JP5501258B2 - Superconducting wire connection structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to electrical connection between superconducting wires, and particularly relates to a connection structure having high quench resistance and used for a superconducting device and a permanent current switch that are energized with alternating current, and a method for manufacturing the same.

The technology for electrically connecting superconducting wires is one of important technologies for applying superconducting wires. The simplest connection method is a method in which superconducting wires are overlapped with a sufficient length and soldered (referred to as a solder connection method). Here, since a superconducting wire generally has a structure in which a number of superconducting filaments made of a superconductor are covered with a base material (for example, copper, aluminum, etc.), one of the superconducting filaments is connected by a solder connection method. The current that has flowed from the current flows into the other superconducting filament via the base material, solder, and base material. That is, the connection resistance in the solder connection method includes the electrical resistance between the base material and the solder. As a result, even when the superconducting wires are overlapped with each other by several meters, the connection resistance is about 10 ⁻⁹ Ω.

Typical products using superconducting wires and superconducting magnets there are a nuclear magnetic resonance analyzer (NMR) and a nuclear magnetic resonance imaging device (MRI), which are widely used in the biotechnology field and the medical field. These devices are normally operated in a permanent current mode, and require extremely small magnetic field attenuation rates of 0.1 ppm / h or less in magnetic field accuracy. In order to achieve the permanent current mode and the magnetic field attenuation factor, connection with a low connection resistance of at least 10 ⁻¹² Ω (so-called superconducting connection) is an essential technique.

As a method to achieve such a low connection resistance, the superconducting filament is exposed by removing the base material at the connection portion between the superconducting wires to be connected, and then the exposed superconducting filaments are overlapped and inserted into a metal pipe. A method of crimping and connecting the superconducting wire filaments by pressurizing and crushing the metal pipe (referred to as a caulking connection method) has been reported (for example, see Patent Document 1 and Non-Patent Document 1). In the caulking connection method, since the superconducting wire filaments to be connected are in direct contact without passing through a normal conductor such as a base material or solder, a connection resistance of 10 ⁻¹³ Ω or less can be realized. For this reason, the caulking connection method is often applied to superconducting connections in NMR and MRI superconducting magnets, which have strict requirements on connection resistance.

  Patent Document 2 discloses a superconducting connection structure, which is a kind of caulking connection method, in which a superconducting powder containing magnesium diboride is interposed between the superconducting wire filaments to be connected. According to Patent Document 2, it is said that connection with a low electric resistance is possible even if the superconducting wire connection portion is arranged in a high magnetic field.

JP-A-4-319280 JP 2003-022719 A

Kenji Shimohata, Shunji Yamamoto, Shiro Nakamura, Takeo Kawaguchi: “Superconducting connection of NbTi superconducting wires”, Cryogenic Engineering Vol. 30 pp. 70-75.

  When a superconducting wire or a superconducting magnet is energized, a phenomenon called quenching may occur in which superconductivity suddenly disappears at a current value lower than the rated current. Generation | occurrence | production of a quench is a problem regarding the operation stability and reliability of the product using a superconducting wire, and prevention of quench is one of the most important subjects in a superconducting product.

  A superconducting connection portion to which the caulking connection method is applied (see, for example, Patent Document 1 and Non-Patent Document 1) is a portion where quenching is particularly likely to occur compared to other portions. One of the causes is considered that the base material is removed for connection. The base material has a role of enlarging the heat capacity of the superconducting wire to suppress the temperature rise due to disturbance and promoting the diffusion of the generated heat. However, since the caulking connection method removes this for connection, it is considered that the quench resistance is reduced. Moreover, even in the superconducting connection structure described in Patent Document 2, the quench resistance is not always sufficient.

  On the other hand, in a superconducting wire used for a superconducting device that is energized with alternating current or a superconducting wire used in a permanent current switch that is essential for a superconducting device that operates in a permanent current mode, a base material of an ordinary superconducting wire (for example, oxygen-free copper) Since a superconducting wire using a base material (for example, a copper-nickel alloy) having a higher electrical resistivity than that of the solder is generally used, it is considered that the solder connection method is inappropriate. Furthermore, since metals with high electrical resistivity have low thermal conductivity, these superconducting wires tend to be less resistant to quenching than ordinary superconducting wires, even when the base material is attached. A highly durable connection method and connection structure have been highly desired.

  Accordingly, an object of the present invention is to provide a connection structure having both a low connection resistance and a high quench resistance in an electrical connection between superconducting wires used for an alternating current superconducting device and a permanent current switch, and a method for manufacturing the same. There is.

In order to achieve the above object, the present invention provides a connection structure for electrically connecting a first superconducting multicore wire and a second superconducting multicore wire having a structure in which a plurality of superconducting filaments are covered with a base material. There,
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A tip region of the first superconducting filament exposed by removing the base material of the first superconducting multicore wire, and a second superconducting filament exposed by removing the base material of the second superconducting multicore wire. The tip region constitutes a joint part that is caulked and connected,
The remaining area of the exposed first superconducting filament and the remaining area of the exposed second superconducting filament constitute a bypass portion connected via a covering member;
The covering member is made of a metal material having an electric resistivity lower than that of the base material of the superconducting wire for the alternating current conduction or the permanent current switch under the operating environment of the connection structure. Provide a structure.

In order to achieve the above object, the present invention electrically connects a first superconducting multicore wire having a structure in which a plurality of niobium titanium alloy filaments are covered with a base material and a second superconducting multicore wire. A structure manufacturing method comprising:
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A filament exposing step of removing the base material in the connection planned region in the first and second superconducting multicore wires to expose the first and second niobium titanium alloy filaments;
Inserting the exposed tip regions of the first and second niobium titanium alloy filaments into a metal pipe and pressing and deforming the metal pipe, the first and second niobium titanium alloy filaments are crimped together to form a joint portion. A joint part forming step to be formed;
Under the operating environment of the connection structure, a covering member made of a metal material having a lower electrical resistivity than the base material of the superconducting wire for the alternating current conduction or the permanent current switch is left behind the exposed first superconducting filament. And a bypass portion forming step of forming a bypass portion by covering and integrating the remaining region of the exposed second superconducting filament with the remaining region of the exposed second superconducting filament. provide.

  ADVANTAGE OF THE INVENTION According to this invention, in the electrical connection of the superconducting wire used for the superconducting apparatus and permanent current switch of alternating current conduction, the connection structure which has low connection resistance and high quench tolerance, and its manufacturing method are provided. it can.

It is a perspective schematic diagram which shows an example of the conventional connection structure of the superconducting wire material by caulking connection. 1 is a schematic perspective view showing an example of a superconducting wire connecting structure according to the present invention and a schematic cross-sectional view of a bypass portion. It is an equivalent circuit which shows the connection structure of the superconducting wire which concerns on this invention. It is the perspective schematic diagram which shows another example of the connection structure of the superconducting wire which concerns on this invention, and the cross-sectional schematic diagram of a bypass part. It is the perspective schematic diagram which shows another example of the connection structure of the superconducting wire which concerns on this invention, and the cross-sectional schematic diagram of a bypass part. It is a cross-sectional schematic diagram which shows the modification of the joint part of the connection structure of the superconducting wire which concerns on this invention. It is a schematic diagram which shows the sample shape for measuring the electricity supply characteristic of the connection structure of a superconducting wire. It is the perspective schematic diagram which shows Example 1 which concerns on this invention, and the cross-sectional schematic diagram of a bypass part. It is a schematic diagram which shows the test system for measuring the electricity supply characteristic of the connection structure of a superconducting wire. It is a chart which shows one example of the result of energization characteristics of comparative example 1 (time change of the captured magnetic flux). It is a chart which shows one example of the result of energization characteristics of Example 1 (time change of the captured magnetic flux).

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the scope of the invention.

As described above, the superconducting wire connecting structure according to the present invention electrically connects the first superconducting multicore wire and the second superconducting multicore wire having a structure in which a plurality of superconducting filaments are covered with a base material. A connection structure connected to
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A tip region of the first superconducting filament exposed by removing the base material of the first superconducting multicore wire, and a second superconducting filament exposed by removing the base material of the second superconducting multicore wire. The tip region constitutes a joint part that is caulked and connected,
The remaining area of the exposed first superconducting filament and the remaining area of the exposed second superconducting filament constitute a bypass portion connected via a covering member;
The covering member is made of a metal material having an electric resistivity lower than that of the base material of the superconducting wire for the AC energization or the permanent current switch in the operating environment of the connection structure.

In addition, the present invention can be improved or changed as follows in the superconducting wire connecting structure according to the present invention.
(1) The superconducting filament of the superconducting wire for alternating current or permanent current switch is a niobium titanium alloy, and the base material of the superconducting wire is any one of a copper nickel alloy, a copper manganese alloy, or a copper manganese nickel alloy, The covering member is any one of copper, aluminum, indium, tin, bismuth, and alloys composed of these elements.
(2) In the bypass portion, an outer layer member different from the covering member is further disposed on the outer periphery of the covering member, and the outer layer member is used for the AC energization or permanent in the operating environment of the connection structure. It is made of a metal material having a higher thermal conductivity than the base material of the superconducting wire for the current switch.
(3) The outer layer member is any one of copper, aluminum, indium, tin, bismuth, and an alloy composed of these elements.
(4) In the bypass portion, an intermediate layer different from the covering member is further disposed between the first superconducting filament and the covering member and between the second superconducting filament and the covering member. The intermediate layer is made of a metal material having an electrical resistivity lower than that of the base material of the superconducting wire for the AC energization or permanent current switch in the operating environment of the connection structure.
(5) The intermediate layer is any one of copper, aluminum, indium, tin, bismuth, and an alloy composed of these elements.
(6) An intervening superconductor is provided in contact with the first superconducting filament and the second superconducting filament in the joint portion, and the interposing superconductor is operated under the operating environment of the connection structure. The critical current density is lower than that of the first and second superconducting filaments.
(7) The intervening superconductor has a plate shape, the first superconducting filament is electrically connected to one main surface of the intervening superconductor, and the second main surface of the intervening superconductor is connected to the second main surface. A superconducting filament is electrically connected.
(8) A superconducting device including the connection structure of the superconducting wire.
(9) A nuclear magnetic resonance analyzer or a nuclear magnetic resonance imaging apparatus comprising the above-described superconducting wire connecting structure.

In addition to the connection structure described above, the method for manufacturing a connection structure for a superconducting wire according to the present invention includes a first superconducting multicore wire having a structure in which a plurality of niobium titanium alloy filaments are covered with a base material, and a second structure. A method of manufacturing a connection structure for electrically connecting a superconducting multicore wire,
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A filament exposing step of removing the base material in the connection planned region in the first and second superconducting multicore wires to expose the first and second niobium titanium alloy filaments;
The exposed tip region of the first and second niobium titanium alloy filaments is inserted into a metal pipe, and the metal pipe is pressed to crimp the first and second niobium titanium alloy filaments together to form a joint portion. A joint part forming step,
Under the operating environment of the connection structure, a covering member made of a metal material having a lower electrical resistivity than the base material of the superconducting wire for the alternating current conduction or the permanent current switch is left behind the exposed first superconducting filament. And a bypass portion forming step of forming a bypass portion by covering and integrating the exposed region and the remaining region of the exposed second superconducting filament.

In addition, the present invention can be improved or changed as follows in the method of manufacturing a superconducting wire connection structure according to the present invention.
(10) After the bypass portion forming step, an outer layer pipe made of a metal material different from the covering member is placed on the outer periphery of the covering member, and the outer layer member integrated with the covering member is formed by pressing the outer layer pipe. And an outer layer member disposing step.

(First embodiment of the present invention)
Hereinafter, the present invention will be described in more detail. First, a conventional connection structure will be described. FIG. 1 is a schematic perspective view showing an example of a conventional connection structure between superconducting wires by caulking connection.

As shown in FIG. 1, the conventional connection structure 14 by caulking connection is such that the superconducting filament 6 (first superconducting filament 61, second superconductor filament 61, second superconductor filament 61, and second superconductor filament) exposed by removing the base materials of the two superconducting multicore wires 4 respectively. The superconducting filament 62) is inserted into a metal pipe (for example, an oxygen-free copper pipe 15 '), and the metal pipe is pressed and deformed to have a joint portion 1 in which the superconducting filaments 6 are joined by pressure bonding. In the joint portion 1, since the superconducting filaments 6 are directly joined to each other, a very low connection resistance of 10 ⁻¹³ Ω or less can be obtained.

  Further, in the conventional connection structure 14, the superconducting multi-core wire 4 in the vicinity of the joint portion 1 is often fixed with the solder 16 for the purpose of mechanical protection in the vicinity of the joint portion 1 and suppression of wire movement. In general, the superconducting filament 6 and the solder 16 are not so good in wettability, so that the solder is fixed mainly in a region where the base material is coated (a region where the base material is not removed).

  Here, when both the base materials of the superconducting multi-core wire 4 are made of a material having a low electrical resistivity such as oxygen-free copper, when a normal conduction region (quenching bud) occurs in the joint portion 1, The effect that the fixed portion functions as a solder connection and suppresses the expansion of quenching (that is, the effect of improving quench resistance) can be expected. However, as described above, in a superconducting wire for alternating current conduction or a permanent current switch, a base material having a high electrical resistivity (for example, a copper nickel alloy, a copper manganese alloy, etc.) is used to suppress electrical coupling between superconducting filaments. In addition, it has been confirmed by the present inventors' investigation and research (details will be described later) that the conventional connection structure 14 has extremely low quench resistance.

  FIG. 2 is a schematic perspective view showing an example of a superconducting wire connecting structure according to the present invention and a schematic cross-sectional view of a bypass portion. In the superconducting wire connecting structure 11 according to the present invention, at least one of the two superconducting multicore wires 4 (the first superconducting multicore wire 41 and the second superconducting multicore wire 42) is used for alternating current conduction or A superconducting wire for a permanent current switch, and the tip region of the superconducting filament 6 exposed by removing the base material of the two superconducting multicore wires 4 is in a metal pipe 15 (for example, an oxygen-free copper pipe 15 '). The joint portion 1 is inserted, the metal pipe 15 is pressed and deformed, and the superconducting filaments 6 are joined by pressure bonding. Further, as shown in FIG. 2, a bypass portion 2 connected via a coating material 5 is formed in the remaining region of the exposed superconducting filament 6. At this time, the coating material 5 is a metal material (for example, copper, aluminum, indium, etc.) having an electrical resistivity lower than that of the base material of the superconducting wire for AC conduction or permanent current switch in the operating environment of the connection structure 11. Tin, bismuth, or an alloy composed of these elements).

(Method for manufacturing connection structure)
An example of the manufacturing process of the superconducting wire connecting structure 11 according to the present invention is as follows. Needless to say, it is not limited to the following.
(I) The superconducting filament 6 (first superconducting filament 6 (first superconducting multicore wire 41, first superconducting multicore wire 41, second superconducting multicore wire 42) is dissolved in nitric acid or the like in the region to be connected. The first superconducting filament 61 and the second superconducting filament 62) are exposed (filament exposing step).
(Ii) The exposed tip region of the superconducting filament 6 is inserted into the metal pipe 15, and the first superconducting filament 61 and the second superconducting filament 62 are connected by a caulking connection method to form the joint portion 1 ( Joint part forming step).
(Iii) Covering the remaining region of the exposed superconducting filament 6 with the covering member 5 to form the bypass portion 2 in which the covering member 5 and the superconducting filament 6 are integrated (bypass portion forming step). More specifically, after covering the outer periphery of the bundle of the remaining region of the superconducting filament 6 exposed with a coating material 5 made of tin, indium, bismuth, or an alloy thereof, a copper or aluminum pipe is applied to the outer periphery. Then, the pipe is deformed under pressure so that the coating material 5 is sufficiently integrated into the gap between the superconducting filaments 6 and integrated. Note that after the covering member 5 and the superconducting filament 6 are integrated, the pipe used for the integration may or may not be removed.

(Consideration of effects of the present invention)
Next, the effect of the present invention will be described by modeling with an equivalent circuit. FIG. 3 is an equivalent circuit showing a superconducting wire connecting structure according to the present invention. As shown in FIG. 3, the resistance of the joint part 1 is expressed as R _j , the resistance of the bypass part 2 is expressed as R _b, and the inductance of the connection structure loop 3 composed of the joint part 1 and the bypass part 2 is L _j is written. Also, the inductance of the superconducting coil connected to the two superconducting multicore wires 4 (first superconducting multicore wire 41 and second superconducting multicore wire 42) is L _c (generally about 10 to 100 H). ).

For example, it is assumed that the superconducting coil (superconducting magnet) connected to the connection structure 11 is operated in the permanent current mode operation. Since “R _j << R _b ” in the steady state of the permanent current mode, current flows through the joint portion 1. Here, it is assumed that a normal conducting region (quenching bud) is generated in the joint portion 1. At this time, the following process is followed.
(A) With the occurrence of the normal conducting region in the joint portion 1, R _j increases and becomes R _jN (R _j <R _jN ).
(B) When “R _jN > R _b ”, the current of the joint portion 1 moves to the bypass portion 2 (R _b is typically about 10 ⁻⁸ to 10 ⁻⁷ Ω).
(C) Since the Joule heat generation in the joint portion 1 is settled and cooled, the joint portion 1 returns to the superconducting state (R _j << R _b ).
(D) The current returns to the joint 1 again.

The magnetic field decay rate in the superconducting magnet by the above process will be described. The time Δt _{j → b} required for the current to move from the joint part 1 to the bypass part 2 is “Δt _{j → b} = L _j / R _jN ”, and the decay time constant τ _{j → b} of the magnetic field during this time is “ τ _{j → b} = L _c / R _jN ”. On the other hand, the time Δt _{b → j} required for the current to return from the bypass part 2 to the joint part 1 is “Δt _{b → j} = L _j / R _b ”, and the decay time constant τ _{b → j} of the magnetic field during this time Is expressed as “τ _{b → j} = L _c / R _b ”. Therefore, the central magnetic flux density of the superconducting magnet is attenuated at a rate given by Equation 1 through the processes (a) to (d). B ₀ : Initial magnetic flux density, ΔB: (a) to (d) The amount of change in magnetic flux density in one cycle of the process.

Since the superconducting wire connecting structure 11 according to the present invention uses a metal material having a lower electrical resistivity than the base material of the superconducting wire for AC energization or permanent current switch as the covering member 5, the bypass portion 2 The resistance _Rb can be reduced. Therefore, Joule heat generation can be suppressed even when the current is transferred to the bypass unit 2. Further, in the bypass portion 2, since each superconducting filament 6 is covered with the covering member 5 having excellent thermal conductivity, heat can be quickly released. With these effects, quenching in the bypass unit 2 can be prevented.

Furthermore, L _c is about 10 to 100 H as described above, and L _j can be reduced to about 10 ⁻⁹ H if the joint portion 1 and the bypass portion 2 are sufficiently brought close to each other. Therefore, when approximated from Equation 1, the magnetic field attenuation rate ΔB / B by one cycle of the steps (a) to (d) is only about 1 ppb. This is a level that does not cause a problem in the operation of the NMR analyzer and the MRI apparatus.

  From the above, the connection structure of the superconducting wire according to the present invention is prevented from expanding even if a normal conduction region is generated in the joint part produced by the caulking connection method, and the central magnetic flux of the superconducting magnet operated in the permanent current mode. There is an effect that the attenuation of the density is suppressed to a minute amount. In other words, it can be said that the superconducting wire connecting structure according to the present invention is suitable for use in superconducting equipment such as an NMR analyzer and an MRI apparatus.

(Second embodiment of the present invention)
FIG. 4 is a perspective schematic view showing another example of a superconducting wire connection structure according to the present invention and a cross-sectional schematic view of a bypass portion. As shown in FIG. 4, the connection structure 12 according to the second embodiment is different from the bypass portion 2 only in that an outer layer member 7 different from the covering member 5 is disposed on the outer periphery of the covering member 5. Different from the connection structure 11 according to the first embodiment. The outer layer member 7 is made of a metal material having higher thermal conductivity than the base material of the superconducting wire for alternating current or permanent current switch under the operating environment of the connection structure, for example, copper, aluminum, indium, tin, Bismuth or an alloy composed of these elements is preferably used.

  In addition to the same effects as the connection structure 11 according to the first embodiment, the connection structure 12 according to the second embodiment provides the bypass portion 2 by disposing the outer layer member 7 on the outer periphery of the covering member 5. Therefore, the temperature rise when the current is transferred to the bypass unit 2 is suppressed. Thereby, there is an effect that quenching of the bypass unit 2 is further prevented.

(Third embodiment of the present invention)
FIG. 5 is a schematic perspective view showing another example of the superconducting wire connecting structure according to the present invention and a schematic cross-sectional view of the bypass portion. As shown in FIG. 5, in the connection structure 13 according to the third embodiment, an intermediate layer 8 different from the covering member 5 is disposed between the covering member 5 and the superconducting filament 6 in the bypass portion 2. It differs from the connection structure 11 according to the first embodiment only in that it is. The intermediate layer 8 is made of a metal material having an electrical resistivity lower than that of the base material of the superconducting wire for alternating current or permanent current switch under the operating environment of the connection structure, for example, copper, aluminum, indium, tin, Bismuth or an alloy composed of these elements is preferably used.

In addition to the same effects as the connection structure 11 according to the first embodiment, the connection structure 13 according to the third embodiment has an intermediate layer 8 disposed between the coating material 5 and the superconducting filament 6. As a result, the adhesiveness between the coating material 5 and the superconducting filament 6 is increased, so that the resistance _Rb of the bypass portion 2 can be further reduced. As the formation process of the intermediate layer 8, for example, a vapor phase film formation method such as vapor deposition is preferably used.

(Fourth embodiment of the present invention)
FIG. 6 is a schematic cross-sectional view showing a modification of the joint portion of the connection structure of the superconducting wire according to the present invention. As shown in FIG. 6, the joint portion 1 ′ according to the fourth embodiment is provided with a plate-shaped intercalating superconductor 17 in contact between the first superconducting filament 61 and the second superconducting filament 62. It has been. The intervening superconductor 17 has a lower critical current density than the first superconducting filament 61 and the second superconducting filament 62 under the operating environment of the connection structure.

  A superconducting wire is generally designed such that its critical current has some margin at the maximum empirical magnetic field in the environment of use (or the device (eg, superconducting coil) is designed to do so). On the other hand, the connection structure between the superconducting wires is usually installed in a low magnetic field region from the viewpoint of spatial restriction of the installation location and superconducting stability. Therefore, in the low magnetic field region where the connection structure is installed, the superconducting filament in the connection structure has an excessive critical current with respect to the operating current, and only a part of the poles among the many superconducting filaments is used. It is considered possible to transport the operating current at Therefore, as time passes, the current distribution between the superconducting filaments 6 is considered to be biased only to the superconducting filaments having a good bonding interface. As a result, it is considered that when Jolt buds are generated, large Joule heat due to excessive drift is likely to occur.

  As described above, in the joint portion 1 ′ according to the fourth embodiment, the intervening superconductor 17 having a lower critical current density than the superconducting filament is disposed between the first and second superconducting filaments 61 and 62. For this reason, the transport current is prevented from drifting to a part of the pole of the superconducting filament 6 due to the limitation of the critical current density of the interposing superconductor 17, and the current distribution approaches an even current distribution. As a result, there is an effect that it is possible to suppress large Joule heat due to excessive drift in the transport current and to suppress the occurrence of quenching in the joint portion. Needless to say, the fourth embodiment can be combined with any of the first to third embodiments described above.

  Hereinafter, specific examples of the present invention will be described by way of examples. In addition, this invention is not limited to a following example.

  FIG. 7 is a schematic diagram showing a sample shape for measuring the current-carrying characteristics of the superconducting wire connecting structure. As shown in FIG. 7, the measurement sample is composed of two superconducting multi-core wires 4. In the first superconducting multi-core wire 41, the material of the superconducting filament 6 is a niobium titanium alloy, and the material of the base material is oxygen-free copper. In the second superconducting multi-core wire 42, the material of the superconducting filament 6 is a niobium titanium alloy, and the material of the base material is a copper nickel alloy (Cu-10 mass% Ni). The first superconducting multicore wire 41 formed a loop part in the middle, and the second superconducting multicore wire 42 remained straight. Further, a connection structure was formed at two locations opposite to each other across the loop portion, and the first superconducting multicore wire 41 and the second superconducting multicore wire 42 were connected. The first superconducting multicore wire 41 and the second superconducting multicore wire 42 have the same configuration except for the material of the base material.

  As Comparative Example 1, a conventional connection structure 14 (see FIG. 1) was produced by the following procedure. Each of the first and second superconducting multi-core wires 41 and 42 was immersed in nitric acid at both end portions 35 mm to dissolve the base material, thereby exposing the superconducting filament. Next, the exposed first and second superconducting filaments 61 and 62 were stacked and inserted into an oxygen-free copper pipe 15 '(thickness 5 mm, length 25 mm). The oxygen-free copper pipe 15 'was uniaxially pressed and crushed to form the joint portion 1 in which the two superconducting filaments 61 and 62 were integrated (crimped) in the oxygen-free copper pipe 15'. In addition, the base materials of the two superconducting multi-core wires 41 and 42 having a length of 25 mm from the boundary from which the base material was removed were fixed with solder 16.

  As Example 1, a connection structure 12 ′ (see FIG. 8) according to the second embodiment was produced by the following procedure. FIG. 8 is a schematic perspective view showing the first embodiment according to the present invention and a schematic cross-sectional view of the bypass portion. Each of the first and second superconducting multicore wires 41 and 42 was immersed in nitric acid at 50 mm on both ends to dissolve the base material to expose the superconducting filament. Next, the exposed first and second superconducting filaments 61 and 62 are stacked, and the tip region of the exposed superconducting filament (region having a distance from the tip of 0 to 25 mm) is connected to an oxygen-free copper pipe 15 ′ (thickness 5). mm, length 25 mm). The oxygen-free copper pipe 15 'was uniaxially pressed and crushed to form the joint portion 1 in which the two superconducting filaments 61 and 62 were integrated (crimped) in the oxygen-free copper pipe 15'.

  Next, an indium sheet was wound as a covering member 5 ′ on the remaining regions of the exposed first and second superconducting filaments 61 and 62 (regions having a distance from the tip of 25 to 50 mm). An oxygen-free copper pipe 15 ”(5 mm thick, 25 mm long) previously inserted was placed on the outer periphery of the wound indium sheet. After that, the indium covering member 5 ′ was placed in the gap between each superconducting filament 6. The oxygen-free copper pipe 15 ″ was uniaxially pressed and crushed so as to sufficiently enter, thereby forming the bypass portion 2.

  The energization characteristics of the measurement sample prepared above were measured as follows. FIG. 9 is a schematic diagram showing a test system for measuring the current-carrying characteristics of the superconducting wire connection structure. As shown in FIG. 9, a test system composed of an induction coil 21, a sample heater 22, and a hall element 23 is assembled in the cryostat 20, and the measurement sample is placed so that the loop portion of the measurement sample enters the region of the induction coil 21. Was installed. The cryostat 20 was filled with liquid helium, and the measurement sample was energized in the following procedure.

  First, the sample heater 22 was heated, and the superconductivity of a part of the measurement sample (part of the superconducting multicore wire 4) was lost. In this state, the induction coil 21 was energized, and a magnetic flux was generated so as to penetrate the loop portion of the measurement sample. Next, after heating of the sample heater 22 is stopped and the superconductivity of the measurement sample is restored, when the energization of the induction coil 21 is stopped, a current is supplied to the superconducting multi-core wire 4 so that the magnetic flux in the loop portion of the measurement sample is preserved. Flows. At this time, the center magnetic flux density of the loop portion was measured by the Hall element 23, and the change with time was recorded.

  FIG. 10 is a chart showing an example of a result of energization characteristics of Comparative Example 1 (time change of captured magnetic flux). As shown in FIG. 10, a discontinuous decrease in the central magnetic flux density suddenly occurred after about 300 seconds from the start of measurement. This was thought to be because quenching occurred in the conventional connection structure 14 and the magnetic energy held in the measurement sample disappeared as Joule heat. The magnetic field decay rate at this time was about 90%.

  FIG. 11 is a chart showing an example of a result of energization characteristics of Example 1 (change in captured magnetic flux with time). As shown in FIG. 11, a discontinuous decrease in the center magnetic flux density suddenly occurred after about 1500 seconds from the start of measurement. This was also thought to be due to the occurrence of quenching in the connection structure 12 'according to the second embodiment. However, the magnetic field attenuation rate at this time was only about 1%. In addition, it confirmed separately that the same result was obtained also in the connection structure which concerns on other embodiment.

The above results will be considered with the equivalent circuit shown in FIG. The inductance of the measurement sample is about 10 ⁻⁷ H, and the inductance of the loop 3 including the joint portion 1 and the bypass portion 2 is about 10 ⁻⁹ H. When these inductance and electrical resistivity were substituted into Equation 1, the magnetic field attenuation rate for Example 1 was in good agreement. That is, the model phenomenon described in the equivalent circuit of FIG. 3 is considered to have occurred. Further, if this connection structure 12 ′ is applied to a general superconducting magnet (10 to 100 H), it is suggested from Equation 1 that the magnetic field attenuation rate is about 0.1 ppb. This sufficiently satisfies the level required for NMR analyzers and MRI apparatuses.

  On the other hand, Comparative Example 1 did not agree with the result of Formula 1. This is because when a normal conduction region occurs in the joint part 1 and current flows to the solder fixing part, Joule heat generation in the solder fixing part is too large to catch up with heat diffusion, and the temperature of the solder fixing part rises and the measurement sample This was thought to be due to the progress of quenching throughout.

  As described above, the connection structure of the superconducting wire according to the present invention is prevented from expanding even if a normal conduction region (quenching bud) occurs in the joint portion 1, and the magnetic field of the superconducting magnet operated in the permanent current mode. The effect that the attenuation rate can be suppressed to the minimum was demonstrated. That is, it can be said that it has both low connection resistance and high quench resistance. Therefore, the superconducting wire connection structure according to the present invention includes an NMR analyzer, an MRI apparatus, a large superconducting magnet, a power storage device, a magnetic separation device, a magnetic levitation train, a superconducting generator, a fusion reactor magnet, etc. It can be applied to superconducting equipment.

1, 1 '... Joint part, 2 ... Bypass part,
3. Connection structure loop consisting of joint part and bypass part,
4 ... Superconducting multicore wire, 41 ... First superconducting multicore wire, 42 ... Second superconducting multicore wire,
5,5 '... covering member, 6 ... superconducting filament,
61 ... first superconducting filament, 62 ... second superconducting filament,
7 ... outer layer member, 8 ... intermediate layer, 11, 12, 12 ', 13, 14 ... connection structure,
15 ... metal pipe, 15 ', 15 "... oxygen-free copper pipe, 16 ... solder, 17 ... intervening superconductor,
20 ... Cryostat, 21 ... Induction coil, 22 ... Sample heater, 23 ... Hall element.

Claims (12)

A connection structure for electrically connecting a first superconducting multicore wire and a second superconducting multicore wire having a structure in which a plurality of superconducting filaments are covered with a base material,
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A tip region of the first superconducting filament exposed by removing the base material of the first superconducting multicore wire, and a second superconducting filament exposed by removing the base material of the second superconducting multicore wire. The tip region constitutes a joint part that is caulked and connected,
The remaining area of the exposed first superconducting filament and the remaining area of the exposed second superconducting filament constitute a bypass portion connected via a covering member;
The covering member is made of a metal material having an electric resistivity lower than that of the base material of the superconducting wire for the alternating current conduction or the permanent current switch under the operating environment of the connection structure. Structure. In the connection structure of the superconducting wire according to claim 1,
The superconducting filament of the superconducting wire for the AC energization or permanent current switch is a niobium titanium alloy,
The base material of the superconducting wire is either a copper nickel alloy, a copper manganese alloy, or a copper manganese nickel alloy,
The superconducting wire connecting structure, wherein the covering member is one of copper, aluminum, indium, tin, bismuth, and an alloy composed of these elements. In the connection structure of the superconducting wire according to claim 1 or 2,
The bypass portion is further provided with an outer layer member different from the covering member on the outer periphery of the covering member,
The outer layer member is made of a metal material having a higher thermal conductivity than the base material of the superconducting wire for the AC current supply or the permanent current switch under the operating environment of the connection structure. Structure. In the connection structure of the superconducting wire according to claim 3,
A superconducting wire connecting structure, wherein the outer layer member is one of copper, aluminum, indium, tin, bismuth, and an alloy composed of these elements. In the connection structure of the superconducting wire according to any one of claims 1 to 4,
The bypass portion is further provided with an intermediate layer different from the covering member between the first superconducting filament and the covering member and between the second superconducting filament and the covering member,
The intermediate layer is made of a metal material having an electrical resistivity lower than that of the base material of the superconducting wire for the alternating current conduction or the permanent current switch under the operating environment of the connection structure. Structure. In the connection structure of the superconducting wire according to claim 5,
A connection structure for a superconducting wire, wherein the intermediate layer is one of copper, aluminum, indium, tin, bismuth, and an alloy composed of these elements. In the connection structure of the superconducting wire according to any one of claims 1 to 6,
An interposed superconductor is provided in contact with the first superconducting filament and the second superconducting filament in the joint portion,
A superconducting wire connecting structure, wherein the intervening superconductor has a lower critical current density than the first and second superconducting filaments in an operating environment of the connecting structure. In the connection structure of the superconducting wire according to claim 7,
The intervening superconductor is plate-shaped,
The first superconducting filament is electrically connected to one main surface of the intervening superconductor, and the second superconducting filament is electrically connected to the other main surface of the interposing superconductor. A superconducting wire connection structure.   A superconducting device comprising the connection structure for a superconducting wire according to any one of claims 1 to 8.   A nuclear magnetic resonance analyzer or a magnetic resonance imaging apparatus comprising the superconducting wire connecting structure according to any one of claims 1 to 8. A method for producing a connection structure for electrically connecting a first superconducting multicore wire having a structure in which a plurality of niobium titanium alloy filaments are covered with a base material and a second superconducting multicore wire,
At least one of the first and second superconducting multicore wires is a superconducting wire for alternating current conduction or a permanent current switch,
A filament exposing step of removing the base material in the connection planned region in the first and second superconducting multicore wires to expose the first and second niobium titanium alloy filaments;
Inserting the exposed tip regions of the first and second niobium titanium alloy filaments into a metal pipe and pressing and deforming the metal pipe, the first and second niobium titanium alloy filaments are crimped together to form a joint portion. A joint part forming step to be formed;
Under the operating environment of the connection structure, a covering member made of a metal material having a lower electrical resistivity than the base material of the superconducting wire for the alternating current conduction or the permanent current switch is left behind the exposed first superconducting filament. And a bypass portion forming step of forming a bypass portion by covering and integrating the region and the remaining region of the exposed second superconducting filament. A method for manufacturing a connection structure of a superconducting wire. In the manufacturing method of the connection structure of the superconducting wire according to claim 11,
After the bypass portion forming step, an outer layer member formed by covering the outer periphery of the covering member with an outer layer pipe made of a metal material different from the covering member and pressing the outer layer pipe to form an outer layer member integrated with the covering member The manufacturing method of the connection structure of a superconducting wire characterized by further having an arrangement process.

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