JPH06275874A - Oxide superconducting current lead device - Google Patents

Abstract

PURPOSE:To relatively lower the intensity of a magnetic field affecting a current lead and to prevent a drop in the super-conductive-characteristic, especially the critical current density and the critical current value of an oxide super- conducting bulk current lead by a method wherein a magnetic field in a direction opposite to a leakage magnetic field from a superconducting apparatus is applied. CONSTITUTION:When a leakage magnetic field 4 acts perpendicularly to an oxide superconducting bulk current lead 2, permanent magnets 1 are installed, an application magnetic filed 5 is given, and the intensity of a magnetic field affecting the current lead is lowered relatively. When the magnetic field in a direction opposite to the leakage magnetic field 4 is applied, the intensity of the magnetic field affecting the current lead is lowered relatively, and it is possible to prevent a drop in the superconductive characteristic, especially the critical current density and the critical current value of the oxide superconducting current lead 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current lead device provided with a magnetic shield for suppressing a decrease in critical current of an oxide superconducting current lead.

[0002]

2. Description of the Related Art It is known that an oxide superconducting bulk has a low superconducting property, particularly a critical current density (Jc), under a magnetic field. FIG. 1 shows a graph of the magnetic field dependence of the critical current density of a Bi-based oxide superconducting bulk. When a magnetic field perpendicular to the current-carrying direction and a magnetic field parallel to the current-carrying direction act at the liquid nitrogen temperature (77K), and also when a magnetic field perpendicular to the current-carrying direction acts at the liquid helium temperature (4.2K). Is shown.

In the figure, the graph line with plot marks shows the hollow cylindrical oxide superconducting bulk current lead, and the solid graph line shows the solid round bar-shaped oxide superconducting bulk current lead.

From this graph, the critical current density of the cylindrical bulk is halved at several tens of millitesla at the liquid nitrogen temperature of 77K, and the lowering of the critical current density is larger when the magnetic field is applied perpendicularly to the energizing direction. I understand.

Therefore, when there is a concern about the influence of the leakage magnetic field on the oxide superconducting bulk current lead, it is necessary to provide some kind of magnetic shield to prevent the reduction of the critical current density. As magnetic shields, magnetic shields made of metal such as iron and magnetic shields of oxide superconductors are currently used.

[0006]

As described above, an oxide superconductor or a metal is used as the magnetic shield material used for the oxide superconducting bulk current lead. In the case of metal that has been used as a magnetic shield material for a long time,
In order to improve the magnetic shield performance, it is necessary to have thickness and size, and it is difficult to obtain sufficient magnetic shield performance.

The metal magnetic shield body is disadvantageous in that it is inconvenient to manufacture and handle because it is bulky in size and weight. In addition, since metal generally has high thermal conductivity, there is a problem in using it as a magnetic shield material for an oxide superconducting bulk current lead for supplying power to a superconducting device which is insensitive to heat penetration.

A magnetic shield using an oxide superconductor is
Since the thermal conductivity is low, it has been developed with the aim of improving the cooling efficiency, etc., but at present, the shield magnetic field is still only about several tens of millitesla.

In order to put power into practical use using the oxide superconducting bulk current lead, it is necessary to shield the leakage magnetic field from the superconducting device, maintain the superconducting characteristics of the oxide superconducting bulk current lead, and stabilize the energized state. It is essential.

An object of the present invention is to obtain a magnetic shield method capable of effectively shielding a leakage magnetic field from a superconducting device, to protect superconducting characteristics of an oxide superconducting bulk current lead at the time of power feeding, and to stabilize energization.

[0011]

In order to solve the above-mentioned problems, in the device of the present invention, a magnetic field is applied to the oxide superconducting current lead in a direction opposite to the magnetic field leaking from the superconducting device. It realizes the effect.

By applying a magnetic field in the direction opposite to the leakage magnetic field, the strength of the magnetic field affecting the current lead is relatively reduced, and the superconducting characteristics of the oxide superconducting current lead, particularly critical current density and critical current value Prevent decline.

2 and 3 are explanatory views of the magnetic shield used in the apparatus of the present invention. The figure shows a plan view of the case where the leakage magnetic field 4 acts perpendicularly on the oxide superconducting bulk current lead 2. The permanent magnet 1 can be installed as shown in the figure to apply an applied magnetic field 5 to relatively reduce the strength of the magnetic field affecting the current lead.

FIGS. 4 and 5 are graphs showing the relationship between the strength of the magnetic field applied to the current lead and the applied current in the device of the present invention, showing the case where a permanent magnet is arranged in the oxide superconducting current lead. There is. In FIG.
The leakage magnetic field from the superconducting device increases almost in proportion to the applied current, but when a permanent magnet is installed so that the direction of the magnetic field is opposite to the leakage magnetic field, the magnetic field strength is increased. Since the absolute value of the magnetic field that cancels out and affects the current lead becomes small, it is possible to suppress the deterioration of the superconducting characteristics such as the critical current density.

The relationship diagram shown in FIG. 5 is a region in which the current flow is high and the reduction of the critical current density is most likely to occur by increasing the strength of the magnetic field applied by the permanent magnets as compared with FIG. It further reduces the strength of the magnetic field that affects the.

As a method of applying a magnetic field in the direction opposite to the leakage magnetic field, the method using a permanent magnet as described above is simple, but the same effect can be obtained using an electromagnet. FIG. 6 is an explanatory diagram of another example of the magnetic shield method for the oxide superconducting current lead of the present invention, which acts perpendicularly to the oxide superconducting bulk current lead 2 as in FIGS. 2 and 3. A case where a magnetic shield is applied to the leakage magnetic field 4 by using the electromagnet 3 is shown. When applying the applied magnetic field 5 in the opposite direction to the leakage magnetic field 4 using the electromagnet 3 as shown in FIG. 6, the magnetic field can be applied according to the strength of the leakage magnetic field. It is possible to adjust the combined magnetic field of the leakage magnetic field and the applied magnetic field to approximately 0.

FIG. 7 is an explanatory view of the relationship between the strength of the magnetic field applied to the current lead and the applied current in another example of the present invention, in the case where an electromagnet for magnetic shielding is installed on the oxide superconducting current lead. Is shown. The magnetic field generated from the electromagnet is controlled and a magnetic field according to the magnitude of the leakage magnetic field is applied. By canceling the leakage magnetic field with the electromagnet, the magnetic field applied to the current lead can be made zero.

[0018]

As described above, the magnetic shield of the oxide superconducting current lead device of the present invention suppresses the magnetic field perpendicular to the current lead conduction direction by applying a magnetic field using a permanent magnet or an electromagnet, It is possible to prevent deterioration of superconducting properties, especially critical current density, and to stabilize the current flow. By controlling the applied magnetic field with the electromagnet, it is possible to almost eliminate the magnetic field that reaches the current lead.

Since the device of the present invention can protect the superconducting property of the current lead from the leakage magnetic field, there is an effect that the oxide superconducting current lead can be expected to be put into practical use for supplying power to the superconducting device.

[Brief description of drawings]

FIG. 1 is a graph showing the magnetic field dependence of the critical current density of a Bi-based oxide superconducting bulk.

FIG. 2 is an explanatory diagram of a magnetic shield of the oxide superconducting current lead device of the present invention.

FIG. 3 is an explanatory diagram of a magnetic shield of the oxide superconducting current lead device of the present invention.

FIG. 4 is a graph showing the relationship between the strength of the magnetic field applied to the current lead and the energizing current of the superconducting device.

FIG. 5 is a graph showing the relationship between the strength of the magnetic field applied to the current lead of the present invention and the energizing current of the superconducting device.

FIG. 6 is an explanatory view of an example of a magnetic shield means of the oxide superconducting bulk current lead of the present invention.

FIG. 7 is an explanatory diagram of the relationship between the strength of the magnetic field applied to the current lead and the energizing current of the superconducting device in the device of the present invention.

[Explanation of symbols]

 1 Permanent magnet 2 Oxide superconducting current lead 3 Electromagnet 4 Leakage magnetic field 5 Applied magnetic field

Claims (3)

[Claims] 1. A means for applying a magnetic field in a direction opposite to a leakage magnetic field from a peripheral device such as a superconducting device to a current lead made of an oxide superconductor used for supplying power to the superconducting device or the like. Oxide superconducting current lead device. 2. The superconducting current lead device according to claim 2, wherein the means for applying a magnetic field in a direction opposite to the leakage magnetic field is a permanent magnet. 3. The superconducting current lead device according to claim 1, wherein the means for applying a magnetic field in a direction opposite to the leakage magnetic field comprises an electromagnet.