JPH07111198A - Rfq linear accelerator - Google Patents

Abstract

PURPOSE:To form an RFQ linear accelerator which is more compact than a conventional split coaxial RFQ linear accelerator in the case where a low resonance frequency zone is required. CONSTITUTION:In an RFQ linear accelerator, an intermediate cylindrical body 12 of a cylindrical form is disposed surrounding four vane electrodes 16, 18 in a beam acceleration axis direction inside a cylindrical casing 10. The intermediate cylindrical body 12 is supported on an inner wall of the cylindrical casing 10 through a conductive stem. Among the four vane electrodes one pair of the vane electrodes facing each other are supported on an inner wall surface of the intermediate cylindrical body 12, and the other pair of the wane electrodes are supported on both end parts of the cylindrical casing 10 in a beam acceleration axis direction.

Description

Detailed Description of the Invention

[0001]

The present invention relates to RFQ (Radio).
Frequency quadrupole linear accelerator, and more specifically, it is capable of accelerating and ejecting ions by generating a high-frequency electric field between four vane electrodes. The present invention relates to an RFQ linear accelerator that can be used for an ion implanter for research or semiconductor manufacturing.

[0002]

2. Description of the Related Art Recently, an RFQ linac capable of accelerating an ion beam and simultaneously accelerating it has been developed.

This RFQ linear accelerator is a quadrupole electrode (four vane electrodes) having a tip end formed in a wave shape in the longitudinal direction in a conductive cylindrical casing whose inside is in a vacuum state.
Are opposed to each other so as to be orthogonal to each other along the beam acceleration axis, and the opposing vane electrodes face each other such that peaks and peaks and valleys and valleys face each other, and the peaks and valleys of adjacent vane electrodes that are separated by 90 degrees are adjacent to each other. It is arranged as follows.

In these four vane electrodes, a pair of vane electrodes facing each other and a pair of vane electrodes facing each other are supplied with high-frequency power so that their signs are different from each other, and a quadrupole When the ion beam is incident on the center surrounded by the electrodes, the ion beam is focused and accelerated by the high-frequency quadrupole electric field, and is emitted from the cylindrical housing as a high-energy ion beam. It will be.

7 and 8 show a conventional RFQ linear accelerator as described above, which is a so-called four-blade type RF accelerator.
An RFQ linac, referred to as a Q linac, is shown, with each opposing vane electrode 102, 102 and 104, 104 arranged 90 degrees out of phase within a conductive cylindrical cavity 100. , This cylindrical cavity 100
To each vane electrode 102, 102 and 104, 104
The cavity resonator is electrically short-circuited between them, and a high-frequency electric field is generated between the vane electrodes 102, 102 and 104, 104 by the high-frequency power supplied from the high-frequency introducing device 106.

In the above-mentioned conventional four-blade type RFQ linear accelerator shown in FIGS. 7 and 8, since a high frequency electric field is generated by using a cavity resonator, there is an advantage that power loss can be suppressed low. Have

However, when such a conventional four-blade RFQ linear accelerator is used for ion implantation for semiconductor manufacturing, etc., a low resonance frequency is generated depending on the ion species used and the required ion beam energy. Although it may be required, there is a problem that when such a low resonance frequency is required, the size of the cavity resonator becomes extremely large, which is disadvantageous in terms of space.

Further, since the size of the entire apparatus is increased in this way, the manufacturing cost thereof is also high, and there is a problem that it is technically difficult to realize.

Therefore, in order to solve the above-mentioned various problems, for example, as shown in FIGS. 9 and 10, each of the opposed vane electrodes 12 is disposed inside the cylindrical cavity 120.
A split coaxial type RFQ linear accelerator in which 2, 122 and 124, 124 are arranged in a split type has been proposed.

In the above-mentioned conventional split coaxial type RFQ linear accelerator, a pair of vane electrodes 122, 1 facing each other are provided.
22 is supported on the upper and lower portions of the cylindrical cavity 120 via the stems 126, 126, respectively, and the other pair of opposite vane electrodes 124, 124 are supported on both end surfaces 120a, 120a of the cylindrical cavity 120 to introduce a high frequency wave. Device 128
The high frequency power supplied from the Vane electrode 12
It is configured to generate a high frequency electric field between 2, 122 and 124, 124.

Then, the conventional split coaxial type RFQ described above is used.
In the linear accelerator, when a high frequency quadrupole electric field is generated between the vane electrodes 122, 122 and 124, 124, A → B → is generated between the cylindrical cavity 120 and the stems 126, 126 supporting the vane electrodes 122, 122. A high-frequency current flows in the C → D direction, and the stems 126, 1
26 and Vane electrodes 122, 122 and 124,
A magnetic field is generated around 124.

FIG. 11 is a sectional coaxial RFQ linac shown in FIGS. 9 and 10 in which the capacitance between the vane electrodes 122, 122 and 124, 124 is C _V , and the stems 126, 126. The inductance around L _S , the vane electrodes 122, 12
2 and 124, the inductance around 124, L _T
The equivalent resonance circuit is shown.

From the equivalent resonance circuit of FIG. 11, the resonance frequency F of this cavity resonator is given by F = 1 / [2π × {C _V (L _S + L _T )} ^1/2 ].

Therefore, in the split coaxial type RFQ linear accelerator shown in FIGS. 9 and 10, the inductance is increased as compared with the conventional four-blade type RFQ linear accelerator shown in FIGS. 7 and 8. Therefore, the resonance frequency can be lowered as compared with the conventional four-blade type RFQ linear accelerator of the same size.
It was possible to suppress the size increase of the cavity resonator.

[0015]

However, in the conventional split coaxial type RFQ linear accelerator described above, the resonance frequency can be reduced as compared with the conventional four-blade type RFQ linear accelerator. , For example, 20M
There is a problem in that the diameter dimension and the length of the cavity resonator may become large if an attempt is made to obtain a resonance frequency below HZ.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a conventional split coaxial type RFQ linear accelerator when a low resonance frequency region is required. The present invention aims to provide an RFQ linear accelerator that can be further miniaturized.

[0017]

In order to achieve the above object, the RFQ linear accelerator according to the present invention has a distal end portion of which is corrugated in the longitudinal direction in a conductive cylindrical casing whose inside is in a vacuum state. The four vane electrodes formed in the above are opposed to each other so as to be orthogonal to each other along the beam acceleration axis in the cylindrical casing, and the vane electrodes facing each other among the four vane electrodes are peaks and peaks or valleys. Among the four vane electrodes, the vane electrodes adjacent to each other among the four vane electrodes are arranged so that the peaks and the valleys are adjacent to each other, and the tip ends of the four vane electrodes are formed in the corrugated shape. In an RFQ linear accelerator for converging and accelerating charged particles incident on the enclosed beam accelerating axis region by a high frequency electric field and emitting the charged particles, the four vane electrodes are provided in the cylindrical casing. A conductive intermediate cylindrical body surrounding along the fast axis direction are arranged, while supporting on the inside wall of the tubular casing through the conductive stem of the intermediate cylindrical body, the 4
Among the vane electrodes, one pair of vane electrodes which are opposed to each other are supported on the inner wall surface of the intermediate cylinder, and the other pair of vane electrodes are opposed to each other in the beam acceleration axis direction of the cylindrical casing. It is designed to be supported by the department.

[0018]

The RF according to the present invention constructed as described above
The Q linear accelerator uses a second pair of inner cylinders as inner conductors and a cylindrical casing as outer conductors around a first coaxial line having the other pair of vane electrodes as inner conductors and intermediate cylinders as outer conductors. It has a folded coaxial type structure in which the coaxial lines are connected so as to be folded.A high frequency electric field is generated in the beam acceleration axis region surrounded by each vane electrode, and the inside of the intermediate cylindrical body is surrounded by the vane electrode. A magnetic field is generated in the magnetic field, and this magnetic field induces a high-frequency current inside the other pair of vane electrodes and the intermediate cylinder.

The high-frequency current flows through the inner surface of the cylindrical casing, the surface of the stem, and the outer surface of the intermediate cylinder, and generates a magnetic field around the intermediate cylinder and around the stem.

Therefore, in the RFQ linear accelerator having the folded coaxial type structure according to the present invention, the conventional split coaxial type RF is used.
Compared with the case of the Q linear accelerator, the capacitance between the other pair of vane electrodes and the intermediate cylinder, and the inductance around the other pair of vane electrodes are added, and the size is about the same. Since a resonance frequency lower than that of the conventional split coaxial type RFQ linear accelerator can be obtained, a small RFQ linear accelerator can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the RFQ linear accelerator according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross sectional view showing a first embodiment of an RFQ linear accelerator according to the present invention, FIG. 2 is a vertical sectional view of FIG. 1, and FIG. 3 is an equivalent of the RFQ linear accelerator according to the present invention. FIG. 3 is a resonance circuit diagram, in which a conductive intermediate cylindrical body 12 is arranged inside a cylindrical casing 10 made of a conductive cylindrical cavity whose inside is in a vacuum state, and the intermediate cylindrical body 12 is a stem 14; , 14 are supported on the inner side wall of the tubular casing 10.

Inside the intermediate cylinder 12, four vane electrodes (quadrupole electrodes) 16, 16 and 18, 18 each having a corrugated end portion in the longitudinal direction are arranged along the beam acceleration axis. The vane electrodes 16, 16 and 18, 18 arranged so as to be orthogonal to each other and facing each other have peaks and peaks or valleys and valleys facing each other, and have 90
The adjacent vane electrodes 16 and 16 spaced apart from each other and the vane electrodes 18 and 18 are arranged such that peaks and valleys are alternately adjacent to each other.

Then, these Vein electrodes 16, 16
One of the pair of vane electrodes 16 and 16 facing each other is supported by being electrically short-circuited to the inner wall surface of the intermediate cylindrical body 12, and the other pair of vane electrodes 18 and 18 facing each other. Is supported by both end surfaces 10a of the cylindrical casing 10 in the axial direction, thereby forming a cavity resonator.

Further, a high frequency introducing device 20 is installed at a predetermined position of the cylindrical casing 10, and the high frequency introducing device 20 allows the pair of vane electrodes 1 facing each other.
6 and 16 and the other opposing vane electrodes 18 and 18,
High-frequency power is applied so that the signs are different from each other.

Here, in the RFQ linear accelerator configured as described above, the left and right vane electrodes 18, 18 arranged in the horizontal direction in the figure are used as inner conductors, and the intermediate cylindrical body 12 is used as an outer conductor. A second coaxial line having an intermediate conductor 12 as an inner conductor and a tubular casing 10 as an outer conductor is connected around the coaxial line so as to be folded back. In the following description, the RFQ linear accelerator according to the present invention having such a structure will be referred to as a “folded coaxial RFQ linear accelerator”.

Next, the operating principle of the folded coaxial type RFQ linear accelerator configured as described above will be described.

First, each vane electrode 16, 16 and 1
A high-frequency electric field is generated in the beam acceleration axis region surrounded by 8 and 18, and a magnetic field is generated inside the intermediate cylindrical body 12 so as to surround the vane electrodes 18 and 18. This magnetic field induces a high frequency current inside the vane electrodes 18, 18 and the intermediate cylindrical body 12.

This high frequency current is applied to the inner surface of the cylindrical casing 10,
Flowing on the surfaces of the stems 14, 14 and the outer surface of the intermediate tubular body 12,
A magnetic field is generated around the intermediate cylinder 12 and around the stems 14, 14.

FIG. 3 shows a folded coaxial type R according to the present invention.
In the FQ linear accelerator, the capacitance between each of the vane electrodes 16, 16 and 18, 18 is C _V1 , the capacitance between the left and right vane electrodes 18, 18 and the intermediate cylindrical body 12 is C _V2 ,
An equivalent resonance circuit is shown where the inductance around the stems 14 and 14 is L _S , the inductance around the intermediate tubular body 12 is L _T1 , and the inductance around the left and right vane electrodes 18 and 18 is L _T2 . .

From the equivalent resonance circuit of FIG. 3, the resonance frequency F in the folded coaxial RFQ according to the present invention is F = 1 / [2π × {(C _V1 + C _V2 ) (L _S + L _T1 +
L _T2 )} ^1/2 ].

Therefore, the folded coaxial type RF according to the present invention
In the Q linear accelerator, as compared with the case of the conventional split coaxial type RFQ linear accelerator, the capacitance C _V2 between the vane electrodes 18 and 18 and the intermediate cylindrical body 12, and the vane electrode 18,
Since the inductance L _T2 around 18 is added, even when a low resonance frequency is required, the resonance frequency F can be further reduced in the same size as the conventional split coaxial type RFQ linear accelerator. However, a small RFQ linear accelerator can be obtained.

FIG. 4 and FIG. 5 are a horizontal sectional view and a vertical sectional view, respectively, showing a second embodiment of the RFQ linear accelerator according to the present invention, and the same or corresponding constitution as that of the first embodiment is the same. By indicating with the sign of
Detailed description of the configuration and operation will be omitted.

In the second embodiment, the side wall portion of the cylindrical casing 10 made of a conductive cylindrical cavity whose inside is evacuated has a coaxial casing so as to communicate with the inside of the cylindrical casing 10. The body 22 is installed, and the conductive intermediate tubular body 12 disposed inside the tubular casing 10 is supported by the stem 14 on the bottom wall surface through the central portion of the coaxial casing 22.

A movable short-circuit plate 24 surrounding the stem 14 is provided inside the coaxial housing 22, and the movable short-circuit plate 24 is provided with a longitudinal axis of the stem 14 via an operating arm 26 by a driving device (not shown). It is installed so that it can slide in any direction.

Therefore, the movable short-circuit plate 24 in the coaxial housing 22 is
By sliding up and down to change the electrical length of the stem 14, the inductance L _S around the stem 14 is changed.
Changes, the resonance frequency of the cylindrical casing 10 can be made variable.

That is, the RFQ which is the first embodiment of the present invention.
A coaxial casing 22 is installed on the side wall of the linear accelerator so as to communicate with the inside of the cylindrical casing 10, and a movable short-circuit plate 24 surrounding the stem 14 is provided inside the coaxial casing 22. By sliding the movable short-circuit plate 24 in the body 22 up and down to change the electrical length of the stem 14,
Since the inductance L _S around is changed, the resonance frequency of the cylindrical casing 10 can be changed.

Here, in the RFQ linear accelerator according to the second embodiment described above, the movable short-circuit plate 24 in the coaxial housing 22 installed around the stem 14 changes the electrical length of the stem 14. Since the resonance frequency can be varied, an RFQ linear accelerator capable of varying the resonance frequency can be obtained by appropriately selecting the sizes of the coaxial housing 22 and the movable short-circuit plate 24 according to the required resonance frequency. Obtainable.

As for the structure for varying the resonance frequency, the movable short-circuit plate 24 is arranged in the coaxial housing 22 communicating with the cylindrical housing 10 as shown in the second embodiment. In addition to the above configuration, a so-called movable panel or a movable box may be arranged in the cylindrical casing 10 or the coaxial casing 22.

While the number of stems 14 is two in the first embodiment, and the number of stems 14 is one in the second embodiment, the number and mounting positions of the stems 14 are not limited to this. However, the number of stems 14 and the mounting positions thereof may be appropriately selected according to the volumes of the tubular casing 10 and the intermediate tubular body 12 and the magnitude of high-frequency power.

Further, the intermediate tubular body 12 does not have to be located at the center of the tubular casing 10, but may be at a position eccentric from the center of the tubular casing 10.

Furthermore, the tubular casing 10 and the intermediate tubular body 12
The cross section such as is not limited to a cylindrical shape, and even if it is a rectangular cylinder or a polygonal cylinder, there is no difference in electrical action.

FIG. 6 is a partially cutaway perspective view showing an essential part of an RFQ linear accelerator according to the present invention applied to an actual machine. The inside of the tube is made of a conductive rectangular tube-shaped cavity. Inside the cylindrical casing 30, a conductive intermediate cylindrical body 32 is arranged, and the bottom surface of the intermediate cylindrical body 32 is a support insulator 34,
While being supported by the bottom surface portion of the tubular housing 30 via 34, the upper portion of the intermediate tubular body 32 is supported by the stem 36 on the upper surface portion of the tubular housing 30.

Inside the intermediate cylindrical body 32, four vane electrodes (quadrupole electrodes) 38, 38 and 40, 40 each having a distal end formed in a wave shape in the longitudinal direction are arranged along the beam acceleration axis. Are arranged so as to be orthogonal to each other.

Then, these vane electrodes 38, 38
One of the pair of vane electrodes 38, 38, which is one of the pair of vane electrodes 40, 40, is supported by the inner wall surface of the intermediate tubular body 32, and the other pair of the vane electrodes 40, 40, which are the other pair of opposing vane electrodes 38, 40, It is supported on both end faces 30a, 30a in the direction, and is adapted to be supplied with high-frequency power having different signs.

A movable short-circuit plate 42 is provided around the stem 36, and the movable short-circuit plate 42 is vertically slidable along the stem 36 by a driving device (not shown).

Therefore, the molding dimensions of the cylindrical casing 30 are 70 cm in length, 70 cm in width, and 150 cm in length, the thickness of the movable short-circuit plate 40 is 7.5 cm, and the movable short-circuit plate 42 and the surface of the intermediate cylindrical body 32. When the distance is set to allow sliding in the stroke range of 2 cm to 35 cm, the maximum distance 35c
A resonance frequency of 16 MHz is obtained at m, and the minimum interval is 2c.
A resonance frequency of 40 MHz was obtained in m. Then, the charge q of the charged particles at this time could be accelerated to a maximum value of 450 KeV / q.

Thus, the RF according to the present invention shown in FIG.
According to the Q linear accelerator, the resonant frequency is 16 MHz by sliding the movable short-circuit plate 42 along the stem 36.
It can be arbitrarily changed in the range of -40 MHz.

In the RFQ linac described above, when the stem is attached to one side, the vertical or horizontal symmetry of the electrode arrangement in the cavity is broken, and therefore the electric field in the vane electrode is broken. The symmetry may be poor. However, in such a case, if the cap-shaped electrode is attached from the front and rear surfaces of the cylindrical casing so as to wrap the intermediate cylindrical body, the symmetry of the electric field in the vane electrode can be considerably restored. This will be described in detail below with reference to FIGS. 12 to 15.

In the RFQ linear accelerator shown in FIG.
The arrangement of the vane electrodes 38, 38 and 40, 40 in the tubular casing 30 is vertically asymmetrical. Therefore, when the resonance frequency becomes high, the symmetry of the electric field in the vane electrodes 38, 38, 40, 40 is reduced. become worse. Intermediate cylinder 3
FIG. 13 shows an example of calculation of the electric field at a location (a portion indicated by a broken line in FIG. 11) slightly displaced from the symmetry axis in the horizontal direction near the exit of No.

In FIG. 13, the horizontal axis is the vertical position (scale is in meters), and the vertical axis is the horizontal component of the electric field. Originally, the central portion should be horizontal as shown by the broken line, but in the calculation example in FIG. 13, it is inclined as shown by the solid line.

However, as shown in FIGS. 14 to 15, one end is provided with an end face 30a in the axial direction of the cylindrical casing 30,
When the pair of tubular cap-shaped electrodes 50, 50 respectively supported by 30a are attached so as to wrap both end portions 32a of the intermediate tubular body 32, the central portion becomes horizontal as shown by the broken line in FIG.

[0053]

Since the present invention is constructed as described above, it has the following effects.

Four vane electrodes each having a corrugated top end in a lengthwise direction are provided in a conductive cylindrical casing whose inside is in a vacuum state, and are orthogonal to each other along the beam acceleration axis in the cylindrical casing. Of the four vane electrodes, the vane electrodes facing each other have peaks and peaks or valleys and valleys facing each other, and among the four vane electrodes, adjacent vane electrodes have peaks and valleys. Place them next to each other,
In an RFQ linear accelerator that converges and accelerates charged particles entering a beam acceleration axis region surrounded by the corrugated tips of four vane electrodes by a high frequency electric field, A conductive intermediate cylinder that surrounds the four vane electrodes along the beam acceleration axis direction is arranged, and the intermediate cylinder is supported on the inner wall of the cylindrical casing via the conductive stem. Of the Vane electrodes,
Since one pair of opposing vane electrodes is supported on the inner wall surface of the intermediate cylindrical body, and the other opposing pair of vane electrodes is supported on both ends of the cylindrical casing in the beam acceleration axis direction. In comparison with the case of the split coaxial type RFQ linear accelerator of FIG. 1, the capacitance between the other pair of opposite vane electrodes and the intermediate cylinder, and the inductance around the other pair of opposite vane electrodes are added. It will be.

Therefore, according to the present invention, even when a low resonance frequency is required, the resonance frequency can be further reduced in the same size as the conventional split coaxial type RFQ linear accelerator. A small RFQ linac can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of an RFQ linear accelerator according to the present invention.

FIG. 2 is a vertical sectional view of the RFQ linear accelerator shown in FIG.

FIG. 3 is an equivalent resonant circuit diagram of an RFQ linear accelerator according to the present invention.

FIG. 4 is a cross-sectional view showing a second embodiment of the RFQ linear accelerator according to the present invention.

5 is a vertical cross-sectional view of the RFQ linear accelerator shown in FIG.

FIG. 6 is a partially cutaway perspective view showing a main part when an RFQ linear accelerator according to the present invention is applied to an actual machine.

FIG. 7 is a cross-sectional view of a conventionally used four-blade RFQ accelerator.

8 is a vertical cross-sectional view of the four-blade RFQ linear accelerator shown in FIG.

FIG. 9 is a cross-sectional view showing a conventional split coaxial type RFQ accelerator.

10 is a vertical cross-sectional view of the split coaxial RFQ accelerator of FIG.

FIG. 11 is an equivalent resonance circuit diagram in a conventional split coaxial RFQ accelerator.

FIG. 12 is a schematic cross-sectional view showing a position where an electric field is calculated in the RFQ linear accelerator shown in FIG.

13 is a graph showing the electric field distribution at the calculated position of the electric field shown in FIG. 12 of the RFQ linear accelerator shown in FIG.

14 is a schematic cross-sectional view showing a state in which a cap-shaped electrode is attached to the RFQ linear accelerator shown in FIG.

15 is a schematic vertical sectional view showing a state in which a cap-shaped electrode is attached to the RFQ linear accelerator shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cylindrical housing 10a End surface 12 Intermediate cylinder 14 Stem 16 Vein electrode 18 Vein electrode 20 High frequency introduction device 22 Coaxial housing 24 Movable short-circuit plate 26 Working arm 32 Intermediate cylinder 32a End 50 Cap-shaped electrode

Front page continuation (72) Yoshitoshi Miyazawa, 2-1, Hirosawa, Wako-shi, Saitama, RIKEN (72) Inventor Masatake Itami 2-2-1, Hirosawa, Wako, Saitama (72) Inventor Toshiya Chiba, 2-1, Hirosawa, Wako-shi, Saitama, RIKEN (72) Inventor, Yasushige Yano 2--1, Hirosawa, Wako, Saitama, Japan

Claims (3)

[Claims] 1. A four-dimensional Vane electrode having a corrugated end portion in a lengthwise direction is provided in a conductive cylindrical casing whose inside is evacuated, and is connected to a beam accelerating shaft in the cylindrical casing. The vane electrodes facing each other are orthogonal to each other, and the vane electrodes facing each other among the four vane electrodes have peaks and peaks or valleys and valleys facing each other, and the vane electrodes adjacent to each other among the four vane electrodes are The charged particles, which are arranged so that the peaks and the valleys are adjacent to each other, are incident on the beam acceleration axis region surrounded by the wave-shaped tips of the four vane electrodes are converged by a high-frequency electric field. In the RFQ linear accelerator that accelerates and emits, an electrically conductive intermediate cylinder that surrounds the four vane electrodes along the beam acceleration axis direction is arranged in the cylindrical housing, and the intermediate cylinder is Conductive Of the four vane electrodes, one pair of vane electrodes facing each other is supported on the inner wall surface of the intermediate tubular body, and the other of the vane electrodes is supported by the inner wall surface of the intermediate tubular body. An RFQ linear accelerator characterized in that a pair of vane electrodes are supported on both ends of the cylindrical casing in the beam acceleration axis direction. 2. The RFQ linear accelerator according to claim 1, further comprising a variable device that varies the electrical length of the stem that supports the intermediate tubular body on the inner wall of the tubular casing. 3. The RFQ linear accelerator according to claim 1, further comprising a cap-shaped electrode that encloses both ends of the intermediate cylinder.