JPS60157206A - High uniform magnetic-field magnet - Google Patents

Abstract

PURPOSE:To prevent coupling between an inclined magnetic-field coil and a coil for correcting the magnetic field, and to maintain the high uniformity of the magnetic field by forming a pair of coils for correcting the magnetic field by the combination of two coils, the directions of windings thereof are each directed oppositely and in which the sum of induced electromotive force by inclined magnetic-field coils is zero. CONSTITUTION:Coils 12, 12 for correcting a magnetic field forming a pair by the left and the right are shaped by the combination of two coils 12a, 12b, the directions of windings thereof are directed oppositely and in which the sum of the induced electromotive force of mutual coils by inclined magnetic-field coils is zero. The directions of windings of combination coils 12a, 12b are reversed even in all coils for correcting the magnetic field in even order coil and odd order coil patterns. The turn ratios of windings for the combination coils 12a, 12b are designed so that the algebraic sum of induced electromotive force (the induced electromotive force is determined by a coupling constant of the number of turns and the inclined magnetic-field coil and the magnetic-field rate of the inclined magnetic-field coil) generated in both coils by the magnetic flux of the inclined magnetic-field coil 3 each interlinked to both coils is zero.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a sub-uniform magnetic field magnet used in equipment utilizing nuclear magnetic resonance.

(b) Prior art and its problems At present, the high uniform magnetic field magnets used in nuclear magnetic resonance convenience stores and tomography equipment, etc. include permanent magnets, but most of them are normal or superconducting electromagnets. is occupying. However, in the case of electromagnets, there is a limit to the uniformity of the magnetic field that can be obtained with a simple solenoid shape. Therefore, when a highly uniform magnetic field is required, a Helmholtz coil is used, or a pair of left and right coils are installed inside the main coil (
A method is adopted in which a magnetic field supplementary coil is arranged and the coil is excited so that it faces the center of the magnetic field.

FIG. 1 shows a conventional highly uniform magnetic field magnet, which is the subject of improvement in the present application. By changing the current of the coil used to obtain information at high speed, the uniform magnetic field formed by the main coil and the correction coil is intentionally disturbed, and the value of the six wandering fields at each point in space is changed. Gradient field coils 3, 3 are provided.

The pair of magnetic field correction coils 2, 2 are connected to each other, and the same current flows through them. However, the current direction differs depending on the type of coil. That is, this coil includes an even-order coil that expands the magnetic field strength over a distance of 14IZ from the center and corrects a magnetic field proportional to an even-numbered order of Z, and an odd-order coil that corrects a magnetic field proportional to an odd-numbered order of Z. There are two types. As shown in FIG. 2, an even-order fill is where the left and right coils 2 are energized in the same direction, and an odd-order coil is where the left and right coils are energized in opposite directions as shown in FIG.

On the other hand, as the gradient magnetic field coils 3, 3, in order to generate a non-uniform magnetic field in the Z-axis direction, odd-order coils are used which are energized in the "Q" direction from ○ in FIG. 1 or vice versa.

Here, odd-numbered coils are coupled when their magnetic fluxes interlink with each other. Even-order coils theoretically do not couple with odd-order coils, but depending on manufacturing precision errors, this coil may also cause coupling.

For this reason, in the conventional magnet as shown in FIG. 1, when the gradient magnetic field coil 3 is excited, the current in the magnetic field correction coil 2 fluctuates, making it difficult to maintain the uniformity of the magnetic field.
Further, when the current fluctuation is severe and the magnetic field supplementary coil is a superconducting coil, the critical current value may be exceeded and quenching (transition to normal conductivity) may occur.

(C) Means for Solving the Problems The present invention provides a highly uniform magnetic field magnet that eliminates the problem of coupling between magnetic field correction coils and gradient magnetic field coils.The features of this magnet are shown in FIG. As shown in the figure, the left and right pairs of magnetic field correction coils 12.12 are formed by two coils 12a and 12b whose winding directions are opposite so that the sum of the induced electromotive forces of the mutual coils by the gradient magnetic field coils becomes zero.
It is formed by a combination of

FIG. 5 schematically shows the winding pattern of the even-order coil, and FIG. 6 schematically shows the winding pattern of the odd-order coil. Both magnetic field correction coils are combined coils 12a.

The winding direction of 12b is reversed. As shown in FIG. The power is designed so that the algebraic sum of the number of turns, the coupling constant of the gradient magnetic field coil, and the rate of change of the magnetic field of the gradient magnetic field coil becomes zero.

At this time, if the number of turns of the coils 12a and 12b are completely equal, the magnetic forces of both coils cancel each other out, making it impossible to generate a magnetic field and stop functioning as a gradient magnetic field coil. Therefore, the relative position with respect to the gradient magnetic field coil 3 should be determined appropriately. , it is necessary to make a difference in the number of turns of both coils.

Note that the coil 12a.

Even if the number of turns in 121) is different, the induced electromotive force can be reduced to zero by changing the coupling constant of each coil to the gradient magnetic field coil by, for example, shifting its relative position to the gradient magnetic field coil.

(e) Effects As explained above, in the highly uniform magnetic field magnet of the present invention, the pair of magnetic field correction coils are wound in opposite directions so that the sum of the induced electromotive force by the gradient magnetic field coils becomes zero. By forming a combination of two coils, we can prevent coupling between the gradient magnetic field coil and the magnetic field correction coil when using the same odd-order coil as the gradient magnetic field coil or an even-order coil that has accuracy problems. , current fluctuation of the magnetic field correction coil during excitation of the gradient II Fl field coil does not occur, and high uniformity of the magnetic field can be maintained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view schematically showing a conventional highly uniform magnetic field magnet, Fig. 2 is a diagram showing a general even-order coil, Fig. 3 is a diagram showing an odd-order coil, and Fig. 4 is a diagram showing a highly uniform magnetic field magnet of the present invention. A cross-sectional view schematically showing a magnetic field magnet, Fig. 5 is a diagram showing an even-order coil for magnetic field correction, Fig. 6 is a diagram showing an odd-order coil, and Fig. 7 is a diagram showing a coil for magnetic field correction and a gradient sand field coil. FIG. 3 is a diagram showing relative positional relationships. 1... Main coil, 3... Gradient Gθ field coil 12
...Magnetic field correction coils, 12a, 12b...
Reverse standard coil. Patent applicant Sumitomo Electric Industries Co., Ltd. Agent Kama 1) Bun 2

Claims (1)

[Claims] In a magnet in which a left and right pair of magnetic field correction coils and gradient magnetic field coils are installed near the main coil, the magnetic field correction coils are connected to each other by the magnetic flux of the gradient magnetic field coils with opposite winding directions. A highly uniform magnetic field magnet characterized by being formed by a combination of two coils in which the sum of induced electromotive force generated at zero becomes zero.