JPH04357803A - Current lead superconducting device - Google Patents

Abstract

PURPOSE:To realize a current lead for a superconducting device whose drop of critical current caused by a magnetic field generated by a superconducting coil is suppressed as low as possible. CONSTITUTION:As for a current lead by which current is applied from an energizing power source in cold environment to a superconducting coil 1 immersed in a liquid helium 3 held in a liquid helium container 2, that current lead is constituted by a high temperature superconductor 5 which shows superconducting state at the temperature higher than that of liquid nitrogen, and an axis c which is one of the crystal axes of the high temperature superconductor 5 is allocated in the direction vertical to that of the magnetic field generated by the superconducting coil.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Field of Industrial Application] The present invention relates to an improvement in a current lead for supplying current from an excitation power supply placed at room temperature to a superconducting coil immersed in liquid helium contained in a liquid helium container. .

0003

2. Description of the Related Art A current lead is used as a means for supplying current from an excitation power supply placed in a room temperature environment to a superconducting coil cooled by immersion in liquid helium contained in a liquid helium container. In superconducting equipment,
External heat conduction, radiation, and heat intrusion from the current leads causes the very expensive liquid helium to evaporate. Of this, in a normal superconducting device, the heat that enters from the current leads accounts for most of the total heat.

[0004] Therefore, it has been considered to construct a current lead using a high-temperature superconductor that exhibits a superconducting state above the liquid nitrogen temperature to reduce the intrusion heat (Japanese Patent Laid-Open No. 63-2926).
(See Publication No. 10). For example, the high-temperature end of a ceramic high-temperature superconductor is cooled to around 80 K with liquid nitrogen contained in a liquid nitrogen container to bring it into a superconducting state. Leads made of copper or the like are used from the high temperature end of the high temperature superconductor to room temperature. High-temperature superconductors have low thermal conductivity, so the amount of heat that enters the liquid helium container is small, and since the electrical resistance is zero, there is no Joule heat generation when energized. Therefore, current leads using high temperature superconductors are
It has a great effect on reducing the amount of evaporation of liquid helium.

[0005]

[Problems to be Solved by the Invention] Ceramic high-temperature superconductors have a strong magnetic field dependence, and the critical current decreases significantly depending on the direction of the magnetic field created by the superconducting coil. Furthermore, since the magnetic field created by a superconducting coil spatially changes in direction and strength, a magnetic field in the same direction is not applied throughout a long high-temperature superconductor. Therefore, inside a long high-temperature superconductor, there is a portion where the direction of the magnetic field is oriented in the direction in which the critical current decreases.

An object of the present invention is to provide a current lead for a superconducting device in which a decrease in critical current due to the magnetic field produced by a superconducting coil is suppressed as much as possible.

[Configuration of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, c is one of the crystal axes of high temperature superconductivity.
The axis is placed perpendicular to the direction of the magnetic field created by the superconducting coil.

If the length of the high-temperature superconductor is long, divide the high-temperature superconductor into short pieces and arrange them in series via copper leads, so that the c-axis, which is one of the crystal axes of each high-temperature superconductor, is aligned with the superconductor. It is preferable to arrange the superconducting coil at right angles to the direction of the magnetic field created by the coil, and to arrange the superconducting coil so that the direction of the magnetic field created by the superconducting coil is within 45° from the a-axis, which is another one of the crystal axes.

0010

[Operation] High-temperature superconductors have a crystal structure with a-axis, b-axis
There are crystal axes called axis and c axis. When a magnetic field is applied parallel to this c-axis, the critical current decreases significantly. In the current lead for a superconducting device with this configuration, the c-axis is perpendicular to the direction of the magnetic field, so the critical current does not decrease significantly.

According to the above-mentioned means, when a magnetic field is applied in each direction of the a-axis, b-axis, and c-axis, which are the crystal axes, in a high-temperature superconductor, there is a large anisotropy in the critical current. do. The degree of decrease in the critical current with respect to the magnetic field direction is smallest when the magnetic field is applied in the a-axis direction, and largest when the magnetic field is applied in the c-axis direction.

Generally, the magnetic field generated by a superconducting coil is not spatially uniform in direction, so a magnetic field in the same direction cannot be applied to the entire long high-temperature superelectric body. In the current lead for a superconducting device with this configuration, by dividing the high-temperature superconductor into short pieces, a magnetic field is applied to each high-temperature superconductor in an almost uniform direction, and the c-axis is perpendicular to the direction of the magnetic field. , and since the a-axis is substantially parallel to the direction of the magnetic field, the critical current does not decrease significantly.

[0013]

【Example】

(Example 1) Below, regarding the first example of the present invention, FIG.
This will be explained with reference to FIG. (1) is a superconducting coil made by winding superconducting wire;
) is immersed in liquid helium (3) contained in a liquid helium container (2) made of stainless steel or the like. Further, this liquid helium container (2) is housed in an insulated vacuum container (4) made of stainless steel or the like. (5) is a ceramic-based high-temperature superconductor that exhibits a superconducting state above the liquid nitrogen temperature, and is divided into several short pieces, each of which is connected in series by a short lead (13) made of steel or the like. Several high temperature superconductors (5) and short leads (1
The low-temperature end of the current lead composed of 3) is connected to the superconducting coil terminal (6), and the high-temperature end passes through a liquid nitrogen container (8) containing liquid nitrogen (7), and the current lead made of copper or the like (
9). A normal temperature terminal (10) is provided at the high temperature end of the lead (9). This room temperature terminal (10) is connected to an excitation power source (not shown) placed in a room temperature environment. (11) consists of several high temperature superconductors (5) and short leads (13
) is a gas flow pipe made of stainless steel or the like that is installed around the outer periphery of the current lead, and is connected to a liquid helium container (2).
This becomes a flow path for the helium gas (12) evaporated inside. Figure 2
is a perspective explanatory view showing a current lead composed of a superconducting coil (1), several high temperature superconductors (5), and short leads (13). High temperature superconductor (5) divided into short pieces,
The c-axis, which is one of the crystal axes, is perpendicular to the direction of the magnetic field created by the superconducting coil (1) at each location, and the a-axis, which is the other crystal axis, is within 45 degrees to the direction of the magnetic field. Arrange it so that

(Operation of Example 1) The critical current of the high temperature superconductor (5) changes greatly depending on the direction of the applied magnetic field. For example, a Bi-based high-temperature superconductor manufactured by the crystal pulling method exhibits a critical current that is 10 times or more greater when a magnetic field is applied in the a-axis direction than when it is applied in the c-axis direction. In Example 1, by dividing the high-temperature superconductor (5) into short pieces, the magnetic field created by the superconducting coil (1) is applied to each high-temperature superconductor (5) in an almost uniform direction. , the c axis is perpendicular to the direction of the magnetic field, and a
Since it can be arranged so that the axis is almost parallel (within 45°) to the direction of the magnetic field, the degree of decrease in critical current is small.

(Effects of Embodiment 1) As explained above, according to Embodiment 1, by dividing the high temperature superconductor into short pieces, each high temperature superconductor receives a substantially uniform magnetic field created by the superconducting coil. This current lead for superconducting devices minimizes the drop in critical current because it can be placed so that the c-axis is perpendicular to the direction of the magnetic field and the a-axis is parallel to the direction of the magnetic field. is obtained.

(Embodiment 2) Next, a second embodiment will be described with reference to FIGS. 3 and 4. High temperature superconductor (5)
When is short, division as in Example 1 is not performed, and only one high temperature superconductor (5) is formed. The rest is the same as in Example 1.

(Effects of Embodiment 2) Therefore, according to Embodiment 1, a current lead is obtained in which a decrease in critical current is suppressed as much as possible.

[0018]

[Effects of the Invention] As explained above, according to the present invention, the c-axis, which is one of the crystal axes of the high-temperature superconductor, is arranged perpendicular to the direction of the magnetic field generated by the superconducting coil, thereby suppressing the drop in critical current as much as possible. A current lead for a superconducting device is obtained.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention.

FIG. 2 is a perspective explanatory view of essential parts for explaining the operation of FIG. 1;

FIG. 3 is a longitudinal sectional view showing a second embodiment of the invention.

FIG. 4 is a perspective explanatory view of essential parts for explaining the action of FIG. 3;

[Explanation of symbols]

1...Superconducting coil 2...Liquid helium container 3...Liquid helium 4...Insulated vacuum container 5...High temperature superconductor 6...Superconducting coil terminal 7...Liquid nitrogen 8...Liquid nitrogen container 9...Lead 10…Normal temperature terminal 11...Gas flow pipe 12...Helium gas 13...Short lead

Claims (1)

[Claims] Claim 1: In a current lead for supplying current from an excitation power supply placed in a room temperature environment to a superconducting coil immersed in liquid helium housed in a liquid helium container, the current lead is connected to a liquid nitrogen temperature. A current lead for a superconducting device, which is constructed from a high-temperature superconductor exhibiting a superconducting state, and is characterized in that the c-axis, which is one of the crystal axes of the high-temperature superconductor, is installed at right angles to the direction of the magnetic field generated by the superconducting coil. .