JPS58140102A - Superconductive electro-magnet - Google Patents

Abstract

PURPOSE:To obtain a highly uniform magnetic field in both Z and gamma directions by the simple constitution of a main coil and a pair of compensating coils. CONSTITUTION:A pair of compensating coils 3 are loaded on to the outsides of both ends of cylindrical main coil 2. Taking the inner radius of the main coil 2 as 1, the outer radius of the main coil is made 1.3-1.4 and its length 7.0-7.5. Further, each of compensating coil 3 has its inner radius at 1.4-1.5, its outer radius at 1.6-1.7, and its length at 0.36-0.44. Furthermore, the inner distance of a pair of compensating coils 3 has dimensional ratio of 5.0-5.2 and it is positioned symmetrically with respect to the center of the coil 2. With those dimensional ratios the distribution of magnetic force near the central space of the main coil 2 is made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cylindrical superconducting electromagnet used in nuclear magnetic resonance apparatuses and the like, and particularly to a superconducting electromagnet that generates a highly uniform magnetic field.

The spectral resolution ability of a nuclear magnetic resonance apparatus (hereinafter referred to as NMR) is determined by the uniformity of the magnetic field applied to the sample. If the center magnetic field strength is Ho and the magnetic field strength at a certain distance from the center is Ho±ΔH, then the uniformity of the magnetic field is ΔH
/ Defined by Ho.

For example, in resonance measurements of hydrogen nuclei ('H), 1 to
A high resolution of about 3 x 10" is required, but this resolution cannot be achieved with the superconducting electromagnet alone, so generally the superconducting electromagnet itself achieves a uniformity of about 10-?
The measurement sample wire is spun at 2000 to 3000 rpm to increase it to 1O-8, and then the magnetic field correction coil is used to increase the
A method is used to obtain the final resolution by improving the resolution to 0-9. Note that the above-mentioned magnetic field correction coil is also called a normal temperature shim.

The center of the cylindrical main coil is O, and the axial distance is Z.
, the radial distance is γ, the generated magnetic field strength is Z
In the γ direction, it becomes smaller as it moves away from the center O, and in the γ direction, it becomes larger as it approaches the inner diameter surface of the coil. Therefore, the highly homogeneous magnetic field area that can be obtained with one simple cylindrical coil becomes narrow, and in order to expand this area, the radius and length of the coil must be relatively expanded.

That is, this is not a good idea because it results in a large coil, which increases costs, and also increases the size of the superconducting electromagnet.

In order to compensate for this drawback, the following methods have been used in the past.

FIG. 1 is a cross-sectional view of a conventional notched superconducting electromagnet.

This notched coil 1 has a magnetomotive force added to both ends to correct the magnetic field strength distribution of the main coil.

Since the uniformity of the magnetic field in the notched coil 1 is determined only by the shape, it is difficult to wind the coil uniformly and to finish it in an accurate shape. Therefore, it is difficult to obtain high uniformity. In the examples so far, the highest achieved uniformity is on the order of 10-6.

FIG. 2 is a cross-sectional view of a superconducting electromagnet equipped with a conventional correction coil. Relatively large correction coils 3 are installed on the outer sides of both ends of the cylindrical main coil 20, and two relatively small correction coils 4 are installed near the center between them. This composite type coil is relatively easy to manufacture, but since there are multiple correction coils, the degree of freedom for adjustment increases, and the combination of parameters such as the mutual positions of the correction coils 3 and 4 and excitation current can be adjusted. The alignment becomes extremely complicated.

Also, looking at an example of the design of the shape and dimensions of a conventional correction coil,
Even if multiple pairs of correction coils are installed and their mutual positions and intervals are adjusted, if the uniformity in the axial direction (hereinafter referred to as the Z direction) is improved, the uniformity in the radial direction (hereinafter referred to as the γ direction) decreases. The same is true in the opposite case, and it has been extremely difficult to improve the uniformity. In other words, the configuration was complicated, and it was not very effective in improving uniformity.

An object of the present invention is to eliminate the drawbacks of the prior art and provide a superconducting electromagnet that can obtain a highly uniform magnetic field in both Z and Z directions with a relatively simple configuration of a main coil and a pair of correction coils. , its characteristics are that when the inner radius of the main coil is 1, the outer radius of the main coil is 1.3 to 1,
4. The length of the correction coil is 7.0 to 7.5 degrees, and the inner radius of the correction coil is 1.4 to 1.5 degrees, and the outer radius is 1.6 to 1.7 degrees. The length has a dimension ratio of 0.36 to 0.44, and the inner spacing of the pair of correction coils is located symmetrically with respect to the center of the main coil with a dimension ratio of 5.0 to 5.2. The structure is such that the magnetic force distribution near the central space of the main coil is made uniform.

The design procedure for obtaining such a Hiko condition will be explained below. First, within ±0.25 crn points in both Zlγ directions, 10
After finding a main coil that would give a uniformity of about -4 to 10-5, the procedure was to find the shape and spacing of the correction coils that would give a total uniformity of about 10'' to 10-7.

The design calculation for the main coil 2 was performed by setting the inner radius to 1.0, setting the coil average current density to 200 to 400 A/■2, and obtaining the target generated magnetic field of 6 Tesla (hereinafter referred to as T). , find the outer radius of the main coil 2 of 1.2 to 1.5, and further give the uniformity of 10-4 to 10-5 for a 5W sphere, and find the length of the main coil 2 that satisfies this: 5.0 ~940 was calculated.

At this stage, the following was discovered.

(1) Even if the length of the main coil 2 is slightly changed, the magnitude of the generated magnetic field hardly changes, and the uniformity of the magnetic field also does not change significantly.

(2) Although the outer radius of the main coil 2 is sensitive to the strength of the magnetic field, the magnitude of the magnetic field can be adjusted by changing the average current density flowing through the main coil 2.

In particular, this means that by making the outer radius of the main coil 2 a little larger, it is possible to provide a margin for unstable phenomena peculiar to superconducting coils. After understanding the influence of the main coil 2 on the parameters, calculations for the correction coil 3 were started.

The main dimensions of the correction coil 3 are standardized by the inner radius of the main coil in consideration of the relationship with the main coil 2, and the inner radius is set to 1.3 to 1.6. The outer radius of the coil is 1.6 to 1.7. Adjust the corrected boil length to 0.3 to 0.5. The distance between the correction coils 3 is calculated over a wide range of 1.0 to 8.0, and a combination of parameters is selected such that the total uniformity of the main coil 2 and correction coil 3 is 10"' to 10-7. However, the current densities of the main coil 2 and the correction coil 3 were the same.
Current density is directly related to magnetic field value, but is independent of magnetic field distribution.

Table 1 shows the conditions under which the magnetic field uniformity is 10-6 to 10-7, and we also attempted to find the coil dimensions that would achieve the highest magnetic field uniformity among these combinations. .

Table 1 The main calculation results are shown below.

FIG. 3 is a sectional view of a superconducting electromagnet that is an embodiment of the present invention. The central magnetic field of this superconducting electromagnet is 6.09357
9T, and the main dimensions of the main coil 2 are determined as follows.

The inner radius of the main coil 2 is 5.0 cm, the outer radius is 6.8 crn, and the length is 36.0 crn. Figure 4 shows the magnetic field strength in the Z and γ directions in this case. Ta.

Figure 4 shows the changes in Z and γ of the main coil in Figure 3 and )-(-H
This is a diagram showing the relationship with O, and shows the magnetic field strength distribution when the correction coil 3 is excluded. That is, when moving away from the center of the central axis of the main coil 2 in the axial direction, the magnetic field strength decreases, as shown by the Z line, and when moving away from the main coil 2 in the radial direction, the magnetic field strength increases, as shown by the γ rays.

FIG. 5 is a diagram showing the uniformity obtained from the values in FIG. 4, where the scale of Z and γ on the horizontal axis and the uniformity scale on the vertical axis are shown in logarithmic values. As a result, at Z = 0.25 m and γ = 0, the uniformity is 2.6 x t O'-', Z = 0
, γ=0.25 (1.4×10 −5 at 771).

In order to find the shape of the correction coil 3 that is compatible with the main coil 2, we searched for the outer radius and length of the correction coil 3 by setting the inner radius of the correction coil 3 to 7.2 cm and the coil spacing to 26.0 cm. I got the result.

Figures 6 and 7 are diagrams showing the uniformity in the Z and γ directions when the distance between the correction coils is fixed at 26 m, the length is fixed at 2 cm, and the outer radius of the main coil is varied. Radius 8.0-8.5 cm'! The uniformity is the best when it is changed to 8.2Crn, and the uniformity decreases at least more than this.

In Figures 8 and 9, the outer radius of the correction coil is 8.2 c.
m is a diagram showing the change in uniformity in the Z and γ directions when the coil spacing is fixed at 266n and the length of the correction coil is changed, and the length of the correction coil 3 is 1.8 to 2
．． When the length is changed to 2 cm, the uniformity is highest at 2.0 cm, and even if the length is made longer or shorter than this, the uniformity decreases. In addition, various conditions were calculated by changing the dimensions, but no better combination other than the above was found.

By determining the shape of the correction coil that is compatible with the main coil 2 as described above, it was also possible to obtain the result that the uniformity was simultaneously improved in both the Z and γ directions.

Further, it seemed that even higher uniformity could be expected by finely adjusting the spacing between the correction coils 30, so when the spacing was varied and a detailed investigation was carried out, the following results were obtained as expected.

10 and 11 are diagrams showing the relationship between correction coil spacing and uniformity, and FIG. 10 is a diagram showing the relationship between correction coil spacing and uniformity, and FIG. 10 is for Z = 2.
5 van, Figure 11 shows 2.51 in the r direction at the center position.
This is the uniformity at point a. The spacing between the correction coils 3 showing the highest uniformity is around 25.55 cmIn, which is 10-
It shows good uniformity of 8-10''.

Note that the marks in both figures indicate the case where the magnetic field strength at the position where the uniformity was examined is greater than that of the central magnetic field, and the mark e indicates the case where it is small.

From the above considerations, the following facts have become clear.

When the inner diameter, coil current density, magnetic field value, and uniformity of the main coil 2 are given, the optimum dimensions can be determined uniquely, allowing economical design. That is, the minimum dimension of the inner diameter of the correction coil 3 is determined from the outer diameter of the main coil 2, the bobbin thickness of the correction coil 3, and the dimensions of the holding fitting for moving the correction coil 3. Under these conditions, the magnetic field distribution of the main coil 2 minus the magnitude of the center magnetic field and the magnetic field distribution of the correction coil 3 minus the center magnetic field completely cancel each other out in a space where uniformity is required. Given that there can be only a large number of conditions that meet each other, the optimum size and shape of the correction coil 3 can be determined in a very large number of cases. However, this is a case where the inner diameter is given in advance.

Therefore, considering that each dimension value above is an optimal value and that the magnetic field distribution is proportional to the coil shape and dimension,
When the inner radius of the main coil 2 is set to 1.0, they are given by a - set of dimensional ratios. In this case, it is not necessary that the current densities of the main coil 2 and the correction coil 3 be the same.

In the combination of the main coil 2 and the correction coil 3 as described above, the magnetic field distribution is Z within the calculation domain.

Both the Z direction is expressed by a quadratic equation (Fig. 4), and as the uniformity in the Z direction improves, the uniformity in the Z direction also tends to improve, and it is extremely difficult to adjust the uniformity by adjusting the position of the correction coil 3. It has been found that this method has the advantage of being easy to implement. This means that the magnetic field distribution created by the main coil 2 and the correction coil 3 is expressed by a quadratic equation having equal second-order coefficients with equal absolute values in the Z and γ directions, and with equal first-order coefficients, and the correction coil It is shown that the two coils are an almost ideal combination so that the shape of the quadratic equation hardly changes even if the interval between the two coils is changed. That is, it is shown that there is an optimal value for the distance between both coils, and that uniformity can be improved simply by moving the position of the correction coil 3 to that value.

The superconducting electromagnet of this embodiment has a cylindrical main coil and a magnetic field distribution generated near the center of the main coil whose increasing and decreasing directions are opposite to each other, and where the magnetic field of the main coil decreases in the Z direction and the Z direction. By combining a pair of annular correction coils such that the difference between the increase in the direction and the increase and decrease in the Z direction of the correction coil is small, the magnetic field strength can be increased near the center of the main fill. The effect is that a uniform portion can be obtained.

FIG. 12 is a sectional view of a superconducting electromagnet device using the superconducting electromagnet shown in FIG. 3, and the same parts as in FIG. 3 are given the same reference numerals. In this case, the rotation shaft 6 can correct the movement of the positions of the main coil 2 and the correction coil 3 that occur when the two coils are actually combined and cooled.

Inside the annular cylindrical container 9, a cylindrical main coil 2 and annular correction coils 3a and 3b are installed close to both outer ends of the cylindrical main coil 2. In addition, the holding fittings 4a and 4b to which the correction coils 3a and 3b are attached are provided with different screw holes (when one is a right-hand screw hole, the other is a left-hand screw hole), and the rotating shaft has a left-hand screw and a right-hand screw. is screwed into this. Therefore, when rotating the rotating shaft 6, the holding fittings 4a and 4b are
can be moved in the direction of the arrow to reduce the distance between the correction coils 3a and 3b by about 2.5 rran. Moreover, when the rotating shaft 6 is rotated in the opposite direction, a pair of correction coils 3a,
35 are moved away from each other, so that the spacing between the correction coils 3 can be finely adjusted to an optimum state.

Note that an adjustment amount of the interval between the correction coils 3a and 3b of about 2.5 knots is sufficient.

The main coil/L-2 and the correction coil 3 are immersed in liquid helium 7, and the NMR probe 8 containing the sample liquid is housed in the room temperature section 5, which is the center hole of the cylindrical container 9. There is. This NMR probe 8 contains a sample liquid, and when adjusting the distance between the correction coils 3a and 3b, the NMB for hydrogen measurement and the probe 8 are used to monitor and adjust the NMR spectrum generated therefrom. . In this way, the optimum position of the correction lens 3 can be found in an extremely short time, thereby saving loss of coolant and allowing quick adjustment. That is, the only way to measure the magnetic field strength at the center of the assembled superconducting electromagnet is to use I''JMR, globe 8.

Note that the structure in FIG. 12 is shown in a simplified manner.
The cylindrical container 9 is housed in a double vacuum thermos bottle, and
The main coil 2 and the correction coil 3 are configured to always maintain a coaxial state.

The superconducting electromagnet device of this embodiment is configured so that the spacing between a pair of correction coils can be changed from outside room temperature while maintaining a coaxial state with the main coil. Improve the uniformity of magnetic field strength at 10″″
The effect is that it becomes possible to obtain a uniformity of about 9.

The superconducting electromagnet of the present invention has the effect that a uniform magnetic field can always be obtained in both the Z and γ directions by using the conditions described in the claims, including the coaxial micro-movement conditions of the correction coil.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional notch-shaped superconducting electromagnet, FIG. 2 is a cross-sectional view of a conventional superconducting electromagnet equipped with a correction coil, and FIG. 3 is a cross-sectional view of a superconducting electromagnet that is an embodiment of the present invention.
Fig. 4 is a diagram showing the relationship between changes in Z and γ of the main coil in Fig. 3 and HHo, Fig. 5 is a diagram showing the uniformity obtained from the values in Fig. 4, and Figs. In Figure 7, the distance between the correction coils is 26 cm. A diagram showing the change in uniformity in the Z and γ directions when the length is fixed at 2Crn and the outer radius of the main coil is changed,
In Figures 8 and 9, the outer radius of the correction coil is 8.2 c.
m + A diagram showing the change in uniformity in the Z and γ directions when the coil spacing is fixed at 126 crn and the length of the correction pressure coil is changed. Figures 10 and 11 show the correction coil spacing and uniformity. A line diagram showing the relationship between, Figure 12 is %3
FIG. 2 is a sectional view of a superconducting electromagnet device using the superconducting electromagnet shown in the figure. DESCRIPTION OF SYMBOLS 1...Notch coil, 2...Main coil, 3...Correction coil, 4...Holding metal fitting, butt...Normal temperature section, 6...
Rotating shaft, 7...liquid helium, NMR probe,
9... Same No. 4 Field 1 or Y (C 夙) Otsu (C Asahi 2 γ (Cγ)'11
10th Konan, j1: Three coils Itlη% (c%n supply 1l
EJ funeral positive coil FI interval (C cap'f) /2 II]

Claims (1)

[Claims] 1. Main superconducting solenoid coil (hereinafter referred to as main coil)
In a superconducting electromagnet consisting of a pair of superconducting solenoid coils for magnetic field distribution correction (hereinafter referred to as correction coils) provided at the axial end of the main coil, when the inner radius of the main coil is 1, , the outer radius of the main coil is 1.3 to 1.4. The length is 7.0 to 7.5, and each of the above correction coils has an inner diameter of 1.4 to 1.5. Set the outer radius to 1.
6-1.7. The length has a dimension ratio of 0.36 to 0.44, and the inner distance between the pair of correction coils is 5.0.
A superconducting electromagnet, characterized in that the superconducting electromagnet is arranged symmetrically with respect to the center of the main coil with a dimensional ratio of ~5.2, so as to make the distribution of magnetic force uniform near the center middle part of the main coil. 2. The superconducting electromagnet according to claim 1, wherein the pair of correction coils are coils that maintain a coaxial state with the main coil and are capable of slight movement in opposite directions simultaneously.