JP3218649B2 - Current leads for superconducting devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead for supplying an exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container in a superconducting device such as a magnetic levitation train or a magnetic resonance imaging diagnostic apparatus.

[0002]

2. Description of the Related Art A superconducting coil of a superconducting device is cooled by a cryogenic refrigerant such as liquid helium to maintain a superconducting state. It is stored in the state where it was done. In addition, the current lead is self-cooled by the low-temperature helium gas that vaporizes the liquid helium due to the heat entering the low-temperature side, preventing the heat from the normal temperature side and the Joule heat generated by the current lead from entering the extremely low-temperature portion. Configured to block. Conventionally, electric current conductors such as copper have been used as current conductors.However, copper is a good conductor at the same time as it is a good thermal conductor, so the heat that penetrates into cryogenic parts increases, and expensive liquid helium is vaporized. The loss increases. Therefore, a current lead that uses an oxide-based superconductor, which is a high-temperature superconductor, on the low-temperature side of the current lead, reduces Joule heat to zero, and uses the low thermal conductivity to greatly reduce the heat that enters the cryogenic part. Has already been proposed by the applicant of the present application (for example, Japanese Patent Application No. 2-84252).

FIG. 3 is a simplified cross-sectional view showing a conventional current lead of a superconducting magnet device, and FIG. 4 is an enlarged cross-sectional view showing a main part of the conventional current lead. In the figure, a superconducting coil 1 is housed in a vacuum insulated container 2 in a state of being immersed in liquid helium He, and is electrically connected to a low-temperature terminal 5A of a current lead 3 by a connecting wire 6. The current lead 3 includes a high-temperature side lead 4 made of a good conductor having a normal temperature terminal 4A on an upper part,
It is configured as a series connection of a low-temperature side lead 5 having a low-temperature terminal 5A, and is cooled by low-temperature helium gas GHe passing through the lead to the room-temperature terminal 4A. The low-temperature side lead is made of, for example, stainless steel, as shown in FIG.
A round bar having high rigidity and low thermal conductivity such as manganese steel or nichrome steel is used as a core material 7, and an oxide superconducting conductor 8 is spirally wound around the core bar 7. And a cooling passage made of a low-temperature helium gas is formed with the outer tube, and the temperature of the oxide-based superconducting conductor 8 is cooled to a liquid nitrogen temperature (about 77 K) or lower, so that the oxide-based superconducting conductor is The Joule heat when the current flows in the superconducting state becomes zero. In addition, since the heat transmitted from the high-temperature side lead is blocked by the low-temperature side lead by the oxide-based superconducting conductor 8, which is a thermal insulator, the amount of heat penetrated into the low-temperature terminal 5A is small, and therefore the consumption of liquid helium is small. A current lead for the superconducting device is obtained.

[0004]

The current leads of the superconducting device are required to be configured so as to supply as large an exciting current as possible to the superconducting coil 1 so that the superconducting coil can generate a magnetic field having a high magnetic field strength. Therefore, in the device configured as described above, when a large current flows through the current lead, especially the low-temperature side lead 5, the large current generates a current magnetic field (also referred to as a self-magnetic field) orbiting the low-temperature side lead, The oxide-based superconducting conductor 8 is placed in this self-magnetic field. However, the superconducting conductor has a property that its critical current density decreases under the influence of the magnetic field. Therefore, as the conduction current increases, the critical current density in the oxide-based superconducting conductor 8 of the low-temperature side lead 5 decreases. In addition, there is a problem that the sectional area of the expensive oxide-based superconducting conductor must be increased. In addition, when the cross-sectional area of the oxide-based superconductor is increased, the heat that penetrates due to conduction of the oxide-based superconductor increases, and the vaporization loss of liquid helium increases.
There is a problem that the running cost of the superconducting device is adversely affected.

An object of the present invention is to eliminate the influence of the self-magnetic field of the current lead on the low-temperature side lead, thereby increasing the current density of the oxide-based superconducting conductor and reducing heat penetration.

According to the present invention, a current lead for passing an exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container and immersed in liquid helium is provided by a good conductive metal. And a low-temperature side lead made of an oxide-based superconducting conductor, and the low-temperature side lead is brought into a superconducting state by flowing a low-temperature helium gas into the current lead. Wherein the low-temperature side lead comprises a pair of reciprocating conductors composed of a pair of oxide-based superconducting conductors supported on both sides of the electrical insulating material and arranged to face each other, and the low-temperature terminal side of the reciprocating conductors is a pair of the superconducting coil. It is formed so as to be conductively connected to the terminal, and the reciprocating conductor and the electric insulating material are formed in a zigzag shape in the longitudinal direction. .

[0007]

[0008]

In the structure of the present invention, a high-temperature side lead made of a good conductive metal and a low-temperature side lead made of an oxide superconductor are connected in series, and a low-temperature helium gas flows through the current lead. The low-temperature side lead is thereby brought into a superconducting state, and the low-temperature side lead is provided with a reciprocating conductor composed of a pair of oxide-based superconducting conductors supported on both surfaces of the electric insulating material and arranged to face each other. By configuring the low-temperature terminal side of the conductor to be conductively connected to a pair of terminals of the superconducting coil, a pair of oxide-based superconducting conductors of a reciprocating conductor insulated and supported by an electric insulating material to withstand the voltage between the terminals of the superconducting coil. In this case, the exciting currents of the superconducting coils flow in opposite directions, and the circulating directions of the current magnetic fields generated by the opposite currents also become opposite. Since they cancel each other, it is possible to make the total self-magnetic field almost zero, thereby eliminating the adverse effect of the self-magnetic field on the critical current density of the oxide-based superconductor and reducing the conductor cross-sectional area of the oxide-based superconductor. The function of preventing the increase is obtained.

Further, in addition to the above configuration, the reciprocating conductor and the electrical insulating material made of the oxide-based superconducting conductor are formed in a zigzag shape in the longitudinal direction.
Since the length of the reciprocating conductor can be extended without increasing the length of the low-temperature side lead, the heat conduction of the reciprocating conductor makes it possible to reduce the amount of heat entering the cryogenic part and reduce the consumption of liquid helium. The function is obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments and reference examples. FIG. 1 is a cross-sectional view schematically illustrating a current lead for a superconducting device according to a reference example of the present invention.
A duplicate description will be omitted. In the figure, high-temperature side lead 1
The current lead 10 configured as a series connection body of the low-temperature side lead 15 and the low-temperature side lead 15 includes a pair of oxide-based materials in which the low-temperature side lead 15 is tightly insulated and supported on both surfaces of the electric insulating material 17 in the outer tube 19. It has a reciprocating conductor 18 composed of superconducting conductors 18A and 18B, and the lower end of each of the oxide superconducting conductors 18A and 18B has a low-temperature terminal 15A electrically insulated by an insulating material 17A and a pair of connecting wires 16A and 16B. 16 are connected to both terminals of the superconducting coil 1.

A conductor (not shown) made of a good conductor is also housed in the outer tube as a reciprocating conductor in the high-temperature side lead 14, and the lower end thereof is connected to the reciprocating conductor of the low-temperature side lead 15, and the upper end thereof is formed. It is connected to an external power supply via room temperature terminals 14A and 14B insulated by an electric insulating material 17B. Also, the high-temperature side lead 14 and the low-temperature side lead 15
Is cooled by the low-temperature helium gas GHe passing through the outer tube 19 and the high-temperature side lead, and the invasion heat on the high-temperature side lead is exhausted, and the oxide-based superconducting conductors 18A, 18
B is kept in a superconducting state.

In the current lead constructed as described above, a pair of oxide-based superconducting conductors 18A, 18A of a reciprocating conductor 18 opposed and insulated and supported by an electric insulating material 17 to withstand the voltage between the terminals of the superconducting coil 1 are provided. In 18B, the exciting currents of the superconducting coils flow in opposite directions.
Since the circling directions of the current magnetic fields generated by the opposite currents are also opposite to each other and cancel each other, it is possible to make the total self magnetic field almost zero. Therefore, the influence of the self-magnetic field on the critical current density of the oxide-based superconductor can be eliminated, so that the current can be increased without increasing the cross-sectional area of the oxide-based superconductor and the cutoff of the oxide-based superconductor. Since it is possible to prevent an increase in invasion heat due to conduction of the oxide-based superconducting conductor caused by increasing the area, it is possible to obtain a superconducting device having a small loss of vaporization of liquid helium and a low running cost.

FIG. 2 is an enlarged sectional view showing a main part of the embodiment of the present invention. The electric insulating material 27 accommodated in the outer tube 29 of the low-temperature side lead 25 is formed in a zigzag shape in the longitudinal direction. The reciprocating conductor 28 composed of a pair of oxide-based superconducting conductors 28A and 28B insulated and supported along both zigzag surfaces is also different from the above-described reference example in that it is formed in a zigzag shape (angular wave shape). In this way, by making the reciprocating conductor zigzag, the reciprocating conductor 28 can be lengthened without increasing the length of the low-temperature side lead 25, so that it is possible to further reduce the heat intrusion due to the conduction of the reciprocating conductor, A superconducting device with lower consumption of expensive helium gas and lower running cost is obtained. In addition, the electric insulating material 27 and the reciprocating conductor 18 may be formed in a curved round wave shape, and may be configured to be supported by the outer tube via a spacing piece.

[0014]

As described above, the present invention comprises a series connection of a high-temperature side lead made of a highly conductive metal and a low-temperature side lead made of an oxide-based superconducting conductor. In the case where the low-temperature side lead is brought into a superconducting state by flowing through, a reciprocating conductor consisting of a pair of oxide-based superconducting conductors arranged so that the low-temperature side lead is supported on both surfaces of the electric insulating material and opposed to each other. The reciprocating conductor is configured so that the low-temperature terminal side of the reciprocating conductor is conductively connected to a pair of terminals of the superconducting coil. As a result, a pair of oxide-based superconducting conductors of a reciprocating conductor that is insulated and supported to withstand the voltage between terminals of the superconducting coil by an electric insulating material includes:
The exciting currents of the superconducting coils will flow in opposite directions, and the direction of the current magnetic field generated by the opposite currents will also be opposite, canceling each other out. The problem that the critical current density of the oxide-based superconductor is reduced by the self-magnetic field in the prior art is eliminated, and the current lead is increased without increasing the cross-sectional area of the expensive oxide-based superconductor. In addition to increasing the cross-sectional area of the oxide-based superconducting conductor, it is possible to prevent the increase in heat intrusion and the increase in the consumption of liquid helium based on this, and to reduce the current lead for the superconducting device with a large current flow and low running cost. It can be provided economically advantageously.

Further, in addition to the above configuration, a reciprocating conductor made of an oxide-based superconducting conductor and an electric insulating material are formed so as to meander zigzag in the longitudinal direction. as a result,
Since the length of the reciprocating conductor can be extended without increasing the length of the low-temperature side lead, the heat conduction of the reciprocating conductor reduces the amount of heat entering the cryogenic part, and further reduces the consumption of liquid helium. Benefits are obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a current lead for a superconducting device according to a reference example of the present invention.

FIG. 2 is an enlarged sectional view showing a main part of the embodiment of the present invention.

FIG. 3 is a simplified cross-sectional view showing a conventional current lead of a superconducting device.

FIG. 4 is an enlarged sectional view showing a main part of a conventional current lead.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Superconducting coil 2 Vacuum heat insulation container 3 Current lead 4 High temperature side lead 5 Low temperature side lead 7 Core material 8 Oxide superconducting conductor 9 Outer tube 10 Current lead 14 High temperature side lead 15 Low temperature side lead 16 Connection line 17 Electrical insulation 18 Reciprocation Conductor 18A Oxide superconducting conductor 18B Oxide superconducting conductor 19 Outer tube 25 Low temperature side lead 27 Electrical insulating material 28 Reciprocating conductor 28A Oxide superconducting conductor 28B Oxide superconducting conductor He Liquid helium GHe Helium gas

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-135714 (JP, A) JP-A-63-245909 (JP, A) JP-A-5-175048 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 39/04 ZAA H01F 6/00 ZAA H01F 6/06 ZAA

Claims (1)

(57) [Claims] A current lead for passing an exciting current from an external power supply to a superconducting coil housed in a vacuum insulated container and immersed in liquid helium, a current lead made of a good conductive metal, and an oxide superconducting conductor. And a low-temperature side lead in a superconducting state by flowing a low-temperature helium gas into the current lead. A reciprocating conductor composed of a pair of oxide-based superconducting conductors supported and arranged to face each other, and the low-temperature terminal side of the reciprocating conductor is formed so as to be conductively connected to the pair of terminals of the superconducting coil. A current lead for a superconducting device, wherein the reciprocating conductor and the electrical insulating material are formed in a zigzag shape in a longitudinal direction thereof.