 1 After applying a glass-containing solvent to the inside of a cylindrical base made of Inconel 625 with an outer diameter of 200 mφ, a height of 600 mm, and a thickness of 1.5 mm by a spray method, Thickness of the entire surface is 30
The cylindrical substrate was covered with a Heg foil of 0 μm, and baked in the air at 900° C. for 2 hours while the Ag foil was mechanically pressed against the Inconel substrate to bake the Ag foil onto the inner peripheral surface of the cylindrical substrate. Also, A
The abutting portions of the G foils were joined by TIG welding, and the entire inner peripheral surface of the base was covered with Ag foil. Next, a slurry containing BizSr, Ca, and Cu2O3 was spray-coated onto the Ag foil to form a Bi-based superconducting layer, and after partially melting at 890"C for 30 minutes in an oxygen atmosphere, the slurry was heated at 850°C.
c′l! : was slowly cooled at a cooling rate of 1"C/min and crystallized at 850°C for 15 hours. Thereafter, the
Oxide superconductor C was obtained by heat treatment at °C for 10 hours. The Bi-based superconducting layer of the obtained oxide superconductor C has a thickness of 300 μm.
Met.

[Manufacture of oxide superconductor C] The same method as that used to obtain the above oxide superconductor C was applied to the outer peripheral surface of a cylindrical base made of Inconel 625 with an outer diameter of 100 wφ, a height of 600 mm, and a thickness of 1.5 mm. An oxide superconductor was obtained by baking the Ag foil and further forming a 300 μm Bi-based superconducting layer.

[Manufacture of Cooling Container I Vacuum insulation container with a bottomed double annular body consisting of an outer annular part made of Cu with an outer diameter of 210 a + m and a thickness of 15 + a + a, and an inner annular part with an outer diameter of 95 cm and a thickness of 5 mm [Cooling] Container al, an outer annular part made of AI with an outer diameter of 300 m and a thickness of 20 m, an outer diameter of 90 m,
A simple insulated container [cooling container b] which is a bottomed double annular body consisting of an inner annular part with a thickness of 10m5+ and whose outer and inner surfaces are covered with polystyrene foam, and an outer diameter of 30 made of 5US304.
The outer annular part has a diameter of 90 m and a thickness of 10 m.
A vacuum insulated container [cooling container c1] having a bottomed double annular body consisting of an inner annular portion of +ssO was manufactured.

Examples 1 to 5 and Comparative Examples 1 to 3 Magnetic noise in the magnetic shielding device whose cross-sectional view is shown in FIG. 1 was measured. In FIG. 1, an oxide superconductor 1
After injecting liquid nitrogen 6 into the cooling medium holding part 5 formed by the outer wall 3 and inner wall 4 of the double annular cylindrical cooling container 2, the container was immersed in the liquid nitrogen. After that, a triaxial SQU is placed in the magnetically shielded space 7 surrounded by the inner wall of the cooling container.
ID (Superconducting Quantum)
m Interference Device: Superconducting quantum interference device) An alternating magnetic field with a frequency of 4 to 100 Hz was measured using a magnetometer 8, and the maximum value of the measured alternating magnetic field was defined as magnetic noise. The results are shown in Table 1.

The oxide superconductors and cooling containers manufactured above were used in the combinations shown in Table 1.

Table 1 From the above Examples and Comparative Examples, in the combination of a cooling container and an oxide superconductor using a material of 10-" Gauss or less, the magnetic noise is extremely small, 1O-4 Gauss or less. Even if the oxide superconducting layer is not the innermost layer on the inner wall side of the cooling vessel and the substrate is an oxide superconductor of Inconel 625, if the inner wall of the cooling vessel has an AI with a residual magnetic field of 10-'' Gauss or less, In (Example 5),
It can be seen that although the magnetic noise is larger than that of lo-4 and other examples, the magnetic noise is significantly smaller than that of the combination with the cooling container using 5US304 of Comparative Example 3.

[Effects of the Invention] The magnetic shielding device of the present invention, in a combination of an oxide superconductor and a cooling device, forms a space surrounded by a material with a residual magnetic field of IO4 Gauss or less, thereby reducing the amount of energy within the space. Magnetic noise can be made extremely small, making it highly practical and industrially useful.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of a magnetic shielding device that is an embodiment of the present invention.

Claims (2)

[Claims] (1) In a magnetic shielding device consisting of at least an oxide superconductor and a cooling container, the space surrounded by the oxide superconductor and magnetically shielded is surrounded by a material with a residual magnetic field of 10^-^2 Gauss or less. A magnetic shielding device characterized by: (2) The space is made of Ag, Al, Al alloy, Cu, brass,
2. The magnetic shielding device according to claim 1, wherein the magnetic shielding device is surrounded by one or more of Ti, plastic, carbon, wood, and glass.