JP2012109254A - Superconductive current lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a heat intrusion amount of a superconductive current lead using a high temperature superconductive thin film wire.SOLUTION: A superconductive current lead according to an embodiment includes a high temperature superconductive layer 3 formed on a metal substrate 1 through an intermediate layer 2 and made of a high temperature superconductor, a protective layer 4 formed on the high temperature superconductor layer and made of a metal, a high temperature superconductive thin film wire 104 formed on the protective layer and having a solder connection layer 6 including silver, a reinforcement material 10 provided so as to enclose the high temperature superconductive thin film wire, and electrodes 8 provided at the reinforcement material and disposed so as to connect the solder connection layer of the high temperature superconductive thin film wire through solder 9.

Description

  The present invention relates to a superconducting current lead used for a superconducting device cooled to a cryogenic temperature.

  The biggest feature of the superconducting phenomenon is that the electric resistance of the conductor becomes zero at the critical temperature, so that no heat is generated even when energized, so that a large current can flow without loss. A superconducting magnet device used in a superconducting power storage system is a typical device that applies this superconducting phenomenon.

  In this superconducting magnet device, the following superconducting coil is housed together with liquid helium in an intermediate temperature shield of a cryostat (vacuum insulation container) and thermally shielded from the external environment (approx. -269K for liquid helium temperature). It is necessary to supply a current from an external power supply device via a superconducting current lead.

  In short, the function required for a superconducting current lead is “conducting electricity but not heat”. Superconductors are ideal as materials for such superconducting current leads because of their nearly zero electrical resistance and poor thermal conductivity. High-temperature superconductors are especially used as materials for superconducting current leads that connect the 80K to 4K levels. Yes. Some conventional superconducting current leads use bulk materials such as YBCO and Bi2223, but the bulk materials are particularly fragile and easily damaged, so handling was necessary. Therefore, a device that makes the handling relatively easy is considered by using a high-temperature superconducting wire that allows a certain degree of deformation as a material of the superconducting current lead.

  In manufacturing such a high-temperature superconducting wire, first, an intermediate layer is formed on an oxide metal substrate, and a RE123-based high-temperature superconducting thin film such as YBCO (YBa2Cu3O7-x) is formed thereon. The intermediate layer is a thin film made of, for example, cerium oxide or magnesium oxide that is located between the metal substrate and the high-temperature superconducting layer and promotes crystal growth.

  It is necessary to form an electrical connection at the end of the high-temperature superconducting thin film. As a method for this, a metal layer is formed by a method such as vapor deposition or sputtering and soldered with indium or the like (for example, Patent Documents). 1 and 2) and a method of pressure bonding indium (for example, see Patent Document 3) are known. As the material of the electrode, gold or silver is usually used for any reason that avoids a chemical reaction with the high-temperature superconductor and allows heat treatment in an oxygen atmosphere.

  On the other hand, in a high-temperature superconducting thin film wire (coated conductor) called a second generation wire, in which an intermediate layer is formed on a metal substrate and a RE123-based high-temperature superconducting thin film such as YBCO is formed thereon, the high-temperature superconducting layer is water In order to protect it from reacting with the like, to stabilize the formation of a bypass circuit during normal conduction transition, and to form an electrical connection at the end, a metal protective layer of about several μm is formed on the surface of the high-temperature superconducting layer. Often formed over the entire length of the wire. As the material of the metal protective layer, gold or silver is used for the same reason as that of the metal electrode. High-temperature superconducting thin-film wires are more resistant to strain and stress than high-temperature superconducting bulk materials. Therefore, by manufacturing superconducting current leads using high-temperature superconducting thin-film wires, mechanically robust superconducting current leads can be obtained. .

JP-A-5-251761 JP 2003-298129 A Japanese Patent Laid-Open No. 11-204845

  When producing a superconducting current lead using a high-temperature superconducting thin film wire, it is necessary to form an electrical connection at the end, but this connection is desired to have low electrical resistance and be stable over time. It is. However, it is known that, for example, the method of pressure bonding indium described in Patent Document 3 generally makes it difficult to obtain a low electric resistance. Further, in the method of soldering to a protective layer formed of gold or silver as described in Patent Document 1 or Patent Document 2, electrical resistance is low unless the gold or silver layer is sufficiently thick, and a stable connection is achieved. It is known that it is difficult to obtain. This is because gold and silver easily dissolve in solder materials composed of metals such as lead, tin, and indium, and alloys thereof, and the protective layer may disappear during the soldering process. It is.

  On the other hand, if a thick protective layer made of gold or silver with good thermal conductivity is formed, assuming a certain degree of penetration in the soldering process, heat flows from the high temperature end to the low temperature end via this protective layer, inside the superconducting current lead. Heat transfer occurs, that is, the amount of heat penetration of the superconducting current lead increases.

  The present invention has been made to solve the above-described problems, and easily realizes electrical connection including a soldering process in manufacturing, and reduces the amount of heat penetration from the outside as a superconducting current lead device. With the goal.

  To achieve the above object, the present invention comprises a metal substrate, a high-temperature superconducting layer made of a high-temperature superconductor formed on the metal substrate via an intermediate layer, and a metal formed on the high-temperature superconducting layer. A high-temperature superconducting thin film wire having a protective layer and a solder connection layer containing silver formed on the protective layer, a reinforcing material provided surrounding the high-temperature superconducting thin film wire, and the high temperature provided on the reinforcing material There is provided a superconducting current lead comprising: the solder connection layer of a superconducting wire; and an electrode connected by soldering.

  According to the present invention, it is possible to realize a superconducting current lead that has low connection resistance, is stable over time, and has a small amount of heat penetration.

The perspective view of the high-temperature superconducting thin film wire of Example 1 of the present invention. The perspective view of the high-temperature superconducting thin film wire of the modification of Example 1 of this invention. Sectional drawing of the superconducting electric current lead of Example 2 of this invention. Sectional drawing of the superconducting electric current lead of the modification of Example 2 of this invention. Sectional drawing of the superconducting electric current lead of Example 3 of this invention. Sectional drawing of the superconducting electric current lead of Example 4 of this invention. Sectional drawing of the superconducting electric current lead of Example 5 of this invention.

  Hereinafter, a plurality of embodiments of the superconducting current lead according to the present invention will be described with reference to the drawings.

[Example 1]
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a perspective view showing the configuration of the high-temperature superconducting thin film wire 100 of the present embodiment, and also shows a cross-section for explaining the configuration of each layer.

In the high-temperature superconducting thin film wire 100, a high-temperature superconducting layer 3 is formed on a metal substrate 1 through an intermediate layer 2 made of the above-described cerium oxide, magnesium oxide or the like and promoting crystal growth. Further, a protective layer 4 made of gold, silver or an alloy thereof is formed on the high temperature superconducting layer 3, and a diffusion preventing layer 5 made of copper, nickel or the like is further formed thereon.

  The reason for forming the protective layer 4 on the high-temperature superconducting layer 3 is that the high-temperature superconducting material is an active material that easily reacts with other metals, and reacts when directly in contact with materials other than gold and silver. This is to prevent such performance degradation because it causes degradation. The protective layer 4 also functions as a bypass circuit when a normal conduction transition occurs when a current flows through the high-temperature superconducting layer 3. For these purposes, it is desirable to form the protective layer 4 as thick as possible.

  On the other hand, since gold or silver constituting the protective layer 4 is an expensive material, there is a demand for forming it as thin as possible. However, gold or silver, which is the material of the protective layer 4, has a property that it is easy to dissolve in solder materials composed of metals such as lead, tin, indium and alloys thereof, and high temperature superconductivity when too many protective layers are dissolved. The performance of the thin film wire may be deteriorated. For this reason, when soldering directly to the protective layer 4 for the purpose of electrical connection, the protective layer 4 cannot be formed thin, and it is necessary to ensure a certain thickness.

  Further, the diffusion preventing layer 5 laminated on the protective layer 4 incorporates a high-temperature superconducting thin film wire and considers the ease of electrical connection during manufacturing. In particular, the protective layer 4 is dissolved in the solder in the soldering process. It is provided to prevent the solder connection from being disabled, that is, to suppress diffusion of the protective layer 4 during manufacturing. For this reason, the material of the diffusion preventing layer 5 is preferably copper, nickel, or an alloy thereof that hardly dissolves in the solder material.

  According to the present embodiment, since such a diffusion prevention layer 5 is formed on the protective layer 4 to prevent diffusion of the protective layer 4, even if the protective layer 4 is formed thin, performance deterioration due to electrical connection is caused. A high-temperature superconducting thin film wire that can be prevented can be realized.

  As a modification of the present embodiment, the high-temperature superconducting thin film wire 101 shown in FIG. 2 can be configured. In this modification, a solder connection layer 6 made of silver is further formed on the diffusion prevention layer 5 in FIG. Thereby, in addition to the same effects as the above-described embodiment, silver is easier to solder and has a lower electrical resistance than copper or nickel as the material of the diffusion prevention layer 5. As a high-temperature superconducting thin film wire, better electrical connection can be obtained.

[Example 2]
A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view showing the configuration of the superconducting current lead according to the present embodiment. In the following description, the same reference numerals are given to the same components as those in the above-described embodiment, and the overlapping description is omitted.

  The second embodiment relates to a superconducting current lead 200 using the high-temperature superconducting thin film wire described in the first embodiment. Here, the case where the high-temperature superconducting thin film wire 101 shown in FIG. 2 is used will be described as a representative, but the present invention can be similarly applied to the high-temperature superconducting thin film wire 100 of FIG.

  A high-temperature superconducting thin film wire 101 in which a high-temperature superconducting layer 3 is laminated on a metal substrate 1 through an intermediate layer 2 and a protective layer 4 and a diffusion preventing layer 5 are sequentially laminated is electrically connected to an electrode 8 with solder 9 Is done. Further, the reinforcing material 10 constituting the outline of the superconducting current lead 200 is arranged so as to sandwich the electrode 8, and the inside thereof is impregnated with the impregnating material 7. For example, a resin is used for the impregnating material 7, and in particular, it is conceivable to appropriately select from an epoxy material, a silicon material, a urethane material, and the like.

  As described above, in the conventional superconducting current lead, it is necessary to form the protective layer 4 made of gold or silver with good heat conduction relatively thick in consideration of the penetration in the soldering process. Was the cause of increase in the amount of heat penetration. However, according to the present embodiment, as described in the above-described embodiment 1, since the high-temperature superconducting thin film wire 101 that is formed with a thin protective layer 4 and has no performance deterioration due to electrical connection is used, the electrical resistance is low. A superconducting current lead that is small, mechanically robust, and has a small amount of heat penetration can be realized.

[Example 3]
A third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view showing the configuration of the superconducting current lead according to the present embodiment. In the following description, the same reference numerals are given to the same components as those in the above-described embodiment, and the overlapping description is omitted.

  The high-temperature superconducting thin film wire 102 used for the superconducting current lead 201 shown in FIG. 4 is formed by sequentially laminating an intermediate layer 2, a high-temperature superconducting layer 3, a protective layer 4 and a diffusion prevention layer 5 on a metal substrate 1. Furthermore, the solder connection layer 6 is formed only on the portion of the diffusion prevention layer 5 that is electrically connected to the electrode 8 with the solder 9. Since the material constituting the solder connection layer 6, such as silver, has a high thermal conductivity, this layer is omitted for portions that do not contribute to the connection with the electrode 8, and the solder connection layer 6 is compared to the case shown in FIG. 3. By reducing the amount of the material constituting the material itself, the amount of heat penetration as the superconducting current lead can be further reduced.

According to the configuration of the present embodiment, the same effects as those of the second embodiment can be obtained, and the superconductivity in which the amount of heat penetration is further reduced by arranging the solder connection layer on the high-temperature superconducting thin film wire in a limited manner. A current lead can be realized.

Further, as a modification of the present embodiment, as shown in FIG. 5, not only the solder connection layer 6 but also the diffusion prevention layer 5 located below this high-temperature superconducting thin film wire 103 used for the superconducting current lead 202. However, it is also conceivable to adopt a structure in which it is locally arranged only at the site connected to the electrode 8. In the superconducting current lead 202 thus configured, the material constituting the diffusion preventing layer 5, for example, copper, has a high thermal conductivity and does not contribute to the connection with the electrode 8, like the silver constituting the solder connection layer 6. By eliminating this layer, the amount of heat penetration as a superconducting current lead can be reduced.

[Example 4]
A fourth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view showing the configuration of the superconducting current lead according to the present embodiment. In the following description, the same reference numerals are given to the same components as those in the above-described embodiment, and the overlapping description is omitted.

  The high-temperature superconducting thin film wire 104 used for the superconducting current lead 203 shown in FIG. 6 is formed by sequentially laminating an intermediate layer 2, a high-temperature superconducting layer 3, and a protective layer 4 on the metal substrate 1. 4, the solder connection layer 6 is formed only on the part electrically connected to the electrode 8 by the solder 9. The material constituting the solder connection layer 6, such as silver, has high thermal conductivity, and by eliminating this layer for portions that do not contribute to the connection with the electrode 8, the amount of heat penetration as a superconducting current lead can be reduced. . Furthermore, in this case, since the silver constituting the solder connection layer 6 is easily dissolved in metals such as lead, tin, and indium, which are the materials of the solder 9, and alloys thereof, the locally formed solder connection layer 6 is used as the solder connection layer 6. For example, it is necessary to secure a sufficient thickness of, for example, about 1 μm or more.

  According to the present embodiment, even if silver is dissolved in the solder 9, the high-temperature superconducting thin film wire 104 provided with the solder connection layer 6 having a sufficient thickness is used, so that there is no performance deterioration due to electrical connection. Therefore, it is possible to realize a superconducting current lead having a low electrical resistance, mechanically robust, and a small amount of heat penetration.

[Example 5]
A fifth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view showing the configuration of the superconducting current lead according to the present embodiment. In the following description, the same reference numerals are given to the same components as those in the above-described embodiment, and the overlapping description is omitted.

  The high temperature superconducting thin film wire 104 used for the superconducting current lead 204 shown in FIG. 7 is not directly connected to the electrode 8 by soldering but is connected via a Bi2223 silver sheath wire 11 which is a high temperature superconducting wire. . That is, the electrode 8 and the Bi2223 silver sheath wire 12 are connected by the solder 9A, and the Bi2223 silver sheath wire 11 and the solder connection layer 6 of the high-temperature superconducting thin film wire 1D are connected by the solder 9B. Here, Bi2223 (Bi2Sr2Ca2Cu3O10 + z) is known as a useful high-temperature superconducting material having a superconducting transition temperature exceeding 100K.

  Hereinafter, the case where silver is used for the solder connection layer 6 will be described. The amount of silver dissolved in the soldering process decreases as the temperature and time during soldering are shorter. Further, the smaller the heat capacity of the other party to be connected, the shorter the time for connection. Therefore, according to the superconducting current lead 105 configured in this way, in addition to the operational effects of the present embodiment described above, the amount of silver dissolved into the solder can be reduced.

  As described above, a plurality of examples have been described as preferred embodiments of the present invention. However, the present invention is not limited to the above-described examples, and various modifications can be made without departing from the gist of the invention. be able to. It is also conceivable to configure a superconducting current lead by arbitrarily combining technical features in a plurality of embodiments. For example, the solder connection layer 6 in Example 2 shown in FIG. 3 is uniformly laminated on the diffusion prevention layer 5, and the solder connection layer 6 in Example 3 shown in FIG. 4 is the diffusion prevention layer 5. However, as a modification of such a configuration, the solder connection layer 6 is relatively thick in the vicinity of the connection portion with the electrode 8 and relatively in other positions. Even if it is formed to be thin, substantially the same effect can be obtained. Such a structure for changing the thickness is also conceivable in the diffusion preventing layer 5 in FIG.

  DESCRIPTION OF SYMBOLS 1 ... Metal substrate, 2 ... Intermediate layer, 3 ... High temperature superconducting layer, 4 ... Protective layer, 5 ... Diffusion prevention layer, 6 ... Solder connection layer, 7 ... Impregnation material, 8 ... Electrode, 9 ... Solder, 10 ... Reinforcing material 11 ... Bi2223 silver sheath wire, 100, 101, 102, 103, 104 ... high temperature superconducting thin film wire, 200, 201, 202, 203, 204 ... superconducting current lead.

Claims (4)

  A metal substrate, a high-temperature superconducting layer made of a high-temperature superconductor formed on the metal substrate via an intermediate layer, a protective layer made of metal formed on the high-temperature superconducting layer, and formed on the protective layer A high-temperature superconducting thin film wire having a solder connection layer containing silver, a reinforcing material provided surrounding the high-temperature superconducting thin film wire, and connected to the solder connecting layer of the high-temperature superconducting wire provided on the reinforcing material by soldering A superconducting current lead.   The superconducting current lead according to claim 1, wherein the solder connection layer is laminated on a part of the diffusion preventing layer.   3. The superconducting current lead according to claim 1, wherein the diffusion preventing layer is provided so as to be laminated on a part of the metal protective layer.   It further has a Bi2223 silver sheath wire connected by solder to each of the solder connection layer and the electrode, and the solder connection layer and the electrode are connected via the sheath wire. The superconducting current lead according to any one of claims 1 to 3.

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