JPH097798A - Accelerating tube and accelerator - Google Patents

Abstract

PURPOSE: To obtain an accelerating tube which suppresses a dark current generated in the accelerating tube, and has a high electric field and little dark current. CONSTITUTION: When a high-frequency wave power 1 is inputted to the inside of an accelerating tube 20 through a waveguide 2 and a combined window 3, an accelerating high-frequency wave electric field shown in an electric line of force 5 is generated in an accelerating tube combining unit 4 by the high-frequency wave power 1. By the generated high-frequency wave electric field, electrons are drawn out and accelerated by the field emission from the metal of the inner wall surface of the accelerating tube 20, and the electrons strike to the inner wall of the accelerating tube 20 so as to generate the secondary electrons. As the material of the parts 4a, 22a, and the like of their striking, a material 9 whose secondary electron emission coefficient is smaller than '1' is used. Consequently, the number of the generated secondary electrons is made fewer than the number of the striking electrons, and the breeding of the electrons can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerator for accelerating charged particles, and more particularly to an accelerator tube with a small amount of secondary electron emission and an accelerator using the same.

[0002]

2. Description of the Related Art In recent years, development of high-power high-frequency sources has progressed, and recently, a klystron having a peak power of 100 MW has been developed. Along with this, the high frequency power introduced into the acceleration tube is increasing. Therefore, the accelerating electric field strength of the accelerating tube can be made larger than ever before.

For example, a collision-type linear accelerator JLC (Japan Linea) proposed in Japan for studying elementary particles is proposed.
In the case of r collider), according to Kajikawa, "Geometry of Linear Collider-JLC-I-"("Fiscal 1993 Grant-in-Aid for Scientific Research (General Research A) Research Results Report") To achieve this, the length of the accelerating tube must be 25km. 1
It is planned to set the accelerating electric field strength per m to 22 MV / m. The acceleration gradient of the electron linear accelerator currently in operation at the High Energy Physics Laboratory is about 8 MV / m,
The accelerating electric field strength required by JLC is about three times this.

In the JLC, it is planned to increase the energy of the beam in the future, and in that case, the accelerating electric field strength must be further increased. It is important to increase the accelerating electric field strength not only in such an accelerator for particle research, but also in linear accelerators such as those for physical properties research, medical use, and injectors for synchrotron radiation rings. If the accelerating electric field strength can be increased, the length of the accelerating tube can be shortened in order to obtain the required beam energy, and the entire accelerator can be downsized.

As described above, if the entire accelerator can be downsized, the facility scale can be reduced and the cost can be reduced, but conventionally, it was difficult to increase the accelerating electric field strength of the accelerating tube. FIG. 5 is a longitudinal sectional view of an accelerating tube according to the related art. The accelerating tube 20 includes a cylinder 21, a plurality of hollow disks 22 aligned in the cylinder 21, and a coupling provided at an end thereof. And a waveguide 2 connected to the coupler 4 through a coupling window 3.
When the high frequency power 1 is introduced into the coupler 4 through the waveguide 2 and the coupling window 3, the introduced high frequency power 1
As a result, an accelerating electric field as shown by electric lines of force 5 is generated.

As described above, when the accelerating electric field strength is increased in order to obtain high energy, the electric field on the inner surface of the accelerating tube becomes high, and the electrons 6 are emitted from the inner surface of the tube by field emission. The emitted electrons 6 are accelerated by an accelerating electric field as shown by electric lines of force 5, and when colliding with the disk 22, secondary electrons 7 are emitted. Copper is usually used as the material of the acceleration tube 20. Since the secondary electron emission coefficient of copper is "1.28", which is higher than "1", the collision electron 1
1.28 secondary electrons are emitted per piece, and the number of electrons generated in the accelerating tube exponentially increases. The current caused by the electrons thus emitted is called a dark current. When the electric field on the inner wall of the accelerating tube is increased, the number of electrons generated by field emission is increased and the dark current is increased.

[0007]

The prior art described above is
When the electrons generated in the coupler collide with the inner wall of the accelerating tube, the material of the accelerating tube is copper whose secondary electron emission coefficient is larger than "1", so that electron multiplication cannot be suppressed.
Therefore, secondary electrons other than the electron beam, which is originally necessary, are generated, and this secondary electron causes noise when the beam is finally used. In addition, secondary electrons, which become dark current, are accelerated in the accelerating tube, which wastefully consumes high-frequency power in the accelerating tube, resulting in a problem that the required electron beam acceleration efficiency is deteriorated.

An object of the present invention is to provide an accelerating tube which can reduce noise by reducing emission of secondary electrons and improve acceleration efficiency, and an accelerator using the accelerating tube.

[0009]

The above object is achieved by using a material having a secondary electron emission coefficient of less than "1" for a part or all of the inner wall of the coupler and at least two disks following the inner wall. To be done.

[0010]

Since the material of the portion where the electrons generated by the field emission collide is smaller than the secondary electron emission coefficient "1", the increase of the electron causing the dark current is suppressed. Therefore, the high frequency power is not wastefully consumed, and the charged particles can be efficiently accelerated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a configuration diagram of a linear accelerator according to an embodiment of the present invention. In FIG. 3, four acceleration tubes 20a, 20b, 20c, 20 are provided on the electron beam output side of the electron gun 25.
d are connected in series, and converging magnets 26a, 26b, 26 for suppressing the divergence of the electron beam are provided at the respective connecting portions.
c and 26d are provided. Each acceleration tube 20a, 20
b, 20c, and 20d include a controller 27 for the linear accelerator.
Klystron 28a, 28b (29
a and 29b are high-frequency power from the klystron power supply) and waveguides 2a, 2b and 2 which are power input ends of the respective acceleration tubes.
c, 2d, and each of the acceleration tubes 20a-2
A high frequency electric field for electron beam acceleration is generated inside 0d. In the example shown in the figure, four accelerating tubes are connected, but when a long linear accelerator is required, several tens of similar accelerating tubes are used.
You can connect on the order of hundreds or thousands.

When a high voltage is applied to the electron gun 25 from the electron gun high-voltage power source 24 in response to a command from the linear accelerator control device 27, an electron beam is extracted from the electron gun 25 and 1
It is input into the acceleration tube 20a of the stage. The electron beam input into the accelerating tube 20a is accelerated by the high frequency electric field inside the accelerating tube and is emitted into the accelerating tube 20b of the second stage. After that, similarly, each of the second, third, and fourth accelerating tubes 20
The electron beams sequentially accelerated by b to 20c are emitted from the output end of the fourth stage acceleration tube 20d.

FIG. 1 is a longitudinal sectional view of an essential part of an accelerating tube according to a first embodiment of the present invention. In FIG. 1, when the high frequency power 1 is input to the acceleration tube 20 through the waveguide 2 and the coupling window 3,
This high-frequency power 1 causes an accelerating high-frequency electric field as shown by electric lines of force 5 in the accelerating tube coupler 4. Due to the generated high frequency electric field, electrons are extracted from the metal forming the accelerating tube by field emission and accelerated. The accelerated electrons collide with the inner wall of the acceleration tube to generate secondary electrons.

Therefore, in this embodiment, the secondary electron emission coefficient is smaller than "1" in a portion having a high electric field such as the corner portion 4a of the accelerating tube coupler 4 and the inner peripheral edge portion 22a of the disk 22. Material such as titanium (secondary electron emission count "0.
9 ″) to suppress the multiplication of electrons. Titanium may be used for the inner peripheral edge of all the disks 22 of the accelerating tube 20, but it may be provided only for the disk effective for suppressing the secondary electron emission. The entire coupler 4 may be made of a material having a small secondary electron emission coefficient.

In the example shown in FIG. 1, titanium is provided only on the two disks 22 on the coupler 4 side. In this embodiment,
Titanium is formed into a ring shape, which is fitted and fixed to the corner portion 4a and the inner peripheral portion of the disc.

FIG. 2 is a longitudinal sectional view of the main part of an accelerating tube according to the second embodiment of the present invention. In the present embodiment, the plate-shaped titanium 9 is joined to the corners of the coupler 4 and the disk inner peripheral edge 22a by brazing or soldering. Of course, titanium may be attached to these parts by other methods such as diffusion bonding or coating. Although titanium has been described as an example of the material having a low secondary electron emission count in the above-described embodiment, it goes without saying that the material is not limited to titanium.

FIG. 4 is a configuration diagram of an accelerating tube according to the second embodiment of the present invention. In FIG. 1, the high frequency power 1 is input through the waveguide 2 and the coupling window 3. The input high-frequency electric power 1 generates an accelerating high-frequency electric field in the accelerating tube coupler 4 as shown by electric lines of force 5. Due to the generated high frequency electric field, electrons are extracted from the metal by field emission and accelerated. The accelerated electrons collide with the inner wall of the facing acceleration tube to generate secondary electrons. A part of the inner wall of the acceleration tube facing each other is coated with a thin film of titanium. The thickness of the coated thin film is about the skin thickness determined by the frequency of the acceleration high frequency. For example, when the acceleration high frequency is 2.856 GHz, it is about 1.2 μm. The secondary electron emission coefficient of titanium is 0.9
Since the number of secondary electrons generated is smaller than 1, the number of secondary electrons generated is smaller than the number of colliding electrons, so that electron multiplication can be suppressed.

FIG. 5 is a block diagram of a circular accelerator. In the above-described embodiment, the example of the accelerating tube of the linear accelerator has been described, but it is also possible to use the accelerating tube shown in FIGS. 1 and 2 as the accelerating tube of the circular accelerator. The circular accelerator 220 shown in FIG. 5 includes the accelerator tubes 20a and 20b shown in FIG.
An electron beam from an electron beam injection system connected in series is taken from an injector 221 into a circular orbit and circulated, and is used for synchrotron radiation generation, elementary particle experiments, and the like.

Since the energy gain is increased by constructing the accelerator using the accelerator tube that emits less secondary electrons, it is possible to reduce the size of the accelerator as a whole.

[0020]

According to the present invention, since it is possible to realize an acceleration tube with a high electric field while reducing the dark current extremely,
It is possible to increase the energy gain of the beam per unit length and reduce the scale of the entire accelerator.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an acceleration tube according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an essential part of an accelerating tube according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a linear accelerator to which the accelerating tube shown in FIGS. 1 and 2 is applied.

FIG. 4 is a configuration diagram of a circular accelerator to which the accelerating tube shown in FIGS. 1 and 2 is applied.

FIG. 5 is a vertical cross-sectional view of a main part of a conventional acceleration tube.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency power, 2 ... Waveguide, 3 ... Coupling hole, 4 ... Accelerating tube coupler, 5 ... Electric force line, 6 ... Field emission electron, 7 ... Secondary electron, 8 ... Charged particle beam, 9 ... Titanium , 20, 20a,
20b, 20c, 20d ... Accelerator tube, 21 ... Cylinder, 2
2 ... Disc, 22a ... Titanium.

Claims (10)

[Claims] 1. An accelerating tube for accelerating an incident charged particle beam by high-frequency electric power introduced therein and emitting the accelerating electron beam, wherein the secondary electron emission coefficient is made of a material smaller than "1". Accelerator tube. 2. An accelerating tube, comprising: a coupler for introducing a high frequency wave; and a cylinder connected to the coupler and having an interior defined by a plurality of ring-shaped disks, wherein the charged particles are accelerated by the high frequency wave. At least the corners inside the coupler and the inner peripheral edges of the two ring-shaped disks on the coupler side are made of a material having a secondary electron emission coefficient smaller than "1". tube. 3. An accelerating tube for accelerating an incident charged particle beam by high-frequency electric power introduced therein and emitting the accelerated charged particle beam, the electric field generated by the high-frequency electric power is concentrated on the inner wall surface to become a high electric field. An accelerating tube characterized by being manufactured with a material having a secondary electron emission coefficient smaller than "1". 4. In an accelerating tube for accelerating an incident charged particle beam by high-frequency power introduced therein and emitting the same, a portion of an inner wall surface where electrons generated inside due to field emission move and collide. An accelerating tube characterized by being manufactured from a material having a secondary electron emission coefficient smaller than "1". 5. The accelerating tube according to claim 1, wherein titanium or titanium alloy is used as a material having a secondary electron emission coefficient smaller than “1”. 6. The accelerating tube according to claim 1, wherein a material having a secondary electron emission coefficient smaller than “1” is diffusion-bonded to a required portion of the inner wall portion. 7. The accelerating tube according to claim 1, wherein a material having a secondary electron emission coefficient smaller than “1” is brazed or soldered to a required portion of the inner wall portion. 8. The accelerating tube according to claim 1, wherein a material having a secondary electron emission coefficient smaller than “1” is coated on a required portion of the inner wall portion. 9. A plurality of accelerating tubes according to any one of claims 1 to 8 are connected in series, and a focusing magnet provided at a connecting portion of each accelerating tube and one side of the accelerating tubes connected in series. , A klystron that supplies high-frequency waves to each accelerating tube, and a control command that causes charged particles to be emitted from the charged-particle gun and that high-frequency power synchronized by each klystron be supplied to each accelerating tube. And a control means for controlling the linear accelerator. 10. A circular accelerator for orbiting a charged particle beam, wherein the charged particle injection system of the circular accelerator is provided with the accelerating tube according to any one of claims 1 to 8. .