JP2779210B2 - Conductor for current lead - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a current lead conductor used to supply a current from a current supply source to a superconducting element such as a superconducting magnet cooled with liquid He or the like.

[Conventional technology and its problems]

Magnet using superconductivity, power transmission cable or SQUI
Electronic devices incorporating D and Josephson elements are liquid He
The electric current is supplied to these electronic devices and the like from an external power supply through a current lead conductor during or after operation.

By the way, copper materials are conventionally used for current lead conductors, but superconducting magnets and the like require large currents.Thus, current lead conductors must be large in size to reduce Joule heat generation and prevent fusing due to overcurrent. Is measured. However, when the current lead conductor is made thicker, the amount of heat flowing in from the outside increases, and as a result, there is a problem that the amount of evaporation of the refrigerant such as He increases and the cooling cost increases.

For this reason, a current lead conductor has recently been proposed in which an oxide superconductor 5 that exhibits superconductivity at the temperature of liquid nitrogen as shown in FIG. 63-245910).

In this current lead conductor, current is supplied mainly through an oxide superconductor on the superconducting element side cooled by liquid He or the like, and is supplied through a metal coating layer on a current supply source at room temperature. Oxide superconductors have no resistance on the superconducting element side cooled with liquid He or the like because they have zero resistance, and do not generate Joule heat due to energization.In addition, oxide superconductors have low thermal conductivity, so there is little heat inflow from the outside and current leads It has excellent characteristics as a conductor for use. However, the current lead conductor is as short as several tens of centimeters, one end is cooled to room temperature and the other end is cooled to cryogenic temperature, and the heat cycle between these temperatures is repeated many times. Poor durability, such as cracks in the body, or separation of the oxide superconductor and the metal coating layer, resulting in an increase in current-carrying resistance and burning of the current lead conductor or deterioration of performance over time. There was a problem.

Furthermore, the oxide superconductor has a layered perovskite-type crystal structure and therefore has a strong crystal anisotropy, and the current is ab including Cu-O atoms.
Easily flows on the surface, therefore to orient the C axis in a direction perpendicular to current direction is a necessary requirement for obtaining a high J _c.
However, since the conventional oxide superconductor has a random crystal orientation, a sufficiently high _Jc value cannot be obtained, a long time is required for current supply, and Joule heat is generated when the current supply is accelerated. As a result, there is a problem that a large amount of liquid He evaporates.

[Means for solving the problem]

The present invention has been made as a result of intensive research in view of such circumstances, and it is an object of the present invention to provide a current lead conductor which has excellent durability and can reduce the evaporation amount of a refrigerant such as liquid He. is there.

That is, the present invention is a current lead conductor made of a metal conductor for supplying a current from a current supply source to a superconducting element, and at least a portion connected to the superconducting element has an oxide superconductor in the metal conductor. It is characterized in that the particulate matter is dispersed.

The current lead conductor of the present invention is made of a metal conductor, and at least the oxide superconductor is dispersed in the metal conductor on the side connected to the superconducting element in a granular form.

Thus, the above-mentioned metal conductors have good conductivity Cu, Al, Au, Ag
Or an alloy thereof is applied. Also, as the oxide superconductor dispersed in the metal conductor, which critical temperature (T _c) is substituted the YBa ₂ Cu ₃ O ₇ -δ or the Y of ~93K by other rare earth elements, T _c is 90 ~ 110K Bi ₂ Sr ₂ CaCu ₂ O ₈ , Bi ₂ Sr ₂ Ca ₂
Cu ₃ O ₁₀ , Tl ₂ Ba ₂ CaCu ₂ O _{8 with} T _c of 100 to 125 K, Tl ₂ Ba ₂ Ca ₂ Cu ₃
O ₁₀ , TlBa ₂ Ca ₂ Cu ₃ O _{8.5 and the} like, and further, a part of the metal elements constituting each of the above oxide superconductors is replaced with Pb, In, Sb, an alkali metal or the like, or one of O And the like where the part is replaced by F.

Hereinafter, the configuration of the current lead conductor of the present invention will be described with reference to the drawings.

1A to 1E are longitudinal sectional views showing an embodiment of a current lead conductor according to the present invention. The right end of the figure is connected to a current supply source and the left end is connected to a superconducting element. The current lead conductor has a circular cross section. In the figure, 1 is a metal conductor, and 2 is a dispersed oxide superconductor granular material.

The conductor for a current lead shown in FIG. 2A has a metal conductor 1 on the side connected to the superconducting element and an oxide superconductor granular material 2 in the metal conductor 1.
Are dispersed. The outer diameter of the current lead conductor shown in FIGS. 2 (b) and 2 (c) is gradually increased or tapered from the superconductor element side to the current supply source to make the resistance in the longitudinal direction uniform so that Joule heat is generated. Is reduced, and furthermore, the heat flow into the superconductor element is suppressed. The current lead conductor shown in Fig. 4D is replaced with the current lead conductor shown in Fig.
Metal support 3 such as S, Cu-Ni alloy, Al-Mg-Cu alloy
The conductor for the current lead shown in FIG. 5E is one in which the conductive metal piece 4 is joined to the current supply source side of the conductor for the current lead shown in FIG. is there.

2 (a) to 2 (c) are longitudinal sectional views showing examples of the distribution form of the oxide superconductor particulates 2 in the metal conductor 1 in the current lead conductor of the present invention. The current lead conductor shown in FIG. 2A is a single crystal oxide superconductor granular material 2, and the current lead conductor shown in FIGS. 2B and 2C is a polycrystalline granular material 2 oriented in one direction. Are C-axis oriented and dispersed in the metal conductor 1 respectively. Whisker,
Fibers and granules are also included.

The amount of the oxide superconductor granules 2 to be dispersed in the metal conductor 1 in the present invention, which is determined by the strength of the use conditions, i.e. cooling conditions or a magnetic field, the power supply amount is greater than the J _c current lead conductor Must not be a value.

In the present invention, as a method of distributing the oxide superconductor granules 2 in the metal conductor 1, a powder metallurgy method of mixing the oxide superconductor granules 2 with a matrix metal powder,
A method of dispersing and solidifying the oxide superconductor granular material 2 in a metal melt, laminating and rolling the oxide superconductor and a matrix metal plate to pulverize the oxide superconductor plate between the metal plates And a plastic working method of dispersing.

The above-mentioned oxide superconductor granular material is a method of firing and pulverizing a raw material that can be made into an oxide superconductor, a coprecipitation method, a gas phase method,
It can be synthesized by a quenching method or the like, and a single crystal granular material can be efficiently produced by crushing coarse polycrystalline particles.

When the metal is coated on the oxide superconductor granular material, the bonding property between the oxide superconductor granular material and the matrix metal can be improved. As the coating method, a sputtering method, a vapor phase growth method such as a CVD method,
A solid phase method such as mechanical alloying or a melt method is applied.

In the present invention, it is not necessary to composite the connecting metal by dispersing the oxide superconductor particulates at the ends serving as connecting portions, and thus the structure of the current lead conductor is simplified, and Heat generation due to contact resistance can also be suppressed low.

The effect of the conductor for a current lead of the present invention is further enhanced by cooling it with a coolant having a temperature lower than the critical temperature (T _c ) of the dispersed oxide superconductor, such as liquid nitrogen.

[Action]

Since the current lead conductor of the present invention is obtained by dispersing oxide superconductor particles at least on the side of the metal conductor connected to the superconducting element, the superconductor particles inside the metal conductor are liquid He on the superconductor element side. The electric resistance becomes zero and the Joule heat is suppressed by cooling by the refrigerant such as, and the heat inflow from the outside is prevented because the oxide superconductor has poor thermal conductivity, so that the refrigerant such as liquid He evaporates. Is reduced. On the current supply source side, the current flows through the metal layer, so that a sufficient amount of current can be obtained.In particular, the current lead conductor that does not disperse the oxide superconductor particles that become an insulator at room temperature to the current supply side is much higher. The amount of energization is secured.

The thermal distortion without such J _c becomes lower cracks superconductor granules is absorbed in the metal layer caused by the temperature difference between the superconducting device side and the current supply side, further metal layer Are formed continuously, so that mechanical properties, particularly flexibility and toughness, are improved.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 A calcined powder of YBa ₂ Cu ₃ O ₇ -δ having an average particle diameter of 7 μm was heated at 930 ° C. 12
H heating was performed to obtain a granular material having a diameter of about 50 μm, which was then pulverized to produce a flat powder having an average diameter of about 20 μm. Ag powder having an average particle size of 3 μm was mixed with the flat powder at 50 wt%, and polyvinyl alcohol and butyl cellosolve were added thereto and kneaded. The kneaded body was extruded into a 10 mmφ bar, and the bar was placed in an oxygen stream. Pre-sintering at 890 ° C for 2H. Next, after vacuum-sealing the sintered bar with an Ag sheath, Ar + 1.5 vol% O ₂
HIP treatment of 880 ° C. × 10H was performed in a 1000 atmosphere atmosphere.
Then, peel off the Ag sheath, and machine the section 6
A 4 mm square bar was finished, and the square bar was heated at 600 ° C. for 12 hours in an oxygen stream to produce a current lead conductor.

Example 2 A current lead conductor was manufactured in the same manner as in Example 1 except that the kneaded body was put into a forming die and extruded into a 10 mmφ bar without being extruded.

Example 3 A calcined powder of Bi ₂ Sr ₂ Ca _1.1 Cu _2.3 O _{x having} an average particle size of 30 μm was filled in an Ag pipe having an inner diameter of 18 mm, and this was subjected to diameter reduction by a swager and a draw bench, and further rolled to a thickness of 0.45 mm.
mm (0.3 mm inside thickness) tape material. Thereafter, the tape material was exposed to air at 900 ° C. for 30 minutes, and subsequently at 840 ° C. 12
After H heat treatment, this was cut into chips having a length of 20 mm, and the chips were filled into an Ag pipe having an inner diameter of 18 mm such that the length direction of the chips was aligned with the length direction of the Ag pipe.
Thereafter, the Ag pipe was subjected to a HIP treatment under the same conditions as in Example 1, then the Ag pipe was removed and machined into a square having a cross section of 6 × 4 mm.
Heat treatment was performed at 20 ° C. for 12 hours to produce a current lead conductor.

Example 4 A calcined powder of HoBa ₂ Cu ₃ O _x was melted by heating to 1150 ° C. in a Pt crucible, and the melt was rapidly cooled and solidified.
C., and was moved in a furnace having a temperature gradient of 50 ° C./cm at a speed of 1 mm / 2H to perform a unidirectional solidification treatment. Then, the unidirectionally solidified material is pulverized into a granular material having a particle size of 1 mm,
Ag powder was mixed with the granules at 40 wt%, and the mixture was filled while applying vibration to the Ag container. Thereafter, the Ag container was vacuum-sealed, and then under an 800 atm atmosphere of Ar + 2.5 vol% O _2. At 8
HIP treatment of 90 ° C × 24H was performed. Next, the Ag container was removed, and the mixture subjected to the HIP treatment was machined into a square bar having a cross section of 6 × 4 mm.
2H heat treatment was performed to produce a current lead conductor.

Example 5 A calcined powder of ErBa ₂ Cu ₃ O ₇ -δ having an average particle size of 2.5 μm was mixed with an Ag powder having an average particle size of 1 μm in a weight ratio of 7: 3, and this was pre-sintered after CIP formation. Then, it was filled into an Ag-10% Pd alloy pipe having an outer diameter of 19 mm. Next, this pipe was reduced in diameter to 4 mm by a swager and a draw bench and then rolled to 5.5 mm in width.
Finished to a 1mm thick tape. The cross-sectional dimension of the pre-sintered body of the inner superconductor and the Ag powder was 4.5 mm × 0.7 mm. After heating this tape at 900 ° C. for 12 hours in an N ₂ +5 vol% O ₂ atmosphere,
Heat treatment was performed at 600 ° C. for 24 hours in an oxygen atmosphere to produce a current lead conductor.

Comparative Example 1 In Example 5, ErBa ₂ C to Ag-10 wt% Pd alloy pipe
A current lead conductor was manufactured in the same manner as in Example 5 except that only the calcined powder of u ₃ O ₇ -δ was filled.

Comparative Example 2 A stranded wire obtained by twisting 1200 pure copper wires of 0.5 mmφ was used as a current lead conductor. For each of the current lead conductors obtained as deceiving, the conductors of Examples 1-4 were 400 mm
Cut to length, and add a pure copper rod of 200mm length to this with Pb-30% Sn
A continuous current lead was formed using -15% In solder. The conductors of Example 5 and Comparative Example 1 were cut to a length of 600 mm and cut into 8 mm.
The conductor of Comparative Example 2 was cut into a length of 600 mm to form a current lead conductor.

Thus, for each of the current lead conductors described above, a heat cycle test was conducted in which the oxide superconductor particulate matter dispersed side was periodically taken in and out of the liquid He 120 times, and then the current lead conductor was transferred to the liquid He. It was mounted on a cooled Nb-Ti DC superconducting magnet and energized under the condition of 4.2K0.6T800A, and the amount of evaporation of liquid He during energization was measured. The crystal orientation of each current lead conductor was determined by X-ray diffraction.
The results are shown in Table 1 together with the production conditions. In addition, liquid He
Is obtained by subtracting the evaporation amount of the liquid He when no current is supplied without the current lead from the evaporation amount when the current is supplied.

As is clear from Table 1, the products of the present invention (1 to 5) had an extremely small amount of evaporation of He of less than half that of the comparative product (7). Has high crystal orientation of the present invention product (1,3,4) is adapted less He evaporation amount compared to the non-oriented ones (2), which it has improved J _c by crystal orientation Is attributed to The reason why the evaporation amount of He of No. 5 was relatively large among the products of the present invention was that, in addition to the low crystal orientation, the oxide superconductor was also dispersed on the current supply side because of the oxide superconductor being dispersed on the current supply side. Due to the increase in the resistance.

No6 of comparative contrast to this, the J _c cracks in the oxide superconductor in a heat cycle before the supply to the entire inner layer of the current lead is an oxide superconductor was burnt by energizing decreases Oops. No. 7 has resistance even on the liquid He side due to the use of copper stranded wire, and generates Joule heat to generate liquid He.
Evaporated in large quantities.

〔effect〕

As described above, the current lead conductor of the present invention is excellent in durability and can suppress evaporation of a refrigerant such as liquid He to a small extent, and has an industrially remarkable effect.

[Brief description of the drawings]

1 (a) to 1 (e) are longitudinal sectional views showing an embodiment of a current lead conductor of the present invention, and FIGS. 2 (a) to 1 (c) are diagrams of oxide superconductor particulates in a metal conductor in a current lead conductor of the present invention. FIG. 3 is a longitudinal sectional view showing an example of a dispersion mode, and FIG. 3 is a longitudinal sectional view of a conventional current lead conductor. 1 ... metal conductor, 2 ... oxide superconductor granular material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-123405 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01F 6/00, 6/04

Claims (1)

(57) [Claims] 1. A current lead conductor comprising a metal conductor for supplying a current from a current supply source to a superconducting element, wherein at least a portion connected to the superconducting element includes an oxide superconductor in a metal conductor. What is claimed is: 1. A conductor for a current lead, wherein a granular material is dispersed.