JP2781837B2 - Magnetic field stabilization method and magnetic field stabilizer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for stabilizing an extremely high level constant magnetic field by utilizing the characteristics of a superconductor, and an effective magnetic field stabilizer therefor.

(Prior Art) Recently, many superconductors and the like exhibiting a superconducting state at a high temperature have been discovered, and applied research has been earnestly promoted in various fields. The field of application utilizing magnetic properties also plays an important role, and the present applicant has conducted applied research on superconducting magnetic shields and superconducting magnets, and has already proposed some of the results.

(Problems to be Solved by the Invention) On the other hand, with the rapid progress of the superconductor as described above, various measuring instruments and the like related thereto have been required to have higher accuracy. For example, when detecting a small magnetic signal emitted from a subject placed in a high magnetic field, if the subject is not completely placed in a constant magnetic field environment, the detection purpose is caused by minute magnetic field noise such as terrestrial magnetism. The signal will be canceled. Conventionally, a permanent current switch has been used as a means for producing a constant magnetic field for such a purpose, but even when used in a permanent mode, the strength of the magnetic field decreases over time, and a complete uniform magnetic field cannot be obtained. Was.

In the process of searching for the magnetic properties of various superconductors, the present inventors set a superconductor other than the first type superconductor in a certain mode of change of the magnetic field, and in the vicinity of the superconductor or in the vicinity thereof. It has been found that the surrounding space is maintained at a constant magnetic field stabilized at an extremely high level, and a magnetic field stabilizing method and an effective magnetic field which are extremely suitable for detecting the small magnetic signal based on the knowledge. The ballast has been completed, and the present invention is not provided herein.

(Means for Solving the Problems) The magnetic field stabilizing method of the present invention for achieving the above object is as follows.
When exposed to a magnetic field having a strength equal to or greater than the maximum magnetic shielding amount, a sheet-like or cylindrical molded body that includes a super-electric body that transitions to a mixed state as a constituent member is reduced in intensity from zero to the mixed-state region. It is placed in a variable magnetic field generator, and when the intensity of the environmental magnetic field by the magnetic field generator is increased to reach a mixed state area and thereafter the magnetic field intensity is reduced, a fixed intensity change of the environmental magnetic field is performed. The gist of the invention is that the vicinity of the molded body or its internal space is maintained at a constant magnetic field within the range.

The magnetic field stabilizer according to claim 2 is for effectively performing the above method, and includes a superconductor that transitions to a mixed state when exposed to a magnetic field having a strength greater than the maximum magnetic shielding amount. And a magnetic field generator which surrounds the molded body and can vary the strength of the magnetic field from zero to the mixed state region.

As a molded article used for the ballast, the present applicant has proposed in the past (JP-A-61-183979, JP-A-63-183979).
No. 233577, Japanese Patent Application No. 63-200795, Japanese Patent Application No. 63-132448
, Japanese Patent Application No. 63-250546 and Japanese Patent Application No. 63-307630), which have substantially the same configuration as some superconducting magnetic shields. Specifically, a superconducting thin film layer and a metal sheet are used. A ring-shaped disc-shaped composite sheet comprising a superconducting thin film layer having an annular width of 2 mm or more and a metal layer having good thermal and electrical conductivity, and a ring-closed disc having the same shape as the composite sheet A sheet-like material formed by laminating a gap material, a cylindrical metal core material open at both ends or one end thereof, and a peripheral body of the core material being covered and electrically closed at least about the axis of the core material. And a cylindrical object made of a superconducting film.

In the above case, as a superconducting thin film layer, in terms of the relationship between the thickness and the magnetic shielding effect, a curve is drawn such that the magnetic shielding effect rapidly increases from the origin as the thickness increases, and then gradually increases with a gentle gradient. If the thickness is less than or equal to the thickness corresponding to the inflection point at which the transition to the gradually increasing state is made in the characteristic curve of the magnetic shielding effect, the maximum magnetic shielding amount is desirably high and preferably employed. In this case, it is desirable that a large number of superconducting thin film layers and metal layers are alternately laminated.

If the sheet-like material has a large number of small holes penetrating in the thickness direction, the electromagnetic shielding effect is added to the superconducting shielding effect, and the maximum magnetic shielding amount is increased, so that the above-described desirable effect is achieved.

Further, as the superconducting film in the case of (1), it is also possible to apply the sheet body obtained in (1).

In this case, the reason why the ring width of the superconducting thin film layer is set to 2 mm or more is that an eddy current is generated on the ring band of the superconducting thin film layer when placed in a magnetic field, and this eddy current causes complete diamagnetism. And to induce diamagnetism. That is,
If it is less than 2 mm, the eddy current is less likely to be generated, and the magnetic properties in a mixed state due to complete diamagnetism and diamagnetism tend to decrease, and workability is poor.

The superconductor which is the substance of the superconducting thin film layer and the superconducting film as a constituent member of the above-mentioned and molded bodies is a superconductor other than the first-class superconductor, and is exposed to a magnetic field having a strength not less than the maximum magnetic shielding amount. It has the property of transitioning to a mixed state when it occurs. Specifically, niobium metal, niobium compounds _{[NbN, NbC, Nb 3 Sn,} Nb 3 Al, Nb 3 Ga, Nb 3 G
e, Nb ₃ (AlGe), NbN / TiN mixed crystal, etc.], niobium alloy (Nb-Ti alloy, Nb-Zr alloy, etc.), vanadium compound and vanadium alloy (V ₃ Ga), ceramic superconducting material ( Ba-Y-Cu-O-based compound, La-Sr-Cu-O-based compound,
Bi-Sr-Ca-Cu- O -based compound, Tl-Ba-Ca-Cu -O type compound) or Chevrel superconductor (PbMo ₆ S _6, etc.) and the like are employed.

Such a thin film or film of a superconductor is desirably laminated and integrated with a metal layer as described above, and the lamination and integration of the metal layer and the superconductor layer is performed by sputtering or rolling a superconducting sheet. When a metal is electrodeposited on the surface and the electrodeposited composite is further multilayered, the composite is immersed in a low-melting metal bath and then pressed.
Further, as the metal layer, a metal having good thermal conductivity and electric conductivity such as copper, aluminum, nickel, stainless steel, titanium, niobium and a niobium-titanium alloy is employed.

As other modified forms of the above-mentioned molded body, those having substantially the same configuration as that disclosed in the above-mentioned prior application are employed.

As the magnetic field generator, a superconducting magnet or a normal conducting magnet can be used.

(Operation) In describing the operation of the magnetic field stabilizing method and the magnetic field stabilizer of the present invention, the basic principle will be described with reference to FIG. FIG. 6 shows the intensity of the environmental magnetic field Bo (X-axis) and the intensity of the magnetic field Br (in the vicinity of or inside the superconductor other than the first type superconductor placed in the environmental magnetic field). Y axis)
FIG. 4 is a magnetic characteristic curve diagram showing a relationship with the graph.

In the figure, Br is zero while increasing Bo and reaching B1 (point A). This is due to the perfect diamagnetism (Meissner effect) of the superconductor. Zero to B1 is a region where the environmental magnetic field is completely cut off by the superconductor, and B1 is the lower critical magnetic field (Hc1), that is, the maximum magnetic shielding. Quantity. Then Bo
When is made larger than B1, the magnetic field partially penetrates, and Br is detected by the detector. This is a region where the complete diamagnetism and diamagnetism are mixed, and eventually reaches the critical magnetic field Hc2 where the environmental magnetic field and the penetration magnetic field are equal. This upper critical magnetic field Hc2
When the ambient magnetic field Bo stops increasing at the point of exceeding, and decreasing it in reverse, magnetic flux is trapped in the superconductor, so Br draws a curve like Hc2 ~ D, and Bo becomes zero Then, the magnetic flux of B3 is trapped in the superconductor. When the direction of the magnetic field of Bo is applied in the opposite direction, Br detects the magnetic field in the opposite direction, and a similar curve is drawn in the third quadrant of FIG. 6, and the above operation is performed while maintaining the superconducting state. By repeating, a closed loop curve including a broken line portion is drawn.

And the increase of Bo is stopped at any B2 in the mixed state area,
If Bo is to be decreased from this point, the superconductor attempts to increase by the change in the environmental magnetic field, and as a result, Br changes from point B to point C.
Is maintained at B4 until Such a behavior is considered to be based on the principle of flux linkage invariance. The present inventors have proposed that B
Focusing on the behavior between -C, as a result of repeating many tests,
Extremely high accuracy of 1/10 ^{10 in} B4, BC
It was found that the gap was completely diamagnetic.
Therefore, even if the external magnetic field fluctuates between B and C, the vicinity of the superconductor or its internal space is completely maintained at the constant magnetic field B4.

Thus, the present invention utilizes the above-described basic principle, and collects in advance the above-mentioned magnetic characteristic data of a molded body having each superconductor as a constituent member, and uses this data as a magnetic field generator capable of varying the magnetic field strength. And maintained in a superconducting state (extremely low temperature state by liquid helium or liquid nitrogen), and then increase Bo to the environmental magnetic field strength B2 corresponding to a desired constant magnetic field B4, and then reduce Bo. Then, the vicinity or the internal space of the molded body is maintained at a constant magnetic field of B4 strength. Therefore, if a sample to be measured according to various purposes is placed in the vicinity of or inside the molded body and a minute magnetic signal for the purpose is detected, the change in the magnetic field due to the fluctuation of the applied current of the magnetic field generator can be achieved. Alternatively, magnetic noise or the like added from the outside is completely blocked by the molded body, and only a change in a target minute magnetic signal can be accurately detected.

(Example) Next, an example of the present invention is described based on an accompanying drawing. FIG. 1 is a schematic longitudinal sectional view showing an application example of the magnetic field stabilizer of the present invention, and FIGS. 2 to 5 are perspective views showing various aspects of a molded body employed therein.

In FIG. 1, a superconducting magnet 2 is provided in a low-temperature container 1, and leads 21, 21 for applying a current are led out of the superconducting magnet 2. In the internal space of the superconducting magnet 2, the formed body 3 configured as described above is arranged. The cryogenic vessel 1 has a double vacuum layer 11, 11 inside and outside.
Liquid nitrogen 4 is filled between the vacuum layers 11, 11 and liquid helium 5 is filled in the low temperature vessel 1.
The superconducting magnet 2 and the compact 3 are maintained in a superconducting state.

FIG. 1 shows that the molded body 3 is a cylindrical body as shown in FIG. 2, a sample 6 to be measured is placed inside the cylinder of the cylindrical molded body 3, and the sample to be measured is placed near the test 6 to be measured. A detector 7 such as a Hall element for detecting a small magnetic signal generated by the detector 6 is provided.

Thus, in the apparatus arranged as described above, a current is applied to the superconducting magnet 2 to generate a magnetic field in its internal space, and the molded body 3 having the superconductor as a component is in a mixed state. Increase the strength of the magnetic field. The strength of the environmental magnetic field (corresponding to B4 in FIG. 6) corresponding to a desired constant magnetic field (corresponding to B4 in FIG. 6) corresponding to the measurement purpose is read from the magnetic characteristic curve prepared in advance for each molded body 3, and the superconducting magnet is read. 2 increases the read field until it matches B2. In this state, the strength of the environmental magnetic field is slightly reduced, and the molded body 3 is made to protrude into a region between B and C shown in FIG. Once in the area between B and C, even if the environmental magnetic field fluctuates between B and C, the internal space of the molded body 3 is maintained at the constant magnetic field of B4 as described above. Therefore, in this state, the detector 7 can accurately read only the change in the minute magnetic signal of the sample 6 to be measured.

3 to 5 show various aspects of the molded body 3,
FIG. 3 shows a cylindrical body with one end closed, FIG. 4 shows a disk-shaped sheet body, and FIG. 5 shows an annular sheet body. All of them, including the open-ended molded body 3 shown in FIG. 2, are prepared in the same manner as the method disclosed in the above-mentioned prior application. In the case of the molded body shown in FIGS. 2 and 3,
Although the measurement sample 6 is placed in the cylinder, in the case of the molded body shown in FIG. 4, near the surface opposite to the direction of the magnetic flux of the environmental magnetic field,
In the case of the compact shown in FIG. 5, it is placed in the ring.

(Effects of the Invention) As described above, in the magnetic field stabilizing method and the magnetic field stabilizer of the present invention, the vicinity of the molded body or the internal space thereof is stabilized at an extremely high level within the fixed intensity change range of the environmental magnetic field. Is maintained at a constant magnetic field. Therefore, even if there is a magnetic field change or external magnetic noise caused by a magnetic field generator due to a change in the applied current, this is completely shut off, and the vicinity of the molded body or its internal space is an environment that is extremely suitable for detecting minute magnetic signals and the like. Become.

The present invention, which has such remarkable effects, greatly contributes to expansion of the field of use of superconductors and high precision of related devices and various devices in other fields, and its useful value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an application example of the magnetic field stabilizer of the present invention, FIGS. 2 to 5 are perspective views showing various aspects of a molded body employed therein, and FIG. FIG. 4 is a magnetic characteristic curve diagram showing a relationship between the strength of a magnetic field detected in the vicinity of or within the internal space of a superconductor placed in the environmental magnetic field. (Explanation of symbols) 1... Low-temperature container, 2... Magnetic field generator (superconducting magnet), 3... Molded object, 6... Sample to be measured, 7.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaru Inoue 1-5 Doyama-cho, Kita-ku, Osaka-shi, Osaka High-pressure gas industry Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) H01F 6 / 00

Claims (8)

(57) [Claims] 1. A sheet-like or cylindrical molded body containing a superconductor which moves into a mixed state when exposed to a magnetic field having a strength equal to or greater than the maximum magnetic shielding amount as a constituent member from zero to a magnetic field ranging from the mixed state region. Is placed in a magnetic field generator capable of varying the intensity of the magnetic field, and when the intensity of the environmental magnetic field by the magnetic field generator is increased to reach a mixed state area and then the intensity of the magnetic field is reduced, the environmental magnetic field is reduced. A method for stabilizing a magnetic field, wherein a magnetic field in the vicinity of or within the molded body is maintained at a constant magnetic field within a predetermined range of intensity change. 2. A sheet-like or cylindrical molded article containing a superconductor as a constituent member, which transitions to a mixed state when exposed to a magnetic field having a strength not less than the maximum magnetic shielding amount; A magnetic field generator capable of varying the strength of the magnetic field over the state region, increasing the strength of the environmental magnetic field by the magnetic field generator, reaching the mixed state region, and thereafter reducing the strength of the magnetic field. A magnetic field stabilizer in which the vicinity of the molded body or its internal space is maintained at a constant magnetic field within an intensity variation range where the environmental magnetic field is sometimes fixed. 3. The magnetic field stabilizer according to claim 2, wherein said molded body is a sheet-like material in which a superconducting thin film layer and a metal sheet are integrally laminated. 4. A laminated closed disk-shaped composite sheet comprising a superconducting thin film layer having an annular width of 2 mm or more and a metal layer having good thermal conductivity and electric conductivity, and a closed ring having the same shape as the composite sheet. 3. The magnetic field stabilizer according to claim 2, wherein the magnetic field stabilizer is a sheet-like material formed by laminating a disk-like gap material. 5. The superconducting thin film draws a curve in the relationship between the thickness and the magnetic shielding effect such that the magnetic shielding effect rapidly increases from the origin as the thickness increases, and then gradually increases with a gentle gradient. 5. The magnetic field stabilizer according to claim 3, wherein the thickness of the magnetic field stabilizer is equal to or less than a thickness corresponding to an inflection point at which the transition to the gradually increasing state occurs in the characteristic curve of the magnetic shielding effect. 6. The magnetic field stabilizer according to claim 3, wherein the sheet has a plurality of small holes penetrating in a thickness direction. 7. A superconducting body comprising: a cylindrical metal core material having both ends or one end open; and a superconducting body which is covered with a peripheral body of the core material and is electrically closed at least around an axis of the core material. 3. The magnetic field stabilizer according to claim 2, wherein the magnetic field stabilizer is a cylindrical member made of a film. 8. The magnetic field stabilizer according to claim 7, wherein the superconducting film is formed of the sheet according to claim 3.