JPH05283200A - High frequency quadrupole accelerator - Google Patents

Abstract

(57) [Abstract] [Purpose] A high-frequency quadrupole accelerator that allows the resonance frequency to be set freely without increasing the diameter of the acceleration cavity and that the positioning accuracy of the acceleration electrode in the acceleration cavity can be sufficiently secured. I will provide a. [Structure] In the acceleration cavity 21, four acceleration electrodes 23a to 23d are arranged along the axis of the acceleration cavity 21 so as to face each other in a direction orthogonal to the axis. There is. Bent current introducing members 24a, 24b, 25a, 25b are connected to these acceleration electrodes 23a-23d. The acceleration electrodes 23a to 23d are mechanically fixed in the acceleration cavity 21 via the insulating support material 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency quadrupole accelerator for accelerating particles, and more particularly to a high-frequency quadrupole accelerator used for first-stage acceleration such as an ion implanter, a neutral particle injector, a high energy accelerator and the like. ..

[0002]

2. Description of the Related Art There are various types of accelerators that accelerate ions while concentrating them. High frequency quadrupole accelerator is also part 1
Is one.

As one type of this high-frequency quadrupole accelerator, one having a structure as shown in FIG. 4 is known. This high-frequency quadrupole accelerator has a particle entrance 1 at one end.
a, four accelerating electrodes 3a to 3d formed in a rod shape are arranged in an accelerating cavity 2 having a particle emission port 1b on the other end side, and these accelerating electrodes 3a to 3d are respectively connected to a current introducing member 4a. , 4b, 5a, 5b are fixed to a base 6 provided in the acceleration cavity 2.

The acceleration electrodes 3a to 3d are provided along the axis of the acceleration cavity 2 so as to face each other in a direction orthogonal to the axis. The facing surface of each accelerating electrode 3a-3d is actually formed as an uneven surface 7 having periodicity as shown in FIG. And each acceleration electrode 3a-3d
Is a pair of accelerating electrodes 3a and 3d, and accelerating electrodes 3b and 3d.
c and c are arranged so that the uneven surface phase of the accelerating electrodes forming one pair is opposite to the uneven surface phase of the accelerating electrodes forming the other pair.

The current introducing member 4a is a pair of acceleration electrodes 3
The current introducing member 4b is connected to a pair of accelerating electrodes 3b and 3c. Similarly, the current introducing member 5a is connected to the pair of acceleration electrodes 3b and 3c, and the current introducing member 5b is connected to the pair of acceleration electrodes 3a and 3d.

A hole 8 is formed in the peripheral wall of the base 6 and the acceleration cavity 2 between the base ends of the current introducing members 4a and 4b.
Is provided, and this hole 8 is connected to a high frequency source (not shown) via a transmission line 9. The high frequency power supplied from this high frequency source is supplied to the acceleration cavity 2 via the loop antenna 10.

The high-frequency quadrupole accelerator thus constructed accelerates particles according to the following principle. That is, when high-frequency power is supplied into the acceleration cavity 2 through the transmission line 9 and the loop antenna 10, the current supply members 4a, 4 are supplied.
A current is introduced into the acceleration electrodes 3a to 3d via b, 5a and 5b, and the acceleration electric field and the focusing electric field are excited on the central axis of the space surrounded by the acceleration electrodes 3a to 3d. Each acceleration electrode 3a
In 3d, as described above, two accelerating electrodes facing each other form a pair, and each pair is connected to another current introducing member. Therefore, when high frequency power is supplied into the accelerating cavity 2, As shown in FIGS. 6 (a) and 6 (b), an alternating electric field 11 which is inverted every half cycle is excited between two pairs of accelerating electrodes, and this acts as a converging electric field. Further, each accelerating electrode 3a is arranged such that the uneven surface phase of the accelerating electrodes forming one pair is opposite to the uneven surface phase of the accelerating electrodes forming the other pair.
Since ~ 3d is arranged, the alternating electric field 11 shown in FIG. 6 has a component in the extending direction of the accelerating electrodes 3a to 3d, and this acts as an accelerating electric field. Therefore, as shown by the arrow 12 in FIG. 4, when an ion is injected into the acceleration cavity 2 from the particle entrance 1a, the ion is injected into the acceleration electrode 3
It is accelerated while receiving a converging force between a and 3d. The accelerated ions are sent out from the particle emission port 1b.

However, the high frequency quadrupole accelerator constructed as described above has the following problems.
That is, in this high frequency quadrupole accelerator, the acceleration electrodes 3a ...
3d and the current introducing members 4a, 4b, 5a, 5b work as a main part of the resonator, and these determine the resonance frequency. According to a simple model, the approximate resonant frequency f is determined by: 2Z ₁ tan (2πfL / C) = Z ₂ cot (πfS / 2C) (1)

However, Z ₁ is the current introducing members 4a, 4b,
Impedance when the current introducing members 5a and 5b are regarded as one set of lines, Z ₂ is an impedance when the pair of acceleration electrodes 3a and 3b and the pair of acceleration electrodes 3c and 3d are regarded as one set of lines, and L is the current Introductory members 4a, 4b, 5a, 5
b is the length from the base 6, S is the axial length of the acceleration electrodes 3a to 3d, f is the resonance frequency, and C is the speed of light.

As can be seen from the equation (1), in order to lower the resonance frequency f without changing Z ₁ , Z ₂ and S, it is necessary to lengthen L. For this reason, in the high frequency quadrupole accelerator having the structure shown in FIG.
The length L of the current introducing members 4a, 4b, 5a, 5b must be increased, which causes a problem that the diameter of the acceleration cavity 2 is increased.

Therefore, in order to solve this problem, FIG.
As shown in FIG. 2, a high frequency quadrupole accelerator has been devised in which the acceleration electrodes 3a to 3d are supported by a current introducing member 13 formed in a spiral shape (A. Schempp et al.,
IEEE Trans. Nucl. Sci., Vol.NS-30,4 (1983) p.3536
Or RH Stokes et al., IEEE Trans. Nucl. Sci.,
Vol.NS-30,4 (1983) p.3530).

In this high frequency quadrupole accelerator, the acceleration electrode 3
Since the current introducing member 13 is provided in the shape of spirally surrounding a to 3d, the low resonance frequency f can be realized without increasing the diameter of the acceleration cavity.

However, the current introducing member 13 also has a function of mechanically fixing the acceleration electrodes 3a to 3d. Therefore, if the shape is a flexible shape such as a spiral shape, the current introducing member 13 is easily displaced by the weight of the accelerating electrodes 3a to 3d, which causes sufficient positional accuracy of the accelerating electrodes 3a to 3d in the acceleration cavity. It was difficult to raise. In addition, there is a problem in that the manufacturing cost of the current introducing member 13 increases if the positional accuracy is increased.

[0014]

As described above, in the high-frequency quadrupole accelerator including the four accelerating electrodes formed in the rod shape, the length of the current introducing member is increased when the resonance frequency is lowered. As a result, there is a problem that the diameter of the acceleration cavity becomes large. Further, if a spiral current introducing member is used to prevent the diameter of the acceleration cavity from increasing, it is difficult to improve the positional accuracy of the acceleration electrode in the acceleration cavity.

Therefore, the present invention provides a high-frequency quadrupole accelerator in which the resonance frequency can be freely set without increasing the diameter of the accelerating cavity and the positional accuracy of the accelerating electrode in the accelerating cavity can be sufficiently ensured. It is intended to be provided.

[0016]

In order to achieve the above object, in the high frequency quadrupole accelerator according to the present invention, the accelerating electrode is fixed to the accelerating cavity via an insulating support material. That is, the accelerating electrode is fixed by the insulating support material, and the current is introduced into the accelerating electrode by the current introducing member.

[0017]

[Operation] Since the accelerating electrode is fixed in the accelerating cavity by the insulating support material, the accelerating electrode can be fixed with high positional accuracy by using the insulating support material having structural strength. .. Since the insulating support material for fixing the accelerating electrode is provided as described above, it is not necessary to increase the mechanical strength of the current introducing member related to the determination of the resonance frequency. Therefore, the length of the current introducing member can be freely set by extending the current introducing member, for example, in the direction along the accelerating electrode or in a spiral shape in order to lower the resonance frequency.

[0018]

Embodiments will be described below in detail with reference to the drawings. FIG. 1 shows a high frequency quadrupole accelerator according to an embodiment of the present invention.

In the figure, reference numeral 21 indicates an acceleration cavity. A particle entrance 22a is formed at one end of the acceleration cavity 21, and a particle exit 22b is formed at the other end.

Inside the accelerating cavity 21, four accelerating electrodes 23a to 23d having the structure shown in FIG. 5 are arranged similarly to the conventional accelerator (see FIG. 2), and these accelerating electrodes 23a to 23d.
23d are current introducing members 24a, 24b, 25, respectively.
It is electrically and mechanically connected to the respective tip portions 26 of a and 25b. Each tip 26 is fixed to a base 28 provided in the acceleration cavity 21 via an insulating support member 27.

Here, the tip portion 26 of the current introducing member 24a
Is connected to a pair of acceleration electrodes 23a and 23d, and the tip portion 26 of the current introducing member 24b is connected to a pair of acceleration electrodes 23b and 23d.
23c. Similarly, the current introducing member 25a
The tip end portion 26 of the current introducing member 25b is connected to the pair of accelerating electrodes 23b and 23c, and the tip portion 26 of the current introducing member 25b is connected to the pair of accelerating electrodes 23a and 23d.

Each current introducing member 24a, 24b, 25a,
25b respectively extend from the above-mentioned tip portion 26 to the outer side in the radial direction by a predetermined distance, then extend along the axis of the acceleration cavity 21 and then extend again to the outer side in the radial direction to reach the inner surface of the acceleration cavity 21. It is connected to the fixed plate member 29.
That is, each current introducing member 24a, 24b, 25a, 2
5b extends in a key shape from the tip 26 to the base.

A hole 30 is provided in a portion of the peripheral wall of the plate member 29 and the acceleration cavity 21 located between the base ends of the current introducing members 24a and 24b, and the hole 30 has a high frequency through a transmission line 31. Connected to the source 32. This high frequency source 32
The high frequency power given by the above is given into the acceleration cavity 21 via the loop antenna 33.

The acceleration principle of this high-frequency quadrupole accelerator is the same as the conventional one. Then, the resonance frequency f is, as shown in the equation (1), the current introducing members 24a, 24, 25.
It depends on the length L of a and 25b. Acceleration electrodes 23a-23
The axial length S of d, the impedance Z ₁ of the current introduction portion, the lower the resonance frequency f without changing the impedance Z ₂ of the accelerating electrode, the current introducing member 24a, 24, 25
It is necessary to increase the length L of a and 25b.

In this case, the acceleration electrodes 23a to 23d are fixed to the base 28 via the tip portion 26 and the insulating support material 27. That is, the fixing of the accelerating electrodes 23a to 23d into the accelerating cavity 21 can be realized firmly by the insulating support material 27 and with high positional accuracy. Therefore, the tips 26 of the current introducing members 24a, 24b, 25a, 25b are
No mechanical strength is required for the part from the base to the base end. Therefore, without increasing the diameter of the acceleration cavity 21, the portion from the tip portion 26 to the base end portion of the current introducing members 24a, 24b, 25a, 25b is bent in the axial center line direction of the acceleration cavity 21. As a result, the length of this portion can be freely selected, and in the end, the resonance frequency f can be freely set. Figure 3
Shows a high frequency quadrupole accelerator according to another embodiment of the present invention. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

In this embodiment, each current introducing member 24a,
24b, 25a, 25b extend outwardly in the radial direction from the tip portion 26 by a predetermined distance, and thereafter, the acceleration cavity 21
End plates 34a, 3 of the acceleration cavity 21 extending along the axis of the
It is connected to the inner surface of 4b. Even with this configuration, the same effect as that of the above-described embodiment can be obtained.

The present invention is not limited to the above embodiments. That is, in each of the above-described embodiments, the portions other than the tip end portions of the current introducing members 24a, 24, 25a, 25b are bent into a key shape and the length L is selected by this, but no force is applied to this portion. Therefore, it may be formed in a spiral shape or a meandering shape. Besides, various modifications can be made without departing from the scope of the present invention.

[0028]

As described above, according to the present invention,
Since the mechanical fixing function and the current introduction function are demonstrated by separate members, the resonance frequency can be freely set without increasing the diameter of the acceleration cavity, and the position accuracy of the acceleration electrode in the acceleration cavity is high. Can be secured enough.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a high frequency quadrupole accelerator according to an embodiment of the present invention,

2 is a view of the same high-frequency quadrupole accelerator taken along the line AA in FIG. 1 and viewed in the direction of the arrow,

FIG. 3 is a longitudinal sectional view of a high frequency quadrupole accelerator according to another embodiment of the present invention,

FIG. 4 is a perspective view showing a conventional high frequency quadrupole accelerator with a part thereof cut away;

FIG. 5 is a perspective view locally showing an accelerating electrode incorporated in the high frequency quadrupole accelerator;

FIG. 6 is a diagram for explaining an acceleration principle of the high frequency quadrupole accelerator;

FIG. 7 is a view showing an accelerating electrode supporting means that has been conventionally proposed to reduce the resonance frequency.

[Explanation of symbols]

21 ... Acceleration cavity 22a ... Particle entrance 22b ... Particle exit 23a-23d ...
Accelerating electrodes 24a, 24b, 25a, 25b ... Current introducing member 26 ... Tip part 27 ... Insulating support material 33 ... Loop antennas 34a, 34b ...
End plate

Claims (1)

[Claims] 1. An accelerating cavity, a plurality of accelerating electrodes arranged inside the accelerating cavity so as to face each other along the axis of the accelerating cavity, and a current introduction connected to these accelerating electrodes. A high-frequency quadrupole accelerator in which the length of the current-introducing member participates in the resonance frequency, wherein the current-introducing member comprises an insulative support member for fixing each accelerating electrode in the accelerating cavity. High frequency quadrupole accelerator.