JP2007139525A - Method and device for focusing positron beam - Google Patents
Method and device for focusing positron beam Download PDFInfo
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本発明は、磁場で輸送してきた陽電子ビームをターゲットに集束するための陽電子ビーム集束方法および集束装置に関する。 The present invention relates to a positron beam focusing method and a focusing apparatus for focusing a positron beam transported by a magnetic field on a target.
物性計測等に使われる陽電子ビームは、材料の物性計測等では微小な径の陽電子ビームが必要な場合があるが、一般的にソレノイド磁場あるいはヘルムホルツコイルによって発生する地磁気より十分磁場強度の高い０．００１テスラ以上の磁場を利用した磁気輸送部で発散を防ぎ真空容器中を輸送される。磁場輸送の陽電子ビームを磁場中で微小なビーム径に集束することは難しい。
ここで、０．００１テスラ以上の磁場を磁気輸送磁場、０．００１テスラを含んでそれ以下の磁場を弱磁場という。非磁場とは、地磁気と同等かそれより磁場強度の低い磁場をいう。
そこで、磁場中の陽電子ビームを非磁場あるいは弱磁場中に引き出し、非磁場・弱磁場中で陽電子減速材上に集束し入射して減速材から再放出した陽電子を加速し集束する方法が試みられてきた。
陽電子ビームを非磁場あるいは弱磁場中に引き出し、減速材上に集束する方法としては、たとえば、図２に示すように、磁気輸送部内の磁気輸送部の磁場中で陽電子ビームを加速した後、弱磁場へ引き出し、弱磁場に引き出した後に集束レンズによりビームを集束する方法が知られている。( 非特許文献1参照)。
A positron beam used for measuring physical properties may require a positron beam with a small diameter for measuring physical properties of materials. Generally, the positron beam has a sufficiently higher magnetic field strength than a geomagnetic field generated by a solenoid magnetic field or a Helmholtz coil. Diversity is prevented by a magnetic transport unit using a magnetic field of 001 Tesla or higher, and it is transported through a vacuum vessel. It is difficult to focus a positron beam for magnetic field transport to a small beam diameter in a magnetic field.
Here, a magnetic field of 0.001 Tesla or higher is called a magnetic transport magnetic field, and a magnetic field including 0.001 Tesla and lower is called a weak magnetic field. A non-magnetic field refers to a magnetic field equivalent to or lower than the geomagnetism.
Therefore, a method has been attempted in which a positron beam in a magnetic field is extracted into a non-magnetic field or a weak magnetic field, focused on the positron moderator in the non-magnetic field or weak magnetic field, and accelerated and focused on the positron re-emitted from the moderator. I came.
As a method of extracting the positron beam into a non-magnetic field or a weak magnetic field and focusing it on the moderator, for example, as shown in FIG. 2, after accelerating the positron beam in the magnetic field of the magnetic transport part in the magnetic transport part, A method is known in which a beam is focused by a focusing lens after being pulled out to a magnetic field and pulled to a weak magnetic field. (See Non-Patent Document 1).
図２は従来の陽電子ビーム集束装置（１）の説明図である。
図２の装置１００は、磁場中の電場により陽電子ビームを加速する加速部１０２を備えた磁気輸送部１０１と、磁気輸送部１０１で発生する磁場が支配的な磁場領域からビーム方向に離して次段の弱磁場又は非磁場領域内に設ける集束レンズ１０３と、集束レンズ１０３を透過し集束した陽電子ビームが衝突し陽電子を再放出する減速材１０４と、減速材１０４から再放出された陽電子ビームを加速する加速部１０５と、加速部１０５で加速された陽電子ビームを集束する集束レンズ１０６を有する。
また、図３に示すように、磁気輸送部内の磁場中で陽電子ビームを加速し、磁気輸送部の一部を覆うように設置した磁気シールドを通して磁場領域から弱磁場領域へ引き出し、弱磁場領域に引き出した後に集束レンズによりビームを集束する方法が知られている。(非特許文献２参照)。
FIG. 2 is an explanatory view of a conventional positron beam focusing apparatus (1).
The apparatus 100 of FIG. 2 includes a magnetic transport unit 101 including an acceleration unit 102 that accelerates a positron beam by an electric field in a magnetic field, and a magnetic field generated by the magnetic transport unit 101 that is separated from the magnetic field region in the beam direction. A focusing lens 103 provided in a weak magnetic field or a non-magnetic field region of the stage, a moderator 104 that is transmitted through the focusing lens 103 and collides with the focused positron beam and re-emits positrons, and a positron beam re-emitted from the moderator 104 An acceleration unit 105 that accelerates and a focusing lens 106 that focuses the positron beam accelerated by the acceleration unit 105 are included.
Further, as shown in FIG. 3, the positron beam is accelerated in the magnetic field in the magnetic transport part, and is extracted from the magnetic field region to the weak magnetic field region through the magnetic shield installed so as to cover a part of the magnetic transport part. A method of focusing a beam by a focusing lens after drawing out is known. (Refer nonpatent literature 2).
図３は従来の陽電子ビーム集束装置（２）の説明図である。
図３の装置１０７は、磁場中の電場により陽電子ビームを加速する加速部１０２を備えた磁気輸送部１０１と、磁気輸送部１０１と弱磁場又は非磁場領域の間に位置し、磁気輸送部１０１で発生する磁場の弱磁場又は非磁場領域への浸入を遮蔽する磁気シールド部１０８と、磁気シールド部１０８を通過した陽電子ビームを集束する集束レンズ１０３と、集束レンズ１０３を透過し集束した陽電子ビームが衝突し陽電子を再放出する減速材１０４と、減速材１０４から再放出された陽電子ビームを加速する加速部１０５と、加速部１０５で加速された陽電子ビームを集束する集束レンズ１０６を有する。
磁気シールド部１０８は、筒状体の一方端に設けた端板に、中央に陽電子ビームが通過できる開孔を有する。陽電子ビームが通過できる開孔を有するならば、全体は任意の形状にできる。
FIG. 3 is an explanatory diagram of a conventional positron beam focusing device (2).
The apparatus 107 in FIG. 3 is located between a magnetic transport unit 101 having an acceleration unit 102 that accelerates a positron beam by an electric field in a magnetic field, and between the magnetic transport unit 101 and a weak magnetic field or a non-magnetic field region. A magnetic shield part 108 that shields the weak magnetic field or non-magnetic field generated by the magnetic field from entering, a focusing lens 103 that focuses the positron beam that has passed through the magnetic shield part 108, and a positron beam that passes through the focusing lens 103 and is focused. Has a moderator 104 that re-emits positrons, an acceleration unit 105 that accelerates the positron beam re-emitted from the moderator 104, and a focusing lens 106 that focuses the positron beam accelerated by the acceleration unit 105.
The magnetic shield part 108 has an opening through which a positron beam can pass in an end plate provided at one end of the cylindrical body. As long as it has an aperture through which the positron beam can pass, it can have any shape.
また、図４に示すように、磁気輸送部内の磁場中で陽電子ビームを加速し、集束レンズの一部または全体を覆うように設置した磁気シールドを通して磁場領域から弱磁場領域へ引き出し、弱磁場領域に引き出した後に集束レンズによりビームを集束する方法が知られている。（非特許文献３）
図４は従来の陽電子ビーム集束装置（３）の説明図である。
図４の例は、図３の装置と比べると、磁気シールド１０９の配置場所が異なっている。磁気シールド１０９を除く他の構成要素は同じ構成を有するので、図３の説明を援用し、ここでは説明を省略する。
FIG. 4 is an explanatory view of a conventional positron beam focusing device (3).
The example of FIG. 4 differs from the apparatus of FIG. 3 in the location of the magnetic shield 109. Since the other components except for the magnetic shield 109 have the same configuration, the description of FIG. 3 is used and the description is omitted here.
図２の例では、磁気輸送部１０１で発生する０．００１テスラ以上の磁気輸送磁場は、陽電子ビームを陽電子ビーム発生源から陽電子ビームの利用場所に輸送するために必要であるが、他方磁場中を通過する陽電子ビームは集束レンズを用いてビーム径を小さくすることが難しい。集束レンズにより陽電子ビームを絞るためには、陽電子ビームを弱磁場領域に適切なビーム径で直進性を良くして引き出す必要があるが、従来の手法では、磁気輸送部の磁気輸送磁場領域から弱磁場領域に引き出すさいに、ビームの直進性が悪くなる。そのため、陽電子ビームは集束レンズ１０３を介しても所望のようにビーム径が小さくならない。その結果、減速材１０４に当たる単位面積あたりの陽電子ビームの強度は低くなり、減速材より放出される単位面積あたりの陽電子ビーム強度が減少してしまう。これでは実用に供しない。 In the example of FIG. 2, a magnetic transport magnetic field of 0.001 Tesla or more generated in the magnetic transport unit 101 is necessary for transporting the positron beam from the positron beam generation source to the positron beam utilization place. It is difficult to reduce the beam diameter of the positron beam passing through the beam using a focusing lens. In order to focus the positron beam with the focusing lens, it is necessary to extract the positron beam with a suitable beam diameter in the weak magnetic field region with good straightness, but in the conventional method, the positron beam is weakened from the magnetic transport magnetic field region of the magnetic transport part. When the magnetic field is extracted, the straightness of the beam is deteriorated. Therefore, the beam diameter of the positron beam does not decrease as desired even through the focusing lens 103. As a result, the intensity of the positron beam per unit area hitting the moderator 104 is lowered, and the intensity of the positron beam per unit area emitted from the moderator is reduced. This is not practical.
図３および図４の例では、磁気輸送部１０１で発生する強磁界を磁気シールドで遮蔽し弱磁場領域を形成できるが、磁気輸送部１０１から弱磁場領域に引き出された陽電子ビームは直進性が悪くなりビーム径が小さくならない。直進性が悪い陽電子ビームは集束レンズ１０３を介しても所望のようにビーム径が小さくならない。その結果、減速材１０４に当たる単位面積あたりの陽電子ビームの強度は低くなり、減速材より放出される単位面積あたりの陽電子ビーム強度が減少してしまう。これでは実用に供しない。
微小なビーム径を得るには、非磁場・弱磁場中の陽電子減速材に入射する陽電子ビームの直進性を良くする必要がある。しかし、これまでの方法では、磁場から非磁場あるいは弱磁場に引き出す際にビームの直進性が悪くなり、それによりその後のレンズでの集束具合も悪かった。このような方法でビームを減速材に入射すると、再放出した陽電子を加速し集束しても、たとえば磁場輸送部中の磁場中で１０ｍｍ径のビームを１０μｍといった微小な径にすることは困難であった。そのため、減速材から再放出した陽電子を加速集束して再び減速材に入射し、この減速材で再放出した陽電子の径を小さくするためにさらに加速集束しなければならなかった。このように減速材への入射、再放出した陽電子の加速・集束を複数段行うと、ビーム強度が一段あたり数分の一に減少することから、ビーム強度が低下するという問題があった。また、装置が複雑になるとう問題もあった。
3 and 4, the strong magnetic field generated in the magnetic transport unit 101 can be shielded by a magnetic shield to form a weak magnetic field region. However, the positron beam extracted from the magnetic transport unit 101 to the weak magnetic field region has a straightness. The beam diameter will not be reduced. A positron beam having poor straightness does not have a small beam diameter as desired even through the focusing lens 103. As a result, the intensity of the positron beam per unit area hitting the moderator 104 is reduced, and the intensity of the positron beam per unit area emitted from the moderator is reduced. This is not practical.
In order to obtain a very small beam diameter, it is necessary to improve the rectilinearity of the positron beam incident on the positron moderator in a non-magnetic field or weak magnetic field. However, in the conventional methods, when the magnetic field is extracted from the non-magnetic field or the weak magnetic field, the straightness of the beam is deteriorated, and the focusing condition by the subsequent lens is also deteriorated. When the beam is incident on the moderator in this way, it is difficult to make a 10 mm diameter beam as small as 10 μm in the magnetic field in the magnetic field transport part even if the re-emitted positron is accelerated and focused. there were. For this reason, the positrons re-emitted from the moderator must be accelerated and focused, and then enter the moderator again. In order to reduce the diameter of the positrons re-emitted by the moderator, it has to be further accelerated and focused. When the acceleration / focusing of the positrons incident on the moderator and re-emitted in this way is performed in a plurality of stages as described above, the beam intensity is reduced to a fraction of one stage, resulting in a problem that the beam intensity is lowered. There is also a problem that the apparatus becomes complicated.
本発明の目的は、陽電子ビームを陽電子ビーム源から利用場所にまで輸送してくるための磁気輸送磁場領域と、陽電子ビーム径が小さくなるように集束させる弱磁場又は非磁場領域とを近接させながら、直進性の良いビームを弱磁場または非磁場領域に引き出しビーム径を小さくする陽電子ビーム集束方法および集束装置を提供することにある。 An object of the present invention is to bring a magnetotransport magnetic field region for transporting a positron beam from a positron beam source to a use site and a weak magnetic field or a non-magnetic field region focused so as to reduce the positron beam diameter close to each other. Another object of the present invention is to provide a positron beam focusing method and a focusing apparatus that draws a beam with good straightness in a weak magnetic field or non-magnetic field region and reduces the beam diameter.
陽電子ビーム源にて生成され一般に数ミリのビーム径をもつ陽電子ビームは、一般にビームの進行方向とは垂直方向の運動エネルギーの幅（約１ｅＶ（エレクトロンボルト））をもっているため、陽電子ビーム源で生成直後のビーム径よりもさらにビーム径が数ミリ拡がらないように利用場所まで輸送するためには、約０．００１テスラ（Ｔ）以上の磁場が必要である。本発明では、上記目的を達成するため、引き出し用コイルを磁気輸送部が形成する０．００１テスラ以上の磁気輸送磁場領域と非磁場・弱磁場領域の間に設置して、このコイルに磁気輸送部が形成するビーム輸送磁場とは逆向きの磁場を発生させ、磁気輸送部の磁場中から、弱磁場あるいは非磁場領域に直進性の高い陽電子ビームを引き出す。例えば、引き出し用コイルが発生する磁気輸送部の磁場とは逆向きの磁場の強度は、ひき出し用コイルの設置場所に磁気輸送部のコイルが形成する磁場の強さの５０％〜１５０％としたとき、逆向きの磁場をかけない場合に比べて適切なビーム径で顕著に直進性の良いビームが引き出せる。 A positron beam generated by a positron beam source and having a beam diameter of several millimeters generally has a kinetic energy width (about 1 eV (electron volts)) in a direction perpendicular to the traveling direction of the beam. A magnetic field of about 0.001 Tesla (T) or more is necessary to transport the beam diameter to the place of use so that the beam diameter does not further expand several millimeters from the beam diameter immediately after. In the present invention, in order to achieve the above object, a drawing coil is installed between a magnetic transport magnetic field region of 0.001 Tesla or more formed by the magnetic transport part and a non-magnetic / weak magnetic field region, and magnetic transport is performed on this coil. A magnetic field in the direction opposite to the beam transport magnetic field formed by the unit is generated, and a positron beam having high straightness is extracted from the magnetic field of the magnetic transport unit to a weak magnetic field or a non-magnetic field region. For example, the strength of the magnetic field in the direction opposite to the magnetic field of the magnetic transport unit generated by the extraction coil is 50% to 150% of the strength of the magnetic field formed by the coil of the magnetic transport unit at the installation location of the pulling coil. As a result, it is possible to draw out a beam with a remarkably good straightness with an appropriate beam diameter as compared with the case where a reverse magnetic field is not applied.
図５は本発明の磁場強度分布特性図である。
図６は従来の引き出し用コイル不使用時のビーム軌道の図である。
図７は本発明の引き出し用コイル使用時のビーム軌道の図である。
図５に、引き出し用コイルに磁場を発生させなかった場合におけるビーム軸上の磁場の分布図と、引き出し用コイルに磁場輸送部の磁場とは逆向きの磁場を発生させる場合のビーム軸上の磁場の分布図を示す。横軸Ｚは磁気輸送部（内部）から弱磁場領域（内部）までのビーム方向の距離（ｍ）、縦軸は磁場の強さ（ｆＢＺ）を単位テスラで表す。引き出し用コイルを使用しない場合の特性と引き出し用コイルを使用する場合の特性は、距離Ｚが０．３〜０．５ｍの範囲で磁場の強さに顕著に差がでる。この特性の差から、本発明の引き出し用コイルを使用する場合、最初の集束レンズの位置を、例えば、Ｚ＝０．６ｍ以上にすると（図７参照）、ビームの直進性が良くなり好ましい結果が出る。前記好ましい結果がでる位置は、図５の特性から、適宜選択する。
FIG. 5 is a magnetic field strength distribution characteristic diagram of the present invention.
FIG. 6 is a diagram of a beam trajectory when a conventional extraction coil is not used.
FIG. 7 is a diagram of a beam trajectory when the extraction coil of the present invention is used.
FIG. 5 is a distribution diagram of the magnetic field on the beam axis when no magnetic field is generated in the extraction coil, and on the beam axis when the extraction coil generates a magnetic field opposite to the magnetic field of the magnetic field transport unit. The distribution map of a magnetic field is shown. The horizontal axis Z represents the distance (m) in the beam direction from the magnetic transport part (inside) to the weak magnetic field region (inside), and the vertical axis represents the magnetic field strength (fBZ) in unit Tesla. The characteristic when the extraction coil is not used and the characteristic when the extraction coil is used are significantly different in the strength of the magnetic field when the distance Z is in the range of 0.3 to 0.5 m. Due to this difference in characteristics, when the extraction coil of the present invention is used, if the position of the first focusing lens is set to, for example, Z = 0.6 m or more (see FIG. 7), the straightness of the beam is improved and a preferable result is obtained. coming out. The position where the preferable result is obtained is appropriately selected from the characteristics shown in FIG.
図６には、従来のように、引き出し用コイルおよび磁気シールドを有しない場合で、引き出し用コイルに磁場を発生させなかった場合に３ｋｅＶ陽電子ビームが、磁気輸送磁場（あるいは、磁気輸送部の磁場）中から弱磁場・非磁場中に引き出される際の軌道計算の結果を示す。陽電子ビームは弱磁場・非磁場領域で発散する。横軸Ｚは磁気輸送部（内部）から弱磁場領域（内部）までのビーム方向の距離（ｍ）、縦軸はビームライン幅（ｍ）で表す。図のように直進性の悪いビームは集束させようとしても、小さい径とするのに限度があった。
図７には、本発明のように、引き出し用コイルに磁場輸送部の磁場とは逆向きの磁場を発生させた場合における、３ｋｅＶの陽電子ビームが磁気輸送部の磁場中から、弱磁場・非磁場中に引き出される際の軌道計算の結果を示す。陽電子ビームは弱磁場・非磁場領域で、直進性のよいビームとなる。
図７の場合、引き出し用コイルを距離Ｚが０．３６ｍ付近に配置した場合の例である。弱磁場あるいは非磁場に引き出された直進性の高いビームは、磁気レンズあるいは静電レンズ等の集束レンズを用いて集束し、微小な径で減速材上に入射する。減速材から再放出された陽電子ビームは、加速と集束を行うことにより、さらに微小な径のビームにすることができる。
FIG. 6 shows a case where the extraction coil and the magnetic shield are not provided and a 3 keV positron beam is generated by the magnetic transport magnetic field (or the magnetic field of the magnetic transport unit) when no magnetic field is generated in the extraction coil. ) Shows the result of trajectory calculation when it is drawn from the inside into a weak magnetic field / non-magnetic field. A positron beam diverges in a weak magnetic field / non-magnetic field region. The horizontal axis Z represents the distance (m) in the beam direction from the magnetic transport part (inside) to the weak magnetic field region (inside), and the vertical axis represents the beam line width (m). As shown in the figure, there is a limit to reducing the diameter of a beam having poor linearity, even if the beam is focused.
FIG. 7 shows that, as in the present invention, a 3 keV positron beam is generated from the magnetic field of the magnetic transport unit when the magnetic field in the direction opposite to the magnetic field of the magnetic field transport unit is generated in the extraction coil. The result of trajectory calculation when it is pulled out in a magnetic field is shown. The positron beam is a weak magnetic field / non-magnetic field region, and becomes a beam with good straightness.
In the case of FIG. 7, the drawing coil is an example in which the distance Z is arranged in the vicinity of 0.36 m. A beam with high rectilinearity extracted by a weak magnetic field or a non-magnetic field is focused using a focusing lens such as a magnetic lens or an electrostatic lens, and is incident on the moderator with a small diameter. The positron beam re-emitted from the moderator can be further reduced in diameter by accelerating and focusing.
具体的には、以下のようになる。
（１）陽電子ビーム集束方法は、磁気輸送部の磁場中で陽電子ビームを加速する手順１、前記加速された陽電子ビームを該陽電子ビームの進行方向において前記磁場の方向とは逆方向に磁場を重ね合わせて弱磁場領域に引き出し集束する手順２、からなることを特徴とする。
（２）陽電子ビーム集束方法は、磁気輸送部の磁場中で陽電子ビームを加速する手順１、
前記加速された陽電子ビームを該陽電子ビームの進行方向において前記磁場の方向とは逆方向に磁場を重ね合わせて弱磁場領域に引き出し集束する手順２、前記集束された陽電子ビームを減速材によって減速し弱磁場領域において加速し集束する手順３、からなることを特徴とする。
（３）上記（１）又は（２）記載の陽電子ビーム集束方法は、前記逆方向の磁場を、前記手順１の磁場が前記逆方向の磁場の発生している場所に形成する磁場の強さの５０パーセントから１５０パーセントのうちの任意の値に設定したことを特徴とする。
（４）陽電子ビーム集束装置は、少なくとも、陽電子ビームの加速部を含む磁気輸送部と、前記磁気輸送部の磁場中から非磁場あるいは弱磁場中に陽電子ビームを引き出すための１つ以上の磁気輸送部の磁場とは逆方向の磁場を発生する引き出し用コイルとを有することを特徴とする。
（５）上記（４）記載の陽電子ビーム集束装置は、陽電子ビームの加速部を含む磁気輸送部と、前記磁気輸送部の磁場中から非磁場あるいは弱磁場中に陽電子ビームを引き出すための１つ以上の引き出し用コイルと、前記非磁場あるいは弱磁場中に引き出された陽電子ビームを集束する集束レンズと、集束した前記陽電子ビームを減速する減速材と、前記減速材から再放出された陽電子ビームを加速する加速部と、前記加速部により加速された陽電子ビームを集束する集束レンズとを有し、前記引き出し用コイルの発生磁場の向きを前記磁気輸送部の磁場の方向と逆方向にしたことを特徴とする。
（６）上記（４）又は（５）記載の陽電子ビーム集束装置は、前記引き出し用コイルの磁場を、前記磁気輸送部が前記引き出し用コイル磁場の発生している場所に形成する磁場の強さの５０パーセントから１５０パーセントのうちの任意の値にし、磁場の向きを逆方向に設定したことを特徴とする。
（７）上記（４）乃至（６）のいずれか１項記載の陽電子ビーム集束装置は、前記磁気輸送部の磁場の強さを０．００１テスラ（Ｔ)以上としたことを特徴とする。
Specifically, it is as follows.
(1) The positron beam focusing method is a procedure 1 for accelerating a positron beam in a magnetic field of a magnetic transport unit, and superimposing the accelerated positron beam in a direction opposite to the direction of the magnetic field in the traveling direction of the positron beam. It is characterized in that it comprises the procedure 2 in which it is extracted and focused together in a weak magnetic field region.
(2) The positron beam focusing method is a procedure 1 for accelerating the positron beam in the magnetic field of the magnetic transport unit,
Step 2 of converging the accelerated positron beam in a weak magnetic field region by superimposing a magnetic field in a direction opposite to the direction of the magnetic field in the traveling direction of the positron beam, decelerating the focused positron beam with a moderator It is characterized by comprising step 3 of accelerating and focusing in a weak magnetic field region.
(3) In the positron beam focusing method described in (1) or (2) above, the strength of the magnetic field that forms the reverse magnetic field in the place where the magnetic field in the procedure 1 generates the reverse magnetic field. It is characterized in that it is set to any value from 50 percent to 150 percent.
(4) The positron beam focusing device includes at least a magnetic transport unit including a positron beam acceleration unit and one or more magnetic transports for extracting a positron beam from a magnetic field of the magnetic transport unit into a non-magnetic field or a weak magnetic field. And a drawing coil that generates a magnetic field in a direction opposite to the magnetic field of the part.
(5) The positron beam focusing apparatus described in (4) above is a magnetic transport unit including a positron beam acceleration unit, and one for extracting a positron beam from a magnetic field of the magnetic transport unit into a non-magnetic field or a weak magnetic field. The above extraction coil, a focusing lens for focusing the positron beam extracted in the non-magnetic field or weak magnetic field, a moderator for decelerating the focused positron beam, and a positron beam re-emitted from the moderator An accelerating unit that accelerates and a focusing lens that focuses the positron beam accelerated by the accelerating unit, and the direction of the magnetic field generated by the extraction coil is opposite to the direction of the magnetic field of the magnetic transport unit. Features.
(6) In the positron beam focusing apparatus according to the above (4) or (5), the magnetic field strength of the magnetic field generated by the magnetic transport unit at the place where the magnetic field for the extraction coil is generated. The magnetic field is set to an arbitrary value from 50% to 150%, and the direction of the magnetic field is set in the reverse direction.
(7) The positron beam focusing apparatus according to any one of (4) to (6) is characterized in that the magnetic field strength of the magnetic transport part is 0.001 Tesla (T) or more.
本発明は、引き出し用コイルを用いたので、非磁場あるいは弱磁場に引き出した陽電子のビーム直進性が良く、集束レンズを用いてビーム径を減速材上で従来の方法よりも小さくできることから、たとえば磁場輸送部中の磁気輸送部の磁場中で１０ｍｍ径のビームを減速材に入射・再放出した陽電子ビームを加速し集束することで１０μｍといった微小な径にすることができる。また、従来陽電子の減速材への入射・再放出陽電子の加速集束が２段以上必要だったものの段数を減らすことができる。これによって集束効率を高めることができるだけでなく、部品点数を減らすことができ、より安価にできる。さらに、装置をコンパクトにできる。 Since the present invention uses the extraction coil, the beam straightness of the positron extracted in a non-magnetic field or weak magnetic field is good, and the beam diameter can be made smaller than that of the conventional method on the moderator by using a focusing lens. By accelerating and converging a positron beam that is incident and re-emitted on a moderator in a magnetic field of a magnetic transport section in a magnetic transport section, the diameter can be made as small as 10 μm. In addition, the number of stages can be reduced although two or more stages of acceleration / focusing of the positrons that are conventionally incident and re-emitted on the moderator are required. As a result, not only the focusing efficiency can be increased, but also the number of parts can be reduced and the cost can be reduced. Furthermore, the apparatus can be made compact.
本発明の実施の形態を図に基づいて詳細に説明する。 Embodiments of the present invention will be described in detail with reference to the drawings.
本発明は、材料の物性計測などに用いられる陽電子ビームを効率的に磁場中から非磁場あるいは弱磁場中に引き出し集束する陽電子ビーム集束方法及び集束装置に関する。
図１は本発明の実施例１の陽電子ビーム集束装置の説明図である。
図１の装置１は、電場により陽電子ビームを加速する加速部２ａを備えた磁気輸送部２と、磁気輸送部２で発生する磁場が支配的な磁場領域からビーム方向に離して次段の弱磁場又は非磁場領域内に設ける集束レンズ４と、集束レンズ４を透過し集束した陽電子ビームが衝突し陽電子を再放出する減速材５と、減速材５から再放出された陽電子ビームを加速する加速部６と、加速部６で加速された陽電子ビームを集束する集束レンズ７を有する。磁気輸送部２と集束レンズ４の間のビーム径路に沿って特定位置に引き出し用コイル３を設ける。引き出し用コイル３は、ビーム径路に沿って複数設けることができる。
The present invention relates to a positron beam focusing method and a focusing apparatus for efficiently extracting and focusing a positron beam used for measuring physical properties of a material from a magnetic field into a non-magnetic field or a weak magnetic field.
FIG. 1 is an explanatory diagram of a positron beam focusing apparatus according to Embodiment 1 of the present invention.
The apparatus 1 in FIG. 1 includes a magnetic transport unit 2 having an acceleration unit 2a for accelerating a positron beam by an electric field, and the next stage weakening away from the magnetic field region where the magnetic field generated by the magnetic transport unit 2 is dominant in the beam direction. A focusing lens 4 provided in a magnetic field or a non-magnetic field region, a moderator 5 that collides with a positron beam transmitted through the focusing lens 4 and re-emits positrons, and an acceleration that accelerates the positron beam re-emitted from the moderator 5 And a focusing lens 7 that focuses the positron beam accelerated by the acceleration unit 6. An extraction coil 3 is provided at a specific position along the beam path between the magnetic transport unit 2 and the focusing lens 4. A plurality of extraction coils 3 can be provided along the beam path.
引き出し用コイル３の発生磁場の向きは磁気輸送部２の発生磁場の向きと反対に設定する。また、引き出し用コイル３の発生磁場の強さは磁気輸送部２の発生磁場の強さの５０〜１５０パーセントのうちの任意の値に設定する。
図１に示すように、陽電子ビームの加速部を含んだ磁気輸送部２と、磁気輸送部２の磁場中から非磁場あるいは弱磁場中に引き出すための１つ以上の引き出し用コイル３と、非磁場あるいは弱磁場中に引き出した後に集束する集束レンズ４と、集束したビームを減速する減速材５と、減速材５から再放出した陽電子ビームを加速する加速部６と、集束レンズ７で構成され、引き出し用コイル３の発生磁場の向きを磁気輸送部２の磁場の方向と逆転させることを特徴とすることにより、磁気輸送部２の磁場中から、弱磁場あるいは非磁場領域に直進性の高い陽電子ビームを引き出す。例えば、引き出し用コイル３が発生する磁気輸送部２の磁場とは逆向きの磁場の強度は、ひき出し用コイル３の設置場所に形成する磁場の強さの例えば５０％としたとき、直進性の良いビームが引き出せる。弱磁場あるいは非磁場に適切な径で引き出された直進性の高いビームは、磁気レンズあるいは静電レンズ等の集束レンズを用いて集束し、微小な径で減速材に入射する。減速材から再放出された陽電子ビームは、加速と集束を行うことにより、さらに微小な径のビームにすることができる。本発明により、陽電子ビームを用いた計測法の応用範囲が飛躍的に広がる。
The direction of the magnetic field generated by the extraction coil 3 is set opposite to the direction of the magnetic field generated by the magnetic transport unit 2. The strength of the magnetic field generated by the extraction coil 3 is set to an arbitrary value of 50 to 150 percent of the strength of the magnetic field generated by the magnetic transport unit 2.
As shown in FIG. 1, a magnetic transport unit 2 including a positron beam acceleration unit, one or more extraction coils 3 for extracting the magnetic transport unit 2 from a magnetic field into a non-magnetic field or a weak magnetic field, The focusing lens 4 is configured to focus after being drawn into a magnetic field or weak magnetic field, the moderator 5 that decelerates the focused beam, the acceleration unit 6 that accelerates the positron beam re-emitted from the moderator 5, and the focusing lens 7. The direction of the magnetic field generated by the extraction coil 3 is reversed to the direction of the magnetic field of the magnetic transport unit 2 so that the magnetic field of the magnetic transport unit 2 is highly linear in the weak magnetic field or non-magnetic field region. Pull out the positron beam. For example, when the strength of the magnetic field opposite to the magnetic field of the magnetic transport unit 2 generated by the lead-out coil 3 is, for example, 50% of the strength of the magnetic field formed at the place where the pull-out coil 3 is installed, straightness is achieved. A good beam can be pulled out. A beam with high rectilinearity extracted with a suitable diameter in a weak magnetic field or a non-magnetic field is focused using a focusing lens such as a magnetic lens or an electrostatic lens, and enters the moderator with a small diameter. The positron beam re-emitted from the moderator can be further reduced in diameter by accelerating and focusing. The scope of application of the measurement method using a positron beam is greatly expanded by the present invention.
図８は本発明の実施例２の陽電子ビーム集束装置の説明図である。
図８では、ビーム径路に沿って、磁気輸送部１２、引き出し用コイル１３、集束レンズ１４、減速材１５、陽電子ビーム加速部１６、集束レンズ１７、減速材（または、測定物）１８を所定間隔で配置する。磁気輸送部１２から放出された陽電子ビームは引き出し用コイルの磁場により直進性を保ちながら集束レンズ１４へ向けられる。磁気輸送部１２は、図１の磁気輸送部２の円筒状の輸送用コイル（ソレノイドコイル）のかわりに輸送用コイルとしてリング状のコイル（ヘルムホルツコイル）を複数並べることにより構成される。
図８に示すように、装置に約０．００７Ｔの磁場中で１０ｍｍ径の陽電子ビームを３ｋｅＶで加速し、引き出し用コイルに逆向きの磁場を発生するように電流を流し、集束レンズ１４を用いて集束したところ、集束点で１ｍｍ以下のビーム径が得られた。この位置にタングステンやニッケル等の陽電子ビーム用の減速材１５を置いて陽電子を減速させ、減速材から再放出した陽電子ビームを再び加速し集束レンズ１７で集束させることにより、１０μｍ程度の陽電子ビームを得ることができる。したがって、従来陽電子の減速材１５への入射・再放出陽電子の加速集束が２段以上必要だったものを１段で済ませることができる。これによって集束効率を高めることができるだけでなく、加速・集束の段数が減ることにより、部品点数を減らすことができ、より安価にできる。
図８に示した実施例では、一度、減速材１５に陽電子ビームを入射した後、入射した面とは逆の面から再放出する陽電子ビームを再び加速し集束することにより微小な径の陽電子ビームを得ている。
FIG. 8 is an explanatory diagram of a positron beam focusing apparatus according to Embodiment 2 of the present invention.
In FIG. 8, along the beam path, the magnetic transport unit 12, the extraction coil 13, the focusing lens 14, the moderator 15, the positron beam accelerator 16, the focusing lens 17, and the moderator (or measurement object) 18 are spaced at predetermined intervals. Place with. The positron beam emitted from the magnetic transport unit 12 is directed to the focusing lens 14 while maintaining straightness by the magnetic field of the extraction coil. The magnetic transport unit 12 is configured by arranging a plurality of ring-shaped coils (Helmholtz coils) as transport coils instead of the cylindrical transport coil (solenoid coil) of the magnetic transport unit 2 of FIG.
As shown in FIG. 8, a 10 mm diameter positron beam is accelerated at 3 keV in a magnetic field of about 0.007 T, and a current is passed through the extraction coil so as to generate a reverse magnetic field. As a result of focusing, a beam diameter of 1 mm or less was obtained at the focusing point. A positron beam moderator 15 such as tungsten or nickel is placed at this position to decelerate the positron, and the positron beam re-emitted from the moderator is accelerated again and focused by the focusing lens 17 to produce a positron beam of about 10 μm. Obtainable. Therefore, the conventional positron incident / re-emitted positron on the moderator 15 that requires two or more stages of accelerated focusing can be completed in one stage. As a result, not only the focusing efficiency can be increased, but also the number of parts can be reduced and the cost can be reduced by reducing the number of stages of acceleration and focusing.
In the embodiment shown in FIG. 8, after the positron beam is incident on the moderator 15 once, the positron beam re-emitted from the surface opposite to the incident surface is accelerated and focused again to focus the positron beam with a small diameter. Have gained.
図９は本発明の実施例３の陽電子ビーム集束装置の説明図である。
図９の例は、実質的に、図８の例における減速材１５に陽電子を入射した後、入射した側の面から放出される減速した陽電子を利用する場合である。この例では、集束レンズ１９および２１が図１および図８の例と異なる構成のもので構成する。そのほかの図８の例と同じ番号の部品は、図８の説明を援用して、ここでは説明を省略する。
図９に示した実施例のように、一度、減速材に陽電子ビームを入射した後、入射した面と同じ面から再放出する陽電子ビームを再び加速し集束することにより微小な径の陽電子ビームを得ることもできる。
FIG. 9 is an explanatory diagram of a positron beam focusing apparatus according to Embodiment 3 of the present invention.
The example of FIG. 9 is a case in which, after the positron is incident on the moderator 15 in the example of FIG. 8, the decelerated positron emitted from the incident side surface is used. In this example, the focusing lenses 19 and 21 are configured with different configurations from the examples of FIGS. 1 and 8. The other parts having the same numbers as those in the example of FIG. 8 are referred to in FIG.
As in the embodiment shown in FIG. 9, after a positron beam is once incident on the moderator, the positron beam re-emitted from the same plane as the incident surface is accelerated and focused again to produce a positron beam with a small diameter. It can also be obtained.
１、１０、２０ 陽電子ビーム集束装置
２ 磁気輸送部
２ａ 加速部
３、１３ 引き出し用コイル
４、７、１４、１７、１９、２１ 集束レンズ
５、１５、１８ 減速材
６、１６ 加速部
１２ 磁気輸送部
DESCRIPTION OF SYMBOLS 1, 10, 20 Positron beam focusing apparatus 2 Magnetic transport part 2a Acceleration part 3, 13 Extraction coil 4, 7, 14, 17, 19, 21 Focusing lens 5, 15, 18 Decelerator 6, 16 Acceleration part 12 Magnetic transport Part
Claims (7)
The positron beam focusing apparatus according to any one of claims 4 to 6, wherein a magnetic field strength of the magnetic transport part is set to 0.001 Tesla or more.
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