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Journal Articles

Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; Ishikawa, Yoshihisa*; Torii, Shuki*; Yonemura, Masao*; Koda, Akihiro*; Komatsu, Kazuki*; Machida, Shinichi*; Sano, Asami; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The layered perovskite PrBaCo$$_{2}$$O$$_{5.5}$$ demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero thermal expansion. The NTE was found to be intimately associated with the spontaneous magnetic ordering, known as magneto-volume effect (MVE). Here we report with compelling evidences that the continuous-like MVE in PrBaCo$$_{2}$$O$$_{5.5}$$ is intrinsically of discontinuous character, originating from an magnetoelectric transition from an antiferromagnetic insulating large-volume (AFILV) phase to a ferromagnetic less-insulating small-volume (FLISV) phase. Furthermore, the magnetoelectric effect (ME) shows high sensitivity to multiple external stimuli such as temperature, carrier doping, hydrostatic pressure, magnetic field etc. In contrast to the well-known ME such as colossal magnetoresistance and multi-ferroic effect which involve symmetry breaking of crystal structure, the ME in the cobaltite is purely isostructural. Our discovery provides a new path way to realizing the ME as well as the NTE, which may find applications in new techniques.

Journal Articles

Strong lattice anharmonicity exhibited by the high-energy optical phonons in thermoelectric material

Wu, P.*; Fan, F.-R.*; Hagihara, Masato*; Kofu, Maiko; Peng, K.*; Ishikawa, Yoshihisa*; Lee, S.*; Honda, Takashi*; Yonemura, Masao*; Ikeda, Kazutaka*; et al.

New Journal of Physics (Internet), 22(8), p.083083_1 - 083083_9, 2020/08

 Times Cited Count:2 Percentile:51.78(Physics, Multidisciplinary)

Thermoelectric material SnSe has aroused world-wide interests in the past years, and its inherent strong lattice anharmonicity is regarded as a crucial factor for its outstanding thermoelectric performance. However, the understanding of lattice anharmonicity in SnSe system remains inadequate, especially regarding how phonon dynamics are affected by this behavior. In this work, we present a comprehensive study of lattice dynamics on Na$$_{0.003}$$Sn$$_{0.997}$$Se$$_{0.9}$$S$$_{0.1}$$ by means of neutron total scattering, inelastic neutron scattering, Raman spectroscopy as well as frozen-phonon calculations. Lattice anharmonicity is evidenced by pair distribution function, inelastic neutron scattering and Raman measurements. By separating the effects of thermal expansion and multi-phonon scattering, we found that the latter is very significant in high-energy optical phonon modes. The strong temperature-dependence of these phonon modes indicate the anharmonicity in this system. Moreover, our data reveals that the linewidths of high-energy optical phonons become broadened with mild doping of sulfur. Our studies suggest that the thermoelectric performance of SnSe could be further enhanced by reducing the contributions of high-energy optical phonon modes to the lattice thermal conductivity via phonon engineering.

Journal Articles

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex, 2; Neutron scattering instruments

Nakajima, Kenji; Kawakita, Yukinobu; Ito, Shinichi*; Abe, Jun*; Aizawa, Kazuya; Aoki, Hiroyuki; Endo, Hitoshi*; Fujita, Masaki*; Funakoshi, Kenichi*; Gong, W.*; et al.

Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.

Journal Articles

ITPA (International Tokamak Physics Activity) meeting report, 53

Kawano, Yasunori; Akiyama, Tsuyoshi*; Ishikawa, Masao; Isobe, Mitsutaka*; Itami, Kiyoshi; Ejiri, Akira*; Peterson, B.*

Purazuma, Kaku Yugo Gakkai-Shi, 92(2), P. 145, 2016/02

no abstracts in English

Journal Articles

ITPA (International Tokamak Physics Activity) meeting report, 50

Kawano, Yasunori; Akiyama, Tsuyoshi*; Ishikawa, Masao; Isobe, Mitsutaka*; Itami, Kiyoshi; Ejiri, Akira*; Peterson, B.*

Purazuma, Kaku Yugo Gakkai-Shi, 91(8), P. 565, 2015/08

no abstracts in English

Journal Articles

ITPA (International Tokamak Physics Activity) meeting report, 48

Kawano, Yasunori; Akiyama, Tsuyoshi*; Ishikawa, Masao; Isobe, Mitsutaka*; Itami, Kiyoshi; Ejiri, Akira*; Peterson, B. J.*

Purazuma, Kaku Yugo Gakkai-Shi, 91(1), P. 76, 2015/01

no abstracts in English

Journal Articles

ITPA (International Tokamak Physics Activity) meeting report, 46

Kawano, Yasunori; Akiyama, Tsuyoshi*; Ishikawa, Masao; Isobe, Mitsutaka*; Itami, Kiyoshi; Ejiri, Akira*; Peterson, B.*

Purazuma, Kaku Yugo Gakkai-Shi, 90(7), P. 431, 2014/07

no abstracts in English

Journal Articles

Progresses in development of the ITER edge Thomson scattering system

Yatsuka, Eiichi; Bassan, M.*; Hatae, Takaki; Ishikawa, Masao; Shimada, Takahiko; Vayakis, G.*; Walsh, M.*; Scannell, R.*; Huxford, R.*; Bilkova, P.*; et al.

Journal of Instrumentation (Internet), 8(12), p.C12001_1 - C12001_10, 2013/12

 Times Cited Count:6 Percentile:34.98(Instruments & Instrumentation)

Journal Articles

Surface amorphization in Al$$_{2}$$O$$_{3}$$ induced by swift heavy ion irradiation

Okubo, Nariaki; Ishikawa, Norito; Sataka, Masao; Jitsukawa, Shiro

Nuclear Instruments and Methods in Physics Research B, 314, p.208 - 210, 2013/11

 Times Cited Count:12 Percentile:73.42(Instruments & Instrumentation)

Microstructure in single crystal Al$$_{2}$$O$$_{3}$$ specimens developed during irradiation by 70-160 MeV-Xe ions has been examined with transmission electron microscope (TEM). Amorphization was observed around 800 nm depth through from ion-beam incident surface of the specimen. The amorphization was also evaluated with XRD technique. TEM observation also indicated that tracks were formed by irradiation at the deeper region than that of the amorphous layers. The number density and size of the tracks have been decreased with the depth from the ion-incident surface. It suggests that amorphization has been occurred by the overlapping of the tracks. It was also obvious that the thickness of the amorphous layers were smaller than those observed in poly-crystal alumina specimens. This may be interpreted by the difference of electronic energy loss in the specimen; lower energy loss for single crystal specimens for their crystallographic orientation against to the incident ion-beam.

Journal Articles

Electronic stopping power dependence of ion-track size in UO$$_{2}$$ irradiated with heavy ions in the energy range of $$sim$$1MeV/u

Ishikawa, Norito; Sonoda, Takeshi*; Sawabe, Takashi*; Sugai, Hiroyuki*; Sataka, Masao*

Nuclear Instruments and Methods in Physics Research B, 314, p.180 - 184, 2013/11

 Times Cited Count:16 Percentile:82.29(Instruments & Instrumentation)

In order to investigate electronic stopping power dependence of ion-track size in UO$$_{2}$$, ion-tracks in UO$$_{2}$$ irradiated with various ions with the specific energy in the order of 1 MeV/u have been observed by a transmission electron microscope. The ion-tracksize shows monotonic increase as a function of the electronic stopping power. Theion-track size obtained for UO$$_{2}$$ is smaller than that obtained for CeO$$_{2}$$, although these two compounds have same crystallographic structure and similar thermal properties. The ion-track sizes for irradiations with ions having relatively low energy of about1 MeV/u are smaller than those expected from the thermal spike models based on melting temperature criterion. The possible interpretations for the unusually smallion-tracks observed for UO$$_{2}$$ are discussed.

Journal Articles

Development of divertor IR thermography for ITER

Takeuchi, Masaki; Sugie, Tatsuo; Ogawa, Hiroaki; Ishikawa, Masao; Shimada, Takahiko; Kusama, Yoshinori

Plasma and Fusion Research (Internet), 8(Sp.1), p.2402147_1 - 2402147_5, 2013/11

Divertor IR Thermography is one of the diagnostics which Japan is in charge of development in ITER project. The conceptual design has been performed so far, and the progress is reported here. By reducing the size of mirrors, and making the optical path a labyrinthine structure, the design of a new optics that fills requirements of both spatial resolution and neutron shielding has been advanced. To achieve the required measurement accuracy, the detected signal and the noises such as bremsstrahlung light, detector noise and thermal noise of optical components were evaluated. Higher photons than the bremsstrahlung light are obtained, excluding the low temperature range. The simulation calculation of reflection from wall was started. Detailed method of data processing of deriving the profiles of surface temperature in the divertor plates from the observed signals and in-situ calibration strategies of the optical system are important issues and will be discussed.

Journal Articles

Neutronic analysis for ${it in situ}$ calibration of ITER in-vessel neutron flux monitor with microfission chamber

Ishikawa, Masao; Kondoh, Takashi; Kusama, Yoshinori; Bertalot, L.*

Fusion Engineering and Design, 88(6-8), p.1377 - 1381, 2013/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Neutronic analysis is performed for ${it in situ}$ calibration of the in-vessel neutron flux monitor in ITER, the Microfission Chamber (MFC). The transfer system of a neutron generator, which consists of two toroidal rings and a neutron generator holder, has been designed and its effect on the detection efficiency of the MFC is estimated through neutronic analysis with MCNP. The result indicates that the designed transfer system is unaffected for the detection efficiency of the MFC. ${it In situ}$ calibrations for the point by point method and the rotation method are simulated and compared through neutronic analysis. It is found that the rotation method is appropriate for full calibration because this method has the advantage that the calibration time can be shortened and all neutron flux monitors can be calibrated simultaneously.

Journal Articles

Issues on the absolute neutron emission measurement at ITER

Sasao, Mamiko*; Ishikawa, Masao; Yuan, G.*; Patel, K.*; Jakhar, S.*; Kashchuk, Y.*; Bertalot, L.*

Plasma and Fusion Research (Internet), 8(Sp.1), p.2402127_1 - 2402127_3, 2013/09

Fusion power output of ITER is measured by a group of neutron flux monitors combined with a neutron activation system and neutron profile monitors. These systems should be absolutely calibrated by use of DD/DT generators moving inside the ITER vacuum vessel (in-situ calibration). Each neutron monitor has a limited measurement range of emission rate, but the ranges are connected by cross-calibration using the ITER plasma with at least one decade overlapping. The over all dynamic range covered by the group of neutron flux monitors is 10$$^{14}$$ n/sec to 10$$^{21}$$ n/sec. Effects of vertical/radial movement of plasma on the measurement accuracy were reviewed. It was found that cross-calibration using specially planned jog shots, and a vertical neutron camera is important to minimize the inaccuracy caused by the plasma movement.

Journal Articles

Nonlinear simulation of energetic particle modes in JT-60U

Bierwage, A.; Aiba, Nobuyuki; Shinohara, Koji; Todo, Yasushi*; Deng, W.*; Ishikawa, Masao; Matsunaga, Go; Yagi, Masatoshi

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10

Journal Articles

Nonlinear simulation of energetic particle modes in high-beta tokamak plasma

Bierwage, A.; Aiba, Nobuyuki; Todo, Yasushi*; Deng, W.*; Ishikawa, Masao; Matsunaga, Go; Shinohara, Koji; Yagi, Masatoshi

Plasma and Fusion Research (Internet), 7(Sp.1), p.2403081_1 - 2403081_4, 2012/07

JAEA Reports

Conceptual design of multipurpose compact research reactor; Annual report FY2010 (Joint research)

Imaizumi, Tomomi; Miyauchi, Masaru; Ito, Masayasu; Watahiki, Shunsuke; Nagata, Hiroshi; Hanakawa, Hiroki; Naka, Michihiro; Kawamata, Kazuo; Yamaura, Takayuki; Ide, Hiroshi; et al.

JAEA-Technology 2011-031, 123 Pages, 2012/01

JAEA-Technology-2011-031.pdf:16.08MB

The number of research reactors in the world is decreasing because of their aging. However, the planning to introduce the nuclear power plants is increasing in Asian countries. In these Asian countries, the key issue is the human resource development for operation and management of nuclear power plants after constructed them, and also the necessity of research reactor, which is used for lifetime extension of LWRs, progress of the science and technology, expansion of industry use, human resources training and so on, is increasing. From above backgrounds, the Neutron Irradiation and Testing Reactor Center began to discuss basic concept of a multipurpose low-power research reactor for education and training, etc. This design study is expected to contribute not only to design tool improvement and human resources development in the Neutron Irradiation and Testing Reactor Center but also to maintain and upgrade the technology on research reactors in nuclear power-related companies. This report treats the activities of the working group from July 2010 to June 2011 on the multipurpose low-power research reactor in the Neutron Irradiation and Testing Reactor Center and nuclear power-related companies.

Journal Articles

Neutronic analysis of the ITER poloidal polarimeter

Ishikawa, Masao; Kawano, Yasunori; Imazawa, Ryota; Sato, Satoshi; Vayakis, G.*; Bertalot, L.*; Yatsuka, Eiichi; Hatae, Takaki; Kondoh, Takashi; Kusama, Yoshinori

Fusion Engineering and Design, 86(6-8), p.1286 - 1289, 2011/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The nuclear heating rates of the optical mirrors of the poloidal polarimeter installed in the equatorial port plug of ITER are calculated. Since the system cannot have a sufficiently labyrinthine structure and the second mirrors are located nearly as close to the plasma as the first mirrors due to limited space, the nuclear heating rate of the second mirrors is as high as that of the first mirrors. However, it is possible to reduce the nuclear heating rates of the mirrors if the blanket shield module provides a sufficient degree of neutron shielding.

Journal Articles

Nuclear technology aspects of ITER vessel-mounted diagnostics

Vayakis, G.*; Bertalot, L.*; Encheva, A.*; Walker, C.*; Brichard, B.*; Cheon, M. S.*; Chitarin, G.*; Hodgson, E.*; Ingesson, C.*; Ishikawa, Masao; et al.

Journal of Nuclear Materials, 417(1-3), p.780 - 786, 2011/10

 Times Cited Count:19 Percentile:83.81(Materials Science, Multidisciplinary)

Journal Articles

Nonlinear hybrid simulations of energetic particle modes in realistic tokamak flux surface geometry

Bierwage, A.; Todo, Yasushi*; Aiba, Nobuyuki; Shinohara, Koji; Ishikawa, Masao; Yagi, Masatoshi

Plasma and Fusion Research (Internet), 6, p.2403109_1 - 2403109_5, 2011/08

Journal Articles

Effect of thermal neutrons on fusion power measurement using the microfission chamber in ITER

Ishikawa, Masao; Kondoh, Takashi; Nishitani, Takeo; Kusama, Yoshinori

Fusion Engineering and Design, 86(4-5), p.417 - 420, 2011/06

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

A Microfission Chamber (MFC) provides time-resolved measurements of global neutron source strength in ITER. Measurements of the neutron source strength could be affected by cooling water in branch pipes installed near the MFC. The effect of the branch pipes upon the MFC is assessed through neutron transport calculation. Results indicate a significant increase in the MFC response rate due to the branch pipe. The increase in the MFC response is caused by the slowing down of the neutrons due to the cooling water in the branch pipes. One possible solution to reduce the effect is to cover the MFC with a material that absorbs thermal neutrons such as cadmium. The ways in which the absorbent material may affect MFC response is analyzed through neutron transport calculation. Results indicate that the increase in the MFC response can be reduced to $$<$$ 10% through cadmium coating.

177 (Records 1-20 displayed on this page)