CN105408969A - superconducting current leads - Google Patents

Abstract

The superconducting current lead of the present invention includes: a strip-shaped superconducting wire rod, which is formed by sequentially laminating an intermediate layer, a superconducting layer, and a stabilizing layer on a metal substrate; and metal electrodes, which are bonded to both ends of the superconducting wire rod and a reinforcing member that positions and accommodates a lead body including the superconducting wire and the metal electrode so as to have a predetermined electrode pitch. The superconducting wire has a bend between the metal electrodes.

Description

superconducting current leads

technical field

The present invention relates to a superconducting current lead using an oxide superconducting wire, and in particular, to a superconducting current lead configured by accommodating a superconducting wire and a metal electrode in a reinforcing member.

Background technique

In recent years, in the field of superconducting application devices using superconductivity, such as superconducting cables and superconducting magnets, research and development for practical use have been actively carried out. Generally, the superconducting application equipment is installed in the low-temperature section (cryogenic container), and is connected to an external equipment (such as a power supply) installed in the normal-temperature section through a current lead.

Since superconducting equipment operates in an extremely low temperature environment, the heat insulation of the low temperature part becomes extremely important. This is because, if the thermal insulation of the low-temperature part is poor and the heat intrusion 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. It will result in inoperability of superconducting application equipment. As the route of the heat intrusion into the low temperature part, the route of heat transfer through the cryogenic container and the route of heat transfer through the current lead are considered.

As a method for preventing heat intrusion through a cryogenic container, there is known a cryogenic container having a dual structure of a refrigerant tank containing a refrigerant such as liquid nitrogen and a superconducting application device, and a vacuum tank Installed on the outside of the refrigerant tank. According to this low-temperature container, the intrusion of heat into the low-temperature portion is reduced by vacuum insulation.

As a method for preventing heat intrusion through a current lead, a superconducting current lead using an oxide superconductor has been proposed. Oxide superconductors have zero resistance below the temperature of liquid nitrogen and low thermal conductivity (a few tenths of copper). Therefore, in the superconducting current lead, Joule heat is not generated when electricity is applied, and the amount of heat transfer to the low-temperature portion is also extremely small. Therefore, the intrusion of heat into the low-temperature portion is reduced by the superconducting current lead.

In general, a superconducting current lead includes a strip-shaped superconducting wire, a first metal electrode disposed at one end (high temperature side) of the superconducting wire, and a first metal electrode disposed at the other end (low temperature side) of the superconducting wire. two metal electrodes. For example, the superconducting wire is joined to the first metal electrode and the second metal electrode by welding.

A lead body composed of a superconducting wire, a first metal electrode, and a second metal electrode is accommodated and supported while being positioned in a reinforcing member (for example, Patent Document 1). The reinforcing member is made of a material with low thermal conductivity (for example, fiber reinforced plastics (GFRP: Glass Fiber Reinforced Plastics), stainless steel alloys, nickel-based alloys, titanium alloys, and the like). In this way, when the lead body is accommodated in the reinforcing member, the superconducting wire is generally kept linear.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 07-297025

Contents of the invention

The problem to be solved by the invention

However, if the above-mentioned superconducting current lead is used in an extremely low temperature environment, the following disadvantages arise due to thermal shrinkage of each component.

For example, when the thermal shrinkage rate of the superconducting wire is larger than that of the reinforcing member, the superconducting wire shrinks greatly, which may cause excessive damage to the junction (welded portion) between the superconducting wire and the metal electrode. load and damage it. Furthermore, since the connection resistance increases when the junction part is damaged, it becomes difficult to flow a large current.

On the other hand, when the thermal shrinkage rate of the superconducting wire is smaller than that of the reinforcing member, only the superconducting wire is deflected, and at first glance it can be considered that the joint between the superconducting wire and the metal electrode There is no excessive load on the part. However, since the thermal conductivity of the superconducting wire differs from that of the reinforcing member, the degree of progress of cooling also differs. That is, a superconducting wire having a high thermal conductivity progresses faster in cooling, and the superconducting wire has a larger contraction amount at the initial stage of cooling than a reinforcing member. Therefore, an excessive load still occurs at the junction between the superconducting wire and the metal electrode. In particular, general oxide superconducting wires have a stabilizing layer made of Ag or Cu having high thermal conductivity, so such a problem is significant.

It is an object of the present invention to provide a highly reliable superconducting current lead capable of preventing damage to a joint between a superconducting wire and a metal electrode due to heat shrinkage during cooling.

solution to the problem

The superconducting current lead of the present invention is characterized in that it comprises:

A strip-shaped superconducting wire, which is formed by sequentially stacking an intermediate layer, a superconducting layer, and a stabilization layer on a metal substrate;

metal electrodes joined to both ends of the superconducting wire; and

a reinforcing member positioning and accommodating a lead body including the superconducting wire rod and the metal electrode so as to have a predetermined electrode pitch,

The superconducting wire has a bend between the metal electrodes.

Invention effect

According to the present invention, the thermal shrinkage generated in the superconducting wire during cooling is absorbed by the deflection formed in the superconducting wire, so that an excessive load is not generated at the junction between the superconducting wire and the metal electrode, and a relatively high temperature is ensured. high reliability.

Description of drawings

FIG. 1 is a diagram showing a superconducting magnet device using a superconducting current lead according to an embodiment of the present invention.

Fig. 2 is an external view of a superconducting lead according to the embodiment.

FIG. 3 is a diagram showing a general structure of a superconducting wire.

4 is a plan view of a superconducting current lead viewed from the front end side in the Z direction.

Fig. 5 is a sectional view taken along line VI-VI in Fig. 6 .

Fig. 6 is a front view of the superconducting current lead viewed from the base end side in the Y direction.

Fig. 7 is a sectional view taken along line IV-IV in Fig. 4 .

In FIG. 8 , FIG. 8A is a diagram showing the exposed length of the superconducting wire (the state before being housed in the reinforcement member), and FIG. 8B is a diagram showing the deflection formed in the superconducting wire (the state after being housed in the reinforcement member).

Symbol Description

1 superconducting magnet device

10 superconducting current leads

11 superconducting wire

111 metal substrate

112 middle layer

113 superconducting layer

114 stabilization layer

12 first electrode (metal electrode)

13 Second electrode (metal electrode)

14 reinforcement parts

15 Normally Conducting Current Leads

20 superconducting coils

30 power

40 cryogenic containers

detailed description

Hereinafter, embodiments of the present invention will be described in detail based on 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 structure of the superconducting wire 11 . 4 is a plan view of a superconducting current lead viewed from the front end side in the Z direction. Fig. 5 is a sectional view taken along line VI-VI in Fig. 6 . Fig. 6 is a front view of the superconducting current lead viewed from the base end side in the Y direction. Fig. 7 is a sectional view taken along line IV-IV in Fig. 4 .

As shown in FIG. 1 , the superconducting magnet device 1 includes a superconducting current lead 10 , a normal conduction 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 container 41 and an outer vacuum chamber 42 . The container 41 is connected to a refrigerator (not shown), and the inside is kept at an extremely low temperature (for example, 77K) by using liquid helium, for example. The vacuum tank 42 is connected to a vacuum pump (not shown in the figure) to maintain a vacuum state inside.

The superconducting coil 20 is a coil formed by winding a superconducting wire. The superconducting coil 20 is arranged in a container 41 which is a low-temperature part. The superconducting coil 20 has a coil electrode 21 for connection to the superconducting current lead 10 .

The power supply 30 is arranged outside the cryogenic container 40 which is a room temperature section. The power source 30 supplies current to the superconducting coil 20 through the normally conducting current lead 15 and the superconducting current lead 10 . The normally conducting current lead 15 is, for example, a copper wire.

The superconducting current lead 10 has a superconducting wire 11 , a first electrode 12 , a second electrode 13 , and a reinforcing member 14 . The superconducting current lead 10 is arranged 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 is described, but the present invention can also be applied to a superconducting current lead including a plurality of superconducting wires 11 as in Example 2 described later.

As shown in FIG. 3 , the superconducting wire 11 is a tape-shaped wire having a superconducting layer 113 . The superconducting wire 11 has, for example, a laminated structure in which an intermediate layer 112 , a superconducting layer 113 , and a stabilization layer 114 are sequentially formed on a strip-shaped metal substrate 111 .

The metal substrate 111 is a low-magnetism non-oriented material represented by Ni alloy (such as Hastelloy (registered trademark)), W-Mo type, Fe-Cr type (such as austenitic stainless steel), or Fe-Ni type material. 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 from reaching the superconducting layer 113, and a second intermediate layer (diffusion prevention layer) for orienting the crystals of the superconducting layer 113 in a certain direction. Multiple intermediate layers such as two intermediate layers (orientation layers). The first intermediate layer consists, for example, of a gallium zinc oxide layer (GZO) or a yttrium-stabilized zirconia layer (YSZ). For the formation of the first intermediate layer, for example, an ion beam assisted deposition method (IBAD: Ion Beam Assisted Deposition) can be applied. The second intermediate layer consists of, for example, a cerium oxide layer (CeO ₂ ). For film formation of the second intermediate layer, for example, a radio frequency sputtering method can be applied.

The superconducting layer 113 is, for example, made of oxides such as RE superconductors (RE: one or more rare earth elements selected from Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb). Composition of superconductors. The RE-based superconductor is represented by an yttrium-based superconductor represented by YBa ₂ Cu ₃ O ₇ . For forming the superconducting layer 113 , metal-organic deposition (MOD: Metal-organic deposition), pulsed laser deposition (PLD: Pulsed Laser Deposition), sputtering, or metal-organic chemical vapor deposition (MOCVD: Metal Organic Chemical Vapor Deposition) can be applied.

Oxide particles containing at least one of Y, Zr, Sn, Ti, and Ce and having a diameter of 50 μm or less are preferably dispersed in the superconducting layer 113 as magnetic flux pinning points. In this case, the TFA-MOD method using trifluoroacetate (TFA) is suitable as a method for forming the superconducting layer 113 . For example, Zr-containing oxide particles (BaZrO ₃ ) can be dispersed as magnetic flux pinning sites by mixing a Zr-containing naphthenate with a high affinity for Ba into a Ba solution containing TFA. in the superconducting layer 113 composed of RE superconductors. In addition, as a method of dispersing magnetic flux pinning points in the superconducting layer 113 , known techniques (for example, Japanese Patent Laid-Open No. 2012-059468 ) can be applied.

By dispersing magnetic flux pinning points in the superconducting layer 113 , even when the superconducting wire 11 is used in a bent state, it is less susceptible to the influence of a magnetic field and stable superconducting characteristics can be exhibited.

The stabilization layer 114 is a layer that protects the superconducting layer 113 and detours a current when the superconducting state is partially destroyed to generate resistance (transfer of normal conduction). Preferably, the stabilization layer 114 is made of a material with low resistivity and high thermal conductivity, such as Ag or Cu. For forming the stabilizing layer 114 , for example, a sputtering method can be applied.

The heat shrinkage rate of the superconducting wire 11 mainly depends on the metal substrate 111 . The heat shrinkage rate of Hastelloy when cooling from room temperature to 77K is 0.204%. In addition, the thermal conductivity of the superconducting wire 11 mainly depends on the metal substrate 111 and the stabilizing layer 114. The thermal conductivity of Hastelloy alloy at 77K is 5.164W/(m·K), and the thermal conductivity of Ag is 237.3W/(m·K). K).

The first electrode 12 (high temperature side electrode) and the second electrode 13 (low temperature side electrode) are made of a metal material such as copper or copper alloy. The first electrode 12 is disposed near the bottom surface of the container 41 and connected to the normal conduction current lead 15 through a conductor lead-out portion (not shown). The temperature near the first electrode 12 is, for example, 77K. The second electrode 13 is arranged near the superconducting coil 20 and connected to the coil electrode 21 of the superconducting coil 20 . The temperature near the second electrode 13 is, for example, 4.2K.

The first electrode 12 and the second electrode 13 each have fixing grooves 12a, 13a for fixing the superconducting wire 11 on one end surface in the longitudinal direction (X direction). Both ends in the width direction (Y direction) of the fixing grooves 12a and 13a may be opened or closed. The height (Z direction) of the fixing grooves 12 a and 13 a is set to be slightly larger than the thickness of the superconducting wire 11 . The depths (X direction) of the fixing grooves 12a and 13a are sufficient as long as they are firmly bonded to the superconducting wire 11 and the connection resistance is sufficiently small and can be supported.

One end of the superconducting wire 11 is inserted into the fixing groove 12a of the first electrode 12 until it touches the bottom of the fixing groove 12a. The other end of the superconducting wire 11 is inserted into the fixing groove 13a of the second electrode 13 until it touches the bottom of the fixing 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 is bonded to the first electrode 12 and the second electrode 13 by welding and electrically connected.

In this way, for the superconducting current lead 10, since the superconducting wire 11 is inserted into the fixing grooves 12a, 13a and bonded, the assembly process of the lead main body is extremely easy. In addition, in realizing the miniaturization of the superconducting current lead 11 Also useful.

The thermal conductivity of the reinforcing member 14 is lower than that of the superconducting wire 11 . Thereby, the amount of heat intrusion from the outside can be reduced.

GFRP is suitable from the viewpoint of reducing the amount of heat intrusion. The thermal conductivity of GFRP at 77K is 0.39 W/(m·K), which is significantly smaller than that of the superconducting wire 11 . In addition, the heat shrinkage rate of 77K GFRP is 0.213%, which is larger than the heat shrinkage 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 broken, stainless steel alloys, nickel-based alloys, titanium alloys, and the like that function as bypasses are suitable. The thermal conductivity of the 77K stainless steel alloy (SUS304, SUS316) is 7.9 W/(m·K), which is smaller than that of the superconducting wire 11 . In addition, the thermal contraction rate of the 77K stainless steel alloy (SUS304) is 0.281, which is larger than the thermal contraction rate of the heat conduction wire 11 .

The reinforcing member 14 is obtained by joining the first electrode 12 and the second electrode 13 to both ends of the superconducting wire 11 so that a predetermined electrode pitch (the pitch between the first electrode 12 and the second electrode 13) is obtained. The lead body is accommodated in a state where the lead body is positioned. The reinforcing member 14 is a hollow rectangular parallelepiped member, and has an accommodating portion 142 whose top surface is opened and a cover portion 141 that closes the opening. After the lead wire main body is housed in the housing part 142 , the lid part 141 is bonded so as to close the opening of the housing part 142 . In addition, openings may be partially formed in the housing portion 142 and the cover portion 141 .

The lead body is accommodated in the accommodation portion 142 , and the lead body is positioned so as to have a predetermined electrode pitch. Specifically, a positioning portion (not shown) for positioning the lead body is provided in advance on the reinforcement member 14 , and the first electrode 12 and the second electrode 13 are fixed at predetermined positions by this.

In the present embodiment, the superconducting wire 11 has a bend between the electrodes between the first electrode 12 and the second electrode 13 after the lead body is housed in the reinforcing member 14 . The deflection formed in the superconducting wire 11 is shown in FIG. 8 .

As shown in FIG. 8A , the exposed length Lsc of the superconducting wire 11 is the length obtained by subtracting 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 . When the lead body is housed in the reinforcement member 14 , the electrode pitch Le is shorter than the exposed length Lsc of the superconducting wire 11 , as shown in FIG. 8B , a deflection ΔD is formed in the superconducting wire 11 .

For example, when the respective depths of the fixing grooves 12 a and 13 a are 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 lead main body is housed in the reinforcing member 14 and the electrode pitch Le 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 ratio ΔD/Le to 0.5% or more, the thermal shrinkage generated on the superconducting wire 11 during cooling can be reliably absorbed by deflection, so that the superconducting wire 11 and the first electrode 12 and the second electrode 12 can be reliably prevented. The junction between the two electrodes 13 imposes an excessive load.

In addition, from the viewpoint of absorbing thermal shrinkage generated in the superconducting wire 11 , the upper limit of the deflection ratio ΔD/Le is not particularly limited. However, if the deflection is too large, it may be difficult to be accommodated in the reinforcement member 14 or the superconducting characteristics may be lowered. From such a viewpoint, the deflection rate ΔD/Le is preferably 10% or less.

In this way, the superconducting current lead 10 of the embodiment includes: a tape-shaped superconducting wire 11 formed by sequentially stacking an intermediate layer 112, a superconducting layer 113, and a stabilizing layer 114 on a metal substrate 111; The first electrode 12 and the second electrode 13) are joined to both ends of the superconducting wire 11; , 13) The lead wire main body is housed in a state where the lead wire main body is positioned. Furthermore, the superconducting wire 11 has a bend between the metal electrodes (12, 13).

In the superconducting current lead 10 , when the reinforcing member 14 is made of GFRP, stainless steel alloy, or the like, the thermal shrinkage rate of the superconducting wire 11 is smaller than that of the reinforcing member 14 . In this case, since the cooling of the superconducting wire 11 with higher thermal conductivity proceeds faster, the shrinkage of the superconducting wire 11 at the initial stage of cooling is larger than that of the reinforcing member 14. Therefore, if no bending is formed on the superconducting wire 11 , 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, since the deflection formed in the superconducting wire 11 is used to absorb the thermal shrinkage generated in the superconducting wire 11 during cooling, there is no gap between the superconducting wire 11 and the first electrode 12 and the second electrode 12. The junction between the electrodes 13 generates an excessive load, ensuring high reliability.

In addition, when the thermal contraction rate of the superconducting wire 11 is larger than that of the reinforcing member 14, not only in the initial stage of cooling, but also in an extremely low temperature environment during operation, the difference in the thermal contraction amount causes the An excessive load is applied to the junction between the superconducting wire 11 and the first electrode 12 and the second electrode 13 . Even in this case, by forming a deflection in the superconducting wire 11, it is possible to absorb the thermal shrinkage generated in the superconducting wire 11, and prevent the joints between the superconducting wire 11 and the first electrode 12 and the second electrode 13 from being damaged. generate an excessive load.

[Example 1]

In Example 1, a superconducting wire having a superconducting layer made of YBCO was prepared, and metal electrodes made of oxygen-free copper with tin-plated surfaces were bonded to both ends of the superconducting wire, and housed in Superconducting current leads were fabricated using reinforced components made of GFRP. The electrode pitch Le was set at 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.

[Refer to example 1]

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

With respect to the superconducting current leads of Example 1 and Reference Example 1, critical current characteristics in an extremely low temperature environment were evaluated. Specifically, a heat conduction plate was installed on the metal electrode of the superconducting current lead, and the entire superconducting current lead was cooled to 73-78K by conduction cooling, and the critical current value Ic (design value 200A) was measured. In addition, the external magnetic field was set to 0T (from the magnetic field). The evaluation results are shown in Table 1.

Table 1

[Example 2]

In Example 2, two superconducting wires having a superconducting layer made of YBCO were prepared, and their metal substrate surfaces were bonded together to produce a composite superconducting wire. Then, two composite-type superconducting wires are arranged side by side in the width direction, metal electrodes made of oxygen-free copper with tin-plated treatment applied to the surface are joined at both ends, and housed in a GFRP-made Strengthened parts, and made superconducting current leads. That is, in Example 2, a superconducting current lead using four superconducting wires was fabricated. The electrode pitch Le was set at 100 mm, and the deflection rate of the superconducting wire between electrodes was changed to 1.2%, 2%, 6%, and 18% by changing the total length of the superconducting wire.

[Refer to example 2]

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

With respect to the superconducting current leads of Example 2 and Reference Example 2, critical current characteristics in an extremely low temperature environment were evaluated. Specifically, a heat conduction plate was installed on the metal electrode of the superconducting current lead, and the entire superconducting current lead was cooled to 73-78K by conduction cooling, and the critical current value Ic (design value 800A) was measured. In addition, the external magnetic field was set to 0T (from the magnetic field). The evaluation results are shown in Table 2.

Table 2

As shown in Table 1 and Table 2, in Examples 1 and 2 in which the deflection rate ΔD/Le was 0.5% or more, critical current characteristics substantially equal to the design values were obtained. Thus, the effectiveness of the present invention, which is so-called forming a bend in a superconducting wire rod, was confirmed. In addition, in Examples 1-4 and Examples 2-4, although the critical current characteristic as the design value was obtained, the superconducting wire was greatly deflected, and it was difficult to accommodate it in the reinforcing member. Thus, since Examples 1-4 and Examples 2-4 are not practical, Table 1 and Table 2 are shown as a reference example.

As mentioned above, although the invention made by the inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.

It should be thought that embodiment disclosed this time is an illustration and not restrictive description in the whole content. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all changes within the meaning and range equivalent to the claims are included.

The disclosure of Japanese Patent Application Japanese Patent Application No. 2013-159228 filed on July 31, 2013 including the specification, drawings, and abstract is incorporated herein by reference in its entirety.

Claims (7)

1. a superconductive current lead, is characterized in that, comprising:

Banded superconducting wire, its by stacking gradually intermediate layer on metallic substrates, superconducting layer, stabilizing layer form;

Metal electrode, it is engaged in the both ends of described superconducting wire; And

Reinforced member, it is located in the mode of the electrode spacing with regulation and accommodates lead-in wire main body, and described lead-in wire main body comprises described superconducting wire and described metal electrode,

Described superconducting wire has flexure between described metal electrode.

2. superconductive current lead as claimed in claim 1, is characterized in that,

Described electrode spacing is being set to L1, and when the amount of deflection of described superconducting wire is set to Δ D, the flexure rate represented with Δ D/L1 is more than 0.5%.

3. superconductive current lead as claimed in claim 1 or 2, is characterized in that,

Holddown groove is had at one end mask of described metal electrode,

By the end of described superconducting wire being inserted into described holddown groove and engaging with described holddown groove, described metal electrode is electrically connected with described superconducting wire.

4., as the superconductive current lead in claims 1 to 3 as described in any one, it is characterized in that,

Described reinforced member is made up of the material that superconducting wire described in thermal conductivity ratio is low.

5., as the superconductive current lead in Claims 1 to 4 as described in any one, it is characterized in that,

Described reinforced member is made up of fibre reinforced plastics.

6., as the superconductive current lead in Claims 1 to 5 as described in any one, it is characterized in that,

TFA-MOD method is utilized to form described superconducting layer,

Be dispersed with in described superconducting layer a kind of element at least comprised in Y, Zr, Sn, Ti, Ce, the oxide particle of less than 50 μm, as flux pinning point.

7., as the superconductive current lead in claim 1 ~ 6 as described in any one, it is characterized in that,

Described stabilizing layer is made up of Ag.