JPH05114753A - Current lead of superconductive magnet device - Google Patents

Abstract

PURPOSE:To keep stably in magnetic shielding effect by a method wherein the magnetic shield is arranged so as to surround a low temperature lead from outside. CONSTITUTION:A current lead 3 composed of a high-temperature lead 4 and a low-temperature lead 5 connected together in series is housed in a vacuum heat insulating chamber 2, where the low-temperature lead 5 is surrounded with a cylindrical magnetic shield 11. The magnetic shield 11 is made of oxide superconductor, and it is preferable that a flange-shaped constricted part 12 is provided to the lower end of the shield 11. The magnetic shield 11 concerned is cooled by cryogenic helium gas vaporized from liquid helium, and kept in a superconductive state. If the lower end of the shield 11 is directly dipped into liquid helium, the shield 11 can be kept at a lower temperature and kept stable in a superconductive state. By this setup, a magnetic shield can be kept stable in magnetic shield effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet device used in a superconducting application device such as a magnetic levitation train and a magnetic resonance imaging apparatus, and an exciting current from an external power source to a superconducting coil housed in a vacuum heat insulation container. It relates to a current lead that carries current.

[0002]

2. Description of the Related Art Since a superconducting coil of a superconducting device is kept in a superconducting state by being cooled by a cryogenic refrigerant such as liquid helium, it is immersed in liquid helium in a vacuum insulation container having a radiation shield using liquid nitrogen and a multilayer insulation layer. It will be stored in the closed condition. In addition, the current lead is self-cooled by the low temperature helium gas, which is liquid helium vaporized by the heat entering the low temperature side, and the heat entering from the room temperature side and the Joule heat generated in the current lead enter the cryogenic part. Configured to block. Conventionally, a good electrical conductor such as copper was used for the current lead as a conductor, but since copper is a good conductor and a good heat conductor at the same time, heat entering the cryogenic part increases, and expensive liquid helium vaporizes. The loss will increase. Therefore, an oxide-based superconducting conductor, which is a high-temperature superconductor, is used on the low temperature side of the current lead to reduce Joule heat to zero and at the same time utilize its low thermal conductivity to greatly reduce the heat entering the cryogenic part. Has already been proposed by the applicant of the present application (for example, Japanese Patent Application No. 2-84252).

FIG. 2 is a sectional view showing a conventional current lead of a superconducting magnet device in a simplified manner, and FIG. 3 is an enlarged sectional view showing an essential part of the conventional current lead. In the figure, a superconducting coil 1 is housed in a vacuum heat insulating 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 lead wire 6. The current lead 3 is a high temperature side lead 4 made of a good conductor having a room temperature terminal 4A on the top.
And the low temperature side lead 5 having the low temperature terminal 5A is connected in series, and the low temperature helium gas GHe is cooled by passing through the lead to the room temperature terminal 4A side. As shown in FIG. 3, the low temperature side lead is made of, for example, a stainless steel, manganese steel, or nichrome steel round bar having high rigidity and low thermal conductivity as a core material 7, and an oxide superconducting conductor 8 is spirally wound on the outside thereof. It is wound in a circular shape and is housed in an outer tube 9 made of a metal having a low thermal conductivity, and a cooling passage is formed between the outer tube and the outer tube by a low temperature helium gas. By cooling below 77K),
The oxide-based superconducting conductor is in a superconducting state, and the Jule heat becomes zero when a current is passed. Further, since the oxide superconducting conductor 8 which is a heat insulator blocks the heat entering from the high temperature side lead by the low temperature side lead, the heat entering the low temperature terminal 5A side is small, and therefore the consumption of liquid helium is small. The current lead of the superconducting device can be obtained.

[0004]

In the current lead of the superconducting magnet device, an exciting current as large as possible is applied to the superconducting coil 1.
Is supplied to the superconducting coil, and the superconducting coil is required to be configured to generate a magnetic field having high magnetic field strength. Therefore, in the device constructed as described above, the current lead, especially the low temperature side lead 5 is located in the high magnetic field generated by the superconducting coil. However, since the critical current density of the superconductor has the property of being lowered by the influence of the magnetic field, the superconducting coil 1
As the strength of the generated magnetic field is increased, the critical current density in the oxide-based superconducting conductor 8 of the low temperature side lead 5 decreases, and there is a problem that the cross-sectional area of the expensive oxide-based superconducting conductor must be increased. In addition, when the cross-sectional area of the oxide-based superconducting conductor is increased, the invasion heat due to the conduction of the oxide-based superconducting conductor is increased, which increases the vaporization loss of liquid helium and adversely affects the running cost of the superconducting magnet device. Occurs.

An object of the present invention is to eliminate the influence of the magnetic field generated by the superconducting coil on the low temperature side lead.
It is to increase the current density of the oxide-based superconducting conductor and reduce the heat of penetration.

[0006]

In order to solve the above-mentioned problems, according to the present invention, a current flowing through an exciting current from an external power source to a superconducting coil housed in a vacuum heat insulation container and immersed in liquid helium. The lead is composed of a series connection body of a high temperature side lead made of a good conductive metal and a low temperature side lead made of an oxide-based superconducting conductor, and the low temperature side lead is formed by flowing a low temperature helium gas into the current lead. In a superconducting state, a magnetic shield made of an oxide-based superconductor is arranged so as to surround the low temperature side lead from its outer peripheral side.

Further, it is assumed that the magnetic shield is formed in a cylindrical shape having a narrowed portion at its lower end.

Further, it is assumed that the magnetic shield is formed so as to be cooled by low temperature helium gas, or that the lower end portion of the magnetic shield is formed so as to be cooled by liquid helium.

[0009]

In the structure of the present invention, the magnetic shield made of the oxide-based superconductor is arranged so as to surround the low temperature side lead from the outer peripheral side thereof, so that the magnetic shield of the oxide-based superconductor is excellent. By utilizing the effect, it is possible to reduce the magnetic flux generated in the superconducting coil that intersects the low temperature side lead to near zero, eliminate the effect of the magnetic field on the critical current density of the oxide superconducting conductor, and cross-section the conductor. The function to prevent the increase of

Further, if the magnetic shield is formed in a cylindrical shape having a narrowed portion at the lower end thereof, it is possible to prevent the magnetic field from the superconducting coil located below the low temperature side lead from entering the low temperature side lead side. The function of effectively eliminating is obtained.

Further, if the magnetic shield is formed so as to be cooled by the low temperature helium gas, the low temperature helium gas vaporized in the liquid helium container is effectively utilized to keep the magnetic shield in a superconducting state. The magnetic shield effect of the oxide-based superconducting conductor can be obtained.

Furthermore, if the lower end of the magnetic shield is formed so as to be cooled by liquid helium, the temperature of the magnetic shield can be maintained near the liquid helium temperature, and the magnetic shield effect of the oxide-based superconducting conductor can be maintained. A more stable function can be obtained.

[0013]

EXAMPLES The present invention will be described below based on examples. FIG. 1 is a cross-sectional view showing a simplified current lead of a superconducting magnet device according to an embodiment of the present invention. The same components as those of the prior art are designated by the same reference numerals, and a duplicate description will be omitted. In the figure, a current lead 3 formed as a series connection of a high temperature side lead 4 and a low temperature side lead 5 is a vacuum heat insulation container in a state where the low temperature side lead 5 is surrounded by a cylindrical magnetic shield 11. 2, and the low temperature terminal 5A is connected to the superconducting coil 1 via the lead wire 6. The magnetic shield 11 is made of, for example, a non-magnetic material as a support material and a magnetic shield layer made of a thin oxide superconductor formed on the surface thereof, preferably a flange-shaped narrowed portion at the lower end of the cylinder. 12 is formed. The magnetic shield 11 thus formed is cooled by the low temperature helium gas GHe obtained by vaporizing the liquid helium He to maintain the superconducting state. If the lower end portion is directly immersed in liquid helium, the magnetic shield 11 can be kept at a lower temperature and its superconducting state can be kept stable.

In the current lead of the superconducting magnet device having the magnetic shield 11 thus constructed, it is surrounded by the magnetic shield 11 by utilizing the excellent magnetic shield effect of the oxide superconductor. Since it is possible to prevent the magnetic flux from penetrating into the open space, it is possible to reduce the generated magnetic flux of the superconducting coil intersecting the low temperature side lead 11 to near zero, which affects the critical current density of the oxide superconducting conductor. The influence of the magnetic field can be eliminated. Therefore, if the current flowing through the current lead is constant, the oxide-based superconducting conductor 8 of the low temperature side lead 5 can be compared with a conventional current lead having no magnetic shield.
The advantage of being able to reduce the conductor cross-sectional area (see FIG. 3) is obtained,
Further, if the conductor cross-sectional area is kept the same as the conventional one, there is an advantage that the current flowing through the current lead can be increased. Further, since the conductor cross-sectional area of the oxide-based superconducting conductor is reduced, the heat entering the low temperature terminal 5A is reduced, and the amount of vaporization of expensive liquid helium is also reduced. By utilizing the characteristics of the current lead used on the side lead side, it is possible to economically provide a superconducting magnet device with low consumption of liquid helium and low running cost.

[0015]

As described above, according to the present invention, the magnetic shield made of the tubular oxide superconductor is provided which surrounds the low temperature side lead made of the oxide superconductor from the outer peripheral side thereof. As a result, it is possible to reduce the magnetic flux generated in the superconducting coil that intersects the low temperature side lead to near zero by utilizing the excellent magnetic shield effect of the oxide superconductor, which is a problem with conventional current leads. If the effect of the magnetic field on the critical current density of the oxide-based superconducting conductor in the low temperature side lead is eliminated, and the current flowing through the current lead is constant, then it is better than the conventional current lead without magnetic shield. Since it is possible to reduce the cross-sectional area of the oxide-based superconducting conductor and the heat that enters the low temperature terminal side, it is economically advantageous to use a superconducting magnet device equipped with a current lead with low vaporization amount of expensive liquid helium and low running cost. Can be provided to. Further, if the conductor cross-sectional area of the oxide-based superconducting conductor in the low temperature side lead is kept the same as that of the conventional one, there is an advantage that the current flowing through the current lead can be increased without increasing the penetration heat.

Further, if the magnetic shield is formed in a cylindrical shape having a narrowed portion at its lower end, the magnetic field from the superconducting coil located below the low temperature side lead is prevented from entering the low temperature side lead side. It is possible to provide a superconducting magnet device including a current lead that is effectively eliminated and has a higher magnetic shield effect.

Further, if the magnetic shield is constructed so as to be cooled by low temperature helium gas, the low temperature helium gas vaporized in the liquid helium container is effectively utilized to keep the magnetic shield in a superconducting state and There is an advantage that the shield effect can be exhibited. Also, if the lower end of the magnetic shield is configured to be cooled by liquid helium, the magnetic shield can be maintained near the liquid helium temperature and the magnetic shield effect of the oxide-based superconducting conductor can be maintained more stably. The advantage that can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a current lead of a superconducting magnet device according to an embodiment of the present invention.

FIG. 2 is a sectional view schematically showing a conventional current lead of a superconducting magnet device.

FIG. 3 is an enlarged cross-sectional view showing a main part of a conventional current lead.

[Explanation of symbols]

 1 Superconducting Coil 2 Vacuum Insulation Container 3 Current Lead 4 High Temperature Side Lead 5 Low Temperature Side Lead 7 Core Material 8 Oxide Superconductor 9 Outer Tube 11 Magnetic Shield (Oxide Superconductor) 12 Constriction He Liquid Helium GHe Helium gas

Claims (4)

[Claims] 1. A high-temperature-side lead whose current lead for passing an exciting current from an external power source is made of a good conductive metal in a superconducting coil housed in a vacuum heat insulation container and immersed in liquid helium, and an oxide superconducting conductor. A series connection body with a low temperature side lead, wherein the low temperature side lead is in a superconducting state by flowing a low temperature helium gas into the current lead. A current lead of a superconducting magnet device, characterized in that a field is arranged so as to surround the low temperature side lead from the outer peripheral side thereof. 2. The current lead of a superconducting magnet device according to claim 1, wherein the magnetic shield is formed in a cylindrical shape having a narrowed portion at its lower end. 3. The current lead of a superconducting magnet device according to claim 1, wherein the magnetic shield is formed so as to be cooled by a low temperature helium gas. 4. The current lead of a superconducting magnet device according to claim 1, wherein the lower end of the magnetic shield is formed so as to be cooled by liquid helium.