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Development of a multialkali photocathode preparation system

西森 信行; 羽島 良一; 永井 良治; 沢村 勝

Proceedings of 56th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs (ERL 2015) (Internet), p.100 - 102, 2015/12

We have developed a multialkali photocathode preparation system at JAEA for high current operation of DC photoemission gun. The system will be connected to a 250 kV-50 mA gun for beam generation test. The status of development will be presented.



西森 信行; 永井 良治; 沢村 勝; 羽島 良一

Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.508 - 510, 2015/09




西森 信行; 永井 良治; 森 道昭; 羽島 良一; 山本 将博*; 本田 洋介*; 宮島 司*; 内山 隆司*; Jin, X.*; 帯名 崇*; et al.

Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.511 - 515, 2015/09




羽島 良一; 沢村 勝; 永井 良治; 西森 信行; 早川 岳人; 静間 俊行; Angell, C.

Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.79 - 83, 2015/09




沢村 勝; 羽島 良一; 西森 信行; 永井 良治; 岩下 芳久*; 頓宮 拓*; 久保 毅幸*; 佐伯 学行*

Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.583 - 586, 2015/09



Review of experimental results from high brightness DC guns; Highlights in FEL applications

西森 信行

Proceedings of 37th International Free Electron Laser Conference (FEL 2015) (Internet), p.269 - 273, 2015/09

Future energy recovery linac light sources and high repetition rate X-ray FELs require high-brightness and high-current electron guns capable of delivering an electron beam with an emittance lower than 1 mm-rad and currents up to 100 mA. A DC photoemission gun is one of the most promising candidates for such guns, because a record high current of 65 mA and generation of high brightness beam with 90% normalized emittances of 0.3 mm-mrad with bunch charge of 77 pC were recently demonstrated at the Cornell photo injector with a 350 kV photoemission gun. Further increase of the gun high voltage is desirable to reduce space charge induced emittance growth especially for high bunch charge application such as X-ray FEL. Employment of a segmented insulator is a key to reach higher voltage. This technique led to generation of 500 keV beam from the JAEA gun with 160 mm acceleration gap, conditioning voltage more than 500 kV at the Cornell gun with gap /lt 50 mm, and demonstration of 500 kV holding for 10 hours at the KEK gun with 70 mm gap. In this talk, we present recent experimental results of high brightness DC guns and discuss highlights and limitations in FEL applications.


Diffraction of $$gamma$$-rays with energies of 1.17 and 1.33 MeV by a flat Si crystal

松葉 俊哉*; 早川 岳人; 静間 俊行; 西森 信行; 永井 良治; 沢村 勝; Angell, C.; 藤原 守; 羽島 良一

Japanese Journal of Applied Physics, 54(5), p.052203_1 - 052203_5, 2015/05

 被引用回数:3 パーセンタイル:14.47(Physics, Applied)

Diffraction of $$gamma$$-rays by a flat Si crystal has been demonstrated using a high flux $$^{60}$$Co source with an intensity of 2.3 TBq. The diffraction intensities of the $$gamma$$-rays with energies of 1.17 and 1.33 MeV have been measured as a function of the rotation angle of the crystal. Three peaks corresponding to the Si(440) and Si(220) diffractions for 1.17 MeV and the Si(440) diffraction for 1.33 MeV have been measured. The heights and shapes of these three peaks are well reproduced by taking into account Bragg's law and the experimental geometry.


High order harmonics from relativistic electron spikes

Pirozhkov, A. S.; 神門 正城; Esirkepov, T. Z.; Faenov, A. Y.*; Pikuz, T. A.*; 河内 哲哉; 匂坂 明人; Koga, J. K.; 森 道昭; 川瀬 啓悟*; et al.

RAL-TR-2015-025, P. 22, 2015/00

We provide a description of experiments performed with the J-KAREN and Astra Gemini lasers where we discovered a new regime of relativistic high-order harmonic generation by multi-terawatt femtosecond lasers in gas targets. The results were explained using particle-in-cell simulations and catastrophe theory. Our work paves the way towards a bright coherent X-ray source based on compact lasers and accessible, repetitive, and debris-free gas jet targets. Such a source will be crucial for fundamental research and numerous applications requiring pumping, probing, imaging of microscopic objects and for attosecond science.


Development of a high-brightness and high-current electron gun for high-flux $$gamma$$-ray generation

西森 信行; 永井 良治; 松葉 俊哉; 羽島 良一; 山本 将博*; 本田 洋介*; 宮島 司*; 内山 隆司*; 栗木 雅夫*

Nuclear Physics and $$gamma$$-ray sources for Nuclear Security and Nonproliferation, p.321 - 326, 2014/12

The quantification of fissile materials such as uranium-235 and plutonium-239 in spent fuel assemblies requires isotope-specific identification. We propose the use of nuclear resonance fluorescence (NRF) to identify the isotopic composition of sample materials nondestructively. The proposed nondestructive isotope identification system requires a high-intensity mono-energetic $$gamma$$-ray beam. Although a mono-energetic $$gamma$$-ray beam can be generated using a conventional laser Compton scattering technique, the generation of a high-intensity $$gamma$$-ray beam requires an electron beam of unprecedentedly high brightness, which can be generated with an advanced accelerator system known as the energy recovery linac (ERL). A technological challenge of the ERL system, which we have addressed, is the development of a high-brightness, high-current electron gun. Our current status of development and operational experience of our gun is presented.



西森 信行; 永井 良治; 松葉 俊哉; 沢村 勝; 羽島 良一

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.1031 - 1033, 2014/10

高輝度大電流光陰極電子源が注目を集めている。メガヘルツ繰り返しのX線自由電子レーザー(LCLS-II)、リソグラフィ用自由電子レーザー、核種分析用のコンプトン散乱$$gamma$$線源等、応用範囲が急速に広がりつつある。我々は光陰極直流電子源から世界初の500keV電子ビーム生成を達成することで高輝度化の目処を立てた。ガリウムヒ素光陰極を用いて1.8mAの 電流生成を達成しているが、さらなる大電流化や長寿命化の観点からは 光陰極表面の繊細さが不安視されている。そこで、我々は大電流化を目指しマルチアルカリ光陰極の開発に着手した。近年のコーネル大学などのデモンストレーションにより、大電流化の切り札として期待されている。本発表では、原子力機構における光陰極準備システムの開発状況、既存の50mA-250kV電子源と組み合わせた大電流試験計画について報告する。



西森 信行; 永井 良治; 山本 将博*

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.165 - 170, 2014/10




沢村 勝; 永井 良治; 西森 信行; 羽島 良一; 岩下 芳久*; 藤澤 博*; 頓宮 拓*; 久保 毅幸*; 佐伯 学行*

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.618 - 620, 2014/10




永井 良治; 沢村 勝; 西森 信行; 羽島 良一

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.1016 - 1018, 2014/10



High order harmonics from relativistic electron spikes

Pirozhkov, A. S.; 神門 正城; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.*; 河内 哲哉; 匂坂 明人; et al.

New Journal of Physics (Internet), 16(9), p.093003_1 - 093003_30, 2014/09

 被引用回数:30 パーセンタイル:81.8(Physics, Multidisciplinary)

We present a detailed description of our discovery of a new regime of high-order harmonic generation, including experimental data, simulations, and description of new harmonic generation mechanism. The harmonics are generated by multi-terawatt relativistic-irradiance ($$>$$ 10$$^{18}$$ W/cm$$^2$$) femtosecond ($$approx$$ 30-50 fs) lasers focused to gas jet targets. According to our model, the harmonics are produced by sharp, structurally stable, oscillating electron spikes at the joint of boundaries of wake and bow waves excited by the laser pulse.


Analysis on effects of transverse electric field in an injector cavity of compact-ERL at KEK

Hwang, J.-G.*; Kim, E.-S.*; 宮島 司*; 本田 洋介*; 原田 健太郎*; 島田 美帆*; 高井 良太*; 久米 達哉*; 長橋 進也*; 帯名 崇*; et al.

Nuclear Instruments and Methods in Physics Research A, 753, p.97 - 104, 2014/07

 被引用回数:7 パーセンタイル:49.88(Instruments & Instrumentation)

For a future synchrotron light source based on a linac, e.g. an X-ray free electron laser and an energy recovery linac (ERL), an injector is a key component to generate a high brightness electron beam. For the acceleration and transportation of the electron beam in the injector, the adjustment of beam orbit inside the cavity is important to avoid the deterioration of the beam quality due to the transverse electric field of it, which causes the transverse emittance growth. To adjust the beam orbit, an investigation of the electromagnetic center of the cavity is required in the beam operation. This paper shows a new method for measuring the electromagnetic center of the cavity, and describes an analytical model of emittance growth due to a combination of transverse electric field and orbit offset. The validation of the method was confirmed by the emittance measurement in the compact ERL (cERL) injector at KEK.



西森 信行; 永井 良治; 松葉 俊哉; 羽島 良一; 山本 将博*; 宮島 司*; 本田 洋介*; 内山 隆司*; 飯島 北斗*; 栗木 雅夫*; et al.

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.174 - 178, 2014/06




沢村 勝; 永井 良治; 西森 信行; 羽島 良一

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (インターネット), p.956 - 959, 2014/06



Application of laser Compton scattered $$gamma$$-ray beams to nondestructive detection and assay of nuclear material

羽島 良一; 早川 岳人; 静間 俊行; Angell, C.; 永井 良治; 西森 信行; 沢村 勝; 松葉 俊哉; 小菅 淳*; 森 道昭; et al.

European Physical Journal; Special Topics, 223(6), p.1229 - 1236, 2014/05

 被引用回数:17 パーセンタイル:48.69(Physics, Multidisciplinary)

Generation of energy-tunable $$gamma$$-rays via laser Compton scattering is of great interest for applications of MeV photons -which interact with nuclei- and scientific studies. One of the promising applications of such energy-tunable $$gamma$$-rays is the nondestructive detection and assay of nuclides, which are necessary for nuclear security and safeguards. We are developing technologies relevant to $$gamma$$-ray nondestructive detection and assay, which include a high-brightness $$gamma$$-ray source based on modern laser and accelerator technologies, and $$gamma$$-ray measurement methods optimized for highly radioactive samples.


Experimental investigation of an optimum configuration for a high-voltage photoemission gun for operation at $$geq$$ 500 kV

西森 信行; 永井 良治; 松葉 俊哉; 羽島 良一; 山本 将博*; 本田 洋介*; 宮島 司*; 飯島 北斗*; 栗木 雅夫*; 桑原 真人*

Physical Review Special Topics; Accelerators and Beams, 17(5), p.053401_1 - 053401_17, 2014/05

 被引用回数:23 パーセンタイル:81.52(Physics, Nuclear)

We have demonstrated generation of a 500-keV electron beam from a high DC voltage photoemission gun for an energy recovery linac light source. This demonstration was achieved by addressing two discharge problems that lead to vacuum breakdown of the DC gun. One is field emission generated from a central stem electrode. The other is microdischarge at an anode electrode or a vacuum chamber, which is triggered by microparticle transfer or field emission from a cathode electrode. An experimental investigation has revealed that larger acceleration gap optimized to mainly reduce surface electric field of anode electrode results in suppression of the microdischarge events which accompany gas desorption. It has also been found that non evaporable getter pumps placed around the acceleration gap greatly help suppress those microdischarge events. The applied voltage as a function of the total gas desorption is shown to be a good measure to find the optimum DC gun configuration.


New design of HOM coupler using coaxial-like rounded waveguide

沢村 勝; 羽島 良一; 永井 良治; 西森 信行

Proceedings of 16th International Conference on RF Superconductivity (SRF 2013) (Internet), p.1081 - 1084, 2014/02


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