JPS629278A - Super conductive shielding body - Google Patents

Abstract

PURPOSE:To increase a magnetic shielding effect by forming the laminating structure of the first kind super conductive body layer and a resin reinforcing layer. CONSTITUTION:A super conductive shielding body 20 is made as the laminating structure providing respectively the epoxy resin layer 21, 23 as a resin reinforcing layer on the front and back faces of the first kind super conductive body layer 22 of a Pb, etc. And this resin layers 21, 23 are formed as the epoxy plate impregating an epoxy resin on a glass base cloth. The mechanical strength of the shielding body as the whole in therefor big and the resin layers 21, 23 are made to protect chemically as well the super conductive body layer 22 and in case of the external part magnetic field being small the super conductive body layer 22 keeps a Meissner state and can show a high magnetic shielding effect.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a superconducting shield body used in a 5QLJID (superconducting quantum interference device) magnetometer and the like.

(Prior art and its problems) When measuring minute magnetic flux with the SQLJIDii force meter, for example when trying to detect a monoball (magnetic monopole), it is necessary to avoid the influence of induced electromagnetic waves from peripheral equipment and the earth's magnetism. Since it is necessary to block the magnetic field and perform precise measurements, some kind of magnetic shielding is required. Magnetic shields used for this purpose include those using high magnetic permeability alloys such as permalloy, and superconducting shields using superconductors.

Of these, the former requires a large magnetic shield made of a high magnetic permeability alloy to be provided around the cryogenic container filled with liquid helium, resulting in considerably high material and processing costs. Furthermore, even if a large amount of money is spent in this way, there is a drawback that the magnetic shielding effect is not very large.

On the other hand, in the latter method, a superconducting shield made of a superconductor such as lead (Pb) or niobium (Nb) is immersed in liquid helium to surround the pickup coil and the like. However, in type 1 superconductors such as PB, the magnetic field 1i (Hc) is large and the Meissner state is maintained even in high magnetic fields, so while it has the advantage of obtaining a high shielding effect, it has the advantage of being mechanically It is difficult to handle because it is soft, and pinholes can form due to scratches when used for a long period of time. It also has the disadvantage of being chemically unstable and easily susceptible to oxidation and other chemical modifications.

On the other hand, when using a type 2 superconductor such as Nb, the mechanical and chemical instability described above does not pose much of a problem, but due to the nature of the type 2 superconductor, the lower critical magnetic field ( Hc
Since l) is small, vortices invade at a relatively low magnetic field, and this vortex fluctuation causes distortion in the magnetic field inside the shield body. Furthermore, materials such as Nb are expensive and have poor workability.

(Purpose of the Invention) This invention was made to overcome the above-mentioned problems.It is mechanically and chemically stable, easy to handle, inexpensive, and has a high magnetic shielding effect. The purpose is to provide a superconducting shield.

(Means for achieving the object) In order to achieve the above object, a superconducting shield body according to the present invention is formed to have a laminated structure of a first type superconductor layer and a resin reinforcing layer. .

(Example) FIG. 1 is a diagram showing the basic configuration of a SQU ID magnetometer as an example of a device that can utilize the superconducting shield of the present invention. In the figure, a minute magnetic flux from a system to be measured (not shown) interlinks with a pickup coil 1 formed by a Nb 1DNb Ti ring or the like.
This minute magnetic flux is converted into magnetic flux of the input coil 2 connected to the pickup coil 1. The inductance of the 5QUID element 4 having the Josephson junction 3 changes in a ratm manner depending on the magnitude of the magnetic flux from the input coil 2.

On the other hand, from the RF (radio frequency) oscillator 5 to the tank circuit 6
The RF lightning current given to this 5QUID element 4
The modulated wave is amplified by the RF amplifier 7 and then detected by the detector 8, thereby measuring the magnetic flux of the system under test. Among these, the input coil 2.5 QUID The magnetic coupling system 9 including the element 4 and the tank circuit 6 and the pickup coil 1 are immersed in liquid helium LHe. It is formed as a superconducting shield as shown below.

FIG. 2 is a partial sectional view showing the structure of a superconducting shield according to an embodiment of the present invention.

In the figure, this superconducting shield body 20 is constructed as a laminated structure in which epoxy resin layers 21 and 23 are provided as resin reinforcing layers on both the front and back surfaces of a first type superconductor W422 such as Pb. . The epoxy resin layers 21 and 23 are formed as epoxy plates made by impregnating a glass base fabric with epoxy resin. However, the resin reinforcing layer is not limited to such an epoxy resin layer.
It can also be formed using RP (fiber reinforced plastic) or the like.

FIG. 3 is a partial perspective view of a cylindrical shield body 30 using the superconducting shield body having the above structure. this is,
It has a structure in which the hollow part 31 is surrounded by the above laminated structure so as to be suitable for shielding the magnetic coupling system 9 shown in FIG. 111.

As can be seen from these examples, the first type superconductor layer 2
2 is reinforced by the epoxy resin layer 21.23, so not only does the shield body as a whole have a high mechanical strength, but this epoxy resin layer 21.23 also chemically protects the 11th superconductor layer 22. That means you are doing it.

When the external magnetic field is small, the first type superconductor layer 22 maintains the Meissner state and exhibits a high magnetic shielding effect. However, the external magnetic field is the critical magnetic field Hc (10
'A/m ~ 125 G), it undergoes a phase transition to a normal conduction state and the shielding effect disappears, but since the normal external magnetic field is about several hundred mQ, there is almost no problem in practice.

By the way, as is well known, a superconducting shield has the property that external magnetic flux can penetrate even through extremely small gaps. For this reason, even when forming a superconducting shield according to the present invention, it is important to prevent gaps from forming in the connection portions between the first type superconductor layers.

FIG. 4 is a diagram showing an example of processing (end processing) for preventing such gaps. In the figure, a laminate 40 constituted by a first type superconductor 122a and epoxy resins 1i21a, 23a and a first type superconductor 1!2 are shown.
2b and a laminate 41 made up of epoxy resin layers 21b and 23b. In this case, the first type superconductor layers 22a and 22b are each stacked in the laminate 4.
By projecting from the 0° 41 end and folding them back along the outward direction of the epoxy tree 111121a in a state in which they are in close contact with each other, it is possible to prevent the generation of gaps. By performing such folding, end treatment can be achieved without performing difficult processing such as fusing the ends of the first type superconductor layers 22a and 22b.

In the above example, resin reinforcing layers are provided on both sides of the first type superconductor layer to enhance mechanical and chemical reinforcement and protection, but they may also be provided on only one side. The above laminated structure may also be used.

(Effects of the Invention) As explained above, according to the present invention, the layered structure of the type 1 superconductor layer and the resin reinforcing layer provides high shielding properties and economic efficiency of the type 1 superconductor. In addition, the reinforcing and protective effects of the resin reinforcing layer are added synergistically, making it mechanically and chemically stable and easy to handle.
A superconducting shield body that is inexpensive and has a high magnetic shielding effect can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the basic configuration of a 5QLIID magnetometer that can utilize the superconducting shield of the present invention;
The figure is a partial sectional view of an embodiment of the present invention, FIG. 3 is a diagram showing a cylindrical shield body formed using a superconducting shield body according to an embodiment of the present invention, and FIG. 4 is an example of end treatment. This is a diagram. 1...Pickup coil, 4...SQU ID
jll child, 21.21a, 21b, 23, 23a, 23
b... Epoxy resin layer 2.22a, 22b... Type 1 superconductor layer Patent applicant Shimadzu Corporation No. 4rj! J2b

Claims (2)

[Claims] (1) A superconducting shield body having a laminated structure of a type 1 superconductor layer and a resin reinforcing layer. (2) The superconducting shield according to claim 1, wherein the resin reinforcing layer is an epoxy resin layer.