JPH0668984A - Tandem type electrostatic accelerator - Google Patents

Abstract

PURPOSE:To accelerate various molecular ions consisting of a plurality of atoms by utilizing ionization by means of light to convert polarities of charged particles at a high voltage terminal part. CONSTITUTION:A negative ion acceleration tube 3 and a positive ion acceleration tube 4 are provided on a tandem type electrostatic accelerator 1, and the acceleration tubes 3, 4 are connected together at a high voltage terminal part 5. A high voltage generation part 6 is provided in a high voltage gas tank 2 for insulation, and the generation part 6 is connected to the terminal part 5, an inlet 3a of the acceleration tube 3, and to an outlet 4a of the acceleration tube 4. The charged particles from a particle generator 7 provided on the extended part of the inlet 3a of the acceleration tube 3, outside of the tank 2, are brought into the acceleration tube 3 along a beam axis 8, and are accelerated. After the laser beam from a laser generator is utilized and the polarities are converted at the terminal part 5, the laser beam is accelerated at the acceleration tube 4, and is emitted from the outlet 4a. The wavelength of the laser beam started by the generator 9 matches with a resonance transition of the charged particles, and the polarities are converted, and molecular ions consisting of a plurality of atoms can thus be accelerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tandem electrostatic accelerator capable of generating various molecular ions composed of a plurality of atoms, crystallite ions or high-energy neutral particles.

[0002]

2. Description of the Related Art A tandem electrostatic accelerator is a charged particle accelerator that has a DC high voltage terminal unit of several 100 kV to 20 MV in the center of acceleration, with the entrance and exit of the accelerator both grounded. It is called a "tandem type" because it accelerates in two stages from the high voltage terminal section to the high voltage terminal section and 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 acceleration of charged particles with a wide variety of variations, starting from molecular ions composed of multiple atoms to cluster 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 is 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 radiation damage, tracer analysis in vivo, isotope separation for dating, biology, medical science or archeology, it is rather 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 are respectively charged with 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 charge has been done.

For example, in a large tandem type electrostatic accelerator, as shown in FIG. 3, a plurality of carbon thin films are formed in a high voltage terminal section 5 connecting a negative ion accelerator tube 3 and a positive ion accelerator tube 4.
An endless belt 15 carrying 14 is provided, and the endless belt 15 is rotated to position one of the carbon thin films 14 so as to block the beam axis 8 of the charged particles incident from the charged particle generator 7.
The charged particles having a negative charge accelerated to a high energy by the negative ion accelerator tube 3 are converted into polyvalent positively charged particles by passing through the carbon thin film 14. In the positive ion accelerator, the converted positively charged particles are converted. Is further accelerated to high energy to efficiently generate 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 charged particles having a negative charge. By doing so, charge conversion is performed.

In this method of performing charge conversion of charged particles by collision between the gas and charged particles, the required positive charge valence can be obtained by adjusting the gas pressure 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, charged particles are not separated into a plurality of molecules such as molecular ions or clusters. In the case of being composed of atoms, the constituent atoms individually cause electron loss and ionize,
Molecules and clusters are dissociated by mutual electrostatic repulsion.

That is, in order to ionize molecules or clusters without dissociating them, it is necessary to accurately control the number of electrons stripped from one charged particle composed of a plurality of atoms. When adjusting the film thickness and gas pressure to be transmitted,
Since it is not possible to control the number of electrons stripped from such charged particles, therefore, charged particles composed of multiple atoms such as molecular ions and cluster ions cannot be controlled by the conventional tandem-type static charge conversion that involves carbon thin film permeation or gas collision. There is a major drawback in that it cannot be accelerated by an electric accelerator.

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 high-pressure gas tank must be opened and closed each time.

[0016]

In order to solve the above problems, the present invention utilizes the ionization effect by light as a means for neutralizing or reversing the polarity of charged particles in the high voltage terminal of a tandem electrostatic accelerator. We propose a tandem type electrostatic accelerator.

As the light exhibiting the above-mentioned ionizing action which can be used in the present invention, the intensity can be adjusted by the wavelength variable generated from the excimer laser, the dye laser and the Nd: YAG laser connected to the continuous wavelength variable oscillator, and the directivity is strong. Laser light can be used.

These laser beams are emitted from a laser provided outside the insulating high-pressure gas tank in which the accelerator is housed, and pass through a high voltage through an optical window provided in each of the insulating high-pressure gas tank and the high-voltage terminal section. The light enters the terminal portion, where the electrons are stripped from the charged particles having a negative charge by the photoionization action to be in a neutral or positive charge state.

When the charged particles are composed of a plurality of atoms, the number of electrons to be stripped is controlled by adjusting the wavelength of light and the irradiation intensity so as not to dissociate the charged particles.

On the other hand, 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 is incident along the beam axis of the charged particle. The charge polarity of charged particles can be changed at the high voltage terminal.

That is, since the wavelength of the light seen by the moving charged particles changes depending on the velocity of the charged particles due to the Doppler effect, the wavelength of the light seen by the charged particles passing through the high voltage terminal is The wavelength of the incident light is adjusted so as to exactly match the resonance transition of the charged particle, and the charge polarity of the charged particle can be converted only at the high voltage terminal section.

[0022]

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 more predetermined number of electrons can be stripped, and the charged particles from which the electrons have been stripped can be accelerated by the positive ion accelerator tube.

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

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 degree of vacuum 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. .

[0027]

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 tube 3 and a positive ion accelerator tube 4, The ion accelerator tube 3 and the positive ion accelerator tube 4 are connected by a high voltage terminal unit 5.

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

On the other hand, outside the insulating high-pressure gas tank 2, a charged particle generator 7 is provided on the extension of the inlet 3a of the negative ion accelerator tube 3.
The charged particle from the charged particle generator 7 is provided with a beam axis 8
Along with the negative ion acceleration tube 3, and is accelerated here, after the polarity is changed in the high-voltage terminal unit 5, is accelerated by the positive ion acceleration tube 4, the exit 4a of the positive ion acceleration tube 4 as high-energy particles It is configured to be released more.

A laser generator 9 such as an Nd: YAG laser connected to an excimer laser or an optical parametric oscillator is provided outside the insulating high-pressure gas tank 2, and the insulating high-pressure gas tank 2 further includes an optical window 10 and an optical window 10. The high voltage terminal section 5 is provided with an optical window 11, and the laser from the laser generator 9 is irradiated through the optical windows 10 and 11 orthogonally to the beam axis 8 of the high voltage terminal section 5.

In the above structure, Na _n ⁻ , Mg _n ⁻ , (SF ₆ ) _n ⁻ , (n = 2-1) generated by the charged particle generator 7.
Charged particles having a negative charge composed of a plurality of atoms such as 0) are accelerated in the negative ion accelerating tube 3 and pass through the high voltage terminal section 5.

On the other hand, from the laser generator 9 from 200 nm
Light with a wavelength of about 2 μm (light intensity of 10 to 100 μJ / cm ² pulse) is generated, and this light is orthogonally incident on the ion beam axis 8 of the high voltage terminal unit 5 through the optical windows 10 and 11. To be done.

As a result, an appropriate number of electron valences are stripped off from the above-mentioned charged particles having a negative charge composed of a plurality of atoms,
The charged particles having a positive charge composed of a plurality of atoms are accelerated by the positive ion accelerator 4 and emitted from the outlet 4a of the acceleration tube 4. In this example, a charged particle composed of a plurality of atoms could be accelerated with an efficiency of 10% or more.

FIG. 2 shows an embodiment in which a short wavelength laser beam is incident along the beam axis 8 when charged particles having a negative charge have an optically strong resonance transition. In this embodiment, an inlet tube 12 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 the inlet tube 12, and an outlet of the positive ion accelerator tube 4 is provided. A guide tube 13 curved along the beam axis 8 is provided at 4a, and a 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 particle passing through the high-voltage terminal section 5 from the laser generator 9 is a short wavelength whose wavelength is adjusted so that it coincides with the resonance transition of the charged particle. 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 polarity-converted charged particles are accelerated by the positive ion accelerating tube 4 and are discharged through the outlet tube 13.

[0037]

In summary, according to the present invention, it is possible to accelerate various molecular ions and cluster 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 drawings]

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

FIG. 2 is a schematic view of a tandem electrostatic accelerator showing another embodiment of the present invention.

FIG. 3 is a schematic diagram of a conventional tandem electrostatic accelerator that utilizes charge conversion by thin film transmission.

FIG. 4 is a schematic view 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 10,11 Optical window 12 Introduction Pipe 13 Outlet pipe 14 Carbon thin film 15 Endless belt 16 Flow rate control valve 17 Charge conversion gas supply unit

Claims (3)

[Claims] 1. A tandem electrostatic accelerator in which accelerating parts for charged particles having different polarities are connected to each other by a high-voltage terminal part and the polarities of the charged particles are neutralized or inverted at the high-voltage terminal part for acceleration. A tandem electrostatic accelerator characterized by utilizing an ionization effect by light as means for neutralizing or reversing the polarity of charged particles in a high voltage terminal section. 2. The laser light is composed of a laser light whose intensity can be adjusted by variable wavelength generated from an excimer laser, a dye laser and an Nd: YAG laser connected to a continuous wavelength tunable oscillator, and which has a strong directivity. The tandem-type electrostatic accelerator according to claim 1, wherein is irradiated from outside the accelerator and is incident on the high-voltage terminal portion through the optical window of the high-voltage terminal portion. 3. For charged particles having an optically strong resonance transition, laser light is incident along the beam axis of the charged particles, and only charged particles passing through the high voltage terminal portion undergo resonance transition due to the Doppler effect. The tandem electrostatic accelerator according to claim 1, wherein