JP3701985B2 - Oxide superconducting current lead - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a superconducting current lead, and more particularly to an oxide superconducting superconducting current lead imparted with durability against mechanical shock or the like.
[0002]
[Prior art]
As is well known, with the advent of oxide superconductors, the critical temperature of superconducting materials has exceeded the liquid nitrogen temperature of 77.3 K. If these oxide superconductors exhibit superconducting characteristics comparable to those of conventional metal superconductors when cooled with liquid nitrogen, the application range is expected to be greatly expanded. That is, the metal superconductor requires liquid helium cooling, and the cooling means using liquid nitrogen can be simplified as compared with the liquid helium cooling that requires advanced cryogenic technology. .
A potential lead field of the oxide superconductor is a current lead. For example, in an MRI apparatus using a superconducting magnet or a magnetically levitated superconducting device, a power supply in a room temperature region and a superconducting magnet in a cryogenic region (immersed in liquid helium) are electrically connected to supply a required current. Current leads are used for this purpose. For this type of current lead, attention is focused on low resistance, and copper leads are generally used. However, because of the high thermal conductivity, there is a large amount of steady heat penetration due to conduction. = Joule heating of I ² × R (I is the current carrying current and R is the resistance of the current lead). Here, as the energization current I increases, a larger amount of Joule heat is generated, leading to evaporation or consumption (consumption) of liquid helium. Therefore, a countermeasure to reliquefy the evaporated liquid helium is required. In other words, a large amount of heat penetration through the current leads not only increases the cost of the system or system, but also increases the size of the refrigerating mechanism (such as the refrigerator) for low liquefaction, resulting in low power consumption. -There is a problem that the advantages of superconductivity such as small size and light weight cannot be fully utilized.
[0003]
Attempts have been made to use oxide superconducting ceramics as current leads as a solution to the problems caused by heat penetration from the current leads. That is, when the current lead is formed of an oxide superconducting ceramic, the current lead is disposed (installed) in a low temperature region below the critical temperature of the oxide superconducting ceramic, so that the electric resistance is zero and no Joule heat is generated. In addition, since the thermal conductivity is much smaller than that of copper, the heat intrusion into the superconducting device is suppressed, so that the evaporation of liquid helium can be reduced / prevented. FIG. 3 shows an example in which oxide superconducting ceramics is used as a current lead. 1 is a cryostat, 2 is a superconducting magnet housed and mounted in the cryostat 1, and 3 is dipping and cooling the superconducting magnet 2. Liquid helium 4 is a copper lead connected to the power source outside the cryostat 1, 5 is a liquid nitrogen tank through which the copper lead 4 is inserted and cooled, and 6 is an oxide connecting the superconducting magnet 2 and the copper lead 4. Each superconductor lead is shown. Here, the lead 6 made of an oxide superconductor generally has a copper terminal 6b directly connected to both ends of a linear or plate-like oxide superconductor 6a as schematically shown in FIG. The arrangement is taken.
[0004]
[Problems to be solved by the invention]
As mentioned above, problems based on heat penetration through copper current leads can be greatly eliminated by using oxide superconductors as current leads. That is, in the case of oxide superconductors (ceramics), the thermal conductivity is not less than an order of magnitude less than that of copper, and if it is cooled below the critical temperature, no Joule heat is generated. It can function well as a current lead. In other words, by utilizing the low thermal conductivity characteristic, the current at room temperature is obtained by connecting the superconducting wire in the cryogenic region and the current lead terminal at room temperature with the current lead made of oxide superconductor. A required current can be supplied from the lead terminal while preventing heat from entering the superconducting wire at a very low temperature.
[0005]
By the way, in the usage mode of the oxide superconductor-based current lead 6, the smaller the diameter and the longer the heat penetration is reduced, so the use of the oxide superconductor (wire) 6 a as long as possible is desired. It is. However, unlike a metal, an oxide superconductor generally hardly undergoes plastic deformation, and its bending and tensile strength is only about 10 kg / mm ² . Therefore, if the oxide superconductor wire with a reduced diameter is exposed to the outside, it will be damaged due to mechanical stress such as bending or pulling, especially cracking or breaking due to impact. The fear is remarkable and the utilization as a current lead is inhibited.
[0006]
For this mechanical problem, as shown in a cross-sectional view in FIG. 5, the oxide superconductor current lead 6 is inserted into a protective tube 7 made of metal such as stainless steel having high mechanical strength in an electrically insulating manner.・ A configuration to be installed is also being studied. However, in the case of the strength reinforcement measure using the protective tube 7, the oxide superconductor 6a is subjected to a large strain and breaks during cooling due to the difference in heat shrinkage between the protective tube 7 and the oxide superconductor 6a. There is a concern that it is easy, and effective means have not been developed yet. For example, looking at thermal shrinkage at -196 ° C (77 K), silver-coated Bi-based oxide superconductor wire: -0.14%, stainless steel: -0.27%, and fiber reinforced resin (GFRP) support material:- Due to the difference in heat shrinkability, the heat shrinkage distortion has a great influence and breakage easily occurs. For example, if a 100mm long current lead and a SUS (stainless steel) protective tube are used, the difference in thermal shrinkage will be 0.13% (0.13mm), and if the oxide superconductor does not deform, 20 kgf / mm Problems such as breakage due to stress of ² or more occur.
[0007]
The present invention has been made in view of the above circumstances, and improves mechanical characteristics, prevents breakage, cracks and superconductivity deterioration due to strain and stress generated during cooling, and provides a highly reliable current. An object of the present invention is to provide an oxide superconducting current lead that can always exhibit a current-carrying function.
[0008]
[Means for Solving the Problems]
The first oxide superconducting current lead according to the present invention comprises an oxide superconductor lead main body, a flexible superconductor, and a conductor lead portion disposed on the low temperature region side of the oxide superconductor lead main body. Connecting one end of the conductor lead portion in series to the low temperature region side end of the oxide superconductor lead body, and holding the end portion of the oxide superconductor lead body; and Oxide superconductor lead main body, connecting portion and conductor lead portion are inserted and attached in a form spaced from the inner wall surface to protect the peripheral surface portion, and connected to the other end of the conductor lead portion, the protection A first connection terminal portion that is electrically insulated and integrated with the tube, and is connected to a high-temperature region side end portion of the oxide superconductor lead body, and is electrically insulated and integrated with the protective tube; Second connection end It is characterized by comprising a part.
The second oxide superconducting current lead according to the present invention comprises an oxide superconductor lead body and a flexible superconductor, and is a first conductor disposed on the low temperature region side of the oxide superconductor lead body. a lead portion made of a superconductor having a flexible property, the oxide superconductor and the second conductor lead portion disposed in the hotter regions of the lead body, the oxide superconductor lead body of the low-temperature region side end portion A first connecting portion for connecting one end portion of the first conductor lead portion in series and holding the low temperature region side end portion of the oxide superconductor lead body, and the oxide superconductor lead. A second connection portion for connecting one end portion of the second conductor lead portion in series to the high temperature region side end portion of the main body and holding the high temperature region side end portion of the oxide superconductor lead main body; the oxide Conductor lead body, the first connecting portion and second connecting portion, the protective tube for protecting an insertion-mounting to the peripheral surface at spaced form the first conductor lead portions and the second conductor lead portions from the inner wall surface A first connection terminal portion connected to the other end portion of the first conductor lead portion and electrically insulated and integrated with the protective tube; and the other end portion of the second conductor lead portion. And a second connection terminal portion that is connected to the end portion and is electrically insulated and integrated with the protective tube .
[0009]
That is, the present invention has a configuration in which a conductor lead portion having flexibility made of a superconductor is connected in series to at least one end side with respect to an oxide superconductor lead body for current conduction inserted and mounted in a protective tube. The main point is to absorb the distortion caused by the difference in heat shrinkability between the oxide superconductor lead body and the protective tube.
[0010]
In the present invention, the oxide superconductor lead body and the flexible conductor lead portion are inserted and mounted in a form separated from the inner wall surface, and as a protective tube contributing to mechanical protection, for example, a fiber reinforced resin tube Body, polyfluoroethylene resin cylinder, ceramic cylinder, or metal cylinder subjected to electrical insulation treatment. Here, as the ceramic cylinder, for example, an alumina cylinder or a magnesia cylinder, and as the metal cylinder, for example, a copper alloy such as stainless steel, copper or brass, aluminum, zinc, tin or the like. Generally, a non-magnetic material such as an alloy is preferable, but a magnetic material such as iron, cobalt, nickel, or an alloy thereof may be used. The cross-sectional shape may be a polygon such as a circle, an ellipse, or a rectangle. Moreover, if a through hole is appropriately drilled or a slit is formed in the side wall surface of the protective tube, the amount of heat penetration due to heat conduction through the protective tube can be reduced. Moreover, the assembly of the current leads is simplified, and it is convenient for the arrangement of the measurement lines.
[0011]
In the present invention, the oxide superconductor constituting the oxide superconductor lead body includes, for example, a La-based oxide superconductor, a Y-based oxide superconductor, a Bi-based oxide superconductor, and a Tl-based oxide superconductor. Can be mentioned. The shape of the oxide superconductor lead main body may be a columnar shape, a prismatic shape, a plate shape, a cylindrical shape, or a linear shape, and the form thereof is not formed solely by the oxide superconductor, for example, A silver sheath coating type or a configuration in which an oxide superconductor is coated using a conductive metal or ceramic as a support may be employed.
[0012]
Furthermore, in this invention, the conductor lead part which has flexibility consists of a superconductor . Here, as the superconductor, for example, Nb ₃ Sn-based, Ru include NbTi based and metal-based superconductors. And the said flexibility can be provided by taking the form of a conductor lead part, for example, a spring shape, zigzag-shaped bending, or a mesh shape. The conductor lead portion having flexibility is connected in series to at least one end side of the oxide superconductor lead body and functions as a conductive lead . The conductor lead portion made of a metallic superconductor is connected to the superconducting device side ( It is desirable to install on the low temperature side. It is more effective to provide both of these (see FIG. 1B). In addition, a spacer may be arranged so that the lead does not vibrate within the protective tube.
[0013]
Furthermore, the oxide superconductor lead according to the present invention connects at least one of the power supply connection side and the superconducting device connection side, for example, a flexible conductor such as a mesh conductor, in series outside the part integrated with the protective tube. In this case, the distortion caused by the heat shrinkage between the current lead and a superconducting device (such as a superconducting magnet) connected to the current lead via a flexible conductor is also possible. New effects such as absorption and elimination of adverse effects due to external impact can be obtained.
[0014]
[Action]
As described above, according to the present invention, an oxide superconductor is used as a lead body, and a flexible conductor lead portion is connected to the lead body in series, and these are inserted and attached in a protective tube in a non-contact manner with the inner wall surface. It is composed. By adopting such a configuration, it is possible to easily reduce the amount of heat penetration into liquid helium (very low temperature region) in which the superconducting magnet is immersed. On the other hand, this oxide superconductor lead body is protected from mechanical shocks from the outside by a protective tube on the outer peripheral surface side along the axial direction. In other words, mechanical stress applied from the outside, such as bending and pulling, is blocked by the protective tube, reducing the mechanical load applied to the oxide superconductor lead body, and breaking or breaking due to mechanical shock from the outside. Will be easily avoided. In addition, the difference in thermal shrinkage between the protective tube and the oxide superconductor lead body during cooling is easily and reliably absorbed by the flexible portion of the conductor lead connected in series with the oxide superconductor lead body. Vibrations are also suppressed by the above. Therefore, the oxide superconductor lead body due to the difference in heat shrinkability is prevented or avoided, so that it has high reliability and superconducting characteristics in combination with the reduction of the heat penetration amount. It can function as a superconducting current lead.
[0015]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 (a), 1 (b) and FIG.
[0016]
Example 1
FIG. 1 (a) shows an example of the structure of an oxide superconducting current lead according to the present invention in a cross-sectional view in the axial direction. Reference numeral 8 denotes an oxide superconductor lead body for current conduction, for example, about 5 mm in diameter, long The three Y-based oxide superconductor rods 8a and 9 having a thickness of about 100 mm are flexible conductive leads electrically connected in series to the Y-based oxide superconductor lead body 8 through a copper connecting portion 8b. NbTi-based superconducting wire wound in a coil shape, for example, 10 is a cylinder in which the Y-based oxide superconductor lead body 8 and flexible conductive lead portion 9 are inserted and arranged in a form separated from the inner wall surface Insulating protective tube, for example, a cylindrical body made of fiber reinforced resin having an outer diameter of mm, an inner diameter of mm, and a length of mm. In FIG. 1 (a), 8c and 8d are connection terminal portions, 11 is a flexible lead wire for connecting in series between one connected portion 12a and the connection terminal portion 8c, The spacer is interposed between the peripheral surface of the connection portion 8b and the inner wall surface of the protective tube 10, and prevents the connection portion 8b from shaking.
[0017]
The oxide superconducting current lead 14 is configured by the following procedure. First, the Y-based oxide superconductor rod 8a, a connecting portion 8b for concentrically connecting and holding one end of the Y-based oxide superconducting rod 8a, and a conductive material having one end connected to the connecting portion 8b The lead part 9, the terminal part 8c to which the other end side of the conductive lead part 9 is connected, the terminal part 8d for concentrically connecting and holding the other end side of the Y-based oxide superconductor rod 8a, and the axial direction are divided into two. (Vertical) Prepare a fiber reinforced resin cylindrical body (protection tube) 10 as a material.
[0018]
Next, a flexible conductive lead portion in which one end side of the Y-based oxide superconductor rod 8a is convergedly connected to the connecting portion 8b, and the other end is connected in advance to the terminal portion 8c. One end side of 9 is electrically connected. Further, the other end side of the Y-based oxide superconductor rod 8a is intensively connected to the terminal portion 8d to assemble the lead body portion. After that, the lead main body portion is coaxially disposed and integrated in the fiber reinforced resin cylindrical body (protection tube) 10 with the spacers 13 being arranged, if necessary, so that the oxide superconducting current leads 14 are formed. Constitute. The superconducting current lead 14 assembled and configured in this way is used with the connecting terminal portion 8c connected to, for example, the superconducting magnet side (low temperature side) and the connecting terminal portion 8d connected to the external power supply side (high temperature side). The
[0019]
The Y-based oxide superconducting rod 8a used for the structure of the oxide superconducting current lead is manufactured as follows. That is, Y ₂ O ₃ , BaCO ₃ , and CuO were used as raw materials, prepared and mixed at a ratio of Y: Ba: Cu = 1: 2: 3, and calcined at 900 ° C. for 50 hours. In the temperature lowering process at the end of the calcination, a superconducting phase was generated, and the temperature was slowly decreased from 600 ° C. to 400 ° C. at a rate of 2 ° C./min. The calcined powder obtained in this way was finely crushed and compacted to a diameter of 5 mm and a length of 100 mm using a pressing jig. This compacted body is subjected to a primary heat treatment at 925 ° C x 200 h in the atmosphere, followed by an intermediate press, and then a silver paste is applied to the end, and then a heat treatment is again carried out at 925 ° C x 200 h. Y-based oxide superconductor rod 8a was obtained. With respect to this Y-based oxide superconductor rod 8a, the critical current Ic was measured by the four probe method in liquid nitrogen. As a result, a value of Ic = 80 A was shown.
[0020]
The oxide superconducting current lead with the above configuration was evaluated using the 77K-4.2K part of the lead with liquid nitrogen anchor, and the current penetration of 200A was reduced while the heat penetration amount was reduced to about 1/4 of the copper lead. Has been confirmed to be able to flow stably.
[0021]
In the above configuration, the conductive lead portion 9 having flexibility is connected in series to one end side of the oxide superconducting current lead main body 8, but as shown in FIG. 1B, for example, the oxide superconducting current lead main body. It is also possible to adopt a configuration in which conductive lead portions 9 having flexibility are respectively connected in series to both end sides of 8, and similar actions and effects can be obtained .
[0022]
Reference example 1
Figure 2 is a configuration Zorei oxide superconducting current lead as reference example, those shown in the axial direction in cross section, 8 oxide superconductor lead body for current conduction, for example a diameter of about 5mm, length Bi-based oxide superconductor rod of about 50 mm, 9 'is a flexible conductive lead portion electrically connected in series to the Bi-based oxide superconductor lead body 8 via a copper connection portion 8b, for example, copper A braided wire 10 ′ is a cylindrical insulation in which the Bi-based oxide superconductor lead body 8 and a flexible conductive lead portion 9 ′ are inserted and arranged in a manner spaced from the inner wall surface. Protective tube, for example , a cylindrical body made of stainless steel with an outer diameter of 17 mm, an inner diameter of 15 mm, and a length of 100 mm, which is insulated. In FIG. 2, 11 is a flexible lead wire that connects in series between one connected portion 12a and 12a 'and the other connected portion 12b and 12b'. The superconducting current lead 14 is configured in the following procedure. First, the Bi-based oxide superconductor rod 8, a connecting portion 8b connected to and held at one end of the Bi-based oxide superconductor rod 8a, and a flexible conductive lead portion 9 having one end connected to the connecting portion 8b. ', A copper terminal portion (high temperature side) 8d connected to the other end side of the conductive lead portion 9', a terminal portion (low temperature side) 8c connected to the other end side of the Bi-based oxide superconductor rod 8a, and a shaft A stainless steel cylinder (protection tube) 10 'divided into two in the direction (vertically divided) is prepared as a material.
[0023]
Next, one end side of the Bi-based oxide superconductor rod 8a is connected to the connecting portion 8b, and the connecting portion 8b and the other end of the conductive lead portion 9 'having flexibility are previously connected to the terminal portion 8d. One end side is electrically connected. Further, the other end side of the Bi-based oxide superconductor rod 8a is connected to the terminal portion 8c to assemble the lead body portion. Thereafter, the lead body is coaxially disposed on the stainless steel cylindrical body (protective tube) 10 ′, and the divided pieces constituting the protective tube 10 ′ are electrically insulated by, for example, the terminal portions 8c and 8d. The superconducting current lead 14 is formed by bolting 15 and integrating them. The superconducting current lead 14 assembled and configured in this way has the connecting terminal portion 8c on the superconducting magnet side (low temperature side), the connecting terminal portion 8d on the external power source side (high temperature side), and the flexible part, Connected to each other.
[0024]
The Bi-based oxide superconducting rod 8a used for the configuration of the oxide superconducting current lead is manufactured as follows. In other words, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO are used as raw materials, and prepared and mixed at a ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2 at 800 ° C., 20 h Calcination was performed. The calcined powder thus obtained was finely pulverized and formed into a rod shape having a diameter of 7 mm and a length of 100 mm by cold isostatic pressing. This compact is sintered in the atmosphere at 840 ° C for 50 h, and then the bulk crystal is oriented in the longitudinal direction by melt growth in the floating melting method using this sintered rod as a raw material rod and a CO ₂ laser as the heating source. A 5 mm diameter Bi-based oxide superconductor rod was obtained. This Bi-based oxide superconductor rod was cut out to a length of 50 mm, a silver paste was applied to the end portion 10 mm, and baked to obtain a Bi-based oxide superconductor rod 8a. With respect to this Bi-based oxide superconductor rod 8a, the critical current Ic was measured in liquid nitrogen by the four-terminal method, and a value of Ic = 150 A was shown.
[0025]
When the oxide superconducting current lead 14 with the above configuration is used for the 40 K-4.2 K portion of the current lead of the superconducting magnet cooled by the refrigerator, the heat penetration amount is reduced to about 1/10 of the copper lead. However, it was confirmed that a current of 130 A could be flowed stably.
[0026]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the protective tubes 10 and 10 'are not limited to a cylindrical shape, and may have a polygonal shape such as a square cross section. That is, the cross-sectional shape of the oxide superconducting lead main body or the like is not particularly limited as long as it can be inserted into and attached to the inner wall surface in a contacted manner.
[0027]
【The invention's effect】
As described above, according to the superconducting current lead according to the present invention, the oxide superconducting lead body for current application is provided by a protective tube that is spaced apart along the axial direction on the peripheral surface of the superconducting lead body. While the oxide superconductor lead body weak in mechanical strength is protected, thermal contraction in the axial direction or the like is easily absorbed by the flexible current lead portion. That is, the oxide superconductor lead body through which a current is passed is shielded from mechanical external force from the direction perpendicular to the length direction, so that the possibility of breakage due to mechanical impact is eliminated. Further, the difference in thermal contraction between the protective tube and the oxide superconductor lead body during cooling is easily and reliably absorbed by the flexible portion of the conductor lead connected in series with the oxide superconductor lead body. Therefore, cracks and breakage of the oxide superconductor lead body due to the heat shrinkage difference are prevented or avoided. In addition, since heat intrusion from the outside can be reduced, it can greatly contribute to reduction of power consumption of the cooling mechanism required for maintaining (holding) the cryogenic temperature.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views in the axial (length) direction showing different configuration examples of main parts of an oxide superconducting current lead according to the present invention.
FIG. 2 is a cross-sectional view in the axial (length) direction showing another configuration example of the main part of the oxide superconducting current lead according to the present invention.
FIG. 3 is a cross-sectional view showing the main configuration of a superconducting device equipped with a conventional superconducting current lead.
FIG. 4 is a cross-sectional view showing a configuration example of a main part of a conventional superconducting current lead.
FIG. 5 is a cross-sectional view showing another configuration example of a main part of a conventional superconducting current lead.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cryo stud 2 ... Superconducting magnet 3 ... Liquid helium 4 ... Copper lead 5 ... Liquid nitrogen tank 6, 14 ... Oxide superconductor current lead 7, 10 '... Metal protective tube 8 ... Oxide superconductor current lead body 8a ... Oxide superconducting rod 8b ... Connecting part 8c, 8d ... Connecting terminal part 9 ... Flexible conductive lead part 10 ... Protection tube made of insulating resin 11 ... Lead wire 12a, 12b, 12a ', 12b' ... Connected part 13 …spacer

Claims (2)

An oxide superconductor lead body;
A conductor lead portion made of a superconductor having flexibility, and disposed on a low temperature region side of the oxide superconductor lead body ,
With connecting one end of the front Kishirube lead section in series to the low-temperature region side end portion of the oxide superconductor lead body, and a connecting portion for holding said end portion of said oxide superconductor lead body ,
A protective tube for protecting the oxide superconductor lead body, connecting portion Oyo insertion in a manner spaced from the inner wall surface beauty guide lead section-mounted to the peripheral surface,
A first connection terminal portion connected to the other end portion of the conductor lead portion and electrically insulated and integrated with the protective tube;
An oxide superconducting current comprising: a second connection terminal portion connected to an end portion on a high temperature region side of the oxide superconductor lead body and electrically insulated and integrated with the protective tube. Lead. An oxide superconductor lead body;
A first conductor lead portion made of a superconductor having flexibility and disposed on a low temperature region side of the oxide superconductor lead body;
A second conductor lead portion made of a superconductor having flexibility and disposed on a high temperature region side of the oxide superconductor lead body;
One end of the first conductor lead is connected in series to the low temperature region side end of the oxide superconductor lead body, and the low temperature region side end of the oxide superconductor lead body is held. A first connection;
One end portion of the second conductor lead portion is connected in series to the high temperature region side end portion of the oxide superconductor lead body, and the high temperature region side end portion of the oxide superconductor lead body is held. A second connection;
The oxide superconductor lead body, the first connection portion and the second connection portion, the first conductor lead portion and the second conductor lead portion are inserted and attached in a form separated from the inner wall surface to protect the peripheral surface portion. A protective tube,
A first connection terminal portion connected to the other end portion of the first conductor lead portion and electrically insulated and integrated with the protective tube;
A second connection terminal portion connected to the other end of the second conductor lead portion and electrically insulated and integrated with the protective tube;
An oxide superconducting current lead comprising:

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