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Journal Articles

Relaxation of plasmas created from irradiation of a heavy ion

Moribayashi, Kengo

JPS Conference Proceedings (Internet), 1, p.013089_1 - 013089_4, 2014/03

Journal Articles

Theoretical study on isotope-selective dissociation of the lithium chloride molecule using a designed terahertz-wave field

Ichihara, Akira; Matsuoka, Leo; Kurosaki, Yuzuru; Yokoyama, Keiichi

JPS Conference Proceedings (Internet), 1, p.013093_1 - 013093_4, 2014/03

Isotope-selective dissociation of the lithium chloride (LiCl) molecule was investigated by quantum mechanical calculations. $$^7$$Li$$^{35}$$Cl in the initial rovibrational state (v=0,J=0) was excited by an optical frequency comb whose spectral frequencies were tuned to the rotational transition frequencies of $$^7$$Li$$^{35}$$Cl. $$^7$$Li$$^{37}$$Cl was not highly excited by the comb because of the difference of the transition frequencies. The time evolution of rovibrational population was evaluated using the close-coupling method during the comb irradiation. The dissociation process in the second pulse was calculated by the wave packet method. The amplitudes of close-coupling were employed as the input of the wave packet computation. The dissociation probability was estimated by absorbing wave packet using a damping function. By the optical pulses adopted, about 60% of $$^7$$Li$$^{35}$$Cl was dissociated. The dissociation probability of $$^7$$Li$$^{37}$$Cl was less than 2%t.

Journal Articles

Delbr$"{u}$ck scattering calculation using the LoopTools package

Koga, J. K.; Hayakawa, Takehito

JPS Conference Proceedings (Internet), 1, p.016008_1 - 016008_4, 2014/03

Journal Articles

A Percolation model of the streamer discharges

Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kanazawa, Seiji*

JPS Conference Proceedings (Internet), 1, p.015029_1 - 015029_4, 2014/03

Although streamer discharges have long been studied, the mechanism of sudden formation of the complex discharge path has not been fully understood. We show that a simulation based on the percolation model reproduces such development of the streamer. In the model, the discharge medium is divided into cells and is considered to form an electrical circuit network, which is used to calculate the current. In contrast to the characteristic feature of a single electron avalanche is explained by the Townsend theory, when the size of the system becomes greater, random formation of the avalanche in the medium and connection between them determines the propagation of the steamer, which is analyzed using the percolation model. Figure shows the simulated discharge from the initial pre-discharge activity near the electrode to rapid growth of the stepped leader, which causes breakdown.

Journal Articles

Study on the pulse shape of thermal and cold neutrons provided by the decoupled moderator of JSNS

Oikawa, Kenichi; Harada, Masahide; Maekawa, Fujio

JPS Conference Proceedings (Internet), 1, p.014012_1 - 014012_4, 2014/03

Japanese Spallation Neutron Source (JSNS) of MLF at J-PARC has launched successfully on May 30, 2008, and now provides pulsed neutrons in stable condition at 0.3 MW proton beam power. Among three moderators in JSNS, a decoupled moderator has been studied extensively by the instrument NOBORU. Most important feature of the moderator is short tail of the pulse shape realized by a silver-indium-cadmium (AIC) decoupler which has a neutron decoupling energy, Ed, up to 1 eV. Two dimensionally aligned crystal, Muscovite, was used to measure pulse shape of cold neutrons, where as single crystal diamond to measure pulse shape up to several hundreds meV. The results showed good agreement with the expected pulse shape calculated using a Monte Carlo simulation. In this presentation, we will show the evaluation of the pulsed structure in detail.

Journal Articles

Instrument design and performance evaluation of a new single crystal neutron diffractometer SENJU at J-PARC

Oikawa, Kenichi; Kawasaki, Takuro; Ohara, Takashi; Kiyanagi, Ryoji; Kaneko, Koji; Tamura, Itaru; Nakamura, Tatsuya; Harada, Masahide; Nakao, Akiko*; Hanashima, Takayasu*; et al.

JPS Conference Proceedings (Internet), 1, p.014013_1 - 014013_5, 2014/03

A new single crystal time-of-flight neutron diffractometer has been installed at BL18 of the Materials and Life Science Experimental Facility of J-PARC. The diffractometer "SENJU" was designed for precise crystal and magnetic structure analyses using a small crystal less than 1.0 mm$$^3$$ under multiple extreme environments such as low-temperature and high-magnetic field. The first neutron beam was delivered to the sample position on March 5, 2012. Subsequently, the hardware and software of SENJU have been checked and confirmed that they worked fine. At the same time, diffraction experiments of several organic and inorganic crystals have been done using NaCl, C12A7, and so on. In these measurements, Bragg reflections in the high-Q region (d-spacing $$<$$ 0.5 ${AA}$) were clearly observed and analyzed successfully. In this presentation, we will show the instrument design and performance evaluation of SENJU in detail.

Journal Articles

Stochastic transport of runaway electrons due to low-order perturbations in tokamak disruption

Matsuyama, Akinobu; Yagi, Masatoshi; Kagei, Yasuhiro*

JPS Conference Proceedings (Internet), 1, p.015037_1 - 015037_4, 2014/03

no abstracts in English

Journal Articles

Energy- and $$Q$$-resolution investigations of a chopper spectrometer 4SEASONS at J-PARC

Iida, Kazuki*; Ikeuchi, Kazuhiko*; Ishikado, Motoyuki*; Suzuki, Junichi; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Arai, Masatoshi

JPS Conference Proceedings (Internet), 1, p.014016_1 - 014016_4, 2014/03

Journal Articles

Exotic quantum phenomena of the spin nanotubes

Sakai, Toru; Okamoto, Kiyomi*

JPS Conference Proceedings (Internet), 1, p.012025_1 - 012025_4, 2014/03

The spin nanotubes are theoretically investigated by the numerical diagonalization and the density matrix renormalization group calculation. As a result, it is found that a quantum phase transition from the spin gapped to the gapless phases is induced by the lattice distortion. We also discuss about a possible superconductivity induced by the chirality degrees of freedom.

Journal Articles

Deformation behavior of an austenitic steel by neutron diffraction

Harjo, S.; Abe, Jun; Aizawa, Kazuya; Gong, W.; Iwahashi, Takaaki

JPS Conference Proceedings (Internet), 1, p.014017_1 - 014017_6, 2014/03

Journal Articles

2D neutron diffraction imaging on an ammonite

Shamoto, Shinichi; Kodama, Katsuaki; Imaki, Tadashi*; Nakatani, Takeshi; Oshita, Hidetoshi*; Kaneko, Naokatsu*; Masuko, Kenji*; Sakamoto, Kensaku; Yamaguchi, Kenji; Suzuya, Kentaro; et al.

JPS Conference Proceedings (Internet), 1, p.014011_1 - 014011_5, 2014/03

2D neutron diffraction imaging of an ammonite fossil was carried out at high-intensity total diffractometer NOVA in J-PARC. Observed diffraction profiles consist of calcite, siderite and amorphous structures.

Journal Articles

Negative triangularity as a possible tokamak scenario

Kikuchi, Mitsuru; Takizuka, Tomonori*; Furukawa, Masaru*

JPS Conference Proceedings (Internet), 1, p.015014_1 - 015014_4, 2014/03

Recent scaling of SOL e-folding length by Goldston shows pessimistic prediction to ITER and DEMO. This seems caused by the SOL acceleration mechanism found by Takizuka. In the negative D shaped plasma, this SOL acceleration may be significantly reduced. Negative D also has TEM eigen mode structure tilted poloidally and confinement in L mode is two times of L-mode. Based on these facts, we discuss possibility of negative D as a possible operation candidate of tokamak.

Journal Articles

Current status and future prospects of "J-KAREN"; High contrast, high intensity laser for studying relativistic laser-matter interactions

Kiriyama, Hiromitsu; Mori, Michiaki; Okada, Hajime; Shimomura, Takuya; Nakai, Yoshiki*; Tanoue, Manabu; Kondo, Shuji; Kanazawa, Shuhei; Yogo, Akifumi; Sagisaka, Akito; et al.

JPS Conference Proceedings (Internet), 1, p.015095_1 - 015095_5, 2014/03

We present the design and characterization of a high-contrast, petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. Two saturable absorbers and low-gain optical parametric chirped-pulse amplification (OPCPA) preamplifier in the double CPA laser chain have improved the temporal contrast to 1.4$$times$$10$$^{12}$$ on the subnanosecond time scale at 70 terawatt level. Final uncompressed broadband pulse energy is 28 J, indicating the potential for reaching peak power near 600 terawatt. We also discuss our upgrade to over petawatt level at a 0.1 Hz repetition rate briefly.

Journal Articles

Phase transition of Bi$$_2$$WO$$_6$$ below 300 K

Yoneda, Yasuhiro; Takeda, Hiroaki*; Tsurumi, Takaaki*

JPS Conference Proceedings (Internet), 1, p.012103_1 - 012103_4, 2014/03

Bi$$_2$$WO$$_6$$ is the simplest member of the Aurivillius family of (Bi$$_2$$O$$_2$$)(A$$_{m-1}$$B$$_m$$O$$_{3m+1}$$) with one oxygen octahedron sandwiched between two Bi$$_2$$O$$_2$$ layers (m=1). We report the high-energy synchrotron X-ray diffraction study of ferroelectric Bi$$_2$$WO$$_6$$ at low temperatures, and a new phase transition was found around 200 K. The mechanism of this phase transition was examined by atomic pair-distribution function (PDF) method.

Journal Articles

Single crystal neutron diffraction study of high neutron absorbing compound EuGa$$_{4}$$

Kawasaki, Takuro; Kaneko, Koji; Aso, Naofumi*; Nakamura, Ai*; Hedo, Masato*; Nakama, Takao*; Onuki, Yoshichika*; Ohara, Takashi; Kiyanagi, Ryoji; Oikawa, Kenichi; et al.

JPS Conference Proceedings (Internet), 1, p.014009_1 - 014009_4, 2014/03

Journal Articles

Performance of optical devices for energy-selective neutron imaging in NOBORU at J-PARC

Harada, Masahide; Oikawa, Kenichi; Oi, Motoki; Kai, Tetsuya; Shinohara, Takenao; Sakai, Kenji; Maekawa, Fujio

JPS Conference Proceedings (Internet), 1, p.014015_1 - 014015_4, 2014/03

NOBORU at MLF in J-PARC serves a test beam port. Energy-selective neutron imaging is one of the important developments performed at NOBORU. In order to improve a spatial resolution and to reduce a background as the imaging experiment, a rotary collimator and a neutron filter device were installed on the middle of the beam-line. A revolver-shape shielding equipped with four holes is remotely rotated to change the collimator ratio from 140 to 1875. It was found from the neutron radiography test that neutron transmission images with high spatial resolution ($$<$$ 100 $$mu$$m) could be obtained. In the remote-controlled filter device, it was confirmed that an acrylic resin plate and a borosilicate glass attenuated high-energy and cold neutrons, and bulk lead plates and bismuth single crystal ones attenuated the $$gamma$$ rays.

Journal Articles

Photon-in, photon-out gas-phase experiments at the SPring-8 compact SASE source SCSS

Harries, J.; Iwayama, Hiroshi*; Okihara, Lisa*; Nagasono, Mitsuru*; Shigemasa, Eiji*

JPS Conference Proceedings (Internet), 1, p.013083_1 - 013083_6, 2014/03

Journal Articles

Minimum condition of target gas material at an ionization-stage control scheme in a laser-plasma electron acceleration

Mori, Michiaki; Kando, Masaki; Kotaki, Hideyuki; Hayashi, Yukio; Kiriyama, Hiromitsu; Okada, Hajime; Pirozhkov, A. S.; Bulanov, S. V.; Kondo, Kiminori; Bolton, P.

JPS Conference Proceedings (Internet), 1, p.015094_1 - 015094_6, 2014/03

We report on the appropriate and inappropriate gas materials to generate energetic electrons. The 4-TW peak power and 40-fs pulse duration laser beam illuminated the gas-jet target with intensity of 9$$times$$10$$^{17}$$W/cm$$^{2}$$ measured in vacuum. We investigated energetic electron beam generation using neon and argon. Energetic electron beam was observed in argon at the lowest neutral gas density of 5$$times$$10$$^{18}$$cm$$^{-3}$$. However, no energetic electrons ($$>$$ 1 MeV, $$>$$ 1 pC) were observed in neon although neutral gas density is increased from5$$times$$10$$^{18}$$cm$$^{-3}$$ to 5$$times$$10$$^{19}$$cm$$^{-3}$$. By considering ionization stage at such an intensity, the maximum plasma density is reached to be a quarter critical plasma density, at which the maximum growth-rate of laser-plasma instability is expected. On the other hand, propagation of the pumping laser was observed in neon and argon by using optical probing. Significantly different images were observed. The structure of the laser channel for energetic electron beam generation that observed in argon was absent in neon. These results imply that the additional increase of the plasma density due to ionization cannot explain the electron generation. The analysis including the propagation of a laser in ionizing gas would be necessary.

Journal Articles

General formulae for the optimized design of Fermi chopper spectrometer

Nakamura, Mitsutaka; Kajimoto, Ryoichi

JPS Conference Proceedings (Internet), 1, p.014108_1 - 014108_4, 2014/03

We report the procedures for the design optimization of a slitpackage which determine the performance of Fermi chopper spectrometer at a pulsed neutron source. The analytical formulae shown in this paper provide a wide variety of guidelines on the instrument design and contribute to the development for the next-generation Fermi chopper spectrometer.

Journal Articles

Molecular dynamics simulation of the three-dimensional ordered state in laser-cooled heavy-ion beams

Yuri, Yosuke

JPS Conference Proceedings (Internet), 1, p.013014_1 - 013014_4, 2014/03

32 (Records 1-20 displayed on this page)