JP2008166093A - Linear ion accelerator, and ion acceleration system - Google Patents

Linear ion accelerator, and ion acceleration system Download PDF

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JP2008166093A
JP2008166093A JP2006353846A JP2006353846A JP2008166093A JP 2008166093 A JP2008166093 A JP 2008166093A JP 2006353846 A JP2006353846 A JP 2006353846A JP 2006353846 A JP2006353846 A JP 2006353846A JP 2008166093 A JP2008166093 A JP 2008166093A
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JP4656055B2 (en
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Kazuo Yamamoto
和男 山本
Hirobumi Tanaka
博文 田中
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Mitsubishi Electric Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To obtain a linear ion accelerator capable of accelerating ion beams more efficiently, and to provide an ion acceleration system. <P>SOLUTION: The linear ion accelerator is provided with a plurality of drift tubes 2 installed in a resonance cavity 1 along the acceleration direction of ion beams, a pair of ridges 4 installed on the inner wall of the resonance cavity, and stems 3 which support the plurality of drift tubes 2 by connecting alternately to the pair of ridges 4, and accelerates ion beams entering into the resonance cavity 1 by generating accelerating electric field between the plurality of drift tubes 2 by a magnetic field generated along the acceleration direction in the resonance cavity 1. The diameter of the resonance cavity end part on the ion beam incidence side is larger than the diameter of the central part of the resonance cavity, and these large diameter portions 11, 12 are installed from the resonance cavity end to the position where the pair of ridges 4 are installed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

この発明は、炭素や陽子等のイオンビームを高エネルギーに加速する線形イオン加速器、特にＩＨ（Ｉｎｔｅｒｄｉｇｉｔａｌ−Ｈ）型線形加速器に関するものである。また、この線形イオン加速器を用いたイオン加速システムに関するものである。   The present invention relates to a linear ion accelerator that accelerates an ion beam of carbon, protons, or the like to high energy, and more particularly to an IH (Interdigital-H) type linear accelerator. The present invention also relates to an ion acceleration system using this linear ion accelerator.

従来のＩＨ型線形加速器は、共振空胴内に設置される複数のドリフトチューブ間に発生する加速電場を使用してイオンビームを高エネルギーに加速する。
ＩＨ型線形加速器の電磁場発生モードはビーム加速方向に磁場が発生するＴＥモードであり、間接的にドリフトチューブ間に電場を発生させるが、ＴＥモードで励起された加速電場は共振空胴端部でゼロ、共振空胴中央部でピークになる山形の電場分布になる。このような電場分布では、中央部でのピーク電場により放電限界が決められるため、発生電場を効率よく利用できない。したがって、発生電場を効率的に使用するためには、共振空胴内に均一な電場分布を形成する必要がある。 A conventional IH type linear accelerator accelerates an ion beam to high energy by using an acceleration electric field generated between a plurality of drift tubes installed in a resonant cavity.
The electromagnetic field generation mode of the IH type linear accelerator is a TE mode in which a magnetic field is generated in the beam acceleration direction, and an electric field is indirectly generated between the drift tubes. The acceleration electric field excited in the TE mode is at the end of the resonant cavity. Zero, a mountain-shaped electric field distribution that peaks at the center of the resonant cavity. In such an electric field distribution, since the discharge limit is determined by the peak electric field at the center, the generated electric field cannot be used efficiently. Therefore, in order to use the generated electric field efficiently, it is necessary to form a uniform electric field distribution in the resonant cavity.

従来のＩＨ型線形加速器では、電場分布調節機構として板状のリッジを設置して共振空胴内の電場分布の均一化を達成している。リッジはドリフトチューブを支持するステムを支持する土台に位置し、加速方向に発生する磁場の流れを共振空胴端部まで導く役割がある。また、エンドリッジチューナーと呼ばれるリッジの端部を切り欠く方法を用いて、均一電場分布を形成するようにしている（例えば、非特許文献１参照。）。   In the conventional IH type linear accelerator, a plate-like ridge is installed as an electric field distribution adjusting mechanism to achieve uniform electric field distribution in the resonant cavity. The ridge is located on the base that supports the stem that supports the drift tube, and has a role of guiding the flow of the magnetic field generated in the acceleration direction to the end of the resonant cavity. Further, a uniform electric field distribution is formed by using a method of notching an end portion of a ridge called an end ridge tuner (see, for example, Non-Patent Document 1).

一方、他機種ではあるが、ＲＦＩ（Ｒｆ Ｆｏｃｕｓｅｄ Ｉｎｔｅｒｄｉｇｉｔａｌ）型線形加速器では、リッジを用いずに共振空胴の空胴径を段階的に、もしくはコーン状に変化させて電場分布を均一化している。また、共振空胴端部の空胴径を拡大することで共振空胴端部での電場強度を増加させ、加速方向に亘って共振空胴内の電場分布の均一化を達成している（例えば、非特許文献２参照。）。   On the other hand, although it is another model, in the RFI (Rf Focused Interdigital) type linear accelerator, the electric field distribution is made uniform by changing the cavity diameter of the resonant cavity stepwise or conically without using a ridge. . In addition, by increasing the cavity diameter at the end of the resonant cavity, the electric field strength at the end of the resonant cavity is increased, and the electric field distribution in the resonant cavity is made uniform over the acceleration direction ( For example, refer nonpatent literature 2.).

Ｙ．Ｉｗａｔａ，ｅｔ ａｌ．「Ａｌｔｅｒｎａｔｉｎｇ−ｐｈａｓｅ−ｆｏｃｕｓｅｄ ＩＨ−ＤＴＬ ｆｏｒ ａｎ ｉｎｊｅｃｔｏｒ ｏｆ ｈｅａｖｙ−ｉｏｎ ｍｅｄｉｃａｌ ａｃｃｅｌｅｒａｔｏｒｓ」（Ｎｕｃｌｅａｒ Ｉｎｓｔｒｕｍｅｎｔｓ ａｎｄ Ｍｅｔｈｏｄｓ ｉｎ Ｐｈｙｓｉｃｓ Ｒｅｓｅａｒｃｈ Ｓｅｃｔｉｏｎ Ａ，５６９（２００６）６８５）Y. Iwata, et al. “Alternating-phase-focused IH-DTL for an injector of heavy-ion medical accelerators” (Nuclear Instruments and Methods in Physics 6) Ｄ．Ａ．Ｓｗｅｎｓｏｎ ｅｔ．ａｌ．「Ｓｔａｔｕｓ ｏｆ ｔｈｅ ＲＦＩ Ｌｉｎａｃ Ｐｒｏｔｏｔｙｐｅ」（Ｐｒｏｃ． ｏｆ ＬＩＮＡＣ Ｃｏｎｆ．，Ｌｕｂｅｃｋ，Ｇｅｒｍａｎｙ，２００４，ｐ．３２１）D. A. Swenson et. al. “Status of the RFI Linac Prototype” (Proc. Of LINAC Conf., Lubeck, Germany, 2004, p.321)

従来のＲＦＩ型線形加速器では、共振空胴の空胴径を変化させて電場強度の均一化を図っているが、リッジを備えていないのでステム間に磁場が回りこむ影響があり、共振空胴中央部での電場分布の均一性を崩す場合があった。
また、従来のＩＨ型線形加速器では、ＴＥモードで励起された加速電場分布を調節する機構としてリッジが用いられているが、このようなリッジを設けたＩＨ型線形加速器は、磁場が共振空胴端部まで行き渡るため共振空胴中央部において均一の電場分布を発生させることが可能となる。しかしながら、共振空胴端部領域における電場は微量しか発生せず、その領域においてビームに与える加速力、収束力が弱くなる。そのため、重い粒子ビームを加速する場合や粒子ビームの電流量が小さい場合には大きな問題はないが、例えば陽子等の軽い粒子ビームを加速する場合や大電流ビームを加速する場合には、空間電荷効果によりビームを多く失う問題があった。特に、ＡＰＦ（Ａｌｔｅｒｎａｔｉｎｇ Ｐｈａｓｅ Ｆｏｃｕｓｅｄ）法のようなビーム収束機器を要しない収束法により加速を行うと、従来のＩＨ型線形加速器ではビームを多く失う問題があった。 In the conventional RFI type linear accelerator, the electric field strength is made uniform by changing the cavity diameter of the resonant cavity, but since there is no ridge, there is an effect that a magnetic field wraps around between the stems, and the resonant cavity In some cases, the uniformity of the electric field distribution at the center was lost.
In the conventional IH type linear accelerator, a ridge is used as a mechanism for adjusting the distribution of the acceleration electric field excited in the TE mode. In the IH type linear accelerator provided with such a ridge, the magnetic field is a resonant cavity. Since it reaches to the end, it is possible to generate a uniform electric field distribution in the center of the resonant cavity. However, only a small amount of electric field is generated in the resonance cavity end region, and the acceleration force and convergence force applied to the beam in that region are weakened. Therefore, when accelerating a heavy particle beam or when the current amount of the particle beam is small, there is no big problem, but for example when accelerating a light particle beam such as a proton or accelerating a large current beam, the space charge There was a problem of losing many beams due to the effect. In particular, when acceleration is performed by a convergence method that does not require a beam convergence device such as an APF (Alternating Phase Focused) method, the conventional IH linear accelerator has a problem of losing many beams.

この発明は、上記のような問題点を解決するためになされたものであり、リッジを設けたＩＨ型の線形イオン加速器において、共振空胴の加速方向に亘ってより均一な電場分布を達成することを目的とし、軽い粒子ビームを加速する場合や大電流ビームを加速する場合においても、より効率的に加速することが可能なＩＨ型線形加速器を得ることを目的としている。
また、このような線形イオン加速器を用いて、イオンビームをより効率的に加速することが可能なイオン加速システムを得ることを目的としている。 The present invention has been made to solve the above-described problems, and achieves a more uniform electric field distribution in the acceleration direction of the resonant cavity in the IH type linear ion accelerator provided with a ridge. Therefore, an object of the present invention is to obtain an IH type linear accelerator capable of accelerating more efficiently even when a light particle beam is accelerated or a large current beam is accelerated.
Another object of the present invention is to obtain an ion acceleration system capable of accelerating an ion beam more efficiently using such a linear ion accelerator.

この発明に係わる線形イオン加速器は、イオンビームの加速方向に沿って共振空胴内に設置された複数のドリフトチューブ、共振空胴内壁に設置された一対のリッジ、および上記複数のドリフトチューブを上記一対のリッジに交互に接続して支持するステムを備え、上記共振空胴内に上記加速方向に沿って発生させた磁場により上記複数のドリフトチューブ間に加速電場を発生させて、上記共振空胴内に入射する上記イオンビームを加速する線形イオン加速器において、イオンビーム入射側の共振空胴端部の空胴径は、上記共振空胴中央部の空胴径より大きく、かつこの径拡大部は、上記共振空胴端より上記一対のリッジが設けられている個所に至る位置まで設けられているものである。   A linear ion accelerator according to the present invention includes a plurality of drift tubes installed in a resonance cavity along an acceleration direction of an ion beam, a pair of ridges installed on an inner wall of the resonance cavity, and the plurality of drift tubes. A stem that is alternately connected to and supported by a pair of ridges, and an accelerating electric field is generated between the plurality of drift tubes by a magnetic field generated in the accelerating direction along the accelerating direction; In the linear ion accelerator for accelerating the ion beam incident therein, the cavity diameter of the resonance cavity end portion on the ion beam incident side is larger than the cavity diameter of the resonance cavity central portion, and this diameter enlarged portion is , And the position from the resonance cavity end to the position where the pair of ridges are provided.

また、この発明に係わるイオン加速システムは、イオン源、該イオン源から出射するイオンビームを加速する前段加速器、および該前段加速器から出射するイオンビームを加速する後段加速器を備えたイオン加速システムにおいて、上記後段加速器として、本発明の上記線形イオン加速器を用いたものである。   Further, an ion acceleration system according to the present invention includes an ion source, a front-stage accelerator that accelerates an ion beam emitted from the ion source, and a rear-stage accelerator that accelerates an ion beam emitted from the front-stage accelerator. As the post-stage accelerator, the linear ion accelerator of the present invention is used.

この発明によれば、リッジを設けた線形イオン加速器において、共振空胴内の加速方向に沿ってより均一な電場分布を達成することが可能となり、より効率的に加速することが可能となる効果がある。   According to the present invention, in the linear ion accelerator provided with the ridge, it is possible to achieve a more uniform electric field distribution along the acceleration direction in the resonance cavity, and it is possible to accelerate more efficiently. There is.

また、この発明によれば、イオン加速システムにおいて、イオン源からの出力ビームを本発明の上記線形イオン加速器を用いて効率的に加速するので、コンパクトなイオン加速システムを構築でき、かつビーム電流量に依存しないイオン加速システムとすることができる。   Further, according to the present invention, in the ion acceleration system, the output beam from the ion source is efficiently accelerated using the linear ion accelerator of the present invention, so that a compact ion acceleration system can be constructed and the beam current amount can be increased. The ion acceleration system can be made independent of.

実施の形態１．
図１は本発明の実施の形態１によるＩＨ型線形イオン加速器を示す断面構成図である。共振空胴１内には、ビーム加速方向（Ｚ方向）に沿って、加速電場を発生するための複数のドリフトチューブ２が設置されている。ドリフトチューブ２を支持するステム３は、加速方向に垂直な方向（Ｙ方向）に配列し、共振空胴内壁に設置された一対のリッジ４に交互に接続されている。
電場分布調節機構であるリッジ４の端部は、均一電場分布を達成するように調節するエンドリッジチューナー５が設けられている。エンドリッジチューナー５は、リッジ４を切り欠くことにより構成されている。
低エネルギー側エンドドリフトチューブ６は、ステム３ではなく、ビーム入射側となる低エネルギー側共振空胴端板７により支持され、同様に高エネルギー側エンドドリフトチューブ８は、ビーム出射側となる高エネルギー側共振空胴端板９に支持される。
低エネルギー側エンドドリフトチューブ６と隣接するドリフトチューブ２との間には加速ギャップ１０があり、以下、ドリフトチューブ２の個数に応じ、加速ギャップ数も増えていく。複数のドリフトチューブ間の加速ギャップを、低エネルギー側から順に加速ギャップ１０ａ、加速ギャップ１０ｂ、加速ギャップ１０ｃ・・・と表記する。 Embodiment 1 FIG.
FIG. 1 is a sectional configuration diagram showing an IH type linear ion accelerator according to Embodiment 1 of the present invention. A plurality of drift tubes 2 for generating an accelerating electric field are installed in the resonance cavity 1 along the beam acceleration direction (Z direction). The stems 3 that support the drift tube 2 are arranged in a direction perpendicular to the acceleration direction (Y direction) and are alternately connected to a pair of ridges 4 installed on the inner wall of the resonant cavity.
An end ridge tuner 5 that adjusts so as to achieve a uniform electric field distribution is provided at an end of the ridge 4 that is an electric field distribution adjusting mechanism. The end ridge tuner 5 is configured by cutting out the ridge 4.
The low energy side end drift tube 6 is supported not by the stem 3 but by the low energy side resonance cavity end plate 7 on the beam incident side. Similarly, the high energy side end drift tube 8 has a high energy on the beam emission side. It is supported by the side resonance cavity end plate 9.
There is an acceleration gap 10 between the low energy side end drift tube 6 and the adjacent drift tube 2, and the number of acceleration gaps increases according to the number of drift tubes 2 hereinafter. The acceleration gap between the plurality of drift tubes is expressed as an acceleration gap 10a, an acceleration gap 10b, an acceleration gap 10c,.

低エネルギー側の共振空胴端部の空胴径は、共振空胴中央部の空胴径より大きく、かつこの径拡大部（以下、低エネルギー側拡大空胴と記す。）１１は、低エネルギー側共振空胴端板７からリッジ４が設けられている個所に至る位置までの空胴長Ｌ１をもって存在する。また、リッジ４に掛かる拡大空胴部分には、リッジ４が延長して設けられている（リッジ４１）。リッジ４１の形状に関しては、好ましくは図１に示すように、リッジ４をそのまま延長した形状とするとよい。こうすることで、電場分布調節機構であるリッジ４の設計を変更しなくて済む。
同様に、高エネルギー側の共振空胴端部の空胴径も、共振空胴中央部の空胴径より大きく、かつこの径拡大部（以下、高エネルギー側拡大空胴と記す。）１２は、高エネルギー側共振空胴端板９からリッジ４が設けられている個所に至る位置までの空胴長Ｌ２をもって存在する。また、リッジ４に掛かる拡大空胴部分には、リッジ４が延長して設けられている（リッジ４２）。 The cavity diameter of the resonance cavity end portion on the low energy side is larger than the cavity diameter of the resonance cavity central portion, and this diameter enlarged portion (hereinafter referred to as the low energy side expansion cavity) 11 is low energy. It has a cavity length L1 from the side resonance cavity end plate 7 to a position where the ridge 4 is provided. In addition, the ridge 4 is extended and provided in the enlarged cavity portion of the ridge 4 (ridge 41). As for the shape of the ridge 41, it is preferable that the ridge 4 is extended as it is, as shown in FIG. By doing so, it is not necessary to change the design of the ridge 4 that is the electric field distribution adjusting mechanism.
Similarly, the cavity diameter at the resonance cavity end portion on the high energy side is larger than the cavity diameter at the resonance cavity central portion, and this diameter enlarged portion (hereinafter referred to as the high energy side enlarged cavity) 12 is. The cavity length L2 from the high energy side resonance cavity end plate 9 to the position where the ridge 4 is provided exists. Further, the ridge 4 is extended and provided in an enlarged cavity portion that hangs on the ridge 4 (ridge 42).

低／高エネルギー側拡大空胴１１、１２の設計指針を以下に記す。
最初に、低エネルギー側拡大空胴１１の拡大空胴径および拡大空胴長Ｌ１について、３次元電磁場解析により得られる電場分布から、上記拡大空胴径および拡大空胴長Ｌ１を評価し、低エネルギー側拡大空胴１１内で均一電場分布を達成するように、拡大空胴径および拡大空胴長Ｌ１の最適化を行う。また、高エネルギー側拡大空胴１２についても低エネルギー側拡大空胴１１と同様に行う（ステップ１）。 Design guidelines for the low / high energy side expansion cavities 11 and 12 are described below.
First, the expansion cavity diameter and the expansion cavity length L1 of the low energy side expansion cavity 11 are evaluated from the electric field distribution obtained by the three-dimensional electromagnetic field analysis, and the low The expansion cavity diameter and the expansion cavity length L1 are optimized so as to achieve a uniform electric field distribution in the energy-side expansion cavity 11. Further, the high energy side expansion cavity 12 is also performed in the same manner as the low energy side expansion cavity 11 (step 1).

次に、低／高エネルギー側拡大空胴１１、１２と共振空胴中央部とが一体となった共振空胴１の共振周波数が、加速器の運転周波数になるように、以下のようにして共振空胴１の全体設計を行う。
共振周波数を決定する大きな要因はドリフトチューブ間に発生する電気容量と磁場が流れる共振空胴断面積である。低／高エネルギー側拡大空胴１１、１２を搭載すると、共振空胴端部における磁場が流れる領域が増大するため、共振周波数は拡大空胴１１、１２を搭載する前に比べ減少する。したがって、減少した共振周波数を増加させるためには、ドリフトチューブ間で発生する電気容量は拡大空胴１１、１２を搭載しても変わらないため、磁場が流れる共振空胴断面積を縮小することで達成できる。そのため、ステップ１で得られた低／高エネルギー側拡大空胴１１、１２の空胴径、および共振空胴中央部の空胴径を同じ割合で縮小し、３次元電磁場解析により、共振空胴１の共振周波数が、設計値の加速器運転周波数になるように、上記それぞれの空胴径を最適化する（ステップ２）。 Next, resonance is performed as follows so that the resonance frequency of the resonance cavity 1 in which the low / high energy side expansion cavities 11 and 12 and the resonance cavity central part are integrated becomes the operating frequency of the accelerator. The entire cavity 1 is designed.
The major factor that determines the resonance frequency is the cross-sectional area of the resonance cavity in which the electric capacity and magnetic field generated between the drift tubes flow. When the low / high energy side expansion cavities 11 and 12 are mounted, the region in which the magnetic field flows at the end of the resonance cavity increases, so that the resonance frequency decreases compared to before the expansion cavities 11 and 12 are mounted. Therefore, in order to increase the decreased resonance frequency, the electric capacity generated between the drift tubes does not change even when the expansion cavities 11 and 12 are mounted. Therefore, by reducing the cross-sectional area of the resonance cavity through which the magnetic field flows. Can be achieved. Therefore, the cavity diameters of the low / high energy side expansion cavities 11 and 12 obtained in step 1 and the cavity diameter at the center of the resonance cavity are reduced at the same rate, and the resonance cavity is analyzed by three-dimensional electromagnetic field analysis. The respective cavity diameters are optimized so that the resonance frequency of 1 becomes the designed accelerator operating frequency (step 2).

最後に、各空胴径を縮小したことで、低／高エネルギー側拡大空胴により拡張された磁場が流れる領域が変化し電場分布も変化するので、再度、低／高エネルギー側拡大空胴径を最適化し、均一電場分布を得るようにする（ステップ３）。   Finally, by reducing each cavity diameter, the region where the magnetic field expanded by the low / high energy side expansion cavity changes and the electric field distribution also changes, so the low / high energy side expansion cavity diameter again. To obtain a uniform electric field distribution (step 3).

このように、低／高エネルギー側拡大空胴１１、１２の空胴径と空胴長、共振空胴中央部の空胴径、および共振周波数をパラメーターにして前述の過程を繰り返すことにより最適形状を設計する（ステップ４）。
なお、上記各ステップにおいて、拡大空胴の空胴径と共振空胴中央部の空胴径との大小関係が変ることはない。 As described above, the optimum shape is obtained by repeating the above-described process using the cavity diameter and cavity length of the low / high energy side expansion cavities 11 and 12, the cavity diameter at the center of the resonance cavity, and the resonance frequency as parameters. Is designed (step 4).
In each of the above steps, the magnitude relationship between the cavity diameter of the enlarged cavity and the cavity diameter at the center of the resonance cavity does not change.

このような構成にすれば、ＴＥモードにより励起される磁場が、低／高エネルギー側端部において多く流れることにより誘導電流が増加し、この領域での電場が上昇するので、共振空胴の低／高エネルギー側端部領域における電場分布も含め、共振空胴全体に亘って均一電場分布を形成することができ、かつ、設計値の運転周波数で共振するＩＨ型線形加速器が達成できる。   With such a configuration, a large amount of the magnetic field excited by the TE mode flows at the end of the low / high energy side, so that the induced current increases and the electric field increases in this region. / A uniform electric field distribution can be formed over the entire resonant cavity including the electric field distribution in the end region on the high energy side, and an IH linear accelerator that resonates at the design operating frequency can be achieved.

低／高エネルギー側拡大空胴１１、１２の空胴径および空胴長について、以下にさらに詳細に説明する。
図２は、低エネルギー側拡大空胴１１を搭載前の低エネルギー側共振空胴における電場分布を示しており、リッジ４により電場分布を均一化した後の低エネルギー側端部領域の電場分布を示す。なお、図２はドリフトチューブの数が図１に示すものより多い構成の線形加速器に対する電場分布である。横軸は加速軸であり、加速方向の位置を示す。縦軸は加速軸上に発生する電場強度（右側縦軸）であり、空胴中央部での均一電場分布の電場強度により規格化した電場（左側縦軸）を併記する。また、曲線Ａ0は電場分布そのものを示し、曲線Ａは各加速ギャップ１０ａ、１０ｂ、１０ｃ・・・での電場強度のピークをつなげたものである。 The cavity diameter and cavity length of the low / high energy side expansion cavities 11 and 12 will be described in more detail below.
FIG. 2 shows the electric field distribution in the low energy side resonant cavity before the low energy side expansion cavity 11 is mounted. The electric field distribution in the low energy side end region after the electric field distribution is made uniform by the ridge 4 is shown in FIG. Show. FIG. 2 shows an electric field distribution for a linear accelerator having a configuration in which the number of drift tubes is larger than that shown in FIG. The horizontal axis is the acceleration axis and indicates the position in the acceleration direction. The vertical axis represents the electric field strength (right vertical axis) generated on the acceleration axis, and the electric field (left vertical axis) normalized by the electric field strength of the uniform electric field distribution in the cavity center is also shown. A curve A 0 shows the electric field distribution itself, and the curve A is obtained by connecting the electric field intensity peaks at the respective acceleration gaps 10a, 10b, 10c.

図２に示すように、リッジ４による均一電場分布の調節は共振空胴端部領域を除いて達成できるが、共振空胴端部領域、とくに低エネルギー側において電場強度が弱く、加速ギャップ１０ａでの電場強度は均一電場強度の３０％程度しかないことがわかる。   As shown in FIG. 2, the adjustment of the uniform electric field distribution by the ridge 4 can be achieved except for the resonance cavity end region, but the electric field strength is weak in the resonance cavity end region, particularly on the low energy side. It can be seen that the electric field strength is only about 30% of the uniform electric field strength.

前述したように、ドリフトチューブ間に発生させる電場の最大値は放電限界値により上限があり、最大値の電場で放電限界が決まるので、空胴内部で発生する電場強度が不均一の場合、最大値以外の加速電場は放電限界までまだ余裕があるにもかかわらず、それ以上に電場を大きくすることができず、加速効率が低い。したがって、効率的にビームを加速するには空胴内部で発生する電場強度が均一であること必要がある。
さらに、リッジ４を用いた従来のＩＨ型線形加速器では、図２に示すように、加速ギャップ１０ａで発生する電場強度が一番弱く、共振空胴中央部の均一な電場強度の３０％程度の電場しかない。そのため、加速ギャップ１０ａでの加速ゲインが小さいので、大電流ビームを加速する場合は空間電荷効果により失うビームが多くなってしまう。これを改善するためにも、特に低エネルギー側共振空胴端部領域での電場の立ち上りを改善し、より均一化する必要がある。
さらに、ＩＨ型線形イオン加速器にＡＰＦ法による自己収束法を用いる場合、加速電場を収束にも用いるために、加速電場が弱いと収束力も弱くなり、大電流ビームを加速する場合、空間電荷効果により失うビームはさらに多くなるという問題がある。 As described above, the maximum value of the electric field generated between the drift tubes has an upper limit depending on the discharge limit value, and the discharge limit is determined by the maximum electric field, so if the electric field strength generated inside the cavity is not uniform, the maximum Although the acceleration electric fields other than the values still have room to the discharge limit, the electric field cannot be increased further, and the acceleration efficiency is low. Therefore, in order to accelerate the beam efficiently, the electric field intensity generated inside the cavity needs to be uniform.
Furthermore, in the conventional IH type linear accelerator using the ridge 4, as shown in FIG. 2, the electric field strength generated in the acceleration gap 10a is the weakest, which is about 30% of the uniform electric field strength at the center of the resonant cavity. There is only an electric field. Therefore, since the acceleration gain in the acceleration gap 10a is small, when accelerating a large current beam, many beams are lost due to the space charge effect. In order to improve this, it is necessary to improve the rise of the electric field particularly in the low energy side resonance cavity end region and make it more uniform.
Furthermore, when the self-focusing method based on the APF method is used for the IH type linear ion accelerator, since the acceleration electric field is also used for the convergence, if the acceleration electric field is weak, the convergence force becomes weak. There is a problem that more beams are lost.

本実施の形態では、共振空胴端部に拡大空胴を設けることにより、共振空胴端部領域での電場強度を増加させ、空胴内部で発生する電場強度を共振空胴全体に亘ってより均一となるようにしており、特に低エネルギー側（入射側）の電場分布を均一電場に近づけて、より効率的に大電流を加速できるようにしている。   In the present embodiment, by providing an enlarged cavity at the end of the resonant cavity, the electric field strength in the resonant cavity end region is increased, and the electric field strength generated inside the cavity is spread over the entire resonant cavity. In particular, the electric field distribution on the low energy side (incident side) is made closer to the uniform electric field so that a large current can be accelerated more efficiently.

図３は、低エネルギー側共振空胴端部の空胴径を拡大したときの電場分布を示す。横軸は加速軸を示し、縦軸は共振空胴中央部での均一電場強度で規格化した電場強度を示す。ここでは、一般的に加速器の運転周波数に用いられる２００ＭＨｚ共振空胴を例に取り、曲線Ａはリッジ４により電場分布を調節後（共振空胴拡大前）の低エネルギー側共振空胴端部領域の電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｂ1は、単純に低エネルギー側共振空胴端からリッジ手前までの低エネルギー側共振空胴の空胴径を、共振空胴中央部の空胴径の２倍に拡大したときの電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｂ2は同様に、空胴径を４倍拡大したときの電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）を示す。 FIG. 3 shows the electric field distribution when the cavity diameter of the low energy side resonance cavity end is enlarged. The horizontal axis represents the acceleration axis, and the vertical axis represents the electric field strength normalized by the uniform electric field strength at the center of the resonant cavity. Here, a 200 MHz resonance cavity generally used for an operating frequency of an accelerator is taken as an example, and a curve A is a low energy side resonance cavity end region after adjusting the electric field distribution by the ridge 4 (before resonance cavity expansion). The electric field distribution (curve connecting the peak of the electric field intensity at each acceleration gap), the curve B 1 is simply the cavity diameter of the low energy side resonant cavity from the low energy side resonant cavity end to the ridge. The electric field distribution (curve connecting the peak of the electric field intensity at each acceleration gap) expanded to twice the cavity diameter at the center of the resonant cavity, and the curve B 2 similarly expanded the cavity diameter by four times. Shows the electric field distribution (curve connecting electric field intensity peaks at each acceleration gap).

２００ＭＨｚ共振空胴の場合、共振空胴径はφ３００ｍｍ程度であり、２倍、４倍とはそれぞれφ６００ｍｍ、φ１２００ｍｍである。
図３に示すように、低エネルギー側共振空胴径を共振空胴中央部の空胴径の２倍、４倍と拡大すると、それに伴い、磁場の流れる領域が拡大するため、低エネルギー側共振空胴端部領域の電場強度は全体に増加するが、共振空胴端に一番近い加速ギャップ１０ａでの電場強度は、空胴径を２倍、４倍に拡大してもあまり増加しない（図３のＰ1、Ｐ2）。
これはリッジ４により端部まで導かれる磁場はリッジ付近において密であるため、リッジ手前の空胴径をいくら拡大してもその効果は小さいためと考えられる。
したがって、加速ギャップ１０ａにおける電場強度を増加させるためには、リッジ４も含めた領域まで拡大空胴１１の空胴長Ｌ１を拡大する必要がある。 In the case of a 200 MHz resonant cavity, the resonant cavity diameter is about φ300 mm, and the double and quadruple are φ600 mm and φ1200 mm, respectively.
As shown in FIG. 3, when the resonance cavity diameter of the low energy side is increased to 2 times or 4 times the cavity diameter of the center of the resonance cavity, the region where the magnetic field flows is increased accordingly. The electric field strength in the cavity end region increases as a whole, but the electric field strength in the acceleration gap 10a closest to the resonant cavity end does not increase much even when the cavity diameter is increased by two or four times ( P 1, P 2 in FIG. 3).
This is probably because the magnetic field guided to the end by the ridge 4 is dense in the vicinity of the ridge, so that the effect is small even if the cavity diameter before the ridge is increased.
Therefore, in order to increase the electric field strength in the acceleration gap 10a, it is necessary to expand the cavity length L1 of the expansion cavity 11 to the region including the ridge 4.

次に、リッジ４も含めた領域まで拡大した拡大空胴１１の空胴長Ｌ１をどこまで拡大すると良いかについて説明する。
図４は低エネルギー側共振空胴端部の空胴径を拡大したときの電場分布であり、低エネルギー側拡大空胴１１をリッジ４を含んだ領域まで拡大し、空胴長さＬ１が、共振空胴端よりリッジ４が設けられている個所に至る位置までとした場合の電場分布を示す。横軸は加速軸を示し、縦軸は共振空胴中央部での均一電場強度で規格化した電場分布を示す。
曲線Ａはリッジ４により電場分布を調節後（共振空胴拡大前）の低エネルギー側共振空胴端部領域の電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｃ1は加速ギャップ１０ｂの入射側端部（図１のｂ１）まで拡大空胴長Ｌ１をとった場合の電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｃ2は加速ギャップ１０ｂの出射側端部（図１のｂ２）まで拡大空胴長Ｌ１をとった場合の電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）である。 Next, how far the cavity length L1 of the expansion cavity 11 expanded to the area including the ridge 4 should be expanded will be described.
FIG. 4 shows the electric field distribution when the cavity diameter at the end of the low energy side resonance cavity is expanded. The low energy side expansion cavity 11 is expanded to a region including the ridge 4, and the cavity length L1 is The electric field distribution in the case of extending from the resonance cavity end to the position where the ridge 4 is provided is shown. The horizontal axis represents the acceleration axis, and the vertical axis represents the electric field distribution normalized by the uniform electric field strength at the center of the resonant cavity.
Curve A is the electric field distribution in the low-energy side resonance cavity end region after adjusting the electric field distribution by ridge 4 (before expansion of the resonance cavity) (curve connecting electric field intensity peaks at each acceleration gap), and curve C 1. incident side end (curve connecting the peaks of the electric field intensity at each accelerating gap) electric field distribution when taking enlarged cavity length L1 to (b1 in FIG. 1), the curve C 2 is acceleration gap of acceleration gap 10b is It is an electric field distribution (curve connecting electric field intensity peaks in each acceleration gap) when the extended cavity length L1 is taken up to the emission side end portion (b2 in FIG. 1) of 10b.

このように、曲線Ｃ1と曲線Ｃ2とは、共に拡大空胴１１が、イオンビーム入射側の共振空胴端より加速ギャップ１０ｂの部分まで設けられており、加速電場の立ち上り領域を含んで設けられている。リッジ４を含み、加速電場の立ち上り領域を含む領域まで拡大空胴長Ｌ１をとると、リッジ４により端部まで導かれる磁場の通る断面積が拡大することで、図４に示すように、共振空胴端に一番近い加速ギャップ１０ａでの電場強度（図４のＰ3、Ｐ4）も含めて低エネルギー側共振空胴端部領域の電場強度が増加する。その結果、共振空胴全体に亘ってより均一な電場分布を達成することができる。 Thus, in both the curves C 1 and C 2 , the expansion cavity 11 is provided from the resonance cavity end on the ion beam incident side to the acceleration gap 10 b and includes the rising region of the acceleration electric field. Is provided. When the extended cavity length L1 is extended to the region including the ridge 4 and the region including the rising region of the acceleration electric field, the cross-sectional area through which the magnetic field guided to the end by the ridge 4 is expanded. The electric field strength in the low energy side resonance cavity end region increases, including the electric field strength (P 3 and P 4 in FIG. 4 ) at the acceleration gap 10a closest to the cavity end. As a result, a more uniform electric field distribution can be achieved over the entire resonant cavity.

また、図４において、曲線Ｃ1と曲線Ｃ2とを比較すると、曲線Ｃ1より曲線Ｃ2の方が均一電場を達成しているといえる。すなわち、曲線Ｃ2は、低エネルギー側共振空胴端部の電場分布が、共振空胴中央部での均一電場強度の±２０％の範囲内に入っており、共振空胴全体に亘ってより均一な電場分布となるので、より効率的にビームを加速することが可能となる。 Further, in FIG. 4, when the curve C 1 and the curve C 2 are compared, it can be said that the curve C 2 achieves a more uniform electric field than the curve C 1 . That is, the curve C 2 shows that the electric field distribution at the resonance cavity end of the low energy side is within a range of ± 20% of the uniform electric field strength at the resonance cavity center, and is more spread over the entire resonance cavity. Since the electric field distribution is uniform, the beam can be accelerated more efficiently.

ここで、均一電場の定義について説明する。
共振空胴内に発生させる均一電場強度の設定値は、放電限界電場強度よりも余裕を持たせて設計するのが通例である。したがって、最大でも均一電場分布の１．２倍程度までなら許容範囲である。したがって、低エネルギー側共振空胴端部での電場強度を増加させる場合、入射側電場強度の上限は放電に対する安全係数によりある程度決定されるが、下限、とくに加速ギャップ１０ａでの電場強度の下限は大電流ビーム、たとえば陽子ビームを加速する場合は重要になってくる。 Here, the definition of the uniform electric field will be described.
The set value of the uniform electric field strength generated in the resonance cavity is usually designed with a margin more than the discharge limit electric field strength. Accordingly, the maximum allowable range is up to about 1.2 times the uniform electric field distribution. Therefore, when increasing the electric field strength at the resonance cavity end of the low energy side, the upper limit of the incident side electric field strength is determined to some extent by the safety factor against discharge, but the lower limit, particularly the lower limit of the electric field strength at the acceleration gap 10a is It becomes important when accelerating large current beams, such as proton beams.

図５は、入射する陽子のエネルギーに対する加速ギャップ１０ａでの必要電場強度を示す図であり、一般的に用いられる２００ＭＨｚ運転のＩＨ型線形加速器にＡＰＦ法を適応した場合の必要電場強度である。縦軸の電場強度は、共振空胴中央部での均一電場強度で規格化したものである。
大電流ビームによる空間電荷効果はβ2γ3（β：ｖ／ｃ ｖは粒子速度、ｃは光速、γ：１／√（１−β2））に反比例するため、低エネルギーからの加速の場合、とくに陽子などの質量の軽いビームを加速する場合、空間電荷効果が顕著になる。したがって、入射エネルギーが下がれば下がるほど加速ギャップ１０ａでの電場強度を増加させ、早期に加速してエネルギーを大きくする必要があることがわかる。
一般的に、陽子加速用前段加速器としてはＲＦＱ型線形加速器が使われ、このＲＦＱ型線形加速器からの出射エネルギーとしては１ＭｅＶ程度が使われている。ＲＦＱ型線形加速器は出射エネルギーが高いほど大型になるため、ここでは更なる加速器の小型化を念頭に、ＲＦＱ型線形加速器より低エネルギービームを入射して、早期に効率よく加速することとし、そのための指標として必要電場強度（共振空胴中央部での均一電場強度で規格化した時の加速ギャップ１０ａでの必要電場強度。）０．８を設定し、低エネルギー側端部電場分布が±２０％の範囲内になるよう空胴端部電場強度を均一化させるとよい。 FIG. 5 is a diagram showing the required electric field strength at the acceleration gap 10a with respect to the energy of the incident proton, and is the required electric field strength when the APF method is applied to a commonly used IH linear accelerator operating at 200 MHz. The electric field strength on the vertical axis is normalized by the uniform electric field strength at the center of the resonant cavity.
The space charge effect due to the large current beam is inversely proportional to β 2 γ 3 (β: v / c v is the particle velocity, c is the speed of light, and γ: 1 / √ (1-β 2 )), so acceleration from low energy In particular, the space charge effect becomes significant, especially when accelerating a light beam such as protons. Therefore, it can be seen that as the incident energy decreases, the electric field strength in the acceleration gap 10a increases, and the energy needs to be increased by accelerating early.
In general, an RFQ linear accelerator is used as a pre-accelerator for proton acceleration, and about 1 MeV is used as an output energy from the RFQ linear accelerator. Since the RFQ type linear accelerator becomes larger as the output energy becomes higher, it is assumed here that a low energy beam is made incident from the RFQ type linear accelerator and is accelerated quickly and efficiently with the aim of further downsizing the accelerator. The required electric field strength (required electric field strength at the acceleration gap 10a when normalized by the uniform electric field strength at the center of the resonance cavity) is set to 0.8, and the low-energy side end electric field distribution is ± 20. It is preferable to make the cavity end electric field strength uniform so as to be in the range of%.

図４の曲線Ｃ2の構成にすると、加速ギャップ１０ａでの規格化電場が０．８以上となっており、このことから、用いるＩＨ型線形イオン加速器の構成としては、図１の加速ギャップ１０ｂの低エネルギー出射側端部（図１のｂ２）まで拡大空胴長Ｌ１をとった（曲線Ｃ2）構成とすれば、小型で効率の良いイオン加速システムを実現することができる。 With the configuration of the curve C 2 in FIG. 4, the normalized electric field in the acceleration gap 10a is 0.8 or more. Therefore, the configuration of the IH linear ion accelerator to be used is the acceleration gap 10b in FIG. If the configuration has an extended cavity length L1 (curve C 2 ) up to the low energy emission side end (b2 in FIG. 1), a small and efficient ion acceleration system can be realized.

なお、上記イオン加速システムの説明では、低エネルギー側共振空胴端部領域の電場分布を増加させる際の必要電場強度の下限の値として、規格化電場強度０．８を指標とし、拡大空胴長Ｌ１を設計する例を示したが、上記下限の指標は、入射するイオンビームのエネルギーに応じて変化するので、入射するイオンビームのエネルギーに応じた指標に基づき、拡大空胴長Ｌ１を設計すればよい。   In the description of the ion acceleration system, the lower limit value of the required electric field intensity when increasing the electric field distribution in the low energy side resonance cavity end region is used with the normalized electric field intensity of 0.8 as an index, and an expanded cavity. Although an example of designing the length L1 has been shown, since the lower limit index changes according to the energy of the incident ion beam, the extended cavity length L1 is designed based on the index according to the energy of the incident ion beam. do it.

また、図４においては、加速ギャップ１０ｂの入射側端部（図１のｂ１）まで拡大空胴長Ｌ１をとった場合（曲線Ｃ1）と、加速ギャップ１０ｂの出射側端部（図１のｂ２）まで拡大空胴長Ｌ１をとった場合（曲線Ｃ2）について説明したが、拡大空胴１１の空胴長Ｌ１は、上記例に限らず、共振空胴端よりリッジ４を含み、好ましくは共振空胴内に発生する加速電場の立ち上り領域を含む位置までの長さであって、かつその時の低エネルギー側共振空胴端部領域の電場分布が、必要とされる均一性を満たす長さの位置まで、ビーム加速方向に沿って拡大空胴１１を拡大して設ければよい。 Further, in FIG. 4, when the enlarged cavity length L1 is taken to the incident side end (b1 in FIG. 1 ) of the acceleration gap 10b (curve C 1 ), the emission side end (in FIG. 1). Although the case where the extended cavity length L1 is taken up to b2) (curve C 2 ) has been described, the cavity length L1 of the enlarged cavity 11 is not limited to the above example, and preferably includes the ridge 4 from the resonance cavity end. Is the length up to the position including the rising region of the accelerating electric field generated in the resonant cavity, and the electric field distribution in the low energy side resonant cavity end region at that time satisfies the required uniformity. The enlarged cavity 11 may be enlarged and provided along the beam acceleration direction up to this position.

また、図４においては、低エネルギー側共振空胴端部の空胴径を拡大したときの電場分布について説明したが、高エネルギー側に設けた拡大空胴１２の空胴長さに関しても、同様に高エネルギー側共振空胴端よりリッジ４が設けられている個所に至る位置まで、好ましくは共振空胴内に発生する加速電場の立ち上り領域を含む位置まで設けるとよい。   In FIG. 4, the electric field distribution when the cavity diameter at the resonance cavity end of the low energy side is expanded has been described, but the same applies to the cavity length of the expansion cavity 12 provided on the high energy side. Further, it is preferable to provide from the end of the resonance cavity on the high energy side to the position where the ridge 4 is provided, preferably to the position including the rising region of the acceleration electric field generated in the resonance cavity.

また、図１では、拡大空胴１１、１２を設けた例を示したが、拡大空胴を設ける効果は特に入射側において顕著であるため、拡大空胴１２を設けず、拡大空胴１１のみを設けても良い。   FIG. 1 shows an example in which the enlarged cavities 11 and 12 are provided. However, since the effect of providing the enlarged cavities is particularly remarkable on the incident side, the enlarged cavity 12 is not provided, and only the enlarged cavity 11 is provided. May be provided.

以上のように、本実施の形態１によれば、リッジを設けた線形イオン加速器において、少なくともイオンビーム入射側の共振空胴端部の径を、共振空胴中央部の径より大きくし、かつイオンビーム入射側の径拡大部の加速方向の長さを、共振空胴端よりリッジが設けられている個所に至る位置までの長さ、好ましくは加速電場の立ち上り領域を含む位置までの長さとしたので、共振器空胴端部領域の電場強度を増加させることができ、共振空胴中央部のみならず共振空胴端部領域においてもより均一な電場分布を達成できる。その結果、効率的に大電流を加速できる効果がある。   As described above, according to the first embodiment, in the linear ion accelerator provided with the ridge, at least the diameter of the resonance cavity end on the ion beam incident side is made larger than the diameter of the resonance cavity center, and The length in the acceleration direction of the enlarged diameter portion on the ion beam incident side is the length from the resonance cavity end to the position where the ridge is provided, preferably the length to the position including the rising region of the acceleration electric field. As a result, the electric field strength in the cavity end region can be increased, and a more uniform electric field distribution can be achieved not only in the resonant cavity center but also in the resonant cavity end region. As a result, there is an effect that a large current can be accelerated efficiently.

また、本実施の形態１では、リッジを設けたＩＨ型線形加速器を用いているので、ステム間に磁場が回りこむ影響が少なく、共振空胴中央部での電場分布の均一性が達成できる。特に、ＡＰＦ法のような収束法を用いた場合には、加速位相が一定でないためステム間隔がビーム速度に比例しない場合、リッジを用いないとステム間に磁場が回りこむ影響が大きく、共振空胴中央部での電場分布の均一性を崩す問題があるが、本実施の形態ではリッジによる電場分布調節機構が搭載されているので、このような問題を低減できる。
さらに、ＲＦＩ型線形加速器では、ステム間に磁場が回りこむ影響が大きいために、ステム自身に流れる電流量が増加することで消費電力量が高くなり冷却機構が必要になるが、特にＡＰＦ法のような別途収束用機器を必要としない収束法を適用した場合にはドリフトチューブ長が短くなるため、冷却機構を搭載するための十分なステム径を設置することができないという問題がある。本実施の形態ではリッジを設けたＩＨ型線形加速器を用いているので、ＲＦＩ型線形加速器におけるような問題は生じない。 Further, in the first embodiment, since the IH linear accelerator provided with the ridge is used, the influence of the magnetic field flowing between the stems is small, and the uniformity of the electric field distribution at the center of the resonance cavity can be achieved. In particular, when a convergence method such as the APF method is used, the acceleration phase is not constant, and if the stem interval is not proportional to the beam speed, the effect of the magnetic field flowing between the stems is great unless the ridge is used. Although there is a problem that the uniformity of the electric field distribution in the central portion of the trunk is lost, the present embodiment can reduce such a problem because the electric field distribution adjusting mechanism using the ridge is mounted.
Furthermore, in the RFI type linear accelerator, the influence of the magnetic field flowing between the stems is large, so that the amount of current flowing through the stem itself increases, which increases the power consumption and requires a cooling mechanism. When a convergence method that does not require a separate convergence device is applied, the drift tube length becomes short, so that there is a problem that a sufficient stem diameter for mounting the cooling mechanism cannot be installed. In this embodiment, since the IH linear accelerator provided with the ridge is used, the problem as in the RFI linear accelerator does not occur.

実施の形態２．
図６は本発明の実施の形態２によるＩＨ型線形イオン加速器の主要部を示す断面構成図であり、拡大空胴を二段式拡大空胴としたものである。
図６において、低エネルギー側拡大空胴は、低エネルギー側拡大空胴端板７と、拡大空胴Ａ２０と、拡大空胴Ｂ２１とにより構成され、拡大空胴Ａ２０は、共振空胴中央部の空胴径より大きな空胴径Ｒ１、空胴長さＬ３により構成され、拡大空胴Ｂ２１は、共振空胴中央部の空胴径より大きな空胴径Ｒ２（Ｒ１＞Ｒ２）、空胴長さＬ４により構成される。
また、高エネルギー側拡大空胴も、同様に二段式拡大空胴で構成されている（図示を省略）。 Embodiment 2. FIG.
FIG. 6 is a cross-sectional configuration diagram showing the main part of an IH type linear ion accelerator according to Embodiment 2 of the present invention, in which the expansion cavity is a two-stage expansion cavity.
In FIG. 6, the low energy side expansion cavity includes a low energy side expansion cavity end plate 7, an expansion cavity A20, and an expansion cavity B21. The expansion cavity A20 is formed at the center of the resonance cavity. The cavity C21 is composed of a cavity diameter R1 larger than the cavity diameter and a cavity length L3, and an enlarged cavity B21 has a cavity diameter R2 (R1> R2) larger than the cavity diameter at the center of the resonance cavity, and the cavity length. L4.
Similarly, the high energy side expansion cavity is also composed of a two-stage expansion cavity (not shown).

実施の形態１において、低エネルギー側拡大空胴１１を設計するに当たり、加速ギャップ１０ａに発生する電場強度を共振空胴中央部における均一電場強度近くまで増加させると、加速ギャップ１０ｂに発生する電場強度もそれにつられて増加することがある。このような現象は、電場強度が立ち上り領域にある加速ギャップの数が多い場合に生じ易い。
このような場合は、低エネルギー側拡大空胴１１を段違い式にすることが有効である。ここでは二段式拡大空胴による例を示すが、段の数は二段に限らない。 In the first embodiment, when designing the low energy side expansion cavity 11, if the electric field strength generated in the acceleration gap 10a is increased to near the uniform electric field strength in the central portion of the resonance cavity, the electric field strength generated in the acceleration gap 10b. May increase accordingly. Such a phenomenon is likely to occur when the number of acceleration gaps in the rising region of the electric field strength is large.
In such a case, it is effective to make the low energy side expansion cavity 11 a stepped type. Although an example using a two-stage expansion cavity is shown here, the number of stages is not limited to two.

低エネルギー側端部径を拡大することにより拡大空胴とした領域における電場強度は増加するので、増加しすぎた領域において拡大空胴径を縮小すれば電場強度を減少することができ、低エネルギー側空胴を段式にすることで電場分布の微調節を行うことができる。   Since the electric field strength increases in the region where the enlarged cavity is formed by enlarging the end diameter on the low energy side, the electric field strength can be reduced if the enlarged cavity diameter is reduced in the region where it has increased too much. The electric field distribution can be finely adjusted by using a stepped side cavity.

図７に低エネルギー側拡大空胴を一段式（段違いになっていない拡大空胴）および二段式にしたときの電場分布を示す。
図７において、曲線Ｄ1は、一段式入射側拡大空胴１１による電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｄ2は単純に二段式空胴を設けたときの電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）、曲線Ｄ3は二段式拡大空胴の各空胴径および空胴長さを３次元電磁場解析により最適化した後の電場分布（各加速ギャップでの電場強度のピークをつなげた曲線）を示す。 FIG. 7 shows the electric field distribution when the low energy side expansion cavity is of a one-stage type (expansion cavity that is not stepped) and a two-stage type.
In FIG. 7, a curve D 1 is an electric field distribution (a curve connecting electric field intensity peaks in each acceleration gap) by the one-stage incident side expansion cavity 11, and a curve D 2 is simply provided with a two-stage cavity. after optimizing the field distribution (curve connecting the peaks of the electric field intensity at each accelerating gap), the curve D 3 is 3-dimensional electromagnetic field analysis of each cavity diameter and cavity length of the two-stage expansion cavity when The electric field distribution (a curve connecting electric field intensity peaks at each acceleration gap) is shown.

段違い式による低エネルギー側拡大空胴の設計指針について説明する。
拡大空胴Ｂ２１の空胴径Ｒ２は、増加しすぎた加速ギャップ１０ｂでの電場強度を弱める目的があるため、まず、拡大空胴１１が一段（段違いになっていない拡大空胴）の場合について、実施の形態１と同様に、３次元電磁場解析を用いて電場分布を解析し、加速ギャップ１０ａ、加速ギャップ１０ｂにて発生する電場強度がともに増加し、とくに加速ギャップ１０ｂの電場強度が共振空胴中央部での均一電場強度を越える状態となる場合、加速ギャップ１０ａでの電場強度が、共振空胴中央部における均一電場強度に近い空胴径Ｒ１、空胴長Ｌ３＋Ｌ４を選択する（ステップ１）。
その状態で、拡大空胴１１を二段とし、加速ギャップ１０ｂでの電場強度を弱め、低エネルギー側共振空胴端部領域の電場分布がより均一となる拡大空胴Ｂ２１の空胴径Ｒ２、空胴長Ｌ４を３次元電磁場解析により求め、均一電場分布を得る形状を最適化する（ステップ２）。
高エネルギー側拡大空胴の設計指針も同様である。
その後、共振空胴全体の電場分布および共振周波数を調節する方法は実施の形態１に準ずる。 The design guideline for the low energy side expansion cavity by the stepped equation will be explained.
Since the cavity diameter R2 of the expansion cavity B21 has the purpose of weakening the electric field strength in the acceleration gap 10b that has increased too much, first, the case where the expansion cavity 11 is one stage (expansion cavity that is not stepped). As in the first embodiment, the electric field distribution is analyzed by using the three-dimensional electromagnetic field analysis, and the electric field strength generated in the acceleration gap 10a and the acceleration gap 10b is increased. In particular, the electric field strength of the acceleration gap 10b is resonant sky. When the state exceeds the uniform electric field strength at the center of the cylinder, the cavity diameter R1 and the cavity length L3 + L4 are selected such that the electric field intensity at the acceleration gap 10a is close to the uniform electric field intensity at the center of the resonance cavity (step 1). ).
In this state, the expansion cavity 11 has two stages, the electric field strength in the acceleration gap 10b is weakened, and the cavity diameter R2 of the expansion cavity B21 in which the electric field distribution in the low energy side resonance cavity end region becomes more uniform. The cavity length L4 is obtained by three-dimensional electromagnetic field analysis, and the shape for obtaining a uniform electric field distribution is optimized (step 2).
The same applies to the design guidelines for the high energy side expansion cavity.
Thereafter, the method for adjusting the electric field distribution and the resonance frequency of the entire resonant cavity is the same as in the first embodiment.

以上のように、共振空胴端部を拡大空胴とすることにより、共振空胴内に突出した電場強度が発生する場合、本実施の形態２のように、上記拡大空胴を段式拡大空胴とすることで、この突出部分を選択的に減少することができるので、共振空胴端部領域での電場分布の微調整を行うことが可能となる。   As described above, when an electric field intensity protruding into the resonant cavity is generated by using the resonant cavity end portion as an enlarged cavity, the enlarged cavity is expanded stepwise as in the second embodiment. Since the projecting portion can be selectively reduced by using the cavity, the electric field distribution in the resonance cavity end region can be finely adjusted.

実施の形態３．
図８は本発明の実施の形態３によるＩＨ型線形イオン加速器の主要部を示す断面構成図であり、拡大空胴をコーン状拡大空胴としたものである。
図８において、低エネルギー側拡大空胴は、低エネルギー側拡大空胴端板７と、空胴径が、加速方向に沿ってコーン状に徐々に変化しているコーン状拡大空胴２２とにより構成されており、コーン状拡大空胴２２の空胴径は、Ｒ１よりＲ２（Ｒ１，Ｒ２は共振空胴中央部の空胴径より大、Ｒ１＞Ｒ２）まで徐々に変化し、かつ空胴長さはＬ５となるように構成される。
また、高エネルギー側拡大空胴も、同様にコーン状拡大空胴で構成されている（図示を省略）。 Embodiment 3 FIG.
FIG. 8 is a cross-sectional configuration diagram showing the main part of an IH type linear ion accelerator according to Embodiment 3 of the present invention, in which the expansion cavity is a cone-shaped expansion cavity.
In FIG. 8, the low energy side expansion cavity includes a low energy side expansion cavity end plate 7 and a cone-shaped expansion cavity 22 whose cavity diameter gradually changes in a cone shape along the acceleration direction. The cone-shaped cavity 22 has a cavity diameter that gradually changes from R1 to R2 (R1 and R2 are larger than the cavity diameter at the center of the resonant cavity, R1> R2), and the cavity The length is configured to be L5.
Similarly, the high energy side expansion cavity is also formed of a cone-shaped expansion cavity (not shown).

実施の形態２において、拡大空胴を段式拡大空胴にすることは加速ギャップごとの電場強度を調節するためであり、加速ギャップ位置での空胴径に大きく依存する。したがって、拡大空胴を設けることにより、加速ギャップ１０ｂの電場強度が共振空胴中央部での均一電場強度を越える状態となる場合には、拡大空胴を段式拡大空胴に替るかわりに、コーン状の空胴にしても同様の効果が得られる。   In the second embodiment, the expansion cavity is changed to a stepped expansion cavity in order to adjust the electric field strength for each acceleration gap, and greatly depends on the cavity diameter at the acceleration gap position. Therefore, when the electric field strength of the acceleration gap 10b exceeds the uniform electric field strength at the center of the resonance cavity by providing the expansion cavity, instead of replacing the expansion cavity with a step-type expansion cavity, The same effect can be obtained even with a cone-shaped cavity.

コーン状拡大空胴２２の空胴径Ｒ１、Ｒ２、空胴長さＬ５に関しては、実施の形態２と同様に、はじめに拡大空胴１１が一段の場合について、３次元電磁場解析を用いて電場分布を解析し、加速ギャップ１０ａ、加速ギャップ１０ｂにて発生する電場強度がともに増加し、とくに加速ギャップ１０ｂの電場強度が共振空胴中央部での均一電場強度を越える状態となる場合、加速ギャップ１０ａでの電場強度が、共振空胴中央部における均一電場強度に近い空胴径Ｒ１、空胴長Ｌ５を選択する（ステップ１）。
その状態で、拡大空胴１１をコーン状とし、加速ギャップ１０ｂでの電場強度を弱め、低エネルギー側共振空胴端部領域の電場分布がより均一となる拡大空胴２２の空胴径Ｒ２を３次元電磁場解析により求め、均一電場分布を得る形状を最適化する（ステップ２）。
高エネルギー側拡大空胴の設計指針も同様である。
その後、共振空胴全体の電場分布および共振周波数を調節する方法は実施の形態１に準ずる。 Concerning the cavity diameters R1 and R2 and the cavity length L5 of the cone-shaped expanded cavity 22, as in the second embodiment, the electric field distribution is first obtained using the three-dimensional electromagnetic field analysis in the case where the expanded cavity 11 is one stage. When the electric field strength generated in the acceleration gap 10a and the acceleration gap 10b increases, and particularly when the electric field strength of the acceleration gap 10b exceeds the uniform electric field strength at the center of the resonance cavity, the acceleration gap 10a The cavity diameter R1 and cavity length L5 are selected so that the electric field intensity at is close to the uniform electric field intensity at the center of the resonant cavity (step 1).
In this state, the expansion cavity 11 is formed in a cone shape, the electric field strength in the acceleration gap 10b is weakened, and the cavity diameter R2 of the expansion cavity 22 in which the electric field distribution in the low energy side resonance cavity end region becomes more uniform. The shape obtained by the three-dimensional electromagnetic field analysis to obtain a uniform electric field distribution is optimized (step 2).
The same applies to the design guidelines for the high energy side expansion cavity.
Thereafter, the method for adjusting the electric field distribution and the resonance frequency of the entire resonant cavity is the same as in the first embodiment.

以上のように、共振空胴端部を拡大空胴とすることにより、共振空胴内に突出した電場強度が発生する場合、本実施の形態３のように、上記拡大空胴をコーン状拡大空胴とすることで、この突出部分を選択的に減少することができるので、共振空胴端部領域での電場分布の微調整を行うことが可能となる。   As described above, when an electric field intensity protruding into the resonant cavity is generated by using the resonant cavity end as an enlarged cavity, the enlarged cavity is expanded in a cone shape as in the third embodiment. Since the projecting portion can be selectively reduced by using the cavity, the electric field distribution in the resonance cavity end region can be finely adjusted.

実施の形態４．
図９は本発明の実施の形態４によるイオン加速システムを示すブロック図であり、シンクロトロン等の円形加速器に入射するためのイオンビームを生成し、予備加速するイオン加速システムである。
図９において、ＰＩＧイオン源、ＥＣＲイオン源等のイオン源２３から発生した陽子ビームまたは重粒子ビームを、低エネルギービーム輸送路２４を経由して、ＲＦＱ型線形加速器等の前段加速器２５に入射し、前段加速器２５により前段加速する。前段加速したビームは、実施の形態１〜３のいずれかの構成のＩＨ型線形加速器（後段加速器）２６に入射する。ＩＨ型線形加速器２６から出射するビームは中エネルギービーム輸送路２７より輸送され、シンクロトロン等の円形加速器に入射する。 Embodiment 4 FIG.
FIG. 9 is a block diagram showing an ion acceleration system according to a fourth embodiment of the present invention, which is an ion acceleration system that generates and pre-accelerates an ion beam to be incident on a circular accelerator such as a synchrotron.
In FIG. 9, a proton beam or a heavy particle beam generated from an ion source 23 such as a PIG ion source or an ECR ion source is incident on a pre-stage accelerator 25 such as an RFQ linear accelerator via a low energy beam transport path 24. The front stage accelerator 25 accelerates the front stage. The beam accelerated at the front stage is incident on the IH linear accelerator (rear stage accelerator) 26 having any one of the configurations of the first to third embodiments. The beam emitted from the IH linear accelerator 26 is transported from the medium energy beam transport path 27 and is incident on a circular accelerator such as a synchrotron.

このような構成にすれば、イオン源２３からの出力ビームをＩＨ型線形加速器２６において効率的に加速できるため、コンパクトなイオン加速システムを構築でき、かつＩＨ型線形加速器２６の低エネルギー空胴端部領域において十分な強度の電場が発生するため、大電流ビームであっても空間電荷効果によりビームが失われる率が少ないので、ビーム電流依存性の小さなイオンビーム加速システムを構築することができる。   With such a configuration, since the output beam from the ion source 23 can be efficiently accelerated in the IH linear accelerator 26, a compact ion acceleration system can be constructed, and the low energy cavity end of the IH linear accelerator 26 can be constructed. Since an electric field with sufficient intensity is generated in the partial region, the rate of beam loss due to the space charge effect is small even with a large current beam, so that an ion beam acceleration system with small beam current dependency can be constructed.

本発明の実施の形態１によるＩＨ型線形イオン加速器を示す断面構成図である。It is a section lineblock diagram showing the IH type linear ion accelerator by Embodiment 1 of the present invention. 本発明の実施の形態１に係わる低エネルギー側拡大空胴を搭載前の低エネルギー側共振空胴における電場分布を示す図である。It is a figure which shows the electric field distribution in the low energy side resonance cavity before mounting the low energy side expansion cavity concerning Embodiment 1 of this invention. 本発明の実施の形態１に係わる低エネルギー側拡大空胴の空胴径を変化させた場合の電場分布を示す図である。It is a figure which shows the electric field distribution at the time of changing the cavity diameter of the low energy side expansion cavity concerning Embodiment 1 of this invention. 本発明の実施の形態１に係わる低エネルギー側拡大空胴の空胴長を変化させた場合の電場分布を示す図である。It is a figure which shows the electric field distribution at the time of changing the cavity length of the low energy side expansion cavity concerning Embodiment 1 of this invention. 本発明の実施の形態１によるＩＨ型線形加速器に入射する陽子のエネルギーに対する加速ギャップ１０ａでの必要電場強度を示す図である。It is a figure which shows the required electric field strength in the acceleration gap 10a with respect to the energy of the proton which injects into the IH type | mold linear accelerator by Embodiment 1 of this invention. 本発明の実施の形態２によるＩＨ型線形イオン加速器の主要部を示す断面構成図である。It is a cross-sectional block diagram which shows the principal part of the IH type | mold linear ion accelerator by Embodiment 2 of this invention. 本発明の実施の形態２に係わる低エネルギー側拡大空胴の形状を変化させた場合の電場分布を示す図である。It is a figure which shows electric field distribution at the time of changing the shape of the low energy side expansion cavity concerning Embodiment 2 of this invention. 本発明の実施の形態３によるＩＨ型線形イオン加速器の主要部を示す断面構成図である。It is a cross-sectional block diagram which shows the principal part of the IH type | mold linear ion accelerator by Embodiment 3 of this invention. 本発明の実施の形態４によるイオン加速システムを示すブロック図である。It is a block diagram which shows the ion acceleration system by Embodiment 4 of this invention.

符号の説明Explanation of symbols

１ 共振空胴、２ ドリフトチューブ、３ ステム、４ リッジ、５ エンドリッジチューナー、６ 低エネルギー側エンドドリフトチューブ、７ 低エネルギー側空胴端板、８ 高エネルギー側エンドドリフトチューブ、９ 高エネルギー側空胴端板、１０ａ，１０ｂ，１０ｃ 加速ギャップ、１１ 低エネルギー側拡大空胴、１２ 高エネルギー側拡大空胴、２０ 拡大空胴Ａ、２１ 拡大空胴Ｂ、２２ コーン状拡大空胴、２３ イオン源、２４ 低エネルギービーム輸送路、２５ 前段加速器、２６ ＩＨ型線形加速器、２７ 中エネルギービーム輸送路。   1 Resonant cavity, 2 drift tube, 3 stem, 4 ridge, 5 end ridge tuner, 6 low energy side end drift tube, 7 low energy side cavity end plate, 8 high energy side end drift tube, 9 high energy side sky Cylinder end plate, 10a, 10b, 10c Acceleration gap, 11 Low energy side expansion cavity, 12 High energy side expansion cavity, 20 Expansion cavity A, 21 Expansion cavity B, 22 Cone-shaped expansion cavity, 23 Ion source 24 Low energy beam transport path 25 Pre-stage accelerator 26 IH linear accelerator 27 Medium energy beam transport path

Claims (5)

イオンビームの加速方向に沿って共振空胴内に設置された複数のドリフトチューブ、共振空胴内壁に設置された一対のリッジ、および上記複数のドリフトチューブを上記一対のリッジに交互に接続して支持するステムを備え、上記共振空胴内に上記加速方向に沿って発生させた磁場により上記複数のドリフトチューブ間に加速電場を発生させて、上記共振空胴内に入射する上記イオンビームを加速する線形イオン加速器において、イオンビーム入射側の共振空胴端部の空胴径は、上記共振空胴中央部の空胴径より大きく、かつこの径拡大部は、共振空胴端より上記一対のリッジが設けられている個所に至る位置まで設けられていることを特徴とする線形イオン加速器。 A plurality of drift tubes installed in the resonant cavity along the acceleration direction of the ion beam, a pair of ridges installed on the inner wall of the resonant cavity, and the plurality of drift tubes are alternately connected to the pair of ridges. An accelerating electric field is generated between the plurality of drift tubes by a magnetic field generated along the acceleration direction in the resonant cavity, and the ion beam incident on the resonant cavity is accelerated. In the linear ion accelerator, the cavity diameter at the resonance cavity end on the ion beam incident side is larger than the cavity diameter at the center of the resonance cavity, and the enlarged diameter part is more than the pair of resonance cavities from the resonance cavity end. A linear ion accelerator characterized by being provided up to a position where a ridge is provided. 径拡大部は、イオンビーム入射側の共振空胴端より、上記加速方向に沿って共振空胴内に発生する加速電場の立ち上り領域を含む位置まで設けられていることを特徴とする請求項１記載の線形イオン加速器。 2. The diameter enlargement portion is provided from a resonance cavity end on the ion beam incident side to a position including a rising region of an acceleration electric field generated in the resonance cavity along the acceleration direction. The linear ion accelerator described. 径拡大部の空胴径は、加速方向に沿って段階的に変化していることを特徴とする請求項１または２記載の線形イオン加速器。 3. The linear ion accelerator according to claim 1, wherein a cavity diameter of the enlarged diameter portion changes stepwise along the acceleration direction. 4. 径拡大部の空胴径は、加速方向に沿ってコーン状に徐々に変化していることを特徴とする請求項１または２記載の線形イオン加速器。 3. The linear ion accelerator according to claim 1, wherein the cavity diameter of the enlarged diameter portion gradually changes in a cone shape along the acceleration direction. 4. イオン源、該イオン源から出射するイオンビームを加速する前段加速器、および該前段加速器から出射するイオンビームを加速する後段加速器を備えたイオン加速システムにおいて、上記後段加速器として、請求項１〜４のいずれかに記載の線形イオン加速器を用いたことを特徴とするイオン加速システム。 In an ion acceleration system comprising an ion source, a pre-accelerator for accelerating an ion beam emitted from the ion source, and a post-accelerator for accelerating an ion beam emitted from the pre-accelerator, the post-accelerator includes: An ion acceleration system using the linear ion accelerator according to any one of the above.
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