JPH0821733B2 - Method for manufacturing superconducting wire for thermal permanent current switch, and superconducting wire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a superconducting wire for a thermal permanent current switch and a method for manufacturing the same.

[Conventional technology]

FIG. 2 is a circuit diagram showing an example of an exciting circuit for a superconducting coil.

The persistent current switch 2 is connected to the superconducting coil 3 so as to form a closed circuit.

When the permanent current switch 2 is in the ON state (the heater 22 is not energized), the closed circuit is formed via the connecting portion 7, and hence the permanent current mode is set.

However, since a slight loss occurs in the connecting portion 7, the current value gradually decreases.

FIG. 3 is an explanatory diagram showing the details of the permanent current switch 2.

Persistent current switch body constructed by winding superconducting wire 1
The heater 21 and the heater 22 are arranged close to each other.

The switch body 21 is kept at an extremely low temperature by liquid helium or the like, and when the heater 22 is not energized, the persistent current switch superconducting wire 1 is in a superconducting state (this state is a switch ON state).

If the heater 22 is energized and the temperature of the main body 21 of the permanent current switch is set to be equal to or higher than the critical temperature of the superconducting wire 1 for permanent current switch (the maximum temperature at which the superconducting state can be maintained), the superconducting wire 1 wound in this Example 21 It becomes a normal conducting state and shows a large resistance (this state is the switch OFF state).

When energizing the superconducting coil 3 from the excitation power supply 6 shown in FIG. 2, the permanent current switch 2 is turned off and the coil excitation speed is set. Corresponding to the voltage ( Here, L is performed by applying the inductance of the superconducting coil 3. At this time, a current flows through the permanent current switch 2 by I _P = E / R _P.

Here, I _P : current value flowing in the persistent current switch, R _P : resistance value of the persistent current switch.

Due to the current I _P , Joule heat is generated by Q _P = I _P ² · R _P , and the refrigerant (for example, liquid helium) is wastefully evaporated.

Therefore, it is desirable to keep the I _P value as low as possible.

Especially when exciting / demagnetizing the superconducting coil 3 at high speed,
The above formula Is large, the terminal voltage E increases, the current I _P flowing through the permanent current switch 2 also increases, and the Joule heat generation Q _P tends to increase. Here, in order to reduce the Joule heat generation Q _P , it is necessary to take measures to increase the OFF resistance value R _P of the persistent current switch 2 and reduce the current I _P flowing through the persistent current switch. Permanent current switches are being developed. Furthermore, from the excitation power supply at room temperature,
The cross-sectional area of the power lead for passing an electric current to the superconducting coil 3 in the refrigerant is determined from both the current carrying capacity and the amount of heat intrusion through the power lead, but if the excitation / demagnetization speed of the superconducting coil is large, Since the power lead energization time is shortened and the cross-sectional area of the power lead can be reduced accordingly, this is also effective in reducing the refrigerant consumption.

From the above consideration, it can be understood that the evaporation amount of the refrigerant can be suppressed if the resistance of the permanent current switch 2 at the time of OFF (electrical resistance in the non-superconducting state) can be increased.

[Problems to be Solved by the Invention]

Therefore, it is required to increase the resistance when the permanent current switch is off.

Possible methods for increasing the resistance at the time of OFF are (a) lengthening the winding line of the permanent current switch body 21.

(B) Make the winding wire of the permanent current switch body 21 thin.

(C) The stabilizing base material resistance of the superconducting wire 1 for the permanent current switch is increased.

Is.

The winding line length of (a) above is restricted by the size of the persistent current switch 2.

Further, the wire diameter of (b) is restricted by the current carrying capacity I _C.

Here, the direction of the study is directed to the increase of the resistivity of the stabilized base material described in (c) above.

Ordinary superconducting wires are made of superconducting filaments (ultra-fine wires with a diameter of several μm to 100 μm, NbTi alloy is generally used for permanent current switches) to ensure stability and oxygen-free copper with low specific resistance at low temperatures. The structure is embedded in a stabilizing base material such as high-purity aluminum. The term "stability" as used herein means the degree to which the superconducting state can be kept stable, and the role of the stabilizing base material is (a) mechanically holding and reinforcing the superconducting filament, and (b) the superconducting filament. If normal conduction occurs in some of the parts due to some influence, the current is bypassed, and it waits for the disturbance to disappear before returning to the superconducting state.

Regarding the function of the above item (b), it is desirable that the specific resistance at cryogenic temperature is small.

However, as a problem that is difficult to be compatible with the above, in the case of a conducting wire for a persistent current switch, it is necessary to increase the resistance at OFF, that is, the resistance when the superconducting filament is in the normal conducting state.

Therefore, CuNi (about 1000 times Cu at liquid helium temperature, which is almost the same as the normal resistance of NbTi superconducting filament at liquid helium temperature) is used as a stabilizing base material. In this case, there is a drawback that the connection resistance at the connection portion 7 in FIG. 2 also becomes large.

This problem will be described with reference to FIG. The present FIG. 4 is an explanatory view in which the connecting portion 7 of FIG. 2 is enlarged and shown in cross section. here,
The superconducting coil lead wire 31 and the superconducting wire 1 for a permanent current switch are connected via solder 8. In the superconducting state, the electric current flows through the superconducting filament 32 in the superconducting coil lead wire 31 and is first shunted to the low resistance stabilizing base material (Cu) 33 at this connection portion 7, and the solder 8 and the high resistance stabilizing are performed. Base material (CuNi)
And then to the superconducting filament 11. The low resistance stabilizing base material 33 and the solder 8 have a small resistance and there is no problem, but the high resistance stabilizing base material 12 of the superconducting wire for a persistent current switch 12
Has a large resistance, the resistance value as a superconducting closed circuit, heat generation,
This causes problems such as a decrease in I _C due to heat generation. A measure to increase the connection wrap length may be considered in order to reduce the connection resistance, but there are structural restrictions and dimensional restrictions, so that this alone cannot be expected to have a sufficient effect.

The stabilizing base material of the superconducting wire for the permanent current switch is a high resistance stabilizing base material such as CuNi for the most part in the lengthwise direction, and only its both ends are low resistance stabilizing material such as Cu. It has been studied to use it as a base material. As a technique for forming such a superconducting wire, Japanese Patent Laid-Open No. 59-1170
34 is known.

The above-mentioned publicly known technology constitutes a superconducting wire of CuNi base material, and removes the CuNi base material at the mouths of both ends of the superconducting wire by means of chemical treatment with a solvent such as nitric acid, thereby exposing the superconducting wire. The treatment is performed by a method in which copper is sprayed or plated on the filament to be attached.

According to the above-mentioned known technology, when the CuNi base material is chemically treated to expose the superconducting filament, I _C of the superconducting wire (the maximum critical current that can flow in the superconducting state) is deteriorated, or
There is a problem that a coating film of oxide or nitride is formed on the surface of the superconducting filament (NbTi alloy or the like), which increases the shunt resistance to the copper substrate to be attached later.

The present invention has been made in view of the above circumstances, and has a structure that does not cause deterioration of the superconducting wire at the outlet in the course of the manufacturing process, and the surface of the superconducting filament is oxide or nitrided. It is intended to provide a method for manufacturing a superconducting wire for a persistent current switch, which has a structure that does not cause a film of an object, and another object is to provide a superconducting wire for a persistent current switch, which can perform the above method accurately. To provide.

[Means for solving the problem]

The superconducting wire of the present invention created in order to achieve the above-mentioned object is a low resistance stabilizing base material (for example, CuNi) where a high resistance stabilizing base material (for example, CuNi) is removed by a chemical agent as in the above-mentioned known technique. ) Is not attached to the structure, but the high resistance stabilizing base material is configured to be slightly shorter, and the low resistance stabilizing base material is welded to both ends thereof.

In the prior art, since the superconducting wire once constructed was subjected to chemical treatment and thermal spraying (or plating), welding could not be applied, but the superconducting wire of the present invention is backed by the invention of the manufacturing method described later, It is a creation of a welded structure.

Further, the manufacturing method of the present invention created to form a superconducting wire having the above-mentioned structure is a material for forming the superconducting wire, that is, a high resistance stabilizing base material (eg CuNi) and a low resistance stabilizing base material. (For example, Cu) and a superconducting filament material (for example, NbTi) are combined in a raw material state before drawing, that is, in a thick and short state, subjected to required welding, and then drawn to obtain a superconducting wire.

Multi-core superconducting wires are obtained by cutting and drawing the once drawn intermediate products, bundling them and repeating drawing again in the same manner as above.

As a specific configuration for applying the above-mentioned principle to a practical technique, a method for manufacturing a superconducting wire according to the present invention comprises a tubular member made of a high resistance stabilizing material, and at both ends of the tubular member, Welding a short tube made of a low resistance stabilizing material, and fitting a superconducting filament material ingot longer than the tubular member and not protruding from the short tube into the tubular member, A plug is capped and welded to each, and the assembly member thus configured is drawn by, for example, the hydrostatic extrusion method to obtain a single-core superconducting wire. This is the basic operation of the method of the present invention, and a multifilamentary superconducting wire can be obtained by repeating the same wire drawing operation. That is, the drawn material (single core) is cut again into a length that is longer than the tubular member and does not protrude from the short tube, and this is bundled and stored in the tubular member, A plug is capped and welded to each of the short cylinders, and the assembly member having the above configuration is drawn again to obtain a multicore superconducting wire.

Therefore, the superconducting wire of the present invention is a tubular member made of a high-resistance stabilizing base material, and a short tube that is welded to both ends of the tubular member along the axial direction and has the same outer diameter as the tubular member. A superconducting filament material ingot that is inserted into the tubular member and the short tube and has a length longer than the tubular member and does not protrude from the short tube, and a plug capped by welding on each outer end of the short tube. A single core is formed by drawing an assembly member including the tubular member, the short tube, the superconducting filament material ingot, and the plug.

[Action]

According to the above-mentioned method of the invention, the high resistance stabilizing base material and the low resistance stabilizing base material are welded in a state before wire drawing, and thus the wire drawing is not necessary, so that chemical treatment such as pickling is not required, There is no risk of degrading the superconducting filament material.

In addition, since the superconducting filament material is enclosed in the stabilizing material tube, there is no risk of producing an oxide film or the like, and the superconducting filament material and the stabilizing base material are pressed against each other by the high pressure during wire drawing.

Further, the superconducting wire according to the present invention has actually produced industrial utility value (practicality) for the first time by the above-mentioned invented method, and the high resistance stabilized base material and the low resistance stabilized base material are welded together. Since there is no possibility of deterioration of the superconducting filament material during the manufacturing process, there is no intervening oxide film, nitride film or the like that interferes with the electrical resistance with the stabilizing base material.

That is, the superconducting wire of the present invention is a tubular member made of a high resistance stabilizing base material, and a short tube that is welded to both ends of the tubular member along the axial direction, and has the same outer diameter as the tubular member. A superconducting filament material ingot that is inserted into the tubular member and the short tube and has a length longer than the tubular member and does not protrude from the short tube, and a plug capped by welding on each outer end of the short tube. Since the assembly member composed of the tubular member, the short tube, the superconducting filament material ingot, and the plug is drawn to form a single core, the above method can be properly performed.

〔Example〕

FIG. 1 is a perspective view showing a superconducting wire which is a target product in the manufacturing method according to the present invention, that is, an end portion of the superconducting wire 1 according to the present invention.

In this superconducting wire 1, a plurality of superconducting filaments 11 are embedded over the entire length of a long stabilizing base material 80.

The stabilizing base material 80 is composed almost entirely of the high resistance stabilizing base material 12 in the length direction, and the low resistance stabilizing base material 13 is welded and bonded only to both ends. 14 is a joint surface by welding.

In the prior art, it was not possible to weld and join the high resistance stabilizing base material and the low resistance stabilizing base material without damaging the embedded superconducting filament 11, but the present invention is as follows. I made it possible to weld.

FIG. 5 is an explanatory view of the first stage of the manufacturing method according to the present invention.

A tube with a length of L ₁ made of CuNi, which is a material for high resistance stabilizing base material.
NbTi ingot 41, which is a material for superconducting filaments and which has a length dimension of L ₁ + 2L ₂ , constitutes 42 and both ends are L ₂
Project each one.

Where L ₁ >> L ₂ .

Two copper short cylinders 43 having the same diameter as the CuNi cylinder 42 and a length dimension longer than L ₂ (about twice) are formed, and are fitted onto both end protrusions of the NbTi ingot 41.

Before inserting the NbTi ingot 41 into the CuNi tube 42, the copper short tube 43 is friction welded 46 to both ends of the CuNi tube 42 in advance.

Further, covering the open end of the copper short tube 43, the copper plugs 44, 4
4'is connected by electron beam welding 45.

The assembled parts constructed in this way are
Call it 40.

Since the electron beam welding 45 is performed by placing the constituent members of the single billet 40 in the vacuum chamber, after welding, Nb
The outer circumference of the Ti ingot 41 is held in vacuum. Therefore, there is no possibility that an oxide film or a nitride film is formed on the surface of the ingot 41.

The single billet 40 is extruded and drawn by the hydrostatic extrusion device 70 shown in FIG.

This hydrostatic extrusion device 70 is a known device and is a container.
A billet 60 is put in a cylinder 63a formed in 63, the gap is filled with a pressure medium 62, a stem 64 is press-fitted, and the billet 60 is pushed out from a die 61. In the present case, the single billet 40 shown in FIG. 5 is used as the billet 60.

The NbTi ingot 41 and the CuNi cylinder 42 are joined by surface diffusion because they are subjected to a high pressure by the wire drawing action. Further, the NbTi ingot 41 and the copper short tube 43 are also joined by surface diffusion.

As mentioned above, the outer circumference of the NbTi ingot is kept in a vacuum and is in a clean state where no oxide film or nitride film is formed.Therefore, the above-mentioned surface diffusion bonding is completely performed without intervening contaminants, Has low electrical resistance.

Further, as can be easily understood from FIG. 5, when the electron beam welding 45 is performed, the electron beam does not hit the NbTi ingot 41. Therefore, there is no possibility that the NbTi ingot deteriorates the superconducting property.

Therefore, the superconducting wire of the embodiment has a CuNi tube 42 and its Cu
Both ends of the Ni tube 42 are welded along the axial direction, and Cu
Copper short cylinder 43 having the same outer diameter as the Ni cylinder 42, and the copper short cylinder
43 and NbTi ingot 41 inserted in CuNi tube 42
And a copper plug 44, 44 'which is capped by welding on each of the outer ends of the copper short pipe 43, and these CuNi pipe 42, copper short pipe 43, NbTi ingot 41, copper plugs 44, 44'. A single core is constructed by drawing an assembly member consisting of.

After the wire drawing work, the central portion C shown in FIG.
The portions corresponding to D and D ′ at both ends are cut off, leaving the portion corresponding to.

Such a single-core member that is drawn in the length dimension L ₁
Align + 2L ₂ into a bundle to form the bundle 49 of single wires shown in FIG. 7.

Then, a multi-billet 50 having a structure in which the NbTi ingot 41 of the single billet 40 shown in FIG. 5 is replaced by a bundle 49 of single wires is constructed, and again extruded and drawn by the hydrostatic extrusion device 70 shown in FIG. , The ends corresponding to D and D'are cut off, the multi-conductor superconducting wire 1 shown in Fig. 1
Is obtained.

In the present example in which the superconducting wire 1 according to the present invention was constructed by the manufacturing method of the present invention, the following effects were confirmed.

I. Superconducting wire At the manufacturing stage, the superconducting filament is not exposed to the atmosphere, so that a CuNi-based superconducting wire having copper-based materials on both ends can be obtained, which has good characteristics without losing the original superconducting characteristics.

II. Since the copper plug is electron beam welded, a vacuum in the billet can be easily obtained and no oxide or nitride intervenes.

III. Since the structure where the electron beam does not directly hit NbTi, Nb
It does not deteriorate the characteristics of the Ti edge.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, a tubular member made of a high-resistance stabilizing base material is formed, and a low-resistance stabilizing base material is provided at both ends of the tubular member. Welded end tubes made of steel, fit in the tubular member a superconducting filament material ingot that is longer than the tubular member and does not protrude from the short tube, and plugs into each of the short tubes. It is attached and welded, and the assembly member having the above configuration is drawn. Therefore, since the high resistance stabilizing base material and the low resistance stabilizing base material are welded in the state before wire drawing and then the wire drawing is performed, no chemical treatment such as pickling is required, and the superconducting filament is not necessary. There is no danger of degrading the material, and the superconducting filament material ingot is placed in a tube made of a stable base material of high resistance and low resistance,
Since the plugs are attached to each of the short cylinders made of low resistance stabilizing base material by welding, there is no risk of oxide film being formed on the superconducting filament material.As a result, the resistance is high at the time of OFF, the connection resistance of the connection part is small, Moreover, there is an effect that a superconducting wire that can obtain uniform superconducting properties over the entire length can be easily manufactured.

Further, according to the superconducting wire of the present invention, a tubular member made of a high resistance stabilizing base material and a short member having the same outer diameter as the tubular member are welded to both ends of the tubular member along the axial direction. A cylinder,
A superconducting filament material ingot that is inserted into the tubular member and the short tube and has a length that is longer than the tubular member and does not project from the short tube, and a plug that is capped by welding on each outer end of the short tube. However, since the single core is formed by drawing the assembly member including the tubular member, the short tube, the superconducting filament material ingot, and the plug, there is an effect that the above method can be appropriately performed.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a superconducting wire according to the present invention. FIG. 2 is a circuit diagram showing an example of an exciting circuit for a superconducting coil. FIG. 3 is an explanatory diagram of the permanent current switch. FIG. 4 is a cross-sectional view for explaining the superconducting wire connecting portion. FIG. 5 is a sectional view of a single billet in one embodiment of the method of the present invention, and FIG. 6 is a sectional view of the same hydrostatic extrusion device.
FIG. 7 is a sectional view of the same multi-billet. 1 ... Superconducting wire for permanent current switch, 2 ... Permanent current switch, 3 ... Superconducting coil, 4 ... Protective resistance, 5 ...
Excitation current circuit breaker, 6 ... Excitation power supply, 7 ... Connection, 8 ...
… Solder, 11 …… Superconducting filament of superconducting wire for permanent current switch, 12 …… Superconducting wire high resistance stabilizing base material for permanent current switch, 13 …… Superconducting wire low resistance stabilizing base material for permanent current switch, 14… … Stabilized substrate joint surface, 21 …… Permanent current switch body, 22 …… Permanent current switch heater, 23 ……
Heater switch, 24 ... Heater power supply, 31 ... Superconducting coil lead wire, 32 ... Superconducting filament of superconducting coil wire, 33 ... Superconducting coil wire stabilizing material, 40 ... Single billet, 41 ... NbTi ingot , 42 …… CuNi tube,
43 …… Copper short tube, 44,44 ′ …… Copper plug, 45 …… Electron beam welding, 46 …… Friction welding, 49 …… Single wire, 50 ……
Multi billet, 60 …… billet, 61 …… dice, 62…
… Pressure medium, 63 …… Container, 64 …… Stem.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Sato 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (56) References JP-A-61-224218 (JP, A) Actually open 60-60102 (JP, U)

Claims (4)

[Claims] 1. A superconducting filament in which a low resistance stabilizing base material is electrically connected to both ends of a high resistance stabilizing base material, and the low resistance stabilizing base material and the high resistance stabilizing base material are penetrated. In the method of manufacturing a superconducting wire in which the above is embedded, a tubular member made of a high resistance stabilizing base material is configured, and a short tube made of a low resistance stabilizing base material is welded to both ends of the tubular member. In the tubular member, a superconducting filament material ingot longer than the tubular member and having a length that does not protrude from the short tube is fitted, and a plug is capped and welded to each of the short tube, A method of manufacturing a superconducting wire for a thermal permanent current switch, which comprises drawing an assembly member having the above structure. 2. A superconducting filament in which a low resistance stabilizing base material is electrically connected to both ends of a high resistance stabilizing base material, and the low resistance stabilizing base material and the high resistance stabilizing base material are penetrated. In the method of manufacturing a superconducting wire in which the above is embedded, a tubular member made of a high resistance stabilizing base material is configured, and a short tube made of a low resistance stabilizing base material is welded to both ends of the tubular member. In the tubular member, a superconducting filament material ingot longer than the tubular member and having a length that does not protrude from the short tube is fitted, and a plug is capped and welded to each of the short tube, The assembly member consisting of the configuration is drawn to form a tubular member made of a high resistance stabilizing base material, and a short tube made of a low resistance stabilizing base material is welded to both ends of the tubular member, respectively, Cut the drawn material into a length that is longer than the tubular member and does not protrude from the short tube. Then, this is bundled and housed in the tubular member, and a plug is capped and welded to each of the short tubes, and the assembly member having the above configuration is drawn. Method of manufacturing superconducting wire for permanent current switch. 3. A superconducting filament in which a low resistance stabilizing base material is electrically connected to both ends of a high resistance stabilizing base material, and the low resistance stabilizing base material and the high resistance stabilizing base material are penetrated. In a superconducting wire formed by embedding, a tubular member made of a high resistance stabilizing base material, and a short tube having the same outer diameter as the tubular member, which are welded to both ends of the tubular member along the axial direction. A superconducting filament material ingot that is inserted into the tubular member and the short tube and has a length longer than the tubular member and does not protrude from the short tube, and a plug capped by welding on each outer end of the short tube. Have these tubular members,
A superconducting wire for a thermal permanent current switch, characterized in that an assembly member consisting of a short cylinder, a superconducting filament material ingot and a plug is drawn to form a single core. 4. A superconducting filament in which a low resistance stabilizing base material is electrically connected to both ends of a high resistance stabilizing base material, and the low resistance stabilizing base material and the high resistance stabilizing base material are penetrated. In a superconducting wire formed by embedding, a first cylindrical member made of a high-resistance stabilizing base material, and welded to both ends of the cylindrical member along the axial direction, and having the same outer diameter as the first cylindrical member. And a first tubular member having a plurality of single cores inserted into the first tubular member and the first tubular member and having a length longer than the first tubular member and not protruding from the first tubular member. An assembly member that includes a bundle and a first plug that is welded to the outer ends of the first short cylinder, and that includes the first tubular member, the first short cylinder, the single core bundle, and the first plug. To form a multi-core bundle, and each of the single-core bundles includes a second tubular member made of a high-resistance stabilizing base material and a second tubular member. A second short cylinder having the same outer diameter as the second cylindrical member, which is welded to both ends along the axial direction, and is inserted into the second cylindrical member and the second short cylinder. Also has a superconducting filament material ingot of a length that is also long and does not protrude from the second short cylinder, and a second plug that is capped by welding to each of the outer ends of the second short cylinder. A superconducting wire for a thermal permanent current switch, characterized in that an assembly member consisting of two short cylinders, a superconducting filament material ingot, and a second plug is drawn to form a single core.