JP2843447B2 - Superconducting current lead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid He
The present invention relates to a superconducting current lead used to supply a current to a superconducting device such as a superconducting magnet cooled by the above method.

[0002]

2. Description of the Related Art SMES generators, MHD generators, fusion reactors, magnetic levitation trains, medical MRI, magnets for accelerators, and the like have been developed as low-temperature devices using superconducting magnets. The supply of current to the low-temperature equipment as described above is performed from an external power supply via a current lead, and the current lead is mainly made of a Cu-based metal material. However, the metal current lead as described above has a problem that a large amount of refrigerant in a cryostat in which a low-temperature device is disposed evaporates due to Joule heat or external heat inflow. As a method for solving this problem, the resistance of the current lead becomes zero at the liquid He temperature (4.2 K),
It has been proposed to use a metal-based superconductor of Nb-Ti and Nb ₃ Sn, which does not cause Joule heat, these superconducting s body only at a low temperature equipment near to be cooled to liquid He temperature,
The effect was not exhibited and the utility was poor. For this reason, instead of a metal-based superconductor, a recently developed Y-Ba that becomes superconductive at a liquid nitrogen temperature (77 K) is developed.
Applications of oxide superconductors such as -Cu-O-based and Bi-Sr-Ca-Cu-O-based have been proposed.

A current lead using this oxide superconductor is, for example, shown in FIG. 5 and FIG. 6 in a perspective view and a cross-sectional view of a base portion, respectively. The body 5 is arranged in parallel, and a brass base A13 and a base B14 are connected to both ends thereof by solder 6, respectively. This superconducting current lead connects the copper bus bar 7 connected to the base A13 to an external power supply, and the base B14. Is connected to a superconducting device immersed in liquid He for use. The oxide superconductor rod-shaped compact 5 is usually formed by compacting a raw material that can be made into an oxide superconductor.
It is manufactured by a powder sintering method in which it is heated and sintered while undergoing an interfacial reaction with oxygen in an oxygen-containing atmosphere.

[0004]

However, such a superconducting current lead made of an oxide superconductor requires an interfacial reaction with oxygen in the process of producing a rod-shaped formed body made of an oxide superconductor, but it requires a large current. The reaction does not proceed to the inside of a large-sized rod-shaped molded product for energization, so that only a product having low superconductivity can be manufactured. The larger the rod-shaped molded body, the smaller the surface area as compared with the cross-sectional area, so that the heat loss during use increases. Since the rod-shaped molded body is connected to the die by soldering, the solder layer is cracked or peeled off during repeated cooling and use, resulting in poor reliability. There was such a problem.

[0005]

SUMMARY OF THE INVENTION The present invention has been made as a result of intensive studies in view of the above-mentioned circumstances, and its object is to reduce the amount of evaporation loss of the liquid He and reduce a large current. It is an object of the present invention to provide a superconducting current lead which can supply electricity with high reliability. That is, the present invention relates to an oxide superconductor molded article, which is formed by joining longitudinally cracked oxide superconductor molded articles formed so that through holes are formed in the longitudinal direction of the bonding interface. A desired number of oxide superconductor hollow molded bodies having through holes in the directions are bundled at both ends by low melting point metal bases. In the oxide superconductor molded product used in the present invention, a longitudinal direction formed by joining the vertically cracked oxide superconductor molded products formed so that through holes are formed in the longitudinal direction of the bonding interface. The reason for using an oxide superconductor hollow molded body having through holes is that each divided oxide superconductor molded body can be produced in a vertically multi-divided state, so that the compaction of the raw material is made at a high density, In addition, since the interface reaction with oxygen during heat sintering of the green compact is performed from both inside and outside, even if the oxide superconductor hollow molded body is large, it can be manufactured with excellent superconducting properties. That's why. In addition, in the oxide superconductor hollow molded body formed by abutting the divided bodies, the liquid He vapor is released upward through a through hole formed in the longitudinal direction of the bonding interface during use. The hollow molded body is also cooled from the inside, and the cooling efficiency is improved.

In the present invention, the use of a low-melting-point metal in a die for bundling a desired number of the hollow molded bodies made of oxide superconductor is because the low-melting-point metal is soft and has good workability, and is broken by repeated cooling during use. In addition to the above, the connection with the oxide superconductor hollow molded body is easily made by caulking or the like,
This is because cracking or peeling of the solder layer can be avoided. Thus, when the connection method is specifically shown, for example, when a low melting point metal such as In or Pb is used for the base, a desired number of oxidations formed by joining the divided bodies to the connection holes formed in the base are provided. The base is compressed from outside through a hollow molded body made of a superconductor, and the connection is made by caulking. When the low-melting-point metal is liquid at room temperature, such as Hg, Hg is put into a dish-shaped vessel having a hole through which a hollow molded body made of an oxide superconductor is passed and used as a base. or,
In connection, it is preferable that an Ag paste is interposed between the hollow molded body made of the oxide superconductor and the die, because the contact resistance can be reduced. Further, in the superconducting current lead of the present invention, if the low-melting-point metal is coated in a layer on the abutting surface of the molded body made of an oxide superconductor, the low-melting-point metal is soft. While being held, the distortion due to the difference in thermal expansion during cooling is absorbed by the low melting point metal layer, thereby preventing the occurrence of cracks and the like. In the superconducting current lead of the present invention, it is preferable to use a plurality of oxide superconductor hollow molded bodies arranged in parallel because the surface area is increased as compared with the cross-sectional area and the cooling property is improved. The shape and arrangement of the hollow molded body can be arbitrarily designed.

Hereinafter, the present invention will be specifically described with reference to the drawings. FIGS. 1 and 2 are a perspective view and a cross-sectional view of a base portion of the superconducting current lead according to the present invention, respectively. An oxide superconductor hollow molded body 2 in which two oxide superconductor molded bodies 1 each having a semicircular groove formed in a semicircular cross section are joined so as to form a circular hollow hole therein. A base A3 and a base B4 made of a low melting point metal are connected by caulking to both ends, respectively. The abutting portion of the hollow molded body 2 is plated with a low melting point metal to maintain airtightness. FIG. 3 is a cross-sectional view of a base portion showing a second embodiment of a superconducting current lead according to the present invention. The oxide superconductor has two triangular cross sections each having a semicircular groove in one longitudinal direction. 7 molded holes 1 made of an oxide superconductor having a square cross section formed by abutting the molded bodies 1 such that circular hollow holes are formed therein, and 7 connection holes provided at intervals in a base 3 , And the base 3 is compressed from the outside, caulked and connected. Also, FIG.
FIG. 6 is a cross-sectional view of a base portion showing a third embodiment of the superconducting current lead of the present invention, in which an oxide superconductor molded body 1 having two trapezoidal cross sections and provided with semicircular grooves in the longitudinal direction of the bottom is provided. Seven hollow molded bodies 2 made of oxide superconductor having a hexagonal cross section and joined together so as to form a circular hollow hole are bundled and passed through one connection hole provided in the base 3, and the base 3 Compressed from the side, crimped and connected. The oxide superconductor molded product used in the present invention is obtained by compacting a raw material that can be converted into an oxide superconductor into a molded product having a desired shape, and performing a predetermined heat treatment in an oxygen-containing atmosphere. It is manufactured by a usual powder sintering method.

[0008]

The present invention will be described below in detail with reference to examples. Example 1 (Bi _1.6 Pb _0.4 ) ₂ Sr ₂ Ca ₂ Cu fired in advance
_A calcined powder of ₃ O _10-y and a silver powder having an average particle size of 8 μm are mixed at a ratio of 8: 2, and the mixed powder is cut into a semicircular cross section obtained by vertically dividing a cylindrical pipe into two sections at 200 MPa. The powder was compacted under pressure. The two compacts having a semicircular cross section and having a semicircular groove on the inner surface are abutted so that a hollow hole is formed in the longitudinal direction, and the length is 30 cm, the outer diameter is 11 mm, and the inner diameter is 1.5 mm.
7 compacted green compacts were prepared. After this, this 7
The cylindrical green compact is subjected to a heat treatment at 840 ° C. × 50 hr in the atmosphere to form an oxide superconductor hollow molded body,
Next, these seven hollow formed bodies were passed through connection holes provided at intervals in an In-made base having a thickness of 20 mm, and the bases were caulked and connected to form an oxide superconductor having the same shape as that shown in FIG. Two body-made superconducting current leads were produced. An ag paste was applied to the butted surface of the green compact having a semicircular cross section and a semicircular groove on the inner surface, and the connection length between the hollow molded body and the die was 20 mm, which is the thickness of the die. And A 70 cm long copper busbar was connected to each of the bases A and B of the two superconducting current leads manufactured in this manner, and the busbar on the base B side was immersed in liquid He in a cryostat to have a cross-sectional area of 10 mm ² . It was connected to both ends of the Cu / Nb-Ti composite superconducting wire, the bus bar on the base A side was pulled out of the cryostat, and connected to an external power supply. In the above, the superconducting current lead was disposed immediately above the liquid He. After wiring in this manner, a direct current was applied to the composite superconducting wire in the liquid He from an external power supply, and the amount of evaporation of the liquid He was converted into a calorific value (watts, W) and measured. The heat loss can be calculated by increasing the current in 200 A steps and
Determined after holding for minutes.

Comparative Example 1 A mixture of the calcined powder and the silver powder used in Example 1 was compacted to obtain seven rod-shaped compacts each having a length of 30 cm and a cross section of 9.6 mm square. Using this rod-shaped compact, two superconducting current leads were produced in the same manner as in Example 1, and using these two superconducting current leads, wiring was performed in the same manner as in Example 1, and electricity was supplied by conducting electricity. Was measured. The results are shown in Table 1.

[0010]

[Table 1]

As is apparent from Table 1, the heat loss when the product of the present invention is used increases almost in proportion to the increase in current up to a current flow of about 2000 A, which is not much different from that of the comparative product. At the peak at 2000 A, the heat loss of the product of the present invention turned flat, while the product of the comparative example continued to increase in proportion to the increase in the current, and a large difference occurred from the product of the present invention. When the product of the present invention is used, the heat loss is 2,000 A
The reason for the plateau turning to the peak at the time is that the temperature rise accompanying the increase in the current capacity accelerates the evaporation of the liquid He, and this liquid He
A large amount of the vapor passed through the hollow portion of the oxide superconductor hollow molded body of the superconducting current lead, and as a result, the overall length of the superconducting molded body was kept at zero resistance, and the original effect of the superconducting current lead was sufficiently exhibited. That's why. On the other hand, in the case of the comparative example product, since the oxide superconductor molded body did not have a hollow portion and was not sufficiently cooled, the oxide superconductor molded body was manufactured in a peeled state. In addition, the interfacial reaction with oxygen was not sufficiently performed, and as a result, the superconductivity was lowered.

[0012]

As described above, the superconducting current lead of the present invention has a remarkable industrial effect because a large amount of current can be supplied with high reliability while suppressing the evaporation loss of the liquid He.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of a superconducting current lead according to the present invention.

FIG. 2 is a cross-sectional view of a mouth portion of the superconducting current lead shown in FIG.

FIG. 3 is a cross-sectional view of a base showing a second embodiment of the superconducting current lead of the present invention.

FIG. 4 is a cross-sectional view of a base showing a third embodiment of the superconducting current lead of the present invention.

FIG. 5 is a perspective view of a conventional superconducting current lead.

FIG. 6 is a cross-sectional view of a base portion of the conventional superconducting current lead shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded body made of oxide superconductor 2 Hollow molded body made of oxide superconductor 3,13 Cap A 4,14 Cap B5 Bar-shaped molded article made of oxide superconductor 6 Solder 7,8 Copper busbar

Claims (1)

(57) [Claims] 1. A longitudinal direction obtained by joining longitudinally cracked oxide superconductor molded articles formed so that through holes are formed in the longitudinal direction of the joining interface as an oxide superconductor molded article. A superconducting current lead characterized in that a desired number of hollow molded bodies made of an oxide superconductor having through holes are bundled at both ends with low melting point metal bases.