JP2004063128A - Compound-based superconductive wire showing strain dependency and superconductive magnet using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound-based superconductive wire whereof mechanical characteristics and stress characteristics of a critical current valve are enhanced and the critical current valve is also enhanced, and to provide a superconductive magnet using this compound-based superconductive wire. <P>SOLUTION: After a bending strain is added to the compound-based superconductive wire showing strain dependency, to which heat treatment has been applied, the bending strain is unloaded to enhance mechanical characteristics and stress characteristics of the critical current value of the compound-based superconductive wire while enhancing the critical current value. After the bending strain is added to the compound-based superconductive wire showing strain dependency, to which heat treatment is applied, the bending strain is unloaded and the compound-based superconductive wire is coiled to enhance its mechanical characteristics and its critical current value. This superconductive magnet uses it. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compound superconducting wire (including a high-temperature superconducting wire) exhibiting strain dependency and a superconducting magnet using the compound superconducting wire exhibiting strain dependency.
[0002]
[Prior art]
Practical superconducting wires used for superconducting magnets are mainly niobium titanium alloy wires and Nb ₃ Sn compound wires. Niobium titanium has excellent mechanical properties because it is an alloy, and is used for many superconducting magnets. However, since its upper critical magnetic field is low, a magnetic field that can be generated is 8 to 9 T at 4.2 K.
On the other hand, a compound superconducting wire represented by Nb ₃ Sn has a high critical magnetic field and can be applied to a 20 T class superconducting magnet. However, it is very sensitive to strain, and the critical current density greatly depends on strain. Is a problem. In order to overcome this problem, a method of attaching strongly processed copper to the outside of the Nb ₃ Sn superconducting wire after heat treatment for generating Nb ₃ Sn, a wire structure in which high-strength CuNb, alumina-dispersed copper, and the like are arranged in advance. The method is adopted. With such a configuration, the magnitude of strain for the same stress can be reduced, and as a result, a decrease in critical current density due to the stress is suppressed.
[0003]
Furthermore, the conventional Nb ₃ Sn wire rod is very sensitive to stress, so it is difficult to use the react & wind method of winding the coil after heat treatment. However, high strength Nb ₃ Sn is used. Therefore, in the case of a large-diameter magnet having a small bending distortion, a react-and-wind method can be adopted.
As a result, it has become possible to control bending and tensile strain during coil winding.
[0004]
[Problems to be solved by the invention]
However, in order to actually produce a magnet using an Nb ₃ Sn superconducting wire, a method of controlling the strain over a long wire of km class and applying a constant strain to the wire has not yet been established. There is no prospect of practical application just because a method using is disclosed. Such a phenomenon was the same in the case of a compound-based composite superconducting wire and an oxide superconducting wire other than the Nb ₃ Sn superconducting wire.
The present invention, when winding a compound superconducting wire showing a long-strain dependence of the km class in a coil shape, after applying a bending strain in advance over the entire superconducting wire, unloading this, mechanical properties, An object of the present invention is to provide a superconducting wire having excellent superconducting properties and a superconducting magnet using the superconducting wire.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 is to provide a compound-based superconducting wire exhibiting a strain dependency subjected to a reactive treatment, after applying a bending strain, and then unloading the bending strain, thereby providing a mechanical property and a stress property of a critical current value, and a critical current value. A compound-based superconducting wire having an improved current value.
The invention according to claim 2 is to apply a bending strain to the reactive superconducting compound-based superconducting wire, and then unload the bending strain and wind a coil around a reel to obtain a mechanical property and a critical current value. It is a superconducting magnet using a compound superconducting wire characterized by being improved.
[0007]
[Action]
In general, stress-strain characteristics called mechanical characteristics are divided into elastic deformation in a region where strain or stress is low, and plastic deformation in a region where it is high, and the boundary line is a yield point. In elastic deformation, strain changes linearly with applied stress, but when plastic deformation occurs beyond the yield point, the response of strain to stress becomes extremely large. When the stress applied after the plastic deformation is caused beyond the yield point is unloaded, the wire undergoes work hardening, and apparent mechanical properties are improved, and residual stress is generated.
[0008]
Even in the case of a compound-based composite superconducting wire exhibiting strain dependency like an Nb ₃ Sn superconducting wire, the yield point is generally not clear, but for example, a CuNb reinforced Nb ₃ Sn wire has a strain of about 0.02%. It is known that the response of the strain generated when a stress is applied gradually increases due to the plastic deformation when the stress exceeds the limit. It is known that, when stress is applied to the area of plastic deformation and then unloaded, the strain does not return to zero and the residual stress remains, and the strain response to stress apparently decreases due to work hardening.
[0009]
In the present invention, bending distortion is applied to the superconducting wire wound by the coil, and the distortion is unloaded.
When a bending strain is applied to a superconducting wire, the wire is equivalent to a tensile or compressive strain in a local region, and when a tensile strain higher than the yield point is applied, local work hardening occurs. Thus, the magnitude of the strain relative to the stress becomes smaller as shown in FIG. 3 until the strain once experienced is reached. In the present invention, a bending strain is imparted to the wire, but the bending strain is equivalent to giving different strains depending on the position of the wire, so that the strain response at low stress is not linear, but becomes a curve that is upwardly convex. In that it differs from general work hardening.
[0010]
At this time, the strain when the stress is zero is not zero but takes a finite value as shown in FIG. 4, but when the compound superconducting wire is Nb ₃ Sn or the like, the difference in the heat shrinkage from the composite material at low temperature is low. The critical current density at zero stress also increases because the compressive strain (prestrain) resulting from the pre-bending is reduced due to the residual strain introduced by the pre-bending strain.
Further, due to the improvement of the mechanical properties due to the work hardening, the stress dependency of the critical current density is remarkably improved as shown in FIG.
[0011]
From a similar point of view, an idea to improve the superconductivity by introducing a residual stress by applying a tensile strain in advance and then unloading has been announced, but as described above, over the entire long wire of km class. It is difficult to apply the tensile strain while controlling it, it is impossible to apply a stable strain, there is no feasibility, and it has not been implemented.
[0012]
The present invention focuses on the fact that, as a method for imparting strain to a long superconducting wire, it is possible to easily control the strain given by applying strain by bending and to apply a stable strain. By applying and controlling the bending strain to the wire, and further improving the mechanical properties, the critical current density of the compound-based composite superconducting wire exhibiting the strain dependence is improved, and the compound-based composite superconducting wire becomes more critical. The current has been improved, and a compact and low-cost superconducting magnet has been put to practical use.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a compound-based composite superconducting wire and a superconducting magnet using the superconducting wire of the present invention will be described in detail based on one illustrated embodiment.
FIG. 1 is an explanatory view showing a manufacturing process of a compound-based composite superconducting wire of the present invention, particularly a Nb ₃ Sn superconducting wire. As shown in FIG. Is passed through a die 11 to be drawn into a fine wire having a specified value to form a superconducting wire 3 and wound up on a reel 12. The superconducting wire 3 wound on the reel 12 is placed in a furnace 13 as shown in FIG.
[0014]
The superconducting wire 3 is placed in a furnace 13 and subjected to a reacting treatment (heat treatment) to form a composite superconducting wire 2. The composite superconducting wire 2 has an outer periphery in the next step as shown in FIG. The superconducting wire 2 coated with the insulator 7 is taken up by the caterpillar 14 and wound around the reel 15. The superconducting wire 2 is given a bending strain by being wound on the reel 15, and the bending strain given by being pulled out from the reel 15 in the next step (not shown) is unloaded, and the mechanical properties and the critical current The compound-based composite superconducting wire 1 has an improved critical current value as well as the stress characteristic of the compound.
[0015]
FIG. 2 is an explanatory view showing a manufacturing process of a magnet using the compound-based composite superconducting wire of the present invention, particularly, Nb ₃ Sn. The pretreatment shown in FIG. 1, that is, the superconducting wire ₃ made of Nb ₃ Sn wound around a reel 12 is put into a furnace 13 and subjected to a reactor treatment (heat treatment). The superconducting wire 3 is placed in a furnace 13 and subjected to a reacting treatment (heat treatment) to form a superconducting wire 2. The outer periphery of the superconducting wire 2 is coated with an insulator 7 in the next step shown in FIG.
[0016]
Next, the superconducting wire 2 covered with the insulator 7 is wound around the bobbin 16 to form the superconducting magnet 5.
In the step of winding the superconducting wire 2 around the bobbin 16, the superconducting wire 2 is subjected to a bending strain that maximizes a critical current by excitation. In FIG. 2, a pulley 17 is disposed in front of the bobbin 16, and the superconducting wire 2 is bent by the pulley 17 to apply a bending strain to the superconducting wire. The bending strain imparted to the superconducting wire 2 by the pulley 17 is released (unloaded) when passing through the pulley 17, and exhibits a mechanical property and a stress property of a critical current value, as well as a strain dependency with an improved critical current value. The superconducting wire 1 is wound around the bobbin 16 and becomes a superconducting magnet.
[0017]
Generally, in a superconducting magnet, the magnitude of the electromagnetic force applied to the superconducting wire varies depending on the magnetic field region used, the aperture of the magnet, and the like. The present invention provides a superconducting magnet that can easily control and impart bending strain such that the critical current density is maximized in the electromagnetic force region used according to the design of the magnet by changing its diameter with a pulley or the like at the time of winding. In particular, it is possible to reduce the size of a large object to which a large electromagnetic force is applied, and to design a magnet to which a larger electromagnetic force is applied.
[0018]
Further, the compound superconducting wire is subjected to the heat treatment and insulation treatment shown in FIG. 2 and then subjected to bending strain application using a pulley 17 and then rewinding to another bobbin. A superconducting wire having improved characteristics and superconductivity can be manufactured. This wire is expected to improve the critical current value by about 20% at maximum compared to the wire before treatment even at zero stress. For this reason, for example, in the case of power transmission wires used near zero stress, it is possible to control the critical current value to the optimum value by giving bending strain that is the residual strain that maximizes the critical current It is.
[0019]
In the above embodiment, the Nb ₃ Sn superconducting wire is particularly described as an example, but the same effect as in the above embodiment can be obtained by adding bending strain to a compound-based composite superconducting wire such as a high-temperature superconducting wire and unloading it. Is obtained.
Further, in the above embodiment, a pulley is employed to impart bending strain to the superconducting wire, but as another method of imparting bending strain, a straightening device combining a fixed roller and a movable roller may be used. it can.
[0020]
【The invention's effect】
The present invention imparts bending strain to a compound-based superconducting wire exhibiting strain dependency, and improves stress dependency of mechanical properties and superconducting properties by work hardening by unloading.
1. The compressive strain applied to the superconducting portion of the composite superconducting wire can be freely controlled by the difference in the heat shrinkage, and the critical current density at zero stress can be improved.
2. The response of strain to stress can be reduced.
3. Due to the above effects, the stress dependence of the critical current can be improved.
4. By optimizing the stress-strain characteristic with respect to the critical current, the critical current density can be improved, and the magnet can be made compact and low in cost.
And so on.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a step of manufacturing a superconducting wire of the present invention.
FIG. 2 is an explanatory view showing a step of manufacturing a superconducting magnet of the present invention.
FIG. 3 is a graph showing stress-strain characteristics when a pre-bending strain is applied to a superconducting wire.
FIG. 4 is a graph showing elongation of a wire when pre-bending strain is applied to a superconducting wire.
FIG. 5 is a graph showing stress dependence of a critical current when a bending strain of 0.05% is applied to a superconducting wire in advance.
[Explanation of symbols]
1 Compound-based superconducting wire showing strain dependence 2 Compound-based superconducting wire 3 Wire for superconducting wire (thin wire)
4 Superconducting wire (thick wire)
5 Compound superconducting wire magnet 12 Reel 13 Furnace 15 Reel 16 Bobbin 17 Pulley

Claims (2)

After adding bending strain to the compound-based superconducting wire exhibiting the strain dependency subjected to the reactor treatment, the critical current value was improved together with the mechanical characteristics and the stress characteristics of the critical current value by removing the bending strain. A compound superconducting wire characterized by the following. A compound characterized by improving the mechanical properties and critical current value by adding bending strain to a compound-based superconducting wire exhibiting strain dependence subjected to a reactor treatment, and then unloading the bending strain and winding the coil to improve mechanical properties and critical current value. Superconducting magnet using superconducting wire.

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