JPH05267725A - Superconducting magnet - Google Patents

Abstract

PURPOSE:To stably cool a superconducting magnet by a method wherein, when the superconducting magnet receives an external fluctuating magnetic field, the quantity of evaporation of helium, caused by the relative vibration generated between a shield plate and a superconducting coil by an induced current, is reduced. CONSTITUTION:Pertaining to the shielding plate 2 of a superconducting magnet, the part opposing to a superconducting coil 1 is composed of the material of high conductivity, and other part is composed of the material of low conductivity. The magnetic shield effect against the superconducting coil 1 is unchanged in the above-mentioned constitution, but the electromagnetic force of the whole shield plate 2 is decreased, its rigity is increased, and relative vibration is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the construction of superconducting magnets.

[0002]

2. Description of the Related Art A conventional superconducting magnet will be described with reference to FIGS.

The superconducting magnet comprises a superconducting coil 1, a shield plate 2 and a vacuum container 3. Superconducting coil 1
Is a superconducting coil placed in a metal container.
The container is filled with liquid helium for cooling the superconductor.

Further, in order to stably maintain the superconducting coil 1 in a superconducting state, it is necessary to reduce heat generated in the superconducting coil 1 and heat entering the superconducting coil 1 from the outside as much as possible. This is partly because the liquid helium that cools the superconducting conductor has a small heat capacity, so if the amount of intrusion heat / heat generation increases, the amount of liquid helium consumed by evaporation will increase and stable cooling of the superconducting conductor will not be possible. is there. In this way, the temperature of the superconducting conductor rises due to insufficient cooling or heat generation inside the superconducting coil, and when the temperature exceeds the critical temperature, the superconducting conductor changes to the normal conducting state and functions as a superconducting magnet. Will be lost.

Therefore, the superconducting coil 1 is fixed to the vacuum container 3 by the coil supporting member 4 made of a low heat conductive material. Further, in order to prevent convective heat transfer, the inside of the vacuum container is kept vacuum, and in order to reduce radiant heat, a shield plate cooled between the wall of the vacuum container 3 at room temperature and the superconducting coil 1 by liquid nitrogen or the like. 2 are installed.

When a fluctuating magnetic field acts on the superconducting coil 1 from the lateral direction 5 (arrow), in order to prevent the fluctuating magnetic field from the outside from causing an induced current to flow in the metal container and the superconducting conductor of the superconducting coil 1 to generate heat, Conventionally, vacuum container 3
Further, the shield plate 2 is made of a material having a high conductivity, and an inductive current is generated in the vacuum container 3 and the shield plate 2 to shield the fluctuating magnetic field with the reaction magnetic field.

[0007]

However, in such a structure, the induced current flowing through the vacuum container and the shield plate is
An electromagnetic force is generated by the interaction with the magnetic field created by the superconducting coil, causing the wall of the vacuum container and the shield plate to vibrate. The vibration of the vacuum vessel wall is further transmitted to the shield plate 2 and the superconducting coil 1 via the coil supporting member 4 and vibrates them.
Due to these vibrations, relative vibration is generated between the shield plate 2 and the superconducting coil 1.

Due to this relative vibration, the conductive plate vibrates in the DC magnetic field created by the superconducting coil.
An induced current is induced there. Further, when the fluctuating magnetic field generated by the induced current reaches the superconducting coil, heat is generated in the metal container / superconducting conductor of the superconducting coil due to the influence of the fluctuating magnetic field, and the consumption of liquid helium cooling the superconducting coil 1 is reduced. There is a problem that the number of the superconducting conductors cannot be stably cooled due to the increase in the number.

According to the present invention, in a superconducting magnet subjected to a fluctuating magnetic field, the heat generation of the metal container and the superconducting conductor of the superconducting coil cooled by liquid helium is reduced to stably cool the superconducting conductor and stabilize as a superconducting magnet. The purpose is to improve sex.

[0010]

Therefore, in the present invention, only the portion of the shield plate of the superconducting magnet facing the superconducting coil is made of a material having a high conductivity, and the other portions are made of a material having a low conductivity. Constitute.

[0011]

[Function] Since the portion of the shield plate facing the superconducting coil has a high conductivity, the fluctuating magnetic field attempting to enter the superconducting coil is shielded by the induced current induced in this portion,
The fluctuating magnetic field from the outside does not reach the superconducting coil.

On the other hand, since the other portions are formed of a material having a low conductivity, the induced current which has been conventionally induced in this portion is hardly generated, and therefore the electromagnetic force in this portion is also significantly reduced. Further, conventionally, it was difficult to increase the rigidity of the shield plate because copper or aluminum was used as the material having high conductivity, but in the present invention, a high-strength material is used in the central portion that greatly contributes to the rigidity of the shield plate. Because you can
It also has the effect of increasing the rigidity of the shield plate, and can reduce the vibration of the shield plate from both aspects of electromagnetic force and rigidity.

Further, even if the shield plate and the superconducting coil vibrate relative to each other due to the transmission of the vibration of the vacuum container, a part of the shield plate is made of a material having a low electric conductivity, so that an induced current is induced. Is restricted, the induced current in the shield plate is reduced, and the amount of the variable magnetic field generated by the induced current reaching the superconducting coil can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the embodiments shown in FIGS.

In the shield 2 provided in the vacuum container 3, the portion 2a facing the superconducting coil 1 is made of copper or aluminum having a high electric conductivity, and the other portion 2b has a low electric conductivity such as high strength stainless steel. Constructed of highly rigid material. It should be noted that in the embodiment, a material having a high conductivity is used only in the direction in which the fluctuating magnetic field enters, assuming that the fluctuating magnetic field from the outside is applied from the direction 5, but the fluctuating magnetic field from the outside is applied from other directions. When intruding or intruding from multiple directions, the portion facing the superconducting coil 1 accordingly.
2a shall be set.

Further, in this embodiment, the material having a high conductivity and the material having a low conductivity are joined at the joint portion 8. However, for convenience of manufacturing, for example, the entire shield plate 2 is made of a material having a conductivity. Even if the material is made of a low material and the material having high conductivity is placed only on the portion 2a facing the superconducting coil 1 so as to overlap the material having low conductivity, the operation and effect are not changed.

As described above, since the portion 2a of the shield plate 2 facing the superconducting coil 1 is made of a material having a high conductivity, the external fluctuating magnetic field trying to enter the superconducting coil 1 is shielded by the shield plate 2. To be done.

Further, since the other portion 2b of the shield plate 2 which does not face the superconducting coil is made of a material having a low electric conductivity, the induced current and electromagnetic force of the shield plate as a whole are reduced and vibration can be reduced. Further, since the high strength material is used for the other portion 2b, the rigidity of the shield plate 2 as a whole is increased, and therefore vibration is suppressed also from that point.

Further, even when the superconducting coil 1 and the shield plate 2 vibrate relative to each other, the flow path of the induced current induced by the magnetic field generated by the superconducting coil 1 is limited,
The induced current and the varying magnetic field produced thereby are also reduced.

According to the present invention, an induced current is generated in the superconducting coil by the relative vibration of the shield plate and the superconducting coil,
It is possible to suppress heat generation in the superconducting coil. Another embodiment of the present invention will be described with reference to FIG.

A comb-shaped good heat conductive material 6 is provided on a material having a low electric conductivity in a portion 2b of the shield plate 2 which does not face the superconducting coil 1 so as not to serve as a flow path for an induced current.

In general, since a material having a low electric conductivity has a low thermal conductivity, the corresponding portion of the shield plate 2 is not sufficiently cooled and radiative heat transfer to the superconducting coil 1 is prevented from increasing. This is the addition of a heat conductive material. in this case,
A material having a high conductivity of the portion 2a facing the superconducting coil,
If a closed loop is formed with the good thermal conductive material 6, the effect becomes a flow path of an induced current, and the effect is reduced. Therefore, the effect of the invention is reduced by installing the good thermal conductive material 6 in a comb shape so that the closed loop is not formed. Without doing so, an increase in radiant heat transfer to the superconducting coil 1 can be prevented. Generally, a material having a high electrical conductivity also has a high thermal conductivity, so that the good thermal conductive material 6 and the material having a high electrical conductivity can be integrated as the same material.

[0023]

According to the present invention, the induced current induced in the shield plate by the fluctuating magnetic field from the outside is reduced, the electromagnetic force of the shield plate as a whole is reduced, and the rigidity of the shield plate is enhanced, whereby the shield plate is increased. Vibration of the superconducting coil can be reduced. Even when the shield plate and the superconducting coil oscillate relative to each other, the flow path of the induced current is limited to reduce the induced current and the fluctuating magnetic field generated by it, thereby suppressing heat generation in the superconducting coil and stabilizing the superconducting conductor. It is possible to provide a highly safe superconducting magnet by cooling the material.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting magnet according to the present invention.

FIG. 2 is an explanatory view of a magnetic shield action according to a detail of FIG.

FIG. 3 is a perspective view of a shield plate according to another embodiment of the present invention.

FIG. 4 is a perspective view of a conventional superconducting magnet.

5 is a view taken along the line VV of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Superconducting coil 2 ... Shield plate 2a ... Portion facing the superconducting coil 2b ... Portion not facing the superconducting coil 3 ... Vacuum container 5 ... Direction of influx of fluctuating magnetic field from the outside 6 ... Good thermal conductive material 7 ... Joined portion

Claims (3)

[Claims] 1. A superconducting magnet comprising a vacuum container, a shield plate, and a superconducting coil, wherein the shield plate is made of a material having a high electrical conductivity at a portion facing the superconducting coil and a material having a lower electrical conductivity than the other portion. A superconducting magnet characterized by being formed. 2. The superconducting magnet according to claim 1, wherein a high-strength and high-strength stainless material is used as the material having a low electric conductivity. 3. A material having a low electrical conductivity for the shield plate,
The superconducting magnet according to claim 1 or 2, wherein a good heat conductive material having a shape that does not form a flow path of an induced current is formed.