JPH08330125A - Magnetic shielding apparatus - Google Patents

Abstract

PURPOSE: To provide a magnetic shielding apparatus capable of normally conductively transferring by friction of eddy current and electromagnetic force without reducing the shielding effect even if an exciting speed is large. CONSTITUTION: A good conductor 12 is provided between a superconducting magnetic shield 14 for preventing the external leakage of a magnetic field generated from a superconducting magnet 10 and the magnet 10. An eddy current of the direction for cancelling the magnetic field generated from the magnet 10 flows to the conductor 12 to alleviate the change of the magnetic field applied to the shield 14. The conductor 12 and the shield 14 are thermally and electrically insulated, and the part or all of the shield 14 is prevented from being normally conductively transferred by the friction generated between the conductor 12 and the shield 14 by the heat or electromagnetic force generated by the eddy current flowing to the conductor 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield device, and more particularly to a magnetic shield device for preventing magnetic leakage of a superconducting magnet.

[0002]

2. Description of the Related Art Conventionally, a magnetic field generator capable of generating a strong magnetic field using a superconducting magnet has been used for various purposes. Since the strength of the magnetic field generated by these magnetic field generators reaches from several thousand gauss to several tesla, it is necessary to arrange a magnetic shield device around the magnetic field generators in order to prevent adverse effects on the human body. An example of such a magnetic shield device is disclosed in Japanese Patent Laid-Open No. 6-275430.

FIG. 4 shows a sectional view of the superconducting magnetic field generator disclosed in the above-mentioned conventional example. In FIG.
Superconducting magnet 100 is housed inside an inner tank 103 that stores liquid helium 102. The inner layer 103 is
The periphery of the shield plate 104 is covered with a shield plate 104 made of a superconductor and a metal plate having good heat conductivity. The shield plate 104 is cooled by the liquid nitrogen layer 105 that stores liquid nitrogen. All of these are housed in the outer tank 106 arranged on the outermost periphery, and the space between the inner layer 103 and the outer layer 106 is in a vacuum state.

With the above structure, the superconducting magnet 10
The magnetic field generated by 0 is blocked by the shield plate 104 and is prevented from leaking to the outside of the device.

[0005]

However, in the above-mentioned conventional example, when the changing speed of the magnetic field generated in the superconducting magnet 100 and applied to the shield plate 104, that is, the exciting speed of the superconducting magnet 100 is high, the shield plate 104 is not affected. A flux jump occurs and the shield plate 10
There was a problem that the magnetic shield ability of No. 4 decreased to one third or less of the true ability.

Further, as the shield plate 104, a commercially available composite material of Nb-Ti and Al or Cu film is used, but an eddy current is generated in Al or Cu by the magnetic field generated in the superconducting magnet 100. There is also a problem that a part of the shield plate 104 is transferred to the normal conduction state and the quench spreads due to the flow and heat generation or the friction between Nb-Ti and Al or Cu due to the electromagnetic force.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is not to reduce the shield effect even if the excitation speed is high, and to make a normal conduction transition due to friction due to eddy current or electromagnetic force. It is to provide a magnetic shield device that does not have the above.

[0008]

In order to achieve the above object, the present invention is a magnetic shield device for preventing leakage of a magnetic field generated by a magnetic field generator to the outside, which is provided around the magnetic field generator. A state in which there is no electrical and thermal contact between the superconducting magnetic shield body, which is provided and blocks the magnetic field from the magnetic field generating body, and between the magnetic field generator and the superconducting magnetic shield body. And a good conductor having a low resistivity arranged in.

Further, the magnetic shield device according to the present invention further includes a plurality of shield plates attached to the support pins for supporting the magnetic field generator and the superconducting magnetic shield body by using a good thermal conductor, and the shield plate. Is characterized in that it blocks magnetic leakage and heat intrusion from a through hole for penetrating the support pin in the superconducting magnetic shield.

[0010]

According to the above-mentioned structure, a good conductor having a low resistivity is disposed between the magnetic field generator and the superconducting magnetic shield in a state where the superconducting magnetic shield is not electrically and thermally contacted with each other.
Since an eddy current flows in a direction that relaxes the rate of change of the magnetic field applied to the superconducting magnetic shield, this can prevent the shield effect of the superconducting magnetic shield from being lowered.

Further, since there is no thermal contact between the good conductor and the superconducting magnetic shield body, a part of the shield body is not heated and a normal conduction transition does not occur due to heat due to an eddy current generated in the good conductor or friction due to an electromagnetic force.

Further, since the shield plate is provided on the support pin for supporting the generation of the magnetic field, it is possible to prevent magnetic leakage and heat intrusion from the through hole for penetrating the support pin.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a sectional view of a superconducting magnet in which the magnetic shield device according to the present invention is used. In FIG. 1A, a low-resistivity good conductor 12 made of, for example, a plate of Al, Cu, Ag, or the like is disposed outside the superconducting magnet 10 that is a magnetic field generator. A superconducting magnetic shield 14 made of a superconducting material is arranged outside the good conductor 12. The good conductor 12 is provided in a state where it is not in electrical or thermal contact with the superconducting magnetic shield body 14.

The superconducting magnetic shield 14 is shown in FIG.
As shown in FIG. 3, a superconducting material, for example, a Nb-Ti plate is provided with a layer of Cu or the like as a stabilizing material on both surfaces or one surface.

The above superconducting magnet 10 and good conductor 12
The superconducting magnetic shield 14 is housed in the inner tank 16 and cooled with liquid He or the like. A radiation shield 18 made of Cu is provided on the outer side of the inner tank 16 to block heat entering from the outside. The radiation shield 18 is cooled by liquid nitrogen 20 or a cooler (not shown) or the like. All the components described above are housed in the outer tank 22 and the outer tank 22 and the inner tank 1
The space 24 between 6 and 6 is kept in a vacuum state.

In this embodiment, the superconducting magnet 1
The magnetic field generated from 0 is blocked by the superconducting magnetic shield 14 to prevent magnetic leakage to the outside. As described above, the good conductor 12 is provided inside the superconducting magnetic shield body 14, and an eddy current is generated in the good conductor 12 by the magnetic field generated from the superconducting magnet 10. This eddy current flows in a direction that resists the change in the magnetic field generated from the superconducting magnet 10, so that the change in the magnetic field applied to the superconducting magnetic shield body 14 is alleviated. Therefore, even if the exciting speed of the superconducting magnet 10 is increased and the changing speed of the magnetic field is increased, the flux jump is less likely to occur in the superconducting magnetic shield body 14, and the superconducting magnetic shield body 1 is
The magnetic shield ability of No. 4 can be maintained high.

Further, since the good conductor 12 and the superconducting magnetic shield 14 are provided in a state where they are not in electrical and thermal contact with each other, heat generated by an eddy current flowing in the good conductor 12 and a good conductor due to electromagnetic force. Since friction is generated between the superconducting magnetic shield 12 and the superconducting magnetic shield 14, a part or all of the superconducting magnetic shield 14 does not undergo normal conduction transition.

The radiation shield 18 for preventing heat invasion from the outside is made of Cu. If this is a composite body in which a high temperature superconducting material is combined with Cu, Al, etc., The superconducting magnetic shield body 14 and the radiation shield 18 can be used together.

The superconducting magnet 10 and the superconducting magnetic shield 14 are supported by the support pins 26 with the outer tank 22. Since the outer tank 22 is normally at room temperature and the superconducting magnet 10 and the like are at the temperature of liquid helium, the support pin 26 has a poor thermal conductivity in the FRP.
And so on. The support pin 26 penetrates the superconducting magnetic shield body 14, the inner tank 16, and the radiation shield 18 and is fixed to the outer tank 22. Therefore, there is a possibility that magnetic field leakage or heat intrusion may occur from this through hole.

FIG. 1C is a sectional view showing a structural example for preventing the magnetic field leakage and heat intrusion. FIG.
In (c), a shield plate 28 made of the same superconducting material as the superconducting magnetic shield body 14 is provided outside the radiation shield 18 and around the support pin 26. The shield plate 28 is made of Ag solder, Pb solder, Pb-.
The fixing material 30 such as In solder is attached to the support pin 26 in a state where thermal contact is good.

Since the shield plate 28 is made of the same superconducting material as the superconducting magnetic shield body, it can block the magnetic field leaking from the through hole of the radiation shield 18, thereby preventing the magnetic leakage to the outside. Can be prevented.

Further, the radiation shield 18 is made of Cu having a high thermal conductivity, and the shield plate 28 also has a structure shown in FIG.
As shown in (b), since a Cu layer is formed on the surface of the superconducting material, this also has a high thermal conductivity. Then, the radiation shield 18 and the shield plate 2
Since No. 8 maintains good thermal contact with the fixing material 30, the radiation shield 18 and the shield plate 28 are kept at the temperature of almost liquid nitrogen by the liquid nitrogen 20. Therefore, the heat entering from the outside is blocked by the radiation shield 18 and the shield plate 28, and the heat entering from the through hole of the radiation shield 18 can be prevented.

FIG. 2 shows a sectional view of another embodiment of the magnetic shield device according to the present invention. In FIG.
The superconducting magnet 10 and the good conductor 12 and a part of the superconducting magnetic shield 14 are shown, and the inner tank 16 and the members outside thereof shown in FIG. 1A are the same as those in FIG. 1A. , Are omitted. Therefore, each member shown in FIG. 2A is cooled by liquid helium or the like. The functions of the good conductor 12 and the superconducting magnetic shield 14 are similar to those described in the embodiment of FIG.

In FIG. 2, the good conductor 12 is formed in a film shape. In order to support the film of the good conductor 12 and to cut off thermal contact and electrical contact between the good conductor 12 and the superconducting magnetic shield body 14, the good conductor 1
A shield support 32 made of FRP is provided between the superconducting magnetic shield body 2 and the superconducting magnetic shield body 14.

In this embodiment, the magnetic field generated by the superconducting magnet 10 is the strongest at the point A in FIG. 2, so that the superconducting endless coil 34 centered at the point A is used to cancel the change in the magnetic field. It is arranged. Since a current flows in the superconducting endless coil 34 in a direction of canceling the change in the magnetic field generated by the superconducting magnet 10, the changing speed of the magnetic field applied to the superconducting magnetic shield 14 near the point A is relaxed. can do. Therefore, it is possible to prevent the normal conduction transition due to the flux jump from occurring in the superconducting magnetic shield body 14.

Further, since the magnetic field at the point A in the figure is large, the structure is such that a layer of the shield support 32 and the superconducting magnetic shield body 14 is further added around the magnetic field.
Generally, when the number (thickness) of the superconducting magnetic shield 14 is increased, the strength of the magnetic field that can be interrupted also increases.

FIG. 3 shows a diagram in which the magnetic shield capacity of the magnetic shield device according to the present invention is compared with that of the conventional example. In FIG. 3, black circles indicate the present embodiment, and white circles indicate the conventional example. Further, the horizontal axis represents the excitation speed, that is, the changing speed of the magnetic field, as the changing speed of the current flowing through the superconducting magnet. The vertical axis represents the magnitude of the magnetic field in which the flux jump has occurred in the superconducting magnetic shield body 14 at a constant excitation speed.

As shown in FIG. 3, in the present embodiment, the flux jump generating magnetic field is higher than in the conventional example, and it is shown that the magnetic shield ability is improved as compared with the conventional example.

[0030]

As described above, according to the present invention,
The good conductor provided between the magnetic field generator and the superconducting magnetic shield reduces the rate of change of the magnetic field, preventing the shield effect of the superconducting magnetic shield from deteriorating even if the excitation speed of the magnetic field generator increases. it can.

Further, since the good conductor and the superconducting magnetic shield are thermally and electrically insulated from each other, heat caused by an eddy current generated in the good conductor and friction between the good conductor and the superconducting magnetic shield are caused. It is possible to prevent a part or all of the superconducting shield from being transferred to the normal conducting state.

Further, since the shield plate is provided around the outer tub side of the support pin that supports the superconducting magnet and the like, it is possible to prevent magnetic leakage and heat intrusion in the support pin portion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a superconducting magnet using a magnetic shield device according to the present invention.

FIG. 2 is a cross-sectional view of another embodiment of a superconducting magnet using the magnetic shield device according to the present invention.

FIG. 3 is a graph diagram for explaining a difference in magnetic shield ability between this embodiment and a conventional example.

FIG. 4 is a cross-sectional view of a conventional superconducting magnetic field generator using a magnetic shield device.

[Explanation of symbols]

10 superconducting magnet, 12 good conductor, 14 superconducting magnetic shield, 16 inner tank, 18 radiation shield, 2
0 liquid nitrogen, 22 outer tank, 24 space, 26 support pin, 28 shield plate, 30 fixing material, 32 shield support, 34 superconducting endless coil.

Claims (2)

[Claims] 1. A magnetic shield device for preventing a magnetic field generated by a magnetic field generator from leaking to the outside, the superconducting magnet being disposed around the magnetic field generator and blocking a magnetic field from the magnetic field generator. Between the shield body, the magnetic field generator and the superconducting magnetic shield body,
A magnetic shield device, comprising: a good conductor having a low resistivity, which is arranged in a state where the superconducting magnetic shield body is not in electrical and thermal contact. 2. The magnetic shield apparatus according to claim 1, further comprising a plurality of shield plates attached to the support pins supporting the magnetic field generator and the superconducting magnetic shield body by using good thermal conductors, and the shield. A plate shields magnetic leakage and heat intrusion from a through hole for penetrating the support pin in the superconducting magnetic shield body.