WO2012066940A1

WO2012066940A1 - Tandem accelerator and charge exchanger

Info

Publication number: WO2012066940A1
Application number: PCT/JP2011/075422
Authority: WO
Inventors: 元和田; 貴弘剣持; 眞實子笹尾; 純男北島; 岡本　敦; 健祐寺井
Original assignee: 学校法人同志社; 国立大学法人東北大学
Priority date: 2010-11-15
Filing date: 2011-11-04
Publication date: 2012-05-24
Also published as: JPWO2012066940A1

Abstract

Provided are: a charge exchanger with highly efficient exchange from negative ions to positive ions, a long life, and a simple structure; and a tandem accelerator using same. A low energy-side accelerator tube that electrostatically accelerates negative ions (D^-) pulled out from an ion source (2), a charge exchanger that converts incident negative ions (D^-) to positive ions (D⁺), and a high energy-side accelerator tube that again electrostatically accelerates the converted positive ions (D⁺) are housed, in that order, inside a pressure tank in the tandem accelerator. The charge exchanger comprises a plurality of plates (61) made from a high-fusion point metal arranged in parallel at prescribed intervals. The plurality of plates (61) have a smooth surface on one surface (61S), and each plate is arranged such that said surface (61S) forms an angle of 10° or less with the incident direction of the negative ions (D^-). The negative ions (D^-) are reflected by said surface (61S) of each plate (6) and are converted into positive ions (D⁺).

Description

Tandem accelerator and charge exchanger

The present invention relates to a tandem accelerator that obtains a high-energy ion beam by accelerating negative ions, converting them into positive ions, and accelerating them again, and a charge exchanger used in the tandem accelerator.

Neutron generator tubes that irradiate heavy metal targets with high-energy ion beams to generate high-density neutrons by fusion are widely used for inspection of plastic bombs in baggage at airports and as a neutron source for treatment. It is going to be used.

In order to realize the neutron generator tube described above, a long-life, small-sized and highly reliable neutron source is required. To obtain this easily, the deuterium accelerated by the target on which deuterium is adsorbed is obtained. It is effective to use a nuclear reaction to obtain helium and neutrons by colliding with an ion beam.

In order to cause the above-described nuclear reaction, it is necessary to give deuterium energy of about 150 keV, and a tandem accelerator is used as means for generating such a high-energy ion beam (for example, Patent Documents). 1).

The tandem accelerator has a low-pressure side acceleration tube, a charge exchanger, and a high-energy side acceleration tube arranged in this order in a metal pressure tank whose inside is kept in vacuum. Hereinafter, the operation of the tandem accelerator will be briefly described.

First, using a high-voltage power supply, a high positive voltage of about tens of thousands of volts is applied to the charge exchanger, and an ion beam of negative ions is taken out from the ion source. Next, the negative ions are accelerated by the electric field generated in the low energy side acceleration tube, and kinetic energy corresponding to the voltage of the high voltage power source is given.

When a negative ion given kinetic energy passes through the charge exchanger, the negative ion emits two or more electrons that have been held so far to become a positive ion, and enters the opposite region of the charge exchanger with respect to the ion source. Head towards a certain high energy accelerator tube. In the high energy side accelerating tube, there is an electric field having the same strength as the electric field formed in the low energy side accelerating tube and having a direction opposite to 180 degrees. The positive ions are further accelerated in the direction of travel, and obtain an energy that is an integral multiple of that of the high-voltage power supply, depending on the number of electrons lost in the charge exchanger.

By using an acceleration device that is operated based on the above principle called tandem acceleration, it is possible to easily obtain a high-energy positive ion beam that is an integer multiple of 2 or more of simple acceleration by the high-voltage power supply used.

In the conventional tandem accelerator described above, as a method of converting negative ions into positive ions in the charge exchanger, a method using a stripper gas as described in Patent Document 1 and a method described in Non-Patent Document 1 are used. A method using carbon foil has been adopted.

JP 2000-164398 A

Of the above methods, the conversion method using stripper gas requires the gas to be circulated inside the acceleration device, which not only complicates the device but also prevents charge exchange reaction unless a sufficient amount of gas is supplied. It will be enough. Furthermore, the supplied gas increases the operating pressure in the accelerator and adversely affects the insulation of the high voltage power supply. In particular, in order to maintain the gas pressure in the apparatus appropriately, the apparatus becomes large, and it has been difficult to realize a small tandem accelerator that is operated with a power supply of about tens of thousands to hundreds of thousands of volts.

On the other hand, in the conversion method using carbon foil, when negative ions collide with many particles, the particles that have been accelerated are repeatedly collided in the thin film and stopped in the solid. For this reason, it is necessary to reduce the number of collisions by making the carbon foil very thin and allow incident negative ions to pass through. However, a too thin foil has a problem that it has a mechanical strength and is easily broken. As a result, it is necessary to frequently replace the foil, which increases the operating cost of the apparatus.

The present invention has been made in view of the above-mentioned problems, and provides a charge exchanger having a high conversion efficiency from negative ions to positive ions, a long life and a simple structure, and a tandem accelerator using the same. With the goal.

In order to achieve the above object, a tandem acceleration apparatus according to the present invention includes an ion source that generates negative ions, a low-energy side acceleration tube that electrostatically accelerates negative ions extracted from the ion source, and positive ions that are incident on the negative ions. A tandem accelerator that is accommodated in this order in a pressure tank, a charge exchanger that converts the positive ions into a high-energy accelerator tube that electrostatically accelerates the converted positive ions again,
The charge exchanger is composed of a plurality of plates made of a refractory metal arranged in parallel at a predetermined interval,
One side of the plurality of plates has a smooth surface;
Each of the plates is installed such that an angle formed by the one surface with respect to the incident direction of the negative ions is 10 degrees or less,
The negative ions are reflected by one surface of each plate and converted into positive ions.

Here, as for the flatness of one surface of the plate, the root mean square roughness which is a parameter of the surface roughness is preferably 0.071 or less.

The negative ions are preferably deuterium negative ions, and the plate is preferably made of molybdenum. The ion source may extract the deuterium negative ions from the vaporized cesium.

The plurality of plates are held at predetermined intervals in a hollow portion of a rectangular tube-shaped frame, and the frame is centered with respect to the negative ion incidence direction by an angle adjusting member. It is preferable that it is comprised so that can rotate.

If the charge exchanger of the present invention is used, deuterium negative ions can be converted into positive ions with high efficiency. In addition, since it is not necessary to circulate the gas in the apparatus, the structure is simplified, and the degree of vacuum can be maintained high, so that a high energy ion beam can be realized. Furthermore, since it can be used repeatedly once installed, the operating cost of the tandem accelerator can be greatly reduced as compared with the case of using a carbon foil.

FIG. 1 is a cross-sectional view showing a schematic configuration when a tandem accelerator according to an embodiment of the present invention is used as a neutron generating tube. FIG. 2 is a view of the charge exchanger of FIG. 1 as viewed from the incident direction of negative ions. FIG. 3 is a view of one of the molybdenum plates held on the frame of FIG. 2 as viewed from a direction orthogonal to the negative ion entry direction A. FIG. FIG. 4 shows the intensity of a reflected beam when a negative ion (D ⁻ ) having an energy of 75 keV is incident at an angle θ of 10 degrees on a flat surface at the atomic level of a molybdenum plate, based on theoretical calculation. It is a figure which shows the calculated result. FIG. 5 shows the intensity of a reflected beam when a negative ion (D ⁻ ) having an energy of 75 keV is incident at an angle θ of 5 degrees on a flat surface at the atomic level of a molybdenum plate, based on theoretical calculation. It is a figure which shows the calculated result. FIG. 6 shows the intensity of a reflected beam when a negative ion (D ⁻ ) having an energy of 75 keV is incident at an angle θ of 1 degree on a flat surface at the atomic level of a molybdenum plate, based on theoretical calculation. It is a figure which shows the calculated result. FIG. 7 shows the intensity of a reflected beam when a negative ion (D ⁻ ) having an energy of 75 keV is incident at an angle θ of 20 degrees on a flat surface at the atomic level of a molybdenum plate, based on theoretical calculation. It is a figure which shows the calculated result. FIG. 8 is a diagram showing a schematic configuration of an evaluation apparatus for evaluating the performance of the charge exchanger. FIG. 9 is a graph showing an example of the performance evaluation result of the charge exchanger measured using the evaluation apparatus of FIG. FIG. 10 is a graph showing the result of detecting the ratio of the intensity of the ion beam in the low energy accelerator tube and the high energy accelerator tube with the detectors installed at the respective outlets.

Hereinafter, a tandem acceleration device and a charge exchanger according to embodiments of the present invention will be described with reference to the drawings. First, main features of the charge exchanger according to the present invention will be described.

In the present invention, a charge exchanger is configured by utilizing a recoil phenomenon that occurs on the surface of a refractory metal. It can be seen that deuterium negative ions (D ⁻ ) collide at high speed with the surface of a plate made of a refractory metal such as molybdenum or tungsten, and electrons are emitted and converted to positive ions (D ⁺ ). ing. Through experiments, the inventors have found that the directivity of the reflected beam becomes sharp when negative ions of deuterium are incident on a refractory metal plate whose surface is polished smoothly at a shallow angle.

The present invention has been made on the basis of the above experimental results. The charge exchanger is made of a high melting point metal, and a plurality of plates whose one surface is polished smoothly are arranged in parallel at a predetermined interval. These plates are installed so as to be inclined so that the angle formed by the one surface with respect to the incident direction of the negative ion beam is 10 degrees or less.

<Configuration and operation of tandem accelerator>
Next, an embodiment when the tandem accelerator of the present invention is used as a neutron generating tube will be described with reference to FIG. FIG. 1 shows a schematic configuration of a tandem accelerator according to the present embodiment.

The tandem accelerator 1 is basically composed of an ion source 2, a low energy side acceleration tube 3, a high energy side acceleration tube 4, a high voltage terminal 5, a charge exchanger 6, a high voltage power source 7, and a target 8. Each member except the voltage power source 7 is accommodated in a metal pressure tank 9 in a vacuum state.

In the present invention, in order to make the tandem accelerator 1 function as a neutron generating tube, an ion source 2 that generates deuterium negative ions (D ⁻ ) is used. For example, when a chemical obtained by combining deuterium with an alkali metal such as cesium is used as an ion generation source and heated and evaporated, an alkali metal positive ion and a deuterium negative ion are generated. Of these, positive ions of alkali metal are adsorbed on the wall of the pressure tank 9 and removed, leaving only deuterium negative ions (D ⁻ ). In addition, although cesium is optimal as an alkali metal, the same effect is acquired even if it uses another alkali metal.

Although not shown, a high frequency generator is provided inside the ion source 2, and a permanent magnet is provided around the ion source 2. Due to the application of high frequency and the action of a permanent magnet, the deuterium negative ions (D ⁻ ) are in a plasma state, and after being formed into a beam shape by a lens system (not shown), they are released into the low energy side acceleration tube 3 from the ion emission holes. The

The low energy side accelerating tube 3 has a plurality of electrodes 31 having a hole through which an ion beam passes at the center and arranged at equal intervals through a short tube 32 made of an insulator such as alumina ceramic. Is. A voltage dividing resistor is connected between the adjacent electrodes 31 (not shown), and a series of voltage dividing resistors and the electrode 31 constitute a voltage dividing circuit.

Among the electrodes 31, the potential of the electrode on the inlet side of the low energy side acceleration tube 3 is fixed to the ground potential, and the electrode on the outlet side is electrically connected to the high voltage terminal 5.

The high energy side acceleration tube 4 is configured in the same manner as the low energy side acceleration tube 3. In other words, a plurality of electrodes 41 having a hole through which an ion beam passes at the center and arranged at equal intervals are stacked via a short tube 42 made of an insulator such as glass. A voltage dividing resistor is connected between the adjacent electrodes 41 (not shown), and a series of voltage dividing resistors and the electrode 41 constitute a voltage dividing circuit.

Among the electrodes 41, the electrode at the end of the high energy side acceleration tube 4 on the inlet side is electrically connected to the high voltage terminal 5, and the potential of the electrode at the end on the outlet side is fixed to the ground potential.

The high voltage terminal 5 made of cylindrical metal is applied with a positive acceleration voltage with respect to the ground potential from the high voltage power source 7, and each of the low energy side acceleration tube 3 and the high energy side acceleration tube 4. An equal voltage obtained by dividing the acceleration voltage by a voltage dividing circuit is applied between adjacent electrodes. The high voltage terminal 5 accommodates a charge exchanger 6. The configuration of the charge exchanger 6 will be described in detail later with reference to FIGS.

In the present embodiment, a target 8 in which palladium is impregnated with deuterium is used. When an ion beam of deuterium positive ions (D ⁺ ) emitted from the high energy side acceleration tube 4 collides with the target 8 at a high speed, a fusion reaction occurs with the deuterium impregnated in the target 8 by impact. Helium and neutrons are generated.

Next, the operation of the tandem acceleration device 1 will be described. In a state where the low energy side acceleration tube 3, the high voltage terminal 5 and the high energy side acceleration tube 4 are maintained in vacuum, as shown by arrows in FIG. 1, deuterium negative ions (D The ion beam of ⁻ ) enters the low energy side acceleration tube 3.

The ion beam incident on the low energy side acceleration tube 3 is accelerated by the electric field between the electrodes 31 to obtain energy of about 75 keV, and then supplied to the charge exchanger 6 in the high voltage terminal 5. The deuterium negative ions (D ⁻ ) accelerated by the low energy side accelerating tube 3 collide with the atoms of the molybdenum plate 61 as will be described later, whereby the extranuclear electrons are stripped off and positive ions (D ⁺ ). Is converted to

The ion beam of deuterium positive ions (D ⁺ ) output from the charge exchanger 6 is incident on the high energy side acceleration tube 4 and accelerated again toward the ground potential by the electric field between the electrodes 41, and has an energy of about 150 keV. After obtaining, the target 8 collides. Neutrons are emitted from the target 8 by the collision of deuterium positive ions (D ⁺ ).

<Configuration and operation of charge exchanger>
Next, the configuration and operation of the charge exchanger 6 according to the present embodiment will be described with reference to FIGS. FIG. 2 is a view of the charge exchanger 6 as seen from the direction of incidence of negative ions. The charge exchanger 6 includes a plurality of plates 61 made of molybdenum, a frame 62, an arm 63, and an angle adjusting member 64.

The frame 62 is made of a rectangular tube-shaped metal in which the axis of the hollow portion is arranged in the vertical direction (perpendicular to the paper surface). A plurality of grooves are formed at equal intervals on the opposing inner walls of the hollow portion of the frame 62, and both ends of the molybdenum plate 61 are inserted into the grooves. The plurality of molybdenum plates 61 are held by these grooves in a state of being arranged in parallel at a predetermined interval.

The frame 62 is attached to the angle adjusting member 64 via a pair of arms 63. The angle adjusting member 64 is fixed to the high voltage terminal 5 and is configured to be rotated in the vertical direction (perpendicular to the paper surface) and held at the rotated position by an angle adjusting mechanism (not shown).

The surface of each molybdenum plate 61 that is irradiated with a negative ion beam is polished with a polishing agent such as scouring powder, and then surface irregularities are removed using a silk cloth or the like, and the flatness is flat at the atomic level. In particular, a smooth surface having a maximum peak height and a maximum valley depth of 1 μm or less of a roughness curve element, which is a kind of surface roughness parameter, is finished.

FIG. 3 shows a state in which one of the molybdenum plates 61 held by the frame 62 is viewed from a direction orthogonal to the negative ion entry direction. The molybdenum plate 61 is arranged so that the smooth surface 61S polished with the ion beam is irradiated. FIG. 3A shows a case where the angle θ formed between the approach direction A of deuterium negative ions (D ⁻ ) and the polished smooth surface 61S of the molybdenum plate 61 is small, and FIG. 3B shows the angle. The case where θ is relatively large is shown.

As a result of repeated experiments using hydrogen in order to simulate an experiment using deuterium, as shown in FIG. 3A, an angle formed by the entrance direction A of negative ions and the polished surface 61S of the metal plate 61 is formed. When θ is 10 degrees or less, incident negative ions of hydrogen collide with molybdenum atoms of the molybdenum plate 61 and are converted to positive ions with a probability of almost 100%, and most positive ions have an incident angle of It was found to reflect at equal angles. Furthermore, it was found that the directivity of the reflected positive ions is the steepest when the angle θ is around 1 degree.

For reference, in FIG. 4, negative ions (D ⁻ ) with energy of 75 keV are applied to −80 degrees (that is, the negative ion approach direction A and the molybdenum plate 61 shown in FIG. The result of calculating the intensity of the reflected beam when incident at an angle θ formed with the smooth surface 61S of 10 degrees) using ACAT (Atomic Collision in Amorphous Target) is shown.

ACAT is well known as a sputtering analysis code and is described in detail in the following documents, for example.
“(2) Sputtering analysis codes ACAT and ACAT-DIFFUSE” in “Project Materials” of “New Development of Tritium Research Aiming for Realization of Fusion Reactor” Kenji and others (searched on October 14, 2011), Internet <URL: // http: //tritium.nifs.ac.jp/project/02/index.html>

In FIG. 4, the incident angle (−90 degrees to 90 degrees) of negative ions (D ⁻ ) is shown in the circumferential direction. Yield shown in the radial direction indicates the number of particles that are reflected when 100 particles are incident by a circle for each angle. From the figure, it can be seen that when the incident angle is 10 degrees, the reflected beam exhibits excellent directivity.

Similarly, FIG. 5 shows the intensity of the reflected beam when a negative ion (D ⁻ ) having an energy of 75 keV is incident at −85 degrees, that is, at an angle θ of 5 degrees. FIG. 6 shows the intensity of the reflected beam when negative ions (D ⁻ ) having an energy of 75 keV are incident at −89 degrees, that is, at an angle θ of 1 degree. As can be seen from FIGS. 5 and 6, the directivity of the reflected beam becomes steeper as the angle θ decreases. In particular, it converges to a straight line at 1 degree.

On the other hand, when the surface of the molybdenum plate 61 is not sufficiently polished and the surface is not flat at the atomic level, that is, when the maximum peak height or the maximum valley depth of the roughness curve element exceeds 1 μm, the angle θ is 10 It was found that the ion beam is scattered on the reflecting surface even when the angle is less than or equal to the degree, the number of ions incident on the high energy side acceleration tube 4 is reduced, and the conversion efficiency is lowered.

Further, as shown in FIG. 3B, when the angle θ exceeds 10 degrees, the flatness of the surface 61S is flat at the atomic level, that is, the maximum peak height and the maximum valley depth of the roughness curve are It was found that even when the thickness was 1 μm or less, the ion beam was scattered on the reflecting surface, and the conversion efficiency was greatly reduced.

For reference, FIG. 7 shows that a negative ion (D ⁻ ) having an energy of 75 keV is applied to −70 degrees (that is, the negative ion approach direction A shown in FIG. The result of calculating the intensity of the reflected beam when incident at an angle θ of 20 degrees with the smooth surface 61S is calculated using ACAT as in FIG. As shown in the figure, when the angle θ is 20 degrees, the reflected beam spreads and the directivity deteriorates.

<Performance evaluation test>
Next, the performance evaluation test of the charge exchanger 6 will be described. Initially, with reference to FIG. 8, the structure of the evaluation apparatus 10 which evaluates the performance of the charge exchanger 6 is demonstrated.

The evaluation device 10 is installed instead of the target 8 on the ion beam exit side of the high energy side acceleration tube 4 of the tandem accelerator 1 shown in FIG. The evaluation apparatus 10 includes an ion beam detector 11, a shielding plate 12 attached to the entrance of the detector 11 and formed with a slit 12S having a width of about 0.3 mm, and a parallel plate type that deflects the ion beam by an electric field. The pair of

beam deflecting plates

13a and 13b.

The detector 11 detects the intensity of the ion beam incident from the slit 12S of the shielding plate 12 as a current value. The shielding plate 12 is configured to be movable in a direction orthogonal to the traveling direction A of the ion beam by a driving means (not shown) as indicated by an arrow. Further, the shielding plate 12 and the detector 11 move integrally.

When a deflection voltage is not applied between the

beam deflecting plates

13a and 13b, the deuterium positive ion (D ⁺ ) ion beam is substantially parallel to the traveling direction A of the negative ion ion beam as shown by the solid arrow. proceed. On the other hand, when a deflection voltage is applied, the traveling direction of the ion beam is deflected as indicated by the broken arrow.

FIG. 9 shows the result of the performance evaluation test of the charge exchanger 6 measured using the evaluation apparatus 10 of FIG. In this test, performance was evaluated using hydrogen instead of deuterium. In the figure, the horizontal axis indicates the displacement of the slit 12S with respect to the traveling direction of the ion beam when the shielding plate 12 is moved in the arrow direction of FIG. 8, and the vertical axis indicates the current value of the ion beam detected by the detector 11. Indicates. As the

charge exchanger

6, 12 molybdenum plates 61 having a size of 25 mm × 31 mm and a thickness of 0.4 mm held on a frame 62 at a predetermined interval (see FIG. 2) were used. At the time of measurement, an angle θ formed by the negative ion approach direction A and the polished surface 61S of the molybdenum plate 61 was set to 1 degree. The energy of positive ions (H ⁻ ) of the obtained hydrogen was 145 keV.

In the figure, a solid line indicates a measured value when the deflection voltage V is not applied between the

beam deflecting plates

13a and 13b (V = 0 kV), and a one-point difference line indicates a deflection voltage V of 2 kV between the

beam deflecting plates

13a and 13b. The measured value when the voltage is applied, the broken line indicates the value obtained by theoretical calculation.

First, the measurement result when the deflection voltage V (shown by a solid line) is not applied will be described. The negative current value is obtained by detecting that the ion beam of negative ions (H ⁻ ) incident on the charge exchanger 6 leaks and passes between the plates without being reflected by the surface of the molybdenum plate 61. It can be seen that has almost reached the center.

On the other hand, a positive current value in the form of a tail extending away from the central axis was observed at the position where the ion beam of positive ions (H ⁺ ) reached. In the figure, the broken line is a theoretical calculation of the spread of the ion beam when positive ions are reflected on the surface of the molybdenum plate 61, and it can be seen that the calculated value and the measured value indicated by the solid line are almost the same. .

The leakage of the negative ion (H ⁻ ) ion beam can be almost eliminated by adjusting the length and interval of the molybdenum plate 61.

Next, the measurement result when the deflection voltage V (indicated by a one-dot difference line) is applied will be described. Due to the deflection voltage V of 2 kV applied to the

beam deflecting plates

13a and 13b, the negative current value due to negative ions (H ⁻ ) shifts to the left (negative direction), and the positive current value due to positive ions (H ⁺ ) is Shifted to the right (positive direction). However, it can be seen that the shape of the ion beam due to positive ions (H ⁺ ) is only shifted to the right, and there is no significant change in the shape of the beam.

As a result of the performance evaluation described above, the conversion efficiency from negative ions to positive ions in the charge exchanger 6 is almost 100%, the beam diameter is within an allowable size, and hydrogen positive ions (H ⁺ ) Ion beam was found to be obtained.

Next, the graph of FIG. 10 will be described. FIG. 10 shows the ratio of the intensity of the ion beam in the low energy side acceleration tube 3 and the high energy side acceleration tube 4 detected by the detectors 11 installed at the respective outlets. About the intensity | strength of the ion beam of a negative ion (H < ^- >), it detected using the detector 11 installed in the position instead of the charge exchanger 6. FIG. The angle θ formed between the negative ion entry direction A and the polished surface 61S of the molybdenum plate 61 is set to 1 degree.

In the figure, the horizontal axis indicates the energy of the positive ion (H ⁺ ) ion beam obtained by the tandem accelerator, and the vertical axis indicates the current value indicating the intensity of the ion beam at the exit of the high energy side acceleration tube 4. A ratio between Ip and a current value In indicating the intensity of an ion beam of negative ions (H ⁻ ) at the exit of the low energy side acceleration tube 3 is shown. In the figure, the ▲ mark is the value when using a molybdenum plate (polishing level 1) whose surface is polished, and the ● mark is the value when using a molybdenum plate (polishing level 2) that has been finely polished after polishing the surface. Each value is flat at the atomic level. The squares are ideal values obtained by calculation.

Table 1 shows the measurement results of the surface roughness of the molybdenum plate used in this measurement. Each row of Table 1 shows various parameters of the surface roughness, and each column shows a measured value of the polishing level 1 and polishing level 2 molybdenum plates.

As apparent from the graph of FIG. 10, when the surface of the molybdenum plate 61 is finely polished and the root mean square roughness which is a parameter of the surface roughness is 0.014 (polishing level 2), positive ions ( The intensity of the ion beam of H ⁺ ) is high. That is, the directivity of the ion beam becomes sharper by finely polishing the surface of the molybdenum plate 61.

On the other hand, when the surface of the molybdenum plate 61 is normally polished and the root mean square roughness is 0.071 (polishing level 1), the ion beam intensity is slightly lower than that of the molybdenum plate 61 at the polishing level 2. However, it shows a value that can be practically enough.

Further, in the graph of FIG. 10, as the beam energy increases, the ratio of the ion beam when the surface of the molybdenum plate 61 is polished approaches the calculated value. Therefore, as the beam energy increases, the negative ions are positively corrected with higher efficiency. It turns out that it can convert into ion.

As described above, by using the charge exchanger of the present invention, deuterium negative ions can be converted into positive ions with high efficiency. In addition, the structure is simpler than when a stripper gas is used, and a high degree of vacuum can be maintained, so that a high-energy ion beam can be realized. Furthermore, since the installed metal plate can be used repeatedly, the operating cost of the tandem accelerator can be greatly reduced as compared with the case of using a carbon foil.

In the above-described embodiment, the charge exchanger is used to convert deuterium negative ions into positive ions, but the present invention is not limited to this. A tandem accelerator may be used to generate high energy ion beams of various materials.

Further, the configuration of the charge exchanger is not limited to that shown in FIG. Any configuration may be adopted as long as a plurality of metal plates for converting negative ions into positive ions can be arranged in parallel and the angle can be adjusted.

DESCRIPTION OF SYMBOLS 1 Tandem accelerator 2 Ion source 3 Low energy side acceleration tube 4 High energy side acceleration tube 5 High voltage terminal 6 Charge exchanger 7 High voltage power supply 8 Target 9 Pressure tank 10 Evaluation apparatus 11 Detector 12

Shielding plate

13a, 13b Beam deflection Plate 61 Molybdenum plate 62 Frame 63 Arm 64 Angle adjustment member

Claims

An ion source that generates negative ions, a low-energy accelerator tube that electrostatically accelerates negative ions extracted from the ion source, a charge exchanger that converts the incident negative ions to positive ions, and the converted positive ions again A high-energy acceleration tube that electrostatically accelerates is a tandem accelerator accommodated in this order in a pressure tank,
The charge exchanger is composed of a plurality of plates made of a refractory metal arranged in parallel at a predetermined interval,
One side of the plurality of plates has a smooth surface;
Each of the plates is installed such that an angle formed by the one surface with respect to the incident direction of the negative ions is 10 degrees or less,
The tandem accelerator according to claim 1, wherein the negative ions are reflected by the one surface and converted into positive ions.
The tandem acceleration device according to claim 1, wherein the flatness of one surface of the plate has a root mean square roughness which is a parameter of surface roughness of 0.071 or less.
The tandem accelerator according to claim 1, wherein the negative ions are deuterium negative ions, and the plate is made of molybdenum.
4. The tandem accelerator according to claim 3, wherein the ion source takes out negative ions of the deuterium from the vaporized cesium.
A charge exchanger that is used in a tandem accelerator, converts negative ions electrostatically accelerated in a low energy side accelerator tube into positive ions, and supplies the obtained positive ions to a high energy side accelerator tube,
A plurality of plates made of refractory metal are arranged in parallel at a predetermined interval,
One side of the plurality of plates has a smooth surface;
Each of the plates is installed such that an angle formed by the one surface with respect to the incident direction of the negative ions is 10 degrees or less,
The charge exchanger according to claim 1, wherein the negative ions are reflected by the one surface and converted into positive ions.
The charge exchanger according to claim 5, wherein the flatness of one surface of the plate has a root mean square roughness which is a parameter of surface roughness of 0.071 or less.
6. The charge exchanger according to claim 5, wherein the negative ions are deuterium negative ions, and the plate is made of molybdenum.
The plurality of plates are held at predetermined intervals in a hollow portion of a rectangular tube-shaped frame,
6. The charge exchanger according to claim 5, wherein the frame is configured such that a central axis of the hollow portion can be rotated with respect to an incident direction of the negative ions by an angle adjusting member.