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Journal Articles

Spontaneous decays of magneto-elastic excitations in non-collinear antiferromagnet (Y,Lu)MnO$$_{3}$$

Oh, J.*; Le, M. D.*; Nahm, H.-H.*; Sim, H.*; Jeong, J.*; Perring, T. G.*; Woo, H.*; Nakajima, Kenji; Kawamura, Seiko; Yamani, Z.*; et al.

Nature Communications (Internet), 7, p.13146_1 - 13146_6, 2016/10

 Times Cited Count:27 Percentile:17.56(Multidisciplinary Sciences)

Magnons and phonons are fundamental quasiparticles in a solid and can be coupled together to form a hybrid quasi-particle. However, detailed experimental studies on the underlying Hamiltonian of this particle are rare for actual materials. Moreover, the anharmonicity of such magnetoelastic excitations remains largely unexplored, although it is essential for a proper understanding of their diverse thermodynamic behaviour and intrinsic zero-temperature decay. Here we show that in non-collinear antiferromagnets, a strong magnon phonon coupling can significantly enhance the anharmonicity, resulting in the creation of magnetoelastic excitations and their spontaneous decay. By measuring the spin waves over the full Brillouin zone and carrying out anharmonic spin wave calculations using a Hamiltonian with an explicit magnon phonon coupling, we have identified a hybrid magnetoelastic mode in (Y,Lu)MnO$$_{3}$$ and quantified its decay rate and the exchange-striction coupling termrequired to produce it.

Journal Articles

First-principles simulation of the optical response of bulk and thin-film $$alpha$$-quartz irradiated with an ultrashort intense laser pulse

Lee, K.-M.*; Kim, C. M.*; Sato, Shunsuke*; Otobe, Tomohito; Shinohara, Yasushi*; Yabana, Kazuhiro; Jeong, T. M.*

Journal of Applied Physics, 115(5), p.053519_1 - 053519_8, 2014/02

 Times Cited Count:18 Percentile:30.39(Physics, Applied)

A computational method based on a first-principles multiscale simulation has been used for calculating the optical response and the ablation threshold of an optical material irradiated with an ultrashort intense laser pulse. The method was applied to investigate the changes in the optical reflectance of quartz bulk, half-wavelength thin-film and quarter-wavelength thin-film and to estimate their ablation thresholds. Despite the adiabatic local density approximation used in calculating the exchange-correlation potential, the reflectance and the ablation threshold obtained from our method agree well with the previous theoretical and experimental results. The method can be applied to estimate the ablation thresholds for optical materials in general.

Journal Articles

Arc discharge characteristics of a long pulse ion source for the KSTAR neutral beam injector

Chang, D. H.*; Jeong, S. H.*; Jin, J. T.*; Chang, D. S.*; Kim, T. S.*; Lee, K. W.*; In, S. R.*; Oh, B. H.*; Bae, Y. S.*; Kim, J. S.*; et al.

Journal of the Korean Physical Society, 59(2), p.275 - 280, 2011/08

 Times Cited Count:3 Percentile:69.08(Physics, Multidisciplinary)

A long pulse ion source (LPIS) for the neutral beam injector (NBI) has been developed for the Korea Superconducting Tokamak Advanced Research (KSTAR) superconducting tokamak. The arc discharge characteristics of the ion source were investigated on the first KSTAR neutral beam injector (NBI-1). The ion source consists of a magnetic bucket plasma generator with multi-pole cusp fields and a set of prototype tetrode accelerators with circular apertures. Stable and efficient arc plasmas up to an arc power of 70 kW have been produced by using a constant power-mode operation of the arc power supply. The reliable operation region of the arc discharges has been investigated for various filament heating voltages, arc powers, and amounts of injected deuterium gas.

Journal Articles

Results of beam extraction performance for the KSTAR neutral beam injector

Chang, D. H.*; Jeong, S. H.*; Kim, T. S.*; Lee, K. W.*; In, S. R.*; Jin, J. T.*; Chang, D. S.*; Oh, B. H.*; Bae, Y. S.*; Kim, J. S.*; et al.

Japanese Journal of Applied Physics, 50(6), p.066302_1 - 066302_7, 2011/06

 Times Cited Count:9 Percentile:56.35(Physics, Applied)

A stable ion beam extraction of the LPIS-1 was achieved up to 85 kV/32 A for a 5 s pulse length and 80 kV/25 A for a 14 s pulse length. An optimum beam perveance of 1.15 $$mu$$perv was observed at an acceleration voltage of 60 kV. Neutralization efficiency was measured by a water-flow calorimetry (WFC) method using a calorimeter and the operation of a bending magnet. The full-energy species of ion beams were detected by using the diagnostic method of optical multichannel analyzer (OMA). An arc efficiency of the LPIS was 0.6-1.1 A/kW depending on the operating conditions of arc discharge. A neutral beam power of 1.0 MW must be sufficiently injected into the KSTAR plasmas from the LPIS-1 at a beam energy of 80 keV.

Journal Articles

Commissioning results of the KSTAR neutral beam system

Bae, Y. S.*; Park, Y. M.*; Kim, J. S.*; Han, W. S.*; Kwak, S. W.*; Chang, Y. B.*; Park, H. T.*; Song, N. H.*; Chang, D. H.*; Jeong, S. H.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 9 Pages, 2011/03

The neutral beam injection (NBI) system is designed to provide the ion heating and current drive for the high performance operation and long pulse operation of the Korean Superconducting Tokamak Advanced Research (KSTAR). The KSTAR NBI consists of two beam lines. Each beam line contains three ion sources of which one ion source has been designed to deliver more than 2.5 MW of deuterium neutral beam power with maximum 120-keV beam energy. Consequently, the final goal of the KSTAR NBI system aims to inject more than 14 MW of deuterium beam power with the two beam lines. According to the planned NBI system, the first NBI system is to demonstrate the beam injection from one ion source into the KSTAR tokamak plasma in 2010 campaign including the system commissioning of each components and subsystems. In this paper, the construction and the commissioning of the first NBI system with one ion source is presented.

Journal Articles

Status and result of the KSTAR upgrade for the 2010's campaign

Yang, H. L.*; Kim, Y. S.*; Park, Y. M.*; Bae, Y. S.*; Kim, H. K.*; Kim, K. M.*; Lee, K. S.*; Kim, H. T.*; Bang, E. N.*; Joung, M.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

Because the 2010 operation of Korea Superconducting Tokamak Advanced Research (KSTAR) mainly aims to achieve strongly elongated and diverted plasma, all the necessary hardware systems to provide an essential circumstance for the plasma shaping were newly installed and upgraded in 2010. In this paper, general configuration of the upgraded systems described earlier will be outlined. Moreover, several key performances and test results of the systems will be also reported in summary.

Journal Articles

ECRH assisted plasma start-up with toroidally inclined launch; Multi-machine comparison and perspectives for ITER

Stober, J.*; Jackson, G. L.*; Ascasibar, E.*; Bae, Y.-S.*; Bucalossi, J.*; Cappa, A.*; Casper, T.*; Cho, M. H.*; Gribov, Y.*; Granucci, G.*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2010/10

Journal Articles

Efficient production of a collimated MeV proton beam from a Polyimide target driven by an intense femtosecond laser pulse

Nishiuchi, Mamiko; Daido, Hiroyuki; Yogo, Akifumi; Orimo, Satoshi; Ogura, Koichi; Ma, J.-L.; Sagisaka, Akito; Mori, Michiaki; Pirozhkov, A. S.; Kiriyama, Hiromitsu; et al.

Physics of Plasmas, 15(5), p.053104_1 - 053104_10, 2008/05

 Times Cited Count:38 Percentile:14.73(Physics, Fluids & Plasmas)

High-flux energetic protons whose maximum energies are up to 4 MeV are generated by an intense femtosecond Titanium Sapphire laser pulse interacting with a 7.5, 12.5, and 25$$mu$$m thick Polyimide tape targets. The laser pulse energy is 1.7 J, duration is 34 fs, and intensity is 3$$times$$10$$^{19}$$Wcm$$^{-2}$$. The amplified spontaneous emission (ASE) has the intensity contrast ratio of 4$$times$$10$$^{-8}$$. The conversion efficiency from laser energy into proton kinetic energies of $$sim$$3% is achieved, which is comparable or even higher than those achieved in the previous works with nanometer-thick targets and the ultrahigh contrast laser pulses ($$sim$$10$$^{-10}$$).

Journal Articles

Six-party qualification program of FW fabrication methods for ITER blanket module procurement

Ioki, Kimihiro; Elio, F.*; Barabash, V.*; Chuyanov, V.*; Rozov, V.*; Wang, X.*; Chen, J.*; Wang, L.*; Lorenzetto, P.*; Peacock, A.*; et al.

Fusion Engineering and Design, 82(15-24), p.1774 - 1780, 2007/10

 Times Cited Count:11 Percentile:34.46(Nuclear Science & Technology)

In December 2005, the new procurement allocation plan of the ITER components among the seven Parties was prepared. The need to qualify for procurement of the specific components was especially introduced in the document. The main features and milestones of the qualification program are described in "Procurement Plan" for each specific component. Due to the complicated features of FW procurement, the procurement document has to be developed precisely. To guarantee high quality of 1700 FW panels produced by 6 different Parties, a qualification program is essential. The qualification mock-up is 80 mm wide, 240 mm long and 81 mm thick with 3 beryllium tiles 10 mm thick. Heat load tests will be performed on the qualification mock-ups in 2007 in EU and USA facilities. The maximum design heat load on the ITER FW is 0.5 MW/m $$^{2}$$ (steady state) $$times$$ 30,000 shots. Mechanical tests of joints are also required using standardized methods. Only Parties which have satisfied the acceptance criteria of the qualification tests can proceed to the procurement stage of the ITER FW. Semi-prototypes (roughly 1000 mm $$times$$ 200 mm) are also requested before the ITER FW manufacturing.

Journal Articles

Simultaneous proton and X-ray imaging with femtosecond intense laser driven plasma source

Orimo, Satoshi; Nishiuchi, Mamiko; Daido, Hiroyuki; Yogo, Akifumi; Ogura, Koichi; Sagisaka, Akito; Li, Z.*; Pirozhkov, A. S.; Mori, Michiaki; Kiriyama, Hiromitsu; et al.

Japanese Journal of Applied Physics, Part 1, 46(9A), p.5853 - 5858, 2007/09

 Times Cited Count:15 Percentile:45.25(Physics, Applied)

A laser-driven proton beam with a maximum energy of a few MeV is stably obtained using an ultra-short and high-intensity Titanium Sapphire laser. At the same time, keV X-ray is also generated at almost the same place where protons are emitted. Here, we show the successful demonstration of simultaneous proton and X-ray projection images of a test sample placed close to the source with a resolution of $$sim$$10$$mu$$m, which is determined from the source sizes. Although the experimental configuration is very simple, the simultaneity is better than a few hundreds of ps. A CR-39 track detector and imaging plate, which are placed as close as possible to the CR-39, are used as detectors of protons and X-ray. The technique is applicable to the precise observation of microstructures.

Journal Articles

Development of laser driven proton sources and their applications

Daido, Hiroyuki; Sagisaka, Akito; Ogura, Koichi; Orimo, Satoshi; Nishiuchi, Mamiko; Mori, Michiaki; Ma, J.-L.; Pirozhkov, A. S.; Kiriyama, Hiromitsu; Kanazawa, Shuhei; et al.

Proceedings of 7th Pacific Rim Conference on Lasers and Electro-Optics (CLEO-PR 2007) (CD-ROM), p.77 - 79, 2007/00

We are developing a proton accelerator using an intense lasers with a focused intensity of $$>$$ 10$$^{17}$$ W/cm$$^{2}$$. To monitor proton energy spectra as well as plasma parameters at each laser shot, we are using real time detectors. The proton energy of MeV is stably obtained for applications.

Journal Articles

Intense femto-second laser-driven X-ray source coupled with multiple directional quantum beams for applications

Daido, Hiroyuki; Sagisaka, Akito; Ogura, Koichi; Orimo, Satoshi; Nishiuchi, Mamiko; Yogo, Akifumi; Mori, Michiaki; Li, Z.*; Kiriyama, Hiromitsu; Kanazawa, Shuhei; et al.

X-Ray Lasers 2006; Springer Proceedings in Physics, Vol.115, p.595 - 605, 2007/00

At present, using ultra-short high intensity lasers at APRC, JAEA Kansai photon research institute, we are developing laser driven multiple quantum beams such as protons, X-rays, electrons and THz waves. These beams are perfectly synchronized with each other. The pulse duration of each beam is lass than a pico-second. They have sharp directionality with high brightness. If we properly combined these, we have new pump-probe techniques for various applications.

Journal Articles

Scattering of $$^{11}$$Be halo nucleus from $$^{209}$$Bi at coulomb barrier

Mazzocco, M.*; Signorini, C.*; Romoli, M.*; De Francesco, A.*; Di Pietro, M.*; Vardaci, E.*; Yoshida, Koichi*; Yoshida, Atsushi*; Bonetti, R.*; De Rosa, A.*; et al.

European Physical Journal A, 28(3), p.295 - 299, 2006/06

 Times Cited Count:36 Percentile:11.36(Physics, Nuclear)

The scattering of the radioactive, weakly bound, halo nucleus $$^{11}$$Be from $$^{209}$$Bi has been studied at 40 MeV. The measurement performed with a low-intensity and a large-emittance secondary beam could be made using an extremely compact, large solid angle ($$sim$$ 2$$pi$$ sr) detecting set-up, based on 8 highly segmented Si telescopes. The $$^{9,11}$$Be scattering angular distributions, as well as their relative reaction cross-sections, resulted to be rather similar. This may suggest that at Coulomb barrier energies the halo structure and the small weakly binding energy of the $$^{11}$$Be projectile have no big influence on the reaction dynamics.

Oral presentation

Efficient production of MeV proton beam from a Polyimide target driven by an intense femto-second laser

Nishiuchi, Mamiko; Daido, Hiroyuki; Yogo, Akifumi; Orimo, Satoshi; Ogura, Koichi; Ma, J.-L.; Sagisaka, Akito; Mori, Michiaki; Pirozhkov, A. S.; Kiriyama, Hiromitsu; et al.

no journal, , 

The efficient proton beam whose maximum energy of up to 4 MeV was produced by the 50TW short pulse intensity Ti:Sap laser irradiated on the polyimide target [(C16H6O4N2)n] with the thicknesses of 7.5$$mu$$m, 12.5$$mu$$m, 25$$mu$$m, which is transparent to the 800nm laser. The laser parameters are energy of 1.7J, pulse width of 35fs and the intensity of 3$$times$$10$$^{19}$$Wcm$$^{-2}$$. The contrast of the ASE component is 4$$times$$10$$^{-8}$$. The conversion efficiency from laser energy into the proton kinetic energy is up to $$sim$$3%. This conversion efficiency is comparable or even higher than the results obtained with the same level laser ($$sim$$ J energy) interacts with the nano-meter level ultra thin target. In this paper we discuss on the comparison between our results and other experimental results obtained in other facilities.

Oral presentation

Applications of the high intensity short-pulse laser driven $$sim$$ MeV proton beam

Nishiuchi, Mamiko; Daito, Izuru; Ikegami, Masahiro; Mori, Michiaki; Orimo, Satoshi; Ogura, Koichi; Sagisaka, Akito; Yogo, Akifumi; Pirozhkov, A. S.; Ma, J.*; et al.

no journal, , 

A laser-driven proton beam with a maximum energy of a few MeV is stably obtained using an ultra-short and high-intensity Titanium Sapphire laser. As compared with the proton beam from the conventional accelerator, this proton beam exhibits peculiar characteristics, such as, more than 10$$^{13}$$ protons per bunch are produced within a short pulse duration of $$sim$$ps at a source, resulting in a very high peak current. It also exhibits a very low transverse emittance. The proton beam has a divergence angle of $$sim$$10 degrees and energy spread of $$sim$$100%. It accompanies electrons and X-rays, which is produced simultaneously. Making the best use of these peculiar characteristics, many possible applications of the laser-driven proton are proposed. In order to make practical laser-driven proton beam for the applications, we carry out series of experiments. We have successfully obtained simultaneous imaging of the target with proton and X-ray or proton and electron beams. In the course of practical use of the proton beam for specific applications, characteristics above should be optimized based on the variations of the applications. For example, in order to apply the laser-driven proton beam for the proton irradiation system, such as used in the medical or the industrial applications, we should obtain focused or parallel proton beam. One of our plans to alter the orbits of the laser-driven protons from the planer tape target is using permanent quadrupole magnets.

Oral presentation

Generation of high-energy protons and THz radiation with the thin-foil target

Sagisaka, Akito; Pirozhkov, A. S.; Daido, Hiroyuki; Ogura, Koichi; Orimo, Satoshi; Yogo, Akifumi; Daito, Izuru; Nishiuchi, Mamiko; Mori, Michiaki; Nashima, Shigeki*; et al.

no journal, , 

no abstracts in English

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