JP4517097B2 - Accelerator generating electron beam - Google Patents

Description

The present invention is a structure suitable for miniaturization, allowing the generation of high energy electron beam accelerated by a small diameter, relates accelerator generates electron beams.

  In the United States, more than 50% of cancer patients benefit from radiation therapy, and the therapeutic effect is comparable to surgery. In particular, recently, new devices such as IMRT (Intensity Modulated Radiation Therapy), SRT (Stereoscopic Radiation Therapy) and IGRT (Image-Guided Radiation Therapy) have been developed and have been effective in treating cancer. However, the conventional X-ray apparatus is not suitable for the treatment of cancer having a diameter of 1 cm or less due to the limitation of the diameter of the X-ray beam.

  For cancer treatment, when X-rays are irradiated multiple times from an arbitrary direction of 360 degrees to the cancerous part, for example, if the diameter of the X-ray beam is D, a spherical region of about D has a plurality of X-rays. Will receive irradiation. When the cancer area is smaller than D, the healthy tissue is irradiated multiple times, and there is a risk of damaging the healthy tissue. Therefore, treatment of cancer smaller than D is not possible. On the other hand, since early treatment is more effective as the area of cancer is smaller, its solution is strongly desired.

In order to have an effect on cancer treatment (early cancer) having a diameter of 1 cm or less, the diameter of the X-ray beam is preferably about 0.7 mm (for example, see Japanese Patent Application No. 2007-33404).
This Japanese Patent Application No. 2007-33404 is an invention relating to an X-ray source, and proposes a configuration in which the spot diameter of the electron beam of the accelerator is 1 mm and the diameter of the X-ray guide hole is 0.6 mm.
Thus, in order to generate this X-ray with a small diameter, it is necessary to excite the X-ray target with a small-diameter electron beam, and the development of an accelerator that generates this electron beam becomes important. In order to generate a small-diameter X-ray beam, an accelerator that generates a small-diameter electron beam is required.

The invention according to Patent Document 1 proposes a linear accelerator including a first prebuncher that applies a microwave electric field to a beam emitted from an electron gun and a second prebuncher connected via a drift tube.
The invention according to Patent Document 2 proposes a linear electron accelerator in which an electric field distribution adjusting metal cylinder is provided around an electron gun and the surface thereof is flush with a thermionic emission surface to improve beam performance.
The invention according to Patent Document 3 obtains an axially symmetric electron distribution using an axially symmetric acceleration cavity in a region where the accelerated electrons are not relatively fast, and effectively uses a side-coupled cavity in a region where the accelerated electrons are fast. An accelerating high electric field small standing wave linear accelerator is proposed.
Japanese Patent Laid-Open No. 01-130500 JP 07-335400 A Japanese Patent No. 3010169

  In the invention according to Patent Document 1, the structure of each part, for example, the structure of an electron gun and a prebuncher is not clear. In the invention according to Patent Document 2, it is not necessarily an optimum structure for reducing the diameter of the electron beam. Furthermore, the high electric field small standing wave linear accelerator according to Patent Document 3 can obtain a high energy electron flow, but there is room for improvement in emittance.

An object of the present invention is to further improve the apparatus of the aforementioned prior art, make it possible to improve the emittance of the beam, provides a accelerator for generating an electron beam capable of generating small-diameter electron beam There is .
To treat the following early cancer diameter 1cm effectively, it is necessary to generate the following small X-ray beam 0.75 mm.
A more detailed object of the present invention is to provide an accelerator that generates an electron beam capable of generating a small-diameter electron beam for exciting an X-ray target.
For this purpose, the structure of the electron gun portion is improved so as to generate a small-diameter thermoelectron beam having excellent emittance characteristics. By not using a grid in the electron gun section, an electron gun structure that prevents the disturbance of the electron beam due to the presence of the grid and the deterioration of the emittance of the beam and improves the emittance characteristics of the generated thermoelectrons is provided.

To achieve the above object, accelerator generates electron beams according to claim 1, wherein according to the invention,
An electron gun portion of an axially symmetric structure comprising a thermionic source, a Wehnelt electrode, and an anode electrode;
And Puribancha portion of axisymmetric structure that the acceleration and advance bunch of electron flow from the electron gun unit,
A buncher portion having an axially symmetric structure in front of the accelerating portion for further bunching and accelerating the electron stream modulated by the pre-buncher portion;
A rear acceleration unit for further accelerating the output of the buncher unit;
In the cylindrical accelerator composed of
The prebuncher cavity of the prebuncher part is provided integrally with the electron gun part so as to maintain the axial symmetry of the electron flow via one or more anode electrodes and an annular insulating plate. It is characterized in that the voltage is given individually.

Accelerator generates electron beams according to claim 2 of the present invention, in the accelerator of claim 1, wherein,
The Wehnelt electrode of the electron gun section is a focusing electrode.

Accelerator generates electron beams according to claim 3 of the present invention, in the accelerator of claim 1 or 2, wherein,
The thermoelectron emission material of the electron gun section of the thermoelectron source whose tip is a truncated cone is heated by a heater, and the heating power is configured to be introduced from the direction perpendicular to the axis of the cylinder. It is.
Accelerator generates electron beam according to claim 4 of the present invention, in the accelerator of claim 1 or 2, wherein,
A focusing coil is provided outside the tube wall of the buncher portion.

Accelerator generates electron beams according to claim 5 of the present invention, in the accelerator of claim 1 or 2, wherein,
The operation mode of the front stage of the acceleration unit is a π / 2 mode on-axis, the rear stage operates with a π / 2 mode side couple, and the front stage forms a buncher part.
Accelerator generates electron beams according to claim 6 of the present invention, in the accelerator of claim 1 or 2, wherein,
The operation mode of the front stage of the acceleration unit is a π mode on axis, the rear stage is operated by a π / 2 mode side couple, and the front stage forms a buncher part.

Accelerator generates electron beams according to claim 7 of the present invention, in the accelerator of claim 1 or 2, wherein,
The output beam of the accelerator is deflected by a deflecting unit and projected onto an X-ray target.

According to the first aspect of the present invention , the beam flow in an ideal state can be obtained by changing the voltage relationship between the anode, the Wehnelt, and the cathode by lengthening the Wehnelt portion in place of the grid electrode used conventionally. As a result, it is possible to obtain a small-sized and small-sized accelerator with excellent emittance characteristics. Since the use of the grid electrode is avoided, the disturbance of the electric field due to the mesh-like grid electrode is eliminated, the electrons are converged by the electric field without the disturbance, and the cost can be reduced. Further, it is possible to provide a structure in which the electron gun pervance does not change with time due to the deformation of the grid due to heat. In addition, since the electron gun unit and the prebuncher unit can be assembled together and joined to the acceleration unit by thermal welding or the like, a combination with the acceleration unit can be selected. Further, it is possible to reduce the size by combining the anode electrode and the prebuncher cavity, and further providing the prebuncher cavity with the function and the function of the anode electrode.
According to the second aspect of the present invention, since the spread of the beam can be suppressed, a small-diameter thermoelectron beam having excellent emittance characteristics can be generated.
According to the third aspect of the present invention, the axial direction of the thermionic gun can be shortened.
According to the fourth aspect of the present invention, since the converging coil is provided outside the tube wall of the buncher portion, the emittance of the electron beam can be improved at the stage of starting acceleration.
According to the fifth and sixth aspects of the present invention, the operation mode of the front stage and the operation mode of the rear stage of the acceleration unit can be set to the hybrid mode.
According to the seventh aspect of the present invention, an electron beam having excellent characteristics can be deflected and projected onto an X-ray target to generate an X-ray beam for treatment or diagnosis.

With reference to the drawings will be described the best mode for carrying out the accelerator to generate by that electron beam in the present invention.
Figure 1 is a schematic view of the whole of the accelerator that generates by that electron beam in the present invention.
The accelerator will be described in the following blocks A to E.
The portion A is a portion in which an electron gun portion that emits thermoelectrons and a prebuncher portion that modulates electrons are integrated.
Part B is a buncher part that generates a symmetrical (axially symmetric) electromagnetic field with respect to the tube axis and accelerates the electron group in the preceding stage of the accelerating part.
Part C is a side-coupled acceleration part that is power efficient to strongly accelerate the electron group. The portion D is an output cavity portion that outputs accelerated electrons.
The E part is a beam deflecting unit that deflects the output electron group in a plane including the XY axes.

Figure 2A is a schematic cross-sectional view showing a first embodiment of the part A with integrated electron gun unit and Puribancha part of the accelerator that generates by that electron beam in the present invention. Consideration is given to the structure of an electron gun which is a preferred electron source for generating a focused X-ray beam.
A heater 201 is built in the cathode 202. Electrons generated by the heating of the heater 201 are accelerated by the V4 voltage 206 and emitted from the cathode 202. In particular, the tip of the cathode 202 is thinner than the diameter of the base of the cathode 202.
Moreover, the tip of the cathode 202 is a flat surface perpendicular to the axis of the accelerating tube (the Z direction is the electron traveling direction), and constitutes a truncated cone-shaped hot cathode.

As described above, it is essential that the emittance characteristic of the electron beam is also good in order to reduce the X-ray diameter and ensure low divergence. In the electron gun used in the present invention, a cathode diameter of 3 mm or less, which is smaller than the currently used cathode diameter (usually about 1 cm), is used. The mesh-type grid is eliminated, and the first anode 212 and the second anode 213 perform the same operation. As a result, in the embodiment according to the present invention, the diameter of the electron beam can be reduced to 0.75 mm or less, and the emittance of the electron beam can be lowered to a level of 1 mm.m radian.

In FIG. 2A, the cathode 202 of the thermoelectron source of the electron gun section is made of a thermoelectron emission material having a truncated cone shape and a cylindrical shape as a whole, and is heated by a heater. Heating power is introduced from a direction perpendicular to the axis of the cylinder.
Electrons emitted from the tip of the cathode 202 are directed to the Z axis.
A Wehnelt electrode 203 constituting a converging electrode is disposed outside the cathode 202, and electrons emitted from the tip of the cathode 202 are converged to the center line of the Z axis.

A positive pulse voltage 207 is applied to the Wehnelt electrode 203 with respect to the cathode 202. As a result, electrons are intermittently emitted. By controlling the timing of the pulse voltage signal, the phase of accelerating the microwave of the bunching cavity in each buncher in the subsequent stage can be matched to increase the acceleration effect of electrons.
Next, the conventional electron gun has a structure in which a mesh-shaped grid is arranged on the front surface of the cathode. However, the mesh shape disturbs the electric field in the vicinity of the mesh, and there is a problem that the electrons are disturbed.

In order to avoid the disturbance of electrons as much as possible, the first anode 212 and the second anode 213 are provided. The voltages applied to each anode are V1 (210), V2 (209), and V3 (208).
Electrical insulation between the anodes is performed by a ceramic insulating material 211 formed of a ring-shaped ceramic.
In this way, the electron stream emitted from the cathode is converged on the Z axis and accelerated at each anode. Since these structures are symmetrical with respect to the Z axis, the electron flow 218 is symmetrical with respect to the Z axis.

This electron stream 218 enters the prebuncher cavity 214.
Microwaves are supplied from a coaxial feeder 215 disposed on the side surface of the pre-buncher cavity 214, the electron flow 218 is bunched by the electric field in the cavity, and the electron group 219 converged from the output end of the cavity is accelerated, which will be described later. It is added to the cavity of the buncher part B in front of the acceleration part.

In the A part in which the electron gun part and the prebuncher part are integrated in this way, the acceleration electromagnetic field maintains high axial symmetry with respect to the direction toward the outer periphery of the Z axis when the electron velocity is relatively slow. Thus, the electron beam can secure axial symmetry.
Thus, since there is no asymmetric microwave acceleration electric field inside the acceleration cavity, the distribution of the accelerated electron beam is axisymmetric and the intensity distribution of the generated X-rays is uniform.

Many conventional electron guns usually employ a configuration in which a grid is attached to take time timing of an electron beam amount and an electron beam output. According to this configuration, the electron beam is disturbed by the grid, and the emittance of the beam is impaired. In the configuration of the present invention, the beam flow in an ideal state can be ensured by elongating the Wehnelt portion instead of the grid and changing the voltage relationship between the anode, the Wehnelt and the cathode. That is, it is possible to improve the emittance of the beam. The cost is reduced by eliminating the grid, and the electron gun pervance does not change with time due to the deformation of the grid due to heat.
Usually, the anode part and the cavity of the prebuncher are separate, but here they are integrated so that the outside of the anode is inside the prebuncher cavity.

Figure 2B is a schematic cross-sectional view showing a second embodiment of the part A with integrated electron gun unit and Puribancha part of the accelerator that generates by that electron beam in the present invention. In this example, the conventional anode is omitted, and the prebuncher cavity 214 has an anode function.
The configurations and operations of the heater 201, the cathode 202, and the Wehnelt electrode 203 are not different from those described above. A positive pulse voltage is applied from the power source 221 to the Wehnelt electrode 203 with respect to the cathode 202, and the thermal electrons are intermittently emitted as described above. This pulse voltage is synchronized with an excitation voltage in which the inner conductor of the coaxial feeder 215 is introduced through the ceramic seal 216 and coupled by the coupling group 217. In the figure, a DC power source 220 is a power source corresponding to the anode voltage, and 222 is a heater power source. In this way, by controlling the timing of the pulse voltage signal applied to the Wehnelt electrode 203 and the signal connected via the coupling group 217, the phase for accelerating the microwave of the bunching cavity in each buncher at the subsequent stage is matched. The same operation as in the example shown in FIG.

  As described above, the structure shown in FIGS. 2A and 2B is a structure in which the electron gun portion and the prebuncher portion are integrated. In the structure shown in FIG. 2A, the feeder for supplying the high voltage and the heater power is connected to the acceleration tube axis (Z axis). By arranging perpendicularly to the direction), the overall length of the accelerating tube in the tube axis direction can be shortened.

The converged electron group 219 enters the buncher 12 (buncher part B, see FIG. 1). FIG. 3A and FIG. 3B are schematic diagrams showing first and second modes of hybrid mode of the acceleration unit of the accelerator.
The buncher 12 is a buncher portion shown in FIG. 3A (or FIG. 3B), and the action of reducing the diameter of the electron group by the magnetic field generated by the solenoid coil 302 works to converge the electron group.
The electric field generated in the cavity 301 accelerates the electron group.
Since the electromagnetic field of this acceleration part has symmetry with respect to the Z axis, the electron group maintains axial symmetry with respect to the Z axis. The acceleration voltage is about 10 KV. The accelerated electrons can obtain a large momentum toward the Z axis.

The solenoid coil 302 of the buncher part B (the front stage of the accelerating part) generates a converging magnetic field for suppressing the spread of the electron beam in the buncher part.
In addition, since the momentum of the electrons in the Z-axis direction is increased, fluctuations in the electrons other than in the Z-axis direction due to an undesired external electromagnetic field are extremely reduced and are not substantially affected.
The joining (see FIG. 1) of the integrated part A and the buncher part B of the electron gun part and the prebuncher part (see FIG. 1) welds the flange, increases the conductivity of the tube wall, and reduces the power loss as much as possible.

As shown in FIG. 3A, an electron group incident from the prebuncher cavity 214 (FIGS. 2A and 2B) and exiting the acceleration portion (buncher) of the standing waveform π / 2 mode on-axis coupling cavity is π / 2 mode. A side-coupled accelerator 14 (part C in FIG. 1) is entered. As shown in FIG. 1, the side-coupled accelerator 14 (C section) mainly includes an acceleration cavity 15, a side cavity 19, and a high-power microwave input port 13. The output of the side-coupled accelerator 14 is connected to the output cavity 16 (D section in FIG. 1).
In the example shown in FIG. 3B, the electron group incident from the prebuncher and exiting the acceleration portion (buncher) of the standing waveform π-mode on-axis coupled cavity is the π / 2 mode side-coupled accelerator 14 (C portion in FIG. 1). Rush into.

Microwaves input from the high power microwave input port 13 excite each acceleration cavity 303 through the side cavities 304 (coupling cavities). 3A and 3B, the coupling portion 305 couples the acceleration cavity 303 and the side cavity 304.
The electric field in the Z-axis direction further accelerates the electrons, and the electrons are transmitted to the next acceleration cavity.
At this time, the microwave excitation is in the π / 2 mode.
The energy of the electrons becomes several megavolts due to the multistage acceleration cavity, and the speed of the electrons reaches a speed close to the speed of light.

  As shown in FIG. 1, the electron group emitted from the output cavity 16 enters the beam deflection unit E. The electron group is deflected in the X-axis and Y-axis directions by the strong magnetic field of the deflection XY magnet 18. Thus, the electron group can be incident on an arbitrary X-ray target selected by the deflection, and X-rays can be generated in different directions from different positions.

Adopt a structure suitable for other miniaturization. For example, a cooling pipe (heat pipe) of the accelerating tube is arranged inside the outer wall and the inner wall of the accelerating tube. Since this structure is disclosed in Japanese Patent Laid-Open No. 11-8099, description thereof is omitted. A shield plate for shielding the electromagnetic field can also be arranged inside the acceleration tube.
As a result, the overall length of the accelerating tube can be reduced to about 30 cm, and the overall diameter can be reduced to about 5 cmφ.

It is a schematic diagram showing the overall structure of the accelerator for generating by that electron beam in the present invention. The electron gun unit and Puribancha part of the accelerator that generates by that electron beam in the present invention is a schematic sectional view showing a first embodiment provided integrally. The electron gun unit and Puribancha part of the accelerator that generates by that electron beam in the present invention is a schematic sectional view showing a second embodiment provided integrally. Is a schematic diagram showing a first embodiment of the hybrid mode the acceleration of the accelerator that generates by that electron beam in the present invention ([pi / 2 mode on-axis). The second embodiment of the hybrid mode the acceleration of the accelerator that generates by that electron beam to the invention ([pi mode on-axis) is a schematic view showing.

Explanation of symbols

A Electron gun part and prebuncher part B Buncher part C Side-coupled acceleration part D Output cavity part E Beam deflection part 11 Weld flange 12 Buncher 13 High-power microwave input port 14 Side-coupled accelerator 15 Acceleration cavity 16 of side-coupled accelerator 16 Output cavity (symmetry acceleration cavity)
17 Vacuum flange 18 XY magnet 19 Side cavity 201 Heater 202 Cathode 203 Wehnelt electrode 204 Feeder for various power supplies 205 Heater power supply 206 V4
207 Pulse voltage 208, 209, 210 Voltage V3 to V1 applied to the anode
211 Ceramic insulating material 212 First anode (anode)
213 Second anode (anode)
214 Prebuncher Cavity 215 Coaxial Feeder for Microwave 216 Ceramic Seal 217 Coupling Group 218 Electron Flow 219 Electron Group 301 Cavity 302 Solenoid Coil 303 Acceleration Cavity 304 Side Cavity 305 Joint

Claims (7)

An electron gun portion of an axially symmetric structure comprising a thermionic source, a Wehnelt electrode, and an anode electrode;
And Puribancha portion of axisymmetric structure that the acceleration and advance bunch of electron flow from the electron gun unit,
A buncher portion having an axially symmetric structure in front of the accelerating portion for further bunching and accelerating the electron stream modulated by the pre-buncher portion;
A rear acceleration unit for further accelerating the output of the buncher unit;
In the cylindrical accelerator composed of
The prebuncher cavity of the prebuncher part is provided integrally with the electron gun part so as to maintain the axial symmetry of the electron flow via one or more anode electrodes and an annular insulating plate. accelerator voltage generates that electron beam to, wherein the given individual. The accelerator according to claim 1, wherein
The accelerator is Wehnelt electrode of the electron gun unit generates you wherein electron beam to be a focusing electrode. The accelerator according to claim 1 or 2,
The thermoelectron emission material of the electron gun section of the thermoelectron source whose tip is a truncated cone is heated by a heater, and the heating power is configured to be introduced from the direction perpendicular to the axis of the cylinder. accelerator to generate other electron beams. The accelerator according to claim 1 or 2,
Accelerator that generates that electron beam to said convergence coil is provided in the tube wall outwardly of the buncher section. The accelerator according to claim 1 or 2,
The front operating mode of the accelerator is [pi / 2 mode on-axis, accelerator rear stage operate at [pi / 2 mode side couple, the previous stage generates you wherein electron beam that forms a buncher section . The accelerator according to claim 1 or 2,
The front operating mode of the accelerator is [pi mode on-axis, accelerator rear stage operate at [pi / 2 mode side couple, the previous stage generates you wherein electron beam that forms a buncher section. The accelerator according to claim 1 or 2,
The accelerator output beam accelerator for generating you wherein electron beams to be projected on the X-ray target is deflected by the deflection means.

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