JPH0260199A - Magnetic shielding device - Google Patents

Abstract

PURPOSE:To realize a magnetic shielding effect of high efficiency by a method wherein a magnetic shielding wall is formed of the material which contains oxide superconductor whose critical temperature is higher than that of the material of a superconductive equipment and cooled at the same temperature as the superconductive equipment. CONSTITUTION:An oxide superconductor constituting a magnetic shielding wall 6, which is installed facing toward required directions to magnetically shield the upper, the peripheral, and the lower part of an ultra cooling agent reservoir, is formed of the material whose critical temperature is higher than that of the superconductive material used for the formation of a superconductive magnet 5 and cooled at the same temperature as the superconductive magnet 5 by means of liquid herium or liquid hydrogen. By this structure, the Meissner effect of the oxide super-conductor is made to increase, a magnetic shielding of high efficiency can be realized, and a magnetic shielding device of this design can be made comparatively small.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic shielding device for a superconducting device such as a superconducting magnet, which has an excellent magnetic shielding effect.

(Prior art) In recent years, MHI (Magnetic Re5onan)
BACKGROUND ART Devices that generate high magnetic fields, such as magnetic field generating devices used in medical nuclear magnetic resonance diagnostic imaging (CE Imaging), are beginning to be used in various fields. For example, MRl requires the formation of a strong magnetic field of about 1 to 20 kG. In addition, in the process of forming silicon single crystals using the pulling method, a magnetic field generator is installed around the outer periphery of the raw material melting crucible in order to further improve the uniformity of the single crystal. A so-called MCZ method is being used to perform pulling, and this MCZ device also requires the formation of a strong magnetic field.

In response to such demands, superconducting magnets are increasingly being used as magnetic field generators to generate strong magnetic fields. As superconducting materials used in such superconducting magnets, materials with high critical temperatures such as oxide super conductors have been discovered in recent years, but since they can be stably used in actual devices, Most of them are known metal-based or compound-based superconducting members.

Although this superconducting magnet is capable of generating a high magnetic field, an important issue was how to more efficiently shield magnetic fields leaking to the outside.

However, conventional magnetic shielding materials are generally made of materials with high magnetic permeability such as pure iron, silicon steel, and permalloy. The installed magnetic shielding device cannot be said to have a fully satisfactory magnetic shielding effect, and in order to satisfy the permissible limit of leakage magnetic field, a magnetic shielding member with a considerable thickness must be used. This has the disadvantage that the installation location and equipment cost are high.

(Problems to be Solved by the Invention) As mentioned above, magnetic shielding devices that have been used to shield leakage magnetic fields from superconducting devices such as conventional superconducting magnets are simply made of a material with high magnetic permeability that surrounds the outer periphery. Therefore, in order to obtain a sufficient magnetic shielding effect, it was necessary to use a considerably thick magnetic shielding member, which had the disadvantage of requiring high installation space and equipment costs. .

The present invention was made to address the problems of the prior art, and provides a magnetic shielding device that can reliably obtain a highly efficient magnetic shielding effect with a relatively small device. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) In other words, the present invention provides a method for disposing a magnetic shielding wall on the outer circumferential side of a superconducting device cooled by two or more types of refrigerant liquids having different boiling points. In a magnetic shielding device for shielding a leakage magnetic field by a magnetic shielding device, the magnetic shielding wall is formed of a member made of an oxide superconductor having a critical temperature higher than that of the superconducting member used in the superconducting equipment by at least 4.6- It is characterized by being configured to cool to the same temperature as the equipment.

(Function) As an oxide superconductor having a high critical temperature, perovskite type containing rare earth elements, such as Y-Ba-Cu-
0 series oxide superconductor, B1-8r-Ca-Cu-0
TI-Ca-Ba-Cu-0 based oxide superconductors are known. The critical temperature and critical magnetic field of these oxide superconductors are shown below.

YBa2Cua O7-δ: Tc-90KSHc+
-150eBi Sr Da Cu O:T
c-80~105K.

223x llc+ = 1000e TI Ha Ca Cu O: Tc-1111
~125K.

223X 11c1-1500e Considering the critical temperature of these oxide superconductors, it is possible to sufficiently exhibit superconducting properties even when cooled with liquid nitrogen; Cooling at , further increases the magnetic shielding effect due to the Meissner effect. and,
For example, Nb3 Sn and Nb-
Superconducting devices such as superconducting magnets using superconducting parts such as Tl use supercooling media such as liquid helium and liquid hydrogen to cool these superconducting members, and the evaporation and Its outer periphery is covered with a refrigerant liquid such as liquid nitrogen to promote liquefaction. Therefore, highly efficient magnetic shielding can be achieved by configuring the magnetic shielding wall made of an oxide superconductor to be cooled by a supercooling medium such as liquid helium or liquid hydrogen.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram schematically showing the configuration of an embodiment in which the magnetic shielding device of the present invention is applied to a single crystal manufacturing apparatus using the so-called MCZ method, which pulls a single crystal in a magnetic field.

In the figure, 1 is a crucible for melting raw materials, and a heater 2 is installed around the outer periphery of this crucible 1 so as to surround this crucible 1.
is installed, and this heater 2 is covered with a heat insulating wall 3 made of carbon or the like.

On the outer peripheral side of the heat insulating wall 3, a storage tank 4 for a supercooling medium such as liquid helium or liquid hydrogen is arranged using vacuum insulation or the like. A superconducting magnet 5 made of a superconducting member such as NJ Sn or Nb-Ti is installed in this supercooling medium storage tank 4, and a supercooling medium storage tank te4 is installed.
Magnetic shielding walls 6 made of an oxide superconductor are provided on the inner walls of the upper, outer circumferential side, and lower part of the storage tank 4 for supercooling medium.
It is installed so that it is immersed in a supercooling medium such as liquid helium or liquid hydrogen contained within.

The oxide superconductor constituting the magnetic shielding wall 6 is one having a higher critical temperature than the superconducting member used for the conductive magnet 5. As such an oxide superconductor,
For example, a-Cu-0 system (Lni, tYS
La, 5cSNdSSII% P, u, GtL D
Y% 110% Er, Tm5YbS1. At least one element selected from rare earth elements such as u, δ represents an oxygen defect and is usually a number of 1 or less, and a part of Ba can be replaced with 5rSea or the like. ) and oxide superconductors with the general formula: Bi25r2Ca2Cu30.

Examples include an 11a-8r-Ca-Cu-0-based oxide superconductor represented by the general formula T12Ba2Ca2Cu30x, and a T1-Ba-Ca-Cu-0-based oxide superconductor represented by the general formula: T12Ba2Ca2Cu30x.

The magnetic shielding wall 6 made of this oxide superconductor can be placed in a sintered body, thick film, sheet, or powder in a suitable container as long as it has a volume that can exhibit the desired magnetic shielding effect. It may be of any kind, such as one filled with water.

On the outer periphery side of the supercooling medium storage tank 4, there is a cooling tank containing a refrigerant liquid such as liquid nitrogen so as to cool liquid helium, liquid hydrogen, etc. contained in the supercooling medium storage tank 4. There are 7 containers installed.

Then, a raw material such as Sl or GaAs is put into Ruri 1, heated to above its melting point by a heater 2, and a magnetic field is applied by a superconducting magnet 5 to melt the raw material 8.
A single crystal is produced by making a seed crystal 9 attached to the tip of a crystal pulling shaft 9 disposed above the crucible 1 so as to be able to rise and fall freely, and bringing it into contact with the raw material melt, and pulling it while rotating the crystal pulling shaft 9. It is configured so that it can be obtained.

In a single crystal manufacturing apparatus equipped with a magnetic shielding device having the above configuration, two superconducting magnets were used as the superconducting magnets 5, and the leakage magnetic field was measured at a point 1001 from the outer wall of the single crystal manufacturing apparatus. 12,000 using the magnetic shielding device of this embodiment in which the magnetic shielding wall 6 made of oxide superconductor was cooled.
There was c.

In addition, for comparison with this invention, we have prepared two MCZs: one without magnetic shielding using a superconductor, and one with a magnetic shielding wall made of an oxide superconductor cooled with liquid nitrogen.
When the leakage magnetic field was measured under the same conditions as in the above example in a single crystal manufacturing apparatus using the method, it was 14,000 e for the one without magnetic shielding by a superconducting member, and 13,900 e for the one cooled by liquid nitrogen. Ta.

As described above, in the magnetic shielding device of this embodiment, the storage tank for supercooling medium such as liquid helium or liquid hydrogen, which has been conventionally used to cool superconducting magnets, is used only in the direction where magnetic shielding is required. By simply installing a magnetic shielding wall made of oxide superconductors, highly efficient magnetic Shielding can be achieved.

In addition, by simply adding a magnetic shielding wall made of oxide superconductor to a storage tank for supercooling medium such as liquid helium or liquid hydrogen, which has traditionally been used to cool superconducting magnets, the above-mentioned method can be achieved. Since highly efficient magnetic shielding can be achieved, the magnetic shielding device itself can be significantly downsized.

In the above embodiment, an example was explained in which the magnetic shielding device of the present invention was applied to a single crystal manufacturing apparatus using the MCZ method, but the present invention is not limited to this and can be applied to various types of superconducting magnets such as MRI. Applicable to the equipment used.

[Effects of the Invention] As explained above, according to the magnetic shielding device of the present invention, a compact and highly efficient magnetic shielding can be realized using cooling devices for various superconducting equipment.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing the configuration of a single crystal manufacturing apparatus using the MCZ method to which a magnetic shielding device according to an embodiment of the present invention is applied. 4...Super cooling medium storage tank 5...
......Superconducting magnet 6......Magnetic shielding wall made of oxide superconductor 7...Cooling container Applicant: Toshiba Corporation

Claims (1)

[Claims] (1) In a magnetic shielding device in which a magnetic shielding wall is arranged on the outer circumferential side of a superconducting device cooled by two or more types of refrigerant liquids having different boiling points, and the magnetic shielding wall shields leakage magnetic fields, the magnetic shielding wall is A magnetic shielding device characterized in that it is formed of a member containing at least an oxide superconductor having a higher critical temperature than the superconducting member used in the superconducting device, and is configured to be cooled to the same temperature as the superconducting device.