JP3005308B2 - 6 pole shim coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a six-pole shim coil used for correcting the magnetic field distribution of a charged particle bending electromagnet.

[0002]

2. Description of the Related Art FIGS. 6 and 7 show a conventional 6-pole shim coil. FIG. 6 shows a conventional 6-pole shim coil disclosed in, for example, Japanese Patent Application Laid-Open No. 2-210899. 11 is an outer banana coil, 9 is a middle banana coil, and 8 is an inner banana coil. FIG.
(A) shows the cross-sectional shape of the six-pole shim coil 11. As shown in the figure, the six-pole shim coil 11 is composed of three pairs of banana-shaped coils: outer, middle, and inner.

FIG. 5 (a) shows a conventional charged particle deflection electromagnet 7. The deflection electromagnet 7 composed of the upper and lower banana coils 5 and 6 needs to have a uniform magnetic field in the Z direction in the X direction. It is. FIG. 5B shows an example of the distribution of the magnetic field of the bending electromagnet 7 in the X direction. In the example shown in FIG. 5B, a Z-direction magnetic field (second-order magnetic field component) that increases along a quadratic curve in the X direction is superimposed on a constant magnetic field in the X direction. To obtain a uniform magnetic field in the X direction by correcting this secondary magnetic field component, a secondary magnetic field component that is opposite to the direction of the bending electromagnet 7 may be generated. FIG. 5C shows the X-direction magnetic field distribution of the charged particle bending electromagnet 7 after the correction. By the way, a coil that generates a magnetic field (secondary magnetic field component) that increases in a quadratic curve in the x direction is a six-pole shim coil 11. FIG. 7B shows a magnetic field distribution in the x direction of the z direction magnetic field generated by the six-pole shim coil 11. An intuitive description of the fact that the magnetic field generated by the six-pole shim coil 11 is secondary is as follows. The direction of the current of the six-pole shim coil 11 is as shown in FIG.
Assuming that the current of the inner banana coil is almost the same,
As for the magnetic field distribution on the x-axis, an upward magnetic field is generated between the outer banana coil 8 and the middle banana coil 9, and between the middle banana coil 9 and the inner banana coil 10, Since the directions of the magnetic fields of the inner banana coil 10 are opposite to each other, the magnetic field is almost zero, and the inner banana coil 1
Inside 0, that is, near x = 0, the magnetic field becomes downward. That is, an even-order magnetic field is generated in the x direction. However, in this state, a high-order non-uniform magnetic field component is generated in addition to the secondary magnetic field component (4, 6, 8... Next component). Therefore, it is necessary to make a coil that does not generate this non-uniform magnetic field component, but this can be achieved by adjusting the position between the coils.

[0004]

The conventional six-pole shim coil is composed of three pairs of banana-shaped coils as described above, and has a problem that the structure is complicated and the manufacture is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a 6-pole shim coil which can be simply constructed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and comprises two pairs of banana coils having opposite current directions.

[0007]

In the present invention, since the secondary component is generated by two pairs of banana coils having opposite current directions, the number of coils is reduced.

[0008]

【Example】

Embodiment 1 FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 shows a six-pole shim coil 3 composed of two pairs of coils. In FIG.
Reference numeral 1 denotes an outer banana coil, and 2 denotes an inner banana coil through which a current flows in a direction opposite to that of the outer banana coil 1.

Next, the operation will be described. FIG. 7 (a)
The current directions of the inner banana coil 10 and the middle banana coil 9 of the conventional six-pole shim coil 11 shown in FIG.
Therefore, there is no problem even if the two banana coils 9 and 10 are combined into one. Fig. 2 shows the banana coil combined into one.
(A) is an inner banana coil 2. The outer banana coil 1 has the same current direction as the conventional coil 8.

FIG. 2B shows the magnetic field distribution of the six-pole shim coil 3. The principle of generation of the secondary magnetic field component is as follows. A downward magnetic field is generated inside the inner banana coil 2. An upward magnetic field is generated between the outer banana coil 1 and the inner banana coil 2 (see FIG. 2A). Therefore, an even-order magnetic field is generated in the x direction as shown in FIG. Like the three-pair coil, a higher-order non-uniform magnetic field component may be generated, but this can be achieved by adjusting the position of each coil and the shape of the banana coil.

FIG. 3 shows a state in which a higher-order nonuniform magnetic field component other than the secondary magnetic field component changes when the position of the coil is changed. In the figure, a coil position parameter L2 is a distance between the center of the inner banana coil 2 shown in FIG. 2A and x = 0. The vertical axis is the magnetic field uniformity. This is a standardized non-uniform magnetic field. The definition formula of the magnetic field uniformity is shown below.

Magnetic field uniformity = [Bze (x) max−Bze (x) min ] / Bz0Bze (x): Bz (x) −Bz2 × X ² Bze (x): A quadratic component is obtained from a 6-pole shim coil. Bz (x): X-direction magnetic field distribution of 6-pole shim coil Bz2: Secondary component Bz0: Magnetic field for normalizing magnetic field uniformity (0th-order component)

From the above equation, it can be seen that increasing L2 reduces the non-uniform magnetic field. However, increasing L2 increases the size of the coil. Therefore, if a magnetic field uniformity sufficient for uniforming the magnetic field of the charged particle bending electromagnet can be obtained, it is better to select L2 as small as possible. However, it is not necessary to optimize the magnetic field uniformity, as long as the magnetic field uniformity sufficiently smaller than the magnetic field uniformity of 1 × 10 ⁻³ required for the superconducting electromagnet for charged particles can be obtained.

Next, although not an embodiment of the present invention, a pair of
A coil can generate two pairs of magnetic field components
This will be described with reference to FIG. FIG. 4A shows an example of a pair of six-pole shim coils 4. FIG. 4B shows an example of the magnetic field distribution of this coil, and a negative magnetic field is generated at the center of the coil. A positive magnetic field is generated outside the coil. Therefore, an even magnetic field is generated in the X direction. This may increase the higher-order non-uniform magnetic field components as in the case of the three-pair or two-pair six-pole shim coil, but can be corrected to some extent by adjusting the position of the coil. However, compared to two pairs, one pair
In the configuration, the adjustment range such as coil position is reduced,
Degree decreases.

[0015]

As described above, according to the present invention, the magnetic field
While maintaining a certain degree of uniformity, the banana coil
The number can be reduced and the production is easy.
You.

[Brief description of the drawings]

FIG. 1 is a partial plan view of Embodiment 1 of the present invention.

2A is a cross-sectional view of FIG. 1 and FIG. 2B is a magnetic field distribution diagram.

FIG. 3 is a magnetic field uniformity diagram of FIG.

FIG. 4 shows two pairs of magnetic field components generated by one pair of coils.
(A) indicates that it is possible to produce
(B) is a magnetic field distribution diagram.

5A is a perspective view of a conventional charged particle bending electromagnet, FIG.
FIG. 3B is a magnetic field distribution diagram and FIG. 3C is a corrected magnetic field distribution diagram.

FIG. 6A is a perspective view of a conventional 6-pole shim coil, and FIG.
It is a partial plan view.

7 (a) is a sectional view and FIG. 6 (b) is a magnetic field distribution diagram of FIG.

[Explanation of symbols]

 1 outer banana type coil 2 inner banana type coil 3, 4 6 pole shim coil each

Claims (1)

(57) [Claims] 1. A charged particle Oite to 6-pole shim coils for correcting the magnetic field distribution of the deflection electromagnet, 6-pole, characterized by comprising at banana-shaped coil of two pairs orientation is opposite the direction of the current shim coils.