JP6171126B2 - High frequency charged particle accelerator - Google Patents
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- 239000002245 particle Substances 0.000 title claims description 80
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Description
本発明は荷電粒子を加速するための高周波型荷電粒子加速器に関し、特に、電力効率を向上させた高周波型荷電粒子加速器に関する。 The present invention relates to a high-frequency charged particle accelerator for accelerating charged particles, and more particularly to a high-frequency charged particle accelerator having improved power efficiency.
電子やイオン等の荷電粒子を電気力を用いて人工的に高速状態に加速する加速器は、様々な産業分野に使用されている。特に電子線は広く産業分野に使用されており、高分子材料の架橋や重合を促進したり、医療器具等を滅菌したりするのに利用されている。荷電粒子を加速する加速器としては、直流電圧を使用するものと高周波を使用するものとが知られている。高周波加速方式の方が同一の加速エネルギを得るのに直流電圧加速方式と比べて装置を小型化できるという利点がある。例えば、高周波としてマイクロ波を用いたリニアックの場合には、電子を５ＭｅＶに加速するのに長さ１ｍ程度の直線型の加速空洞が用いられている。これに対して、直流電圧加速器では、電気絶縁耐圧を維持するために高圧ガス（ＳＦ６）を満たしたタンク内に収納されており、タンクの大きさは直径２ｍ以上、高さ７ｍ以上といった巨大なものとなっている。しかしながら、マイクロ波型のリニアックでは、クライストロンを使用しているため高価であり、また電力効率が悪いため大電流を加速できない。このような問題を解決するものとして、偏向磁石を用いて加速ビームを偏向させ、複数の加速回数で繰り返し加速を行う蛇行型のＶＨＦ帯の高周波源を用いた電子加速器が提案されている。これは、マイクロ波の高周波源より取り扱いやすく、また安価なものであった。蛇行型の加速器としては、例えば、フランスのサクレ研究所により提案されたロードトロンや、特許文献１に記載の折畳み軌道高周波電子加速器等が挙げられる。 Accelerators that artificially accelerate charged particles such as electrons and ions to high speed using electric force are used in various industrial fields. In particular, electron beams are widely used in the industrial field, and are used to promote cross-linking and polymerization of polymer materials and to sterilize medical instruments and the like. As an accelerator for accelerating charged particles, one using a DC voltage and one using a high frequency are known. The high-frequency acceleration method has the advantage that the apparatus can be downsized compared to the DC voltage acceleration method in order to obtain the same acceleration energy. For example, in the case of a linac using microwaves as a high frequency, a linear acceleration cavity having a length of about 1 m is used to accelerate electrons to 5 MeV. On the other hand, the DC voltage accelerator is housed in a tank filled with high pressure gas (SF 6 ) in order to maintain the electric withstand voltage, and the size of the tank is 2 m in diameter and 7 m in height. It has become a thing. However, the microwave type linac is expensive because a klystron is used, and a large current cannot be accelerated because power efficiency is poor. In order to solve such a problem, an electron accelerator using a meandering VHF band high-frequency source that deflects an acceleration beam using a deflecting magnet and repeatedly accelerates a plurality of times of acceleration has been proposed. This was easier to handle and cheaper than microwave high-frequency sources. Examples of the meandering type accelerator include a roadtron proposed by the Sacre Institute in France, a folding orbit high-frequency electron accelerator described in Patent Document 1, and the like.
１回の加速回数で加速可能なエネルギは、供給する高周波電力及び加速空洞の構造に依存する。そのため、高いエネルギまで加速しようとすると、加速回数を増やす必要がある。例えば、１回の加速回数で５００ｋｅＶ加速可能だとすると、１０ＭｅＶまで加速するためには、２０回加速する必要がある。そうすると、加速器が複雑且つ巨大化し、高価となってしまう。また、例えば加速電圧を２倍とすれば、加速回数は半分で済むが、加速電圧を２倍とするためには、加速空洞に高周波電力を供給するための高周波源に用いられる真空管の最大定格をそれに合わせて高いものとする必要があった。そうすると、高周波増幅器が高価且つ巨大化してしまう問題があった。 The energy that can be accelerated by one acceleration depends on the high-frequency power supplied and the structure of the acceleration cavity. Therefore, if it is going to accelerate to high energy, it is necessary to increase the frequency | count of acceleration. For example, if it is possible to accelerate 500 keV with one acceleration, it is necessary to accelerate 20 times in order to accelerate to 10 MeV. If it does so, an accelerator will become complicated and huge, and will become expensive. For example, if the acceleration voltage is doubled, the number of accelerations can be halved. However, in order to double the acceleration voltage, the maximum rating of the vacuum tube used for the high frequency source for supplying high frequency power to the acceleration cavity Needed to be high to match. Then, there is a problem that the high frequency amplifier becomes expensive and large.
本発明は、斯かる実情に鑑み、安価に製造可能でビーム電力を増加させたり電力効率を高くすることが可能な高周波型荷電粒子加速器を提供しようとするものである。 In view of such circumstances, the present invention is intended to provide a high-frequency charged particle accelerator that can be manufactured at low cost and can increase beam power or increase power efficiency.
上述した本発明の目的を達成するために、本発明による高周波型荷電粒子加速器は、荷電粒子を加速する加速空洞と、加速空洞に荷電粒子ビームを入射する荷電粒子源であって、荷電粒子ビームの出力電流が可変可能な荷電粒子源と、加速空洞がパルス励振するように高周波電力をパルス的に加速空洞に供給するための真空管を用いる高周波源であって、真空管のピーク出力時の陽極損失が真空管の最大定格を超えつつ平均の陽極損失が真空管の最大定格内に収まるようにパルス駆動可能な高周波源と、高周波源のパルス出力のタイミングに合わせて荷電粒子源の荷電粒子ビームの出力電流をオン・オフさせるように、荷電粒子源及び高周波源を制御するパルス制御部と、を具備するものである。 In order to achieve the above-described object of the present invention, a high-frequency charged particle accelerator according to the present invention is an acceleration cavity for accelerating charged particles, and a charged particle source for injecting a charged particle beam into the acceleration cavity. A high-frequency source using a charged particle source whose output current can be varied and a vacuum tube for supplying high-frequency power to the acceleration cavity in a pulsed manner so that the acceleration cavity is pulse-excited, and the anode loss at the peak output of the vacuum tube Exceeds the maximum rating of the vacuum tube and the average anode loss can be pulsed so that the average anode loss is within the maximum rating of the vacuum tube, and the output current of the charged particle beam of the charged particle source in accordance with the pulse output timing of the high frequency source And a pulse control unit for controlling the charged particle source and the high-frequency source so as to turn on and off.
ここで、高周波源は、ピーク出力が平均出力とデューティ比の逆数との積以上となるようにパルス駆動可能であれば良い。 Here, the high frequency source only needs to be capable of pulse driving so that the peak output is equal to or greater than the product of the average output and the reciprocal of the duty ratio.
また、加速空洞は、ビーム経路が直線状の線形加速空洞であれば良い。 The acceleration cavity may be a linear acceleration cavity having a linear beam path.
また、加速空洞は、ビーム経路を蛇行させる蛇行型加速空洞であり、さらに、荷電粒子を蛇行させながら加速するために、加速空洞の外部に配置され加速される荷電粒子ビームの方向が蛇行するように偏向させるための偏向部を具備するものであっても良い。 The acceleration cavity is a meandering type acceleration cavity that meanders the beam path. Further, in order to accelerate while causing the charged particles to meander, the direction of the charged particle beam that is arranged outside the acceleration cavity meanders. It may be provided with a deflecting section for deflecting the light.
本発明の高周波型荷電粒子加速器には、安価に製造可能でビーム電力を増加させたり電力効率を高くすることが可能であるという利点がある。 The high-frequency charged particle accelerator of the present invention has an advantage that it can be manufactured at low cost, and can increase the beam power and increase the power efficiency.
以下、本発明を実施するための形態を図示例と共に説明する。図１は、本発明の高周波型荷電粒子加速器の概略構成図である。図示の通り、本発明の高周波型荷電粒子加速器は、加速空洞１０と、荷電粒子源２０と、高周波源３０と、パルス制御部４０とから主に構成される。 DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. FIG. 1 is a schematic configuration diagram of a high-frequency charged particle accelerator according to the present invention. As shown in the figure, the high-frequency charged particle accelerator of the present invention is mainly composed of an acceleration cavity 10, a charged particle source 20, a high-frequency source 30, and a pulse controller 40.
加速空洞１０は、荷電粒子を加速するために用いられるものである。本発明の高周波型荷電粒子加速器においては、加速空洞１０としては、例えばビーム経路が直線状の線形加速空洞であれば良い。また、ビーム経路を蛇行させる蛇行型加速空洞であっても良い。蛇行型加速空洞の場合には、荷電粒子を蛇行させながら加速するために、加速空洞１０の外部に配置され、加速される電子ビーム等の荷電粒子ビームの方向が蛇行するように偏向させるための偏向部を設ければ良い。蛇行型加速空洞としては、例えばロードトロンや折畳み軌道高周波加速器等に用いられる加速空洞を用いることが可能である。なお、本発明の高周波型荷電粒子加速器では、用いられる加速空洞は荷電粒子を加速可能なものであれば良く、従来の又は今後開発されるべきあらゆる加速空洞が利用可能である。 The acceleration cavity 10 is used for accelerating charged particles. In the high frequency charged particle accelerator of the present invention, the acceleration cavity 10 may be a linear acceleration cavity having a linear beam path, for example. Further, it may be a meandering type acceleration cavity that meanders the beam path. In the case of the meandering type acceleration cavity, in order to accelerate the charged particles while meandering, the charged particles are arranged outside the acceleration cavity 10 and deflected so that the direction of the charged particle beam such as an accelerated electron beam meanders. A deflection unit may be provided. As the meandering type acceleration cavity, it is possible to use, for example, an acceleration cavity used in a loadtron, a folding orbit high-frequency accelerator, or the like. In the high-frequency charged particle accelerator of the present invention, the acceleration cavity to be used is not limited as long as it can accelerate charged particles, and any conventional acceleration cavity to be developed in the future can be used.
図２に、本発明の高周波型荷電粒子加速器に用いられる蛇行型加速空洞の一例を示す。図２は、本発明の高周波型荷電粒子加速器に用いられる加速空洞の一例として、蛇行型加速空洞を説明するための概略図であり、図２（ａ）がその側断面図であり、図２（ｂ）がそのｂ−ｂ断面図である。図示例の蛇行型加速空洞１０は、ビーム経路を蛇行させて荷電粒子を加速させる折畳み軌道高周波加速器に用いられる加速空洞の一例であり、外導体１１と、その内部に設けられた互いに対向して配置される一対の加速電極１２とを備えるものである。そして、加速電極１２間に、加速ギャップ１３が形成されている。加速電極１２には、複数のビーム通路１４が設けられており、荷電粒子源２０から入射した荷電粒子ビームがビーム通路１４を通って加速ギャップ１３で加速される。そして、加速された荷電粒子ビームは、外導体１１に設けられたビーム孔１５から外導体１１の外に出て、偏向部１６により１８０度偏向させられ、再び別のビーム孔１５から外導体１１内に入り、ビーム通路１４を通って加速ギャップ１３で加速される。なお、偏向部１６としては、例えば偏向電磁石であれば良い。このようにして加速ギャップ１３で加速が繰り返されることにより、荷電粒子ビームは加速ギャップ１３の電圧よりも高いエネルギに加速されて最終的に引き出される。 FIG. 2 shows an example of a meandering acceleration cavity used in the high-frequency charged particle accelerator of the present invention. FIG. 2 is a schematic view for explaining a meandering type acceleration cavity as an example of an acceleration cavity used in the high frequency charged particle accelerator of the present invention, and FIG. 2 (a) is a side sectional view thereof. (B) is the bb sectional view. The meandering type acceleration cavity 10 in the illustrated example is an example of an acceleration cavity used in a folding orbit high-frequency accelerator that meanders a beam path and accelerates charged particles. A pair of acceleration electrodes 12 are provided. An acceleration gap 13 is formed between the acceleration electrodes 12. The acceleration electrode 12 is provided with a plurality of beam paths 14, and the charged particle beam incident from the charged particle source 20 is accelerated through the beam path 14 in the acceleration gap 13. The accelerated charged particle beam exits the outer conductor 11 from the beam hole 15 provided in the outer conductor 11, is deflected by 180 degrees by the deflecting unit 16, and is again deflected from another beam hole 15 to the outer conductor 11. It enters and is accelerated by the acceleration gap 13 through the beam passage 14. The deflection unit 16 may be a deflection electromagnet, for example. By repeating the acceleration in the acceleration gap 13 in this way, the charged particle beam is accelerated to energy higher than the voltage of the acceleration gap 13 and finally extracted.
ここで、荷電粒子源２０は、加速空洞１０に荷電粒子ビームを入射させるものである。そして、本発明の高周波型荷電粒子加速器においては、荷電粒子源２０は、後述のパルス制御部４０により、荷電粒子ビームの出力電流が可変可能なように構成されている。即ち、パルス駆動が可能であり、またその出力電流も可変可能なものである。荷電粒子源２０としては、例えば、陽子やイオンの場合にはイオン源が用いられ、電子の場合には熱や電界や光を利用した電子銃が用いられる。後述の通り、荷電粒子源２０は、その出力電流が高周波源３０のパルス出力のタイミングに合わせてオン・オフ制御が可能なように構成されている。 Here, the charged particle source 20 causes the charged particle beam to enter the acceleration cavity 10. In the high frequency charged particle accelerator of the present invention, the charged particle source 20 is configured such that the output current of the charged particle beam can be varied by a pulse control unit 40 described later. That is, pulse driving is possible and the output current can be varied. As the charged particle source 20, for example, an ion source is used in the case of protons or ions, and an electron gun using heat, electric field, or light is used in the case of electrons. As will be described later, the charged particle source 20 is configured such that its output current can be controlled on and off in accordance with the pulse output timing of the high-frequency source 30.
高周波源３０は、加速空洞１０がパルス励振するように高周波電力をパルス的に加速空洞１０に供給するためのものであり、真空管を用いるものである。そして、高周波源３０に用いられる真空管のピーク出力時の陽極損失が真空管の最大定格を超えつつ平均の陽極損失が真空管の最大定格内に収まるようにパルス駆動可能なものである。高周波源３０は、真空管を自励振させる高周波自励発振器であっても良いし、高周波増幅器に信号発生器からの信号が入力されるものであっても良い。例えば図１では、高周波源３０は、真空管を用いた高周波増幅器３１に信号発生器３２からの信号が入力される例を示した。高周波増幅器３１には、陽極直流電源３３が接続される。そして、真空管の第一格子のバイアスをパルス制御部４０からの信号に同期してパルス的に大きく変化させ、信号を遮断することで、高周波源３０をパルス駆動すれば良い。例えば信号発生器３２と高周波増幅器３１の間にゲート回路を接続し、これをオンオフ制御すれば良い。なお、パルス励振時に大きな陽極直流電流を供給できるように、必要な静電容量のバンクコンデンサ等が陽極直流電源３３と高周波増幅器３１の間に設けられれば良い。 The high-frequency source 30 is for supplying high-frequency power to the acceleration cavity 10 in a pulsed manner so that the acceleration cavity 10 is pulse-excited, and uses a vacuum tube. The anode loss at the peak output of the vacuum tube used for the high-frequency source 30 can be pulse-driven so that the average anode loss is within the maximum rating of the vacuum tube while exceeding the maximum rating of the vacuum tube. The high-frequency source 30 may be a high-frequency self-excited oscillator that self-excites the vacuum tube, or a signal that is input to a high-frequency amplifier from a signal generator. For example, FIG. 1 shows an example in which the high-frequency source 30 receives a signal from the signal generator 32 to a high-frequency amplifier 31 using a vacuum tube. An anode DC power supply 33 is connected to the high frequency amplifier 31. Then, the bias of the first grating of the vacuum tube is greatly changed in a pulse manner in synchronization with the signal from the pulse control unit 40, and the signal is cut off to drive the high frequency source 30 in pulses. For example, a gate circuit may be connected between the signal generator 32 and the high-frequency amplifier 31, and this may be controlled on / off. Note that a bank capacitor or the like having a necessary capacitance may be provided between the anode DC power supply 33 and the high-frequency amplifier 31 so that a large anode DC current can be supplied during pulse excitation.
パルス制御部４０は、高周波源３０のパルス出力のタイミングに合わせて荷電粒子源２０の荷電粒子ビームの出力電流をオン・オフさせるように、荷電粒子源２０及び高周波源３０を上述のように制御するものである。即ち、荷電粒子源２０及び高周波源３０は、パルス制御部４０からの信号に応じてパルス出力のタイミングやデューティ比、荷電粒子ビームの出力電流が可変可能なように構成されれば良い。 The pulse control unit 40 controls the charged particle source 20 and the high frequency source 30 as described above so as to turn on / off the output current of the charged particle beam of the charged particle source 20 in accordance with the pulse output timing of the high frequency source 30. To do. That is, the charged particle source 20 and the high frequency source 30 may be configured so that the pulse output timing, duty ratio, and output current of the charged particle beam can be varied in accordance with a signal from the pulse control unit 40.
ここで、高周波電力と加速エネルギの関係を、折畳み軌道高周波電子加速器を例に説明する。加速空洞１０のシャントインピーダンスをＲｓ［ＭΩ］、加速電圧（発生電圧）をＶｃ［ｋＶ］とすると、加速空洞を励振するための高周波損失（加速空洞励振電力）Ｐｃ［Ｗ］は次式で表される。
（式１）
Ｐｃ＝Ｖｃ２／（２・Ｒｓ）
また、加速電圧Ｖｃ［ｋＶ］のときの加速電流をＩ［ｍＡ］とすると、得られるビーム電力（負荷）Ｐｂ［Ｗ］は次式で表される。
（式２）
Ｐｂ＝ｎ・Ｖｃ・Ｉ
但し、ｎは最終エネルギに達するまでの加速回数である。
したがって、加速空洞を励振するために必要な高周波電力Ｐｒｆ［Ｗ］は、高周波損失Ｐｃとビーム電力Ｐｂの和として次式で表される。
（式３）
Ｐｒｆ＝Ｐｃ＋Ｐｂ
＝Ｖｃ２／（２・Ｒｓ）＋ｎ・Ｖｃ・Ｉ
ここで、例えば加速回数ｎを半分、即ちｎ／２とし、加速電圧Ｖｃを２倍、即ち２・Ｖｃとすると、加速空洞のシャントインピーダンスＲｓは２倍、即ち２・Ｒｓとなる。これは、加速回数が半分になると、折畳み軌道高周波電子加速器においては加速空洞の長さも原理的に半分になる為である。これらの関係を式１に代入すると、加速回数を半分にした場合の高周波損失Ｐｃ'は次式で表される。
（式４）
Ｐｃ'＝２・Ｐｃ
即ち、同じビーム電力を得るためには、加速回数を半分にした場合には高周波電力を２倍にする必要がある。また、加速回数を２倍にすれば、高周波電力は半分で済むことも分かる。
Here, the relationship between the high frequency power and the acceleration energy will be described by taking a folded orbit high frequency electron accelerator as an example. When the shunt impedance of the acceleration cavity 10 is Rs [MΩ] and the acceleration voltage (generated voltage) is Vc [kV], the high frequency loss (acceleration cavity excitation power) Pc [W] for exciting the acceleration cavity is expressed by the following equation. Is done.
(Formula 1)
Pc = Vc 2 / (2 · Rs)
Further, when the acceleration current at the acceleration voltage Vc [kV] is I [mA], the obtained beam power (load) Pb [W] is expressed by the following equation.
(Formula 2)
Pb = n · Vc · I
Here, n is the number of accelerations until the final energy is reached.
Therefore, the high frequency power Prf [W] necessary for exciting the acceleration cavity is expressed by the following equation as the sum of the high frequency loss Pc and the beam power Pb.
(Formula 3)
Prf = Pc + Pb
= Vc 2 / (2 · Rs) + n · Vc · I
Here, for example, if the number of accelerations n is half, that is, n / 2, and the acceleration voltage Vc is doubled, that is, 2 · Vc, the shunt impedance Rs of the acceleration cavity is doubled, that is, 2 · Rs. This is because, when the number of accelerations is halved, the length of the accelerating cavity is theoretically halved in the folded orbit high-frequency electron accelerator. When these relationships are substituted into Equation 1, the high frequency loss Pc ′ when the number of accelerations is halved is expressed by the following equation.
(Formula 4)
Pc ′ = 2 · Pc
That is, in order to obtain the same beam power, it is necessary to double the high-frequency power when the number of accelerations is halved. It can also be seen that if the number of accelerations is doubled, the high frequency power can be halved.
ここで、加速器をパルス駆動する、即ち、加速空洞をパルス励振することを考える。加速電圧Ｖｃを一定とし、パルス駆動のデューティ比をＤｙとすると、平均高周波電力＜Ｐｒｆ＞は、式３から次式で表される。
（式５）
＜Ｐｒｆ＞＝Ｄｙ・Ｐｒｆ
＝Ｄｙ・（Ｐｃ＋Ｐｂ）
＝Ｄｙ・Ｖｃ２／（２・Ｒｓ）＋ｎ・Ｄｙ・Ｖｃ・Ｉ
式５は、パルス励振を行うと、そのデューティ分だけ加速空洞励振電力及びビーム電力が減少することを示している。
Here, it is considered that the accelerator is pulse-driven, that is, the acceleration cavity is pulse-excited. When the acceleration voltage Vc is constant and the duty ratio of pulse driving is Dy, the average high frequency power <Prf> is expressed by the following equation from Equation 3.
(Formula 5)
<Prf> = Dy · Prf
= Dy · (Pc + Pb)
= Dy · Vc 2 / (2 · Rs) + n · Dy · Vc · I
Equation 5 shows that when pulse excitation is performed, the acceleration cavity excitation power and the beam power are reduced by the duty.
そして、本発明の高周波型荷電粒子加速器では、高周波源３０は、上述のように真空管のピーク出力時の陽極損失が真空管の最大定格を超えつつ平均の陽極損失が真空管の最大定格内に収まるようにパルス駆動可能なものである。即ち、高周波源３０の平均出力は、パルス励振でも連続励振（ＣＷ励振）の場合と同程度となるようにすることが可能である。換言すると、パルス励振時のピーク出力を、平均出力、即ちＣＷ励振における出力の１／Ｄｙ倍となるようにパルス駆動が可能となる。これは、式５の左辺の平均高周波電力をＰｒｆと置き換えることができることになる。即ち、以下の関係となる。
（式６）
Ｐｒｆ＝Ｄｙ・（Ｐｃ＋Ｐｂ'）
但し、Ｐｂ'はパルス励振時のピークビーム電力であり、次式で表される。
（式７）
Ｐｂ'＝ｎ・Ｖｃ・Ｉ'
＝Ｐｒｆ／Ｄｙ−Ｐｃ
但し、Ｉ'は高周波源３０のピーク出力がＰｒｆ／Ｄｙに増えた結果、増加した加速電流のピーク値である。
したがって、本発明の高周波型荷電粒子加速器で得ることができるビーム電力Ｐｂは、式７から次式で表される。
（式８）
Ｐｂ＝Ｄｙ・Ｐｂ'
＝Ｐｒｆ−Ｄｙ・Ｐｃ
In the high-frequency charged particle accelerator of the present invention, the high-frequency source 30 allows the average anode loss to be within the maximum rating of the vacuum tube while the anode loss at the peak output of the vacuum tube exceeds the maximum rating of the vacuum tube as described above. Can be pulse-driven. That is, the average output of the high-frequency source 30 can be set to the same level as that in the case of continuous excitation (CW excitation) even in pulse excitation. In other words, pulse driving can be performed so that the peak output during pulse excitation is 1 / Dy times the average output, that is, the output during CW excitation. This means that the average high-frequency power on the left side of Equation 5 can be replaced with Prf. That is, the following relationship is established.
(Formula 6)
Prf = Dy · (Pc + Pb ′)
However, Pb ′ is a peak beam power at the time of pulse excitation, and is expressed by the following equation.
(Formula 7)
Pb ′ = n · Vc · I ′
= Prf / Dy-Pc
However, I ′ is the peak value of the acceleration current increased as a result of the peak output of the high frequency source 30 increasing to Prf / Dy.
Therefore, the beam power Pb that can be obtained with the high-frequency charged particle accelerator of the present invention is expressed by the following equation from Equation 7.
(Formula 8)
Pb = Dy · Pb ′
= Prf-Dy · Pc
式８によると、パルス励振によりデューティ比Ｄｙに比例して高周波損失が減ることが分かる。その結果、ビーム電力を増やすことが可能となる。このとき、加速電流、即ち、荷電粒子源２０の荷電粒子ビームの出力電流を増やすことになる。荷電粒子ビームの、ＣＷ励振時の出力電流に対する、本発明の高周波型荷電粒子加速器の出力電流のピーク値の増加割合Ｉ'／Ｉは、式３と式７から次式で表される。
（式９）
Ｉ'／Ｉ＝（Ｐｒｆ−Ｄｙ・Ｐｃ）／［Ｄｙ・（Ｐｒｆ−Ｐｃ）］
According to Equation 8, it can be seen that high-frequency loss is reduced in proportion to the duty ratio Dy by pulse excitation. As a result, the beam power can be increased. At this time, the acceleration current, that is, the output current of the charged particle beam of the charged particle source 20 is increased. The increase rate I ′ / I of the peak value of the output current of the high-frequency charged particle accelerator of the present invention with respect to the output current of the charged particle beam during CW excitation is expressed by the following equation from Equation 3 and Equation 7.
(Formula 9)
I ′ / I = (Prf−Dy · Pc) / [Dy · (Prf−Pc)]
図３に、パルス励振時とＣＷ励振時における高周波電力の関係を説明するためのグラフを示す。横軸は時間であり１周期分を表し、縦軸は電力である。１周期分の電力は縦軸と横軸の値の積で表される。即ち、図示された範囲の面積が１周期分の電力となる。このように、真空管を用いた高周波増幅器の平均出力は、パルス励振の場合でもＣＷ励振の場合と同程度となるようにすることが可能である。 FIG. 3 shows a graph for explaining the relationship between the high-frequency power during pulse excitation and CW excitation. The horizontal axis represents time and represents one cycle, and the vertical axis represents power. The power for one cycle is represented by the product of the values on the vertical axis and the horizontal axis. In other words, the area of the range shown in the figure is power for one cycle. As described above, the average output of the high-frequency amplifier using the vacuum tube can be set to the same level as in the case of CW excitation even in the case of pulse excitation.
本発明の高周波型荷電粒子加速器では、このように、ピーク出力が平均出力とデューティ比の逆数との積以上となるようにパルス駆動すれば、ＣＷ励振の場合以上のビーム出力が得られることが分かる。このとき、真空管のピーク出力時の陽極損失が真空管の最大定格を超えつつ、平均の陽極損失が真空管の最大定格内に収まるようにパルス駆動すれば良い。仮に平均出力がＣＷ励振の場合と同程度で良い場合には、ピーク出力を平均出力とデューティ比の逆数の積と同程度とすれば良い。この場合にも、式７及び図３から明らかな通り、加速空洞励振電力がＤｙ倍に減少するので、電力効率は向上することになる。 In the high-frequency charged particle accelerator of the present invention, if the pulse drive is performed so that the peak output is equal to or greater than the product of the average output and the reciprocal of the duty ratio, a beam output higher than that in the case of CW excitation can be obtained. I understand. At this time, pulse driving may be performed so that the anode loss at the peak output of the vacuum tube exceeds the maximum rating of the vacuum tube and the average anode loss is within the maximum rating of the vacuum tube. If the average output is about the same as that of CW excitation, the peak output may be about the same as the product of the average output and the reciprocal of the duty ratio. Also in this case, as is apparent from Equation 7 and FIG. 3, the acceleration cavity excitation power is reduced by a factor of Dy, so that the power efficiency is improved.
以下、本発明の高周波型荷電粒子加速器において、図２に示される折畳み軌道高周波電子加速器の加速空洞を用いた場合の実験結果を具体的な数値を挙げて説明する。例えばＮ．Ｈａｙａｓｈｉｚａｋｉ ｅｔ ａｌ．， Ｎｕｃｌｅａｒ Ｉｎｓｔｒｕｍｅｎｔｓ ａｎｄ Ｍｅｔｈｏｄｓ， Ｂ１８８（２００２） Ｐ．２４３−２４６に記載されている実験結果を用いる。即ち、高周波損失Ｐｃ、ビーム電力Ｐｂ、加速回数ｎは以下の通りである。
高周波損失Ｐｃ＝３５ｋＷ
ビーム電力Ｐｂ＝５．３ｋＷ
加速回数ｎ＝５回
このとき、高周波電力Ｐｒｆは、式３より
高周波電力Ｐｒｆ＝４０．３ｋＷ
となる。例えばデューティ比が０．２のパルス駆動をした場合、得られるビーム電力は、式８より
Ｐｂ＝（４０．３−０．２・３５）＝３３．３ｋＷ
となる。即ち、本発明により、ＣＷ励振時に比べて、得られるビーム電力が約６倍となることが分かる。また、このときの加速電流の増加割合Ｉ'／Ｉは、式９より
Ｉ'／Ｉ≒３１．４
となる。即ち、パルス制御部では、荷電粒子ビームの出力電流が約３１倍となるように荷電粒子源を制御すれば良い。
Hereinafter, in the high-frequency charged particle accelerator of the present invention, the experimental results when using the acceleration cavity of the folded orbit high-frequency electron accelerator shown in FIG. 2 will be described with specific numerical values. For example, N.C. Hayashizaki et al. , Nuclear Instruments and Methods, B188 (2002) P.M. The experimental results described in 243-246 are used. That is, the high frequency loss Pc, the beam power Pb, and the number of accelerations n are as follows.
High frequency loss Pc = 35kW
Beam power Pb = 5.3 kW
The number of accelerations n = 5. At this time, the high-frequency power Prf is calculated from Equation 3 as follows:
It becomes. For example, when pulse driving with a duty ratio of 0.2 is performed, the obtained beam power is Pb = (40.3−0.2 · 35) = 33.3 kW from Equation 8.
It becomes. That is, according to the present invention, it can be seen that the obtained beam power is about 6 times that of CW excitation. Further, the acceleration current increase rate I ′ / I at this time is expressed by the following equation 9 from I ′ / I≈31.4.
It becomes. That is, the pulse control unit may control the charged particle source so that the output current of the charged particle beam is about 31 times.
また、ビーム電力を増加させるのではなく、同じビーム電力として電力効率を向上させる場合についても具体例を挙げて説明する。この例でも、高周波損失Ｐｃ、ビーム電力Ｐｂ、加速回数ｎは上記の例と同様とし、デューティ比も０．２とする。同じビーム電力とするので、式８よりただちに次式が得られる。
（式１０）
Ｐｒｆ＝Ｄｙ・Ｐｃ＋Ｐｂ
ここで、上述の具体的な数値を代入すると、
Ｐｒｆ＝０．２・３５＋５．３＝１２．３ｋＷ
となる。したがって、必要な高周波電力はＣＷ励振時と比べて約１／３となったことが分かる。
A case where the beam efficiency is not increased but the power efficiency is improved with the same beam power will be described with a specific example. Also in this example, the high-frequency loss Pc, the beam power Pb, and the number of accelerations n are the same as in the above example, and the duty ratio is 0.2. Since the same beam power is used, the following equation is obtained immediately from Equation 8.
(Formula 10)
Prf = Dy · Pc + Pb
Here, substituting the above specific numerical values,
Prf = 0.2 · 35 + 5.3 = 12.3 kW
It becomes. Therefore, it can be seen that the necessary high-frequency power is about 1/3 compared with that during CW excitation.
ここで、電力効率ηを次式で定義する。
（式１１）
η＝ビーム出力／高周波入力
＝Ｐｂ／Ｐｒｆ
したがって、式１１を［００２５］段落の結果に適用すると、電力効率は４３．１％となる。なお、従来のＣＷ励振時の電力効率は、１３．２％となるため、本発明は約３倍の電力効率となる。但し、この場合、荷電粒子ビームの出力電流は、デューティ比０．２の逆数である５倍、即ち、Ｉ'＝５・Ｉとする。
Here, the power efficiency η is defined by the following equation.
(Formula 11)
η = beam output / high frequency input = Pb / Prf
Therefore, when Equation 11 is applied to the result of the [0025] paragraph, the power efficiency is 43.1%. In addition, since the power efficiency at the time of the conventional CW excitation is 13.2%, this invention becomes a power efficiency of about 3 times. However, in this case, the output current of the charged particle beam is five times the reciprocal of the duty ratio of 0.2, that is, I ′ = 5 · I.
以上説明したように、本発明の高周波型荷電粒子加速器は、必要によりビーム電力を増加させたり、逆に電力効率が高くなるように制御可能である。また、ピーク出力時の陽極損失が真空管の最大定格内に収まる真空管を用いる必要が無く、平均の陽極損失が最大定格内に収まる真空管を用いれば良いため、大きく高価な真空管を用いる必要がないので安価に製造可能なものである。 As described above, the high-frequency charged particle accelerator of the present invention can be controlled such that the beam power is increased as necessary, or the power efficiency is increased. In addition, it is not necessary to use a vacuum tube whose anode loss at peak output is within the maximum rating of the vacuum tube, and it is only necessary to use a vacuum tube whose average anode loss is within the maximum rating, so there is no need to use a large and expensive vacuum tube. It can be manufactured at low cost.
なお、本発明の高周波型荷電粒子加速器は、上述の図示例にのみ限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。 The high-frequency charged particle accelerator of the present invention is not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the scope of the present invention.
１０ 加速空洞
１１ 外導体
１２ 加速電極
１３ 加速ギャップ
１４ ビーム通路
１５ ビーム孔
１６ 偏向部
２０ 荷電粒子源
３０ 高周波源
３１ 高周波増幅器
３２ 信号発生器
３３ 陽極直流電源
４０ パルス制御部
DESCRIPTION OF SYMBOLS 10 Acceleration cavity 11 Outer conductor 12 Acceleration electrode 13 Acceleration gap 14 Beam path 15 Beam hole 16 Deflection part 20 Charged particle source 30 High frequency source 31 High frequency amplifier 32 Signal generator 33 Anode DC power supply 40 Pulse control part
Claims (4)
荷電粒子を加速する加速空洞と、
前記加速空洞に荷電粒子ビームを入射する荷電粒子源であって、荷電粒子ビームの出力電流が可変可能な荷電粒子源と、
前記加速空洞がパルス励振するように高周波電力をパルス的に加速空洞に供給するための真空管を用いる高周波源であって、真空管のピーク出力時の陽極損失が真空管の最大定格を超えつつ平均の陽極損失が真空管の最大定格内に収まるようにパルス駆動可能な高周波源と、
前記高周波源のパルス出力のタイミングに合わせて荷電粒子源の荷電粒子ビームの出力電流をオン・オフさせるように、荷電粒子源及び高周波源を制御するパルス制御部と、
を具備することを特徴とする高周波型荷電粒子加速器。 A high-frequency charged particle accelerator for accelerating charged particles, the high-frequency charged particle accelerator comprising:
An accelerating cavity that accelerates charged particles,
A charged particle source for injecting a charged particle beam into the accelerating cavity, wherein the output current of the charged particle beam is variable; and
A high-frequency source using a vacuum tube for supplying high-frequency power to the acceleration cavity in a pulsed manner so that the acceleration cavity is pulse-excited, wherein the anode loss at the peak output of the vacuum tube exceeds the maximum rating of the vacuum tube and the average anode A high-frequency source that can be pulsed so that the loss is within the maximum rating of the vacuum tube;
A pulse control unit for controlling the charged particle source and the high frequency source so as to turn on and off the output current of the charged particle beam of the charged particle source in accordance with the timing of the pulse output of the high frequency source;
A high-frequency charged particle accelerator comprising:
さらに、荷電粒子を蛇行させながら加速するために、加速空洞の外部に配置され加速される荷電粒子ビームの方向が蛇行するように偏向させるための偏向部を具備する、
ことを特徴とする高周波型荷電粒子加速器。 The high-frequency charged particle accelerator according to claim 1 or 2, wherein the acceleration cavity is a meandering type acceleration cavity that meanders a beam path,
Furthermore, in order to accelerate while causing the charged particles to meander, the deflecting unit is arranged outside the acceleration cavity and deflected so that the direction of the accelerated charged particle beam meanders.
A high-frequency charged particle accelerator characterized by that.
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