JP5118412B2 - Assembled conductor of oxide superconducting wire and method for producing the assembled conductor - Google Patents

Description

  The present invention relates to an assembly conductor in which a plurality of oxide superconducting wires are assembled, and a method for manufacturing the assembly conductor.

  In recent years, various devices have been developed as power application devices using superconducting wires. For example, a superconducting magnetic energy storage device (hereinafter abbreviated as SMES) has features such as higher energy storage efficiency and faster energy loading / unloading speed than other energy storage devices. Development is underway energetically. In addition, development of AC coils typified by transformers, superconducting rotating machines typified by electric motors and generators, current limiters using high-resistance wires during normal conduction, and the like are also under development.

When a metal-based superconducting wire such as NbTi or Nb ₃ Sn is used for such power application equipment, it will be in a superconducting state unless the wire is cooled to a temperature close to 4.2 K using liquid helium as a coolant. Therefore, the cooling cost increases, which is an adverse effect of practical use. On the other hand, Bi-based and Y-based oxide superconducting wires have a high superconducting transition temperature and can use 77.3K liquid nitrogen as a coolant for achieving a superconducting state, so that the cooling cost can be greatly reduced. is there. For example, in the case of a Y-based oxide superconducting tape wire, a typical superconducting material having a tape width of 10 mm, a critical current of about 100 to 300 A when cooled to 77.3 K with liquid nitrogen and an external magnetic field of 0 T is used. Those having characteristics are available and can be used as, for example, pancake coils.

In general, in the case of a metal-based superconducting wire such as NbTi or Nb ₃ Sn, if a current exceeding the critical current flows, a normal conducting transition occurs immediately and the superconducting state cannot be maintained. Therefore, for example, when the SMES is configured using such a metal-based superconducting wire, when a current exceeding the critical current flows, the normal conduction transition occurs immediately and the energy accumulated in the coil is released. On the other hand, in the case of a Y-based oxide superconducting tape wire, a superconducting state can be maintained without causing a normal conducting transition as long as it is in a current range called a magnetic flux flow region even if a current exceeding the critical current is passed. . Therefore, applications utilizing the advantages of such Y-based oxide superconducting tape wires are expected.

Further, when applied to various power application devices such as SMES and transformers, further increase in current is required. Therefore, it has been considered that a plurality of superconducting wires are connected in parallel and assembled to increase the allowable current that can flow as a whole (see, for example, Patent Document 1).
JP 2001-256841 A

  By the way, in order to connect a plurality of superconducting strands in parallel, an electrode made of a normal conducting material such as copper is used at the connecting portion, and a plurality of superconducting strands are connected in series in order to obtain a superconducting strand having a predetermined length. Even in this case, an electrode made of a normal conducting material is used at the connecting portion. Further, in order to connect such a superconducting element wire to an external circuit, it is necessary to always connect it to an electrode made of a normal conducting material. Then, even if each superconducting wire itself is in a superconducting state and the resistance is zero, if there is a slight variation in the connection resistance between each superconducting wire and each electrode, the current flowing through each superconducting wire will be biased. As a result, current drift occurs in which a large current flows in some superconducting wires.

  As a result, the critical current of the superconducting element wire through which the largest current flows due to the drift current limits the current that can flow through the entire assembly conductor. There was an inconvenience that the total current was lower.

  The present invention has been made in view of such circumstances, and provides an aggregated conductor of oxide superconducting wires capable of reducing current drift while using a plurality of oxide superconducting wires. Objective. And it aims at providing the manufacturing method of the assembly conductor of such an oxide superconducting strand.

  As a result of intensive studies to solve the above problems, the present inventors have determined connection resistances between a plurality of oxide superconducting element wires and a plurality of electrodes respectively connected to both ends of the plurality of oxide superconducting element wires. The inventors have found that current drift between a plurality of oxide superconducting wires can be reduced by setting the resistance value range within a predetermined range.

That is, an assembly conductor of oxide superconducting wires according to the present invention includes a plurality of oxide superconducting wires for parallel connection and electrodes respectively connected to both ends of the plurality of oxide superconducting wires. When the length of each oxide superconducting wire is L (mm) and the critical current of each oxide superconducting wire on the basis of 0.01 μV / mm in an external magnetic field of 0 T is Ic (A), The connection resistance R (Ω) between the superconducting element wire and the electrodes connected to both ends of each oxide superconducting wire is expressed by the following formula (1) at the operating temperature of each oxide superconducting wire, respectively. Each of the oxide superconducting wires is connected in parallel through electrodes connected to both ends, and is assembled.
0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (1)
According to this configuration, current drift can be reduced while using a plurality of oxide superconducting wires.

Moreover, it is preferable that the connection resistance R (Ω) satisfies the condition represented by the following formula (2).
0.1 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 2 × 0.01 × 10 ⁻⁶ × L / Ic (2)
According to this configuration, current drift can be further reduced.

  The oxide superconducting element wire and the electrode are preferably soldered with solder using a bismuth (Bi) -containing alloy. The solder is preferably an alloy of bismuth (Bi) and tin (Sn). The solder may be an alloy of bismuth (Bi) and indium (In).

  According to this configuration, variations in connection resistance R can be reduced.

  Moreover, it is preferable to further provide a connection part for connecting the plurality of oxide superconducting wires in parallel. According to this configuration, a plurality of oxide superconducting wires are connected in parallel by the connecting portion to form an assembly conductor, and a current that can be passed through the assembly conductor is greater than a current that can be passed through a single oxide superconducting wire. Can be increased.

Moreover, the manufacturing method of the assembly conductor of the oxide superconducting wire which concerns on this invention is 100 degreeC using the solder containing bismuth (Bi) for the both ends and several electrodes of a some oxide superconducting wire. By soldering at a predetermined temperature within a range of ˜200 ° C., both ends of the plurality of oxide superconducting wires are connected to a plurality of electrodes, and the plurality of oxide superconductivity is connected via the plurality of electrodes. By connecting the strands in parallel, the plurality of oxide superconducting strands are assembled, and the length of each of the oxide superconducting strands is L (mm) on the basis of 0.01 μV / mm at an external magnetic field of 0T. When the critical current of each oxide superconducting element wire is Ic (A), the connection resistance R (Ω) between each of the oxide superconducting element wires and electrodes connected to both ends of each of the oxide superconducting element wires At the operating temperature of each oxide superconducting wire. And are set so as to satisfy the conditions represented by the following formula (1) .
0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (1)

According to this configuration, it is possible to manufacture an aggregated conductor of oxide superconducting wires that can reduce current drift while using a plurality of oxide superconducting wires. Further, according to this configuration, it is possible to reduce variations in the connection resistance R.

  The solder is an alloy of bismuth (Bi) and tin (Sn), and the temperature is preferably in the range of 140 ° C to 200 ° C. The solder may be an alloy of bismuth (Bi) and indium (In), and the temperature may be in the range of 100 ° C to 200 ° C. According to this configuration, variations in connection resistance R can be reduced.

  The connection resistance R (Ω) is preferably set by adjusting the connection area between the oxide superconducting element wire and the electrode. According to this configuration, it is easy to set the connection resistance R (Ω) within a resistance value range that satisfies the above-described conditions.

According to the assembly conductor of the oxide superconducting wire having such a configuration and the method of manufacturing the assembly conductor, the plurality of oxide superconducting wires are connected to both ends of the plurality of oxide superconducting wires. A plurality of electrodes, the length of each of the oxide superconducting wires is L (mm), and the critical current on the basis of 0.01 μV / mm at an external magnetic field of 0 T is Ic (A), the oxide superconductivity The connection resistance R (Ω) between each of the strands and each of the electrodes is 0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic. By satisfying the conditions, current drift can be reduced while using a plurality of oxide superconducting wires.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. FIG. 1 is an explanatory diagram conceptually showing an example of the configuration of an aggregated conductor of oxide superconducting wires according to an embodiment of the present invention and a measurement circuit for measuring the characteristics of the aggregated conductor. . FIG. 2 is an enlarged view of the assembly conductor in the vicinity of the electrode shown in FIG. 1 and an explanatory diagram conceptually showing a measurement circuit for measuring the characteristics of the assembly conductor.

  An assembled conductor 1 shown in FIG. 1 is an example of a conductor obtained by assembling oxide superconducting wires. For example, liquid nitrogen cooling represented by superconducting coils such as magnetic energy storage, transformers, and fusion coils. It is an oxide superconducting wire used as a constituent material of a superconducting magnet of a type and a superconducting magnet cooled by a refrigerator. An application example in which the oxide superconducting wires according to the present invention are assembled includes a pancake coil.

  The assembly conductor 1 shown in FIG. 1 is connected to the oxide superconducting element wires 11 and 21, electrodes 12 and 13 respectively connected to both ends of the oxide superconducting element wire 11, and both ends of the oxide superconducting element wire 21. Electrodes 22 and 23 are provided.

For example, the oxide superconducting wires 11 and 21 are formed by depositing 1 μm of Gd—Zr oxide as an intermediate layer on a Hastelloy substrate having a thickness of 100 μm, a width of 10 mm, and a length of 10 m, and a thickness of 0.5 μm. the CeO ₂ layer was formed as a cap layer of, formed by _YBa 2 _Cu 3 _{O 7-x} superconducting film a CVD (Chemical Vapor deposition) apparatus thick 1μm thereon, finally forming a Ag layer as a protective layer It is cut out from a Y-based superconducting tape wire obtained by film formation. 1 and 2 show the oxide superconducting wires 11 and 21 as viewed from the thickness direction.

  The electrodes 12, 13, 22, and 23 are made of a normal conductive material such as copper. The oxide superconducting wire 11 and the electrode 12 are soldered by a solder 14, and the oxide superconducting wire 11 and the electrode 13 are soldered by a solder 15. The oxide superconducting wire 21 and the electrode 22 are soldered by a solder 24, and the oxide superconducting wire 21 and the electrode 23 are soldered by a solder 25.

  The electrodes 12, 13, 22, and 23 may be connection terminals for connecting, for example, the oxide superconducting strands 11 and 21 to a normal conducting circuit unit. For example, a plurality of oxide superconducting strands are connected in series. It may be a connection terminal for connecting and extending.

  In addition, in the assembly conductor 1 shown in FIG. 1, both ends of the oxide superconducting element wire 11, that is, the electrodes 12 and 13, in order to confirm the current drift reduction effect in Comparative Example 1 and Examples 1 to 3 described later. Since it is necessary to individually measure the voltage V1 generated between them and the voltage V2 generated between both ends of the oxide superconducting element wire 21, that is, between the electrodes 22 and 23, the electrodes 12 and 22 and the electrodes 13 and 23 are connected to each other. The oxide superconducting wires 11 and 21 are connected in parallel by connecting the electrodes 12 and 22 and the electrodes 13 and 23 by connecting portions made of conductors such as wirings. Of course as well. In addition, the electrode 12 and the electrode 22, and the electrode 13 and the electrode 23 are each configured as a single electrode. For example, a part of one electrode is the electrode 12, the other part is the electrode 22, and one of the other electrodes By using the part as the electrode 13 and the remaining part as the electrode 23, a single electrode may be used as the connection part.

  As the solders 14, 15, 24, and 25, various solders such as Sn—Ag—Cu, Bi—Sn, and Bi—In can be used. In this specification, “solder” refers to “a filler metal for brazing having a low melting point of less than 450 ° C.” in accordance with the definition of JIS Z 3001, and “soldering” refers to “ It refers to a welding method that is performed without melting the material as much as possible.

  A connecting portion between the oxide superconducting wires 11 and 21 and the electrodes 12, 13, 22, and 23 is, for example, in a range of width 10 mm × length 14 mm. The area of the connecting portion between the oxide superconducting wires 11 and 21 and the electrodes 12, 13, 22 and 23 is such that the length of the oxide superconducting wire is L (mm) and 0.01 μV / in external magnetic field 0T. When the critical current on the mm basis is Ic (A), the connection resistance R (Ω) between the oxide superconducting element wire and the electrode is an area that satisfies the condition represented by the following expression (1). What is necessary is just to be 10 mm in width x 14 mm in length.

0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (1)
As described above, the connection resistance R (Ω) between the oxide superconducting element wire and the electrode is adjusted so as to satisfy the condition represented by the expression (1) by adjusting the area of the connecting portion between the oxide superconducting element wire and the electrode. Set to.

  Here, the length L of the oxide superconducting wire indicates the length of the oxide superconducting wire sandwiched between the electrodes connected to both ends. For example, the length L of the oxide superconducting wire 11 is 1 means the length of the oxide superconducting element wire 11 from the position indicated by reference numeral X1 to the position indicated by reference numeral X2. For example, the length L of the oxide superconducting element wire 12 in FIG. It means the length of the oxide superconducting element wire 12 from the position indicated by Y1 to the position indicated by reference numeral Y2.

  When Bi-Sn having a melting point of 130 ° C. is used as the solder 14, 15, 24, 25, the soldering temperature is desirably in the range of 140 ° C. to 200 ° C., for example, 150 ° C. Further, when Bi-In having a melting point of 80 ° C. is used as the solders 14, 15, 24, 25, the soldering temperature is desirably in the range of 100 ° C. to 200 ° C., for example, 120 ° C. Thus, deterioration of the oxide superconducting element wires 11 and 21 can be reduced by setting the soldering temperature to 200 ° C. or lower. At the time of soldering, after melting the solder, the oxide superconducting element wire 11 and the electrodes 12, 13 and the oxide superconducting element wire 21 and the electrodes 22, 23 are cooled in a state where both are fixed so as not to be peeled off. By doing so, a stable connection resistance can be obtained.

  The following findings were obtained from the experimental results shown in Comparative Example 1 and Examples 1 to 3 described below for the aggregated conductor 1 of the oxide superconducting wires thus obtained.

  The first finding is as follows. That is, in a state where the assembled conductor 1 is cooled and the oxide superconducting element wires 11 and 21 are in a superconducting state, the current path L1 from the electrode 12 to the electrode 13 via the oxide superconducting element wire 11 and the electrode 22 When the current paths L2 reaching the electrodes 23 through the oxide superconducting wires 21 are connected in parallel and assembled, and current is passed through the parallel circuit, the resistance values of the oxide superconducting wires 11 and 21 are zero. Therefore, the current I1 flowing through the current path L1 and the current I2 flowing through the current path L2 are current values depending on the balance of the connection resistances R between the oxide superconducting wires 11, 21 and the electrodes 12, 13, 22, 23. Difference, that is, current drift occurs.

  In order to eliminate current drift, ideally, each connection resistance R should be all zero or each connection resistance R should be completely the same. However, in an actual device, each connection resistance R is all zero. It is difficult to make each connection resistance R completely the same. Rather, it has been experimentally confirmed that when the resistance value is decreased so as to bring each connection resistance R close to zero, current drift increases conversely due to variations among the connection resistances R.

  Then, each connection resistance R is set to a resistance value obtained in relation to a voltage generated in the oxide superconducting element wires 11 and 21 by the magnetic flux current resistance, specifically to a resistance value satisfying the condition of the following expression (3). As a result, it has been found that current drift between the current paths L1 and L2 can be suppressed. This is a knowledge that has not been known as a countermeasure for preventing the drift of the conventional metallic superconducting wire.

R ≧ 0.01 × 0.01 × 10 ⁻⁶ × L / Ic (3)
However, the length of each oxide superconducting wire: L (mm)
Critical current on the basis of 0.01 μV / mm at an external magnetic field of 0 T: Ic (A)
The second finding is as follows.

  When a plurality of oxide superconducting wires are created, the critical current Ic of each oxide superconducting wire varies, so it is difficult to create an oxide superconducting wire having the same critical current. The resistance value of the oxide superconducting element wire has a property that the flowing current slightly increases when the current approaches the critical current Ic and rapidly increases when the current exceeds the critical current Ic.

  Here, when the oxide superconducting element wire 11 having a critical current Ic1 and the oxide superconducting element wire 21 having a critical current Ic2 are connected in parallel, the connection resistance R with the electrode is zero ohms. In the circuit, an ideal condition is assumed in which only the resistance generated in the oxide superconducting wires 11 and 21 itself exists. It is assumed that the critical current Ic1 is smaller than the critical current Ic2. Then, the current flowing through the oxide superconducting wires 11 and 21 first approaches the critical current Ic1 in the oxide superconducting wire 11 first. Then, a slight resistance is generated in the oxide superconducting element wire 11, the current flowing through the oxide superconducting element wire 11 is decreased, and the current is distributed so that the current flowing through the oxide superconducting element wire 21 is increased.

  In this way, under the ideal conditions as described above, the currents flowing through the oxide superconducting wires 11 and 21 are automatically balanced in the vicinity of the critical current Ic1, so that, for example, the critical current Ic1 and the critical current Ic2 Even if there is a difference, the current flowing in the oxide superconducting element wire 11 can be increased to near the critical current Ic1, and the current flowing in the oxide superconducting element line 21 can be increased to near the critical current Ic2. A current of (Ic1 + Ic2) can be passed through the parallel circuit of the strands 11 and 21.

  However, in practice, it is difficult to realize such ideal conditions, and there is a connection resistance R between the oxide superconducting element wire and the electrode. The resistance values of the current paths L1 and L2 are obtained by adding the resistance values of the oxide superconducting wires 11 and 21 and the connection resistance R, respectively. As a result, the ratio of the resistance value of the oxide superconducting element wires 11 and 21 themselves to the resistance value of the entire current paths L1 and L2 becomes relatively small. As a result, in one oxide superconducting element wire 11, the flowing current becomes the critical current Ic1. Even when the resistance is generated in the oxide superconducting element wire 11 near, current distribution that does not exceed the critical current Ic1 is hardly generated in the oxide superconducting element wire 11 as described above. As the connection resistance R increases, the influence of the resistance of the oxide superconducting element wire 11 itself on the current distribution between the oxide superconducting element wires 11 and 21 decreases. As a result, the oxide superconducting element wire 11, The current that can flow through the 21 parallel circuits is smaller than the current (Ic1 + Ic2) that flows under the ideal conditions as described above. Such a situation is the same even when three or more oxide superconducting wires are connected in parallel.

  In the case where a plurality of oxide superconducting element wires are connected in parallel, the inventors of the present application change the connection resistance R of each oxide superconducting element wire to a resistance value that satisfies the following expression (4), thereby providing a parallel connection. It has been found that the total current value that can be passed through a plurality of connected oxide superconducting wires can be increased.

R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (4)
As described above, from the first and second findings, the value of the connection resistance R is set in the range indicated by the expression (1) that satisfies the conditions of the expressions (3) and (4) at the same time. The current can be increased to near the critical current for each of the oxide superconducting wires 11 and 21, that is, the allowable current that can flow through the assembled conductor 1 can be increased while reducing the current drift between them.

  Here, as apparent from the equation (1), the range of the appropriate resistance value of the connection resistance R is the length L (mm) of the oxide superconducting element wire, 0.01 μV / mm standard in the external magnetic field 0T. It changes according to the critical current Ic (A), and there is no appropriate resistance value range as an absolute value.

  In addition, although the assembly conductor 1 showed the example using two oxide superconducting strands, the oxide superconducting strand should just have two or more, and may aggregate three or more. Further, the length L of each oxide superconducting wire may be the same or different. Furthermore, the length L of each oxide superconducting wire may be the same, and the material and structure of each oxide superconducting wire, the thickness of the superconducting layer, and the like may be changed.

  The third finding is as follows. That is, as the solder 14, 15, 24, 25, using a bismuth (Bi) -containing alloy having a low melting point such as Bi—Sn having a melting point of 130 ° C. or Bi—In having a melting point of 80 ° C., a temperature of 200 ° C. or less, For example, in the case of Bi-Sn, the solder is heated and melted at a temperature in the range of 140 ° C. to 200 ° C., for example, in the case of Bi—In, in the range of 100 ° C. to 200 ° C., and then cooled and soldered. We found that the connection resistance per unit area can be controlled with good reproducibility. Thereby, the connection area between the oxide superconducting element wire and the electrode is set to a connection resistance R satisfying the expression (1) while suppressing the connection area within a practical range, for example, a range of about 10 mm width × about 100 mm length. Became easier.

  Next, with respect to the assembly conductor 1 of the oxide superconducting wire shown in FIG. 1, an example in which current drift was experimentally measured using a sample, and the structure similar to that of the assembly conductor 1, the oxide superconducting wire A comparative example in which current drift is experimentally measured using a sample in which the connection resistance R between the electrode and the electrode does not satisfy the condition of formula (1) will be described.

Comparative Example 1

  In Comparative Example 1, the connection resistance R between the oxide superconducting wire 11 and the electrodes 12 and 13 and the connection resistance R between the oxide superconducting wire 21 and the electrodes 22 and 23 are expressed by the formula (1). An evaluation result of current drift between the oxide superconducting element wire 11 and the oxide superconducting element wire 21 when the condition is not satisfied is shown.

  The electrodes 12, 13, 22, and 23 were fixed to a disc-shaped FRP (Fiber Reinforced Plastics) winding frame (not shown) having an outer diameter of 60 mm. Then, Sn—Pb solder is placed in a range of width 10 mm × length 14 mm of the electrode 22 and heated to 280 ° C., and then the Ag side of one end of the oxide superconducting element wire 21 is brought into contact with the molten solder. Fixed. Next, Sn—Pb solder is placed in a range of width 10 mm × length 14 mm of the electrode 12 and heated to 280 ° C., and then the Ag side of one end of the oxide superconducting element wire 11 is brought into contact with the molten solder. Fixed.

  Then, the oxide superconducting wires 11 and 21 are arranged along an unillustrated winding frame, and Sn—Pb solder is placed on the electrode 23 in a range of width 10 mm × length 14 mm, heated to 280 ° C., and then oxide superconductivity. The other end of the strand 21 was fixed so that the Ag side was in contact with the molten solder. Next, Sn—Pb solder is placed in a range of 10 mm width × 14 mm length of the electrode 13, and after heating to 280 ° C., the Ag side of the other end of the oxide superconducting wire 11 is brought into contact with the molten solder. Fixed.

  At this time, in FIG. 1, the oxide superconducting element wires 11 and 21 are illustrated as having different lengths for the sake of explanation, but actually the oxide superconductivity between the electrode 12 and the electrode 13 is illustrated. The length L of the element wire 11 and the length L of the oxide superconducting element wire 21 between the electrode 22 and the electrode 23 were both fixed to 120 mm. Then, the assembled conductor 1 was naturally cooled to room temperature to fix the solder.

In the sample thus obtained, the self-inductances of the oxide superconducting wires 11 and 21 are both about 1.0 × 10 ⁻⁷ H.

  Further, when the critical currents Ic1 and Ic2 of the oxide superconducting wires 11 and 21 were measured under the conditions of a temperature of 77.3K and an external magnetic field of 0T, the critical current Ic1 of the oxide superconducting wire 11 was 143A and the oxide superconductivity. The critical current Ic2 of the strand 21 was 147A. In this case, the critical current is defined as “the electric field when the generated voltage is divided by the length L (for example, 120 mm) of the oxide superconducting wires 11 and 21 between the electrodes 12 and 22 and the electrodes 13 and 23. , The current value when 0.1 μV / cm (= 0.01 μV / mm) (that is, when the generated voltage is 1.2 μV).

  Next, the assembled conductor sample thus obtained is immersed in liquid nitrogen and cooled, and the oxide superconducting element wires 11 and 21 are brought into a superconducting state. And current deviation between the oxide superconducting wires 11 and 21 were evaluated.

  First, a method for measuring the connection resistance R will be described. As shown in FIG. 2, the measurement point P <b> 1 provided at a position within 5 mm from the end of the solder 14 on the oxide superconducting wire 11 and the position within 5 mm from the interface between the electrode 12 and the solder 14. A predetermined measurement current Im is caused to flow between the provided measurement point P2 using the direct current source 101, and a voltage V1 generated between the measurement point P1 and the measurement point P2 is measured using a voltmeter. . Then, the connection resistance R between the oxide superconducting wire 11 and the electrode 12 is obtained as V1 / Im.

  Further, the measurement point P3 provided at a position within 5 mm from the end of the solder 24 on the oxide superconducting wire 21 and the measurement point provided at a position within 5 mm from the interface between the electrode 22 and the solder 24. A predetermined measurement current Im is passed between the P4 and the DC current source 102, and a voltage V2 generated between the measurement point P3 and the measurement point P4 is measured using a voltmeter. Then, the connection resistance R between the oxide superconducting element wire 21 and the electrode 22 is obtained as V2 / Im.

  As described above, the distance between the end portions of the solders 14 and 24 and the measurement points P1 and P3, and the distance from the interface between the electrodes 12 and 22 and the solders 14 and 24 to the measurement points P2 and P4 are set within 5 mm. This is because when the distance is longer than this, the resistance of the copper electrode itself becomes larger than the connection resistance between the oxide superconducting element wire and the copper electrode, and it is difficult to accurately obtain the connection resistance R.

Similarly, the connection resistance R between the oxide superconducting wire 11 and the electrode 13 and the connection resistance R between the oxide superconducting wire 21 and the electrode 23 were determined. Then, the connection resistance R between the oxide superconducting element wire 11 and the electrodes 12 and 13 was 3.18 × 10 ⁻⁶ Ω and 3.89 × 10 ⁻⁶ Ω. Further, the connection resistance R between the oxide superconducting element wire 21 and the electrodes 22 and 23 was 3.64 × 10 ⁻⁶ Ω and 3.48 × 10 ⁻⁶ Ω.

Here, since the length L of the oxide superconducting wire 11 is 120 mm and the critical current Ic1 is 143 A, 5 × 0.01 × 10 ⁻⁶ × L / Ic = 4.20 × 10 ⁻⁸ Ω. Then, the connection resistance R between the oxide superconducting element wire 11 and the electrodes 12 and 13 greatly exceeds the value of 5 × 0.01 × 10 ⁻⁶ × L / Ic and satisfies the condition of the formula (1). Absent.

In addition, since the length L of the oxide superconducting element wire 21 is 120 mm and the critical current Ic2 is 147A, 5 × 0.01 × 10 ⁻⁶ × L / Ic = 4.17 × 10 ⁻⁸ Ω. Then, the connection resistance R between the oxide superconducting element wire 21 and the electrodes 22 and 23 also greatly exceeds the value of 5 × 0.01 × 10 ⁻⁶ × L / Ic and satisfies the condition of the formula (1). Absent.

  Next, the evaluation result of current drift will be described. First, as shown in FIG. 1, using a direct current source 103, a current was passed through a parallel circuit of a current path L1 and a current path L2, and a total current It flowing through the oxide superconducting element wires 11 and 21 was measured. . The output current of the direct current source 103 was gradually increased at a speed of 60 A / min. At this time, the voltage V11 generated in the oxide superconducting wire 11 is measured from the measurement point P1 provided on the oxide superconducting wire 11 at a position within 5 mm from the end of the solder 14 and the end of the solder 15. It measured between the measurement points P5 provided in the position within 5 mm. Similarly, the voltage V21 generated in the oxide superconducting element wire 21 at this time is measured at a measurement point P3 provided within 5 mm from the end of the solder 24 on the oxide superconducting element 21 and the end of the solder 25. Measured with respect to a measurement point P6 provided at a position within 5 mm from.

The self-inductances of the oxide superconducting wires 11 and 21 are both about 1.0 × 10 ⁻⁷ H, and the voltage generated by the self-inductance is determined by the oxide superconducting wires 11 and 21 and the electrodes 12, 13, 22, and 23. The voltage generated by the connection resistance R and the voltage generated by the magnetic flux flow resistance are made sufficiently smaller.

  For convenience, the current It when the voltage V11 generated in the oxide superconducting wire 11 is 1.2 μV is the current Itc1 and the current It when the voltage V21 generated in the oxide superconducting wire 21 is 1.2 μV. , Measured as current Itc2. As a result, 238A was obtained as the current Itc1, and 226A was obtained as the current Itc2.

  In this case, when there is no current drift in the oxide superconducting wires 11 and 21 and the critical currents Ic1 and Ic2 of the oxide superconducting wires 11 and 21 flow simultaneously, Itc1 / (Ic1 + Ic2) = Itc2 / Ic1 + Ic2 ) = 1.0. From this, it can be seen that the current drift increases as the values of Itc1 / (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2) become smaller than 1.0. Therefore, in the following description, Itc1 / (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2) are used as the evaluation values of the drift.

  In this specification, the drift means a case where a large current flows through a specific wire, and a small amount of current flows through a certain wire as compared with a critical current.

  Since current Itc1 = 238A and current Itc2 = 226A, itc1 / (Ic1 + Ic2) = 0.82 and Itc2 / (Ic1 + Ic2) = 0.78 are significant when calculating Itc1 / (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2). It was confirmed that a large drift occurred.

  As described above, in Comparative Example 1, the connection resistance R between the oxide superconducting element wire 11 and the electrodes 12 and 13 and the connection resistance R between the oxide superconducting element wire 21 and the electrodes 22 and 23 are as follows. When the condition of formula (1) was not satisfied, 0.82 and 0.78 were obtained as evaluation values of current drift.

  In Example 1, Sn96.5Ag3Cu0.5 having a melting point of 280 ° C. was used as the solders 14, 15, 24, and 25. Further, a plurality of samples with different connection resistances R were prepared by changing the length L of the oxide superconducting element wire, the connection area between the oxide superconducting element wire and the electrode, and the heating temperature of the solder, and itc1 / The current drift was evaluated by calculating the values of (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2). In addition, in this specification, the description of the kind (composition) of a solder shall follow JIS Z 3282.

  First, as in Comparative Example 1, two Y-based superconducting tape strands were prepared as oxide superconducting strands 11 and 21, and critical currents Ic1 and Ic2 were measured under conditions of a temperature of 77.3K and an external magnetic field of 0T. The critical current Ic1 of the oxide superconducting wire 11 was 151A, and the critical current Ic2 of the oxide superconducting wire 21 was 146A. Using the oxide superconducting wires 11 and 21 thus obtained, the comparative example 1 is assembled in the same configuration except that Sn96.5Ag3Cu0.5 is used as the solders 14, 15, 24, and 25. A sample of conductor 1 was prepared.

When the connection resistance R of this sample was measured in the same manner as in Comparative Example 1, the connection resistance R between the oxide superconducting element wire 11 and the electrodes 12 and 13 was 3.61 × 10 ⁻⁸ Ω, 3.29. × 10 ⁻⁸ Ω was obtained. Further, the connection resistance R between the oxide superconducting element wire 21 and the electrodes 22 and 23 was 3.37 × 10 ⁻⁸ Ω and 3.58 × 10 ⁻⁸ Ω.

Here, the length L of the oxide superconducting wire 11 is 120 mm, the critical current Ic1 is 151 A, and 0.01 × 0.01 × 10 ⁻⁶ × L / Ic = 0.08 × 10 ⁻⁹ Ω, 5 Since × 0.01 × 10 ⁻⁶ × L / Ic = 3.97 × 10 ⁻⁸ Ω, the connection resistance R between the oxide superconducting wire 11 and the electrodes 12 and 13 is expressed by the formula (1 ) Is satisfied.

Further, since the length L of the oxide superconducting element wire 21 is 120 mm and the critical current Ic2 is 146 A, 0.01 × 0.01 × 10 ⁻⁶ × L / Ic = 0.08 × 10 ⁻⁹ Ω, 5 Since × 0.01 × 10 ⁻⁶ × L / Ic = 4.11 × 10 ⁻⁸ Ω, the connection resistance R between the oxide superconducting element wire 21 and the electrodes 22 and 23 is represented by the formula (1 ) Is satisfied.

  As in Comparative Example 1, when the critical currents Itc1 and Itc2 were measured, the critical current Itc1 was 283A and the critical current Itc2 was 273A. Then, Itc1 / (Ic1 + Ic2) = 0.95 and Itc2 / (Ic1 + Ic2) = 0.92, and 92% or more of the total of the critical currents Ic1, Ic2 is secured as the currents Itc1, Itc2 flowing through the entire assembly conductor 1. I was able to.

  That is, the value of Itc1 / (Ic1 + Ic2), Itc2 / (Ic1 + Ic2) increases in Example 1 that satisfies the condition of Expression (1) as compared to the case of Comparative Example 1 that does not satisfy the condition of Expression (1). It was confirmed that current drift can be reduced.

  FIG. 3 shows a plurality of samples in which the connection resistance R is varied by changing the length L of the oxide superconducting element wire, the connection area between the oxide superconducting element wire and the electrode, and the heating temperature of the solder. It is a graph which shows the result of having calculated the value of Itc1 / (Ic1 + Ic2), Itc2 / (Ic1 + Ic2).

As shown in FIG. 3, a range satisfying 0.01 ≦ R × Ic / (0.01 × 10 ⁻⁶ × L) ≦ 5, that is, 0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ It can be confirmed that both Itc1 / (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2) are 0.90 or more in a range satisfying R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic. It was confirmed that current drift can be effectively suppressed within the range satisfying the condition (1).

A more desirable range of the connection resistance R is 0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 2 × 0.01 × 10 ⁻⁶ × L / Ic, and in this range, itc1 / (Ic1 + Ic2) and Itc2 / (Ic1 + Ic2) can both be confirmed to be 0.95 or more, that is, it can be confirmed that current drift can be more effectively suppressed within the range satisfying the expression (2). It was.

  In addition, although the said experimental result is a thing at the time of using a Y-type superconducting tape wire as the oxide superconducting strands 11, 21, even if it uses a Bi-type oxide superconducting wire using Ag and an Ag base alloy sheath, Since the surface is Ag or an Ag-based alloy like the Y-based superconducting tape wire, the same result can be obtained.

  In Example 2, as in Example 1, Sn96.5Ag3Cu0.5 having a melting point of 280 ° C. was used as the solders 14, 15, 24, and 25, and the oxide superconducting wires 11 and 21 and the electrode 12 were heated at 280 ° C. , 13, 22, and 23 were prepared by soldering. Then, the connection resistance R was measured under the conditions of a temperature of 77.3 K and an external magnetic field of 0 T in the same manner as in Comparative Example 1 at all the connection locations of the oxide superconducting element wires and the electrodes in the five samples.

As a result, all of the 20 connection resistances R varied within the range of 5.38 × 10 ⁻⁹ Ω ≦ R ≦ 4.03 × 10 ⁻⁸ Ω, but the resistance value range represented by Equation (1) 7 The condition of .92 × 10 ⁻¹¹ Ω ≦ R ≦ 4.16 × 10 ⁻⁸ Ω was satisfied.

  By using Bi58Sn42 having a melting point of 130 ° C. as the solder 14, 15, 24, 25, and heating to 150 ° C. and then cooling, the oxide superconducting wires 11, 21 and the electrodes 12, 13, 22, 23 are soldered. Except for the above, five samples of the assembled conductor 1 were prepared by using the same example 2 as in Example 2. Then, the connection resistance R was measured under the conditions of a temperature of 77.3 K and an external magnetic field of 0 T in the same manner as in Example 2 at all the connection locations of the oxide superconducting element wires and the electrodes in the five samples.

As a result, for all of the 20 connection resistances R, 0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic represented by the formula (1) The conditions were satisfied, and they were within the range of 3.18 × 10 ⁻⁸ Ω ≦ R ≦ 3.56 × 10 ⁻⁸ Ω, and the variation range of the connection resistance R was smaller than that of Example 2.

  In addition, the heating temperature of soldering is not restricted to 150 degreeC, The same result is obtained in the temperature range of 140 to 200 degreeC.

  Also, using In65Bi35 having a melting point of 80 ° C. as the solder 14, 15, 24, 25, heating to 120 ° C. and then cooling, the oxide superconducting strands 11, 21 and the electrodes 12, 13, 22, 23 are formed. Five samples of the assembled conductor 1 were prepared under the same conditions as in Example 2 except for soldering. Then, the connection resistance R was measured under the conditions of a temperature of 77.3 K and an external magnetic field of 0 T in the same manner as in Example 2 at all the connection locations of the oxide superconducting element wires and the electrodes in the five samples.

As a result, for all of the 20 connection resistances R, 0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic represented by the formula (1) The condition was satisfied, and it was within the range of 3.25 × 10 ⁻⁸ Ω ≦ R ≦ 3.72 × 10 ⁻⁸ Ω, and the variation range of the connection resistance R could be made smaller than that in Example 2.

  In addition, the heating temperature of soldering is not restricted to 120 degreeC, The same result is obtained in the temperature range of 100 to 200 degreeC.

It is explanatory drawing which showed notionally the example of a structure of the assembly conductor of the oxide superconducting wire which concerns on one Embodiment of this invention, and the measurement circuit for measuring the characteristic of this assembly conductor. FIG. 2 is an enlarged view in the vicinity of an electrode of the assembly conductor shown in FIG. 1 and an explanatory diagram conceptually showing a measurement circuit for measuring the characteristics of the assembly conductor. It is a graph which shows the result of having calculated the value of Itc1 / (Ic1 + Ic2), Itc2 / (Ic1 + Ic2) about the some sample from which connection resistance R was varied.

Explanation of symbols

1 Assembly conductor 11, 21 Oxide superconducting wire 12, 13, 22, 23 Electrode 14, 15, 24, 25 Solder

Claims (10)

A plurality of oxide superconducting wires for parallel connection;
Electrodes respectively connected to both ends of the plurality of oxide superconducting wires,
When the length of each oxide superconducting wire is L (mm) and the critical current of each oxide superconducting wire on the basis of 0.01 μV / mm in an external magnetic field of 0 T is Ic (A), each oxide The connection resistance R (Ω) between the superconducting element wire and the electrodes connected to both ends of each oxide superconducting element wire is represented by the following formula (1) at the operating temperature of each oxide superconducting element wire. An aggregated conductor of oxide superconducting wires, characterized in that the respective oxide superconducting wires satisfy the conditions and are connected in parallel via electrodes connected to both ends, respectively.
0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (1) The assembly conductor of an oxide superconducting element wire according to claim 1, wherein the connection resistance R (Ω) satisfies a condition represented by the following formula (2).
0.1 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 2 × 0.01 × 10 ⁻⁶ × L / Ic (2) The assembly of the oxide superconducting element wire according to claim 1 or 2, wherein the oxide superconducting element wire and the electrode are soldered by solder using a bismuth (Bi) -containing alloy. conductor. The aggregated conductor of an oxide superconducting element wire according to claim 3, wherein the solder is an alloy of bismuth (Bi) and tin (Sn). The aggregated conductor of an oxide superconducting wire according to claim 3, wherein the solder is an alloy of bismuth (Bi) and indium (In). The assembly conductor of the oxide superconducting wire according to any one of claims 1 to 5, further comprising a connecting portion that connects the plurality of oxide superconducting wires in parallel. By soldering both ends of a plurality of oxide superconducting wires and a plurality of electrodes at a predetermined temperature within a range of 100 ° C. to 200 ° C. using solder containing bismuth (Bi), A plurality of oxide superconducting wires are assembled by connecting both ends of the oxide superconducting wire and a plurality of electrodes, and connecting the plurality of oxide superconducting wires in parallel via the plurality of electrodes. and reduction,
When the length of each oxide superconducting wire is L (mm) and the critical current of each oxide superconducting wire on the basis of 0.01 μV / mm in an external magnetic field of 0 T is Ic (A), each oxide The connection resistance R (Ω) between the superconducting element wire and the electrodes respectively connected to both ends of each oxide superconducting element wire is represented by the following formula (1) at the operating temperature of each oxide superconducting element wire. A method for producing an aggregated conductor of oxide superconducting wires, characterized in that it is set so as to satisfy a condition .
0.01 × 0.01 × 10 ⁻⁶ × L / Ic ≦ R ≦ 5 × 0.01 × 10 ⁻⁶ × L / Ic (1) The solder is an alloy of bismuth (Bi) and tin (Sn),
The said temperature is a temperature within the range of 140 degreeC-200 degreeC. The manufacturing method of the assembly conductor of the oxide superconducting wire of Claim 7 characterized by the above-mentioned. The solder is an alloy of bismuth (Bi) and indium (In),
The said temperature is the temperature in the range of 100 to 200 degreeC. The manufacturing method of the assembly | attachment conductor of the oxide superconducting strand of Claim 7 characterized by the above-mentioned. 10. The oxidation according to claim 7, wherein the connection resistance R (Ω) is set by adjusting a connection area between the oxide superconducting element wire and the electrode. A method for manufacturing an assembly conductor of a superconducting element wire.

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