JPH0620011B2 - Superconducting magnetic field generator - Google Patents

Description

The present invention relates to a superconducting magnetic field generator, and more particularly to a superconducting solenoid coil, a correction superconducting coil connected in series with the superconducting solenoid coil, and both coils. The present invention relates to a superconducting magnetic field generator having a liquid helium container, a superconductor, and the like.

[Background of the Invention]

FIG. 1 shows a conventional example of a superconducting magnetic field generator used in a nuclear magnetic resonance diagnostic apparatus. As shown in the figure, the superconducting magnetic field generator comprises a superconducting solenoid coil 1, correction superconducting coils 2a and 2b, a liquid helium container 4 containing these and liquid helium 3 as a cryogen, and this liquid helium container 4 Is constituted by a liquid nitrogen container 6 which surrounds the liquid nitrogen container 5 through a vacuum heat insulating tank 5, an outer wall 8 which surrounds the liquid nitrogen container 6 through a vacuum heat insulating tank 7, and the like. The superconducting solenoid coil 1 generates a magnetic field necessary for nuclear magnetic resonance, and the correction superconducting coils 2a and 2b
This magnetic field has a high homogeneity in the central space 9, and a nuclear magnetic resonance diagnosis is performed using the high homogeneity magnetic field of the high homogeneity space 9 which is the central space.

In the superconducting magnetic field generator configured as described above, when magnetic field disturbance occurs outside, it directly affects the high homogeneity space 9, and the homogeneity of the magnetic field deteriorates, which hinders diagnosis.

FIG. 2 shows a conventional example of a superconducting magnetic field generator which replaces this. The superconducting solenoid coil 1 and the correction superconducting coils 2a and 2b are provided with thin walled hollow cylindrical superconductors 10 which are concentric with the superconducting solenoid coil 1 and whose centers coincide with each other. Body 10
The effect of the disturbance magnetic field is removed by. Since the superconductor 10 having the through hole has a property of keeping the magnetic flux passing through the hole constant, the effect of the disturbance magnetic field is reduced by utilizing this property. That is, the superconductor 10 has a function of making the magnetic flux passing through the opening constant, but when a disturbance magnetic field is generated, this is a current that is in the opposite direction to the disturbance magnetic field and generates a magnetic field of the same magnitude, That is, a diamagnetic current flows through the superconductor 10 to cancel the disturbance magnetic field and keep the magnetic flux constant. However, in this superconducting magnetic field generator, the diamagnetic current flows over the entire superconducting conductor 10 covering the superconducting solenoid coil 1 and has a drawback that the magnetic field in the high homogeneity space 9 becomes unpleasant.

[Object of the Invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a superconducting magnetic field generator capable of reducing the influence of a disturbance magnetic field and maintaining a highly uniform magnetic field.

[Outline of Invention]

That is, the present invention comprises a superconducting solenoid coil, a correction superconducting coil connected in series with the superconducting solenoid coil, and a liquid helium container accommodating both coils, and a disturbance magnetic field around the superconducting solenoid coil. In a superconducting magnetic field generator provided with a superconductor for removing the effect of, the cross-sectional area of the superconductor is formed smaller than the cross-sectional area of the superconducting solenoid coil, and the superconductor is coaxial with the superconducting solenoid coil. The superconducting solenoid coil is provided at least on both sides in the axial direction, and each of these superconductors is provided with a persistent current switch for transitioning from a superconducting state to a normal conducting state. So that it flows through a superconductor with a cross-sectional area smaller than that of the solenoid coil. It made.

Example of Invention

Hereinafter, the present invention will be described based on the illustrated embodiments. One embodiment of the present invention is shown in FIGS.
Since the same parts as those of the prior art are designated by the same reference numerals, the description thereof will be omitted. In the present embodiment, the cross-sectional area (cross-section 11) of the superconductors 10a and 10b is made smaller than the cross-sectional area of the superconducting rhenoid coil 1, and the superconductors 10a and 10b are coaxial with the superconducting solenoid coil 1 and the axis of the superconducting solenoid coil 1 is the same. Provided on both sides in the direction, and each of these superconductors 1
0a and 10b were equipped with persistent current switches 12a and 12b that transition from a superconducting state to a normal conducting state. By doing so, the diamagnetic current is reduced to the superconductor 1 having a small cross section.
0a, 10b, the high-conductivity magnetic field 9 (high-uniformity space) is not affected, the influence of the disturbance magnetic field is reduced, and the high-uniformity magnetic field 9 can be maintained. A magnetic field generator can be obtained.

That is, a pair of superconductors 10a and 10b forming a closed circuit are provided at the shaft end of the superconducting solenoid coil 1 coaxially with the superconducting solenoid coil 1 and symmetrically about the center. The superconductors 10a and 10b are provided with permanent current switches 12a and 12b for transferring the superconductors from the superconducting state to the normal conducting state.
And the cross-section 11 thereof is made smaller than the conventional one. To reduce the cross section 11, a single winding or a multiple winding may be used to form a single winding 11a or a multiple winding 11b. By doing so, when a disturbance magnetic field is generated, the superconductor 10
A diamagnetic current flows through a and 10b to cancel the disturbance magnetic field, and because its cross section is made smaller, it does not flow over the entire superconducting solenoid coil 1 as in the conventional case. Will not affect.

That is, when the superconducting solenoid coil 1 and the correction superconducting coils 2a and 2b are excited by the superconducting coil power source 13, the heater power source 14 heats the heater wires 15, 15a, 15b.
b is heated to cause the permanent current switches 12, 12a, 12b to transition from the superconducting state to the normal conducting state. The superconducting solenoid coil 1 and the correction superconducting coils 2a, 2
b is excited, and when the combined magnetic field of these coils 1, 2a, 2b reaches a predetermined value, the heater wires 15, 15a, 15b
The current flowing through the switch to turn off the permanent current switch 12, 12a,
12b is changed from the normal conducting state to the superconducting state. In this way, the closed circuit including the superconducting solenoid coil 1 and the correction superconducting coils 2a and 2b and the superconductor 10 are formed.
The closed circuit of a and 10b becomes a permanent current state, and stably holds the high-uniformity magnetic field 9. When a disturbance magnetic field is generated, a diamagnetic current flows through the superconductors 10a and 10b to cancel the disturbance magnetic field as described above.
Since it flows through a small closed circuit of cross section 11 of 0a and 10b,
The influence on the highly uniform magnetic field 9 can be reduced, and the highly uniform magnetic field 9 can be stably maintained.

FIG. 6 shows another embodiment of the present invention. In this embodiment, superconductors 10c, 10d and 10 having a small cross section and a closed circuit are formed at the shaft end of the superconducting solenoid coil 1.
Two pairs of e and 10f were provided coaxially with the superconducting solenoid coil and symmetrically about the center. And superconducting solenoid coil 1
Centrally symmetric superconductors 10g and 10h which are concentric with the superconducting solenoid coil 1 are provided on the outer periphery of the. This superconductor 1
It goes without saying that 0g and 10h are also formed in a closed circuit having a small cross section. Thus, the superconductors 10c, 10d, 10
Since e, 10f, 10g, and 10h are provided in multiple stages, the influence of the disturbance magnetic field can be prevented over multiple stages as compared with the case described above, and the high-uniformity magnetic field 9 can be stably held.

FIG. 7 shows still another embodiment of the present invention. In this embodiment, the superconductors 10c and 10d are fixed to the inner wall of the liquid helium container 4 in the axial direction of the superconducting solenoid coil 1, and the superconductors 10g and 10h are fixed to the inner wall of the liquid helium container 4 in the radial direction of the superconducting solenoid coil 1. . By doing so, the superconductors 10c, 10d, 10
Position setting and fixing of g and 10h can be performed more accurately and easily than in the case described above.

FIG. 8 shows still another embodiment of the present invention. In this embodiment, the superconductors 10c and 10d are fixed to the outer wall of the liquid helium container 4 in the axial direction of the superconducting solenoid coil 1, and the superconductors 10g and 10h are fixed to the outer wall of the liquid helium container 4 in the radial direction of the superconducting solenoid coil 1. . Also in this case, the superconductors 10c, 10d, 10g, and 10h can be accurately set in position and can be easily fixed, and the same effect as the above case can be obtained.

FIG. 9 shows still another embodiment of the present invention. In this embodiment, the superconductors 10i and 10j are formed in a square shape. In this case as well, it is possible to obtain the same effects as the above-mentioned case.

In this embodiment, the ring-shaped superconductors 10a to 10h and the paddle-shaped superconductors 10i and 10j are used separately, but the present invention is not limited to this, and both may be used together.

〔The invention's effect〕

As described above, in the present invention, the diamagnetic current flowing in the superconductor cancels the disturbance magnetic field, but does not affect the high homogeneity magnetic field, so that the influence of the disturbance magnetic field can be reduced and the high homogeneity magnetic field can be reduced. It is possible to obtain a superconducting magnetic field generator capable of holding.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of a conventional superconducting magnetic field generator, and FIG.
FIG. 3 is a vertical cross-sectional view of a main part of a superconducting magnetic field generator of another example of the conventional superconducting magnetic field generator, and FIG. FIG. 4 is a partially longitudinal front view of a superconductor of the same embodiment, FIG. 5 is an equivalent circuit diagram of FIG. 3, and FIG. 6 is a superconducting device of another embodiment of the superconducting magnetic field generator of the present invention. FIG. 7 is a vertical sectional side view of a main part of a magnetic field generator, FIG. 7 is a vertical sectional side view of a main part of a superconducting magnetic field generator of still another embodiment of the superconducting magnetic field generator of the present invention, and FIG. 8 is a superconducting magnetic field generator of the present invention. FIG. 9 is a vertical sectional side view of a main part of a superconducting magnetic field generator according to still another embodiment of the present invention. FIG. 9 is a front view and a side view of a main part of a superconducting magnetic field generator according to still another embodiment of the superconducting magnetic field generator of the present invention. 1 ... Superconducting solenoid coil, 2a, 2b ... Correction superconducting coil, 4 ... Liquid helium container, 9 ... Highly uniform magnetic field (space), 10a, 10b, 10c, 10d, 1
0e, 10f, 10g, 10h, 10i, 10j ... Superconductor, 11 ... Section, 12, 12a, 12b ... Permanent current switch, 13 ... Superconducting coil power supply, 14 ...
Power supply for heater, 15, 15a, 15b ... Heater wire.

Claims (3)

[Claims] 1. A superconducting solenoid coil, a correction superconducting coil connected in series with the superconducting solenoid coil, and a liquid helium container accommodating both of these coils, and a disturbance around the superconducting solenoid coil. In a superconducting magnetic field generator provided with a superconductor for removing the influence of a magnetic field, a cross-sectional area of the superconductor is formed smaller than that of the superconducting solenoid coil, and the superconductor is coaxial with the superconducting solenoid coil. 2. A superconducting magnetic field generator, characterized in that it is provided on at least both axial sides of a superconducting solenoid coil, and each of these superconductors is provided with a persistent current switch for transitioning from a superconducting state to a normal conducting state. 2. The superconducting magnetic field generator according to claim 1, wherein the superconductor is arranged on an inner wall surface or an outer wall surface of the liquid helium container. 3. The superconducting magnetic field generator according to claim 1, wherein an inner diameter of the superconductor is larger than an inner diameter of the superconducting solenoid coil.