JP3067784B2 - Electrostatic accelerator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrostatic accelerator.

More particularly, the present invention relates to an electrostatic accelerator capable of generating a high-current charged particle beam with high convergence and high current.

(Prior Art) Conventionally, for an electrostatic accelerator that electrostatically accelerates a charged particle beam to a high energy region of about several tens keV to several MeV, for example, a single electrode hole (A) as illustrated in FIG. ) Are known in which a plurality of accelerating electrodes (a) are arranged in multiple stages.

In such an electrostatic accelerator, an electrostatic field is applied between the accelerating electrodes (a) from the accelerating electrodes (c), and an ion source (d) is applied.
The charged particle beam (h), in which the supply gas (f) is plasma (g) excited by the applied voltage from the plasma generation power supply (e) provided in the above, is accelerated. The convergence of the charged particle beam (h) has been performed by an electrostatic lens effect received from an electrostatic field when passing through the electrode hole (a) of each acceleration electrode (a).

(Problems to be Solved by the Invention) Generally, when accelerating a charged particle beam (h), the diverging force is increased by the space charge of the beam itself as the current value of the charged particle beam (h) increases, and the beam The convergence of is deteriorated. In order to prevent this and improve the convergence of the charged particle beam (h), it is necessary to increase the intensity of the electric field applied between the accelerating electrodes (a) of the electrostatic accelerator to increase the lens action.

However, since the electric field strength that can be applied between the accelerating electrodes (a) is restricted by the withstand voltage of the vacuum, the generation of a large current beam with good convergence has been limited in the past.

On the other hand, between the accelerating electrodes (a), as shown in FIG. 7, low-speed secondary particles such as electrons (ke) and ions (ko) generated by collision between the beam particles and surrounding gas molecules are generated. Is accelerated in the direction of the electric field, and is accelerated to high energy as it sequentially passes through the electrode holes (A). These accelerated high-energy electrons (ke) and ions (ko)
Is generally easy to take a trajectory that collides with the acceleration electrode (a) on the downstream side, and once colliding with the acceleration electrode (a), X-rays (sa) and secondary electrons (shi) are generated, which causes There is a problem that the withstand voltage characteristics are deteriorated. When the degree of vacuum in the accelerator is high, the generation of secondary particles is small and does not cause a significant problem. However, as the beam current is increased, the gas (f) supplied to the ion source (d) is increased. When the supply amount increases and the gas pressure in the accelerator increases, the electrons generated between the accelerating electrodes (a)
It is extremely important how to suppress secondary particles such as ions and ions (co). That is, there is a problem that such secondary particles must be processed in a low energy state without being accelerated to a high energy state.

The present invention has been made in view of the above circumstances, and solves the drawbacks of the conventional electrostatic accelerator, with a large current,
It is another object of the present invention to provide a new electrostatic accelerator capable of generating a high-intensity charged particle beam with good convergence.

(Means for Solving the Problems) In order to solve the above problems, the present invention arranges a plurality of magnets around an electrode hole of an acceleration electrode and generates a magnetic quadrupole magnetic field in the electrode hole. An electrostatic accelerator characterized by the following.

In a preferred embodiment of the present invention, a quadrupole magnetic field having opposite polarities is generated in adjacent electrode holes.

(Operation) In the electrostatic accelerator of the present invention, a plurality of magnets are arranged around the electrode hole of the accelerating electrode, and a magnetic quadrupole magnetic field is generated in the electrode hole, so that the charged particle beam is Each time the light passes through, the charged particle beam is alternately converged and diverged in the vertical and horizontal directions of its cross section with this quadrupole magnetic field, and finally becomes an accelerated charged particle beam with good convergence Can be. In addition, secondary particles such as electrons and ions generated by the collision of a particle beam and surrounding gas molecules between the accelerating electrodes can be deflected by a quadrupole magnetic field, so that these secondary particles are accelerated to a high energy state. And the generation of X-rays and secondary electrons from the surface of the acceleration electrode due to collision with the acceleration electrode can be suppressed.

(Example) Hereinafter, an example is shown along with a drawing and an electrostatic accelerator of the present invention is explained in more detail.

FIGS. 1 (a) and 1 (b) are a cross-sectional view and a front view, respectively, of an essential part schematically showing an embodiment of the electrostatic accelerator of the present invention.

In this example, in an electrostatic acceleration system (2) for accelerating a charged particle beam through a single electrode hole (1), a pair of quadrupole magnetic fields is applied to each of the multistagely arranged acceleration electrodes (3). (4a) The magnets (5) for generating (4b) are arranged one by one at the top, bottom, left and right. Usually, by using a pair of equal quadrupole magnetic fields (4a) and (4b), the charged particle beam can be converged in both the vertical and horizontal directions of its cross section. The type of the magnet (5) that generates the quadrupole magnetic fields (4a) and (4b) is not particularly limited, and may be, for example, a permanent magnet, an electromagnet, or the like.

Further, in this example, adjacent magnets (5A) and (5B) are arranged with the polarities reversed so that the quadrupole magnetic fields in the adjacent electrode holes (1) have opposite polarities. I have.

In the example shown in FIG. 1, when the charged particle beam is incident on the quadrupole magnetic field (4 A) on the downstream side, the energy of the beam is higher than on the downstream side. By making the intensity of the quadrupole magnetic field (4B) on the upstream side stronger than that of the quadrupole magnetic field (4A), a charged particle beam converged in both the horizontal and vertical directions can be obtained.

FIGS. 2A and 2B are a cross-sectional view and a front view of a main part schematically showing another example of the present invention.

In this example, a pair of magnets (5a) and (5b) having opposite polarities are arranged on one accelerating electrode (3). Similarly to the example shown in FIG. 1 (a), the magnet (5) is polarized so that the polarities of the quadrupole magnetic fields in the adjacent single electrode hole (1) are also opposite to each other. They are arranged in reverse.

In the case of the example shown in FIG. 2, unlike the example of FIG. 1, the energy of the charged particle beam does not increase between the quadrupole magnetic fields between the electrodes (3). It is not necessary to increase the magnetic field strength of each electrode (3) according to the energy of the beam passing through the electrode hole (1).

FIG. 3 is a front view of a main part schematically showing another example of the present invention.

A magnet (5) for generating quadrupole magnetic fields having opposite polarities is disposed in an electrode hole (1) adjacent to the porous electrode hole (1) formed in the acceleration electrode (3). The charged particle beam is accelerated by passing through the electrode hole (1) in the shape of a circle. In the case of the example shown in FIG. 3, since the magnetic field generated by the magnet (5) does not leak out of the acceleration electrode (3), there is an advantage that the ion source is not adversely affected.

For example, FIGS. 4 (a), (b) and 5 show examples of the acceleration action of the charged particle beam by the electrostatic accelerator of the present invention which can be exemplified as described above.

As shown in FIGS. 4 (a) and 4 (b), each time the charged particle beam (6) passes through the electrode hole (1) of the accelerating electrode (3), a pair of quadrupole magnetic fields (4a) ( According to 4b), as shown in FIG. 5, the convergence function (7) and the divergence function (8) are alternately repeated in the vertical and horizontal directions of the beam cross section, and finally the convergence is good by the principle of strong convergence. It becomes a boom. A large current beam with good convergence can be generated without increasing the intensity of the electric field applied between the accelerating electrodes (3), that is, without increasing the intensity of the electrostatic lens.

Secondary electrons generated by collision between the beam particles and the surrounding gas between the accelerating electrodes (3) have a mass about 1/1800 smaller than that of the charged particles, so the quadrupole magnetic field (4a)
The beam is largely deflected by (4b) and collides with the electrode (3) along the trajectory (9) shown in FIG. 4 (a). On the other hand, secondary ions generated by collision between beam particles and gas molecules are:
Since the energy obtained before passing through the electrode hole (1) is small, the quadrupole magnetic field (4a) (4b)
And collides with the electrode (3) in a trajectory (9). For this reason, secondary particles such as secondary electrons and secondary ions leak to the upstream side of the accelerating electrode (3), and it becomes impossible to obtain further energy. Generation of secondary electrons from the surface of the electrode (3) can be suppressed. Further, since the acceleration of the secondary particles to high energy can be greatly reduced, the heat load on the acceleration electrode (3) can be significantly reduced.

Of course, the present invention is not limited by the above examples. It goes without saying that various aspects are possible for details such as the structure and configuration of the accelerating electrode, the type of magnet and the arrangement thereof.

(Effects of the Invention) As described in detail above, according to the present invention, a large current beam with good convergence can be generated. Also,
The withstand voltage characteristics of the electrostatic accelerator can be improved, and the thermal load on the acceleration electrode can be reduced. The electrostatic accelerator of the present invention is a high-current ion accelerator for ion implantation or surface treatment / surface modification in the range of several hundred keV to several MeV, a large-current negative ion accelerator for plasma heating / current driving of a fusion experimental device, It can be used as a strong neutron source for developing neutron-resistant materials or a high-intensity ion accelerator for material testing.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are a cross-sectional view and a front view, respectively, of an essential part schematically showing an embodiment of the electrostatic accelerator of the present invention. FIGS. 2 (a) and 2 (b) are a main part sectional view and a main part front view schematically showing another example of the present invention. FIG. 3 is a front view of a main part schematically showing another example of the present invention. FIGS. 4 (a), (b) and 5 are a main part sectional view, a main part front view, a traveling direction and a beam, respectively, schematically showing the acceleration action of the charged particle beam by the electrostatic accelerator of the present invention. It is a correlation diagram with a width | variety. 6 and 7 are cross-sectional views schematically showing a conventional electrostatic accelerator and an operation state thereof. DESCRIPTION OF SYMBOLS 1 ... Electrode hole 2 ... Electrostatic acceleration system 3 ... Acceleration electrode 4a, 4b, 4A, 4B ... Quadrupole magnetic field 5,5a, 5b, 5A, 5B ... Magnet 6 ... Charged particle beam 7 ... … Convergence action 8… divergence action 9… orbit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05H 5/03 H05H 7/04

Claims (4)

(57) [Claims] 1. An electrostatic accelerator for electrostatically accelerating a charged particle beam through an electrode hole of an acceleration electrode to which an electrostatic field is applied, wherein a plurality of magnets are provided around the electrode hole of the acceleration electrode. , And a magnetic quadrupole magnetic field is generated in the electrode hole. 2. The electrostatic accelerator according to claim 1, wherein said electrostatic accelerator comprises acceleration electrodes in which electrode plates are arranged in multiple stages. 3. The electrostatic accelerator according to claim 1, wherein quadrupole magnetic fields having opposite polarities are generated in adjacent electrode holes. 4. The electrostatic accelerator according to claim 1, wherein a plurality of magnets are arranged around the electrode holes of the porous acceleration electrode having grid electrode holes.