WO2007148571A1

WO2007148571A1 - Pulse magnetization method of bulk superconductor

Info

Publication number: WO2007148571A1
Application number: PCT/JP2007/061859
Authority: WO
Inventors: Teruo Matsushita; Edmund Soji Otabe
Original assignee: Kyushu Institute Of Technology
Priority date: 2006-06-19
Filing date: 2007-06-13
Publication date: 2007-12-27
Also published as: JP4769301B2; JPWO2007148571A1

Abstract

A pulse magnetization method of a bulk superconductor characterized in that a copper material is arranged on upper and/or lower portion of the bulk superconductor when the bulk superconductor is magnetized by pulse magnetization. Magnetization can be controlled by varying the thickness of the copper material used in the method. For using the bulk superconductor not as an electric conductor but as a permanent magnet having a very large magnetic force, the bulk superconductor can be magnetized efficiently by a simple pulse magnetization method.

Description

Specification

Pulse magnetization of Balta superconductors

Technical field

[0001] The present invention relates to a pulse magnetization method for a Balta superconductor to magnetize a Balta superconductor to make a permanent magnet.

Background

[0002] The discovery of high-temperature superconductors has pioneered application fields in the form of Balta (bulk) superconductors! Conventional metal superconductors have been limited to applications at extremely low temperatures near absolute zero. In other words, conventional metal superconductors cannot be applied to Balta because the specific heat of the material is too low, and the application has been realized only in the form of wire or thin film. In contrast, high-temperature superconductors have a much higher specific heat than the liquid nitrogen boiling point, so the instability of the superconductor does not occur so much and the superconductor can be applied with Balta. It was. And the most promising is an application field where magnetizing is used instead of permanent magnets. A normal permanent magnet cannot generate a magnetic flux density of several hundreds mT (Tesla) (several thousand G (Gauss)) at most, but a Nore superconductor can generate a magnetic flux density as high as 17T. Successful.

[0003] For example, in the following Non-Patent Document 1, a high-temperature Balta superconductor has succeeded in generating a magnetic flux density of 17T at 29K. This magnetic flux density is achieved by a method of cooling in a magnetic field. In other words, the Balta superconductor is kept at a temperature higher than the critical temperature, and a high magnetic flux density is applied from the outside using a superconducting magnet. In this state, the Balta superconductor is cooled (cooled in a magnetic field) to a superconducting state so that the magnetic flux density is maintained. However, this method has a drawback that a large superconducting magnet is always required for magnetization. Therefore, a simpler magnetization method is desired.

Non-Patent Literature l: M. Tomita and M. Murakami, Nature, vol. 421, pp. 517-520 (2003) [0004] Pulse magnetization is attracting attention as a simple method of generating magnetic flux density in a Balta superconductor. (For example, see Patent Document 1). In this method, a pulse current is passed through a copper coil near the Balta superconductor to magnetize it. In this method, compared to superconducting magnets Although there is an advantage that it can be magnetized by a simple and simple device, the magnitude of the magnetic flux density to be magnetized is about several τ, which is low compared to cooling in a magnetic field. The reason for the small trapped magnetic flux density is that when the magnetic flux density is magnetized from the outside to the superconductor, it is pulsed, so the heat generated by the movement of the magnetic flux lines is high, and the superconductivity is high. This is because the body temperature rises for a moment, the force that supplements the magnetic flux weakens, and the magnetic flux that once enters the interior cannot be captured with the decrease of the pulse magnetic field and escapes to the outside. In other words, a husband who suppresses heat generation is necessary. Therefore, a device for efficiently removing the generated heat has been proposed (see Patent Documents 2 and 3). In this method, a thick disc-shaped bulk superconductor is sandwiched by ring-shaped copper to release heat, but the achieved magnetic flux density is still insufficient.

Patent Document 1: Japanese Patent Laid-Open No. 10-154620

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-319797

Patent Document 3: Japanese Patent Laid-Open No. 2005-294471

Disclosure of the invention

Problems to be solved by the invention

[0005] The present invention efficiently magnetizes a Balta superconductor by a simple pulse magnetizing method in order to use it as a permanent magnet having a very large magnetic force, rather than using a Balta superconductor as a conductor. It is intended to provide a method.

Means for solving the problem

[0006] Of the present invention, the invention described in claim 1 (hereinafter referred to as "claim 1" etc.)

This is a pulse magnetizing method for a Balta superconductor, characterized in that a copper material is placed on the upper part and Z or the lower part of the Balta superconductor when the Nore superconductor is magnetized by the pulse magnetizing method. For example, when direct cooling by a refrigerator is used to cool a Balta superconductor, the upper or lower force of the Norec superconductor is often cooled, so the shape of the copper material used for the cooling Can be considered. If the side force is cooled, copper material may be placed on the top and Z or bottom of the Balta superconductor.

[0007] The invention described in claim 2 of the present invention controls the magnetization of the Balta superconductor according to claim 1, wherein the magnetization is controlled by changing the thickness of the copper material. It is. [0008] Of the present invention, the invention described in claim 3 is the pulse magnetization method of the Balta superconductor according to Claim 1 or 2, wherein the Balta superconductor is a disk type and the copper material is a disk shape. is there.

[0009] Of the present invention, the invention described in claim 4 is the pulse of the Balta superconductor according to any one of Claims 1 to 3, wherein the Balta superconductor contains a powdered rare earth 123 oxide superconductor. It is a magnetizing method.

[0010] Among the present inventions, the invention described in claim 5 is the one described in any one of claims 1 to 4, wherein the invention is arranged in direct contact with or thermally connected to the Balta superconductor. Balta This is a pulse magnetization method for superconductors.

[0011] In the invention described in claim 6 of the present invention, the shape of the copper material is different between the upper and lower surfaces of the Balta superconductor. The Balta superconductor according to any one of Claims 1 to 5, This is the pulse magnetization method.

[0012] Of the present invention, the invention described in claim 7 is the pulse magnetization method of the Balta superconductor according to any one of claims 1 to 6, wherein the copper material is a copper plate.

[0013] In the invention described in claim 8 of the present invention, the coil for excitation is arranged around the Balta superconductor and the copper material. The force of the Balta superconductor according to any one of Claims 1-7. This is a pulse magnetization method.

The invention's effect

[0014] According to the present invention, the magnitude of the magnetic flux density magnetized on the Balta superconductor by the pulse magnetization method is increased.

In the pulse magnetization method according to the method of the present invention, the movement of the magnetic flux lines is controlled, the heat generated by the movement of the magnetic flux lines is suppressed, and the magnetization effect is improved. Further, in the present invention, by changing the thickness of the copper material, it is possible to control the movement of the magnetic flux lines and improve the magnetization effect.

Brief Description of Drawings

FIG. 1 is a diagram showing a method of pulse magnetization.

FIG. 2 is a diagram showing a model in the finite element method.

FIG. 3 is a diagram showing a model for performing a numerical simulation by a finite element method and a calculation example.

FIG. 4 is a diagram showing a model for performing a numerical simulation by a finite element method and a calculation example. FIG. 5 is a diagram showing the results of a simulation of time dependence of the penetration depth of magnetic flux.

FIG. 6 is a view showing a state in which copper plates having different thicknesses are arranged on the upper and lower surfaces of a Balta superconductor in the present invention.

Explanation of symbols

[0016] 1 Copper plates with different thicknesses at the periphery and center

2 Balta superconductor

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The Balta superconductor is one of the utilization forms of the oxide superconductor, and means a lump (balta-like) superconductor. In general, when magnetizing a Balta superconductor (making it a magnet), it is cooled and magnetized in a superconducting coil that produces a strong magnetic force, but an expensive superconducting coil is required. This is called cooling in a magnetic field as described above. On the other hand, the pulse magnetization method can be performed using a pulse coil using inexpensive copper wire. For example, the pulse magnetization method is a powerful magnet (4-5 Degree). When a strong pulsed magnetic field is applied, a strong magnetic flux density momentarily invades, but Balta generates heat rapidly. As the temperature rises, the superconducting properties of Balta superconductors deteriorate, so the magnetic flux density escapes and the final trapped magnetic flux density also decreases.

[0018] As described above, since the cause of the low magnetic flux density by the Norse magnetization method is heat generation, the present invention is devised to suppress the heat generation itself. For this purpose, the present invention is characterized in that when the Balta superconductor is magnetized by the pulse magnetizing method, a copper material is disposed on the top and bottom or bottom of the Balta superconductor. For example, if a copper material such as a copper plate is placed on the upper or lower part of the Balta superconductor or on both the upper and lower parts, and the pulse magnetization is performed, the movement of the magnetic flux lines is controlled and accompanied by the movement of the magnetic flux lines. Heat generation is suppressed and the effect of magnetization is improved. In the present invention, by changing the thickness of the copper material, it is possible to control the movement of the magnetic flux lines in a fine manner and improve the magnetization effect.

[0019] In pulse magnetization of a Balta superconductor, it is thought that it is necessary to slowly move the magnetic flux lines because the magnetic flux lines move too fast and generate heat. To slow down the flux line changes, you can prepare a large coil and a large capacitor bank. In that case, the magnetizing device becomes too much force, and the purpose of easily magnetizing cannot be achieved. Therefore, in the present invention, a copper material, for example, a copper plate, is disposed on the upper or lower part of the Balta superconductor, or on both the upper and lower parts. The presence of this copper plate causes a shielding current to flow in the copper plate against a sudden change in the pulse magnetic field so as to prevent the magnetic flux density from increasing. Therefore, the movement of the magnetic flux lines becomes much slower, and heat is generated in the Balta superconductor. Can be suppressed. Of course, copper plates can also be expected to release heat generated by Balta superconductors.

[0020] The moving speed of the magnetic flux lines can be controlled by changing the thickness of a copper material, for example, a copper plate. For example, if it is desired to increase the moving speed of the magnetic flux lines near the surface, the shielding effect is reduced by reducing the thickness of the copper plate in the vicinity, and as a result, the moving speed of the magnetic flux lines is increased. Furthermore, if you want to slow down the movement speed of the magnetic flux lines near the center of the butter, increase the thickness of the copper plate near the center. As a result, the shielding effect by the shielding current is increased, and the magnetic flux lines move slowly, which is disadvantageous for increasing the magnetic flux density but can suppress heat generation. Therefore, in the present invention, a method of controlling the magnetization by changing the thickness of the copper material is also preferable.

[0021] In actual magnetization, a method of gradually injecting magnetic flux lines into the Balta superconductor by applying a force magnetic field several times is adopted. At that time, if there is little heat generation according to the method of the present invention, it is considered that the magnetic flux density that can be captured is sufficiently high and magnetization can be performed efficiently.

The Balta superconductor used in the present invention is as follows. In other words, a bulk superconductor made of RE-123 (RE = rare earth) typified by Y-123 (yttrium 123) produced by the melting method is produced. Specifically, the raw materials are mixed, usually formed into a tablet shape, a seed crystal is placed in the center, and it is melted at a temperature in excess of 1000 degrees to cause crystal orientation. At present, almost single-crystal Balta superconductors with a diameter of 10 cm and a height of 3 cm have been made. Balta superconductors can have a larger cross-sectional area than thin film wires, so the critical current can be set to several thousand A.

Example

[0023] Note that the finite element method (FEM) used in the examples is a numerical solution. This method is widely known as one of prayer methods. The analysis target area is divided into a number of sub-areas of relatively simple shape called `` finite elements '', and the unknown variable that you want to find on each element Is approximated by a relatively simple function such as a linear function. Then, on each element, the potential to be obtained is expanded by an approximate function, and the potential is obtained by using the variational principle so that the energy in the analysis object is minimized. This finite element method is a technique often used in electromagnetic field structure analysis (see, for example, Nakata and Takahashi “Finite Element Method of Electrical Engineering” (Morikita Publishing 1982) and Kikuchi “Overview of Finite Element Method” (Science 1980). ).

[0024] Using a powdered Y-123 (yttrium 123) oxide superconductor as a raw material, a single crystal Balta superconductor manufactured by a conventionally known melting method! The method of the present invention is verified at once. For verification, we performed a numerical simulation using the finite element method. A pulsed magnetic field that increases the magnetic flux density by about 2T in 1 second is applied to a disc-shaped superconductor with a diameter of 100 mm and a thickness of 10 mm from the outside. This is shown in Figure 1. As shown in Fig. 1, a pulse magnetic field is applied to the superconductor in the direction of the arrow using a pulse magnet.

[0025] The external and internal magnetic flux densities at this time were calculated using the finite element method. Since the calculation is complicated this time, the effect of heat generated by the movement of magnetic flux is ignored. For the pulsed magnetic field, a pulsed magnetic field of about 100 milliseconds is applied, a time interval is provided, and the pulsed magnetic field is applied multiple times in the same manner. Some heat generation has a time interval, so the cumulative temperature rise is negligible. Magnetization is sequentially accumulated until saturation and further penetrates into the interior.

FIG. 2 shows a model in the finite element method used in the above calculation example. For the purpose of shortening the numerical calculation time of the simulation for the disc-type superconductor, a 1-degree (°) part was cut out and used only as a model. Naturally, the same calculation result can be obtained as when all (360 °) are modeled. As shown in Fig. 2, there is an air layer around the thin bulk superconductor disk, and the whole is surrounded by the air layer. In the case of such a highly symmetric shape, it is possible to greatly reduce the amount of calculation by creating a model by extracting only an angle of 1 degree and performing a simulation by the finite element method.

[0027] Figs. 3 and 4 show a model and a calculation example for performing a numerical simulation by the finite element method. Figures 3 and 4 use a model cut out only once from Figure 2. Overall 4 Divided into layers. The model is based on the horizontal axis of the disk-shaped Balta superconductor, and the inner layer containing the Norc superconductor,

It is divided into outer layers. The inner layer is divided into three layers based on the vertical axis of Balta superconductor. Fig. 3 is a side view of the model and calculation example with the upper and lower air layers. The sandwiched layer is Balta superconductor. The outer layer is an air layer. It can be seen that when the external magnetic flux density is increased to 2T, the magnetic flux penetrates inside. In other words, the magnetic flux lines indicated by arrows on the surface of the superconductor are concentrated at the boundary between the inner layer and the outer layer and penetrate into the inside. However, the magnetic flux lines do not penetrate to near the center in the horizontal axis direction of the Balta superconductor. The direction of the arrow is the direction of the magnetic flux lines. Here, by making the upper and lower air layers into disk-shaped copper plates, the movement of the magnetic flux can be made slow. Figure 4 shows a side view of a model and calculation example using a disk-shaped copper plate.

[0028] In the model, the disk-shaped copper plate does not necessarily have to be electrically connected to the force calculated as being in contact with the disk-shaped Balta superconductor. However, in terms of heat, the direct contact or connection of the two is useful for quickly removing the heat generated in the superconductor from the superconductor to the copper plate and keeping the temperature of the superconductor at a low temperature. Therefore, in practice, the copper plate is preferably in direct contact with or connected to the Balta superconductor.

The Balta superconductor basically works to prevent magnetic flux from entering due to the pinning effect, and the magnetic flux density on the Balta superconductor surface increases due to the so-called shape effect. On the other hand, if a Lorentz force exceeding the pinning force is applied, the magnetic flux penetrates into the inside, and conversely, once entered, the magnetic flux does not go outside due to the pinning force and is captured. In the case of the air layer, it can be seen that the magnetic flux easily penetrates inside. In reality, heat is generated by the movement of the magnetic flux, and as the temperature rises, the pinning force decreases, so that the magnetic flux that has entered the corner cannot be captured with a decrease in the external magnetic field and comes out.

In FIG. 3 and FIG. 4, the portion described as “air” is not a part of the model but an air layer, and the portion written as “superconductor” is the model. On the simulation screen, this is the display. The upper and lower layers described as “copper” in FIG. 4 mean that the simulation is performed when the copper plate is arranged in the upper part and Z or the lower part. It can be considered that an exciting coil is arranged on the right side of the “air” portion. [0031] FIG. 5 shows a simulation result of the time dependence of the penetration depth from the surface of the Balta superconductor at the front of the magnetic flux that penetrates. As shown in Fig. 5, when the penetration depth of the front of the magnetic flux from the Balta superconductor surface is plotted with time, when there is no copper material, the magnetic flux quickly enters the superconductor as time passes. You can see that it is invading. In other words, the movement of the magnetic flux is fast, and heat generation due to the movement of the magnetic flux cannot be avoided in this state.

[0032] Therefore, when a disk-shaped copper plate with a conductivity of 1 X 10 ⁹ [ΐΖΩπι] is attached above and below the Balta superconductor, and the external magnetic field is changed in the same way, The penetration depth from the surface of the Balta superconductor was investigated. The results are also shown in FIG. It can be seen that the movement of the magnetic flux lines is suppressed by attaching a disk-shaped copper plate.

[0033] As shown in FIG. 5, it can be seen that the penetration of the magnetic flux becomes gentler when the disc-shaped copper plate is attached, and the velocity of the magnetic flux is smaller than when the disc is not attached. Note that the velocity of the magnetic flux can be obtained from the tilt force of the plot. Further, FIG. 5 also shows the result of calculation as 1 × 10 ¹⁰ [1 / Ωπι] with the conductivity increased 10 times. It can be seen that the penetration of magnetic flux is more gradual. In other words, the movement of the magnetic flux can be controlled by attaching a disk-shaped copper plate. Naturally, if the thickness of the disk-shaped copper plate is changed, the movement of the magnetic flux can be finely controlled. That is, if the thickness is reduced, the speed of the magnetic flux can be increased. The reverse is also possible.

Here, it can be said that the same effect appears in the actual experiment, which shows the simulation result by the finite element method. It is the power that has so far been able to elucidate many of the superconducting phenomena using a technique called the finite element method. Actually, the present invention utilizes a very basic effect of preventing a change in magnetic flux density due to the pulse magnetic field by a shielding current flowing through the copper material when a pulse magnetic field is applied to the copper material. Therefore, its realization is relatively easy. The simulation results show that the effect of suppressing the movement of the magnetic flux lines is high by increasing the conductivity, which is because the shielding current is more likely to flow, and this is quantitatively determined. I can confirm it. Also, control of the movement of magnetic flux lines using copper material has been attempted in metallic superconductors. Therefore, this simulation result is also valid and accurately reflects actual experiments. It is thought to be.

FIG. 6 is a diagram showing an example of the arrangement of the Balta superconductor and the copper plate when the pulse magnetization method of the present invention is specifically implemented. The figure shows a state in which copper plates 1 with different thicknesses are attached to the upper and lower surfaces of the disc-shaped Balta superconductor 2 at the peripheral and central portions. The arrow indicates the direction of the magnetic field. Since the copper plate is thin in the periphery, the shielding effect against the movement of the magnetic flux lines is small and the speed of the magnetic flux lines is high. On the other hand, since it is thicker in the central part, the velocity of the magnetic flux lines is suppressed, and the magnetic flux lines are difficult to enter. Therefore, the influence of heat generation is reduced. If the heat generation is reduced, the magnetic flux lines tend to stay in the superconductor, and as a result, a high magnetic flux density can be maintained. In this way, it is possible to control the speed of the magnetic flux lines. It is possible to insert copper plates with different shapes on the top and bottom surfaces.

Industrial applicability

[0036] The present invention relates to pulse magnetization in which a Balta superconductor is used as a permanent magnet rather than as a conductor, and a permanent magnet having a very large magnetic force is provided. The resulting Balta superconductor can be used as a powerful permanent magnet by cooling it to a temperature of about liquid hydrogen. As a Balta superconductor pulse magnetized magnet, it can be very downsized and simplified, so we can expect alternative demand and new demand in various fields.

Claims

The scope of the claims

[1] A Balta characterized by comprising a step of preparing a Balta superconductor, a step of placing a copper material on the top and Z or the bottom of the Balta superconductor, and a step of pulse magnetizing the Balta superconductor. Pulsed magnetization of superconductors.

[2] The pulse magnetization method of a Balta superconductor according to claim 1, wherein the magnetization is controlled by changing the thickness of the copper material.

[3] The pulse magnetization method of the Balta superconductor according to [1] or [2], wherein the Balta superconductor is a disc type and the copper material is a disc shape.

4. The Balta superconductor contains a powdered rare earth 123 oxide superconductor.

Pulsed magnetization method for Balta superconductors as described in V, Deviation.

5. The pulse magnetization method for a Balta superconductor according to any one of claims 1 to 4, wherein the copper material is disposed in direct contact with or thermally connected to the Balta superconductor.

6. The shape force of the copper material is different between the upper and lower surfaces of the Balta superconductor.

7. The pulse magnetization method for a Balta superconductor according to any one of claims 1 to 6, wherein the copper material is a copper plate.

8. The pulse magnetization method for a Balta superconductor according to any one of Claims 1 to 7, wherein an exciting coil is arranged around the Balta superconductor and the copper material.