JPH06187936A - Negative ion source - Google Patents

Abstract

(57) Abstract: effectively negative ionization large amounts of H generated in the ion source container 11. The purpose negative ionization process, have been H ^-
Provided is a volume generation type negative ion source in which the production amount of A magnetic filter is formed between the electron source 2 and the extraction port 1c so that the inside of the ion source container 1 is filled with a positive ionization region A
And the negative ionization region B are magnetically divided, and the rare gas Rydberg atom Rg ^** is present in the negative ionization region B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative ion source installed before a tandem type electrostatic accelerator, for example.

[0002]

2. Description of the Related Art When obtaining a positive ion beam of H ⁺ of about 1 MeV with a relatively small device, a tandem electrostatic accelerator is often used.

In the tandem type electrostatic accelerator, it is necessary to generate a negative ion (H ⁻ ) beam in the preceding stage. As an ion source for generating this negative ion, H ₂ to H ₂ ⁺ in the ion source container is used. to generate vibrations excited hydrogen molecules H ₂ ^*, further dissociative electron attachment reaction by slow electron ^{_{(H 2 * + e → H}} 2 - → H - + H) method utilizing so-called volume-generated negative There is an ion source (Phys. Rev. Lett. 42 (1
979) 1538).

In this volume generation type negative ion source, a region having a large proportion of low-speed electrons is formed in the ion source container by using a magnetic filter device, and the amount of H ⁻ produced by the above-mentioned electron attachment reaction is increased. The method of increasing may be adopted.

[0005]

By the way, according to the volume generation type negative ion source, since the hydrogen pressure in the ion source container is relatively high, a large amount of H ₃ ⁺ is produced. Here, H ₃ ⁺ generated in the ion source container produces H by collision with the container wall, and H ₂ ⁺ also produces H in the same manner, but in the conventional ion source, it does so. The structure is not such that H can be used.

The present invention has been made in view of such circumstances, and an object thereof is to effectively negatively ionize H produced in a large amount in the ion source container in the negative ionization process. It is to provide a volume generation type negative ion source in which the production amount of H ⁻ is further increased.

[0007]

A structure for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. According to the present invention, neutralizing particles (H ₂ ) to be ionized are provided inside. An ion source container 1 to be introduced, and an electron source (for electron emission) which is arranged in the container 1 and emits high-speed electrons with energy (up to 100 eV) capable of positively ionizing neutral particles using the container wall as an anode. An ion configured to extract negative ions generated by a reaction originating from positive ionization of neutral particles in the ion source container 1 through the extraction port 1c to the outside of the container. In the source, between the outlet 1c and the electron source 2,
A magnet 8 that forms a magnetic filter that reflects only high-speed electrons from the electron source 2 and magnetically divides the ion source container 1 into two regions, and two regions A that are divided by the magnetic filter. In the region B on the side of the outlet 1c of B, means (for example, rare gas Rg supply source 9, grids 4 to 6 and electron generating filament 7) for allowing the rare gas Ridberg atoms Rg ^** to exist is provided. Characterized by:

[0008]

[Operation] First, as a means for converting a large amount of H produced in the ion source container into negative ions in the process of producing negative ions, it is conceivable to use the impact of ultra-slow electrons (to several tens of meV). An electron source that generates such ultra-slow electrons is difficult to manufacture and practically impossible to realize.

Therefore, in the present invention, a rare gas Rydberg atom is generated and made to exist in the region B, and this atom and H existing in the region B due to the magnetic filter effect are caused to collide with each other. by utilizing electron transfer reaction, the H H ^- converted into.

That is, the Lidberg atom is one of the outermost shell electrons excited in the Lidberg orbital (orbital with main quantum number> 20), and the energy of the electron is about several tens of meV. When an atom collides with another atom, if the electron affinity of the other party is positive, the electron transfer occurs very efficiently and the other atom is negatively ionized. effectively H a large amount of H that are generated in the 1 ^- to convert.

[0011]

1 is a block diagram of an embodiment of the present invention. The ion source container 1 has a stepped cylindrical hermetically sealed structure in which a small diameter portion 1a forming a volume generating chamber and a large diameter portion 1b are integrally formed at the front end thereof, and the front end of the large diameter portion 1b. An extraction port 1c for emitting negative ions is formed in the center of the face wall 11b. In addition, a gas introduction port 12a is provided in the rear end wall 11a of the small diameter portion 1a, and H ₂ from a hydrogen gas supply source (not shown) can be introduced into the container 1 through this port 12a. it can.

Inside the ion source container 1, a filament 2 is arranged in a state of being insulated from the container 1 at a central position of a rear end wall 11a of the small diameter portion 1a. The filament 2 functions as an electron source that emits high-speed electrons (-100 eV) using the ion source container 1 as an anode. Also,
The ion source container 1 is provided with a cylindrical magnet 3 that surrounds a side outer peripheral surface of the small diameter portion 1a. The magnet 3 generates a cusp magnetic field for efficiently confining the plasma generated in the container 1 in the container.

In the large diameter portion 1b of the ion source container 1, three grids 4, 5 and 6 are provided.
The grids 4, 5 and 6 are concentric cylinders with the cylindrical axis of the ion source container 1 as the center, and are arranged at predetermined intervals and insulated from each other. Further, the entire grids 4, 5, 6 are supported by the front end wall 11b of the ion source container 1 while being insulated from the wall 11b.

Further, in the large-diameter portion 1b of the container 1, a ring-shaped filament 7 for electron generation surrounding the lateral periphery of the outermost grid 6 is arranged in a state insulated from the container 1. Has been done. A rare gas introduction port 12b is provided in the wall body at the diametrical end position of the large diameter portion 1b, and the rare gas Rg from the gas supply source 9 is supplied through the port 12b to the large diameter portion of the container. It can be injected into the inside of 1b.

The ion source container 1 has a small diameter portion 1a.
A ring-shaped magnet 8 is provided on the periphery of the corner of the stepped portion of the large diameter portion 1b. The magnet 8 forms a magnetic filter that magnetically divides the inside of the ion source container 1 into a region A and a region B (the inner region of the grid 4 at the innermost circumference), and its magnetic filter effect. As a result, the fast electrons emitted from the filament 2 are reflected and do not reach the region B, but other neutral particles and ions penetrate from the region A into the region B.

In the above structure, a voltage of an individual value is applied to each filament 2, 7 and each grid 4-5 by a power source (not shown). Next, the operation of the embodiment of the present invention will be described.

First, the H ₂ introduced into the ion source container 1 is ionized into H ₂ ^{+ in the} region A by the impact of the high-speed electrons emitted from the filament 2, and the unreacted H _{2 is} further generated.
It becomes H ₂ ^* while colliding with etc. This H ₂ ^* also exists in the area B after passing through the magnetic filter of the magnet 8.

On the other hand, the grids 4, 5 and 6 have a voltage G4V = -30V, G with respect to the ion source container 1, respectively.
When 5V = −150V and G6V = −50V are applied, and the filaments 7 outside the grids are also applied with the voltage F7V = −100V applied to the ion source container 1, the filaments 7 are removed from the container. Electrons e (up to 30 eV) are emitted toward the wall of No. 1, and the noble gas R injected through the inlet 12b by the impact of the electrons e.
g is excited to be ionized (Rg ⁺ ) or in a lidberg state (Rg ^** ). Here, the electron e is reflected by the intermediate grid 5 and the ion (Rg ⁺ ) is reflected by the innermost grid 4, so that only the Ridberg atom Rg ^** can exist in the region B. Become.

As a result of the above, in the region B, H ^{− is} caused by both the reaction of the slow electrons which may exist in the region B due to the magnetic filter effect of the ring magnet 8 with H ₂ ^* and the reaction of Rg ^** with H. Is generated, and this H ⁻ is drawn out of the container through the outlet 1c, and becomes a beam that enters the tandem accelerator in the next stage.

As the rare gas Rg, He, Ne,
An inert gas such as Ar or Kr is used. Also,
The amounts of the H ₂ gas and the rare gas Rg introduced into the ion source container 1 are adjusted so that the generated H ⁻ ions are maximized.

Injecting neutral Rg into the ion source container 1 may adversely affect negative ionization, but this neutral Rg does not hinder the production of H ^−. However, there is a report (Leung at al., Rev. Sei. Instrm 56 , (1985) 2079) that rather seeks to promote the production. Therefore, according to the examples of the present invention, such neutral R
It becomes a highly efficient ion source with the effect of increasing H ⁻ production by g.

[0022]

As described above, according to the negative ion source of the present invention, a magnetic filter is formed between the electron source and the extraction port, and the inside of the ion source container is provided with a positive ionization region due to high-speed electron impact. Since it is magnetically divided into a negative ionization region and a rare gas Rydberg atom is present in the negative ionization region, in generating negative ions of hydrogen,
A large amount of neutral hydrogen atoms generated in the reaction process in the ion source container can be effectively converted into negative ions, and the negative ion generation efficiency is improved. The increase can be achieved relatively easily.

Further, in the conventional volume generation type negative ion source,
In order to increase the generation efficiency of negative ions, Cs (cesium), which is an alkali metal, is often injected into the ion source container, which causes contamination of the ion source, the electron emission filament, and the like. However, in the negative ion source of the present invention, without using such an alkali metal, the production efficiency of negative ions is increased by utilizing the Ridberg atom based on the rare gas which is an inert gas. The inside of the source container is maintained in a clean state, and the life of the ion source can be extended. Further, no pollutant is emitted from the ion source container, and thus there is no influence of contamination on the tandem electrostatic accelerator in the next stage.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

[Explanation of symbols]

1 ... ・ Ion source container 1a ・ ・ ・ ・ Small diameter part 1b ・ ・ ・ ・ Large diameter part 1c ・ ・ ・ ・ Drawout port 12a ・ ・ ・ ・ Gas (H ₂ ) inlet port 12b ・ ・ ・ ・ Rare gas ( Rg) Inlet port 2 ... Filament (for high-speed electron emission) 3 ... Magnet (for cusp magnetic field generation) 4-6 ... Grid 7 ... Filament (for electron emission) 8. .. Magnet (for forming magnetic filter) 9 ... Noble gas Rg supply source A ... Region in ion source container 1 (positive ionization region by high-speed electrons) B ... In ion source container 1 Area (negative ionization reaction area)

Claims (1)

[Claims] 1. An ion source container in which neutralized particles to be ionized are introduced, and a high-speed electron having an energy capable of positively ionizing the neutral particles, which is arranged in the container and uses the container wall as an anode. An ion source configured to extract negative ions generated by a reaction originating from positive ionization of neutral particles due to impact of the high-speed electrons in the ion source container to the outside of the container through an extraction port. In the source, between the outlet and the electron source,
Forming a magnetic filter that reflects only high-speed electrons from this electron source, a magnet that magnetically divides the ion source container into two regions, and two regions divided by the magnetic filter, A negative ion source, characterized in that a means for allowing rare gas Rydberg atoms to exist is provided in the region on the extraction port side.