JP6125350B2 - Superconducting wire connection and superconducting current lead - Google Patents

Description

  The present invention relates to a connecting portion of a superconducting wire in which a metal electrode is connected to an end of a superconducting wire, and more particularly to superconducting for connecting a superconducting application device installed in a low temperature portion and an external device installed in a normal temperature portion. The present invention relates to a technique useful for a current lead.

In recent years, in the field of superconducting applied equipment using superconductivity such as superconducting cables and superconducting magnets, research and development have been conducted for practical use. In general, a superconducting application device is installed in a low temperature part (low temperature container) and connected to an external device (for example, a power source) installed in the normal temperature part via a current lead.
Since the operation of superconducting equipment is performed in a cryogenic environment, the heat insulation of the low temperature part is extremely important. If the heat insulation property of the low temperature part is poor and the heat penetration into the low temperature part is large, the cooling efficiency of the superconducting application equipment will decrease and the cooling cost for maintaining the superconducting state will increase. This is because it becomes impossible to drive. As a path of heat penetration into the low temperature part, a path for transferring heat through the low temperature container and a path for transferring heat through the current leads are conceivable.

  As a technique for preventing heat intrusion through a cryogenic vessel, a dual-structure cryogenic vessel having a refrigerant tank containing a refrigerant such as liquid nitrogen and a superconducting application device and a vacuum tank provided outside the refrigerant vessel It has been known. According to this low-temperature container, heat penetration into the low-temperature part is reduced by vacuum insulation.

  As a technique for preventing heat intrusion through the current lead, a superconducting current lead using an oxide superconductor has been proposed. An oxide superconductor has a lower electrical resistance and lower thermal conductivity than a metal conductor such as copper (a few tenths of copper). Therefore, in the superconducting current lead, Joule heat is not generated during energization, and the amount of heat transferred to the low temperature portion is extremely small. Therefore, according to the superconducting current lead, heat penetration into the low temperature portion is reduced.

A conventional superconducting current lead 50 is shown in FIG. FIG. 1A is an overall view of a superconducting current lead 50. FIG. 1B is a cross-sectional view taken along the line II in FIG. 1A.
As shown in FIG. 1A, a superconducting current lead 50 includes a tape-shaped superconducting wire 51, a first metal electrode 52 disposed at one end (high temperature side) of the superconducting wire 51, and the other end of the superconducting wire 51. A second metal electrode 53 is provided on the (low temperature side). As shown in FIG. 1B, the first metal electrode 52 has a recess 521 into which the superconducting wire 51 is inserted.

  In general, since the connection work is easy and good electrical characteristics are obtained, the superconducting wire 51 and the first metal electrode 52 are connected by solder (for example, Patent Document 1). Specifically, the superconducting wire 51 is inserted into the recess 521 in a state where the melted solder is filled in the recess 521 of the metal electrode 52, and is vertically supported by a support member (not shown). When the solder is solidified by cooling, the superconducting wire 51 is fixed to the metal electrode 52. That is, the superconducting wire 51 and the metal electrode 52 are electrically connected via the solder 56. The connection between the superconducting wire 51 and the second metal electrode 53 is the same.

Japanese Patent Laid-Open No. 10-275641

  However, in the connection portion of the superconducting wire described above, since the thickness of the solder layer interposed between the surface (first surface) of the superconducting wire on the superconducting layer side and the metal electrode is about 1 mm, the connection resistance is low. It becomes higher (for example, 0.08 to 0.20 μΩ). Further, since the thickness of the solder layer is not uniformly controlled, it is difficult to stably obtain a desired connection resistance. Furthermore, when a plurality of superconducting wires are arranged side by side and connected to one metal electrode, variation in connection resistance between the respective connection portions becomes large, and there is a possibility that drift that causes quenching may occur.

  An object of the present invention is to provide a connection part of a superconducting wire and a superconducting current lead capable of reducing a connection resistance and stably obtaining a desired connection resistance.

The connecting portion of the superconducting wire according to the present invention is formed by connecting an end portion of a tape-like superconducting wire in which an intermediate layer, a superconducting layer, and a stabilizing layer are sequentially laminated on a metal substrate to a metal electrode via a solder layer. A connecting portion of a superconducting wire,
The metal electrode has an accommodating recess for accommodating an end of the superconducting wire,
An end of the superconducting wire is inserted into the housing recess, and a wedge member having a V-shaped cross section is inserted along the first surface of the superconducting wire on the metal substrate side,
The superconducting wire is fixed in a state where the second surface on the superconducting layer side is pressed against the metal electrode through the solder layer by the wedge member ,
The housing recess has a first recess inner surface against which the second surface of the superconducting wire is pressed, and a second recess inner surface facing the first recess inner surface,
The inner surface of the second recess has at least one step portion that makes line contact with the wedge member,
The wedge member is supported by an opening edge of the receiving recess and the stepped portion .

  A superconducting current lead according to the present invention is a superconducting current lead for connecting a superconducting application device installed in a low temperature part and an external device installed in a normal temperature part, and includes a connecting part of the above superconducting wire. It is characterized by.

  According to the present invention, since the superconducting wire is pressed against the metal electrode by the wedge member with a uniform pressing force, the solder layer interposed between the superconducting wire and the metal electrode is extremely thin and has a uniform thickness. Therefore, the connection resistance can be reduced and a desired connection resistance can be stably obtained.

It is a figure which shows the connection structure of the superconducting wire and electrode in the conventional superconducting electric current lead. It is a figure which shows the superconducting magnet apparatus using the superconducting current | flow lead which concerns on one embodiment of this invention. It is a figure which shows the general structure of a superconducting wire. It is a figure which shows the connection structure of the superconducting wire in a superconducting electric current lead, a 1st electrode, and a 2nd electrode. It is a perspective sectional view which decomposes | disassembles and shows the connection part of a superconducting wire and a 1st electrode.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a diagram showing a superconducting magnet device using a superconducting current lead according to an embodiment of the present invention. As shown in FIG. 2, the superconducting magnet device 1 includes a superconducting current lead 10, a normal conducting current lead 15, a superconducting coil 20, a power source 30, a cryogenic container 40, and the like.

  The cryogenic container 40 has a double structure including an inner refrigerant tank 41 and an outer vacuum tank 42. The refrigerant tank 41 is connected to a refrigerator (not shown), and is kept at an extremely low temperature (for example, 77 K) by liquid helium, for example. The vacuum chamber 42 is connected to a vacuum pump (not shown), and the inside is kept in a vacuum state.

The superconducting coil 20 is a coil wound with a superconducting wire. The superconducting coil 20 is disposed in a refrigerant tank 41 that is a low temperature part. The superconducting coil 20 has a coil electrode 21 for connecting to the superconducting current lead 10.
The power source 30 is disposed outside the low-temperature container 40 serving as a normal temperature part. The power supply 30 supplies current to the superconducting coil 20 via the normal conducting current lead 15 and the superconducting current lead 10. The normal conductive current lead 15 is, for example, a copper wire.

The superconducting current lead 10 includes a superconducting wire 11, a first electrode 12, and a second electrode 13. The superconducting current lead 10 is disposed in the refrigerant tank 41.
The superconducting wire 11 is a tape-like wire having a superconducting layer 113 (see FIG. 3). One end of the superconducting wire 11 on the high temperature side is connected to the first electrode 12, and the other end on the low temperature side is connected to the second electrode 13.

The 1st electrode 12 (high temperature side electrode) is comprised with metal materials, such as copper or a copper alloy. The first electrode 12 is disposed in the vicinity of the bottom surface of the refrigerant tank 41 and is connected to the normal conductive current lead 15 via a conductor lead-out portion (not shown). The temperature in the vicinity of the first electrode 12 is, for example, 77K.
The second electrode 13 (low temperature side electrode) is made of a metal material such as copper or a copper alloy. The second electrode 13 is disposed in the vicinity of the superconducting coil 20 and connected to the coil electrode 21 of the superconducting coil 20. The temperature in the vicinity of the second electrode 13 is, for example, 4.2K.

  FIG. 3 is a diagram showing a general configuration of the superconducting wire 11. As shown in FIG. 3, the superconducting wire 11 has a laminated structure in which an intermediate layer 112, a superconducting layer 113, and a stabilizing layer 114 are formed in this order on a tape-shaped metal substrate 111.

  The metal substrate 111 has a low magnetic non-orientation represented by Ni—Cr (for example, Hastelloy (registered trademark)), W—Mo, Fe—Cr (for example, austenitic stainless), or Fe—Ni materials. It is a metal substrate.

The intermediate layer 112 has, for example, a first intermediate layer (diffusion prevention layer) for preventing the diffusion of elements from the metal substrate 111 to reach the superconducting layer 113, and orients crystals of the superconducting layer 113 in a certain direction. A second intermediate layer (alignment layer). The first intermediate layer is composed of, for example, a gallium-doped zinc oxide layer (GZO) or an yttrium-stabilized zirconia layer (YSZ). For example, an ion beam assisted deposition (IBAD) can be applied to form the first intermediate layer. The second intermediate layer is composed of, for example, a cerium oxide layer (CeO ₂ ). For example, an RF sputtering method can be applied to form the second intermediate layer.

The superconducting layer 113 is made of, for example, an oxide superconductor such as an RE-based superconductor (RE: rare earth element). A typical example of the RE-based superconductor is an yttrium-based superconductor represented by YBa ₂ Cu ₃ O ₇ . The superconducting layer 113 can be formed by pulsed laser deposition (PLD) or metal organic chemical vapor deposition (MOCVD).

The stabilization layer 114 is a layer for protecting the superconducting layer 113 and bypassing the current when the superconducting state is partially broken and resistance is generated (normal conducting transition). The stabilization layer 114 is made of silver, for example. For example, a sputtering method can be applied to form the stabilization layer 114.
In the superconducting wire 11, the surface on the metal substrate 111 side is referred to as a first surface 11A, and the surface on the superconducting layer 113 side (stabilization layer 114 side) is referred to as a second surface 11B.

In the present embodiment, when the superconducting wire 11 is connected to the first electrode 12 and the second electrode 13, a wedge member 14 having a V-shaped cross section (including a shape having a flat tip) is used.
FIG. 4 is a diagram showing a connection portion between the superconducting wire 11 and the first electrode 12 in the superconducting current lead 10. FIG. 4A is an overall view of the superconducting current lead 10. 4B is a cross-sectional view taken along arrow IV-IV in FIG. 4A. FIG. 5 is an exploded perspective sectional view showing a connection portion between the superconducting wire 11 and the first electrode 12. In FIG. 5, the solder layer 16 is omitted.
4 and 5 show the connecting portion between the superconducting wire 11 and the first electrode 12, the connecting portion between the superconducting wire 11 and the second electrode 13 is the same.

  As shown in FIGS. 4 and 5, the wedge member 14 has a first wedge surface 14 </ b> A that contacts the superconducting wire 11 and a second wedge surface 14 </ b> B that contacts the first electrode 12. The second wedge surface 14B is inclined with respect to the first wedge surface 14A at the tip angle θ. The tip angle θ is preferably 1 to 5 °. When the tip angle θ is less than 1 °, the function as a wedge is not exhibited. When the tip angle θ is larger than 5 °, the first electrode 12 may become large in order to obtain a predetermined fixing force. That is, by setting the tip angle θ of the wedge member 14 to 1 to 5 °, the current lead can be reduced in size without losing the function as the wedge.

  The wedge member 14 preferably has the same heat shrinkability as the first electrode 12, and more preferably is made of the same material (for example, copper or copper alloy). When the superconducting current lead 10 is used in a cryogenic environment, the first electrode 12 and the wedge member 14 are thermally contracted. At this time, if the first electrode 12 and the wedge member 14 have different heat shrinkability, the joint may be damaged. In the present embodiment, since the wedge member 14 has the same heat shrinkability as that of the first electrode 12, both contract similarly in a cryogenic environment. Therefore, it is possible to prevent the joint portion between the wedge member 14 and the first electrode 12 from being damaged due to the difference in heat shrinkability.

  The first electrode 12 has an accommodating recess 121 that accommodates the end portion of the superconducting wire 11 and the wedge member 14. The housing recess 121 is formed in a substantially rectangular parallelepiped shape. The dimensions of the housing recess 121 are appropriately set according to the superconducting wire 11 and the wedge member 14 to be housed.

The housing recess 121 has a first recess inner surface 121A and a second recess inner surface 121B that face each other in the thickness direction of the superconducting wire 11 to be stored.
The first recess inner surface 121A is formed flat. On the second recess inner surface 121B, a stepped portion 121C is formed at a substantially central portion in the depth direction. The step portion 121C is formed such that a ridge line connecting the corner portion of the step portion 121C and the opening end edge of the housing recess 121 is parallel to the second wedge surface 14B of the wedge member 14.

  The end of the superconducting wire 11 is inserted into the housing recess 121 in a state where the housing recess 121 is filled with solder and melted. At this time, the second surface 11B of the superconducting wire 11 faces the first recess inner surface 121A of the housing recess 121, and the first surface 11A of the superconducting wire 11 faces the second recess inner surface 121B of the housing recess 121. .

  In addition, the wedge member 14 is inserted into the accommodating recess 121 along the first surface 11 </ b> A of the superconducting wire 11. By pushing the wedge member 14 into the housing recess 121 with a predetermined insertion force (for example, hammering), the second surface 11B of the superconducting wire 11 is pressed against the first electrode 12 via the solder layer 16. In this state, when the solder is solidified by cooling, the superconducting wire 11 is fixed to the metal electrode 12.

  When the wedge member 14 is inserted into the housing recess 121, the first wedge surface 14A is supported by the first surface 11A of the superconducting wire 11, and the first edge surface of the housing recess 121 and the corner of the step portion 121C are supported by the first edge 11A. Two wedge surfaces 14B are supported. That is, the wedge member 14 is inserted into the housing recess 121 in a stable state, and applies a uniform pressing force to the superconducting wire 11.

  Since the superconducting wire 11 is pressed against the first electrode 12 by the wedge member 14 with a uniform pressing force, the solder layer 16 interposed between the superconducting wire 11 and the first electrode 12 is extremely thin (for example, 10 to 100 μm). ), With a uniform thickness. Therefore, the connection resistance at the connection portion between the superconducting wire 11 and the first electrode 12 is significantly reduced as compared with the conventional structure. Further, when a plurality of current leads 10 are produced, a desired connection resistance can be stably obtained.

  Furthermore, since the insertion direction of the wedge member 14 is self-adjusted by the step portion 121C provided on the second concave portion inner surface 121B, the wedge member 14 can be easily inserted into the accommodating concave portion 121 in a more stable state.

  As described above, the connecting portion of the superconducting wire applied to the superconducting current lead 10 according to the embodiment includes the intermediate layer (112), the superconducting layer (113), and the stabilizing layer (114) on the metal substrate (111). The ends of the tape-shaped superconducting wires (111) stacked in order are connected to the metal electrodes (first electrode 12 and second electrode 13) via the solder layer (16). The metal electrodes (12, 13) have a housing recess (121) that houses the end of the superconducting wire (11). The end of the superconducting wire (11) is inserted into the housing recess (121), and the wedge member has a V-shaped cross section along the first surface (11A) on the metal substrate (111) side of the superconducting wire (11). (14) is inserted. The superconducting wire (11) is fixed in a state where the second surface (11B) on the superconducting layer (113) side is pressed against the metal electrodes (12, 13) via the solder layer (16) by the wedge member (14). Is done.

  Since the superconducting wire (11) is pressed against the metal electrodes (12, 13) by the wedge member (14) with a uniform pressing force, the solder layer interposed between the superconducting wire (11) and the metal electrodes (12, 13). (16) is extremely thin and uniform. Therefore, a desired connection resistance can be stably obtained and the connection resistance can be reduced.

[Example]
In the example, a superconducting current lead having the structure shown in the embodiment was manufactured, and the connection between the superconducting wire and the metal electrode was evaluated for a plurality of samples. Specifically, the superconducting current lead was placed in liquid nitrogen (77K), the critical current value (Ic) was measured, and the connection resistance of the connecting portion between the superconducting wire and the low temperature side electrode was measured.
Further, as a comparative example, a superconducting current lead having a conventional structure (see FIG. 1) was produced and evaluated in the same manner as in the example. The evaluation results are shown in Table 1.

As shown in Table 1, the connection resistance of the connection portion between the superconducting wire and the low-temperature side electrode was 0.096 μΩ in the comparative example, but was reduced to about 1/6, 0.016 μΩ in the example. It was. The Joule heat generation calculated based on the connection resistance was also 1/6, and the total heat penetration amount (heat penetration amount by heat conduction + Joule heat generation amount) could be reduced by about 10%.
In addition, the standard deviation (variation between samples) of the connection resistance was 0.25 in the comparative example, but was 0.020 and about 1/10 in the example.
Furthermore, the critical current value as designed was not obtained in the comparative example, but the coastal current value as designed was obtained in the example.

As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.
For example, in the embodiment, in the superconducting current lead, the connecting portion of the superconducting wire according to the present invention is applied to both the connecting portion between the superconducting wire and the low temperature side electrode and the connecting portion between the superconducting wire and the high temperature side electrode. However, it may be applied to only one of them.
Further, for example, a plurality of stepped portions may be provided on the inner surface of the second recessed portion of the housing recessed portion.

  The present invention can also be applied to a superconducting current lead having a plurality of superconducting wires. Since a stable connection resistance is obtained at the connection portion between each superconducting wire and the metal electrode, the variation in the connection resistance is small and it is possible to prevent the occurrence of a drift that causes quenching.

  The present invention can also be applied to a connection portion between a superconducting cable and a metal electrode having a structure in which a plurality of superconducting wires are spirally wound around a cylindrical former.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Superconducting Magnet Device 10 Superconducting Current Lead 11 Superconducting Wire 11A First Surface (Metal Substrate Side)
11B 2nd surface (superconducting layer side)
111 Metal substrate 112 Intermediate layer 113 Superconducting layer 114 Stabilizing layer 12 First electrode (high temperature side electrode)
121 housing recess 121A first recess inner surface 121B second recess inner surface 121C step 13 second electrode (low temperature side electrode)
14 Wedge member 14A First wedge surface 14B Second wedge surface 15 Normal conductive current lead 16 Solder layer 20 Superconducting coil 30 Power source 40 Low temperature container

Claims (5)

An end portion of a tape-like superconducting wire in which an intermediate layer, a superconducting layer, and a stabilization layer are sequentially laminated on a metal substrate is a connecting portion of a superconducting wire that is connected to a metal electrode through a solder layer,
The metal electrode has an accommodating recess for accommodating an end of the superconducting wire,
An end of the superconducting wire is inserted into the housing recess, and a wedge member having a V-shaped cross section is inserted along the first surface of the superconducting wire on the metal substrate side,
The superconducting wire is fixed in a state where the second surface on the superconducting layer side is pressed against the metal electrode through the solder layer by the wedge member ,
The housing recess has a first recess inner surface against which the second surface of the superconducting wire is pressed, and a second recess inner surface facing the first recess inner surface,
The inner surface of the second recess has at least one step portion that makes line contact with the wedge member,
The connecting portion of the superconducting wire , wherein the wedge member is supported by an opening edge of the receiving recess and the stepped portion. The connection part of the superconducting wire according to claim 1, wherein a tip angle of the wedge member is 1 to 5 °. Connection of a superconducting wire according to claim 1 or 2 the thickness of the solder layer is characterized in that it is a 10 to 100 [mu] m. The superconducting wire connecting portion according to any one of claims 1 to 3 , wherein the wedge member has a heat shrinkability equivalent to that of the metal electrode. A superconducting current lead for connecting a superconducting application device installed in a low temperature part and an external device installed in a normal temperature part, wherein the superconducting wire connecting part according to any one of claims 1 to 4 is connected. A superconducting current lead comprising:

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