JPH06295626A - Nbti superconducting material for pulse - Google Patents

Abstract

PURPOSE:To provide a superconducting material excellent in heat discharging performance and stability by burying collection of NbTi filaments satisfying the stabilization standard in dia., in a cupper alloy matrix, and repeating the process several times. CONSTITUTION:A plurality of holes in the form of rod 10 are formed by Cu-10wt.% of Ni ingot, filaments 11 formed by Nb-47wt.% of Ti ingot are inserted therein to form a complex body satisfying the stabilization standard, and it is inserted in a cupper tube 12 to form a billet. A plurality of wires 13 formed by working and extending the billet are inserted in a cupper pipe 14 to have a composite billet. It is thus possible to prevent deformation or disconnection in filaments upon extrusion work since the difference in deformation resistance between the cupper alloy and NbTi is small, and to maintain high stability, and further to improve heat discharge by the use of the cupper pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to NbTi superconducting wire for pulses.

[0002]

2. Description of the Related Art Generally, an NbTi superconducting wire is composed of a plurality of NbTi filaments and stabilized copper coating the filaments. When this wire is used under a pulse-varying magnetic field, AC loss occurs in the wire. The AC loss includes hysteresis loss mainly generated in the NbTi filament portion and coupling / eddy current loss generated in the stabilized copper portion.

Generally, hysteresis loss in the NbTi filament portion can be reduced by reducing the filament diameter. Specifically, when the NbTi superconducting wire is used as a pulse wire, the filament diameter may be reduced to 2 to 3 μm in order to reduce hysteresis loss.

On the other hand, the coupling / eddy current loss in the stabilized copper portion can be reduced by disposing a copper alloy such as a CuNi alloy on the outer periphery of each filament, between the filaments, or on the outer periphery of the wire. In particular, Cu is used all around the filaments, between filaments, and around the wire.
By disposing the Ni alloy, the coupling / eddy current loss can be further reduced. Based on this idea, an NbTi superconducting wire having a structure in which a stabilizing copper portion is completely eliminated and a matrix portion is made of a CuNi alloy is used as an AC wire material.

It has been reported that the AC wire having such a structure has a very low Jc in a low magnetic field and a large loss due to a change in the magnetic field, resulting in poor stability. For this reason, in the wire for AC, the diameter of the wire is made as thin as possible to improve the heat treatment, and the stabilized copper that is finely partitioned by the CuNi alloy barrier layer is built in the central part of the wire to stabilize it in a low magnetic field. Is improving.

However, in the AC wire material, the NbTi filament diameter is reduced to 0.1 to 0.5 μm in order to reduce hysteresis loss and improve stability, so that the critical current density in a magnetic field is high. It is small and the critical current capacity per wire is small. Therefore, when used for a large current wire, there arises a problem that these wires (strands) have to be twisted in multiple layers.

The pulse wire rod experiences a smaller magnetic field change rate than the AC wire rod, so the AC loss is small, but the instability resulting from the reduction of the evaporation amount of liquid helium and the heat generation due to the AC loss is improved. Therefore, it is essential to reduce the AC loss.

On the other hand, since the pulse wire is used for large-scale equipment such as a fusion coil, a generator coil, and SMES, a large current capacity of 10 kA or more is required. Further, in order to increase the mechanical rigidity of the pulse wire, it is preferable that the number of twisted wires is small. Therefore, it is necessary to increase the critical current capacity per wire, which naturally increases the outer diameter of the wire. When the outer diameter of the wire increases, the heat treatment becomes worse. For this reason, it is not possible to adopt the above-described configuration of the AC wire rod in which the matrix portion is entirely made of CuNi alloy for the pulse wire rod. In other words, when the pulse wire is used in large equipment, quenching of the wire will lead to a major accident.
The amount of copper in the material coating the i-filament must be increased.

As a conventional superconducting wire for pulses, for the purpose of ensuring stability and reducing AC loss, a NbTi filament is covered with a stabilizer composed of copper and a CuNi alloy, and this is embedded in a copper matrix. A wire having a three-layer structure is used.

[0010]

[Problems to be Solved by the Invention] However, this 3
The layered pulsed superconducting wire has the following problems. That is, when copper is present between the NbTi filaments, the deformation resistance of copper is smaller than that of NbTi or CuNi, so the deformability differs between NbTi or CuNi and copper during hot extrusion or wire drawing. Deformation of the filament shape or, in extreme cases, breakage of the filament. In particular, if the residual resistance ratio of copper is increased in order to improve stability, the deformation resistance of copper is further reduced, which adversely affects the workability.

Further, since the thickness of copper outside the NbTi filament is generally thin, nickel atoms diffuse from CuNi into copper by heat treatment in the wire manufacturing process. For this reason, the electrical resistance of copper increases, and conversely the thermal conductivity decreases, so that it does not function as a stabilizing material.

The present invention has been made in view of the above points, and an object of the present invention is to provide an NbTi superconducting wire for pulses, which has good heat resistance, excellent stability, and excellent workability.

[0013]

According to the present invention, a filament assembly in which at least three NbTi filaments are embedded in a first matrix made of a copper alloy, and a plurality of the filament assemblies are embedded. Second made of copper
The NbTi superconducting wire for a pulse, characterized in that the diameter of the filament assembly satisfies the essential stabilization criterion.

Here, as the copper alloy which is the material of the first matrix, CuNi, CuMn, CuSi and CuN are used.
iMn or CuSiMn can be used.

The essential stabilization criterion defining the diameter d of the filament assembly means both the so-called adiabatic stabilization criterion and the dynamic stabilization criterion. By the adiabatic stabilization standard,
The diameter d is determined by the average specific heat of the filament assembly and the critical current density of NbTi. Also, in the dynamic stabilization criteria,
The diameter d is determined by both heat diffusion and magnetic flux diffusion in consideration of the surrounding stabilized copper. In general, the diameters d determined by the adiabatic and dynamic stabilization criteria both have similar values.

At the center of the second matrix, a copper core may be arranged as a stabilizing material for the purpose of improving stabilization.
At this time, the inside of the copper core may be divided by a barrier layer made of a CuNi alloy or the like.

[0017]

In the pulsed NbTi superconducting wire of the present invention, the diameter of the filament assembly obtained by embedding the NbTi filaments in the first matrix made of a copper alloy satisfies the essential stabilization criterion, and a plurality of filament assemblies are provided. The book is embedded in a second matrix made of copper.

Nb in the first matrix of copper alloy
Since the Ti filaments are embedded, there is no copper between the NbTi filaments. Copper alloy and NbTi are
Since the difference in deformation resistance is small, it is possible to prevent filament deformation or filament breakage during hot extrusion or wire drawing.

The filament assembly is embedded in the second matrix made of copper, and the diameter of the filament assembly is set so as to satisfy the essential stabilization standard. That is, the thickness of the copper layer covering the filament assembly is sufficiently thick. Therefore, even if an element other than copper in the copper alloy diffuses into the copper layer as the second matrix due to the heat treatment in the manufacturing process, the electrical resistance is not substantially improved and the thermal conductivity is not lowered. . Therefore, high stability can be maintained, and the heat treatment is good.

[0020]

Embodiments of the present invention will be specifically described below with reference to the drawings.

Example 1 FIG. 1 is a sectional view showing an example of a pulse NbTi superconducting wire of the present invention. This pulse NbTi superconducting wire was produced as follows.

First, a rod-shaped body 10 having an outer diameter of 169 mm was prepared using a Cu-10 wt% Ni ingot, and three holes having an inner diameter of 68 mm were formed along the longitudinal direction of the rod-shaped body 10. A filament 11 made of Nb-47 wt% Ti ingot was inserted into these three holes to obtain a composite.

Next, a copper tube 12 having an outer diameter of 200 mm and an inner diameter of 170 mm was prepared, and the composite body was inserted into the copper tube 12 to prepare a primary composite billet. The primary composite billet was drawn by hot extrusion and cold working to produce a primary strand 13 having a hexagonal cross section. Finally, a large number of these primary wires 13 are used for the copper tube 1 having an outer diameter of 200 mm and an inner diameter of 175 mm
4 into the final composite billet.

The final composite billet obtained was composed of NbTi filaments and CuN coating the NbTi filaments.
It is composed of an i-alloy matrix and a Cu matrix that covers this matrix. The diameter of the CuNi alloy matrix satisfied the so-called essential stabilization criterion in the final linear shape.

Example 2 As shown in FIG. 2, a 37-core final composite billet was produced in the same manner as in Example 1 except that 37 holes for NbTi filaments were formed in the rod-shaped body 10. In addition,
The diameter of the CuNi alloy matrix met the so-called intrinsic stabilization criterion in the final wire diameter.

Example 3 As shown in FIG. 3, a 163-core final composite billet was produced in the same manner as in Example 1 except that the number of holes for NbTi filaments formed in the rod-shaped body 10 was 163. The diameter of the CuNi alloy matrix satisfied the so-called essential stabilization standard in the final wire diameter.

Comparative Example 1 As shown in FIG. 4, Cu having an outer diameter of 200 mm and an inner diameter of 155 mm
A copper tube 41 having an outer diameter of 154 mm and an inner diameter of 130 mm was inserted into the Ni tube 40, and a NbTi filament 42 having an outer diameter of 129 mm was inserted into the copper tube 41 to produce a primary composite billet. The primary composite billet is drawn by hot extrusion and cold working to produce a primary element wire having a hexagonal cross section, and a large number of them are formed into a copper tube 4 having an outer diameter of 200 mm and an inner diameter of 175 mm.
3 to obtain the final composite billet.

COMPARATIVE EXAMPLE 2 As shown in FIG. 5, a rod-shaped body 50 having an outer diameter of 169 mm was prepared using a Cu-10 wt% Ni ingot, and 16 holes for NbTi filaments were formed along the longitudinal direction of the rod-shaped body.
Three pieces were formed. Nb-47 wt% T in these 163 holes
A filament 51 made from an i ingot was inserted to obtain a composite.

Then, the composite is subjected to hot extrusion and cold working to draw a primary wire having a hexagonal cross section, and many of them are made of copper having an outer diameter of 200 mm and an inner diameter of 175 mm. Inserted into tube 52 to obtain the final composite billet.

In the final composite billets of Examples 1 to 3 and Comparative Examples 1 and 2, a stabilizing material 16 made of copper partitioned by a CuNi alloy sheath 15 at 19 was embedded. Next, this final composite billet was subjected to hot extrusion processing and cold processing, and was drawn to a final wire diameter of about 0.6 mm. In this way, a pulse NbTi superconducting wire was produced. In addition, about the thing of Examples 1-3, the diameter of the filament assembly satisfied the essential stabilization standard.

In this NbTi superconducting wire, NbT
In order to control the Jc (critical current density) of i, an appropriate age hardening heat treatment was performed during the wire drawing process. Also, this N
The bTi superconducting wire was subjected to a twisting process and then an insulating process.

Regarding the obtained NbTi superconducting wire, Ic
(Defined as critical current, 10 ^-13 Ω · m), Jc, n
The value (V = K (I / Ic) ⁿ , where V is the generated voltage and I is the applied current), AC loss, stability, and workability were examined. The results are shown in Table 1 below.

Ic and Jc were measured under a magnetic field of 5T. The n value was obtained from the current-voltage curve. AC loss is 5
A fluctuation magnetic field of ± 1T under a magnetic field of T of 10T / se
It was given by c, the magnetization of the NbTi superconducting wire at that time was measured, and it was calculated by integrating the area from the magnetization-applied magnetic field curve. The stability is as follows: In a static magnetic field of 5T, the NbTi superconducting wire is energized to 90% of Ic of the wire,
Heat was locally and adiabatically applied to the NbTi superconducting wire by the heater heating method, and the heat input until the NbTi superconducting wire was quenched was ranked from the one with the highest stability (the one with the highest stability was 1).

[0034]

[Table 1] As is clear from Table 1, the pulsed NbTi superconducting wires of the present invention (Examples 1 to 3) have high Ic, Jc, and n values, small AC loss, and good stability and workability. It was

This is because CuN is used for the NbTi filament.
It is considered that the i alloy is coated and no copper is present between the NbTi filaments, so that the workability is improved, the so-called filament sausage phenomenon does not occur, and the superconducting property originally possessed by NbTi appears. In addition, the stability is improved by the fact that the diameter of the filament assembly satisfies the essential stabilization criterion, there is substantially no diffusion of Ni into the copper layer, and the increase in electrical resistance and the decrease in thermal conductivity do not occur. It is thought to be because.

On the other hand, the pulse NbT of Comparative Example 1
The i superconducting wire had poor superconducting properties, stability, and workability. Since this is a structure in which copper exists between NbTi filaments, the workability is poor, so-called filament sausage phenomenon occurs, and NbT
It is considered that i did not exhibit the superconducting property of i, and further, since the copper layer was thin, Ni diffused into the copper layer, which increased the specific resistance and decreased the thermal conductivity, and deteriorated the stability. Conceivable.

The pulse NbTi superconducting wire of Comparative Example 2 is
The stability was poor. It is considered that this is because the diameter of the filament assembly does not satisfy the essential stabilization criterion.

[0038]

As described above, the pulse Nb of the present invention is used.
In the Ti superconducting wire, the diameter of a filament assembly obtained by embedding NbTi filaments in a first matrix made of a copper alloy satisfies an essential stabilization criterion, and a plurality of filament assemblies made of a second matrix made of copper are used. Since it is embedded in the matrix, a thick copper layer is formed outside the filament assembly. For this reason, this thick copper layer forms a network and becomes an effective heat path, so that the heat treatment is good. Further, since this thick copper layer functions as an original stabilizing material, the stability is excellent.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a pulse NbTi superconducting wire of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the pulse NbTi superconducting wire of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the pulse NbTi superconducting wire of the present invention.

FIG. 4 is a sectional view showing an example of a pulse NbTi superconducting wire of a comparative example.

FIG. 5 is a cross-sectional view showing another example of a pulse NbTi superconducting wire of a comparative example.

[Explanation of symbols]

10 ... Rod-shaped body, 11 ... Filament, 12 ... Copper tube, 13
... primary strands, 14 ... copper tubes, 15 ... CuNi alloy barrier layer, 16 ... stabilizing material.

Claims (1)

[Claims] 1. A filament assembly in which at least three NbTi filaments are embedded in a first matrix made of a copper alloy, and a second matrix made of copper in which a plurality of the filament assemblies are embedded. Equipped with,
A pulsed NbTi superconducting wire, characterized in that the diameter of the filament assembly satisfies the essential stabilization criterion.