JP2005294471A - Method for magnetizing bulk super-conductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for pulse-magnetizing a bulk super-conductor or a method for cooling and magnetizing a magnetic field, wherein a given reinforcement strength is ensured by both an immersion of resin such as epoxy and a metal ring fitting, and besides a cooling efficiency is enhanced by restraining excessive heat generation, resulting in reducing a time period of stabilizing the temperature of an oxide super-conductor bulk, thereby reducing a time required for a magnetization process. <P>SOLUTION: In the method for pulse-magnetizing the bulk super-conductor, a bottom face of the annular, disc-shaped and pillar-shaped oxide super-conductor bulk is brought into contact with a cold stage for mounting, a current is flown to a magnetization coil provided on an outer peripheral side of the bulk to generate a pulse magnetic field, and the bulk is magnetized to a direction perpendicular to the bottom face in a refrigerant or in a low temperature state obtained by a freezer. Prior to the magnetization of the bulk, an immersion resin film in the surface of the bulk is eliminated, and a first metal ring having a lacking part is closely adhered or fitted into the outside of the bulk, and further a second metal ring is closely adhered or fitted into an outside of the first metal ring. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for magnetization of a bulk superconductor, and more particularly to a pulse magnetization method or a magnetic field cooling magnetization method for an oxide superconducting bulk.

  In the pulsed magnetization method of an oxide superconducting bulk, the bottom surface of the oxide superconducting bulk matched with one surface of the superconducting quasi-single crystal is placed in contact with a cold stage and cooled to a predetermined temperature. And applying a current to a magnetized coil provided on the outer peripheral side of the oxide superconducting bulk to generate a pulsed magnetic field so that the oxide superconducting bulk is perpendicular to the bottom surface at a predetermined low temperature obtained in a refrigerant. Magnetize in the direction.

  In the magnetic field cooling magnetization method of the oxide superconducting bulk, the bottom surface of the oxide superconducting bulk matched with one surface of the superconducting quasi-single crystal is placed in contact with a cold stage, and the oxide superconducting bulk is placed. A steady current is passed through a magnetizing coil provided on the outer peripheral side of the steel to generate a steady magnetic field, and then the oxide superconducting bulk is cooled to a predetermined temperature obtained in a refrigerant or by a refrigerator, The strength is lowered and magnetized in a direction perpendicular to the bottom surface.

  As shown in FIG. 1A, the oxide superconducting bulk handled here is generally annular, disc-shaped, or cylindrical, and its bottom surface coincides with the ab plane of the superconducting pseudo single crystal, When magnetized in the thickness direction (c-axis direction) perpendicular to this (for example, Non-Patent Documents 1 and 2) but cooled to the superconducting transition temperature or lower, oxidation occurs when current is passed through the magnetizing coil. There is a possibility that a strong electromagnetic repulsive force acts in the lateral direction of the superconducting bulk and destroys it.

Therefore, as shown in FIG. 1 (B), a measure is taken to wrap the oxide superconducting bulk 1 with a resin film 5 such as an epoxy resin from the outer periphery and impregnate and reinforce it. (Prior art 1)
Further, Patent Document 1 discloses that a compressive stress from the side surface caused by a metal ring is used as a reinforcing structure for a superconducting bulk material. (Prior art 2)

The method of magnetizing the oxide superconducting bulk with the highest performance is field cooling (FC), but it requires a large superconducting magnet using liquid helium, which is not practical and simpler. The pulse magnetization method is used.
In particular, the IMRA method (repetitive magnetization method) has come to be used in the pulse magnetization method, and when the conventional techniques 1 and 2 are combined as a reinforcing treatment, the trapped magnetic field can be recorded at 3.8T at 30K. The trapping magnetic field has a drawback that it is smaller than the FC.

  This is because the temperature rises due to heat generation caused by the penetration of magnetic flux, and in particular, the epoxy resin film impregnated in the oxide superconducting bulk hinders heat dissipation, and it takes a long time to stabilize the temperature. This is because it takes time.

  In addition, since the metal ring is attached to the surface of the epoxy resin film 5 attached to impregnate the resin, heat conduction for heat radiation has not been considered. For this reason, there is a problem that the temperature rises due to heat generation caused by the penetration of the magnetic flux, and it is not possible to obtain a trapped magnetic field larger than a certain level.

  Conventionally, the thickness of the impregnating resin film 5 after impregnation is at most about 1 mm, and it has been considered that the thickness of the resin film 5 is not so much affected by cooling. Due to the presence of the film, it has been found that it takes three times or more to stabilize the temperature of the oxide superconducting bulk (below the superconducting transition temperature) as compared to the case without the resin.

  The reason is that the thermal conductivity k of the oxide superconducting bulk 1 has anisotropy in the direction along the ab plane of the superconducting pseudo single crystal and the direction perpendicular to the ab plane. Yes, the thermal conductivity in the direction along the ab plane is several times higher than the direction perpendicular to the ab plane (c-axis direction). Therefore, the contribution of heat dissipation from the side as well as the bottom is important. I figured out that there was.

  Therefore, as previously disclosed in Patent Document 2, the present inventors have shortened the time for stabilizing the temperature of the oxide superconducting bulk based on the above knowledge, improved the cooling efficiency, and the magnetization process. A pulsed magnetization method for bulk superconductors that can reduce the time required for the above is provided.

  Prior to magnetization of the oxide superconducting bulk, as shown in FIG. 1 (C), the impregnating resin film on the surface portion of the oxide superconducting bulk 1 after impregnation is removed, and the oxide superconducting material is removed. A metal ring is fitted around the bulk 1. (Prior art 3)

  However, when a metal having a high thermal conductivity is used in order to improve heat dissipation through the metal ring according to the prior art 3, generally a metal having a high thermal conductivity has a high electrical conductivity, and an applied pulsed magnetic field for magnetization is used. As a result, the eddy current generated by the current increases, resulting in a new problem that excessive heat generation and the resulting temperature increase may occur.

H. Fujishiro, S. H. Fujishiro and S. Kohayashi: I E E E Trans. Superconductor (IEEE Trans. Supercond.), Volume 12 (2002), p. 1124 H. Fujishiro, M. Ikebe, tea. Naito, K. Noto (H. Fujishiro, M. Ikebe, T. Naito and K. Noto): Japanese Journal of Applied Physics, Jpn. J. Appl. Phys., Vol. 33 (1994) 4965. JP 11-335120 A Japanese Patent Application No. 2003-112116

  The present invention has been made to solve the above-described problems in the pulse magnetizing method. Excess heat generation is ensured by ensuring a predetermined reinforcing strength by both resin impregnation and metal ring fitting such as epoxy. The purpose is to provide a bulk superconductor magnetization method capable of reducing the time required to stabilize the temperature of the oxide superconducting bulk, reducing the time required for the magnetization process, and improving the cooling efficiency And

  The present invention was also made to solve the problems corresponding to the above-mentioned problems that occur in the magnetic field cooling and magnetization method, and has a predetermined reinforcement strength by both resin impregnation such as epoxy and metal ring fitting. Of bulk superconductors that can reduce the time required for the magnetizing process by reducing the time required to stabilize the temperature of the oxide superconducting bulk by suppressing excessive heat generation and improving cooling efficiency. A second object is to provide a magnetization method.

  In order to achieve the above object, the method for magnetizing a bulk superconductor according to the present invention is such that the bottom surface of an oxide, superconducting bulk of a ring, disk or column is coincident with one surface of a superconducting quasi-single crystal. The bottom surface is placed in contact with a cold stage, cooled to a predetermined temperature, and then a current is passed through a magnetizing coil provided on the outer peripheral side of the oxide superconducting bulk to generate a pulsed magnetic field, In the pulse superconducting method of a bulk superconductor, the oxide superconducting bulk is magnetized in a direction perpendicular to the bottom surface at a predetermined low temperature obtained in a refrigerant or by a refrigerator. Prior to magnetization, the resin film for impregnation on the surface portion of the oxide superconducting bulk is removed, and a first metal ring having a cut and / or a notch is fitted outside the oxide superconducting bulk. Let, and before Outside the first metal ring, fitting the second metal ring, characterized in that.

  In order to achieve the above object, the bulk superconductor magnetization method according to the present invention is such that the bottom surface of an annular, disk-shaped or columnar oxide superconducting bulk coincides with one surface of a superconducting quasi-single crystal. Thus, after placing the bottom surface in contact with the cold stage and generating a steady magnetic field by flowing a steady current through a magnetizing coil provided on the outer peripheral side of the oxide superconducting bulk, A method of cooling and magnetizing a bulk superconductor in a magnetic field by lowering the strength of a stationary magnetic field while cooling a conductive bulk to a predetermined temperature obtained in a refrigerant or by a refrigerator, and magnetizing it in a direction perpendicular to the bottom surface. Before the magnetization of the oxide superconducting bulk, the impregnating resin film on the surface portion of the oxide superconducting bulk is removed, and cuts and / or notches are formed outside the oxide superconducting bulk. Having first gold Ring Mate, further outside the first metal ring, fitting the second metal ring, characterized by.

  Preferably, according to a third aspect of the present invention, the first metal ring is fitted into the oxide superconducting bulk through a resin mixed with ceramic powder, and is thermally adhered.

  Preferably, according to a fourth aspect of the present invention, the first metal ring is fitted into the oxide superconducting bulk by shrink fitting and thermally adhered thereto.

  Preferably, according to a fifth aspect of the present invention, the second metal ring is fitted into the first metal ring via a resin mixed with ceramic powder and mechanically adhered.

  Preferably, according to a sixth aspect of the present invention, the second metal ring is fitted into the first metal ring by shrink fitting and mechanically adhered.

  Preferably, according to claim 7, the ceramic powder is made of one or a mixture of silicon nitride, titanium nitride, silicon oxide or titanium oxide.

  Preferably, according to claim 8, the cut and / or notch of the first metal ring is a single or a plurality of cuts, a single or a plurality of cuts in a direction perpendicular to the circumference of the ring, Or a combination of these.

  The present invention can improve the heat dissipation while suppressing the resin heat impregnation and the reinforcing strength by the metal ring, and suppress unnecessary heat generation in the metal ring. The time required for stabilizing the temperature can be shortened, the time required for the magnetizing step can be shortened, and a larger trapping magnetic field can be stably generated than before.

  Embodiments according to the present invention will be specifically described below with reference to the drawings.

Referring to FIG. 1A again, the oxide superconducting bulk 1 according to the present invention is, for example, REBa ₂ Cu ₃ O _7-y (where RE is a rare earth element, and Y, Nd, Sm, One or two or more elements selected from Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu.), And if necessary, RE ₂ BaCuO _{5 in} this phase. Or a dispersion of RE ₄ Ba ₂ Cu ₂ O ₁₀ or the like is used.

  Referring again to FIGS. 1B and 1C, the oxide superconducting bulk 1 is wrapped and impregnated with a resin film 5 such as an epoxy, and then the surface portion (upper surface, bottom surface, and The resin film 5 for impregnation on the outer surface (including the inner surface in the case of an annular shape (not shown)) is removed.

Next, referring to FIG. 2A, the first metal ring 10 having the cut 15 is fitted to the side surface of the oxide superconducting bulk 1.
Next, referring to FIG. 2B, the second metal ring 20 is fitted to the outer surface of the first metal ring 10.
Here, as shown in FIG. 2C, which is an XX cross-sectional view in FIG. 2B, the heights of the oxide superconducting bulk 1, the first metal ring 10, and the second metal ring 20 are as follows. Equally, the upper surface portion and the bottom surface portion after the fitting become flat, and cooling from the bottom surface portion is efficiently performed at the time of magnetization.

Here, the first metal ring 10 is preferably made of a metal having high thermal conductivity, for example, copper or aluminum.
Moreover, it is preferable that the 2nd metal ring 20 consists of a metal with low electrical conductivity compared with the metal of a 1st metal ring, and high rigidity, for example, steel.

In order to enhance the adhesion of the first metal ring 10 to the outer periphery of the oxide superconducting bulk 1 and to enhance the thermal conductivity between the two, a resin adhesive having a high thermal conductivity (for example, nitriding) (Epoxy resin mixed with ceramic powder having high thermal conductivity such as silicon, titanium nitride, silicon oxide, titanium oxide) or the first metal ring 10 is shrink-fitted.
Here, the resin may include grease.

  Further, in order to increase the mechanical reinforcement strength of the second metal ring 20 with respect to the first metal ring 10, a resin adhesive capable of increasing the mechanical adhesion of the first and second metal rings between the two. (For example, epoxy resin mixed with ceramic powder such as silicon nitride, titanium nitride, silicon oxide, or titanium oxide) is used, or the second metal ring 20 is shrink-fitted.

Thus, the oxide superconducting bulk 1 fitted with the double metal ring is placed so that, for example, the bottom surface thereof is in contact with the cold stage connected to the heat transfer section inside the refrigerator.
Then, the magnetizing process is performed by the pulse magnetizing method or the magnetic field cooling method.
For example, in the case of the pulse magnetizing method, after cooling to a predetermined temperature, a current is passed through a magnetizing coil provided on the outer peripheral side of the oxide superconducting bulk 1 to generate a pulsed magnetic field. Is magnetized in a direction perpendicular to the bottom surface (c-axis).

At that time, heat generated inside the oxide superconducting bulk 1 is effectively dissipated from the side surface through the first metal ring 10 in addition to the bottom surface.
A metal having a high thermal conductivity usually has a high electrical conductivity. However, due to the presence of the slit 15, the electrical resistance in the circumferential direction of the entire first metal ring 10 increases, and an eddy current during magnetization is generated. Can be suppressed.

  On the other hand, since the second metal ring 20 has high rigidity, not only can a sufficient compressive stress be applied during magnetization, but also the electrical resistance is large, so that eddy currents during magnetization can be suppressed. .

Since the purpose of providing the first metal ring is good heat conduction and large electrical resistance in the circumferential direction, the first metal ring has one cut 15 as shown in FIG. In addition to the case, as shown in FIG. 3B, two or more cuts 15 and 16 may be provided.
In the case of FIG. 3B, the heat dissipation balance is improved.

Furthermore, as shown in FIG. 3C, a cut 15 and a notch 10c may be provided.
Also in this case, the balance of heat dissipation is improved, and the positioning operation of the first metal ring 10 before fitting can be simplified without substantially increasing the eddy current.

  The cooling of the oxide superconducting bulk in the present invention is not limited to being performed by the cold stage of the cooling unit of the refrigerator as described above. That is, instead of using a refrigerator, the oxide superconducting bulk is cooled or used by using any one kind of refrigerant of liquid nitrogen, liquid neon, liquid helium, and liquid argon. Can have an effect.

  Moreover, a refrigerant | coolant can also be used as a state cooled with a refrigerator, and is not necessarily limited to using at the boiling point. That is, the oxide superconducting bulk can be cooled to a predetermined temperature with a refrigerant in a liquid or gas state cooled using a refrigerator.

  In the case of cooling with such a liquid or gas, the first metal ring may be stretched to have a fin effect and cover part or all of the oxide superconducting bulk as long as heat dissipation is improved. Good.

(A) is a perspective view of an oxide superconducting bulk, (B) is a cross-sectional view of an oxide superconducting bulk showing that an epoxy resin film for impregnation is formed on the surface, and (C) is for impregnation. It is sectional drawing which shows the oxide superconductor bulk after an epoxy resin film is removed. (A) is a perspective view showing a state in which the first metal ring is fitted to the oxide superconducting bulk, and (B) is a perspective view showing a state in which the second metal ring is further fitted to (A). (C) is XX sectional drawing in (B). (A)-(C) are perspective views which show the various aspects of a 1st metal ring.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxide superconducting bulk 5 Resin for impregnation 10, 10a, 10b 1st metal ring 10c Notch 15, 16 Break 20 2nd metal ring

Claims (8)

The bottom surface of the annular, disk-shaped or cylindrical oxide superconducting bulk was placed in contact with the cold stage so that the bottom surface coincided with one surface of the superconducting quasi-single crystal, and cooled to a predetermined temperature. Thereafter, a current is passed through a magnetized coil provided on the outer peripheral side of the oxide superconducting bulk to generate a pulsed magnetic field, and the oxide superconducting bulk is kept in a predetermined low temperature state obtained in a refrigerant or by a refrigerator. In the pulse magnetization method of the bulk superconductor, which is magnetized in a direction perpendicular to the bottom surface,
Prior to magnetization of the oxide superconducting bulk,
Removing the resin film for impregnation on the surface portion of the oxide superconducting bulk;
Fitting a first metal ring having a cut and / or a notch on the outside of the oxide superconducting bulk;
Furthermore, a second metal ring is fitted outside the first metal ring.
A method for magnetizing a bulk superconductor. The oxide superconducting bulk is placed in contact with a cold stage so that the bottom of the annular, disc-shaped or columnar oxide superconducting bulk coincides with one surface of the superconducting quasi-single crystal. A steady current is passed through a magnetizing coil provided on the outer peripheral side of the substrate to generate a steady magnetic field, and then the oxide superconducting bulk is cooled to a predetermined temperature obtained in a refrigerant or by a refrigerator, In the method of cooling and magnetizing a bulk superconductor in a magnetic field, lowering the strength and magnetizing in a direction perpendicular to the bottom surface
Prior to magnetization of the oxide superconducting bulk,
Removing the resin film for impregnation on the surface portion of the oxide superconducting bulk;
Fitting a first metal ring having a cut and / or a notch on the outside of the oxide superconducting bulk;
Furthermore, a second metal ring is fitted outside the first metal ring.
A method for magnetizing a bulk superconductor.   3. The bulk superconductor according to claim 1, wherein the first metal ring is fitted and thermally adhered to the oxide superconducting bulk through a resin mixed with ceramic powder. 4. Magnetization method.   3. The method for magnetizing a bulk superconductor according to claim 1, wherein the first metal ring is fitted into the oxide superconducting bulk and thermally adhered thereto by shrink fitting. 4.   The bulk according to any one of claims 1 to 4, wherein the second metal ring is fitted into the first metal ring via a resin mixed with ceramic powder and mechanically adhered. Magnetization method of superconductor.   5. The bulk superconductor according to claim 1, wherein the second metal ring is fitted into the first metal ring by mechanical shrinkage by shrink fitting. Magnetic method.   The method for magnetizing a bulk superconductor according to claim 3 or 5, wherein the ceramic powder is made of one or a mixture of silicon nitride, titanium nitride, silicon oxide, and titanium oxide. The cut and / or notch of the first metal ring is a single or a plurality of cuts, a single or a plurality of cuts, or a combination thereof in a direction perpendicular to the circumference of the ring. The method for magnetizing a bulk superconductor according to any one of claims 1 to 7.

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