JPH09129045A - Nbti grouped multicore superconductive stranded cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NbTi grouped superconductive stranded cable wherein a couppling loss is reduced and stability is good. SOLUTION: Cu-Ni grouped alloys 5, 9 are disposed around superconductive filaments 2 and between a group 6 of filaments and stabilizing copper 7, 8 respectively, in the case of an NbTi grouped superconductive stranded cable made by stranding a plurality of superconductive strands wherein a multiplicity of superconductive filaments 2 are integrated in the stabilizing copper. In this event, the Cu-Ni grouped alloy 9 disposed between the group 6 of filaments and the stabilizing copper 7, 8 is adapted to have a highrer Ni concentration than the Cu-Ni grouped alloy 5 disposed around the superconductive filaments 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting stranded wire formed by twisting a plurality of superconducting element wires containing a large number of NbTi-based superconducting filaments.

[0002]

2. Description of the Related Art A general NbTi-based superconducting stranded wire is a composite wire material of Cu and NbTi-based superconductor,
In the manufacturing process, a Cu / NbTi composite single billet is extruded, drawn, drawn into a plurality of Cu pipes, extruded again, and then subjected to aging heat treatment and wire drawing to obtain a predetermined size.

NbTi-based superconducting wire rods of various structures have been manufactured for the purpose of reducing AC loss, particularly coupling loss between superconducting filaments. As a concrete technique, for example, a single wire structure is Cu-Ni / C.
It is known that a three-layered structure of u / NbTi and a Cu-Mn-based alloy are interposed in the middle of the stabilized copper filament group.

[0004]

In the former example described above, the longitudinal resistance value of the wire rod becomes small and the coupling loss between filaments becomes large. Further, if the latter structure is adopted, not only does the structure become complicated and no industrial advantage is obtained in terms of cost, but also the thermal conductivity deteriorates and the stability margin decreases.

An object of the present invention is to provide a NbTi-based superconducting stranded wire having reduced coupling loss and good stability.

[0006]

The gist of the present invention is NbT.
In the i-based superconducting element wire, a high resistance C is provided between the superconducting filament group and the stabilized copper and around the superconducting filament.
This is because the u-Ni alloy material was interposed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Since the coupling loss between filaments of a superconducting stranded wire is proportional to the loss time constant, the magnitude of the coupling loss can be evaluated by the time constant. The loss time constant can be expressed by the following formula. The meaning of the variables included in this equation is shown in FIG. From the following equation, it can be seen that the inclusion of the high resistance material increases the longitudinal resistance value, resulting in a smaller loss time constant and a smaller coupling loss.

Τcc = μ ₀ (l _p / 2π) ² (R _f / R
_O ) ² [(k / ρ _I ) + (l / ρ _C ) + (m / ρ _B ) +
(N / ρ _O )] k = (R _f ² −R _C ² ) / R _f ² = 1−l 1 = (R _C / R _f ) ² m = a ₁ ² (R _f ² + S ² R _B ² ) ・ (R _e ² −
R _f ² ) / R _f ² n = a ₂ ² (R _B ² + R _O ² ) · (R _O ² −R _B ² ) /
^{_{R B 2 a 1 = R f}} 2 / (R f 2 + SR B 2) a 2 = [a 1 (1-S) R B 2] / (R B 2 + R O 2) S = [ρ O (R O ² + R _B ² ) + ρ _B (R _O ² −
R _B ² )] / [ρ _O (R _O ² + R _B ² ) −ρ _B (R _O ²
-R _B ^2)] μ: magnetic permeability of vacuum l _p: Twist Pitch [rho: the resistance of each part also, it can be said that wire as follows for stabilization is desired. When mechanical or thermal disturbance occurs and the superconducting state changes to the normal conducting state, it is desirable to have a structure that quickly transfers heat to liquid helium or supercritical helium as a refrigerant to lower the temperature in the superconducting wire. .

[0009] Even if the thickness is the same between the case where the Cu-Ni alloy is on the outermost periphery of the filament and the case where it is in the middle between the stabilized copper filaments, the volume is on the outermost periphery. There are many methods, resulting in poor heat conduction. Further, when the Cu—Ni alloy is divided into a plurality of pieces with good heat conductivity, even if internal heat is generated, the heat propagates from the divided portions and the temperature rise of the wire can be prevented. Therefore, in the present invention, the Cu-Ni-based alloy to be interposed between the superconducting filament group and the stabilized copper does not need to be continuous in the circumferential direction in the cross section of the wire, and a plurality of copper or copper alloys may be used in the circumferential direction. It does not matter if they are divided into two and are arranged at intervals.

In the present invention, Cu-Ni alloys are doubly arranged. The Ni concentration in the alloy is preferably 0.5 to 20% by weight. This is because when the Ni concentration is 0.5% by weight or less, the resistance value is small and almost no reduction of AC loss can be expected, and when the Ni concentration is 20% by weight or more, the deformation resistance of the material is large, so that wire breakage frequently occurs. This is because

The Cu-Ni alloy used in the present invention has different Ni concentrations between the alloy material interposed between the superconducting filament group and the stabilized copper and the alloy material arranged around the superconducting filament. It is preferable that the concentration is lower than that of the latter.

The preferable Ni concentration of the former is 5 to 20% by weight.
The preferable Ni concentration of the latter is 0.5 to 5% by weight.

Impurity components in such Cu-Ni alloys are Fe≤0.5% by weight, Mn≤1.5% by weight, P≤0.5% by weight, and other unavoidable impurities≤
It is preferably 0.5% by weight.

The present invention can be applied to any composition as long as it is NbTi-based, and its effect can be obtained.

[0015]

Embodiments of the present invention will be described below.

FIG. 1 shows a cross section of an example of a superconducting stranded wire, in which a large number of NbTi-based superconducting filaments are covered with stabilized copper and 12 superconducting element wires 1 are twisted and formed into a rectangular shape. Each strand 1 that constitutes this stranded wire is configured as shown in FIG. That is, in each superconducting filament 2, the core 3 of NbTi is copper 4 and Cu-Ni alloy 5
The filament group 6 is arranged so as to cover the stabilizing copper 7 in the central portion, and the outer periphery thereof is covered with the stabilizing copper 8, but between the stabilizing coppers 7 and 8 respectively. It has a structure in which the Cu-Ni alloy 9 is arranged.

(Example 1) As a Cu-Ni alloy 5 around the superconducting filament 2, a Cu-2 wt% Ni alloy was fixed, and Cu between the filament group 6 and the stabilized copper 7 and 8 was fixed.
As shown in Table 1 as the Ni-based alloy 9, various wire materials were manufactured by changing the Ni concentration by the following method.

A composite billet having a three-layer structure of NbTi / Cu / Cu-Ni is processed into a single wire having a hexagonal cross section by hydrostatic extrusion and wire drawing, and the obtained wire is cut into a plurality of pieces. Was again housed in a copper pipe and extruded and drawn to obtain a predetermined multi-wire material. The obtained multi-wire is cut into a plurality of pieces, and seven of them are placed around a stabilized copper rod coated with a Cu-Ni alloy, and a Cu-Ni alloy pipe and a copper pipe are coated around the rod. Then, extrusion processing is performed again, and after wire drawing and aging heat treatment are repeated, twist processing is applied, and wire drawing is further performed: wire diameter 1.1 mm, filament diameter 6.0 μm, number of filaments 74000, twist pitch 20 mm <Cu / Cu-Ni / NbTi is 2.5 /
A 2.0 / 1.0 NbTi fine multi-wire material was produced.

The AC loss was measured for each of the obtained wire rods, and the loss time constant was determined from the measured value. As shown in FIG. 4, the AC loss is measured by winding a superconducting element wire as a measurement sample 10 in a coil shape, setting a pickup coil 11 on the outer side and a cancel coil 12 on the outer side, and placing the coil on the outer circumference. The pickup coil 11 detects a voltage induced by changing the backup magnetic field of the Grown semagnet 18, and the voltage is detected by the integrator 14.
Convert the magnetic flux at to obtain the coupling loss. In FIG. 4, 1
3 is an amplifier, 15 is a digital memory personal computer, 16
Is a shunt resistor, and 17 is a power supply.

The measurement conditions were a temperature of 4.2K and a magnetic flux amplitude of 1T.

From the values thus obtained, the loss time constant was determined using the following formula.

Qc = Bm2 / 2μ ₀ [τ _C / (τ _C + τ _p )] where Qc [J]: coupling loss, Bm [T]: maximum magnetic field, μ ₀ [−]: permeability of vacuum, τ _C [s]: loss time constant of wire rod, τ _p [s]: interruption time constant of background magnetic field.

The results are also shown in Table 1. From this result, it is understood that the bonding loss of the wire can be significantly reduced when the Ni concentration in the Cu-Ni alloy between the filament group and the stabilized copper is 5% by weight or more.

[0024]

[Table 1]

(Example 2) A Cu-10% by weight Ni alloy was used as the Cu-Ni alloy between the filament group and the stabilized copper, and the Ni of the Cu-Ni alloy around the superconducting filament was used.
Various wire rods were produced in the same manner as in Example 1 except that the concentration was changed as shown in Table 2.

Then, for each wire rod, a 12-strand Rutherford type stranded wire conductor as shown in FIG. 1 was used, and the stability margin of each conductor was obtained.

As shown in FIG. 5, the stability margin is measured by an induction heater Lo wound around a conductor serving as a measurement sample, and an alternating current generated by the alternating magnetic field generated at that time causes an alternating current to flow. , The energy was applied to the sample from the outside. The measurement conditions are a temperature of 4.2 K, a current of 1 kA, and an external magnetic field of 5 T.

The limit input energy at which the sample of the superconducting conductor is not quenched is called the stability margin, and usually represents the amount of energy per unit wire volume.

The results are also shown in Table 2. From this result, it is understood that when the Ni concentration in the Cu-Ni alloy is 5% by weight, it is almost the same as that of pure copper, and when it is more than this, the stability margin is extremely lowered.

[0030]

[Table 2]

Example 3 A sub-multi wire was obtained in the same manner as in Example 1, except that the Cu-Ni alloy around the superconducting filament was a Cu-1 wt% Ni alloy. After that, when assembling the composite billet for fine multi-wire, Cu-N
Use a thin Cu-10 wt% Ni alloy wire having a hexagonal cross section instead of the i-based alloy pipe, arrange it on the outer circumference of the filament group, and replace 2/3 of it with a copper wire having the same hexagonal cross section. Thus, the Cu-10 wt% Ni alloy wire was equally distributed at four locations on the outer circumference.

Fine multi-lines were produced in the same manner as in Example 1 using the composite billet thus assembled. Then, the stability margin was obtained in the same manner as in Example 2 except that the wire material was a 12-strand Rutherford-type stranded wire conductor as shown in FIG.

As a result, when the Cu-Ni based alloy interposed between the filament group and the stabilized copper was divided, the stability margin (mJ / cc-strand) of 1210 was about twice as high as 670 when the division was not made. )was gotten.

[0034]

As is clear from the above description, according to the present invention, there is an effect that a coupling loss between filaments of a wire can be reduced and an NbTi-based superconducting stranded wire having good stability can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a superconducting stranded wire according to the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of a strand of a superconducting stranded wire according to the present invention.

FIG. 3 is a diagram showing a model for obtaining a loss time constant of a wire rod.

FIG. 4 is a conceptual diagram showing a method of measuring AC loss.

FIG. 5 is a conceptual diagram showing a method of measuring a stability margin.

[Explanation of Codes] 1 superconducting element wire 2 superconducting filament 4 copper 5,9 Cu-Ni alloy 6 filament group 7,8 stabilized copper

Front page continuation (72) Inventor Shuji Sakai 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. System Materials Research Center

Claims (5)

[Claims] 1. A NbTi-based superconducting stranded wire formed by twisting a plurality of superconducting element wires in which a large number of superconducting filaments are incorporated in stabilized copper, in the vicinity of the superconducting filament, and between the filament group and the stabilizing copper, respectively. A NbTi-based superconducting stranded wire comprising a Cu-Ni-based alloy. 2. The Cu-Ni based alloy disposed between the filament group and the stabilized copper has a higher Ni concentration than the Cu-Ni based alloy disposed around the superconducting filament. The NbTi-based superconducting stranded wire according to 1. 3. The NbTi-based superconducting stranded wire according to claim 1, wherein the Ni concentration of the Cu—Ni-based alloy disposed between the filament group and the stabilized copper is 5 to 20% by weight. 4. C disposed around a superconducting filament
The NbTi-based superconducting stranded wire according to claim 1, 2 or 3, wherein the Ni concentration of the u-Ni-based alloy is 5% by weight or less. 5. The Cu-Ni alloy disposed between the filament group and the stabilized copper is divided into a plurality of pieces in the circumferential direction of the superconducting element wire, according to any one of claims 1 to 4. NbTi-based superconducting stranded wire according to.