JP3011854B2 - Linear electron accelerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear electron accelerator, and more particularly to a linear electron accelerator having improved electron beam focusing.

[0002]

2. Description of the Related Art A linear electron accelerator is disclosed in U.S. Pat.
FIG. 5 shows an example of such a conventional linear electron accelerator.

Referring to FIG. 5, a cathode supporting tube 15 is provided with a cathode for emitting thermoelectrons. The thermoelectrons are extracted in the direction of the electron accelerating tube 14 by microwaves generated from the RF source 13 in the RF electron gun cavity 12.

FIG. 6 is an enlarged view of the vicinity of the tip of the cathode support tube 15 shown in FIG. In FIG. 6, a cathode supporting tube 15 is provided with a cathode 10 that emits thermoelectrons at its tip, and the cathode 10 is heated by a cathode heater 16. Heated cathode 1
The thermoelectrons are emitted from one surface 11 of 0. In front of the thermionic emission surface 11 of the cathode 10 is the above-mentioned RF electron gun cavity 12, which is also generated from the above-mentioned RF source 13 and guides the thermoelectrons 25 toward the accelerating tube 14. There is a microwave electric field 30. Thermoelectrons 25
Is caused by the electric field 30, thermionic emission surface 1 of the cathode 10
1 and is incident on the acceleration tube 14 from the RF electron gun and accelerated to high energy.

[0005]

However, in such a conventional linear electron accelerator, as shown in FIG. 6, an electric field 3 for extracting thermoelectrons 25 near the cathode 10 is required.
The distribution of 0s tends to be non-uniform. That is, the distribution of the electric field 30 does not become parallel to the thermionic emission surface 11. For this reason, since the thermoelectrons 25 do not move parallel to each other toward the accelerating tube 14 (FIG. 5) and the electron beam diverges, the beam performance such as the emittance of the electrons or the convergence of the electron beam deteriorates. was there.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a linear electron accelerator in which the distribution of an extracted electric field near the cathode is made uniform and the beam performance is improved.

[0007]

According to a first aspect of the present invention, there is provided a cathode having a thermoelectron emitting surface, wherein thermoelectrons emitted from the cathode are formed by microwaves. What is claimed is: 1. A linear electron accelerator comprising an RF electron gun which is drawn in the direction of an accelerating tube by an electric field, comprising: a metal surface surrounding the thermoelectron emission surface in substantially the same plane as the thermoelectron emission surface; It is characterized by including an electric field distribution adjusting means for making the distribution of the formed electric field uniform.

A second invention is characterized in that the cathode is directly heated by a carbon heater in contact with the end of the cathode across the end.

A third aspect of the present invention is characterized in that the electric field distribution adjusting means has a cylindrical shape. A fourth invention is characterized in that the electric field distribution adjusting means is an insulator cylinder having a metal film formed at one end.

A fifth invention is characterized in that the electric field distribution adjusting means is a metal cylinder whose thickness is increased only around the cathode.

[0011]

Therefore, according to the above configuration, since the periphery of the thermoelectron emission surface of the cathode is surrounded by the metal surface, the distribution of the electric field for extracting thermoelectrons becomes uniform, and the beam performance of the linear electron accelerator is improved. I do.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 shows a first embodiment of the present invention. The same members as those in the prior art shown in FIGS. 5 and 6 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1A is a sectional view showing the vicinity of the cathode 10 of the linear electron accelerator according to this embodiment, and FIG.
The cathode 10 forward, that is, the RF electron gun cavity 12
The figure seen from the direction is shown.

In FIG. 1A, the cathode support tube 15
The cathode 10 supported by the indirectly heated cathode heater 1
6 to emit thermoelectrons 25 from the thermoelectron emission surface 11. RF electron gun cavity 1 in front of thermionic emission surface 11
An electric field 30 for extracting thermoelectrons 25 in the direction of the accelerating tube 14 shown in FIG. 5 is formed in 2, whereby the thermoelectrons 25 emitted from the thermoelectron emitting surface 11 are guided to the accelerating tube 14. An electric field distribution adjusting cylinder 20 as electric field distribution adjusting means for uniformly adjusting the distribution of the electric field 30 is inserted between the outer periphery of the cathode support cylinder 15 and the inner wall 22 of the RF electron gun cavity 12. The metal surface 17 formed at the tip of the electric field distribution adjusting cylinder 20 is substantially flush with the thermionic emission surface 11. In the case of this embodiment, the electric field distribution adjusting cylinder 20
Is formed of a conductor.

The feature of the present embodiment is that FIG.
As shown in (b), the periphery of the thermionic emission surface 11 of the cathode 10 is surrounded by the metal surface 17.

With the above configuration, in this embodiment,
The distribution of the electric field 30 for extracting the thermoelectrons 25 formed in the RF electron gun cavity 12 becomes uniform on the thermoelectron emission surface 11 of the cathode 10. That is, as shown in FIG. 1A, the distribution of the electric field 30 is parallel to the thermionic emission surface 11. Therefore, the streamline of the thermoelectrons 25 emitted from the thermoelectron emission surface 11 does not diverge, and the electron beam becomes a streamline parallel to the acceleration tube 14 shown in FIG.

As described above, a linear electron accelerator having improved beam performance can be obtained.

Second Embodiment FIG. 2 shows a second embodiment of the present invention.

In the first embodiment, the cathode 1
Although 0 is indirectly heated by the indirectly heated cathode heater 16, in this embodiment, the cathode 10 is directly heated by the carbon heater 18.

As shown in FIG. 2A, the cathode 1
The other end of the 0 thermionic emission surface 11 is rectangular. The rectangular portion is sandwiched from above and below by a carbon heater 18, and the carbon heater 18 is sandwiched and fixed by a cathode support bar 19. FIG. 2B shows this as viewed from the thermoelectron emission surface 11 side. In FIG. 2B, the carbon heater 18
And the cathode support rod 19 are shown by broken lines because they are hidden behind the cathode 10.

In this embodiment, since no filament is used, the reliability can be improved without troubles such as filament breakage. Also, there is an effect that the number of parts can be reduced as compared with the case of the indirectly heated heater.

Third Embodiment FIG. 3 shows a third embodiment of the present invention. This embodiment also has a structure in which the cathode 10 is sandwiched from above and below by the carbon heater 18 as in the case of the second embodiment.

In this embodiment, the electric field distribution adjusting cylinder 20
Is formed of an insulator, and a metal surface 17 surrounding the periphery of the thermionic emission surface 11 is formed of a metal film deposited on the front end surface of the electric field distribution adjusting cylinder 20.

By using the electric field distribution adjusting cylinder 20 made of an insulator as described above, it is not necessary to perform an insulating process between the cathode support rod 19 and the inner wall 22 of the RF electron gun cavity 12, so that the manufacturing can be simplified. This has the effect of being easier.

The method of forming the metal film is not limited to vapor deposition, but may be a film formed by sputtering or the like.

Fourth Embodiment FIG. 4 shows a fourth embodiment of the present invention. This embodiment also has a structure in which the cathode 10 is sandwiched from above and below by the carbon heater 18 as in the case of the second embodiment.

In this embodiment, the electric field distribution adjusting cylinder 20
Is formed of a conductor, as shown in FIG. 4A, the thickness is increased only around the thermionic emission surface 11, and in other portions, the inner wall 22 of the RF electron gun cavity 12 is formed.
The structure is such that a hollow region is formed between the two.
Thus, there is no need to perform insulation between the inner wall 22 of the RF electron gun cavity 12 and the electric field distribution adjusting cylinder 20, and there is an effect that the manufacturing becomes easy.

[0029]

As described above, according to the present invention,
Since the periphery of the thermionic emission surface of the cathode was surrounded by a metal surface, in the RF electron gun cavity in front of the thermionic emission surface, the distribution of the electric field for extracting thermoelectrons was parallel to the thermionic emission surface, and the streamlines of thermionic electrons Is guided to the acceleration tube without diverging. As a result, a linear electron accelerator with improved beam performance is obtained.

[Brief description of the drawings]

FIG. 1A is a sectional view of a linear electron accelerator according to a first embodiment of the present invention, and FIG. 1B is a front view of a cathode.

FIG. 2A is a sectional view of a linear electron accelerator according to a second embodiment of the present invention, and FIG. 2B is a front view of a cathode.

FIG. 3A is a sectional view of a linear electron accelerator according to a third embodiment of the present invention, and FIG. 3B is a front view of a cathode.

FIG. 4A is a sectional view of a linear electron accelerator according to a fourth embodiment of the present invention, and FIG. 4B is a front view of a cathode.

FIG. 5 is an explanatory diagram showing a configuration of a conventional linear electron accelerator.

6 is an enlarged view of the vicinity of the tip of a cathode support cylinder of the linear electron accelerator shown in FIG. 5;

[Explanation of symbols]

Reference Signs List 10 cathode, 11 thermionic emission surface, 12 RF electron gun cavity, 16 cathode heater, 17 metal surface, 18
Carbon heater, 19 Cathode support rod, 20 Electric field distribution adjusting cylinder, 22 Inner wall of RF electron gun cavity, 25 Thermoelectrons, 30 Electric field.

Claims (5)

(57) [Claims] 1. A linear electron accelerator having an RF electron gun having a cathode having a thermionic emission surface and having a thermoelectron emitted from the cathode drawn toward an accelerating tube by an electric field formed by a microwave. A metal surface surrounding the thermoelectron emission surface in substantially the same plane as the thermoelectron emission surface, and an electric field distribution adjusting means for making the distribution of an electric field formed by the microwave uniform. Features a linear electron accelerator. 2. The linear electron accelerator according to claim 1, wherein said cathode is directly heated by a carbon heater sandwiching an end of said cathode and in contact with said cathode. 3. The linear electron accelerator according to claim 1, wherein said electric field distribution adjusting means has a cylindrical shape. 4. The linear electron accelerator according to claim 1, wherein said electric field distribution adjusting means is an insulator cylinder having a metal film formed at one end. . 5. A linear electron accelerator according to claim 1, wherein said electric field distribution adjusting means is a metal cylinder having a thickness only around said cathode. .