JP4063783B2 - Ion beam separation system and ion beam acceleration system equipped with the ion beam separation system - Google Patents

Description

  The present invention relates to an ion beam accelerator for accelerating an ion beam such as a proton, and particularly to an ion beam separation system for accelerating necessary ions and an ion beam accelerator system including the ion beam separation system. .

Conventionally, ion beams accelerated to high energy have been actively used for the treatment of malignant tumors such as cancer and other medical purposes. The ion beam emitted from the ion source emits, for example, monovalent to tetravalent carbon ion beams when generating carbon ions. If this is incident on an accelerator and is accelerated to high energy, acceleration from the accelerator side becomes easier as the number of charges increases, but generally the beam intensity decreases as the number of charges increases. Therefore, it is a common practice to separate the emitted ion beam from the ion source into only desired ions before entering the accelerator.
For example, in Non-Patent Document 1 described later, it is shown that tetravalent carbon ions are accelerated by RFQ which is the first accelerator. In this case, when a carbon ion other than tetravalent is incident on the RFQ, an appropriate convergence force cannot be obtained, and it collides with the acceleration electrode of the RFQ, resulting in a state in which the electrode surface is deteriorated and easily discharged. For this reason, an analysis electromagnet is provided between the ion source and the RFQ so that carbon ions other than tetravalent ions are not incident, a carbon beam having each charge number is extracted with a predetermined radius of curvature, and a desired charge is placed downstream of the electromagnet. A configuration is shown in which slits for passing only a few carbon ion beams are provided, and other beams are not incident on the RFQ.

DESIGN OF A CARBON INJECTOR FOR A MEDICAL ACCELERATOR COMPLEX. European Particulate Accelerator conference, 1998.

  However, the non-patent document 1 discloses an analysis in which an ion beam is deflected by 90 ° between an ion source and a slit in order to cause a desired number of charges, in this case, a tetravalent carbon ion beam to enter the accelerator. Since the electromagnet is provided, there is a problem that the apparatus becomes large, requires a large installation area, and causes an increase in cost.

  The present invention has been made to solve the above-described problems, and is a device in which an ion beam separation system is provided linearly on the central orbit of an ion beam downstream of the ion source, and the apparatus is miniaturized. .

The ion beam separation system according to the first aspect of the present invention includes at least one ion source that emits an ion beam including a predetermined type of ion beam and a convergence field for converging the emitted ion beam. An ion beam converging means composed of either one of two solenoid coils or two or three quadrupole electromagnets, and an ion beam discriminating slit installed downstream of the ion beam converging means, and an ion source And the ion beam converging means and the slit are linearly arranged on the center trajectory of the ion beam, and corresponding to a predetermined kind of ion beam and the distance from the ion beam converging means to the position of the slit, By changing the energization amount of the ion beam converging means and changing the intensity of the convergence field, a predetermined type of ion beam is converged at the slit position. It is obtained by way.

  An ion beam acceleration system according to the second invention includes the ion beam separation system according to the first invention, an ion beam transport system, and an ion beam accelerator.

The ion beam separation system according to the first aspect of the present invention is an ion beam constituted by at least one solenoid coil or two or three quadrupole magnets linearly on the central orbit of the ion beam. Since the converging means and the slit are installed, the system is downsized, and the installation area can be reduced and the cost can be reduced.
In addition, since the ion beam acceleration system of the second invention includes the ion beam separation system of the first invention, the ion beam acceleration system is reduced in size, and the installation area can be reduced and the cost can be reduced.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram showing an ion beam acceleration system 100 according to the first embodiment. The ion beam acceleration system 100 includes an ion beam separation system 200, an ion beam transport system 210, and an accelerator 5. The ion beam separation system 200 includes a beam converging unit 20 and a slit 3 that are installed in a straight line on the central orbit of an ion beam. The beam converging unit 20 includes two beam converging units 20 in the example shown in FIG. The solenoid coil 2 is used. The ion beam transport system 210 is composed of two quadrupole electromagnets 4 in the example of FIG. Here, the ion separation system 200 and the quadrupole electromagnet 4 may be referred to as an ion beam transport system. In the first embodiment, the ion separation system 200 and the ion beam transport system 210 are divided as described above. Define.
The accelerator 5 may be a circular accelerator such as a synchrotron or a FFAG accelerator, or a linear accelerator. The ion beam separation system 200 related to the ion beam acceleration system 100 of the first embodiment will be described in detail below.

The ion source 1 converts hydrogen gas into plasma and extracts hydrogen ions at a high voltage. In addition to protons (H ⁺ ), which are predetermined types of ions necessary for this acceleration system, hydrogen ions include H ₂ ⁺ consisting of _two protons and H ₃ ⁺ consisting of three protons. Although these content rates change with ion sources, a proton may be about 10%.
The extracted hydrogen ions pass through the inside of the vacuum duct 6 of the beam transport system 210 including the solenoid coil 2 and the slit 3 and the beam transport system 210 including the quadrupole electromagnet 4, and an FFAG (Fixed Field Alternating Gradient) accelerator or synchrotron It is incident on an accelerator 5 such as a linear accelerator. In the beam transport system 210 of FIG. 1, two quadrupole electromagnets 4 are provided, but in order to obtain beam parameters (emittance shape) required for the accelerator 5, there may be more quadrupole electromagnets 4. Here, the emittance shape is a distribution of particles on a plane (xx ′ or yy ′) composed of a horizontal or vertical axis in a cross section perpendicular to the beam traveling direction and an axis that gives an inclination in the traveling direction. is there.
In order to accelerate the protons efficiently with the accelerator 5, it is necessary to adjust the beam parameters required by the accelerator 5 with the quadrupole electromagnet 4 of the beam transport system 210. For this reason, the beam transport system 210 includes a beam monitor (see FIG. 1 is omitted), and the beam size and beam current value are measured. However, as described above, if H ₂ ⁺ and H ₃ ⁺ are mixed in addition to protons, parameters of a proton beam of a predetermined type cannot be measured. Since the respective ion beams have different convergence forces received by the solenoid coil 2 and the quadrupole electromagnet 4, the emittance shapes are also different.
The convergence force of the solenoid coil 2 and the quadrupole electromagnet 4 is inversely proportional to the momentum of the beam. Here, a difference in momentum between H ₂ ⁺ and H ₃ ⁺ with respect to the proton is considered. The acceleration voltage of the ion source 1 is V, and the momentum of the proton is m0 · v0. The mass m is such that H ₂ ⁺ is twice the proton and H ₃ ⁺ is 3 times. The velocity v is proportional to the square root of energy per proton, but the energy per proton of H ₂ ⁺ is V / 2 and H ₃ ⁺ is V / 3. Thus, each of the momentum 2 ^0.5 compared to protons, a 3 ^0.5 times, focusing force in the converging device is its inverse.

The present invention positively utilizes this difference in convergence power. A diverging beam is usually output from the ion source 1. The spread ion beam is subjected to a converging force by the solenoid coil 2, and the beam size can be sufficiently reduced downstream depending on the magnetic field strength. Since the solenoid coil 2 generates an axial target magnetic field, the axial target ion beam emitted from the ion source 1 can be focused on the axial target. The magnetic field intensity of the solenoid coil 2 can be set so that the proton beam reduces the beam size downstream thereof, and other types of ion beams do not diverge or are narrowed. The divergence here means that the ion beam expands without being narrowed downstream because the convergence force is insufficient. FIG. 2 shows an example of the calculation. The beam travels from left to right in the figure. The horizontal axis is the beam axis, and the vertical axis is a parameter proportional to the square root of the beam radius. From the top, protons, H ₂ ⁺ , and H ₃ ⁺ are shown. It is assumed that the ion source exit A has the same emittance shape, but emittance (area) is different in inverse proportion to the square root of momentum. It can be seen that the proton beam is focused at the position indicated by B in the figure, but the other beam sizes are not so small. The beam radius ratio at the position B in this calculation example is proton: H ₂ ⁺ : H ₃ ⁺ = 1: 4.6: 7, and the beam cross-sectional area related to the beam intensity is the square proton: H _2. ⁺ : H ₃ ⁺ = 1: 21: 49, and if the ion beam discriminating slit 3 matched to the proton beam size is provided here, the beam other than protons can be reduced to several percent or less.

FIG. 3 shows an embodiment of the slit 3. Except for the cooling water inlet 9 and the cooling water outlet 10, the structure is basically axisymmetric. When the beam intensity increases, heat removal becomes difficult with a simple slit having a hole in the center of a normal flat plate. Therefore, the material is good heat conduction, for example, copper, and in order to increase the area where the ion beam hits, it has a cone shape (beam shielding cone) 7 and is provided with a cooling water passage 8 for heat removal. Various cooling water passages 8 are conceivable. Here, a simple cavity is used, and the cooling water is introduced from the cooling water inlet 9 and taken out from the cooling water outlet 10. The radius of the most constricted part of the beam shielding cone 7 is made approximately equal to the radius of the proton beam. In this example, the circle is axisymmetric, but it is not limited to this shape.
If the slit 3 has a structure that can move in the beam axis direction so that the distance from the ion beam converging means 20 is variable, a higher effect can be obtained. This is because the beam parameter from the ion source 1 is difficult to accurately predict by calculation, and the convergence point may be shifted. In addition, although the example which provides the magnetic field generator by a solenoid coil in the ion beam converging means 20 of the ion beam separation system 200 was shown, it may replace with this and an electric field generator may be sufficient. The intensity of the convergence field of the convergence means 20 can be varied according to a predetermined type of ion beam and the distance between the convergence means 20 and the slit 3.
As described above, in the first embodiment, the beam separation system 200 including the solenoid coil 2 and the slit 3 is linearly provided on the central orbit of the ion beam downstream of the ion source 1, so that ions are linearly separated. Therefore, the ion beam separation system 200 and the ion beam acceleration system 100 can be made compact.

Embodiment 2. FIG.
In the first embodiment, the target ions are hydrogen ions. However, the present invention is not limited to this and can be applied to all ions. In the case of hydrogen ions, there are only three types of protons, H ₂ ⁺ and H ₃ ⁺ , and the charge number to mass number ratio is as large as 1: 1/2: 1/3, so the difference in convergence force is large. , There is a feature that separation is relatively easy. In addition, the same effect can be obtained for the separation of ions of an assembly of a plurality of molecules.

Embodiment 3 FIG.
Embodiment 3 is shown in FIG. In the first embodiment, two solenoid coils 2 are used as the magnetic field generator of the beam focusing means 20 of the ion beam separation system 200. However, the number of solenoid coils 2 may be one, or the same effect can be obtained with two or more. When a strong converging force is required, there is a problem that the solenoid coil 2 becomes very large with one, but depending on the converging force, a small solenoid coil 2 can be used, which has the effect of making the whole compact.

Embodiment 4 FIG.
A fourth embodiment is shown in FIG. In the first embodiment, the solenoid coil 2 is used as the magnetic field generator of the beam focusing means 20 for ion separation, but the same effect can be obtained with the quadrupole electromagnet 12. FIG. 5 shows an example in which three quadrupole electromagnets 12 are used. When a quadrupole electromagnet gives a converging force in the horizontal direction, a diverging force is generated in the vertical direction, and the reverse is possible depending on the polarity. The principle of using triple quadrupole electromagnets is the same as the principle of converging force by combining the converging and diverging lenses, and the polarity of the quadrupole electromagnets at both ends is opposite to that of the central quadrupole electromagnet. This triple system has an effect that it is easy to produce a relatively axisymmetric beam at the downstream convergence point, and can be reduced in size as compared with the solenoid coil 2.
The same effect can be obtained by using two quadrupole electromagnets having different polarities.

Embodiment 5. FIG.
The fifth embodiment will be described with reference to the drawings. FIG. 6 shows a slit according to the fifth embodiment. The emittance of the ion beam from the ion source 1 may be different from the design value. In this case, the slit diameter that allows all necessary types of ion beams to pass through the slit and removes unnecessary types of beams as much as possible differs from the design value. For this reason, the structure which can change a slit diameter easily is desirable.
The slit 3a shown in FIG. 6 is provided with a removal slit 15 on the ion beam exit side of the beam shielding cone 7a so that it can be taken out, and has an opening 15a having a diameter matched to the beam size of the proton beam. Since the removal slit 15 generates a large amount of heat per unit area, it is good in heat conduction and heat resistance, such as molybdenum.
FIG. 7 shows a removal slit 15b with a simplified structure, and the opening 15c has a diameter matched to the beam size. In the slit structure of the fifth embodiment, when the removal slits 15 and 15b are damaged, they can be easily replaced.

Embodiment 6 FIG.
FIG. 8 shows the slit 3c of the sixth embodiment. For example, the slit 3c is provided with a movable multi-slit 3d that can move in the direction perpendicular to the ion beam trajectory on the ion beam exit side of the slit 3 shown in the first embodiment. The movable multi-slit 3d is moved in the vertical direction by a drive mechanism 22 provided outside the vacuum duct 6 through a support bar 15f, and has a plurality of apertures 15e corresponding to the assumed ion beam diameter. It has a plate 15d. As described above, the slit 3c according to the sixth embodiment can select the aperture diameter according to the ion beam size by moving the movable multi-slit 3d, and can easily optimize the slit diameter. Beam adjustment can be performed quickly. Note that the moving direction of the movable multi-slit 3d is not limited to the vertical direction, and may be either the horizontal direction or the diagonal direction.
When the ion beam current value is small, a slit 3e as shown in FIG. 9 may be used. This slit 3e is a movable multi-slit having a plurality of apertures 15e similar to that shown in FIG. 8, and can be moved in the vertical direction by the drive mechanism 22 so that the slit diameter can be easily selected in accordance with the ion beam diameter. Is possible. In addition, although the example shown in this FIG. 9 shows an up-down direction movement, it is not limited to this, A left-right and diagonal direction may be sufficient.

Embodiment 7 FIG.
In the slit structure shown in the fifth and sixth embodiments, the necessary ion species are narrowed down and passed through the slit, and many other ion species are lost in the slit. Thus, if the ion beam focusing means 20 is set so as to expand unnecessary ion species by narrowing unnecessary ion species and a block is arranged instead of the slit 3, for example, many unnecessary ion species are lost on the block. The same effects as those of the fifth and sixth embodiments can be obtained. This method does not need to be limited to one place, and even if blocks are arranged at several places along the trajectory of the ion beam, a higher effect can be obtained. The same effect can be obtained even if the slit and block are used in combination.

  This ion beam separation system and ion beam acceleration system using the ion beam are used to treat malignant tumors such as cancer, other medical treatments, sterilization, or characteristics of metal materials by injecting ion beams into metal materials. It can be used in many ways, such as improvements.

BRIEF DESCRIPTION OF THE DRAWINGS It is an ion beam acceleration system block diagram of Embodiment 1 of this invention. It is a figure which shows the breadth and convergence of the ion beam of Embodiment 1 of this invention. It is a slit structure figure of Embodiment 1 of this invention. It is an ion beam acceleration system block diagram of Embodiment 3 of this invention. It is an ion beam acceleration system block diagram of Embodiment 4 of this invention. It is a slit block diagram of Embodiment 5 of this invention. It is a slit structure figure of Embodiment 5 of this invention. It is a slit structure figure of Embodiment 6 of this invention. It is another slit structure figure of Embodiment 6 of this invention.

Explanation of symbols

1 ion source, 2 solenoid coil, 3, 3a, 3b, 3c slit,
3d, 3e Movable multi slit, 4 quadrupole electromagnet, 5 accelerator,
7 Beam shielding cone, 15, 15b Removal slit,
15a, 15c, 15e opening, 15d multi slit plate,
20 beam focusing means, 100 ion beam acceleration system,
200 ion beam separation system, 210 ion beam transport system.

Claims (6)

An ion source that emits an ion beam including a predetermined type of ion beam , and at least one solenoid coil or two or three quadrupole electromagnets that generate a convergence field for converging the emitted ion beam An ion beam converging means, and an ion beam discriminating slit installed downstream of the ion beam converging means , the ion source, the ion beam converging means, and the slit together they are arranged in a straight line on the central trajectory of the ion beam and the and the predetermined type of ion beam, corresponds to the distance from the ion beam focusing means to a position of the slit, the ion beam converging means The ion beam of the predetermined kind is converged at the slit position by changing the intensity of the convergence field by changing the energization amount. Ion beam separation system adapted to. 2. The ion beam separation system according to claim 1, wherein the slit has a conical shape having a large diameter on an ion beam entrance side and a small diameter on an ion beam exit side. The ion beam separation system according to claim 2, wherein a removal slit is provided on the ion beam exit side of the slit. The ion beam separation system according to claim 2, wherein a movable multi-slit having a plurality of different apertures and movable with respect to the ion beam trajectory is provided on the ion beam exit side of the slit. An ion beam acceleration system comprising an ion beam separation system, an ion beam transport system, and an accelerator for accelerating the ion beam, wherein the ion beam separation system comprises the ion beam separation system according to claim 1. An ion beam acceleration system characterized by 6. The ion beam acceleration system according to claim 5, wherein the accelerator is a circular accelerator or a linear accelerator.

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