JP2687310B2 - Generation method of charged particles in tandem electrostatic 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 tandem type electrostatic accelerator capable of generating various molecular ions composed of a plurality of atoms, crystallite ions or high energy neutral particles.

The tandem electrostatic accelerator is a charged particle accelerator which has a DC high voltage terminal section of several 100 kV to 20 MV in the center of acceleration, in which both the entrance and the exit of the accelerator are grounded. It is called a "tandem type" because it accelerates in two steps, from the voltage terminal section to the high voltage terminal section to the exit.

In the case of the one-step acceleration (single type), the source of the charged particles (ion source) is mounted in the high voltage portion, whereas in the tandem type the ion source can be grounded, so that light ions and heavy ions are It has features such as enabling acceleration of charged particles with a wide variety of variations, starting from molecular ions composed of multiple atoms to crystallite ions.

Conventionally, in the field of nuclear physics, in order to obtain high-energy charged particles as a means for nuclear structure analysis, development of a higher voltage electrostatic accelerator has been promoted, and a large accelerator has been constructed. Then, ion implantation in semiconductor materials, ion beam processing for steel modification, ion beam analysis of hydrogen in materials that are usually difficult to detect, ion beam analysis for material composition and structural analysis, structural materials and biological cells In a wide range of materials science such as ion beam irradiation for investigating irradiation damage, tracer analysis in vivo, isotope separation for dating, biology, medical science or archeology, rather than several 100 kV to 3 MV A relatively small tandem type electrostatic accelerator is widely used.

In the tandem type accelerator, it is necessary to invert the charge polarity of the charged particles at the high voltage terminal portion, but conventionally, from the easiness of polarity conversion, a negative charge is usually provided from the ion source to the high voltage terminal portion, and a high voltage terminal portion. Since then, we have been accelerating the charged particles that carry positive charges.

In the conventional tandem-type electrostatic accelerator, the polarity of the charge of the charged particles in the high voltage terminal is reversed, and the negative charge is made positive by utilizing the electron loss generated when the fast charged particles pass through the substance. Converting into electric charge has been done.

For example, in a large tandem type electrostatic accelerator, as shown in FIG. 2, a negative ion accelerating tube 3 and a positive ion accelerating tube 4 are connected, and an endless belt 15 having a plurality of carbon fibers 14 mounted on a high voltage terminal section 5 is provided. The endless belt 15 is rotated to position one of the carbon thin films 14 so as to block the beam axis 8 of charged particles incident from the charged particle generator 7, and the negative ion accelerating tube 3 provides high energy. The charged particles having the negative charge accelerated up to are converted into multicharged positively charged particles by passing through the carbon thin film 14, and the positive ion accelerator accelerates the converted positively charged particles to higher energy. , Which efficiently generates high-energy charged particles.

On the other hand, in a relatively small tandem type electrostatic accelerator of 3 MV or less, the mass permeability of the charged particles accelerated in the negative ion accelerating tube portion is low, and therefore, as shown in FIG. A charge conversion gas supply unit 17 having a flow rate adjusting valve 16 is provided in the high-pressure gas tank 2, and the flow rate adjusting valve 16 is opened to supply gas to the high-voltage terminal unit 5 where it collides with negatively charged particles. By doing so, charge conversion is performed.

In the method of performing charge conversion of charged particles by collision of the gas and charged particles, the required positive charge valence can be obtained by adjusting the pressure of the gas according to the type and speed of the charged particles. Have advantages.

[0010]

However, in any of the above-described thin film permeation or gas collision methods, when the thin film permeation or gas collision is performed for charge conversion, the charged particles are separated into a plurality of molecules such as molecular ions and crystallites. , The constituent atoms individually cause electron loss and ionize,
Molecules and crysters are dissociated by mutual electrostatic repulsion.

That is, in order to ionize a molecule or a crystal without dissociating it, it is necessary to accurately control the number of electrons stripped from one charged particle composed of a plurality of atoms. It is not possible to control the number of electrons stripped from these charged particles by adjusting the film thickness or gas pressure through which the particles permeate. Therefore, charged particles composed of multiple atoms, such as molecular ions and crystallite ions, cannot pass through the carbon thin film. There is a major drawback that conventional tandem electrostatic accelerators that perform charge conversion by gas collisions cannot be accelerated.

Conventionally, in a relatively small tandem type electrostatic accelerator which performs charge conversion by gas collision, the introduction of gas into the high-voltage terminal portion 5 causes a decrease in the degree of vacuum in the accelerating tube, and the residual gas in the accelerating tube is further reduced. Electrons are emitted by collision with a charged particle beam, and the electrons repeatedly collide with the accelerating tube wall to multiply in an avalanche manner, causing an unstable state of high voltage, which in turn shortens the life of the accelerating tube. Therefore, lowering the degree of vacuum in the acceleration tube is a serious problem.

A tandem type electrostatic accelerator having a high-voltage terminal unit equipped with a vacuum exhaust device has been conventionally used in order to reduce the decrease in the degree of vacuum in the acceleration tube, but this has a structure of the high-voltage terminal unit. This results in complications.

Further, in the charge conversion by introducing gas, it is impossible to directly adjust the gas flow rate from the outside of the insulating high-pressure gas tank because the insulation is damaged, and therefore the insulating high-pressure gas tank 2 is provided. There is an inconvenience that the gas flow rate adjusting valve 16 has to be remotely controlled.

On the other hand, in the charge conversion by the carbon thin film, the carbon thin film is damaged when it is used for a long time, and the life of one sheet is usually several hours to several days. Therefore, the endless belt is used in the tandem electrostatic accelerator as described above. Although a plurality of carbon thin films 14 are mounted on the 15, the carbon thin film still needs to be replenished every few months, and there is the inconvenience that a large insulating gas tank must be opened and closed each time.

[0016]

In order to solve the above problems, in the present invention, a charged particle composed of a plurality of atoms and having an optically strong resonance transition is used as an accelerator for charged particles having different polarities. Is entered from the entrance of the tandem type electrostatic accelerator connected with the high voltage terminal part, and goes straight inside the device, while the wavelength of light caused by the Doppler effect relative to the charged particles passes through the high voltage terminal part. A tandem electrostatic accelerator characterized in that a laser beam whose wavelength is adjusted so as to match the resonance transition of charged particles is incident along the beam axis of the charged particles, and the polarity thereof is neutralized or inverted to accelerate the charged particles. The method of generating charged particles in is proposed.

The laser light used in the present invention is a light having a strong directivity that can be wavelength-variable and whose intensity can be adjusted, and the laser light is emitted from outside the accelerator.

When a charged particle having a negative charge has an optically strong resonance transition, a laser beam whose wavelength is adjusted by utilizing the Doppler effect as in the present invention is made incident along the beam axis of the charged particle. As a result, the charge polarity of the charged particles can be converted at the high voltage terminal portion.

That is, since the wavelength of light seen from the moving charged particles changes depending on the velocity of the charged particles due to the Doppler effect, the wavelength of light seen from the charge current element passing through the high-voltage terminal is By adjusting the wavelength of the incident light so that it exactly matches the resonance transition of the charged particle, the charge polarity of the charged particle can be converted only at the high voltage terminal section.

[0020]

According to the present invention, negatively charged particles accelerated by a negative ion accelerating tube are obtained by adjusting the wavelength and intensity of light such as laser light and making it incident on the high voltage terminal of a tandem electrostatic accelerator. A predetermined number of electrons can be stripped off, and the stripped charged particles of the electrons can be accelerated by the positive ion accelerator tube.

Therefore, according to the present invention, since the number of electrons stripped from one charged particle can be accurately controlled by utilizing the light whose wavelength is variable and whose intensity can be adjusted, molecular ions, crystallite ions, etc. It is possible to accelerate to high energy without dissociating charged particles composed of a plurality of atoms.

Further, according to the present invention, since the number of electrons stripped from the charged particles can be controlled to a neutral state in which the charge of the entire particles is zero, high-energy neutral particles can be generated.

Further, according to the present invention, since only light is introduced into the accelerating tube at the time of charge polarity conversion of the charged particles, the vacuum degree in the accelerating tube is not lowered, and thus an unstable state of high voltage is caused. Without shortening the life of the accelerator
The charged particles can be stably accelerated to high energy.

Further, according to the present invention, since light having a strong directivity is used for charge conversion, it is possible to change the charge polarity of the charged particles by directly operating from the outside of the insulating high pressure gas tank without causing insulation damage. .

[0025]

The present invention will be described in detail below with reference to the illustrated embodiments. 1 is a tandem electrostatic accelerator housed in an insulating high-pressure gas tank 2 showing an embodiment of the present invention. The tandem electrostatic accelerator 1 is provided with a negative ion accelerator 3 and a positive ion accelerator 4, and a negative ion accelerator. 3 and the positive ion accelerator 4 are connected by a high voltage terminal unit 5.

A high voltage generator 6 is provided in the insulating high pressure tank 2, and the high voltage generator 6 has a high voltage terminal 5 and an inlet 3a of the negative ion accelerator tube 3 and an outlet 4a of the positive ion accelerator tube 4. And the inlet and outlet of the insulating high-pressure gas tank 2 are both grounded.

This embodiment shows an embodiment in which a laser beam having a short wavelength is incident along the beam axis 8 when charged particles having a negative charge have an optically strong resonance transition. In the example, an inlet tube 10 curved along the beam axis 8 is provided at the inlet 3a of the negative ion accelerator tube 3,
A charged particle generator 7 is provided at the inlet of 10, while an outlet 4a of the positive ion accelerating tube 4 is provided with a lead-out tube 11 curved along the beam axis 8.
And the laser generator 9 is provided on the extension of the beam axis 8.

In this case, the wavelength of the light seen from the charged particles passing through the high-voltage terminal section 5 from the laser generator 9 is adjusted to a short wavelength so that it coincides with the resonance transition of the elementary charged particles. The laser is incident along the beam axis 8.

As a result, in the high-voltage terminal section 5, the wavelength of the laser beam oscillated from the laser generator 9 coincides with the resonance transition of the charged particles, and the ionization of electrons occurs, so that the polarity of the charged particles is changed. The charged particles whose polarity has been changed are accelerated by the positive ion accelerating tube 4 and emitted through the outlet tube 11.

[0030]

In summary, according to the present invention, it is possible to accelerate various molecular ions and crystallite ions composed of a plurality of atoms, which are not possible with the conventional tandem electrostatic accelerator.

Further, according to the tandem type electrostatic accelerator of the present invention, it is possible to generate a high energy neutral particle beam which has been difficult in the past.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a tandem electrostatic accelerator showing an embodiment of the present invention.

FIG. 2 is a schematic diagram of a conventional tandem electrostatic accelerator that utilizes charge conversion by thin film transmission.

FIG. 3 is a schematic diagram of a conventional tandem electrostatic accelerator that utilizes charge conversion by gas collision.

[Explanation of symbols]

 1 Tandem Electrostatic Accelerator 2 High Pressure Gas Tank for Insulation 3 Negative Ion Accelerator 4 Positive Ion Accelerator 5 High Voltage Terminal 6 High Voltage Generator 7 Charged Particle Generator 8 Beam Axis 9 Laser Generator 10 Introducing Tube 11 Outlet Tube 14 Carbon thin film 15 Endless belt 16 Flow control valve 17 Charge conversion gas supply unit

Claims (1)

(57) [Claims] 1. A charged particle composed of a plurality of atoms and having an optically strong resonance transition is introduced from an entrance of a tandem electrostatic accelerator in which accelerating parts of charged particles having different polarities are connected by a high voltage terminal part. while put, Ru is straight in the converter, load
Of light due to the relative Doppler effect on charged particles
Of the charged particles as the wavelength passes through the high voltage terminal
Laser light whose wavelength is adjusted to match the resonance transition
A method for generating charged particles in a tandem electrostatic accelerator, characterized in that the charged particles are made incident along the beam axis and the polarity thereof is neutralized or inverted to accelerate the particles.