JPH0982516A - Oxide superconducting current lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide current leads of an oxide superconductor whose mechanical strengths to the bendings caused by external forces are improved. SOLUTION: Oxide superconducting current leads comprising a low- temperature side electrode 5c which is disposed on one surface orthogonal to the axial direction of an oxide superconductor 5a and is disposed in the place nearly opposed to the center of gravity of the oxide superconductor 5a, and at least one high-temperature side electrode 5b disposed in the peripheral edge of the oxide superconductor 5a.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconducting current lead for supplying an electric current from an external power source to an oxide superconductor such as a superconducting magnet.

[0002]

Since the discovery of lanthanum-based high temperature oxide superconductors by Bednorz and Muller, great expectations have been placed on the search for new materials and their applications, and vigorous research has been promoted.

So far, the boiling point of liquid nitrogen (77K @ 1
As a substance having a critical temperature (T _c ) exceeding atm),
Many compounds such as yttrium, bismuth, thallium, and mercury have been discovered. In addition, there are many reports of trial production of wire rods and thin films using these materials and their application to superconducting magnets and electronic devices.

By the way, in the application of oxide superconductors,
One of the most influential ones is application to current leads. The current lead is a lead wire for passing a current from an external power source to a metal-based superconducting (NbTi, Nb ₃ Sn) coil that is immersed and cooled in liquid helium, and conventionally copper or a copper alloy was used.

Since the oxide superconductor can be energized without Joule heat generation in the temperature range of T _c or less and has a thermal conductivity as small as 1/100 of that of copper, a current lead with extremely small heat penetration can be formed.

As shown in FIG. 10, the basic structure reported so far is one in which copper electrodes 1b are connected to both ends of a rod-shaped oxide superconductor 1a and an electric current is passed in the longitudinal direction of the lead material. .

An example of using a plate-shaped or pipe-shaped material instead of the rod-shaped lead material (FIGS. 11A and 11B) and a reinforcing material 2 (protective cover) for preventing damage due to external force The example marked with (Fig. 12) is also reported as an improved example.

[0008]

However, one of the problems of the conventional oxide superconducting current leads is that they have a low mechanical strength against an external force acting on the leads. The tensile strength of the oxide superconductor is 50-80 MPa,
00-400MPa, copper alloy 500-1000MPa
Smaller than.

Further, since it is a ceramic, it has a low toughness, and when an excessive stress acts and a crack is generated, it immediately propagates and leads to breakage of the lead. As a typical example, there is a case of single beam bending as shown in FIG.

When the external force F acts on one end of the lead, a stress σ is generated at the other end based on the bending moment, and σ> σ
Cracks occur at _fmax (breaking stress). If there is no reinforcement, it will break with a force of several kgf, depending on the shape of the lead.

In the current lead, it is preferable to increase the effective lead length (L _{0 in} FIG. 10) in order to reduce the amount of heat penetration due to heat conduction. However, since the bending moment (FL ₀ ) with respect to the same external force F also increases at the same time, the problem of mechanical strength becomes greater in a high-performance lead, that is, a lead having a higher degree of reducing the amount of heat penetration.

As shown in FIG. 13B, the lead provided with the reinforcing material can remedy this drawback considerably, but a part of the bending moment is applied to the lead material of the oxide superconductor to cause stress, so that it is not so good. The problem of mechanical strength could not be solved without using a thick and highly rigid reinforcing material. The present invention has been made in view of the above circumstances,
An object of the present invention is to provide an oxide superconducting current lead having improved mechanical strength against bending due to an external force.

[0013]

Therefore, first, in order to achieve the above-mentioned object, the invention according to claim 1 is one surface orthogonal to the axial direction of the oxide superconductor, and said oxide superconductor It is characterized by comprising a low temperature side electrode provided at a position corresponding to a substantial center of gravity of the body, and at least one high temperature side electrode provided on a peripheral edge of the oxide superconductor.

According to a second aspect of the present invention, in the oxide superconducting current lead according to the first aspect, the low temperature side electrode is provided at an inner edge of a hole provided on one surface of the oxide superconductor. It is characterized in that they are closely connected.

Further, the invention according to claim 3 is the same as claim 1.
In the above described oxide superconducting current lead, at least one of the low temperature side electrode and the high temperature side electrode has a pipe shape.

Further, the invention according to claim 4 is the invention according to claim 2.
The oxide superconducting current lead described above is characterized in that a slit is provided in a portion of the low temperature side electrode that is connected to the oxide superconductor.

According to a first aspect of the present invention, a low temperature side electrode is provided on one surface orthogonal to the axial direction of the oxide superconductor, and at a location corresponding to substantially the center of gravity of the oxide superconductor. Since at least one high temperature side electrode is provided on the periphery of the superconductor, it is possible to improve mechanical strength against bending due to an external force. In the invention according to claim 2, in the oxide superconducting current lead according to claim 1, the low temperature side electrode is connected so as to be in close contact with the inner edge of the hole provided on one surface of the oxide superconductor. Further, the mechanical strength against bending due to external force can be improved.

According to a third aspect of the present invention, in the oxide superconducting current lead according to the first aspect, at least one of the low temperature side electrode and the high temperature side electrode has a pipe shape. The connection area with the superconductor can be increased.

According to a fourth aspect of the present invention, in the oxide superconducting current lead according to the second aspect, a slit is provided in a portion of the low temperature side electrode that is connected to the oxide superconductor, so that the thermal contraction rate is different. It is possible to prevent peeling of the connection portion.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> One of the current leads of the oxide superconductor according to the present embodiment is (1) orthogonal to the axial direction (the direction from the high temperature side to the low temperature side) of the plate-shaped oxide superconductor. It is characterized in that the low temperature side electrode is provided at a position corresponding to the surface and substantially at the center of gravity of the oxide superconductor, while the high temperature side electrode is provided at the periphery of the oxide superconductor. As a special case, (2) a hole is formed in the surface of the plate-shaped oxide superconductor on which the low temperature side electrode is provided, and the low temperature side electrode is connected so as to be in close contact with the inner edge thereof.

The basic configurations of the above (1) and (2) are shown in FIGS. 1 (a) and 1 (b). In FIG. 1A, a current supplied from a room temperature power source (not shown) through the high temperature side copper electrode 5b flows into the oxide superconductor 5a from the peripheral portion of the plate-shaped oxide superconductor 5a, and the center It is transmitted to the low temperature side copper electrode 5c (or superconducting wire) connected to the portion.

On the other hand, in FIG. 1B, the current flows into the side surface of the copper electrode 5c on the low temperature side. Further, as a modification of (2), as shown in FIG. 2, a plurality of plate-shaped oxide superconductors 7 may be arranged in parallel to form a lead. Here, in each case, a disk is shown as a typical example of the plate material.

The shape of the plate-shaped lead material used for this lead is such that the ratio d / L of the thickness d shown in FIG. 3 and the maximum in-plane length L (diameter D in the case of a disc) is 1 or less. Using. However,
(D / L) <1 by laminating plate materials with d / L> 1
What was made into these is contained in the scope of the present invention. Also,
The thickness may vary depending on the part, and in that case, the average value is used. Furthermore, the plate-shaped lead may be divided into a plurality of pieces in the circumferential direction.

Next, the oxide superconductor constituting the plate-shaped lead material may be any copper-containing oxide superconductor having a layered perovskite structure, for example, Y-based (YBa ₂
Cu ₃ O _7-x, etc., Bi-based (Bi ₂ Sr ₂ CaCu ₂
O _{8 + x} , Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x,} etc., Tl
System (Tl ₂ Ba ₂ CaCu ₂ O _{8 + x} , Tl ₂ Ba ₂ Ca
₂ Cu ₃ O _{10 + x} , Hg-based (Hg ₂ Ba ₂ CaCu
₂ O _{8 + x} , Hg ₂ Ba ₂ Ca ₂ Cu ₃ O _{10 + x,} etc.) are exemplified.

On the other hand, the high temperature side electrode and the low temperature side electrode connected to the oxide superconductor are made of a good metal conductor.
Examples include copper and its alloys, and silver and its alloys.
The shape is preferably a plate, a round bar, a square bar, a pipe, and the like, and more preferably a pipe. The reason is that it is possible to increase the connection surface area with the oxide superconductor while reducing the weight.

At this time, as shown in FIG. 4, if a slit (cut) 11 is formed in a portion of the low temperature side copper electrode 5c to be connected to the oxide superconductor, the connection portion due to the difference in heat shrinkage rate is formed. Peeling can be prevented. In addition, in the case of alternating current, the pipe is efficient because the current is localized on the surface of the conductor due to the skin effect.

Further, when the temperature on the low temperature side is 4K,
As shown in FIG. 5, it is also effective to attach the superconducting wire 12 to the copper electrode. In this case, current can be supplied without Joule heat generation on the low temperature side. Further, an example in which the copper portion is eliminated and only the superconducting wire is used can be considered.

The response of the present lead to one-sided beam bending is shown in FIG. As shown in the figure, the external force F at the point of action P
However, even if the above occurs, all the bending moments generated are applied to the high temperature side copper electrode 5b, and the oxide superconductor 5a receives almost no force.

Therefore, according to the current lead of the oxide superconductor of the present embodiment, the mechanical strength against bending due to an external force is high, and in some cases, the reinforcing material required in the conventional lead is not necessary. . This also makes the size of the current lead itself compact.

Further, since the high temperature side electrode is provided on the peripheral portion of the oxide superconductor 5a and the low temperature side electrode is provided at a predetermined position on one surface of the oxide superconductor 5a, the lead material may be scraped off or a plurality of lead materials may be removed. It is possible to optimally change the cross-sectional area through which the current flows without sticking the lead materials of. (J at high temperature
_{Since c} is low, a large lead cross-sectional area is required, but _Jc is high on the low temperature side, so the cross-sectional area may be small. The smaller the cross-sectional area, the smaller the amount of heat transfer due to heat conduction. Furthermore, since the oxide lead materials can be arranged in parallel, a large capacity current lead can be formed.

Further, in the superconductor 5a portion, the thermal conductivity is smaller than that of copper by about two orders of magnitude, and it is possible to conduct electricity without Joule heat generation. It can be expected to greatly reduce heat intrusion.

Further, due to the above characteristics, it is possible to apply the oxide superconducting lead to the current lead of a magnetic levitation train in which vibration is always present, or the current lead of a high current fusion device requiring high reliability. become. <Second Embodiment> FIG. 7A shows a disk-shaped (Bi,
Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} (Bi-2223)
It is a figure which shows the structure of the current lead of a 500 A class oxide superconductor using the pellet.

The pellets had a diameter of 20 mm and a thickness of 2 mm, and were manufactured by repeating uniaxial pressing and sintering heat treatment. A part of the obtained pellet was cut into a strip shape and the critical current density J _c (77K, 0T) was measured. As a result, a value of 500 A / cm ² was obtained.

As shown in FIG. 7A, a silver paste is baked on the outer peripheral side surface of the pellet-shaped oxide superconductor 5a, and further soldered to the inner surface of the high temperature side copper electrode (pipe-shaped) 5b. Has been done. On the other hand, on the low temperature side, a hole with a diameter of 5 mm is made in the center of the pellet (center of gravity), and the inner surface is similarly connected to the outer surface of the low temperature side copper electrode 5c (pipe shape) made of oxygen-free copper by soldering with silver paste. ing.

The copper electrode 5c on the low temperature side is provided with a slit as shown in FIG. 4 in order to alleviate the stress caused by the difference in heat shrinkage. Further, FIG. 7 (b) shows FRP as a reinforcing material.
A circular disc 13 made of oxide is used.
It is arranged so as to sandwich a.

If the surface area of the outer peripheral side surface of the oxide superconductor 5a is 1.26 cm ² and the high temperature side is 77K, then 6
It is possible to pass a current of 30A. On the other hand, the inner surface area of the hole on the low temperature side is 0.31 cm ² , but the temperature is 4
At K, J _c is improved 5 to 6 times, so the current capacity on the low temperature side exceeds 1000A. Therefore, the energizing capacity of the lead as a whole is the energizable capacity on the 77K side.

The high temperature end of the prototyped lead was placed in the liquid nitrogen tank 15
The low temperature end was immersed in liquid helium at (77K), and the amount of heat penetration and the voltage generation during non-energization and during energization were examined. At this time, all the helium gas evaporated by heat penetration was recovered through the inside of the low temperature side copper pipe electrode 5c, and electricity was applied in a so-called gas cooling state.

The results are shown together in FIG. The amount of heat penetration at the time of energizing 500 A is 0.3 W (per pair) in the type of Fig. 7 (a) and 0.35 W in the type of Fig. 7 (b). Of 1 W / 1 kA, which is almost proportional to the current), was about 1/3 of the amount of heat penetration.

A vibration test was conducted on the lead shown in FIG. 7 (b). 50 G acceleration at 10 Hz at 10 ⁵
The critical current I _c (@ 77
K, 0T) was measured and found to be 630 A, and there was no change before and after the test. <Third Embodiment> YBCO manufactured by a melting method
A 10 kA class current lead was prototyped using a bulk material.

Generally, YB produced by the partial melting method
The CO material has a very high J compared to that produced by the sintering method.
_c (for example, Morita et al. (Nippon Steel), 1991 Spring Cryogenic Engineering Society Proceedings p. 81). Especially, the characteristics at 77K and high magnetic field are excellent.

However, the shape thereof is a thick disk as shown in FIG. 3, which is not suitable for the conventional oxide current lead material as shown in FIG. What I used here is
A bulk material that has been crystal-grown by quenching + partial melting and has a diameter of 5
The thickness is 0 mm and the thickness is 1 cm. Crystals grow from the center of the disk toward the periphery, and almost no grain boundaries are seen in the radial direction.

As in the second embodiment, when a sample was cut out and J _c was examined, J _c (77K, 0T) = 10.
It was found to be 000 A / cm ² . An oxygen-free copper pipe was used for the copper electrode on the high temperature side. On the other hand, as shown in FIG. 5, the copper electrode on the low temperature side is made of NbTi on an oxygen-free copper pipe.
A superconducting wire was put on the structure. Further, a slit as shown in FIG. 4 was also provided.

A through hole having a diameter of 15 mm was opened in the center of the YBCO material, and silver was sprayed on the outer peripheral side surface and the side surface of the through hole and then heat treated. Connection area of the hot side and cold side are each 15cm ² and 4.7 cm ^2.

Similar to the second embodiment, the high temperature end of the electrode was immersed in a liquid nitrogen tank (77K) and the low temperature end thereof was immersed in liquid helium, and the amount of heat intrusion during non-energization and 10 kA energization was examined. . Power was supplied in a gas cooled state.

The results are shown together in FIG. The amount of heat penetration at the time of energizing 10 kA was 10 W (per pair), which was about half that of the optimally designed gas-cooled copper electrode. As a result, when applied to devices that generate high magnetic fields such as fusion devices, the amount of liquid helium vaporized is 1 /
It is expected that it will be reduced to 2, and that there will be a great advantage in operation, for example, the injection interval can be doubled.

[0046]

As described above in detail, according to the present invention,
It is possible to provide a current lead of an oxide superconductor having improved mechanical strength against bending due to an external force.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an oxide superconducting current lead according to a first embodiment of the present invention.

FIG. 2 is a view showing a modified example of the oxide superconducting current flow lead according to the same embodiment.

FIG. 3 is a diagram for explaining the shape of a plate-shaped lead material.

FIG. 4 is a diagram showing a configuration of a low temperature side copper electrode in which a cut is made in a portion connected to an oxide superconductor.

FIG. 5 is a diagram showing a configuration in which a superconducting wire is attached to a low temperature side copper electrode.

FIG. 6 is a view showing a response of an oxide superconducting current lead of the same embodiment to a half beam bending.

FIG. 7 is a diagram showing a structure of an oxide superconducting current lead according to a second embodiment of the present invention.

FIG. 8 is a diagram for explaining the relationship between the amount of heat penetration of an oxide superconducting current lead and the voltage in the same embodiment.

FIG. 9 is a diagram for explaining a relationship between a heat penetration amount and a voltage of an oxide superconducting current flow lead according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a structure of a conventional oxide superconducting current lead.

FIG. 11 is a diagram showing a structure of a conventional oxide superconducting current lead.

FIG. 12 is a diagram showing a configuration of a conventional oxide superconducting current lead.

FIG. 13 is a diagram showing the response of a conventional oxide superconducting current lead to one-sided bending.

[Explanation of symbols]

1a ... Oxide superconductor, 1b ... Copper electrode, 2 ... Reinforcing material, 5
a ... oxide superconductor, 5b ... copper electrode (high temperature side), 5c ...
Copper electrode (low temperature side), 7 ... Oxide superconductor, 11 ... Slit, 12 ... Superconducting wire, 13 ... FRP disc, 15 ... Liquid nitrogen tank.

Claims (4)

[Claims] 1. A low temperature side electrode provided on one surface orthogonal to the axial direction of the oxide superconductor and corresponding to a substantial center of gravity of the oxide superconductor; An oxide superconducting current lead, comprising: at least one high temperature side electrode provided at a peripheral edge. 2. The oxide superconductor according to claim 1, wherein the low temperature side electrode is connected so as to be in close contact with an inner edge of a hole provided on one surface of the oxide superconductor. Current lead. 3. Of the low temperature side electrode and the high temperature side electrode,
The oxide superconducting current lead according to claim 1, wherein at least one has a pipe shape. 4. The oxide superconducting current lead according to claim 2, wherein a slit is provided in a portion of the low temperature side electrode that is connected to the oxide superconductor.