JP6238623B2 - Superconducting current lead - Google Patents

Description

  The present invention relates to a superconducting current lead using an oxide superconducting wire, and more particularly to a superconducting current lead in which a superconducting wire and a metal electrode are accommodated in a reinforcing member.

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 zero electrical resistance and low thermal conductivity below the liquid nitrogen temperature (one tenth 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.

In general, a superconducting current lead is a tape-shaped superconducting wire, a first metal electrode disposed at one end (high temperature side) of the superconducting wire, and a second disposed at the other end (low temperature side) of the superconducting wire. A metal electrode is provided. The superconducting wire, the first metal electrode, and the second metal electrode are joined by soldering, for example.
A lead body composed of a superconducting wire, a first metal electrode, and a second metal electrode is accommodated and supported in a state of being positioned in the reinforcing member (for example, Patent Document 1). The reinforcing member is made of a material having low thermal conductivity (for example, fiber reinforced plastic (GFRP), stainless alloy, nickel-base alloy, titanium alloy, etc.). Thus, when the lead body is accommodated in the reinforcing member, the superconducting wire is generally held in a straight line.

Japanese Patent Application Laid-Open No. 07-297025

However, when the above-described superconducting current lead is used in a cryogenic environment, the respective components are thermally contracted, resulting in the following problems.
For example, when the thermal contraction rate of the superconducting wire is larger than the thermal contraction rate of the reinforcing member, the superconducting wire contracts more greatly, resulting in an excessive load at the joint (soldering part) between the superconducting wire and the metal electrode. There is a risk of damage. And if a junction part is damaged, since connection resistance will become large, it will become difficult to flow a big electric current.

  On the other hand, when the thermal contraction rate of the superconducting wire is smaller than the thermal contraction rate of the reinforcing member, the superconducting wire only bends. At first glance, an excessive load is not generated at the joint between the superconducting wire and the metal electrode. Conceivable. However, since the heat conductivity of the superconducting wire and the heat conductivity of the reinforcing member are different, the progress of cooling is also different. That is, the superconducting wire having a high thermal conductivity is more rapidly cooled, and the amount of shrinkage at the initial stage of cooling is larger in the superconducting wire than in the reinforcing member. Therefore, too much load is generated at the junction between the superconducting wire and the metal electrode. In particular, since a general oxide superconducting wire has a stabilizing layer made of Ag or Cu having high thermal conductivity, such a problem becomes remarkable.

  An object of the present invention is to provide a highly reliable superconducting current lead capable of preventing damage to a joint portion between a superconducting wire and a metal electrode due to thermal contraction during cooling.

The superconducting current lead according to the present invention is a tape-shaped superconducting wire in which an intermediate layer, a superconducting layer, and a stabilizing layer are laminated in order on a metal substrate,
Metal electrodes bonded to both ends of the superconducting wire;
And a reinforcing member which yield volumes of lead body comprising said metal electrode and the superconducting wire,
The lead body is accommodated in the reinforcing member at a predetermined inter-electrode distance so that the superconducting wire has a bend between the metal electrodes.

  According to the present invention, since the thermal contraction generated in the superconducting wire during cooling is absorbed by the bending formed in the superconducting wire, an excessive load is not generated at the joint between the superconducting wire and the metal electrode, and high reliability is achieved. Sex is secured.

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 an external view of the superconducting lead which concerns on embodiment. It is a figure which shows the general structure of a superconducting wire. It is the top view which looked at the superconducting current lead from the Z direction front end side. It is VI-VI arrow sectional drawing in FIG. It is the front view which looked at the superconducting current lead from the Y direction base end side. It is IV-IV arrow sectional drawing in FIG. It is a figure which shows the bending formed in a superconducting wire.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a superconducting magnet device 1 using a superconducting current lead 10 according to an embodiment of the present invention. FIG. 2 is an external view of the superconducting lead 10. FIG. 3 is a diagram showing a general configuration of the superconducting wire 11. FIG. 4 is a plan view of the superconducting current lead as viewed from the front end side in the Z direction. 5 is a cross-sectional view taken along the line VI-VI in FIG. FIG. 6 is a front view of the superconducting current lead as viewed from the base end side in the Y direction. 7 is a cross-sectional view taken along arrow IV-IV in FIG.

As shown in FIG. 1, 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 composed of an inner container 41 and an outer vacuum chamber 42. The container 41 is connected to a refrigerator (not shown), and the interior thereof is held at a very low temperature (for example, 77 K) by, for example, liquid helium. 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 container 41 serving as 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, a second electrode 13, and a reinforcing member 14. The superconducting current lead 10 is disposed in the container 41. 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.
In this embodiment, a superconducting current lead 10 using one superconducting wire 11 will be described. However, the present invention is applied to a superconducting current lead having a plurality of superconducting wires 11 as in Example 2 described later. You can also.

  The superconducting wire 11 is a tape-like wire having a superconducting layer 113 as shown in FIG. The superconducting wire 11 has a laminated structure in which, for example, 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 is a low magnetic non-oriented metal substrate typified by a Ni alloy (for example, Hastelloy (registered trademark)), W-Mo, Fe-Cr (for example, austenitic stainless steel), or Fe-Ni material. It is.

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 plurality of intermediate layers, such as 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, for example, an oxidation of an RE-based superconductor (RE: one or more rare earth elements selected from Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb). Consists of superconductors. 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 is formed by metal-organic deposition (MOD), pulsed laser deposition (PLD), sputtering, or metal organic chemical vapor deposition (MOCVD). Vapor Deposition) can be applied.

In the superconducting layer 113, it is preferable that 50 μm or less oxide particles containing at least one of Y, Zr, Sn, Ti, and Ce are dispersed as magnetic flux pinning points. In this case, as a method for forming the superconducting layer 113, a TFA-MOD method using trifluoroacetate (TFA) is suitable. For example, a Zr-containing oxide particle (BaZrO ₃ ) is added to the superconducting layer 113 made of a RE-based superconductor by mixing a Zr-containing naphthenate having a high affinity with Ba into a Ba solution containing TFA. It can be distributed as flux pinning points. A known technique can be applied to the method of dispersing the magnetic flux pinning points in the superconducting layer 113 (for example, JP 2012-059468 A).
By dispersing the magnetic flux pinning points in the superconducting layer 113, even if the superconducting wire 11 is used in a curved state, it is hardly affected by the magnetic field and exhibits stable superconducting characteristics.

  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 preferably made of a material having a low electrical resistivity and a high thermal conductivity, for example, Ag or Cu. For example, a sputtering method can be applied to form the stabilization layer 114.

  The thermal contraction rate of the superconducting wire 11 mainly depends on the metal substrate 111. The thermal contraction rate of Hastelloy when cooled from room temperature to 77K is 0.204%. Further, the thermal conductivity of the superconducting wire 11 mainly depends on the metal substrate 111 and the stabilization layer 114. The thermal conductivity of Hastelloy at 77K is 5.164 W / (m · K), and the thermal conductivity of Ag is 237.3 W / (m · K).

  The 1st electrode 12 (high temperature side electrode) and the 2nd electrode 13 (low temperature side electrode) are 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 container 41 and connected to the normal conductive current lead 15 through 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 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.

  The first electrode 12 and the second electrode 13 each have fixing grooves 12a and 13a for fixing the superconducting wire 11 on one end face in the length direction (X direction). Both ends in the width direction (Y direction) of the fixing grooves 12a and 13a may be opened or closed. The heights (Z direction) of the fixing grooves 12 a and 13 a are set slightly larger than the thickness of the superconducting wire 11. The depth (X direction) of the fixing grooves 12a and 13a only needs to be such that it can be firmly joined to the superconducting wire 11, the connection resistance is sufficiently small, and can be supported.

  The first electrode 12 is inserted into the fixed groove 12a until one end of the superconducting wire 11 hits the bottom of the fixed groove 12a. The other end of the superconducting wire 11 is inserted into the fixed groove 13a of the second electrode 13 until it hits the bottom of the fixed groove 13a. The gap between the superconducting wire 11 and the fixing grooves 12a and 13a is filled with molten solder. That is, the superconducting wire 11 and the first electrode 12 and the second electrode 13 are joined and electrically connected by soldering.

  Thus, since the superconducting wire 11 is inserted and joined to the fixing grooves 12a and 13a in the superconducting current lead 11, the assembly process of the lead body is extremely easy, and the superconducting current lead 11 is miniaturized. Also useful above.

The reinforcing member 14 has a lower thermal conductivity than the superconducting wire 11. Thereby, the amount of heat penetration from the outside can be reduced.
From the viewpoint of reducing the amount of heat penetration, GFRP is preferred. The thermal conductivity of GFRP at 77 K is 0.39 W / (m · K), which is significantly smaller than the thermal conductivity of the superconducting wire 11. Moreover, the thermal contraction rate of GFRP at 77 K is 0.213%, which is larger than the thermal contraction rate of the superconducting wire 11.
On the other hand, from the viewpoint of protecting the superconducting magnet device 1 when the superconducting wire 11 is damaged, a stainless alloy, nickel-base alloy, titanium alloy, or the like that functions as a bypass is preferable. The thermal conductivity of the stainless alloy (SUS304, SUS316) at 77K is 7.9 W / (m · K), which is smaller than the thermal conductivity of the superconducting wire 11. Further, the heat shrinkage rate of the stainless alloy (SUS304) at 77K is 0.281, which is larger than the heat shrinkage rate of the heat conductive wire 11.

  The reinforcing member 14 has a lead body in which the first electrode 12 and the second electrode 13 are joined to both ends of the superconducting wire 11, and a predetermined inter-electrode distance (separation between the first electrode 12 and the second electrode 13. It accommodates in the state positioned so that it may become (distance). The reinforcing member 14 is a hollow rectangular parallelepiped member, and includes a housing part 142 whose top surface is open and a lid part 141 that closes the opening. After the lead main body is accommodated in the accommodating portion 142, the lid portion 141 is bonded so as to close the opening of the accommodating portion 142. Note that an opening may be partially formed in the accommodating portion 142 and the lid portion 141.

  The lead 142 is accommodated in the accommodating portion 142 and is positioned so as to have a predetermined inter-electrode distance. Specifically, a positioning portion (not shown) for positioning the lead body is provided in the reinforcing member 14, and the first electrode 12 and the second electrode 13 are fixed at predetermined positions using this. To do.

  In the present embodiment, when the lead body is accommodated in the reinforcing member 14, the superconducting wire 11 is bent between the first electrode 12 and the second electrode 13. FIG. 8 shows the deflection formed in the superconducting wire 11.

  As shown in FIG. 8A, the exposed length Lsc of the superconducting wire 11 is a length obtained by removing the depth of the fixing grooves 12 a and 13 a (length in the X direction) from the entire length of the superconducting wire 11. If the inter-electrode distance Le when the lead body is accommodated in the reinforcing member 14 is shorter than the exposed length Lsc of the superconducting wire 11, a deflection of a deflection amount ΔD is formed in the superconducting wire 11 as shown in FIG. 8B.

  For example, when the depth of each of the fixing grooves 12a and 13a is 25 mm and the total length of the superconducting wire 11 is 151 mm, the exposed length Lsc of the superconducting wire 11 is 101 mm. When the inter-electrode distance Le when the lead body is accommodated in the reinforcing member 14 is 100 mm, a deflection of 1 mm is formed.

  Here, the deflection rate ΔD / Le is preferably 0.5% or more. By setting the deflection rate ΔD / Le to 0.5% or more, the thermal contraction that occurs in the superconducting wire 11 during cooling is reliably absorbed by the deflection, so the superconducting wire 11, the first electrode 12, and the second electrode 13 are absorbed. It is possible to reliably prevent an excessive load from being applied to the joint portion.

  Note that the upper limit of the deflection rate ΔD / Le is not particularly limited from the viewpoint of absorbing thermal shrinkage generated in the superconducting wire 11. However, if the deflection is too large, it may be difficult to accommodate in the reinforcing member 14 or the superconducting characteristics may be deteriorated. From this point of view, the deflection rate ΔD / Le is preferably 10% or less.

  As described above, the superconducting current lead 10 according to the embodiment includes the tape-shaped superconducting wire 11 in which the intermediate layer 112, the superconducting layer 113, and the stabilizing layer 114 are sequentially laminated on the metal substrate 111, and both ends of the superconducting wire 11. The lead body including the metal electrodes (first electrode 12 and second electrode 13) bonded to the portion, the superconducting wire 11 and the metal electrodes (12, 13) is set to a predetermined inter-electrode distance Le. And a reinforcing member 14 accommodated in a positioned state. And the superconducting wire 11 has bending between metal electrodes (12, 13).

In the superconducting current lead 10, when the reinforcing member 14 is made of GFRP, stainless steel, or the like, the thermal contraction rate of the superconducting wire 11 is smaller than the thermal contraction rate of the reinforcing member 14. In this case, the superconducting wire 11 having a higher thermal conductivity is faster in cooling, and the amount of shrinkage in the initial stage of cooling is larger in the superconducting wire 11 than in the reinforcing member 14, so that the superconducting wire 11 is bent. Otherwise, an excessive load is generated at the junction between the superconducting wire 11 and the first electrode 12 and the second electrode 13.
According to the superconducting current lead 10, heat shrinkage that occurs in the superconducting wire 11 during cooling is absorbed by the bending formed in the superconducting wire 11, so that the superconducting wire 11, the first electrode 12, and the second electrode 13 An excessive load is not generated at the joint, and high reliability is ensured.

  Further, when the thermal contraction rate of the superconducting wire 11 is larger than the thermal contraction rate of the reinforcing member 14, not only in the initial stage of cooling but also in the cryogenic environment during operation, the superconducting wire 11 and the superconducting wire 11 differ from the superconducting wire 11 due to the difference in thermal contraction amount. An excessive load is generated at the junction between the first electrode 12 and the second electrode 13. Also in this case, by forming a deflection in the superconducting wire 11, the thermal contraction generated in the superconducting wire 11 is absorbed, and an excessive load is applied to the joint between the superconducting wire 11, the first electrode 12, and the second electrode 13. It can be prevented from occurring.

[Example 1]
In Example 1, one superconducting wire having a superconducting layer made of YBCO is prepared, and an oxygen-free copper metal electrode having a surface plated with tin is bonded to both ends thereof, and a GFRP reinforcement is further provided. A superconducting current lead was prepared by being housed in the member. The interelectrode distance Le was 100 mm, and the deflection rate of the superconducting wire between the electrodes was changed to 1%, 2%, 5%, and 20% by changing the total length of the superconducting wire.

[Reference Example 1]
In Reference Example 1, a superconducting current lead having the same configuration as in Example 1 was produced so that the deflection rate was 0.3%.

  The superconducting current leads according to Example 1 and Reference Example 1 were evaluated for critical current characteristics in a cryogenic environment. Specifically, a heat conduction plate was attached to the metal electrode of the superconducting current lead, and the whole superconducting current lead was cooled by conduction cooling to 73 to 78K, and the critical current value Ic (design value 200A) was measured. The external magnetic field was 0T (in a self magnetic field). The evaluation results are shown in Table 1.

[Example 2]
In Example 2, two superconducting wires having a superconducting layer made of YBCO were prepared, and these metal substrate surfaces were bonded together to produce a composite type superconducting wire. Then, an oxygen-free copper metal electrode whose surface is tin-plated is joined to both ends of the two composite superconducting wires arranged side by side in the width direction, and further accommodated in a reinforcing member made of GFRP. A superconducting current lead was produced. That is, in Example 2, a superconducting current lead using four superconducting wires was produced. The interelectrode distance Le was 100 mm, and the deflection rate of the superconducting wire between the electrodes was changed to 1.2%, 2%, 6%, and 18% by changing the total length of the superconducting wire.

[Reference Example 2]
In Reference Example 2, a superconducting current lead having the same configuration as in Example 2 was produced so that the deflection rate was 0.4%.

  The superconducting current leads according to Example 2 and Reference Example 2 were evaluated for critical current characteristics in a cryogenic environment. Specifically, a heat conduction plate was attached to the metal electrode of the superconducting current lead, and the whole superconducting current lead was cooled by conduction cooling to 73 to 78K, and the critical current value Ic (design value 800A) was measured. The external magnetic field was 0T (in a self magnetic field). The evaluation results are shown in Table 2.

  As shown in Tables 1 and 2, in Example 1 and Example 2 in which the deflection rate ΔD / Le was 0.5% or more, critical current characteristics almost equal to the design values were obtained. This confirmed the effectiveness of the present invention to form a deflection in the superconducting wire. In Examples 1-4 and 2-4, the critical current characteristics as designed were obtained, but the superconducting wire was greatly bent and it was difficult to accommodate the reinforcing member. Thus, since Example 1-4 and Example 2-4 are not practical, it showed as a reference example in Table 1 and Table 2.

  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.

  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.

DESCRIPTION OF SYMBOLS 1 Superconducting magnet apparatus 10 Superconducting current lead 11 Superconducting wire 111 Metal substrate 112 Intermediate layer 113 Superconducting layer 114 Stabilizing layer 12 First electrode (metal electrode)
13 Second electrode (metal electrode)
14 Reinforcing member 15 Normal conducting current lead 20 Superconducting coil 30 Power source 40 Cryogenic container

Claims (8)

A tape-shaped superconducting wire in which an intermediate layer, a superconducting layer, and a stabilizing layer are laminated in order on a metal substrate;
Metal electrodes bonded to both ends of the superconducting wire;
And a reinforcing member which yield volumes of lead body comprising said metal electrode and the superconducting wire,
The lead body is accommodated in the reinforcing member at a predetermined inter-electrode distance so that the superconducting wire is bent between the metal electrodes.   2. The superconducting current lead according to claim 1, wherein a deflection rate represented by ΔD / L1 is 0.5% or more, where L1 is a distance between the electrodes and ΔD is a deflection amount of the superconducting wire. . The metal electrode has a fixing groove on one end surface,
The superconducting current according to claim 1 or 2, wherein the metal electrode and the superconducting wire are electrically connected by inserting and joining an end portion of the superconducting wire into the fixed groove. Lead.   4. The superconducting current lead according to claim 1, wherein the reinforcing member is made of a material having lower thermal conductivity than the superconducting wire. 5.   The superconducting current lead according to any one of claims 1 to 4, wherein the reinforcing member is made of a fiber reinforced plastic. The superconducting layer is formed by a TFA-MOD method,
6. The oxide particle of 50 μm or less containing at least one of Y, Zr, Sn, Ti, and Ce is dispersed as a magnetic flux pinning point in the superconducting layer. The superconducting current lead according to one item.   The superconducting current lead according to any one of claims 1 to 6, wherein the stabilization layer is made of Ag.   The superconducting current lead according to any one of claims 1 to 7, wherein an exposed length of the superconducting wire exposed from the metal electrode is longer than the predetermined inter-electrode distance.

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