JP5037193B2 - Oxide superconducting conductor conducting element - Google Patents

Description

  The present invention relates to an oxide superconducting conductor conducting element using an oxide superconductor used for a current lead, a current limiter, a permanent current switch, a conducting magnet, and the like.

  Oxide superconductors can be used for energizing elements such as current leads, current limiters, permanent current switches, and energizing magnets because they can flow large currents with zero electrical resistance. In Patent Document 1, it is necessary to obtain a longer conductor for the application of a superconducting conductor to a superconducting magnet, a superconducting current lead, or the like. However, there is a problem that the length of the superconducting conductor is short as it is described that the size of the current superconductor is much shorter than expected. In oxide superconductor energization elements, lengthening the oxide superconductor portion reduces heat penetration for current leads, increases normal conduction resistance for current limiters and permanent current switches, and increases magnetic field strength for current magnets. This leads to an increase in performance.

  Regarding the lengthening of the oxide superconductor by making it into a wire, Patent Document 1 describes that a wire using a metal sheath has a problem that it cannot be used as a current lead because its thermal conductivity is too large. Yes. To solve these problems, as shown in FIG. 8, Patent Document 1 proposes joining oxide superconductors to make them longer. Furthermore, Patent Document 1 describes that noble metal is dispersed in the joint, and that superconducting particles are joined to each other at the joint surface and low resistance can be realized.

Japanese Patent Laid-Open No. 5-159928

  As described above, by joining two or more oxide superconductors to form one oxide superconductor, the oxide superconductor portion can be made longer. However, although the junction between the oxide superconductors has a low resistance, there is an electrical resistance, and Joule heat is generated when energized. Due to the effect of Joule heat generation, sufficient superconducting characteristics cannot be obtained, and the function as a current-carrying element is impaired. For example, Patent Document 1 shows that even when the amount of noble metal on the joint surface is optimized, the critical current density is about ½ compared to the case where there is no joint surface.

  An object of the present invention is to provide a long and high-performance oxide superconducting conductor conducting element in view of the above-mentioned problems.

The oxide superconducting conductor conducting element of the present invention is as follows.
(1) An oxide superconductor in which two or more oxide superconductors are electrically joined, an electrode terminal electrically joined to both ends of the oxide superconductor, and an oxide constituting the oxide superconductor An oxide superconducting conductor energization element comprising: a current lead including a heat transfer body connected to a joint between superconductors; and the heat transfer body connected to an electrode terminal on one side .
( 2 ) The oxide superconducting conductive element according to ( 1 ), wherein the heat transfer body is a film formed on a surface of the oxide superconductor.
( 3 ) The cross-sectional area S _{A of} the heat transfer body, the cross-sectional area of the oxide superconductor on which the coating film of the heat transfer body is formed, S _B , the thermal conductivity of the heat transfer body is k _A , and the heat transfer body When the thermal conductivity of the oxide superconductor formed with the film is k _B , the cross-sectional area S _{A of the} heat transfer body is S _A ≦ S _B × (k _B / k _A ). ( 2 ) The oxide superconducting conductor energizing element according to ( 2 ).
( 4 ) The oxide superconductor is in a single-crystal REBa ₂ Cu ₃ O _x phase (RE is one or more selected from Y or rare earth elements, x is 6.8 or more and 7 or less). The oxide superconductor conducting element according to any one of (1) to ( 3 ), wherein the RE ₂ BaCuO ₅ phase is a finely dispersed oxide superconductor.
In the present invention, two or more oxide superconductors joined to form one conductor are expressed as an oxide superconductor.

  According to the present invention, since the substantial length of the oxide superconducting conductor portion in the energization element can be increased by simple means, a long and high-performance oxide superconducting conductor energization element can be provided. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the structure of an oxide superconducting conductor conducting element according to the present invention. In FIG. 1, two oxide superconductors 1 a and an oxide superconductor 1 b are electrically joined to form one oxide superconductor 1. Electrode terminals 2 for external connection are electrically joined to both ends of the oxide superconducting conductor 1 with solder or the like (not shown in the figure). As shown in FIG. 1, by joining two oxide superconductors 1a and 1b, the oxide superconducting conductor portion is longer than the oxide superconductor energizing element manufactured using one oxide superconductor. As a result, high performance of the oxide superconducting conductor conducting element can be achieved.

  As a joining method of two oxide superconductors, for example, a silver film is formed on the joining surface of each oxide superconductor to a thickness of about 1 μm, and the silver film-forming surfaces are joined together by solder, or each oxide superconductor There is a method in which a silver paste is applied to the joint surface of the body, and heating is performed in a state where the coated surface is in close contact, and the electrical resistance of the joint surface can be extremely reduced by these methods. However, although it is very small, there is a junction resistance, and Joule heat is generated on the joint surface when energized. Joule heat generated on the joint surface may impair the function of the oxide superconducting conductor conducting element. In FIG. 1, the heat transfer body 4 is connected to the joint so as to surround the joint surface 3 between the two oxide superconductors 1 a and 1 b. The other end of the heat transfer body 4 is connected to a cooling facility (not shown), for example, a refrigerant such as liquid nitrogen or a cold head of a refrigerator. Since the Joule heat generated by the electrical resistance of the joint surface 3 when energized is transferred to the cooling facility side through the heat transfer body 4, the function of the energization element is not impaired by the Joule heat generated on the joint surface 3. .

  As the heat transfer body 4 used in the present invention, a material having high thermal conductivity such as a metal such as copper, silver or aluminum, or a ceramic such as silicon nitride or silicon carbide is preferable. Furthermore, it is preferable to make the heat transfer body 4 into a thin plate shape or a thin wire shape so that the cross-sectional area is smaller than that of the electrode terminal 2. For example, in the case of application of current leads, by making the cross-sectional area of the heat transfer body 4 smaller than the cross-sectional area of the electrode terminal 2, the two oxide superconductors 1a and 1b can be obtained without greatly increasing the amount of heat penetration. The Joule heat generated on the joint surface 3 can be effectively escaped. Further, the heat transfer body 4 may be formed on the surface of the oxide superconductor as a film.

The oxide superconductor used in the present invention is not particularly limited as long as it is an oxide superconductor. RE-Ba-Cu-O (RE is at least one element selected from Y or rare earth elements) A bulk oxide superconducting body or a bulk oxide superconducting Bi system may be used. However, among oxide superconducting bulk materials, an oxide superconducting bulk in which a RE ₂ BaCuO ₅ phase (211 phase) is finely dispersed in a single-crystal REBa ₂ Cu ₃ O _x phase (123 phase) produced by a melting method. The body has a high critical current density and is a material suitable for energization element application, but it is difficult to increase the size because precise temperature control is required for crystal growth in a single crystal form. Therefore, the energization element using the RE-Ba-Cu-O melt bulk is particularly remarkable in the lengthening effect according to the present invention. Therefore, the RE-Ba-Cu-O melt bulk is A particularly preferred material for the invention. In FIG. 1, the oxide superconductors 1a and 1b having the same size are electrically joined. However, the shape, size, and material system of the oxide superconductor to be joined may be different.

  FIG. 2 is a cross-sectional view showing another example of the structure of the oxide superconducting conductor conducting element in the present invention. In FIG. 2, the other end of the heat transfer body 4 is connected to the electrode terminal 2 on one side. With this structure, Joule heat generated by the electrical resistance of the joint surface 3 between the two oxide superconductors 1a and 1b when energized is transferred to the electrode terminal 2 side through the heat transfer body 4. Therefore, the function of the energization element is not impaired by the Joule heat generated on the bonding surface 3. In the structure shown in FIG. 2, when the heat transfer body 4 is a good electrical conductor such as a metal, the heat transfer body 4 may be a current path. Since it is an element, a current flows through the portion of the oxide superconducting conductor 1 having almost zero electric resistance when used. For this reason, the function is not affected. Furthermore, the trouble of connecting the heat transfer body 4 to a cooling facility such as a refrigerator or a refrigerant can be saved, and the mounting of the energization element is facilitated.

  FIG. 3 is a cross-sectional view showing another example of the structure of the oxide superconducting conductive element in the present invention. In FIG. 3, a support 5 for reinforcing the oxide superconducting conductor conducting element is added to the structure shown in FIG. When two or more oxide superconductors are electrically joined to form one elongated oxide superconductor, the mechanical strength may decrease due to the lengthening. It is preferable to do. As the support 5, fiber reinforced plastics such as GFRP and CFRP are highly rigid and are preferable because the electrode terminals 2 at both ends can be electrically insulated.

  FIG. 4 is a cross-sectional view showing another example of the structure of the oxide superconducting conductive element in the present invention. As shown in FIG. 4, the heat transfer body 4 is a metal film formed on the surface of the oxide superconductor 1b. By using the metal film formed on the surface of the oxide superconductor 1b as the heat transfer body 4, the heat transfer body 4 can be easily accommodated in the support 5 and the configuration of the entire element is simplified. In the oxide superconducting conductor conducting element of the present invention, when the conducting element is a current lead, the heat conducted through the metal film increases the amount of heat penetration, so the metal film should be formed only on one side of the oxide superconductor. Is preferred. In this case, the oxide superconductor 1b provided with a metal film as the heat transfer body 4 can prevent heat intrusion from the electrode terminal 2 on the high temperature side when it is connected to the electrode terminal 2 on the high temperature side. desirable.

Furthermore, it is more preferable that the heat penetration amount transmitted through the metal film does not exceed the heat penetration amount transmitted through the oxide superconductor 1b on which the metal film is formed. That is, the cross-sectional area S _{A of} the heat transfer body 4, the cross-sectional area of the oxide superconductor 1b on which the metal film of the heat transfer body 4 is formed is S _B , the thermal conductivity of the heat transfer body 4 is k _A , and the heat transfer body When the thermal conductivity of the oxide superconductor 1b on which the metal film 4 is formed is k _B , it is preferable to satisfy the condition of S _A ≦ S _B × (k _B / k _A ). For example, when the average thermal conductivity in the operating temperature range of the metal film as the heat transfer body 4 is 800 W / m · K and the average thermal conductivity in the operating temperature range of the oxide superconductor 1b is 10 W / m · K, When a metal film is formed on one side of the surface of the oxide superconductor 1b having a thickness of 1 mm, the thickness is preferably 12.5 μm or less.

  FIG. 5 is a cross-sectional view showing another example of the structure of the oxide superconducting conductor conducting element in the present invention. 2 to 4, the heat transfer body 4 is connected to the electrode terminal 2 on one side, but in FIG. 5, the heat transfer body 4 is connected to the electrode terminals 2 on both sides. When the oxide superconducting conductor energization element is a current lead, it is preferable to connect the heat transfer body 4 only to the electrode terminal 2 on one side in order to reduce the amount of heat penetration. However, the current limiter, permanent current switch, energization When applied to a magnet or the like, it is not necessary to reduce the amount of heat penetration, and only the heat removal of Joule heat generated at the joint surface 3 between the oxide superconductors 1a and 1b has to be taken into consideration. It is preferable to connect to the electrode terminals 2 at both ends.

  FIG. 6 is a cross-sectional view showing another example of the structure of the oxide superconducting conductive element in the present invention. In FIG. 1 to FIG. 5, two oxide superconductors 1a and 1b are electrically joined to form one oxide superconductor 1. However, as shown in FIG. Similarly, it is possible to form an oxide superconducting conductor 1 which is electrically joined and lengthened. In this case, the provision of the heat transfer body 4 on the two oxide superconductors 1b and 1c excluding the oxide superconductor 1a located on the lowest temperature side from the viewpoint of preventing intrusion heat from the electrode terminal 2 on the high temperature side. preferable.

  FIG. 7 is a cross-sectional view showing another example of the structure of the oxide superconducting conductive element in the present invention. 1 to 6, two or more oxide superconductors are electrically joined in one direction in the energizing direction, but as shown in FIG. 7, the oxide superconductors are stacked in a direction perpendicular to the energizing direction. It can also be joined. The method of joining in the stacking direction is compact and high performance when electrically joining oxide superconductors of meander structure or mosquito coil incense-like structure in applications such as current limiters, permanent current switches, and energizing magnets. This is a preferable method. In the case of the structure shown in FIG. 7, the heat transfer body 4 is preferably made of an electrically insulating material in order to prevent an electrical short circuit between the joint surfaces 3. When a good electrical conductor is used for the heat transfer body 4, it is preferable to connect via an insulating heat transfer tape or the like when connecting to a cooling facility for extracting heat.

Example 1
First, a Gd—Ba—Cu—O single crystal oxide superconductor having a diameter of 46 mm and a thickness of 15 mm by a melting method, in which 30 mol% of 211 phase and 5 mass% of silver added to the initial material are finely dispersed in 123 phase. Was made. Then, from this oxide superconductor, two rod-shaped samples having a length of 40 mm, a width of 5 mm, and a thickness of 2 mm are cut out, silver is formed on the joint surface, and then joined with solder to form one oxide superconductor 1. Was made. Next, both ends of the oxide superconducting conductor 1 were joined to the copper electrode terminal 2 by soldering. And it connects to a junction part so that the joint surface 3 of oxide superconductors may be enclosed using a silver paste with the silver foil of thickness 0.1mm which is the heat-transfer body 4, Furthermore, it connects with the electrode terminal 2 of one side. Thus, an oxide superconducting conductive element A having a structure as shown in FIG. 2 was produced. For comparison, an oxide superconductor energization element B having a structure as shown in FIG. 9 was prepared using one rod-shaped sample having a length of 40 mm, a width of 5 mm, and a thickness of 2 mm.

  In the case of the oxide superconductor conducting element A, the energization direction length of the junction 3 between the two oxide superconductors 1 a and 1 b is 5 mm, and the energization direction length of the junction between the oxide superconductor and the electrode terminal 2. Was 5 mm, and the distance between both electrode terminals, which is the effective length of the oxide superconducting conductor 1 of the oxide superconducting conductor conducting element A, was 65 mm.

  On the other hand, in the case of the oxide superconductor energization element B, since the energization direction length of the junction between the oxide superconductor and the electrode terminal was 5 mm, the oxide superconducting conductor of the oxide superconductor energization element B was effective. The distance between both long electrode terminals was 30 mm.

  The heat penetration amount is inversely proportional to the effective length, and the normal conductive resistance value is proportional to the effective length. From the above results, the oxide superconducting conductor energizing element A, when used as a current lead, compared to the oxide superconductor energizing element B, the heat penetration amount is less than half, and as a current limiter or permanent current switch When used, it was confirmed that the normal conductive resistance value was doubled or more.

  Further, when the evaporative gas flow rate was measured with one end of the oxide superconductor conducting element A and the oxide superconductor conducting element B immersed in liquid helium in the cooling vessel, the oxide superconducting conductor conducting element A was oxidized. Compared to the superconductor conducting element B, the evaporative gas flow rate was reduced by 40%. The reason why the flow rate of the evaporative gas did not become half or less is that there is a background heat intrusion amount due to radiation. Therefore, according to the present invention, a long and high-performance oxide superconducting conductor conducting element can be provided by simple means.

(Example 2)
First, a Dy—Ba—Cu—O single crystal oxide superconductor having a diameter of 46 mm, a thickness of 15 mm, and 25 mol% of 211 phase finely dispersed in 123 phase was prepared by a melting method. Then, from this oxide superconductor, two rod-shaped samples having a length of 40 mm, a width of 5 mm, and a thickness of 0.8 mm are cut out, and a silver paste is applied to the bonding surface 3 and heated in a closely contacted state. A 75 mm oxide superconducting conductor 1 was produced. A silver film having a thickness of 10 μm was formed on the surface of the half portion (one oxide superconductor portion) on one side from the joint surface 3 of the oxide superconductor 1 to form a metal film serving as the heat transfer body 4. Next, both ends of the oxide superconducting conductor 1 are solder-connected to the copper electrode terminals 2 and bonded and fixed from both sides of the oxide superconducting conductor 1 with glass fiber reinforced plastics (GFRP), and the structure as shown in FIG. An oxide superconducting conductor conducting element C was prepared. For comparison, an oxide superconducting conductor having a structure without a heat transfer body as shown in FIG. 10 was prepared in the same manner as the oxide superconducting conductor conducting element C by omitting the procedure for forming a metal film serving as a heat transfer body. An energizing element D was produced.

  When the oxide superconducting conductor conducting element C and the oxide superconducting conductor conducting element D were energized in a state where the entire energizing element was immersed in liquid nitrogen, both energizing elements were able to conduct 500 A. Next, when only the electrode terminal portions at both ends were cooled with liquid nitrogen and the current-carrying element central portion was cooled with conduction cooling from the electrode terminals at both ends, the oxide superconducting conductor energization element C was able to carry 500 A. However, with respect to the oxide superconducting conductor conducting element D, the element was melted when 300 A was energized, and no further energization was possible.

  From the above results, it was confirmed that the heat transfer body in the present invention effectively removed Joule heat generated on the oxide superconductor joint surface even under severe cooling conditions. Therefore, according to the present invention, a long and high-performance oxide superconducting conductor conducting element can be provided by simple means.

(Example 3)
First, a 65 mm diameter, 15 mm thick, 20 mol% 211 phase and silver added at 10 mass% to the initial raw material were finely dispersed in the 123 phase by the melting method (0.9 Gd-0.1 Dy) -Ba-Cu-O single A crystalline oxide superconductor was prepared. And 8 pieces of mosquito coil incense-like oxide superconductors having an outer diameter of about 60 mm were cut out from the oxide superconductor. Two mosquito coil incense oxide superconductors are stacked so that the current-carrying direction is the same rotational direction, and is joined with solder at the central part of the mosquito coil incense, and thin insulation is provided at the solder joint in the central part. An aluminum foil having a thickness of 0.1 mm, which is a heat transfer body 4, was connected with an adhesive via a polyimide film. After joining four sets of two pieces joined together with solder on the outside of the mosquito coil incense oxide superconductor, the thickness 0. which is the heat transfer body 4 via a thin insulating polyimide film on the outside solder joint. A 1 mm aluminum foil was connected with an adhesive to produce an oxide superconducting conductor 1 in which eight sheets were laminated. Both ends of this oxide superconducting conductor 1 were soldered to the electrode terminal 2 made of copper. Thereafter, an oxide superconducting conductor conducting element E having a structure similar to that shown in FIG. 7 was produced in which the entire element was reinforced with glass fiber reinforced plastics (GFRP) and an epoxy resin (trade name: Stycast 2850FT).

  The electrode terminal part of the oxide superconducting conductor conducting element E and each heat transfer body were connected to the cold head of the refrigerator. At the time of connection, a polyimide film was sandwiched so as to be electrically insulated from the cold head portion. In this state, it was cooled to 70K with a refrigerator and energized. As a result, it was confirmed that 500 A could be energized and a magnetic field of 1 T or more was generated. Therefore, according to the present invention, a long and high-performance oxide superconducting conductor conducting element can be provided by simple means.

  According to the present invention, it is possible to provide a long and high-performance oxide superconducting conductor conducting element with simple means, so that the industrial application range of the oxide superconductor is expanded.

It is sectional drawing which shows an example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another Example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows another example of the structure of the oxide superconducting conductor energization element of this invention. It is sectional drawing which shows the structural example of the conventional oxide superconducting conductor. It is sectional drawing which shows the structure of the oxide superconductor energization element of a comparative example. It is sectional drawing which shows the structure of the oxide superconducting conductor energization element of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxide superconducting conductor 2 Electrode terminal 3 Joint surface 4 Heat transfer body 5 Support body

Claims (4)

Between an oxide superconductor in which two or more oxide superconductors are electrically joined, an electrode terminal electrically joined to both ends of the oxide superconductor, and the oxide superconductor constituting the oxide superconductor An oxide superconducting conductor conducting element, characterized in that it is a current lead composed of a heat transfer body connected to a joint portion of the heat transfer body , and the heat transfer body is connected to an electrode terminal on one side . Oxide superconductor current device according to claim 1, wherein the heat transfer body, wherein the a film formed on the surface of the oxide superconductor. The cross-sectional area S _{A of} the heat transfer body, the cross-sectional area of the oxide superconductor on which the heat transfer body film is formed, S _B , the thermal conductivity of the heat transfer body k _A , and the heat transfer body film is When the thermal conductivity of the formed oxide superconductor and k _B, according to claim 2 the cross-sectional area S _a of the heat transfer member is characterized in that it is a _{S a ≦ S B × (k} B / k a) An oxide superconducting conductor energizing element according to 1. It said oxide superconductor is a single crystalline REBa ₂ Cu ₃ O _x phase (RE is one or more selected from Y or a rare earth element, x is 7 or less 6.8 or more) RE ₂ BaCuO in The oxide superconductor conducting element according to any one of claims 1 to 3 , wherein the oxide superconductor has _five phases finely dispersed.

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