JPH08107000A - Microtron electron accelerator - Google Patents

Abstract

PURPOSE: To stably obtain an electron beam of a large electric current in a microtron electron accelerator to accelerate an electron by making it perform circular orbit motion by an electric field and a magnetic field by arranging an accelerating cavity in the magnetic field so as to produce the high frequency electric field when a microwave is inputted. CONSTITUTION: An accelerating cavity 1 is constituted in a cylinder shape, and an electron source composed of a cathode 4 and an anode 5 is arranged outside a wall surface of the accelerating cavity 1. An electron is made to perform circular orbit motion in a passage of the cathode → a first passing hole → the inside of a cavity → a second passing hole → the outside of the cavity →the first passing hole → the inside of the cavity → a third passing hole → the outside of the cavity through three electron beam passing holes 61, 62 and 63 arranged in a cavity wall surface. Constitution of which device constitution-operational condition are optimized is formed. Therefore, electrons more than a conventional critical value can be accelerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microtron electron accelerator, and more particularly to a structure of an electron source and an accelerating cavity which are small and suitable for stably obtaining an electron beam of high energy.

[0002]

2. Description of the Related Art Microtron electron accelerators are those that accelerate electrons by microwaves. The acceleration principle of the microtron is that, as shown in FIG. 8A, the acceleration cavity 1 that creates a high-frequency electric field E by the input of the microwave 3 is arranged in an electromagnet 2 that creates a uniform magnetic field B, and these electric fields E are generated. And the magnetic field B causes the electron e to move in a circular orbit and accelerate. An electron source 40 that emits electrons e is provided in the acceleration cavity 1, and in the uniform magnetic field B, a deflection pipe 7 that linearly guides the electron beam,
A take-out pipe 8 for taking out the electron beam to the outside is provided. The electrons e emitted from the electron source 40 are guided into the acceleration cavity 1 and are initially accelerated, and the circular orbit 9 is generated in the uniform magnetic field B.
0B is drawn and re-injected into the acceleration cavity 1. After this, acceleration in the acceleration cavity 1 and circular orbital motion in the uniform magnetic field B (91, 9
2, ... 96) are repeated, and the electron e is accelerated until it has a desired energy. Each time the circular orbit of the accelerated electron e is accelerated, the orbit diameter increases by λ / π (λ: free space wavelength of the microwave 3). The electron beam accelerated to the desired energy is guided tangentially through a movable deflection pipe 7 installed on a circular orbit. The electrons emitted from the deflection pipe 7 are circularly deflected by the uniform magnetic field B toward a point independent of energy, and are taken out of the uniform magnetic field B by the fixed extraction pipe 8.

As an example in which this type of prior art is described,
Invention by the inventors of the present application "Microtron electron accelerator"
Japanese Patent Laid-Open No. 6-118100. In the above prior art, the shape of the accelerating cavity 1 is configured by a rectangular parallelepiped, and particularly in the case of the rectangular parallelepiped, the optimum device configuration and operating conditions for stably obtaining a large current beam are disclosed (FIG. 8 (b). )). For example, the cavity gap (acceleration gap) b of the acceleration cavity is optimally in the range of 18 to 28 mm.

[0004]

With the microtron,
The current amount and stability of the obtained electron beam largely depend on the device configuration and operating conditions. Therefore, in order to realize a microtron that can stably obtain a large current beam, it is necessary to optimize the device configuration and operating conditions. In the above conventional technology,
The optimization of the device configuration and operating conditions to obtain a large current beam stably was limited to the case of a rectangular parallelepiped acceleration cavity. Therefore, in the prior art, there is a limit to the amount of electron beam current that can be obtained even under optimized device configurations and operating conditions. An object of the present invention is to provide a microtron electron accelerator, which is an improvement over the conventional technique and which can stably accelerate a large current beam more than a rectangular parallelepiped acceleration cavity.

[0005]

In order to achieve the above object, in the present invention, an accelerating cavity for receiving a microwave to generate a high frequency electric field E is arranged in a uniform magnetic field B, and these magnetic fields B are In a microtron electron accelerator in which the electrons e are orbitally moved by the electric field E to accelerate, the accelerating cavity is formed in a cylindrical shape, and the circular accelerating cavity has a circular bottom wall at a position sandwiching the electron source. First and second electron beam passage holes, and a third electron passage hole is provided in a wall of the other bottom surface of the cylindrical acceleration cavity at a position facing the first electron beam passage hole to generate the electron e. The electron source is composed of a cathode and an anode having a hole through which an electron beam extracted from the cathode passes, and the electron source is provided with a central axis of the acceleration cavity and the first and second electron beam passage holes. Acceleration above in terms of including From the body of the external and the central axis and the wall of the circular bottom it is provided a certain distance. Furthermore, regarding the device configuration and operating conditions of the microtron, such as the dimensions of the accelerating cavity and the uniform magnetic field B, the optimal conditions for stably obtaining a large-current electron beam are taken into consideration.

[0006]

By configuring the accelerating cavity for accelerating the electrons e with a cylindrical type having a higher Q value than that of the rectangular parallelepiped, more electrons can be accelerated. Furthermore, by optimizing the device configuration and operating conditions of the microtron using the cylindrical acceleration cavity, it is possible to stably accelerate electrons under a wide range of incident conditions. That is, it is possible to realize a microtron that can stably obtain a large current beam. Furthermore,
Since the electron beam source is composed of a cathode and an anode having pores that allow the electron beam to pass therethrough, and is provided outside the acceleration cavity, a stable electron beam can be obtained.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a microtron electron accelerator showing an embodiment of the present invention, in which FIG.
A perspective view of the acceleration cavity is shown in (b). First, in this embodiment, a cylindrical acceleration cavity 1 resonating at 3 GHz is provided in an electromagnet 2 that produces a uniform magnetic field B. In the acceleration cavity 1, a high frequency accelerating electric field E of 3 GHz is created by the input of the microwave 3. Further, on the outer side of the wall surface (cylindrical bottom surface) of the acceleration cavity 1, an electron source including a cathode 4 and an anode 5 coaxially formed is provided. In particular,
The cathode 4 is attached to a part of a cylindrical support rod, and the anode 5 is cylindrical and has a small hole through which an electron beam passes. The acceleration cavity 1 has a first electron beam passage hole 61 through which the accelerated electron beam passes, and an electron beam passage hole 61 on the bottom surface of the cylinder.
Second electron beam passage hole 6 at a position sandwiching the electron source from
2. A third electron beam passage hole 63 is provided at a position facing the electron beam passage hole 61 on the other bottom surface of the cylinder. Here, the first electron beam passage hole 61 is provided on the bottom surface where the high frequency electric field E near the electron source arrangement position is strong, and the second electron beam passage hole 62 is also provided on the bottom surface where the high frequency electric field E is weak. Has been. Further, inside the uniform magnetic field B, a movable deflection pipe 7 and a take-out pipe 8 for taking out the electron beam to the outside are provided.

The operation of this embodiment will be described below. Due to the potential difference between the cathode 4 and the anode 5, thermoelectrons e are extracted from the heated cathode 4. Electronic e pulled out
Draws a circular orbit 90A by the uniform magnetic field B created by the electromagnet 2, and then the acceleration cavity 1 from the first electron beam passage hole 61.
Incident on the inside. Since the high frequency accelerating electric field E of 3 GHz exists in the acceleration cavity 1 in addition to the uniform magnetic field B, the electrons e are deflected by the uniform magnetic field B and simultaneously accelerated by the high frequency accelerating electric field E. Then, it is emitted from the second electron beam passage hole 62 to the uniform magnetic field B region. The emitted electrons e re-enter the acceleration cavity 1 through the electron beam passage hole 61 in a circular orbit 90B. Here, the electrons e are further accelerated by the high frequency accelerating electric field E, and the electrons e
From the electron beam passing hole 61, and re-injects into the acceleration cavity 1 from the electron beam passage hole 61. After that, the acceleration by the high frequency accelerating electric field E and the circular orbital motion by the uniform magnetic field B are repeated, and the electron e reaches a desired energy. The electron e that has reached the desired energy is
It is deflected by the movable deflection pipe 7 installed on the circular orbits 91 to 96, and taken out by the take-out pipe 8. In addition, in FIG. 1 (a), the circular orbit is 96
Although shown up to now, the configuration is such that it can be accelerated up to 30 times.

The optimum conditions in the above configuration were obtained by analyzing the electron orbit by computer simulation. As a result, it was found that the following should be done.
First, FIG. 2 shows an enlarged cross-sectional configuration diagram of the cylindrical acceleration cavity 1, the cathode 4 and the anode 5. FIG. 3 shows the result of obtaining the optimum value of the cavity spacing (cylinder height) b dimension of the cylindrical acceleration cavity 1 in FIG. 2 by computer simulation. Here, the number of stable accelerating electrons on the vertical axis is the number of electrons that can obtain a desired energy when electron orbit analysis is performed by finely changing the cathode emission angle and the initial incident phase of electrons. However, the cathode emission angle is the emission direction of electrons when the direction of the high frequency electric field E is 0 degree,
The initial incident phase is the phase of the microwave when the electron first enters the accelerating cavity. In the simulation, the cathode emission angle is 5 degrees in the optimum 80 degree range from 250 to 360 degrees, and the initial incident phase is 0 to 3 degrees.
A total of 3060 electron trajectories are calculated by changing the angle twice within a range of 60 degrees. The optimum cavity spacing b of the accelerating cavity 1 for obtaining a large beam current is about 19-based on the assumption that the number of stable accelerating electrons is 50 or more in FIG.
It was found to be in the range of 29 mm.

Next, the results of finding the optimum center position of the cathode 4 provided on the outer wall of the bottom surface of the acceleration cavity 1 are shown in FIGS.
Shown in The horizontal axis represents the distance c from the bottom of the cylinder at the cathode center position and the height d from the center axis of the cylinder (see FIG. 2). 4 and 5, similarly, the optimum center position of the cathode 4 is about 2 to 6 m from the bottom of the cylinder to the outside of the cavity.
It was found that the height from the central axis of the cylinder was about 2 to 13 mm. Further, FIG. 6 shows the result of obtaining the optimum value of the uniform magnetic field B intensity by computer simulation. As a result, it was found that the range of 0.17 to 0.23T is suitable.

In consideration of the above simulation results and the condition of resonating with the microwave of 3 GHz, the device is constructed as follows in this embodiment. First, the diameter 2 of the cylindrical acceleration cavity 1
The distance a was 76.5 mm and the cavity distance b was 24 mm. The center position of the cathode 4 is set such that the distance c from the cylinder bottom surface of the acceleration cavity to the outside of the cavity is 4.6 mm, and the height d from the cylinder center axis is 7 mm.
mm. The uniform magnetic field B intensity was 0.194T. According to the present configuration and operating conditions, the Q of the acceleration cavity 1 is higher than that of the rectangular parallelepiped acceleration cavity having the optimum configuration in the prior art.
The value should be about 5% higher, and the total energy of electrons is 3 to 3
It was found by simulation that the number of stable accelerated electrons is increased by about 5% in the range of 0 MeV as compared with the conventional technique. According to this embodiment, a microtron electron accelerator capable of stably accelerating a large-current electron beam as compared with a conventional microtron electron accelerator using an acceleration cavity can be obtained. The current amount of the electron beam extracted at this time is 4M.
About 165mA at eV, about 22mA at 20MeV
Met.

FIG. 7 is a block diagram showing the configuration of a medical device using the microtron electron accelerator according to the present invention.
The electron beam taken out from the take-out pipe 8 of the microtron electron accelerator 100 is conveyed by using a quadrupole lens, a deflector or the like, and the electron beam as it is or converted into the X-ray 101 is irradiated to the patient 97 on the treatment table 98. It is configured into and used for medical treatment.

The embodiments of the present invention have been described above.
The present invention is not limited to the above-mentioned embodiments, and various configurations as shown below are possible. For example, in the above-mentioned embodiment, the cathode 4 and the anode 5 are formed coaxially, but it is sufficient that the electrons e are extracted from the cathode 4 due to the potential difference between the cathode 4 and the anode 5. The electron beam extraction mechanism is also composed of the movable deflection pipe 7 and the fixed extraction pipe 8 in the above-mentioned embodiment, but is not limited to this. Further, the numerical values in the above-mentioned embodiments are examples, and the present invention is not limited to the embodiments. For example,
Although 3 GHz is used as the frequency of the microwave 3 in this embodiment, any frequency may be used as long as it satisfies the synchronization condition of the microwave. In that case, the optimum device configuration described in the present embodiment may be changed to a value proportional to the reciprocal of the frequency of the microwave 3, and the operating condition may be changed to a value proportional to the frequency. Also, the upper limit of the number of accelerations and the total energy of electrons is 30 times, 30 Me
It is not limited to V. Furthermore, you may use it as an injector of a SOR ring.

[0014]

According to the present invention, by using a cylindrical acceleration cavity having a high Q value, it is possible to reduce the power loss in the cavity and accelerate many electrons. Furthermore, by optimizing the device configuration and operating conditions, it is possible to accelerate electrons under a wide range of incident conditions. That is, there is an effect that it is possible to provide a microtron electron accelerator that can stably obtain a high-current electron beam.

[Brief description of drawings]

FIG. 1 is a block diagram of a microtron showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the acceleration cavity in the configuration of FIG.

FIG. 3 is an explanatory diagram of optimum conditions in the configuration of FIG.

4 is an explanatory diagram of optimum conditions in the configuration of FIG.

FIG. 5 is an explanatory diagram of optimum conditions in the configuration of FIG.

FIG. 6 is an explanatory diagram of optimum conditions in the configuration of FIG.

FIG. 7 is a block diagram of a medical device according to another embodiment of the present invention.

FIG. 8 is a block diagram of a conventional microtron.

[Explanation of symbols]

1 ... Accelerating cavity, 61, 62, 63
... electron beam passage hole, 2 ... electromagnet,
90A, 90B ... initial circular orbit, 3 ... microwave,
91-96 ... 1st-6th circular orbits, 4 ...
Cathode, 97 ... Patient, 5 ... Anode, 98 ... Treatment table, 7 ... Deflection pipe, 99 ... Gantry, 8 ... Extraction pipe, 100 ... Microtron electron accelerator, 40 ... Electron source, 101 ... Electron beam or X-ray.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Nishimura 1-1-14 Kanda, Chiyoda-ku, Tokyo Inside Hitachi Medical Co., Ltd.

Claims (7)

[Claims] 1. A microtron electron accelerator in which an accelerating cavity for inputting a microwave to generate a high frequency electric field is arranged in a uniform magnetic field, and electrons are circularly orbitally moved by the magnetic field and the high frequency electric field to accelerate the cathode. An electron source having an anode having a hole for passing an electron beam extracted from the cathode is arranged outside the wall surface of the acceleration cavity, the acceleration cavity is formed in a cylindrical shape, and the electron source on the bottom surface of the acceleration cavity is arranged. A first electron beam passage hole and a second electron beam passage hole are provided in a position sandwiching, and a third electron beam passage hole is provided at a position facing the eleventh electron beam passage hole on the other bottom surface of the acceleration cavity. And the second electron beam passage hole is located at a position where the first electron beam passage hole guides the electron beam from the electron source and the electron beam circularly moved and accelerated into the acceleration cavity. From the source At a position where the electron beam does not pass through the third electron beam passage hole, passes through the same direct bottom surface as the first electron beam passage hole, and goes out of the acceleration cavity, and the third electron beam passage hole. Is provided at a position for guiding an electron beam accelerated in the acceleration cavity to the outside of the cavity from the other bottom surface of the acceleration cavity. 2. The electron source is a cathode having an electron emitting material provided on a part of the surface of a columnar rod and an anode formed coaxially with the columnar rod and having a hole at a position facing the electron emitting material. The microtron electron accelerator according to claim 1, which is configured. 3. The center position of the cathode of the electron source is arranged at a position of 2 to 6 mm from the bottom surface of the cylindrical acceleration cavity toward the outside of the cavity and 2 to 13 mm from the center axis of the cavity. The microtron electron accelerator according to claim 1. 4. The strength of the uniform magnetic field is 0.17 to 0.23.
The two-microtron electron accelerator according to any one of claims 1 to 3, which is set in a range of T. 5. The cylindrical height of the cylindrical acceleration cavity is 19-2.
The microtron electron accelerator according to claim 1, wherein the microtron electron accelerator is set in a range of 9 mm. 6. The microwave has a frequency of 2.5 to 3.5.
The microtron electron accelerator according to claim 1, wherein the microtron electron accelerator is set in a GHz range. 7. A medical device using the microtron electron accelerator according to any one of claims 1 to 6.