JPS6213008A - Uniform magnetic field generator - Google Patents

Abstract

PURPOSE:To compose a magnet having a short axial direction by deciding the ratio of radii of inner, intermediate and outer coils to a distance from the central position, and the ratio of the numbers of windings of the inner, intermediate and outer coils to the prescribed values. CONSTITUTION:Three coil pairs composed of two coils having equal number of windings disposed on a central axis are disposed symmetrically to the central position. When the radii of inner coils 1, 2 of three coil pairs having substantially equal radii of the center of the sections of the coils are 0.5 and the number of windings of the inner coils is N1, the radii of the intermediate coils 3, 4 and the outer coils 5, 6 fall within 0.5+ or -0.05. The distances between the inner, intermediate and outer coils and the central position A fall respectively 0.0510+ or -0.0080, 0.2018+ or -0.0200, 0.5304+ or -0.0400, and the numbers of the windings of the intermediate and outer coils fall respectively within N1X(1.902+ or -0.200), N1X(5.258+ or -0.600).

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a uniform magnetic field generator, for example, NMRCT.
It is used for equipment.

<Prior Art> Conventionally, the method of winding a wire in a superconducting magnet that generates a highly uniform magnetic field has been the solenoid coil method shown in FIG. 2 or the combination method of a solenoid coil and a notch coil shown in FIG. 3.

<Problems to be Solved by the Invention> A drawback of the above-described magnetic field generator is that in order to obtain a highly uniform magnetic field, the magnet becomes long in the axial direction (Z direction).

For this reason, in an NMRCT device using this superconducting magnet, the inner bore into which a person enters is a deep hole, which gives a sense of fear to the patient and makes it difficult to handle in terms of antenna installation and other aspects. Further, since a large amount of coil wire is required and the wire is expensive, there is a problem in that the cost of the NMRCT apparatus increases.

<Means for Solving the Problems> The uniform magnetic field generating device of the present invention generates a magnetic field by arranging three pairs of coils, each consisting of two coils having the same number of turns arranged on the central axis, symmetrically with respect to the center position. In the apparatus, when the radius of the coil among the three coil pairs is set to 0.5 and the number of turns of the inner coil is set to N1, the three pairs of coils have substantially the same cross-sectional center radius. The radius of the middle coil and outer coil of the coil pair is in the range of 0.5±0.05, and the distance between the inner coil, middle coil, and outer coil and the center position is 0.0510±0, respectively. .008
0.0.2018±0.0200.0.5304±0.
0400, and the number of turns of the middle coil and outer coil is N, + x (1,902±0.200), respectively.
It is characterized by being in the range of NI x (5,258±0.600'').

<Example> An embodiment of the present invention will be described below.

FIG. 1 shows a cross-sectional configuration of a magnet of a uniform magnetic field generator. There are three coil pairs: an inner coil pair consisting of two inner coils 1.2, a middle coil pair consisting of two middle coils 3.4, and an outer coil pair consisting of two outer coils 5.6. , are arranged coaxially with the axis Zl by the support member 7 and symmetrically about the center position A of the uniform magnetic field generator. Inner coil 1.2
are arranged at distances d1 left and right in the Z-axis direction from the center position A, middle coils 3.4 are arranged at distances d2 left and right in the Z-axis direction from the center position NA, and outer coils 5.6 is the distance d3 left and right in the Z-axis direction from the center position A.
are placed at the respective positions.

Distance Md2 is greater than distance d1, and distance Mda is greater than distance d2.
It's bigger. Coil 1. , 2. 3. 4. , 5
The center radius of the cross section of °6 is a, and the number of turns of the inner coil 1.2 is Nl
, the number of turns of the middle coils 3 and 4 is N2. The number of turns of the outer coil 5°6 is N3.

A uniform magnetic field in this magnetic field generator is a magnetic field with high uniformity in the Z axis. Therefore, the magnetic field strength H (Zl
As a series of the width of Z, H(Zl=fo+f2 Z2+
When expressed as f4Z' +f6 Z6 +...-(ll (the coil arrangement is symmetrical, the odd bundle term of Z does not appear), so that the coefficients f2.f4.f5... are almost zero. In the present invention, f
By setting 2 and f4 to approximately zero and waiting for the smallest value of f6, a uniform magnetic field is realized in a sufficiently small range of Z.

The magnetic field H (d+, NI, Z) generated on the Z-axis by coils 1 and 2 forming the inner coil pair is equal to the magnetic field H (d2.
N2. Z) is a magnetic field H (da, Na, Z) generated on the Z axis by the coil 5.6 forming the outer coil pair.

Therefore, when the strength of the magnetic field generated by each coil on the two axes is combined, H(Zl is as shown in the following equation.

Equation (2) is expanded by Tiller to obtain Equation 11. In this case, the coefficient fn (n=0.2, 4, 6.=) is determined by the following equation.

nj dz” This is the value at Z=0.

The conditions for realizing the above-mentioned uniform magnetic field can be written as follows.

is the minimum °°°−θJ +41. Constant a so as to satisfy the condition (51, +6)
+dl+d2. Da, N! , N2. By determining Na, a uniform magnetic field can be obtained.

In the case of this 6-coil system, the magnetic field on the Z axis is H(z)c
(H(d+,N1.Z)+H(dz,N2.Z)+H
It can be expressed as (da, Na, Z). Therefore, some points on the Z axis are taken as sample points and the parameters d+, N+, dz, N2 . By varying da and Na, the parameters d1°N1. d
z, N2. da, Na can be found.

The ratios of the parameters determined by the above method to obtain a uniform magnetic field are as follows. If the cross-sectional center radius a of the inner coil 1.2 is 0.5 and the number of turns of the inner coil 1.2 is N1, then the cross-sectional center radius of the middle coil 3°4 and the outer coils 5 and 6 is 0.5±. It is in the range of 0.05, and the inner coils 1, 2 . Medium coil 3. 4 and the distances dl, d2 . between the outer coils 5, 6 and the center position A. da is 0.051 each
0±0.0080.0.2018±0.0200.0.
5304±0.0400, medium coil 3,4
and the number of turns N2 of the outer coils 5 and 6. N3 is each N+X (1
,902±0.200), N+X(5,25
It is in the range of 8±o, eoo>. In this case, if a certain parameter is slightly changed, the optimum values of other parameters will also change little by little, so a certain range is defined as described above.

In this way, the distance dIta2 . A3 and the ratio between the number of turns N1 of the coils 1 and 2, the number of turns N2 of the coils 3 and 4, and the number of turns N3 of the coils 5 and 6 are determined to obtain a uniform magnetic field on the Z-axis. As a result of setting the parameters as described above and performing a calculation simulation,
The uniformity of the magnetic field was 60 ppm inside a spherical space with a radius of 25 cm from the center point.

Although the cross-sectional shape of the coil shown in FIG. 1 is square, it goes without saying that it may be rectangular or circular.

<Effects of the Invention> As explained above, in the present invention, the ratio of the radius of the inner coil, middle coil, and outer coil to the distance from the center position and the turn ratio of the inner coil, middle coil, and outer coil are set to predetermined values. By setting this, it is possible to construct a magnet that is short in the axial direction, making it about 3/4 smaller than a conventional magnet with the same radius, and also reducing the wire material to about 3/4 of the conventional magnet. As a result, cost reduction can be achieved. Furthermore, when this magnet is applied to a superconducting magnet, it can be miniaturized, which reduces the absorption of radiant heat from the surroundings and reduces the energy required for operation. Furthermore, in the NMRCT apparatus using this magnet, the inner bore into which a person enters is shallow, so that the patient does not feel scared.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic cross-sectional configuration of an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing a cross-sectional configuration of a conventional example. 1.2... Inner coil 3.4... Middle coil 5.6... Outer coil A... Center position a... Section center radius dl, a2. d3... Distance patent applicant Shimadzu Corporation Representative Patent attorney Nishi 1) New 1st 2nd UiJ Figure 3 ---1-→2 --1-→2

Claims (1)

[Claims] 3. A magnetic field generating device in which three pairs of coils each consisting of two coils having the same number of turns arranged on a central axis are arranged symmetrically with respect to the center position, and the cross-sectional center radius of each coil is approximately the same. When the radius of the inner coil of the pair of coils is 0.5 and the number of turns of the inner coil is N_1, the radius of the inner coil and outer coil of the three coil pairs is 0.5±0. 05, and the distances between the inner coil, middle coil, and outer coil and the center position are 0.0510±0.0080 and 0.2018±0.0, respectively.
200, 0.5304±0.0400, and the number of turns of the middle coil and outer coil are each N_1×(1.90
2±0.200), Ni×(5.258±0.600)
A uniform magnetic field generator characterized in that the magnetic field is within the range of .