JPH01204399A - Electron accelerator - Google Patents

Abstract

PURPOSE:To make it possible to take out an electron beam of a large beam current, a long time width, a narrow kinetic momentum width, and a small emittance by injecting electrons from the inner diameter side of a vacuum vessel. CONSTITUTION:An electron gun 3 and a means 5 for generating magnetic field for circulation are provided, with the electron gun 3 being for injecting electrons to a vacuum vessel 2 from its inner diameter side and with the means 5 surrounding the vacuum vessel 2 and being for generating a magnetic field Bg which produces a constant magnetic field during a beam injection period, increases the intensity of the magnetic field in synchronism with the electron acceleration during the acceleration period, and circulates electrons in a stabilized manner by producing a constant magnetic field during the jet out period. Further, an acceleration magnetic field producing means 7 surrounding the circulation magnetic field generation means 5 and for producing a magnetic field Ba for inductively producing an electric field for accelerating electrons from the injection period to the jet out period, and a device 8 for taking out a beam from the outer diameter side of the vacuum vessel are provided. This arrangement makes it possible to obtain a large beam current, to make a kinetic momentum width narrow, to take out an electron beam of a small emittance, and to make the time width of the electron beam taken out longer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electron accelerator, and particularly to an electron accelerator whose orbital radius can be changed depending on the acceleration energy of electrons.

[Conventional technology]

Of the betatrons, which are devices that accelerate electrons using an induced electric field, a conventional electron accelerator similar to the present invention is shown in a cross-sectional view in the fourth column. In FIG. 4, electrons incident by an electron gun 6 from the outer diameter side into a vacuum vessel 2 formed in an annular shape around a central axis 1 are exposed to an orbiting magnetic field wound around an orbiting magnetic field yoke 4. Circulating magnetic field Bg (g
It can be stably circulated within the vacuum container 2 by the magnetic field. An accelerating @field yoke 6 provided outside the orbiting magnetic field yoke 4 and an accelerating magnetic field excitation coil 7 wound around the accelerating magnetic field yoke 6 apply acceleration to accelerate an object E to an electron. An accelerating magnetic field Ba (accelerating magnetic field Ba) is generated in the trap and accelerating magnetic field yoke 6 in order to generate it inductively in the direction of circular motion.
Genetic field). The electrons are accelerated by the accelerating electric field E, and when they reach the maximum energy, they are extracted from the vacuum vessel 2 by the beam extraction device 8.

Note that each yoke is used in combination with an excitation coil and its excitation power source to constitute an electromagnet.

The electrons orbit within the vacuum container 2, and this is due to the equilibrium state given by the following equation between the interlocking type P of the electrons and the interlinking orbiting magnetic field Bg.

P=eBgρ ([) where e is the charge of the electron, and ρ is the radius of curvature of its motion.

The electrons are accelerated by an accelerating electric field E induced by the time change of the magnetic flux in the plane of their orbital motion.

This is the area integral within the orbital plane.

In addition, radiationally, the stability of the betatron oscillation of the beam is established when the orbiting magnetic field Bg is given by the following equation.

Bg == B(, (r/R)-n
taJ, BQ is the magnetic field constant, n is 0 (n
(The value satisfies 1.

Equation (3) is mainly satisfied depending on how the structure of the magnetic pole surface of the circulating magnetic field yoke 4 is created. Therefore, in order to stably accelerate the beam, it is necessary to temporally change the orbiting magnetic field Bg and the accelerating magnetic field Ba so as to eliminate equations ill and (2). In order to create such a magnetic field, similar sinusoidal half-wave patterns are applied to the circulating magnetic field excitation coil 5 and the acceleration magnetic field excitation coil 7 with different offset values as shown in the graph of FIG. Pass current. Therefore, a KO half-wave power source is used as the power source. The trajectory of the beam from incidence to emission approximately follows an incident trajectory 11, an acceleration trajectory 12, and an exit trajectory 16 as shown in the plan view of FIG.

[Problem to be solved by the invention]

In conventional electron accelerators, (1) electrons are injected from the outer diameter side of the vacuum vessel, making it impossible to orbit and accelerate electron beams with a wide range of momentum; (2) excitation current for orbiting and excitation current for acceleration; (3) The time width of the emitted electron beam is short, and (4) the emittance of the electron beam is large. Therefore, there was a problem in that an electron beam with a narrow momentum could not be extracted at the time of extraction.

This invention was made to solve the above-mentioned problems; (1) an electron beam with a wide range of momentum can be accelerated through one incident revolution, and therefore a large beam current can be obtained;
(2) The time width of the extracted electron beam is long (, (3)
The objective is to obtain an electron accelerator that can extract an electron beam with a narrow momentum width and (4) an electron beam with a small emittance.

[Means to solve the problem]

The electron accelerator according to the present invention includes: a vacuum vessel having a spatial region for orbiting and accelerating an incident electron beam with a wide range of momentum; an electron gun for injecting the electrons into the vacuum vessel from the inner diameter side; surrounding the container, creating a constant magnetic field during the injection period of the beam, increasing the strength of the magnetic field in synchronization with the acceleration of the electrons during the acceleration period, and creating a constant magnetic field again during the exit period, thereby A circulating magnetic field generating means for generating a magnetic field that stably circulates the electrons, and a magnetic field that surrounds the circulating magnetic field generating means and inductively generates an electric field that accelerates the electrons from the injection period to the exit period. The apparatus is provided with an accelerating magnetic field generating means and a device for extracting the beam from the outer diameter side of the vacuum vessel.

[For production]

By injecting electrons from the inner diameter side of the vacuum vessel, the equilibrium trajectory of the incident energy beam can be set at the exit position of the electron gun, resulting in the betatron amplitude of the electron beam becoming smaller (in other words, the secondary tutance is smaller). Since the orbit is outside the equilibrium orbit, the transition from the equilibrium orbit to the accelerating orbit is easy□.

〔Example〕

An embodiment of the invention is shown in cross-section in FIG.

The components in FIG. 1 are the same as those in FIG. 4, and their symbols are also the same. Electrons are continuously injected into the vacuum container 2 from the inner diameter side by the electron gun 6. As can be seen from the graph in Figure 2, during the injection period, the orbiting magnetic field Bg is held constant so that the beam equilibrium trajectory of the incident energy is at the electron gun exit position, and the accelerating magnetic field Bg is kept constant to accelerate the electron beam. Apply magnetism J4Ba. As the electron beam accelerates, the electron beam moves from the inner circumferential side to the outer circumferential side within the vacuum vessel 2 along a stable equilibrium orbit in a spiral shape around the central axis 10 (see Fig. 6).The electron beam is continuously incident. The incidence of the electron beam is stopped just before the first electron beam reaches the extraction device 8. During this time, the vacuum vessel 2 is kept horizontal in order to receive the electron beam with a wide range of momentum into the vacuum vessel 2. It has a structure with a cross section with a large gap in the direction.In the next acceleration period, the orbiting magnetic field Bg
When is increased in synchronization with the increase in the accelerating magnetic field Ba, the electron beam is accelerated while orbiting along a stable orbit corresponding to each momentum. When the outermost electrons reach a predetermined energy, the circulating magnetic field Bg stops increasing and is held at a constant value. When the accelerating magnetic field Ba continues to increase during the subsequent emission period, the electron beam continues to be further accelerated, so the electron beam moves toward the outer circumference while rotating and jumps into the extraction device 8 one after another. This extraction device 8 includes an electrostatic inflector, a septum electromagnet,
The electron beam is guided from the orbit to the exit orbit by an extraction device 8 composed of a Kitzker electromagnet or the like. Figure 2 shows the orbiting excitation current 1g and the acceleration excitation current 1a which create the orbiting magnetic field Eg and the accelerating magnetic field Ba, respectively.
An example is shown. Furthermore, although FIG. 6 shows the trajectory of the electron beam from the electron gun 6 entering the vacuum vessel 2 to its emission, there is no trajectory of the electron beam unlike in the conventional device, and the incident electrons are immediately accelerated. Then, it enters the turning orbit 14& and performs a turning movement.

Then, during the acceleration period, it enters the orbit 12 and performs a circular motion. The position of this orbit 12 in the radial direction is on the outer side of the orbit of the electron beam incident at the beginning of the injection period. Furthermore, during the emission period, the electron beam also makes a circular movement and flies into the extraction device 8 and is guided to the emission trajectory 13.

〔Effect of the invention〕

As described above in detail, the present invention provides a vacuum container having a spatial region in which an incident electron beam is orbited and accelerated by a wide range of motion lid, and an electron beam which is incident on the vacuum container from the inner diameter side thereof. A gun and the vacuum vessel are surrounded by a constant magnetic field during the injection period of the beam, the strength of the magnetic field increases in synchronization with the acceleration of the electrons during the acceleration period, and a constant magnetic field again during the exit period. and an orbiting magnetic field generating means for generating a magnetic field for stably orbiting the electrons, and an electric field that surrounds the orbiting magnetic field generating means and accelerating the electrons from the input period to the exit period in an inductive manner. Since it is equipped with an accelerating magnetic field generating means that generates a magnetic field for generating a magnetic field, and a device that extracts the beam from the outer diameter side of the vacuum vessel, a large beam current can be obtained and the momentum width is narrow (and the emittance is also small). Take out a small electron beam.

Since the time width of the extracted electron beam is long (and the W and field for the operation of the rotating cutting edge can be controlled separately, the beam control can be easily performed).

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a graph showing the time change of the current used in the embodiment of FIG. 1, and FIG. 6 is a beam diagram in the embodiment of FIG. 1. Figure 4 is a plan view showing the orbit, Figure 4 is a sectional view showing a conventional electron accelerator, Figure 5 is a cross-sectional view showing the conventional electron accelerator.
The figure is a graph showing the temporal change in current used in a conventional electron accelerator, and FIG. 6 is a plan view showing the beam trajectory of the conventional electron accelerator. In the figure, (2) is a container, (6J is an electron gun, (4
) is an orbiting magnetic field yoke, (5) is an orbiting magnetic field excitation coil, (6) is an acceleration magnetic field yoke, (7) is an acceleration magnetic field excitation coil, and (8) is a beam extraction device. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] a vacuum vessel having a spatial region for orbiting and accelerating an incident electron beam with a wide range of momentum; an electron gun for injecting the electrons into the vacuum vessel from the inner diameter side; A magnetic field that creates a constant magnetic field during the period, increases the strength of the magnetic field in synchronization with the acceleration of the electrons during the acceleration period, and creates a constant magnetic field again during the emission period, thereby making the electrons orbit stably. an orbiting magnetic field generating means for generating, and surrounding this orbiting magnetic field generating means,
comprising an accelerating magnetic field generating means for inductively generating an electric field for accelerating the electrons from the injection period to the exit period, and a device for extracting the beam from the outer diameter side of the vacuum container. An electron accelerator featuring