JP5022279B2 - Oxide superconducting current lead - Google Patents

Description

  The present invention relates to a low-temperature device using superconductivity, for example, a current lead using an oxide superconducting wire for supplying current from a power source to a superconducting magnet.

  When operating a superconducting application device, for example, a superconducting magnet, it is necessary to cool the magnet to a cryogenic temperature in order to bring the magnet into a superconducting state, and two methods are known as this cooling method. That is, a method of immersing in a refrigerant such as liquid helium or liquid nitrogen (immersion cooling method) and a method of utilizing heat conduction from a refrigerator or a refrigerant (conduction cooling method). In order to excite the cooled magnet, a current must be passed through the superconducting coil, and a current lead for supplying current from the power source is required. In this case, the current lead needs to be a conductor, but if a metal such as Cu or Al with low electrical resistance and high thermal conductivity is used, in addition to Joule heating of the current lead itself, external heat penetration As a result, the cooling efficiency of the superconducting magnet deteriorates, and there is a problem that the cooling cost becomes enormous in order to maintain the superconducting state. In particular, this tendency is remarkable in the case of a conduction cooling system using a refrigerator, and cooling may be impossible.

  In order to solve this problem, it is necessary to achieve both conductivity and low thermal conductivity as the current lead used in the superconducting magnet. In the superconducting magnet, the current lead part is also cooled below the liquid nitrogen temperature. By using an oxide superconductor having a low thermal conductivity as a current lead, the amount of heat penetration can be suppressed while supplying current.

In this case, as a superconductor used for the superconducting current lead, Bi (2223) -based or Bi (2212) -based Bi-based and Re-based oxide superconductors typified by YBa ₂ Cu ₃ O _y (YBCO) are used. Silver sheath wire with a high critical current density (Jc) of a superconductor portion coated with silver or a silver alloy has been used in which a bulk body is formed into a rod shape or a cylindrical shape, and a superconducting filament is contained in a silver matrix. A tape-shaped current lead in which a large number of wires are arranged is known (for example, see Patent Document 1).

  When the former oxide superconductor bulk body is used for a current lead, the bulk body is brittle and its mechanical strength is low, which causes problems in its manufacture and use. That is, the bulk body itself is not flexible and has a problem that it is damaged when a bending strain of a certain level or more is applied. For this reason, the current lead is attached only in a linear direction, and handling and magnets during attachment work are also included. In order to avoid the application of strain due to vibration during operation, it has been necessary to provide a structure in which strain is not transmitted to the bulk body, such as by providing a flat knitted wire on the electrode portion.

  In addition, the latter silver or silver alloy sheath wire needs to be formed into a tape shape by rolling to increase the crystal orientation, and therefore a silver or silver alloy sheath with a certain thickness is required. Since the sheath material is made of silver or a silver alloy having a very high thermal conductivity, there is a drawback in that the thermal conductivity of the current lead itself is increased.

  On the other hand, as a current lead, the use of a tape-shaped superconductor in which an oxide superconducting layer is provided on a metal substrate has been studied, and a tape-shaped superconducting current lead in which an oxide superconductor and a silver tape are alternately laminated. (For example, refer to Patent Documents 2 and 3). Even in this case, there is a problem that the thermal conductivity of the current lead itself increases.

  Furthermore, a tape having an intermediate layer formed on a metal substrate, an oxide superconducting layer formed on the intermediate layer, and a stabilizing layer (protective layer) such as silver formed on the oxide superconducting layer. An oxide superconducting wire is known (see, for example, Patent Document 4). This tape-shaped oxide superconducting wire has a high critical current value and is a Ni-based alloy that is usually used as a metal substrate. Compared to silver or silver alloy, the substrate has a thermal conductivity as small as about 1/4, and the mechanical strength of this Ni-based alloy substrate is very large and easy to handle, leading to an oxide superconducting current lead. It can be said that it is a wire rod suitable for application.

  Of these tape-shaped oxide superconducting wires, especially Re-based (Re = Y, Gd, etc.) oxide superconductors have a characteristic of maintaining a high critical current value (Ic) even in a high magnetic field, and are formed in a tape shape. However, since the high characteristics are maintained, it can be said that the wire is very suitable for application to an oxide superconducting current lead.

JP-A-9-115356 Japanese Patent Laid-Open No. 5-243044 JP-A-6-28930 JP 2004-171841 A

  However, since the Re-based oxide superconductor uses a high-resistance metal substrate such as Hastelloy (registered trademark) and a thin stabilization layer (protective layer) such as silver, the conduction current exceeds the Ic of the superconducting layer and is always in a superconducting state. When transitioning to the conductive state, a phenomenon (quenching) in which the electrical resistance increases at once occurs, and a phenomenon occurs in which the wire is melted by rapid heat generation.

  In general, it is known that quenching of a superconducting wire is likely to occur when there is a defect such as a crack in the superconducting layer or when there is a part where the cooling is insufficient in a part of the energizing section. In addition, when a plurality of superconducting wires are bundled and used on the current lead, originally, an energization amount corresponding to (Ic × number of wires) is expected, but the connection at the electrode portion is insufficient. If a uniform current is not supplied to the wire and current flows only in a specific wire, overcurrent is supplied to some wires before reaching the amount of current that is equal to (Ic x number of wires) It is a problem that quenching occurs.

  The present invention has been made in order to solve the above-mentioned problems, and an oxide superconducting current lead that prevents the occurrence of quenching at the time of energization is prevented by preventing a drift that easily occurs at the connection portion between the superconducting wire and the current terminal. Its purpose is to provide.

In order to solve the above problem, the oxide superconducting current lead of the present invention is a current lead for supplying power from a power supply source to a superconducting device, and the current lead includes a current lead support, A current terminal made of a conductive material bonded to both ends of the current lead support, and a plurality of tape-shaped oxide superconducting wires connected between the current terminals. The oxide superconducting wire and the current terminal The connection resistance of each connection portion is 0.1 μΩ or less , and each connection length between each current terminal and the tape-shaped oxide superconducting wire connected between each current terminal is equal to that of the tape-shaped oxide superconducting wire. is obtained by the width of three times or more, in particular, it is preferable to less 0.05μΩ the connection resistance of the connection part.

As the tape-shaped oxide superconducting wire in the above invention, a ReBa _x Cu ₃ Oy-based oxide superconducting wire having a superconducting layer and a stabilizing layer laminated on an Ni-based alloy substrate such as Hastelloy via an intermediate layer (Here, Re represents one or more elements selected from Y, Gd, Sm, Nd, Ho, Dy, Eu, Tb, Er, and Yb, and x ≦ 2, y = 6. 2 to 7. The same applies hereinafter), and it is particularly preferable to use a YBa _x Cu ₃ O _y (YBCO) superconducting wire.

Another oxide superconducting current lead of the present invention is an electrically insulating and non-magnetic FRP (fiber reinforced plastic), ceramic or nitride cylindrical or column current lead support, A current terminal made of a conductive material bonded to both ends of the current lead support, and a plurality of tape-shaped ReBas arranged on the current lead support with the substrate surface facing outside and connected between the current terminals. _x Cu ₃ O _y- based oxide superconducting wire, the connection resistance of each connection portion of the oxide superconducting wire and the current terminal is 0.1 μΩ or less, and the connection length of each connection portion is tape-shaped. It is more than three times the width of the oxide superconducting wire, and at each connecting portion, (radius of current lead support / thickness of tape-like oxide superconducting wire) ≧ 50 That.

In the above oxide superconducting current lead, a cylindrical or columnar current lead support made of an electrically insulating and non-magnetic material and a conductive material bonded to both ends of the current lead support, respectively. Cylindrical or columnar current lead support made of any one of copper or copper alloy, aluminum or aluminum alloy, stainless steel alloy, Ni-base alloy or titanium alloy having an electrically insulating layer on the surface instead of the current terminal It is also possible to use current terminals made of a conductive material joined to both ends of the body and the current lead support through intermediate members made of electrically insulating GFRP .

  According to the present invention, by making the connection resistance of each connecting portion of each oxide superconducting wire and current terminal within a predetermined range, it is possible to prevent the drift that easily occurs at the connecting portion between each superconducting wire and each current terminal. In addition, since the currents flowing through the individual wires can be made uniform, a highly stable oxide superconducting current lead that prevents the occurrence of quenching during energization can be obtained.

  FIG. 1 is a plan view of an oxide superconducting current lead 10 of the present invention, and FIG. 2 is a sectional view including the axial direction thereof.

1 and 2, the oxide superconducting current lead 10 has a copper or copper alloy, aluminum or aluminum alloy, stainless steel alloy having an electrically insulating layer (not shown) such as Kapton tape (registered trademark) on the surface thereof. A cylindrical current lead support 1 made of any one of an Ni-base alloy and a titanium alloy, and an electric insulation having the same diameter as the current lead support 1 at both ends of the current lead support 1 and low thermal conductivity Rectangular connection terminal portions 4b and 5b are integrally provided at one ends of discs 4a and 5a having the same diameter as the current lead support, respectively. and a current terminal 4 and 5 made of a conductive material, current lead support 1 on a plurality of tape-shaped ReBa _x Cu ₃ O _y based oxide superconducting wire a is to the substrate surface to the outside It is location. Each superconducting wire A is connected between the current terminals 4 and 5, and is configured such that the connection resistance of each connecting portion between the oxide superconducting wire A and the current terminals 4 and 5 is 0.1 μΩ or less.

  A cylindrical or flat support can be used in place of the cylindrical current lead support 1, and the current lead support 1 is made of an electrically insulating and low thermal conductive and non-magnetic material. In this case, the electrically insulating layer on the current lead support 1 and the intermediate members at both ends thereof can be omitted.

  FIG. 3 is a partially enlarged view of a connecting portion between the tape-shaped oxide superconducting wire A and the current terminal 4. In FIG. 3, the current terminal 4 and the oxide superconducting wire A connected thereto are shown. The connection length L is preferably 3 times or more, particularly 4 times or more, the width W of the tape-shaped oxide superconducting wire A, and the current terminal 5 side is formed in the same manner.

In addition, when the radius of the current lead support is r and the thickness of the tape-shaped oxide superconducting wire A is t at each connection portion between the tape-shaped oxide superconducting wire A and each current terminal, r / t It is preferable that ≧ 50. The connecting portion between the superconducting wire A and each current terminal is preferably flat. However, when a cylindrical or columnar current lead support is used, the ReBa _x Cu ₃ O _y- based oxide superconductor is 1 It is known that when a bending strain of more than% is applied, its Ic deteriorates. For this reason, it is desirable that r / t ≧ 50. When r / t <50, the superconducting wire A is strained by more than 1% at the connecting portion, and the resistance at the connecting portion increases due to the deterioration of the superconducting characteristics due to bending strain. Increases and causes drift.

The ReBa _x Cu ₃ O _y- based oxide superconducting wire A has a width of 1.0 to 5.0 mm, a superconducting layer thickness of 0.5 to 3.0 μm, and a stabilizing layer thickness of 0. The thing in the range of 0.01-0.2 mm is used. If the width of the superconducting wire is less than 1.0 mm, it will be difficult to ensure a current carrying capacity as a current lead. On the other hand, if the width exceeds 5.0 mm, a generally used small diameter columnar or cylindrical shape will be used. It becomes difficult to wind around the outer periphery of the current lead support. On the other hand, if the thickness of the superconducting layer is less than 0.5 μm, it is difficult to secure a current carrying capacity as a current lead. On the other hand, if the thickness exceeds 3.0 μm, the density of the superconducting layer is reduced or cracks are generated. The superconducting properties deteriorate due to the occurrence of. Furthermore, if the thickness of the stabilization layer is less than 0.01 mm, the role as the stabilization layer, that is, when the transition from the superconducting state to the normal conducting state due to overcurrent, temperature rise, etc. is made to split into the stabilizing layer. It becomes difficult to prevent the superconducting layer from being burned out. On the other hand, when the thickness exceeds 0.2 mm, the amount of heat penetration increases and the performance of the current lead is deteriorated.

The ReBa _x Cu ₃ O _y- based oxide superconducting wire A can also be constituted by a laminate in which a plurality of tape-shaped ReBa _x Cu ₃ O _y- based oxide superconducting wires are laminated, and the superconducting wire A is By winding the substrate surface on the outer periphery of the current lead support 1, the deterioration of the superconducting characteristics when bending strain is applied can be suppressed.

Example 1
A cylindrical current lead support made of SUS304 having an outer diameter of 25 mm, a wall thickness of 0.5 mm, and a length of 100 mm is connected to both ends of a circular spacer made of FRP having an outer diameter of 25 mm and a thickness of 5 mm. A current terminal made of oxygen-free copper having a rectangular connection member was joined to one side of the disk.

  After pasting Kapton tape (registered trademark) on the outer periphery of the cylindrical current lead support, a substrate is placed between the current terminals joined to both sides of the current lead support via an intermediate member (spacer). Ten tape-shaped YBCO oxide superconducting wires with a superconducting layer and stabilization layer provided on the intermediate layer on top, with the superconducting layer of each tape-shaped superconducting wire on the inside (with the substrate on the outside) Arranged in parallel so that the connection length of each connection portion between each current terminal and the tape-shaped oxide superconducting wire is 20 mm. The outer periphery of this connection portion is 0.1 mm thick and 5 mm wide silver. After curling with tape, soldering was performed.

The tape-shaped YBCO-based oxide superconducting wire has a Ce-Gd-O-based oxide layer as a first intermediate layer and a Ce-Zr-O-based oxide layer as a second intermediate layer on a Hastelloy (registered trademark) substrate. Further, a YBCO superconducting layer is formed to a thickness of 0.8 μm by a TFA-MOD method on an intermediate layer having a three-layer structure in which a CeO ₂ oxide layer is formed as a third intermediate layer by an RF sputtering method. A film having a thickness of 0.15 mm, a width of 4.5 mm, and a length of 150 mm was used. The critical current value (Ic) of this tape-shaped superconducting wire was 90A as a result of measurement in a self-magnetic field at 77K.

  The connection length L of each current terminal of the oxide superconducting current lead manufactured as described above and the tape-shaped oxide superconducting wire connected between each current terminal and the width of the tape-shaped oxide superconducting wire. The ratio of W (L / W) is 4.44, and the radius r of the current lead support and the thickness of the tape-shaped oxide superconducting wire at each connection portion between each current terminal and the tape-shaped oxide superconducting wire. The ratio of t (r / t) was about 83.

  The connection resistance R of each connection portion between the oxide superconducting wire and the current terminal is 0.03 to 0.06 μΩ, the critical current value (Ic) of the oxide superconducting current lead is 77 K, and the value of 810 A in the self magnetic field. showed that.

Example 2
A cylindrical current lead support made of SUS304 having an outer diameter of 30 mm, a wall thickness of 0.5 mm, and a length of 100 mm is attached to both ends via a disc-shaped spacer made of FRP having an outer diameter of 30 mm and a thickness of 5 mm. A copper current terminal having a rectangular connecting member was joined to one side of the disk.

  An oxide superconducting current lead was manufactured in the same manner as in Example 1 except that 14 tape-shaped YBCO-based oxide superconducting wires were connected to the current terminals on the outer periphery of the cylindrical current lead support. The ratio of the connection length L between each current terminal of the oxide superconducting current lead and the tape-shaped oxide superconducting wire connected between the current terminals to the width W of the tape-shaped oxide superconducting wire (L / W) is 4.44, and the ratio (r / r) of the radius r of the current lead support to the thickness t of the tape-shaped oxide superconducting wire at each connection portion between each current terminal and the tape-shaped oxide superconducting wire. t) was 100.

  The connection resistance R of each connection portion between the oxide superconducting wire and the current terminal is 0.03 to 0.05 μΩ, the critical current value (Ic) of the oxide superconducting current lead is 77 K, and the value of 1150 A in the self magnetic field. showed that.

Example 3
A copper current terminal provided with a rectangular connecting member on one side of a disk with an outer diameter of φ25 mm at both ends of a cylindrical current lead support made of alumina having an outer diameter of φ25 mm, a wall thickness of 2.5 mm, and a length of 100 mm. Were joined.

  The oxide superconducting current lead was the same as in Example 1 except that 10 pieces of tape-shaped YBCO-based oxide superconducting wires having a length of 140 mm were connected to the current terminals on the outer periphery of the cylindrical current lead support. Manufactured. The ratio of the connection length L between each current terminal of the oxide superconducting current lead and the tape-shaped oxide superconducting wire connected between the current terminals to the width W of the tape-shaped oxide superconducting wire (L / W) is 4.44, and the ratio (r / r) of the radius r of the current lead support to the thickness t of the tape-shaped oxide superconducting wire at each connection portion between each current terminal and the tape-shaped oxide superconducting wire. t) was about 83.

  Further, the connection resistance R of each connection portion between the oxide superconducting wire and the current terminal is 0.04 to 0.05 μΩ, the critical current value (Ic) of the oxide superconducting current lead is 77 K, and a value of 815 A in the self magnetic field. showed that.

Example 4
A copper current terminal having a width of 30 mm and a thickness of 5 mm was joined to both ends of a flat plate-shaped current lead support made of FRP having a width of 30 mm, a thickness of 5 mm, and a length of 100 mm.

  Five tape-shaped YBCO-based oxide superconducting wires on both sides of the plate-like current lead support, with the superconducting layer of each tape-shaped superconducting wire inside (with the substrate facing outside), After arranging in parallel so that the connection length of the connection portion between the current terminal and the tape-shaped oxide superconducting wire is 20 mm, the outer periphery of this connection portion is 0.1 mm thick, and wound with a silver tape having a width of 5 mm, Soldered together. The tape-shaped YBCO oxide superconducting wire having a length of 140 mm manufactured by the same method as in Example 1 was used.

  The connection length L of each current terminal of the oxide superconducting current lead manufactured as described above and the tape-shaped oxide superconducting wire connected between each current terminal and the width of the tape-shaped oxide superconducting wire. The ratio of W (L / W) was 4.44.

  The connection resistance R of each connection portion between the oxide superconducting wire and the current terminal is 0.02 to 0.04 μΩ, the critical current value (Ic) of the oxide superconducting current lead is 77 K, and the value of 750 A in the self magnetic field. showed that.

Comparative Example 1
A copper current terminal provided with a rectangular connecting member on one side of a disk with an outer diameter of φ25 mm at both ends of a cylindrical current lead support made of alumina having an outer diameter of φ25 mm, a wall thickness of 2.5 mm, and a length of 100 mm. Were joined.

  Example 10 except that 10 tape-shaped YBCO-based oxide superconducting wires having a length of 120 mm were connected to the outer periphery of the cylindrical current lead support with a connection length of 10 mm to each current terminal. Thus, an oxide superconducting current lead was manufactured. The ratio of the connection length L between each current terminal of the oxide superconducting current lead and the tape-shaped oxide superconducting wire connected between the current terminals to the width W of the tape-shaped oxide superconducting wire (L / W) is 2.22, and the ratio of the radius r of the current lead support to the thickness t of the tape-shaped oxide superconducting wire (r /) at each connection portion between each current terminal and the tape-shaped oxide superconducting wire. t) was about 83.

  Moreover, although the connection resistance R of each connection part of an oxide superconducting wire and an electric current terminal was 0.06-0.15 microhm, the wire cut out by 700A energization.

Comparative Example 2
A copper current terminal having a rectangular connecting member on one side of a disk having an outer diameter of 13 mm is joined to both ends of an alumina cylindrical current lead support having an outer diameter of 13 mm, a thickness of 2 mm, and a length of 100 mm. did.

  The same as in Example 1 except that six tape-shaped YBCO oxide superconducting wires having a length of 140 mm were connected to the outer periphery of the cylindrical current lead support with a connection length of 20 mm to each current terminal. Thus, an oxide superconducting current lead was manufactured. The ratio of the connection length L between each current terminal of the oxide superconducting current lead and the tape-shaped oxide superconducting wire connected between the current terminals to the width W of the tape-shaped oxide superconducting wire (L / W) is 4.44, and the ratio (r / r) of the radius r of the current lead support to the thickness t of the tape-shaped oxide superconducting wire at each connection portion between each current terminal and the tape-shaped oxide superconducting wire. t) was about 43.

  Moreover, although the connection resistance R of each connection part of an oxide superconducting wire and an electric current terminal was 0.05-0.12 microhm, the wire melt | fused at the time of 300A energization.

  The oxide superconducting current lead according to the present invention can be used as a current lead for supplying current from a power supply source to a superconducting device.

It is a top view which shows one Example of the oxide superconducting current | flow lead of this invention. It is sectional drawing including the axial direction which shows one Example of the oxide superconducting current | flow lead of this invention. FIG. 3 is a partially enlarged view of a connecting portion between a tape-shaped oxide superconducting wire and a current terminal showing an embodiment of the oxide superconducting current lead of the present invention.

Explanation of symbols

10 oxide superconducting current lead 1 current lead support 2 intermediate member 4a, 5a disc 4b, and 5b connecting terminals 4 and 5 the current terminal A tape-shaped ReBa _x Cu ₃ O _y based oxide superconducting wire L current terminal Length of oxide superconducting wire W and width W of oxide superconducting wire in tape form

Claims (11)

A current lead for supplying power to a superconducting device from a power supply source, wherein the current lead includes a current lead support, and current terminals made of a conductive material respectively bonded to both ends of the current lead support. And a plurality of tape-shaped oxide superconducting wires connected between the current terminals, the connection resistance of each connecting portion of the oxide superconducting wire and the current terminals is 0.1 μΩ or less , and each current terminal And a tape-shaped oxide superconducting wire connected between each current terminal and the width of the tape-shaped oxide superconducting wire is not less than three times the width of the oxide superconducting wire. . 2. The oxide superconducting current lead according to claim 1 , wherein the connection length is at least four times the width of the tape-shaped oxide superconducting wire. The current lead support is made of any one of copper or copper alloy, aluminum or aluminum alloy, stainless steel alloy, Ni-base alloy or titanium alloy, and has an electrically insulating layer on the surface thereof. 3. The oxide superconducting current lead according to 1 or 2 . 4. The oxide superconducting current lead according to any one of claims 1 to 3 , wherein the current lead support is cylindrical or columnar. The oxide superconducting current lead according to any one of claims 1 to 3 , wherein the current lead support has a flat plate shape. In each of the connecting portions of the tape-shaped oxide superconducting wire and the current terminal, according to claim 4, characterized in that the ≧ 50 (thickness in the radial / tape-shaped oxide superconducting wire current lead support) Oxide superconducting current lead. The oxide superconducting current lead according to claim 1 , 2 or 6 , wherein the tape-shaped oxide superconducting wire is formed of a laminate in which a plurality of tape-like oxide superconducting wires are laminated. The tape-shaped oxide superconducting wire is a ReBa _x Cu ₃ O _y- based oxide superconducting wire having a superconducting layer and a stabilizing layer sequentially laminated on a substrate via an intermediate layer (where Re is Y, Gd , Sm, Nd, Ho, Dy, Eu, Tb, Er, Yb represents one or more elements, and x ≦ 2, y = 6.2-7. 8. The oxide superconducting current lead according to claim 1 , 2, 6, or 7 . 9. The oxide superconducting current lead according to claim 8 , wherein the tape-shaped oxide superconducting wire is disposed on the current lead support with the substrate surface facing outward. A current lead for supplying power from a power supply source to a superconducting device, wherein the current lead is an electrically insulating and nonmagnetic FRP (fiber reinforced plastic), a cylindrical shape made of ceramic or nitride, or A cylindrical current lead support, a current terminal made of a conductive material joined to both ends of the current lead support, and a substrate surface on the current lead support, the current terminals being arranged outside, A plurality of tape-shaped ReBa _x Cu ₃ O _y- based oxide superconducting wires connected between terminals (where Re is selected from Y, Gd, Sm, Nd, Ho, Dy, Eu, Tb, Er, Yb) 1 or 2 or more elements, and x ≦ 2, y = 6.2 to 7)), and the connection between each connecting portion of the oxide superconducting wire and the current terminal 0 resistance 1 μΩ or less, and the connection length of each connection portion is at least three times the width of the tape-shaped oxide superconducting wire, and in each connection portion (radius of current lead support / tape shape) The oxide superconducting current lead is characterized in that the thickness of the oxide superconducting wire) ≧ 50. A current lead for supplying power from a power supply source to a superconducting device, wherein the current lead has copper or copper alloy, aluminum or aluminum alloy, stainless steel alloy, Ni-based alloy having an electrically insulating layer on the surface thereof, or A cylindrical or columnar current lead support made of any one of titanium alloys, and a conductive material joined to both ends of the current lead support via intermediate members made of electrically insulating GFRP , respectively. A plurality of tape-shaped ReBa _x Cu ₃ O _y- based oxide superconducting wires (here , disposed on the current lead support with the substrate surface facing outside, and connected between the current terminals) Re represents one or more elements selected from Y, Gd, Sm, Nd, Ho, Dy, Eu, Tb, Er, and Yb, and x ≦ 2, y Indicating the range of 6.2 to 7.) Becomes from a, the connection resistance of each connection portion between the oxide superconducting wire wherein the current terminals is less 0.1Myuomega, and wherein each of the connecting length of each connection portion And at least three times the width of the tape-shaped oxide superconducting wire, and (the radius of the current lead support / the thickness of the tape-shaped oxide superconducting wire) ≧ 50 in each of the connection portions. Oxide superconducting current lead.

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