Yukimitsu Ohshiro

Development of the National Institute of Radiological Sciences electron cyclotron resonance ion source for the heavy ion medical accelerator in Chiba

The development of an electron cyclotron resonance ion source for the heavy ion medical accelerator in Chiba (HIMAC) injector is reported. The HIMAC is a heavy ion medical accelerator for cancer therapy. The electron cyclotron resonance (ECR) ion source is expected to provide a long lifetime, easy operation, and easy maintenance for medical use. The NIRS‐ECR ion source has a single closed ECR stage, and a microwave frequency of 10 GHz is applied. Under the present performance, the output electrical currents of the ions are 2500 eμA for He1+, 300 eμA for C2+, 480 eμA for Ne3+, and 110 eμA for Ar6+. Stability of the intensity is better than 2%. The transmission efficiency through a low‐energy beam‐transport line with an acceptance of 200 πmm mrad is more than 70%; the typical 50% and 90% emittances of the injection beam with 8 keV/u are 20 and 80 πmm mrad, respectively. These performances satisfy the requirements for radiotherapy.

Nanocluster ion source by plasma-gas aggregation

We are constructing and developing a new type cluster ion source and a detection system. The new cluster ion source consists of a large area plasma source and gas aggregation cell instead of present cluster ion source configuration (magnetron ion source and gas aggregation cell). In new type cluster ion source we adopted a pulsed high-power microwave type plasma source for production of ions and neutral particles. This source can produce dense and stable plasma independent of shape or properties of the sample, and additionally it can produce large sizes of plasma, so that whole area of the sample is sputtered. This feature allows us to produce an intense beam of cluster ions stably compared to the present ion source.

Production of beams from solid materials at Center for Nuclear Study electron cyclotron resonance ion sourcea)

Two methods for the feed of vapor from solid materials in the Center for Nuclear Study ECR ion source are described. A rod placed near the wall of the plasma chamber, operating up to a melting point of 2600 °C, has been used for CaO, SiO2, and FeO. An oven with a number of openings, operating up to 800 °C, has been used for P2O5, Li, and S. Typical ion beam intensities of (7)Li(2+), (6)Li(3+), (40)Ca(12+), and (56)Fe(15+) are achieved 280, 75, 28, and 7 eμA, respectively. High intensity heavy ion beams are stably supplied into the azimuthally varying field cyclotron.

Grating monochromator for electron cyclotron resonance ion source operation

Recently, we started to observe optical line spectra from an ECR plasma using a grating monochromator with a photomultiplier. The light intensity of line spectrum from the ECR plasma had a strong correlation with ion beam intensity measured by a magnetic mass analyzer. This correlation is a significant information for beam tuning because it allows the extraction of the desired ion species from the ECR plasma. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process, but this research gives new insights into its simplification. In this paper, the grating monochromator method for beam tuning of a Hyper-ECR ion source as an injector for RIKEN azimuthal varying field (AVF) cyclotron is described.

Plasma spectroscopy of metal ions for hyper-electron cyclotron resonance ion sourcea)

In this research, the optical line spectra of metal ions from ECR plasma were observed using a grating monochromator with a photomultiplier. The light intensity of line spectrum from the ECR plasma had a strong correlation with ion beam intensity measured by a magnetic mass analyzer. This correlation is a significant information for the beam tuning process, because it allows to conduct the extraction of the desired metal ion species from the ECR plasma. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process, but this research provides a new approach for its simplification. In this paper the grating monochromator method for metal ion beam tuning such as (40)Ca(12+), (56)Fe(15+), and (85)Rb(20+) of hyper-ECR ion source as an injector for RIKEN Azimuthal Varying Field cyclotron is described.

Manufacture of a compact Ku-band electron cyclotron resonance ion source with two resonance zones and variable frequency

A compact ECR ion source working at a Ku band has been manufactured for the production of both low and multiple charged ions. This source can be formed for both the ordinal ECR zone and second Bernstein resonance zone with a half Becr field. The B minimum field configuration is realized by the use of permanent magnets and its axial mirror field can be adjusted within ±0.03 T by a small auxiliary solenoid. Microwave power can be injected from both axial and radial ports. Effective power of 200–250 W can be supplied to the source with a continuously variable frequency in the range of 12.0–14.5 GHz and with a variable pulse mode. The outer dimension of the source is φ180×230 and its total weight is just 30 kg. The design, manufacture and results of the preliminary test are reported.

A cold-cathode pig source for high-intensity Li3+ ion

Abstract An internal cold-cathode Penning ion source has been developed at a cyclotron to accelerate Li beams. A block of single-crystal LiF was used for the charge material and located in the anode chamber opposite the slit. The pulsed-mode operation of the arc yielded high currents up to 2.2 μA for Li 3+ ions.

Broadband Buncher Cavity for Beam Transport Line of HiECR Ion Source

A newly developed rf buncher has been installed in the beam transport line of an electron cyclotron resonance (ECR) ion source, HiECR, at the Center for Nuclear Study (CNS) of the University of Tokyo. The rf buncher is a compact cavity having magnetic alloy (MA) cores and operates in the wide frequency range between 18 and 45 MHz without any tuning systems. Bunched beams of H+, O5+, and Ar8+ ions have been produced successfully and measured using a newly designed Faraday cup with good time resolution. In this paper, the design of the MA-loaded buncher cavity and the results of the beam test are presented. A detailed description of the HiECR beam transport line and the design of the new Faraday cup are also given.

Note: An innovative method for 12C4+ suppression in 18O6+ beam production in an electron cyclotron resonance ion source

It is a major and complex task to accelerate an ion which has the same charge to mass ratio with strong contaminant ions, such as 12C4+ in the 18O6+ beam. An innovative method has been developed to suppress the contaminant ions in the Electron Cyclotron Resonance (ECR) ion source by introducing Li vapor. The ion distribution inside the ECR zone was obtained by the optical analysis of ions inside the ECR ion source. The 12C4+ ions were suppressed as much as by a factor of 10, whereas the 18O6+ beam changed little with the use of this technique.

Status Report of the Operation of the RIKEN AVF Cyclotron

The operation of the RIKEN AVF cyclotron was started in 1989. Since then, it has been operated not only as an injector for the RIKEN ring cyclotron but also as an independent supplier of various ion beams. In this report, we describe both the operational status and the improvement work for increasing accelerating ability of the AVF cyclotron performed in this past year (August 2012-July 2013). 1. はじめに 理研AVFサイクロトロン(AVF)は、K値 70 MeVで 理研加速器研究施設(RARF)において1989年に理 研リングサイクロトロン(RRC)の入射器として稼動 を開始して以来、毎年3000時間を超える運転を行っ てきた。AVF及び周辺実験設備の全体をFigure 1 に 示す。AVFはRRCの入射器として使用されるほか、 単独でも低エネルギーの重イオンビームの供給に使 用されており、それぞれ「RRC入射モード」、 「AVF単独モード」と呼ぶ。 RRC入射モードでは、AVFで水素(H2)からRb までをE=3.78〜7 MeV/uに加速し、RRCでさらに65 ~135 MeV/uまで加速し各実験コースへビームを供 給している。2009年からRIBFでの軽イオン加速が開 始され、AVFはRIBF複合加速器群の入射器としての 役割も果たしている。 AVF単独モードでは、陽子(A/Q=1)から Ca (A/Q=3.5)まで多様な核種のイオンをエネルギー E=3.8〜12 MeV/u(陽子は14 MeV)まで加速し、各実 験コースへ供給している。 また、 3台の外部入射イオン源( Hyper-ECRIS, SCECRIS, PIS)は金属イオン、ガス、偏極重陽子と 加速する粒子によって使い分けられ、マシンタイム のスケジュールを開発や準備期間を考慮して組むこ とにより、ビーム切換えを短時間で円滑に実施でき るように運用されている。 ここでは2012年8月から 2013年7月までのAVF 運 転状況を報告する。 2. 運転実績 AVF で加速された核種とエネルギーの実績を Figure 2に示す。今回の対象期間において AVF単独 モード、RRC 入射モードでそれぞれこれまでに加速 実績のあるビーム 8 種類と 7 種類、初めて加速する ビーム 1種類と 2種類の運転を実施した。 2 つのモードの運転時間の内訳を Figure 3 に示す。 図中の調整時間は、加速の準備の開始時刻からター ゲット上のスポット調整の完了時刻までの時間を積 算したものです。また「C03、E7A、E7B、RIBF、 RRC」は各コースのユーザーにビームを供給した時 間(スポット調整完了時刻から実験終了時刻、ただ し途中の加速器事由のトラブルによる停止時間を除 く )とした。C03 は AVF 取出し後の直線ビーム ラインをまっすぐ延長した先にあり RI 製造のため に増設したコースである。供給するビームは主に 14 MeV の陽子であるが、一昨年より新たに 12 MeV/u の重陽子ビーム供給を開始している。昨年までとは 異なり、今回の対象期間においてはこのコースの利 用時間が最も長かった。E7A コースは東京大学原子 核科学研究センター(CNS)が管理するコースで、学 生実験を含む原子核実験を行っている。E7B コース は非原子核実験と一部の RI製造を行う。 RRC 入射モードのうち RRC からのビームを利用 する RARF 実験施設の実験コースへ供給したものは 「RRC」、RRC の後段に増設した RIBF サイクロト ロン群で加速したビームを利用した実験については 「RIBF」と記した。RARF 実験施設の実験において は故障によってビーム供給時間に支障がある場合は、 ____________________________________________ # tsukiori@riken.jp Proceedings of the 10th Annual Meeting of Particle Accelerator Society of Japan (August 3-5, 2013, Nagoya, Japan)