JP2002110400A - Magnet for charged particle acceleration using permanent magnet and circular charged particle accelerator with high magnetic field - Google Patents

Abstract

(57) [Problem] To provide a circular charged particle accelerator which does not require large electric power and additional equipment, and which can be installed in a building such as an existing medical institution or the like and which is small and lightweight to a certain extent. SOLUTION: In a charged particle accelerator magnet used as a main magnet (a deflecting magnet, a focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator, a plurality of types of rod-shaped rare earth permanent magnets having a cross section of an arbitrary shape are used. A magnet for a charged particle accelerator characterized by being formed by combining a plurality of them is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle accelerating magnet using a permanent magnet and a high magnetic field circular charged particle accelerator. More specifically, a synchrotron, a cyclotron, and a storage ring (storage ring) that enable a charged particle to be accelerated by forming a magnetic field for deflecting, converging, and diverging the charged particle by a permanent magnet.
Etc. related to a circular charged particle accelerator.

[0002]

2. Description of the Related Art A conventional synchrotron,
In the research and development of circular charged particle accelerators such as cyclotrons and storage rings, the emphasis has been on increasing the energy or the number of charged particles. In particular, for collision-type accelerators, efforts have been made to increase the collision frequency (luminosity) of particles.

[0003] In order to realize these, the size of the accelerator is increased in order to increase the acceleration energy of the charged particles.
In addition, it is necessary to increase the magnetic field strength of the magnet for deflecting, converging, and diverging the charged particles. Although superconducting magnet technology was introduced to increase the magnetic field strength, it did not reach the level required in fields such as high-energy physics and nuclear physics, and the size of the accelerator was only enlarged. Eventually, a giant accelerator with a circumference of dozens of kilometers was developed.

In the United States, the Hadron Colander SSC (Superconducti
ng Super Collider) was canceled in the middle of the project after the Ministry of Energy reflected on its size and budget increase. Currently in the United States,
The linear collider, which is a collision type linear accelerator, and the muon collider, which is a circular lepton collision type accelerator, are cited as major accelerators in the development plan, and although VLHC (Very Large Hadron Collider) exceeding SSC has been studied, At present, it can be said that a kind of halt is being put on the enlargement of accelerators like this.

In European countries, construction of a circular accelerator LHC (Large Hadron Collider) using a superconducting electromagnet considered to be the last hadron collider is underway. As in the United States, the development of a muon collider is being considered for the lepton collider.

[0006] The main issues for increasing the acceleration energy of charged particles using the above accelerators are superconducting electromagnet technology in a circular hadron collider and superconducting cavity technology in a linear linear collider. Each has been the subject of much consideration.
In the case of muon colliders, high-field electromagnets capable of high-speed response have been studied due to the short life of muons (C. Johnstone et al., "Fi
xed field circular accelerator designs ", Proceedin
gs of the 1999 Particle accelerator conference, p
p.3067-3070).

On the other hand, in Japan, there is a plan to develop a hadron accelerator having a medium energy but a high beam intensity. The maximum energy of this accelerator is 50G
It is about eV, and an iron-based electromagnet will be used as in the past. At RIKEN, the RI Beam Factory (Radioactively Induced Beam Fact
ory) The plan is in progress. In this RI beam factory, a superconducting electromagnet will be used for the cyclotron forming the low energy part, and an electromagnet made of iron core will be used for the high energy accelerating part.

The above shows the trend of research and development on charged particle accelerators in various countries including Japan. In order to improve the performance and downsizing of charged particle accelerators in the future, the charged particles are deflected and converged. It is understood that the improvement of the magnetic field strength of the electromagnet is extremely important.

In Japan, in particular, the main goal of the development of the next generation of new accelerators is currently focusing on "miniaturization". As a result of the questionnaire survey, 1) It should be able to be stored in an area of about 5m in length × 5m in width × 3m in height 2) Total mass is about 10 tons 3) Beam energy is 1GeV or more of electron beam, proton or heavy ion beam 200 MeV / u (energy per nucleon) or more, 30 to 100 K with a radiation photon beam
eV or higher is set as the main specification target of the next-generation small accelerator.

In recent years, charged particle beams from synchrotrons and cyclotrons have been proved to be useful in the medical field such as cancer treatment. Therefore, in advance of medical applications of charged particle accelerators, miniaturization of charged particle accelerators is required. Is an important issue. In order to realize advanced treatment, it is required to irradiate the affected part with a charged particle beam from various angles, and as one of the measures, a rotating gantry is known. The rotating gantry is a large-sized device having a mechanical rotating mechanism including a large-sized electromagnet system constituting a system for deflecting and converging / diverging a charged particle beam, and its total weight is about 150 tons.
In particular, when realizing heavy ion particle irradiation, the size may exceed the size of a synchrotron or a cyclotron, and the size reduction is strongly desired from the medical side.

From the above, it can be understood that a problem in the development of a charged particle accelerator in the future is to realize downsizing while increasing the charged particle energy.

However, in order to realize proton / heavy ion energies higher than the current state by using a circular charged particle accelerator such as a synchrotron, it is necessary to greatly increase the magnetic field generated by the electromagnets constituting the accelerator. With an iron core type electromagnet, when the magnetic field intensity exceeds 1.5 T, the saturation of iron appears remarkably, so that it was difficult to obtain a stable charged particle beam.

In order to solve the problem of saturation, it has been considered to generate a magnetic field by using a coil without using an iron core type magnet. However, a large current and high voltage power supply is required, and the magnetic field strength is increased. And technical difficulty in generating the required magnetic field distribution. In addition, it emits huge noise when driving,
Since a pulse voltage (current) is required, there are many problems such as a large power supply facility.

Further, by applying the superconducting technology, it is possible to generate a coil generating a magnetic field of several Tesla, but in this case, large additional equipment such as a cryostat and a cooling device is required. Therefore, the equipment becomes large-scale.

The invention of this application has been made in view of the circumstances described above, and does not require a large amount of electric power or additional equipment, and has a certain degree that the entire apparatus can be installed in a building such as an existing medical institution. It is an object of the present invention to provide a small and lightweight circular charged particle accelerator.

[0016]

The invention of the present application solves the above-mentioned problems. First, as a main magnet (deflecting magnet, focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator. Provided is a charged particle accelerator magnet, wherein the magnet is formed by combining a plurality of types of rod-shaped rare earth permanent magnets having a cross section of an arbitrary shape.

Secondly, the invention of this application is directed to a charged particle accelerator magnet used as a main magnet (deflecting magnet, focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator. A magnet for a charged particle accelerator, which is formed by combining a plurality of rod-shaped rare earth permanent magnets having a rectangular cross section, and thirdly, a main magnet (a deflecting magnet, a focusing / diverging magnet) of a circular charged particle accelerator Or a combination thereof), a plurality of kinds of rod-shaped rare-earth permanent magnets having trapezoidal or sector-shaped cross sections are used, and these rare-earth permanent magnets are multilayered in a radial direction perpendicular to the charged particle transport duct. Provided is a magnet for a charged particle accelerator, which is formed by being combined so as to constitute a structure. Fourth, the invention of this application provides a magnet for accelerating charged particles, characterized in that the rare earth permanent magnet is a samarium-based or neodymium-based rare-earth permanent magnet having a high residual magnetic flux density.

Fifthly, the invention of this application provides a circular charged particle accelerator comprising any one of the charged particle accelerator magnets provided as any of the above inventions. Sixthly, the invention of this application is characterized in that the invention is provided with any one of the charged particle accelerator magnets provided as any of the above inventions formed so as to spirally rotate in the main axis direction of the charged particle transport duct. FF
An AG synchrotron is provided.

The invention of this application seventhly provides a medical particle beam irradiation apparatus comprising the above-mentioned circular charged particle accelerator or FFAG synchrotron, and eighthly, a particle beam irradiation apparatus. Provided is a medical particle beam irradiation apparatus characterized by including a rotation mechanism for rotating the entire medical particle beam irradiation apparatus around a patient to be irradiated.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and embodiments thereof will be described below.

In the circular charged particle accelerator according to the present invention, a samarium-based material is used as the material of the charged particle accelerator magnet (main magnet (deflecting magnet, focusing / diverging magnet or a combination thereof)) constituting the circular charged particle accelerator. Alternatively, a rare earth permanent magnet such as neodymium is used. As the rare earth permanent magnet, a magnet having a strong residual magnetic flux density is preferable.

It is desirable that the holding force (H _c ) is also strong. The characteristics of the residual magnetic flux density and the coercive force are determined by the position of the structural cross section of the magnet for a charged particle accelerator according to the present invention, which is the main one.

The commercially available rare earth permanent magnets are:
Because of its small size, it is impossible to obtain a magnetic field sufficient to secure a region through which high-energy charged particles pass even if used as it is. This problem can be solved by increasing the size of the rare-earth permanent magnet, but in practice, the magnetizing equipment and excitation power supply for producing the rare-earth permanent magnet become huge, so practical use is required in both cost and technology. Is considered difficult.

Therefore, in the circular charged particle accelerator of the present invention, first, the rare-earth permanent magnet is processed into a rod having an arbitrary shape. A plurality and kinds of rare-earth permanent magnets are prepared with respect to shape and size. Next, by forming these in combination, dimensions sufficient for utilizing as a magnet for a charged particle accelerator are secured.

As the shape of the polygonal cross section of the rare earth permanent magnet, a polygon is preferable because processing and the magnetization direction can be simplified. For example, as shown in FIG. 1, by combining a plurality of rod-shaped rare earth permanent magnets (11) having a hexagonal cross section and a plurality of rod-shaped rare earth permanent magnets (12) having a square cross section, a donut as shown in FIG. A magnet for a charged particle accelerator having a cross section of a mold is configured. The distribution of the magnetic field generated by the charged particle accelerator magnet can be adjusted by combining the magnetization directions of the rare earth permanent magnets. For example, when the rod-shaped rare earth permanent magnet having the above-described hexagonal cross section is used, the magnetization direction can be adjusted by 60 degrees by rotating one side. By increasing the number of angles, fine adjustment of the magnetization direction becomes possible and the magnetic field can be made strong. However, since the length of one side is shortened, the setting accuracy of the magnetization direction is low. It is considered to be.

In the invention of this application, in order to realize a magnet for a charged particle accelerator having a donut-shaped cross section as shown in FIG. 2, a rod-shaped rare earth permanent magnet having a hexagonal cross section as shown in FIG. A structure made of a high-strength material designed in a honeycomb shape so that the magnet and the rod-shaped rare-earth permanent magnet having a square cross section come into close contact can be used as a fixture for the rare-earth permanent magnet. A structure consisting of a plurality of lattices used as a fixture for the rare earth permanent magnet is:
Hereinafter, it is referred to as a honeycomb color.

The polygonal cross section of the rare earth permanent magnet may have a sector shape or a trapezoid shape. The fan or trapezoidal rare earth permanent magnets are combined to form a multilayer structure in the radial direction perpendicular to the charged particle transport duct,
This will form a charged particle accelerator magnet. In this case, it is necessary to prepare several kinds of magnetization directions of the rare-earth permanent magnet, but only one shape is required, and there is an advantage that the space factor is high.

Of course, the magnet for the circular charged particle accelerator of the present invention is not limited to the examples shown in FIGS. In addition to the honeycomb structure, various shapes and structures may be used.

In the circular charged particle accelerator according to the invention of this application, since the charged particle accelerator magnet is provided, the magnetic field generated in the charged particle transport duct is a direct current. Therefore, it is considered that the FFAG synchrotron is the most suitable as the circular charged particle accelerator of the invention of this application. Since the magnetic field generated in the charged particle transport duct is DC, it is possible to use a permanent magnet, and it is possible to generate a magnetic field having a higher intensity than the AC magnetic field used in a normal synchrotron. For the same reason, the high-field permanent magnet of this application is suitable for various cyclotrons. F
There are two types of main magnets used in the FAG synchrotron, a radial type in which positive and negative polarities are alternately provided in the traveling direction of charged particles, and a spiral type in which a spiral shape is provided in the traveling direction of charged particles. The spiral type is preferable in consideration of miniaturization of the synchrotron. In the FFAG synchrotron, since the magnetic field generated in the charged particle transport duct is a direct current, the radius of the parallel orbit increases with the acceleration of the charged particles, and the acceleration frequency changes accordingly. In order to cope with this change in orbit, the charged particle transport duct used in the FFAG synchrotron has a wide structure. By using the charged particle accelerator magnet according to the invention of this application, it is possible to cope with such a structure. In the invention of this application, FFAG
The main magnet used in the synchrotron is configured, for example, by fixing a rare-earth permanent magnet so as to spirally turn in the main axis direction of the charged particle transport duct so that the end has a spiral shape. When a honeycomb collar is used for fixing, a structure including a plurality of lattices constituting the honeycomb collar is set so as to spirally turn in the main axis direction of the charged particle transport duct. In addition, a main magnet is formed by preparing rare earth permanent magnets of a plurality of types in length and combining rare earth permanent magnets such that the length of the rare earth permanent magnet becomes longer from the inside of the spiral to the outside. .

The magnet for a charged particle accelerator according to the invention of the present application makes it possible to apply a magnetic field having a higher intensity to the charged particles than in the prior art, and to realize a smaller and lighter charged particle accelerator. . Therefore, by incorporating the FFAG synchrotron including the charged particle accelerator magnet according to the invention of the present application, for example, a compact and lightweight medical particle beam irradiation device that cannot be realized by the conventional technology is realized. The medical particle beam irradiation apparatus according to the invention of this application is small and lightweight, so that it has an advantage that it can be easily introduced into existing medical facilities such as hospitals, and also has a rotating mechanism as shown in FIG. Is provided, the entire medical particle beam irradiation apparatus (41) rotates around the patient (42) to be irradiated with the particle beam, and the beam irradiation port (43) can be directed to an arbitrary direction with respect to the patient. It becomes possible. Therefore, it becomes possible to irradiate the outputted particle beam from an arbitrary direction to the affected part.

The invention of this application has the above-mentioned features. Examples will be shown below and will be described more specifically.

[0032]

[Embodiment 1 ] An embodiment relating to heavy ion irradiation will be described with respect to the medical particle beam irradiation apparatus of the present invention.

FIG. 5 is a schematic diagram showing an example of the configuration of an FFAG synchrotron provided in a medical particle beam irradiation apparatus. Heavy ions are injected from a small cyclotron (51) through a converging / diverging quadrupole electromagnet system (52).
3). A foil (54) is installed between the converging / diverging quadrupole electromagnet system (52) and the incident septum (53), and heavy ions are completely ionized. The heavy ion transport duct (55) has a kicker (56), RF
A cavity (57), an extraction septum (58), and a main magnet (59) are installed. The small cyclotron (51) having this configuration may be a smaller FFAG synchrotron, but in any case, it is desirable to use the high magnetic field permanent magnet of the present application. The magnetic field generated by the main magnet in this FFAG synchrotron was calculated by computer simulation. Arrows in FIG. 6 indicate the directions of magnetization. As shown in FIG. 6, 500 mm radius r ₁ of the arc of the right portion of the main magnet, the radius r ₂ of the arc of the left portion was set to 200 mm. In addition, for the gap in which the charged particle transport duct enters, the length h
The length v in the vertical direction was set to 50 mm. FIG.
FIG. 3 is a contour diagram showing distribution of a magnetic field generated by a main magnet as light and shade. In this main magnet, the magnetic flux density was about 2.7 T in the portion where the magnetic field was strongest.

It should be noted that it is possible to further increase the magnetic field strength by partially using iron.

An irradiation port device such as a beam extraction line, a wobble magnet, a collimator, a shutter, a range shifter, and an X-ray tube is added to the FFAG synchrotron, and fixed to a common mount as a single unit. Is configured.

In order to irradiate the ion beam energy of 350 MeV / u, which is the ion beam energy required for medical use, with the medical particle beam irradiation apparatus of this embodiment,
It is estimated that the diameter of the FAG synchrotron needs to be about 6 m. HIMAC (Heavy I
On Medical Accelerator in Chiba) The synchrotron can irradiate heavy ions up to 800 MeV / u, but has a diameter of just over 42 m. Although the ion beam energy is different, it is about 1
/ 7 is realized.

The total weight of all the components of the medical particle beam irradiation apparatus according to the present embodiment is estimated to be about 100 tons. The permanent magnet portion is about 50 tons. Considering that the weight of the conventional rotating gantry is around 150 tons even excluding the accelerator part,
It is considered that the entire configuration of the medical particle beam irradiation apparatus of this embodiment including the synchrotron can be rotated around the patient by the rotation mechanism. Embodiment 2 The magnet for a charged particle accelerator of the invention of this application can be used not only for the FFAG synchrotron as described above but also for any circular charged particle accelerator, and may be used for a storage ring, for example. A storage ring magnet was designed, and the magnetic field generated by the storage ring magnet was calculated by computer simulation. Arrows in FIG. 8 indicate the directions of magnetization. As shown in FIG. 8, the radius r of the left and right semicircles in the storage ring magnet is 500 m.
m, and the width h of the cross section in the horizontal direction was set to 600 mm, and the length v in the vertical direction was set to 50 mm for the gap into which the charged particle transport duct enters. FIG. 9 is a contour diagram showing the distribution of the magnetic field generated by the main magnet as light and shade. In this main magnet, the magnetic flux density was about 2.9 T in the portion where the magnetic field was strongest. In either case, the magnetic field strength can be increased more efficiently by adding iron partially.

[0038]

As described above in detail, according to the invention of this application, large power and additional equipment are not required, and the whole apparatus can be installed in a building such as an existing medical institution, so that the apparatus is small and light to some extent. A circular charged particle accelerator is provided.

The medical particle beam irradiation device provided by the invention of this application is considered to be extremely effective for treating intractable diseases such as cancer. In particular, because of its small size and light weight, it has become practical to incorporate it into a mechanism for irradiating the affected part with a beam from any direction. In addition, since permanent magnets are used, low-cost introduction is possible,
No external power supply or cooling mechanism is required, contributing to lower operating costs.

Since the invention of this application is expected to spread the most advanced radiation therapy to more medical institutions, its practical application is strongly expected.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a magnet for a charged particle accelerator according to the invention of the present application.

FIG. 2 is a schematic diagram showing a configuration of a charged particle accelerator magnet according to the invention of the present application.

FIG. 3 is a schematic diagram showing a structure of a honeycomb collar for fixing a rare earth permanent magnet included in the charged particle accelerator magnet according to the invention of the present application.

FIG. 4 is a schematic diagram showing a configuration of a medical particle beam irradiation apparatus according to the invention of the present application.

FIG. 5 is a schematic diagram showing a configuration of an FFAG synchrotron according to the invention of the present application.

FIG. 6 shows the F designed in the embodiment of the invention of this application.
FIG. 3 is a schematic diagram showing dimensions and magnetization directions of a main magnet of the FAG synchrotron.

FIG. 7 is a contour diagram showing a magnetic field distribution generated by a main magnet of the FFAG synchrotron, which is a simulation result in the example of the present invention.

FIG. 8 is a schematic diagram showing dimensions and magnetization directions of a storage ring magnet designed in an embodiment of the present invention.

FIG. 9 is a contour diagram showing a magnetic field distribution generated by the storage ring magnet as a simulation result in the example of the present invention.

[Explanation of symbols]

11 Bar-shaped rare earth permanent magnet with hexagonal cross section 12 Bar-shaped rare earth permanent magnet with square cross section 41 Medical particle beam irradiation device 42 Patient 43 Beam irradiation port 51 Small cyclotron or small FFAG synchrotron injector 52 Converging / diverging quadrupole electromagnet System 53 Injection septum 54 Foil 55 Heavy ion transport duct 56 Kicker 57 RF cavity 58 Extraction septum 59 Main magnet

Claims (8)

[Claims] 1. A charged particle accelerator magnet used as a main magnet (a deflecting magnet, a focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator, a plurality of types of rod-shaped rare earth permanent magnets having a cross section of an arbitrary shape. A magnet for a charged particle accelerator, which is formed by combining a plurality of magnets. 2. A charged particle accelerator magnet used as a main magnet (deflecting magnet, focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator, wherein a plurality of kinds of rod-shaped rare earth permanent magnets having a plurality of polygonal cross sections are provided. A magnet for a charged particle accelerator characterized by being formed in combination. 3. A charged particle accelerator magnet used as a main magnet (deflecting magnet, focusing / diverging magnet or a combination thereof) of a circular charged particle accelerator, wherein a plurality of types of rod-shaped rare earth permanent magnets having a trapezoidal or fan-shaped cross section are provided. A magnet for a charged particle accelerator, wherein a plurality of these rare earth permanent magnets are used in combination to form a multilayer structure in a radial direction perpendicular to the charged particle transport duct. 4. The magnet for a charged particle accelerator according to claim 1, wherein the rare-earth permanent magnet is a samarium-based or neodymium-based rare-earth permanent magnet having a high residual magnetic flux density. 5. A high magnetic field circular charged particle accelerator comprising the charged particle accelerator magnet according to any one of claims 1 to 4. 6. An FF comprising the magnet for a charged particle accelerator according to any one of claims 1 to 4, which is formed so as to spirally rotate in a main axis direction of the charged particle transport duct.
AG synchrotron. 7. A medical particle beam irradiation apparatus comprising the circular charged particle accelerator according to claim 5 or the FFAG synchrotron according to claim 6. 8. A medical particle beam irradiation apparatus equipped with the circular charged particle accelerator according to claim 5 or the FFAG synchrotron according to claim 6, wherein the medical particle beam irradiation apparatus surrounds a patient to be irradiated with the particle beam. A medical particle beam irradiation device comprising a rotation mechanism for rotating the whole.