JP2004319797A - Pulse magnetizing method of bulk superconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetizing method of a superconducting bulk in which the time required for magnetization process can be shortened by shortening the time required for settling the temperature of an oxide superconducting bulk and enhancing the cooling efficiency. <P>SOLUTION: A flat and annular or planar oxide superconducting bulk 1 is mounted while touching one face of its superconducting false single crystal to a cold stage 2. A current is fed to a magnetization coil 3 provided on the outer circumferential side of the oxide superconducting bulk to generate a pulse magnetic field and the oxide superconducting bulk is magnetized in the direction perpendicular to the face at a cryogenic temperature being attained in a refrigerant or by means of a refrigerating machine. In such a pulse magnetizing method of a bulk superconductor, a resin film for impregnation is removed from the surface part of the oxide superconducting bulk and a metal ring is fitted to the circumference thereof. Since the oxide superconducting bulk is not impregnated with resin or impregnating resin is removed before magnetization and then a metal ring having a high thermal conductivity is fitted to the circumference thereof, the time required for magnetization process can be shortened by shortening the temperature settling time of the oxide superconducting bulk and enhancing the cooling efficiency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, a flat annular or plate-shaped oxide superconducting bulk is placed on one side of a superconducting pseudo-single crystal in contact with a cold stage, and provided on the outer peripheral side of the oxide superconducting bulk. The present invention relates to a pulse magnetizing method for a bulk superconductor in which a current is caused to flow in a magnetizing coil to generate a pulse magnetic field, and the oxide superconducting bulk is magnetized in a coolant in a direction perpendicular to the surface.
[0002]
[Prior art]
The oxide superconducting bulk to be treated here is generally in the shape of a ring, a disk, or a column. As shown in FIG. 1, usually, as shown in FIG. (For example, Non-Patent Documents 1 and 2), but when a current is applied to the magnetizing coil in a state where the magnet is cooled to a superconducting transition temperature or lower, a strong electromagnetic force acts on the oxide superconducting bulk. And could destroy it. Therefore, measures have been taken to impregnate and reinforce a resin such as an epoxy resin from the outer periphery of the oxide superconducting bulk. Patent Literature 1 discloses that a compressive stress by a metal ring is used as a reinforcing structure of a superconducting bulk material.
[0003]
In the pulse magnetization method, the IMRA method (repeated magnetization method) has been used, and a recording magnetic field of 3.8 T can be recorded at 30 K. However, there is a drawback that the magnetic recording field is smaller than that of FC. This is because the temperature rises due to heat generated by the penetration of magnetic flux, but it takes a long time for the temperature to stabilize because the epoxy resin film impregnated in the oxide superconducting bulk prevents heat dissipation. There was a problem.
[0004]
Further, in the metal ring as the reinforcing structure, since the metal ring is attached to the surface of the impregnated epoxy resin film, heat conduction for heat dissipation is not considered. For this reason, there has been a problem that the temperature rises due to heat generated by the penetration of the magnetic flux, and a large trapped magnetic field cannot be obtained.
[0005]
[Non-patent document 1]
Etch. Fujishiro, S. Kobayashi (H. Fujishiro and S. Kohayashi): IEE Trans. Superconductor (: IEEE Trans. Supercond.), Vol. 12, 2002, page 1124 [Non-Patent Document 2]
Etch. Fujishiro, M. Ikeda, TA. Naito, K. Noto (H. Fujishiro, M. Ikebe, T. Naito and K. Noto): Journal of Applied Physics (J. Appl. Phys) 33, 1994
4965 pages [Patent Document 1]
JP-A-11-335120 (page 2, FIG. 1)
[0006]
[Problems to be solved by the invention]
Conventionally, the impregnation of the resin is at most about 1 mm from the surface of the oxide superconducting bulk, and is considered to have little effect on cooling. However, according to experiments by the present inventors, this about 1 mm was considered. It has been found that the presence of the resin requires three times or more time to stabilize the temperature of the oxide superconducting bulk (below the superconducting transition temperature) as compared to the case without the resin.
[0007]
The present invention has been made based on the above circumstances, and it has been found that bulk superconductivity can reduce the time required for stabilizing the temperature of the oxide superconducting bulk, improve the cooling efficiency, and reduce the time required for the magnetization step. It is an object to provide a method of pulse magnetizing a body.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a flat annular or plate-shaped oxide superconducting bulk is placed on one side of a superconducting pseudo-single crystal in contact with a cold stage, and An electric current is applied to a magnetizing coil provided on the outer peripheral side of the conductive bulk to generate a pulsed magnetic field, and the oxide superconductive bulk is vertically attached to the surface in a refrigerant or at a low temperature obtained by a refrigerator. In the magnetized bulk superconductor pulse magnetizing method, prior to magnetizing the oxide superconducting bulk, the impregnating resin film on the surface portion of the oxide superconducting bulk is removed, and the periphery of the oxide superconducting bulk is removed. A metal ring is fitted to the ring.
[0009]
In this case, as an embodiment of the present invention, the metal ring is fitted and adhered to the oxide superconducting bulk via a resin mixed with a ceramic powder having a high thermal conductivity, and the resin is An epoxy resin mixed with ceramic powder such as silicon nitride, titanium nitride, silicon oxide, titanium oxide, or the metal ring is fitted to the oxide superconducting bulk by shrink fitting. ,It is valid.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Here, a flat annular (or disk-shaped or column-shaped) oxide superconducting bulk 1 is placed with one surface of the superconducting pseudo single crystal in contact with a cold stage 2. An electric current is applied to the magnetizing coil 3 provided on the outer peripheral side of the oxide superconducting bulk 1 to generate a pulse magnetic field, and the bulk superconductor for magnetizing the oxide superconducting bulk 1 in a direction perpendicular to the surface is formed. In the pulse magnetization method, prior to the magnetization of the oxide superconducting bulk 1, the epoxy resin on the surface is removed, and a metal ring 5 having a high thermal conductivity is fitted around the surface (see FIG. 1 (c)). .
[0011]
The above-described oxide superconducting bulk 1 is, for example, REBa ₂ Cu ₃ O _7-y (where RE is selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. One or two or more kinds of elements are used as a main component, and if necessary, a material in which RE ₂ BaCuO ₅ , RE ₄ Ba ₂ Cu ₂ O _10, or the like is dispersed in this phase is used. Further, the cold stage 2 is connected to a heat transfer section of a refrigerator, and a sapphire plate 6 may be provided on an upper surface thereof, and the oxide superconductive bulk 1 may be placed on the sapphire plate 6.
In the embodiment, as shown in FIG. 2, the cold stage 2 may be connected to a refrigeration unit 10 of the refrigerator through a copper heat transfer rod 7 having a heat conduction disk 9.
[0012]
Such an oxide superconducting bulk 1 can obtain a magnetic flux density of about 1 T (tesla) by trapping a magnetic field at 77 K (boiling point of nitrogen), such as 63 K (melting point of nitrogen) and 51 K (melting point of oxygen). At a low temperature, a magnetic flux density several times higher than that is achieved. When the above-described oxide superconducting bulk 1 is used in the above-described manner of use as a magnet, there is a fear that the oxide superconducting bulk 1 may be broken by a strong electromagnetic force. Under such circumstances, a stainless steel ring is generally fitted. It is reinforced or impregnated with resin on the surface of the superconducting bulk.
[0013]
In the pulse magnetization method, the IMRA method (repetitive magnetization method) has been used, and a recording magnetic field of 3.8 T can be recorded at 30 K, but the capturing magnetic field is smaller than that of FC. This is due to the fact that the temperature rises due to the heat generated by the penetration of the magnetic flux. When the resin is impregnated as described above, there is a problem that it takes a long time to stabilize the temperature.
[0014]
The inventor of the present invention has found that the thermal conductivity k of the oxide superconducting bulk 1 is anisotropic in the direction along the ab plane of the superconducting pseudo single crystal and in the direction perpendicular to the ab plane. As shown by the experimental data, it is understood that the thermal conductivity in the direction along the ab plane is several times higher than the direction perpendicular to the ab plane. Therefore, in the present invention, as a method of magnetizing the oxide superconducting bulk 1, the ab surface of the superconducting bulk, which is not impregnated with the resin or from which the impregnated resin is removed, is directly placed on the cold stage 2, or The cooling time is reduced by cooling in the cooling section of the refrigerator through the copper heat transfer rod 7 as in the embodiment. In addition, in order to enhance heat radiation in the direction along the ab plane of the oxide superconducting bulk 1 having a high thermal conductivity, a metal ring 5 having a high thermal conductivity is fitted on the outer periphery of the oxide superconducting bulk 1. (See FIG. 1C).
[0015]
In particular, in order to remove the heat generated during the magnetization from the oxide superconducting bulk 1, the outer periphery of the metal superconducting bulk 1 and the metal ring are increased so as to increase the adhesion (thermal conductivity) of the metal ring 5 to the outer periphery. A resin adhesive having a high thermal conductivity (for example, an epoxy resin mixed with a powder of silicon nitride, titanium nitride, silicon oxide, titanium oxide, or the like) is used between them, or the metal ring 5 is shrink-fitted. . In the case of direct cooling with a refrigerant using liquid nitrogen, the entire bulk may be coated with metal.
[0016]
The cooling of the oxide superconducting bulk in the present invention is not limited to being performed by the cooling unit of the refrigerator as described above. That is, instead of using a refrigerator, the oxide superconducting bulk is cooled by using any one kind of refrigerant among liquid nitrogen, liquid neon, liquid helium, and liquid argon, and is used to be equivalent or similar. Can bring effect. The oxide superconducting bulk used in this way is generally cooled by being immersed in a cooling medium. The refrigerant is not limited to a liquid, but may be a gas. Further, the refrigerant can be used in a state of being cooled by a refrigerator, and is not necessarily limited to being used at its boiling point. That is, the oxide superconducting bulk can be cooled to a predetermined temperature by a liquid or gaseous refrigerant cooled using a refrigerator and used.
[0017]
【The invention's effect】
As described in detail above, prior to magnetizing the oxide superconducting bulk, the present invention does not impregnate the resin or removes the impregnated resin and fits a metal ring of high thermal conductivity around the resin ring. Thereby, the time required for stabilizing the temperature of the oxide superconducting bulk can be shortened, the cooling efficiency can be improved, and the time required for the magnetization step can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a cross section of a superconducting bulk, where (a) is a cross section parallel to the surface of a superconducting bulk having an impregnated epoxy resin film formed on the surface, and (b) is perpendicular to the surface. (C) is a sectional view perpendicular to the surface of the superconducting bulk of the present invention.
FIG. 2 is a schematic diagram showing a specific configuration when a pulse magnetizing method of the present invention is performed.
FIG. 3 is an experimental graph disclosing anisotropy with respect to thermal conductivity.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 superconducting oxide bulk 2 cold stage 3 magnetized coil 5 metal ring 6 sapphire plate 7 heat transfer rod 8 vacuum vessel 9 disk 10 refrigerator cooling unit 11 epoxy resin film

Claims (4)

A flat annular or plate-shaped oxide superconducting bulk is placed with one surface of the superconducting pseudo single crystal in contact with a cold stage, and a magnetized coil provided on the outer peripheral side of the oxide superconducting bulk. A current is passed, a pulse magnetic field is generated, and the oxide superconducting bulk is magnetized in a refrigerant or in a low-temperature state obtained by a refrigerator. ,
Prior to the magnetization of the oxide superconducting bulk, the impregnating resin film on the surface portion of the oxide superconducting bulk is removed, and a metal ring is fitted around the oxide superconducting bulk. Pulse magnetization method for superconductors. The pulse magnetizing method for a bulk superconductor according to claim 1, wherein the metal ring is fitted and adhered to the oxide superconducting bulk via a resin mixed with a ceramic powder. 3. The method of claim 2, wherein the ceramic powder comprises one or a mixture of silicon nitride, titanium nitride, silicon oxide, and titanium oxide. The method according to claim 1, wherein the metal ring is fitted to the oxide superconducting bulk by shrink fitting.

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