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論文

Ultralow emittance beam production based on Doppler laser cooling and coupling resonance

野田 章*; 中尾 政夫*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; 想田 光*; 頓宮 拓*; 神保 光一*; Grieser, M.*; He, Z.*; et al.

Proceedings of 5th International Particle Accelerator Conference (IPAC '14) (Internet), p.28 - 33, 2014/07

Three-dimensional (3D) cooling of 40-keV $$^{24}$$Mg$$^+$$ ion beams with Doppler laser cooling and the coupling resonance has been demonstrated in the storage ring S-LSR of Kyoto University toward the production of ultralow-emittance beams, in other words, ultracold beams and so-called crystalline beams. So far, the transverse temperatures of 6 K and 2 K have been experimentally attained in the horizontal and vertical directions, respectively, at a low beam intensity of about $$10^4$$ ions in the ring. These temperatures are the lowest ever attained by laser cooling of ion beams. Systematic molecular dynamics simulations predict the realization of further lower temperatures, $$approx$$ 1 mK and $$approx$$ 0.1 K in the longitudinal and transverse directions, respectively, if the laser spot size and detuning are properly adjusted even with such a low laser power ($$approx$$ 10 mW) as utilized in the experiments at S-LSR. A 3D ordered state of the beam with 3D laser cooling is also predicted. Recent experimental achievements and latest simulation results are presented.

論文

S-LSRにおける水平方向のレーザー冷却に関連したシンクロトロン振動

神保 光一*; 想田 光*; 中尾 政夫*; 百合 庸介; 頓宮 拓*; 野田 章*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.1057 - 1059, 2014/06

A bunched 40-keV Mg$$^+$$ beam at an ion storage/cooler ring, S-LSR, Kyoto University, was cooled transversely through synchro-betatron coupling by a co-propagating laser. The cooled ion beams were optically diagnosed with spontaneous emission in the experiment. As the number of ions is smaller in the beam, however, it is more difficult to observe light emitted from the beam. The synchrotron-oscillation signals induced on a parallel-plate pickup were, therefore, investigated spectroscopically to see whether they were useful for beam diagnostics. We discuss the space charge effect of the signals. It is expected that, if the beam temperature is decreased drastically, the space charge effect is enhanced and the peaks related to the synchrotron oscillation are consequently suppressed.

論文

イオン蓄積・冷却リングS-LSRでのMgイオンビームのレーザー冷却

野田 章*; 中尾 政夫*; 想田 光*; 頓宮 拓*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; 神保 光一*; Grieser, M.*; He, Z.*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.143 - 145, 2014/06

We have experimentally demonstrated transverse indirect laser cooling utilizing synchro-betatron resonance coupling in the ion accumulation cooler ring S-LSR. However, its efficiency was rather poor for relatively high beam intensity of $$10^7$$ ions in the ring due to beam heating by intra-beam scattering and its cooling time was as long as 100 s. By application of beam scraping and optimization of laser detuning together with equilibrium deceleration with the use of an induction accelerator, we could reach the lowest transverse temperatures ever attained by laser cooling as 7.0 K and 2.1 K for the horizontal and vertical directions, respectively. The prospect of generating an ultra-low-temperature beam and realizing beam crystallization will be discussed on the basis of the present result.

論文

Simulation study on transverse laser cooling and crystallization of heavy-ion beams at the cooler storage ring S-LSR

百合 庸介; 大崎 一哉*; 岡本 宏巳*; He, Z.*; 想田 光*; 野田 章*; 中尾 政夫*; 頓宮 拓*; 神保 光一*

Proceedings of Workshop on Beam Cooling and Related Topics (COOL '13) (Internet), p.162 - 165, 2013/11

Efficient transverse laser cooling of a low-intensity heavy-ion beam has been recently accomplished experimentally by means of the resonant coupling method at the cooler storage ring S-LSR of Kyoto University. In parallel with the experimental effort, multi-dimensional laser cooling of the ion beam has been studied also numerically with the molecular dynamics (MD) simulation code in which the stochastic interaction between ions and laser photons is incorporated in order to search optimum laser-cooling conditions and verify the results of the experiment. The present MD result demonstrates that, in spite of the limited experimental conditions of the cooling laser such as low power, fixed frequency, and short cooling section, a three-dimensionally low-temperature beam of 40-keV $$^{24}$$Mg$$^+$$ can be obtained through resonant coupling at a low intensity of $$10^4$$ ions in the ring, which is consistent with the experimental result.

論文

Latest results of experimental approach to ultra-cold beam at S-LSR

野田 章*; 中尾 政夫*; 想田 光*; 頓宮 拓*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; 神保 光一*; Grieser, M.*; He, Z.*

Proceedings of Workshop on Beam Cooling and Related Topics (COOL '13) (Internet), p.157 - 161, 2013/11

We have tried to approach to the lowest attainable beam temperature with laser cooling of a 40-keV $$^{24}$$Mg$$^+$$ ion beam at a cooler storage ring S-LSR, which has a superperiodicity of six and is designed to be tough against resonant perturbation to the circulating beam. The capability of active indirect transverse laser cooling has been experimentally demonstrated with the use of the theoretically-proposed synchro-betatron resonance coupling scheme. For the reduction of beam heating due to intrabeam scattering, an additional scheme has been established to control the intensity of the circulating beam down to $$sim 10^4$$ ions by scraping the outskirt of the beam with the use of a horizontally-moving scraper, which could cool the horizontal and vertical beam temperature down to $$sim 20$$ K and $$sim 30$$ K, respectively, at an operation tune without horizontal-vertical (H-V) coupling. In the present paper, we would like to also present our recent results with H-V coupling in addition to longitudinal-horizontal coupling toward further reduction of the transverse beam temperature.

論文

Parameter optimization for multi-dimensional laser cooling of an ion beam in the storage ring S-LSR

He, Z.*; Wei, J.*; 大崎 一哉*; 岡本 宏巳*; 野田 章*; 中尾 政夫*; 想田 光*; 百合 庸介; 神保 光一*

Proceedings of 25th North American Particle Accelerator Conference (NA-PAC '13) (Internet), p.1298 - 1300, 2013/09

The power of the cooling laser currently available in a compact ion cooler ring S-LSR, Kyoto University, is quite limited for generating ultralow-temperature ion beams. Therefore, parameters of laser cooling should be carefully determined in order to approach the lowest possible temperature in the experiment. This paper mainly concerns optimization of laser-cooling parameters and prediction of a possible lower limit of beam temperature in S-LSR, based on systematic molecular dynamics simulations. The adiabatic capture process of the ion beam was introduced to prevent the emittance from blowing up during bunching. The spot size of the laser was optimized with the total laser power limited. An optimum solenoid field strength was obtained for three-dimensional cooling. The lowest beam temperature achievable in S-LSR was predicted by choosing the parameters optimized.

論文

Possible observation of transverse laser cooled ultimate cold ion beam in S-LSR

神保 光一*; 想田 光*; 百合 庸介; 頓宮 拓*; 中尾 政夫*; 白井 敏之*; 野田 章*

Proceedings of 25th North American Particle Accelerator Conference (NA-PAC '13) (Internet), p.886 - 888, 2013/09

The synchrotron-oscillation signals of 40-keV bunched Mg$$^+$$ ion beams were investigated for the diagnostics of the laser-cooled beams in an ion cooler storage ring, S-LSR, Kyoto University. The signals induced on a parallel-plate pickup were measured with a spectrum analyzer. The coherent and incoherent modes corresponding to the synchrotron tune were observed in the signals. The molecular dynamics simulation predicts, on the other hand, that the synchrotron oscillation of the strongly laser-cooled beam is suppressed by the space-charge force. We thus propose a possibility to detect the space-charge limit by the observation of the predicted suppression of the synchrotron oscillation.

論文

Efficiency enhancement of indirect transverse laser cooling with synchro-betatron resonant coupling by suppression of beam intensity

想田 光*; 中尾 政夫*; 頓宮 拓*; 神保 光一*; 大崎 一哉*; 岡本 宏巳*; 百合 庸介; He, Z.*; Grieser, M.*; 野田 章*

Japanese Journal of Applied Physics, 52(3), p.030202_1 - 030202_4, 2013/03

 被引用回数:4 パーセンタイル:77.11(Physics, Applied)

The efficiency of indirect transverse laser cooling of a heavy-ion beam using synchro-betatron resonant coupling (SBRC) was improved by the reduction of the beam intensity through scraping the tail part of the beam. In order to measure the beam size at low beam intensity, a new scheme was established where the beam profile was determined from the beam survival ratio by changing the insertion position of a beam scraper. At a beam intensity of $$10^4$$ particles in the ring, the transverse cooling time of the beam was reduced to 1.2 s, and horizontal and vertical minimum beam sizes were 0.2 mm and 0.6 mm, corresponding to the beam temperatures of 20 K and 29 K, respectively. The cooling time was much improved compared with that of our previous experiment, 100 s at $$10^7$$ particles (Nakao et al.). The transverse temperature was comparable to that in other work (Madsen et al.), in spite of the limitation in the experimental conditions such as low laser power and short laser-cooling section. This suggests that the present SBRC scheme has a potential capacity for attaining a lower-temperature beam or even Coulomb crystallization.

論文

Approach to the low temperature state oriented for crystalline beam

野田 章*; 中尾 政夫*; 想田 光*; 頓宮 拓*; 神保 光一*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; Meshkov, I.*; Smirnov, A.*; et al.

Proceedings of 23rd Russian Particle Accelerator Conference (RuPAC 2012) (Internet), p.48 - 52, 2012/09

Various approaches to attaining low-temperature beams have been continued in the cooler storage ring S-LSR at Kyoto University. One-dimensional ordering of electron-cooled 7-MeV protons was realized with an abrupt longitudinal temperature jump from 2 K to 0.3 K at a particle number of around 2000. Laser cooling has been applied to 40-keV $$^{24}$$Mg$$^+$$ beams toward the realization of crystalline beams. For a coasting beam, the lowest longitudinal temperature of 3.6 K was attained at $$4 times 10^4$$ ions. The temperature was limited due to intra-beam scattering (IBS). On the other hand, the transverse temperature of the beam indirectly cooled through IBS was saturated at 500 K for $$2 times 10^7$$ ions. In order to cool the transverse direction further, synchro-betatron resonance coupling has been applied to a bunched Mg beam. The transverse temperature has been reduced to the order of $$10^1$$ K at the beam intensity of $$10^4$$ ions by the reduction of the beam intensity using a scraper.

論文

スクレイパーを用いた横方向レーザー冷却効果の観測

想田 光*; 中尾 政夫*; 頓宮 拓*; 野田 章*; 神保 光一*; 大崎 一哉*; 岡本 宏巳*; 百合 庸介; Grieser, M.*; He, Z.*

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.388 - 390, 2012/08

京都大学化学研究所のイオン蓄積・冷却リングS-LSRでは、シンクロ・ベータトロン共鳴によって重イオンビームの運動の進行方向と水平方向の振動を結合させ、レーザー冷却によって横方向を間接的に冷却する実験を進めている。冷却の過程において、粒子数が多い場合Intra-beam散乱による自己加熱作用によって冷却が阻害されるため、スクレイパーによってビーム外縁部の粒子を除去することによって冷却効率を高めている。このとき、2枚のスクレイパーを用い、1枚目のスクレイパーで粒子数を減らした後、2枚目のスクレイパーの挿入距離を変えてビームの残存率を測定することで、ビーム中心からの距離とその内側にある粒子の割合が得られ、この関係から冷却後のビームサイズを測定した。その結果、40keV $$^{24}$$Mg$$^+$$ビームについて、水平・鉛直ベータトロンチューン、及びシンクロトロンチューンがそれぞれ(2.074, 1.120, 0.072)、1枚目のスクレイパーをビーム中心から0.3mmまで挿入して粒子数を1$$times$$10$$^5$$まで減少させた条件で、水平方向ビームサイズが0.3mm、温度に換算して52Kまで冷却されていることを観測した。この時、ビームサイズが1/eになるまでの冷却時間は1.25秒であった。

論文

横方向間接レーザー冷却の効率化に向けた制御ビームスクレーピング

野田 章*; 中尾 政夫*; 想田 光*; 頓宮 拓*; 神保 光一*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; Grieser, M.*; He, Z.*

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.72 - 74, 2012/08

Laser cooling of 40-keV Mg ion has been performed at S-LSR. Indirect transverse laser cooling of a bunched beam with the use of synchro-betatron resonance coupling (SBRC) has been experimentally indicated. However, it is not so efficient due to heating by intra-beam scattering for the ion number of 10$$^7$$. For attaining very low-temperature beam, it is inevitable to reduce the beam intensity without deterioration of beam detection signal. For this purpose, we have applied controlled scraping of a laser-cooled beam. After beam injection, the beam tail is cut off by a scraper moving in the horizontal direction and laser-cooled both in the longitudinal and horizontal directions with SBRC. Then, the horizontal beam size was measured with another scraper moving also in the horizontal direction. With this scheme, the beam intensity could be reduced from 10$$^7$$ to 10$$^5$$, which resulted in rather efficient indirect transverse laser cooling with the cooling time of about 1 sec.

論文

Observation of 2-component bunched beam signal with laser cooling

想田 光*; 中尾 政夫*; 野田 章*; 頓宮 拓*; 伊藤 清一*; 岡本 宏巳*; 百合 庸介; 神保 光一*; Grieser, M.*; He, Z.*

Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.397 - 399, 2012/05

The longitudinal temperature of 40 keV $$^{24}$$Mg$$^+$$ beams was measured through bunch length measurement during laser cooling at S-LSR. The bunch length was measured as time-domain signals from a pair of parallel-plate electrostatic pickups. Injected non-cooled beams gave a bunch length of 2.5 m and cooled beams had two components of broad and sharp distributions. The broad distribution had a longitudinal length of 2.2 m, which is close to that of the initial beam. The length of the sharp distribution shrunk to 0.25 m and is expected as a cooled part. The capture efficiency of cooling, which represents the ratio of particle numbers of the cooled part and the total particle number, varied with laser detuning. With a scanning range of 2 GHz, it was improved from 66% to 92%, while the bunch became longer by 10% with scanning. A new scheme for improving the capture efficiency will be applied to attain a strong signal from a low-current low-temperature beam.

論文

Challenge for more efficient transverse laser cooling for beam crystallization

野田 章*; 中尾 政夫*; 想田 光*; 頓宮 拓*; 伊藤 清一*; 岡本 宏巳*; 大崎 一哉*; 百合 庸介; 神保 光一*; Grieser, M.*; et al.

Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.394 - 396, 2012/05

Mg ion beams have been successfully laser-cooled both in longitudinal and transverse directions at S-LSR in ICR, Kyoto University. The cooling rate, however, is not strong enough to realize a crystalline beam due to heating from intra-beam scattering (IBS). Reduction of the beam intensity is inevitable to suppress this IBS effect, which, however, had resulted in poor S/N ratio for observation of the transverse beam size. We, therefore, describe a new beam-scraping scheme: The scheme selects out ions in the distribution tail of the transverse phase space, keeping the beam density in the core part by simultaneous application of multi-dimensional laser cooling and beam scraping. The strategy to realize the scheme effectively has been searched by combination of the beam experiments and computer simulations.

論文

Prompt in-line diagnosis of single bunch transverse profiles and energy spectra for laser-accelerated ions

榊 泰直; 西内 満美子; 堀 利彦; Bolton, P.; 余語 覚文; 片桐 政樹*; 小倉 浩一; 匂坂 明人; Pirozhkov, A. S.; 織茂 聡; et al.

Applied Physics Express, 3(12), p.126401_1 - 126401_3, 2010/11

 被引用回数:8 パーセンタイル:61.62(Physics, Applied)

これまで、レーザー駆動型粒子線加速実験においては、ビーム診断手法にCR39という固体飛跡検出器を用いることが一般的であった。しかし、固体検出器は実時間性を持たない検出器であるために、不安定なプラズマから粒子が発生するメカニズムの解明においては、その不安定性がレーザーに依存するものか、プラズマ自身が持つものなのかが1ショットごとに分析できなかった。そこで、それらの問題を解決するために、蛍光膜モニタを使った加速粒子のビーム形状とTOF法によるエネルギー分布を1ショットごとに観測できるシステムを構築した。この構築には、原子力機構が開発したPHITSコードを用いて、その設計性能の高さ及び、診断解析への有効性を示している。

論文

レーザー駆動型粒子線装置のための陽子線プロトタイプ輸送系の開発

榊 泰直; 西内 満美子; 堀 利彦; Bolton, P.; 余語 覚文; 小倉 浩一; 匂坂 明人; Pirozhkov, A. S.; 織茂 聡; 近藤 公伯; et al.

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.312 - 315, 2010/08

原子力機構・関西光科学研究所(関西研)では、文部科学省の「先端融合領域イノベーション創出拠点の形成プロジェクト」に採択され、平成19年度より「レーザー駆動型粒子線治療装置」の実用化を目指している。このプロジェクトは、高強度・短パルスのレーザーによる、従来のRF加速よりも高い100GeV/mという電界勾配を利用した加速手法にて、既存のシンクロトロン型粒子線治療装置を小型化するというものである。そこでレーザー駆動型粒子線に対して、これまで単体性能試験が行われた位相回転空洞,PMQ及び偏向電磁石を組合せたプロトタイプビーム輸送系を開発し、PARMILAを用いて空間電荷効果評価を行い装置の標準設計手法の確立を目指した。

論文

Measured and simulated transport of 1.9 MeV laser-accelerated proton bunches through an integrated test beam line at 1 Hz

西内 満美子; 榊 泰直; 堀 利彦; Bolton, P.; 小倉 浩一; 匂坂 明人; 余語 覚文; 森 道昭; 織茂 聡; Pirozhkov, A. S.; et al.

Physical Review Special Topics; Accelerators and Beams, 13(7), p.071304_1 - 071304_7, 2010/07

 被引用回数:25 パーセンタイル:16.63(Physics, Nuclear)

1.9MeVレーザー駆動陽子線のビームライン中に伝送した。ビームラインは、PMQ, RF cavity,monochrometerからなり、伝送の様子をPARMILAのシミュレーションによって再現した。このような試みは世界初のことである。ビームラインの最終端において、6nsのバンチ幅を道、5%のエネルギースプレッドを持つビームが10%の効率で検出された。この様子はPARMILAにより再現でき、PARMILAコードがレーザー駆動陽子線のビームラインの構築に使用できることを証明した。

論文

Laser-driven proton accelerator for medical application

西内 満美子; 榊 泰直; 堀 利彦; Bolton, P.; 小倉 浩一; 匂坂 明人; 余語 覚文; 森 道昭; 織茂 聡; Pirozhkov, A. S.; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.88 - 90, 2010/05

レーザー駆動陽子線の研究の発展により、加速器の小型化が期待されるようになってきている。ここでは、日本原子力研究開発機構、関西光科学研究所内のPMRCセンターにおけるレーザー駆動陽子線加速器開発の現状について述べる。われわれは、医療用のレーザー駆動陽子線加速器開発の一環として、レーザー駆動陽子線のトランスポートラインを構築し、伝送実験を行った。

論文

Designing integrated laser-driven ion accelerator systems for hadron therapy at PMRC (Photo Medical Research Center)

榊 泰直; 堀 利彦; 西内 満美子; Bolton, P.; 大道 博行; 河西 俊一; Sutherland, K.*; 想田 光*; 野田 章*; 井関 康*; et al.

Proceedings of 2009 Particle Accelerator Conference (PAC '09) (DVD-ROM), p.1309 - 1311, 2009/05

レーザー駆動型イオン加速の研究が進むにつれて、レーザー駆動型小型粒子線治療器の現実性が出てきた。そこで、日本原子力研究開発機構の光医療研究連携センター(PMRC)では、レーザー駆動型イオン治療器の開発を挑戦的に行うために創立された。PMRCは、最近のレーザー加速の現状を踏まえた治療器の設計を進めている。今回は、汎用粒子線加速器設計コードPARMILAを用いた粒子線治療用ガントリーを設計したので報告する。

論文

Focusing and spectral enhancement of a repetition-rated, laser-driven, divergent multi-MeV proton beam using permanent quadrupole magnets

西内 満美子; 大東 出; 池上 将弘; 大道 博行; 森 道昭; 織茂 聡; 小倉 浩一; 匂坂 明人; 余語 覚文; Pirozhkov, A. S.; et al.

Applied Physics Letters, 94(6), p.061107_1 - 061107_3, 2009/02

 被引用回数:48 パーセンタイル:13.17(Physics, Applied)

2.4MeVのレーザー駆動陽子線を永久四重極磁石で1Hzで収束させた。磁場勾配は、55T/m, 60T/mであった。陽子線は、ターゲットから650mmにおける2.7mm$$times$$8mmの大きさ(半値全幅)の領域に収束された。この結果は、モンテカルロシミュレーションとよく一致した。

論文

イオン蓄積リングS-LSRにおけるビーム冷却実験

白井 敏之*; 田辺 幹夫*; 想田 光*; 池上 将弘*; 藤本 慎司*; 頓宮 拓*; 野田 章*; 野田 耕司*; 渋谷 真二*; 藤本 哲也*; et al.

Proceedings of 9th Symposium on Accelerator and Related Technology for Application, p.19 - 22, 2007/06

The ion storage ring, S-LSR has an electron beam cooler and a laser cooling system. The electron cooler for S-LSR was designed to maximize the effective cooling length in the limited drift space of the ring. Various experiments have been carried out using the electron beam cooling, such as the sweep electron cooling, the one-dimensional ordering experiment of protons, and the short bunch generation. The laser cooling experiment is also currently in progress. Concerning the one-dimensional ordering experiment, the first proton ordering was successfully confirmed. An abrupt drop in the momentum spread and the Schottky noise power have been observed at the proton number of 2000 with electron currents of 25 mA. The transition temperature of the proton ordering is 0.17 meV in the longitudinal direction.

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