JPH04276593A - Superconductive magnetic shielding device - Google Patents

Abstract

PURPOSE:To use a magnetic shielding vessel having a zero-magnetic field space of a size practically usable and obtain a magnetic shielding device able to cool the magnetic shielding vessel at low cost without crack formation. CONSTITUTION:A superconductive magnetic shielding device is constituted of a cylindrical superconductive shielding vessel 1 having one closed end and the other open end and having a insertion hole 8 for a magnetic flux sensor in the center at the closed end, a temperature control vessel 3 containing the magnetic shielding vessel and charged inside with ceramic powder 2, a liquid nitrogen vessel 5 containing the temperature control vessel 3 and charged inside with liquid nitrogen 4, and a vacuum insulation vessel 6 of double walls containing the liquid nitrogen vessel 5. The insertion hole 8 for the magnetic flux sensor is also provided in the vacuum insulation vessel 6 of the outmost layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a magnetic shielding device that utilizes the property of excluding magnetic flux among superconducting phenomena, and in particular is constructed of an oxide high-temperature superconductor whose critical temperature Tc exceeds the liquid nitrogen temperature of 77K. The present invention relates to a superconducting magnetic shielding device including a magnetic shielding container.

0002

BACKGROUND OF THE INVENTION Conventionally, it has been known that superconductors can be ideal magnetic shielding materials by utilizing their zero electrical resistance and perfect diamagnetic properties. However, conventional metal-based superconductors such as Nb and Pb are not put into practical use because they require expensive liquid helium as a cooling medium. Furthermore, liquid helium cooling containers usually have a two-layer structure, and the outer layer must be cooled with liquid nitrogen, and the inner layer must also be pre-cooled with liquid nitrogen, making the container itself large and cumbersome to handle. For these reasons, conventional metal-based superconductors have not been applied to magnetic shields.

The inventors of the present invention are systematically researching the application of the recently discovered high-temperature oxide superconductor, which becomes superconducting at liquid nitrogen temperatures, to magnetic shielding, and have obtained various results. For example, a large ceramic body with a diameter of 32 cm or more, a depth of 64 cm or more, and a weight of 70 kg or more must be made to create a magnetic shield container large enough to obtain a large zero magnetic field space that can be actually applied to a magnetic shield container. , it is extremely difficult to manufacture such a large magnetically shielded container, and it is also extremely difficult to cool such a large magnetically shielded container without generating cracks due to thermal shock.

An object of the present invention is to provide a magnetic shielding device that uses a magnetically shielded container having a zero magnetic field space of a size that can be practically used, and that can cool the magnetically shielded container at low cost and without generating cracks. That is.

[0005]

[Means for Solving the Problems] The superconducting magnetic shielding device of the present invention comprises a superconducting magnetic shielding container which has a cylindrical shape with one end closed and one end open and has an insertion opening for a magnetometer in the center of the closed end surface, and A temperature-controlled container that houses a shield container and is filled with ceramic powder, a liquid nitrogen container that houses this temperature-controlled container and is filled with liquid nitrogen, and a double-walled vacuum that houses this liquid nitrogen container. An insulating opening for the magnetometer is also provided in the outermost layer of the vacuum insulating container. Further, in the superconducting magnetic shielding device of the present invention, the ceramic powder may be alumina powder, and the particle size of this powder may be smaller at the closed end of the magnetic shielding container than at the open end.

The apparatus of the present invention will be explained below with reference to the drawings, but the present invention is not limited thereto.

In FIG. 1, reference numeral 1 denotes an oxide superconducting magnetic shielding container, and its shape has a depth/diameter ratio of 1 or more;
Preferably it is 2. This is because the magnetic field from the open end leaks in, so the larger the ratio, the better the shielding effect. Further, the bottom of the container has a curvature. For example, the radius of curvature is 1/2 of the diameter of the container. This is to relieve stress when manufacturing the container. The container is made by pressurizing oxide superconductor powder by cold isostatic pressing (CIP) to form a molded body, and sintering this to form the magnetically shielded container 1. The insertion opening 8 for the magnetometer provided in the center of the closed end face of the magnetically shielded container 1 needs to be large enough to allow the insertion of the magnetometer into the insertion opening of the outermost vacuum insulation container. . This creates a structure in which a SQUID magnetometer can be inserted through the insertion opening at the top, and a human head can be inserted through the open end at the bottom.

The magnetically shielded container 1 is housed in a temperature-controlled container 3 filled with ceramic powder 2, specifically alumina powder, and this temperature-controlled container 3 is filled with liquid nitrogen 4. The liquid nitrogen container 5 is housed in a double-walled vacuum insulated container 6. Note that the double-walled vacuum insulated container 6 may be omitted depending on the application. The temperature control container 3 is made of a material with good thermal conductivity such as copper or aluminum. Thereby, when liquid nitrogen is supplied from the liquid nitrogen supply hole 7 to the liquid nitrogen container 5 on the outside, the temperature difference between the upper part and the open end side can be reduced. In addition, this temperature control container 3
The alumina powder to be filled inside should have coarser particles toward the open end. For example, on the open end side, 2 to 3
The particle size is 0.1 mm, and the upper part is 0.1 mm. By doing this, it is possible to reduce the temperature difference between the upper and lower parts when cooling the magnetically shielded container 1.
A large magnetically shielded container weighing as much as 1,000 kg can be cooled to below the critical temperature without cracking, and the inside of the device can be made into a magnetic field-free space.

[0009]

[Example 1] A superconducting magnetically shielded container was produced by CIP molding a Bi-based oxide superconductor powder (Bi-Pb-Sr-Ca-Cu-O) and then firing it. The size of this magnetically shielded container is 32 cm in diameter, 64 cm in depth, and 2.5 cm in thickness.
cm, and its weight was 70 kg. Moreover, the diameter of the insertion opening of the magnetometer was 12 cm.

[0010] The above-described large magnetically shielded container was cooled using the apparatus shown in FIG. The amount of liquid nitrogen required for cooling was approximately 500 liters, and it took 12 hours to cool from room temperature to liquid nitrogen temperature. Additionally, thermocouples were attached to the top and open end of the container to measure the temperature. As a result, the temperature difference between the upper part and the open end was 30K or less.

The shielding effect of the superconducting magnetic shield device cooled in this way was measured using a SQUID magnetometer. As a result, the external magnetic field strength is 0.5 Gauss, and the frequency is 0.
．． At 2 Hz, the external magnetic field was reduced by a factor of 1,000 at the depth/diameter=1 position.

0012

[Effects of the Invention] As described above, the present invention is extremely suitable for detecting minute magnetism emitted from the human brain, biomagnetism emitted from small animals, etc., and detecting the magnetic susceptibility of extremely weak magnetic materials. A suitable superconducting magnetic shielding device can be obtained, and a magnetic shielding container can be easily cooled down to a critical temperature or less with a simple configuration, and a magnetic shielding device that can be put to practical use for the first time is provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of a superconducting magnetic shielding device according to the present invention.

[Explanation of symbols]

1 Magnetic shield container 2 Ceramic powder 3 Temperature controlled container 4. Liquid nitrogen 5. Liquid nitrogen container 6 Vacuum insulation container 7 Liquid nitrogen supply hole 8 Magnetometer insertion hole

Claims (2)

[Claims] Claim 1: A superconducting magnetically shielded container having a cylindrical shape with one end closed and one end open and having a magnetometer fitting opening in the center of the closed end surface, and a temperature in which the magnetically shielded container is housed and the inside is filled with ceramic powder. A control container, a liquid nitrogen container that stores the temperature control container and is filled with liquid nitrogen, and a double-walled vacuum insulation container that stores the liquid nitrogen container; A superconducting magnetic shielding device is also installed in the outermost layer of the vacuum insulation container. 2. The superconducting magnetic shielding device according to claim 1, wherein the ceramic powder is alumina powder, and the powder has a smaller particle size at a closed end of the magnetic shielding container than at an open end.