JPS6015098B2 - Magnetic field generation method and device - Google Patents

Description

Detailed Description of the Invention The present invention relates to a magnetic field generation method and a magnetic field device, and in particular to a particle beam microscope, a particle beam analyzer, a particle accelerator, a particle beam transmission system and a plasma device used in conjunction with the particle accelerator. The present invention relates to a magnetic field generation method and a magnetic field device that can be applied to, etc.

Generally, an electromagnet used in a magnetic field device has a coil wound around a magnetic path having a portion that constitutes a magnetic pole, and a magnetic field is generated by passing through the coil.

In order to obtain a magnetic field with a desired distribution using such an electromagnet, it is necessary to manufacture the shape of the tip of the magnetic pole to match the equimagnetic potential surface of the intended magnetic field.
Therefore, great efforts must be made to realize uniformity of the magnetic material in accordance with the accuracy of the magnetic field distribution and to machine the magnetic pole surface. On the other hand, in particle beam analyzers, etc., there is a difference between the actually generated magnetic field distribution and the designed value due to the hysteresis characteristics of the magnetic material, so it is convenient to configure the device so that the magnetic field distribution can be corrected. . However, due to the structural limitations of electromagnets manufactured by machining the magnetic pole faces, during use, the magnetic field distribution can only be modified locally by shimming such as inserting iron pieces, but the magnetic field distribution can be significantly changed over the entire usage space. Of course, it is not possible to change the desired magnetic field distribution components independently. Furthermore, since the magnetic pole surface is manufactured to match the equal magnetic potential surface,
Another drawback is that in locations that require a large space, the gaps between the magnetic poles become narrower, which often significantly degrades the performance of the device. An object of the present invention is to provide a magnetic field device that can independently control magnetic fields of various distributions.

Another object of the present invention is to provide a magnetic field device that generates a magnetic field having a desired distribution in a yoke of arbitrary shape.

A further object of the present invention is to provide a method for generating a magnetic field that does not require the distribution of magnetic poles to protrude into the space in which the magnetic field is to be generated. Still another object of the present invention is to provide a magnetic field generation method that can effectively utilize superconductivity phenomena.

Here, the present inventor previously described in the specification of Machigao Sho 50-100646 (Tokusei Sho 52-25562) a space surrounded by a yoke with a single polygonal frame shape as a magnetic field generation space,
We proposed a multipolar magnetic field device (hereinafter referred to as a current sheet magnet) that can generate a desired multipolar magnetic field by disposing a coil inside this yoke. According to the present invention, it is possible to obtain a magnetic field generation method which can be applied to a yoke of any shape without being limited to a yoke having a polygonal frame shape in cross section, and which can modify the generated magnetic field.

The present invention provides a method for generating a magnetic field in the space inside the frame yoke by disposing a single or plural coils inside a frame yoke whose cross section is made of continuous or discontinuous curves or broken lines. When the magnetic potential of the desired magnetic field is ■, and the differential line element along the inner surface of the yoke is ds, the distribution of the cross-sectional vertical component of the current on the inner surface of the yoke is -d■/
This is a magnetic field generation method in which coils are arranged to resemble a ship.

This method of generating a magnetic field, given the magnetic field to be obtained,
It is possible to apply the present invention to an arbitrarily shaped space within the yoke regardless of the two-dimensional or three-dimensional coordinate system. This will be explained below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a multipolar magnetic field device used in an ion optical system, and here a device for generating a quadrupole magnetic field is shown.

Referring to FIG. 1, this magnetic field generator has a yoke 1, four magnetic poles 1' protruding inside the yoke 1, and a coil 2 wound around each magnetic pole 1'. The tip of each magnetic pole 1' is machined to match the equimagnetic potential surface of the magnetic field to be generated, and by exciting the coil 2, a desired magnetic field can be generated. In such a magnetic field device, the magnetic field space inside the yoke 1 is limited by the magnetic pole 1' protruding inward, and the leakage magnetic flux is large, so the yoke must be thick. If this is to be ensured, the structure of the entire magnetic field device must be larger than the required magnetic field space. FIG. 2 is a diagram for explaining the principle of the present invention.

First, the space in which the magnetic field should be generated can be recognized as the space S surrounded by the yoke 1, which is a magnetic material. Here, in order to generalize the explanation, a space surrounded by an arbitrarily shaped contour curve C will be considered. Now, if we consider the magnetic permeability in the yoke 1, the magnetic field in the yoke is 0, and the contour curve C
It is assumed that the line element ds is oriented in the tangential direction of the contour line C. Next, we will explain the case where a magnetic field whose magnetic potential is given by ■ is generated in the space S in C.
If the magnetic potential ■ is regular in the space S, then
. By means of a suitably distributed current sheet along this, the desired magnetic field can be generated. Note that when the magnetic potential ■ has a singular point in the space S, it is also necessary to use an isolated current in the space S, but here we will explain the regular magnetic potential ■, which is the most practical.
In Figure 2, when a current with a linear density of i in the direction perpendicular to the cutting plane is placed along C, the magnetic material no longer has equal magnetic potential, but has a certain finite magnetic potential difference, and the magnetic field The sun occurs in space S. Therefore, when Stokes' theorem is applied to PQRS along C, (where Hs is a tangential component on the inner surface of C), the following relationship is obtained.

．． d■ ……………[2}1=
Isshiza No. [Referring to Equation 2', the magnetic potential in the space S is given, so if coils with current densities corresponding to the desired magnetic field are arranged in each layer of C, the desired distribution will be obtained. Can generate a magnetic field.

Furthermore, since Equation (2) holds true regardless of the coordinate system, the above-mentioned relationship can be obtained using any coordinate system.

Here, I explained the case where mountain = target, but in general, even if there is a finite Buddha, the difference from the magnetic field distribution when r = target is (1/Buddha)
It is about 2, and the magnetic field distribution within the circular frame is determined only by the current sheet, regardless of the noise. Furthermore, it can be theoretically proven that even if the thickness of the coil is finite, the difference from the magnetic field obtained from the relationship of equation 2' is practically negligible. Figure 3a
, b, and c are vertical cross-sectional views showing one embodiment of the present invention, in which a frame-shaped yoke 1 having a curved cross section is used. Referring to FIG. 3a, in this embodiment, a coil 2 which is energized in a direction perpendicular to the cross section is arranged on the inner surface of a frame-shaped yoke 1 having a continuous cross section. Further, the case is shown in which the frame-shaped yoke 1 has symmetry with respect to the magnetic field center plane 3. Now, as in FIG. 2, it is assumed that the curve on the inner surface of the yoke 1 is C, the line element in the tangential direction thereof is a ship, and the magnetic potential (2) of the desired magnetic field is regular in the space within C. In this case, the current density on the inner surface of the yoke 1 is 1 d■/
If the coil 2 is arranged so that ds, a desired magnetic field distribution can be obtained in almost the entire space inside the coil 2. still,
In order to simplify the explanation, a current sheet magnet having symmetry is taken as an example, but the above-mentioned relationship also holds true when there is no symmetry. As shown in FIGS. 3b and 3c, even if part of the yoke 1 is cut out, the present invention can be applied to generate a desired magnetic field.

In this case, there is no need to absorb the magnetic flux when cutting out a portion where the magnetic flux is reversed, but a member that absorbs the magnetic flux may be inserted when cutting out a portion where the magnetic flux is not reversed. Incidentally, FIGS. 3b and 3c show the case where the yoke 1 is cut at one place and at two places, respectively, and a non-magnetic smoother 4 is inserted between the cut places. In the present invention, in order to generate a composite magnetic field with a single magnet and to control each magnetic field component independently, coils corresponding to each magnetic field component can be arranged in an overlapping manner.

Figures 4a and 4b show another embodiment of the invention.
Referring to FIGS. 4a and 4b, two types of coils are provided here to generate a composite magnetic field. Fourth
Figure a shows a curved frame type yoke 1, and the order of the magnetic field is coil 2.
This is a case where coil 2', which generates a higher magnetic field, is attached to coil 2. On the other hand, FIG. 4b shows a case in which two types of coils 2 and 2' are disposed on the inner surface of the curved frame type yoke 1 in a vertically divided manner and are alternately dispersed and mixed. FIGS. 5a and 5b are diagrams showing still another embodiment of the present invention. In this embodiment, the coil 1 is embedded in the inner surface of the yoke 1, and saturation of the magnetic material on the inner surface of the yoke 1 is particularly problematic. It is effective when the

Referring to FIG. 5a, all the coils 2 are embedded in the yoke 1, and in this case, the magnetic field distribution is determined by the magnetic potential of the area. Referring to FIG. 5b, in this embodiment the magnetic field center plane 3
A coil 2 is embedded in the inner surface of the yoke 1 except for the upper part. As described above, the magnetic field distribution of the current sheet magnet according to the present invention is determined by the arrangement of the coils 2 on the inner surface of the yoke 1, and is completely unrelated to the coils on the outer surface of the yoke 1, so the shape of the yoke 1 can be freely selected. can do.

It may be rolled. Further, by bending the coil along the inner surface of the yoke 1 at the end of the yoke, it is possible to form coils that conduct electricity in different directions. Figure 6 a, b. Figures 6c and d show examples in which a so-called betatron type magnetic field distribution with three-dimensional concentration is generated in the frame-shaped yoke 1 for a charged particle beam. , c is an embodiment of the present invention, and FIG. 6d is a conventional magnetic field device.

First, referring to Figure 6d, if the magnetic field distribution is determined by the shape of the magnetic pole face as in the past, there is no variability in the magnetic field distribution, and the charged particles traveling in the vertical direction of the figure are There is a drawback that the magnetic pole gap becomes narrower in the region extending in the y-axis direction (in the figure). On the other hand, as shown in FIGS. 6a, b, and c, in the current sheet magnet of the present invention having a rectangular frame type, a U-shaped structure, and a coil-embedded type structure, each of the current sheet magnets has a primary, Coils 2', 2'', and 2 coils are arranged so that the secondary and tertiary magnetic field distributions are variable, and the drawbacks of conventional magnetic field devices can be eliminated. Figs. 7 and 7 FIG. 8 is a diagram showing another embodiment of the present invention, in which the present invention is applied to a particularly effective multipolar magnetic field.

Referring to FIG. 7, this embodiment shows a square frame type current sheet magnet for generating a quadrupole magnetic field, and the coil 2 is embedded in the surface of the fork 1 to reduce the size of the device. Generally, when generating a state polar field within a rectangular frame-like yoke, use (x, y) coordinates as shown in Figure 7, and if the imaginary factor is i, then y = yo and x = lm{N(x+iyo)N-1} and R on the inner surface of xo, respectively
It is sufficient to arrange coils with a density proportional to e{N(pinejuiy)N-}. Here, lm and Re represent the imaginary part and the real part within { }, respectively. Therefore, when generating a quadrupole field in the square frame-shaped yoke 1 as shown in FIG. And? My enemy, my enemy! Since xo holds, it is sufficient to wind the coils on each side with equal density. Note that a quadrupole magnetic field can be generated in the coils 2 disposed on each side of the yoke by energizing the coils on adjacent sides in opposite directions. Further, during manufacturing, an iron plate is inserted between the coil pancakes to form the inner surface of the rectangular yoke 1.
Next, referring to FIG. 8, this embodiment shows a current sheet magnet for generating a quadrupole magnetic field using a yoke 1 having a formal diamond frame shape.

As shown in FIG. 8, the frame-shaped yoke 1 diagonally intersecting on both x and y sides can be generalized and expressed as 1=1. However, a is the intersection of the x-axis and the frame-shaped yoke 1, and b is the intersection of the y-axis and the frame-shaped yoke 1. When a state polar magnetic field is generated for such a frame type York, the crab flow density is It is sufficient to arrange a coil with dependence on the inner surface of the yoke 1.In the embodiment of FIG. Coils are arranged symmetrically on each side.In use, a current in the same direction is applied to half of each adjacent side, and a current in the opposite direction is applied to the other half of each side. is energized. As the multipolar magnetic field device, although those having a rectangular frame shape and a diamond frame shape are explained in FIGS. It is also possible to use a composite type in which a single yoke generates multiple multipolar magnetic fields.

Further, in the embodiment, a case has been described where it is easy to express using an orthogonal coordinate system, but the principle of the present invention is independent of how coordinates are selected, and any coordinate system can be selected. Therefore, the present invention can be easily applied to a curved frame-shaped yoke or a yoke of arbitrary shape. Additionally, in general, the effective 2 (N11) polar magnetic field effect on ion optics can be adjusted by creating a structure in which the opening of the state-polar multipolar magnetic field device is cut diagonally in the axial (or current) direction. You can also do it. As described above, according to the present invention, it is possible to obtain a current sheet magnet having a structure in which a coil is disposed on the inner surface of a frame-shaped yoke whose cross section is formed by continuous or discontinuous curves or broken lines. One or more types of magnetic fields can be arbitrarily generated in a single yoke.

Furthermore, compared to ordinary magnets with protruding magnetic poles, the current sheet magnet of the present invention can generate an ideal magnetic field in a wide space, and the magnetic flux leaking from the magnetic poles can also be significantly reduced. It has advantages. In this way, a single current sheet magnet of the present invention can exhibit variable magnetic field distribution performance comparable to the ability of several conventional magnets. Furthermore, in the present invention, by making the yoke thinner, it is possible to reduce the weight and size of the entire magnet.
In addition, since the electric current distribution determines the magnetic field distribution, the specifications for the yoke material are less strict than those for conventional electromagnets, and the yoke structure is generally simple.
It should be noted that the effects of the present invention will be even more remarkable if the electromagnet utilizes superconductivity.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional magnetic field device, FIG. 2 is a diagram for explaining the principle of the present invention, FIGS. 3 to 5 are diagrams showing an embodiment of the present invention, and FIGS. b and c are diagrams showing the case where the present invention is applied to a magnetic field device for generating a betatron type magnetic field, FIG. 6 d is a diagram showing a conventional magnetic field device for comparison, and FIGS. 7 and 8. The figure shows still another embodiment of the present invention. Explanation of symbols, 1: Yoke, 2, 2', 2'', 2''':
Coil, 3: magnetic field center plane, 4: non-magnetic spacer, S: space, C: function representation by arbitrary coordinates of the curve on the inner surface of the yoke, ds: differential line element in the tangential direction on the curve C. Figure 1Figure 2Figure 3Figure 4Figure 4Figure 5Figure 5Figure 6Figure 6Figure 6Figure 6Figure 7Figure 8

Claims (1)

[Claims] 1. At least one coil is disposed inside a frame-shaped yoke whose cross section is constituted by continuous or discontinuous curves or broken lines, and a magnetic field is applied to the space inside the frame-shaped yoke. In the method for generating , where Φ is the magnetic potential of the magnetic field to be generated in the space within the frame-shaped yoke, and ds is the differential line element along the inner surface of the frame-shaped yoke, the current on the inner surface of the frame-shaped yoke is The coil is arranged inside the frame-shaped yoke so that the distribution of the component in the vertical direction of the cross-section becomes −dΦ/ds, thereby generating a desired magnetic field in the inner space of the frame-shaped yoke. A magnetic field generation method characterized by: 2 A frame-shaped yoke having an arbitrary cross section and configured to surround an inner space, and at least one coil disposed facing the inner space of the frame-shaped yoke, When the magnetic potential of the magnetic field to be generated in the space is Φ, and the differential line element along the inner surface of the frame-shaped yoke is ds, the coil is arranged to generate the vertical component of the current on the inner surface of the frame-shaped yoke. A magnetic field device characterized in that it is arranged so that the distribution of -dΦ/ds.