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O
Yoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Sugiyama, Takeharu*; Oba, Yojiro; Ishikawa, Norito; Kobayashi, Eiichi*; Okudaira, Koji*
Journal of the American Ceramic Society, 103(8), p.4654 - 4663, 2020/08
Times Cited Count：4 Percentile：23.05(Materials Science, Ceramics)X-ray absorption near edge structure (XANES) and small-angle X-ray scattering (SAXS) reveal the damaged structures in MgAlO spinel induced by swift heavy ions. SAXS indicates the formation of ion tracks with cylindrical shape with a diameter of 5 nm. XANES indicates the cationic disordering between tetrahedral and octahedral sites by the irradiation. Quantitative analysis of XANES also reveals that cations preferably occupy the octahedral sites at high fluence.
O induced by swift heavy ionsYoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Ishikawa, Norito; Kobayashi, Eiichi*
Physical Chemistry Chemical Physics, 20(7), p.4962 - 4969, 2018/02
Times Cited Count：5 Percentile：23.21(Chemistry, Physical)Cationic disorder in the MgAlO spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradiation fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calculated spectra based on density function theory indicate that the change in the experimental spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAlO induced by the high density electronic excitation under swift heavy ion irradiation.
Kawaguchi, Kazuhiro*; Yamamoto, Shunya; Yoshikawa, Masahito; Takahiro, Katsumi*
Thin Solid Films, 562, p.648 - 652, 2014/07
Times Cited Count：4 Percentile：19.55(Materials Science, Multidisciplinary)Liquid organic-hydrides such as cyclohexane which can release-absorbing hydrogen in reversible have been proposed approvable carriers to store and transport hydrogen. However, organic-hydrides are known as highly flammable in air. To realize practical use of this hydrogen production process, the monitoring of leakage of organic-hydride gas is strongly required. In the present work, we have examined the plasmonic sensing ability of Au nanoparticle (NP) arrays for dilute cyclohexane. Au NP arrays were prepared on SiO by a sputter deposition technique. The change in an extinction spectrum of Au NP arrays before and after exposure of cyclohexane vapor enabled us to detect it. The Au NP array prepared with 4.4 
10
Au atoms/cm
deposited at 300
C was and demonstrated a high sensitivity for cyclohexane at RT. The experimentally detectable concentration of cyclohexane was as low as 0.5 vol%, much lower than its explosion limit (1.3 vol%).
Takaki, Seiya*; Yasuda, Kazuhiro*; Yamamoto, Tomokazu*; Matsumura, Sho*; Ishikawa, Norito
Nuclear Instruments and Methods in Physics Research B, 326, p.140 - 144, 2014/05
Times Cited Count：39 Percentile：94.83(Instruments & Instrumentation)We have investigated atomic structure of ion tracks in CeO irradiated with 200 MeV Xe ions by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM observations under inclined conditions showed continuous ion tracks with diffraction and structure factor contrast, and the decrease in the atomic density of the ion tracks was evaluated. High resolution STEM with high-angle annular dark-field (HAADF) technique showed that the crystal structure of the Ce cation column is retained at the core region of ion tracks, although the signal intensity of the Ce cation lattice is reduced over a region nm in size. Annular bright field (ABF) STEM observation has detected that the O anion column is preferentially distorted at the core region of ion tracks within a diameter of 4 nm.
Kato, Sho; Yamaki, Tetsuya; Yamamoto, Shunya; Hakoda, Teruyuki; Kawaguchi, Kazuhiro; Kobayashi, Tomohiro*; Suzuki, Akihiro*; Terai, Takayuki*
Nuclear Instruments and Methods in Physics Research B, 314, p.149 - 152, 2013/11
Times Cited Count：2 Percentile：19.73(Instruments & Instrumentation)We implanted 100 keV W
in unpolished GC substrates at nominal fluences up to 
ions/cm
. The implanted samples were electrochemically anodized in a NaOH aqueous solution to etch the surface layer. The analyses were performed by X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). XPS W 4f spectra indicated the formation of carbides as reported previously. The electrochemical etching clearly increased the W concentration on the surface. According to the RBS results, half of the implanted W atoms were retained in the substrate, while the rest should escape to the etching solution. The cross-sectional TEM image revealed a uniform distribution of WC particles with a diameter of less than 10 nm just near the surface region.
irradiated with swift heavy ionsYasuda, Kazuhiro*; Eto, Motoki*; Sawada, Kenichi*; Yamamoto, Tomokazu*; Yasunaga, Kazufumi*; Matsumura, Sho*; Ishikawa, Norito
Nuclear Instruments and Methods in Physics Research B, 314, p.185 - 190, 2013/11
Times Cited Count：34 Percentile：92.6(Instruments & Instrumentation)We have investigated microstructure evolution in CeO irradiated with 210 MeV Xe ions by using transmission electron microscopy to gain the fundamental knowledge on radiation damage induced by fission fragments in nuclear fuel and transmutation target.
Kato, Sho; Yamaki, Tetsuya; Yamamoto, Shunya; Hakoda, Teruyuki; Kawaguchi, Kazuhiro; Kobayashi, Tomohiro*; Suzuki, Akihiro*; Terai, Takayuki*
Transactions of the Materials Research Society of Japan, 38(1), p.81 - 84, 2013/03
Nanoparticles were formed by 100 keV tungsten-ion implantation in unpolished glassy carbon substrates at nominal fluences of 
- 
ions/cm. The implanted samples were analyzed by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, hydrodynamic voltammetry using a rotating disk electrode, and field emission scanning electron microscopy. A significant sputtering effect changed the depth profile during the course of irradiation and limited the amount of tungsten retainable in the substrate in agreement with our calculated distributions. The nanoparticles were composed of tungsten carbide and dispersed uniformly with diameters of around 10 nm.
Yoshida, Kazuhiro*; Sakata, Hideyuki*; Sago, Hiromi*; Shiraishi, Tadashi*; Oyama, Kazuhiro*; Hagiwara, Hiroyuki*; Yamano, Hidemasa; Yamamoto, Tomohiko
Proceedings of 8th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-8) (USB Flash Drive), 9 Pages, 2012/12
To prevent the vortex cavitations, asymmetric flow in the upper plenum due to the radial slit with upper internal structure (UIS) has been mitigated by installing a cylindrical structure named as dummy plug instead of the fuel handling machine only used for refueling period. In this study, the extended brim and the division plate at the slit of UIS have been proposed in order to improve flow pattern in upper plenum for the purpose of the vortex cavitation prevention.
/Si by ion implantationTakahiro, Katsumi*; Ninakuchi, Yuki*; Kawaguchi, Kazuhiro; Isshiki, Toshiyuki*; Nishio, Koji*; Sasase, Masato*; Yamamoto, Shunya; Nishiyama, Fumitaka*
Applied Surface Science, 258(19), p.7322 - 7326, 2012/07
Times Cited Count：2 Percentile：10.02(Chemistry, Physical)A nanometer-sized metallic particle embedded in a transparent dielectric exhibits a nonlinear susceptibility, and going to be applied to nonlinear optical devices. In the present study, well-ordered arrangements of Ag nanoparticles have been found for Ag-implanted SiO. Thermally grown SiO on Si were implanted with 350 keV-Ag ions to fluences of 0.37-1.2 10
ions/cm. Cross-sectional transmission electron microscopy and scanning transmission electron microscopy reveal the presence of a two-dimensional array of Ag nanoparticles of 25-40 nm in diameter located at a depth of 
130 nm, together with the self-organization of tiny Ag nanoparticles aligned along the SiO/Si interface. X-ray photoelectron spectroscopy and X-ray diffraction confirm the stability of these Ag nanoparticles embedded in the SiO/Si is found to be stable against oxidation and sulfidation when stored in ambient conditions for more than one and a half year.
O under swift heavy ion irradiationYasuda, Kazuhiro*; Yamamoto, Tomokazu*; Eto, Motoki*; Kawasoe, Shinji*; Matsumura, Sho*; Ishikawa, Norito
International Journal of Materials Research, 102(9), p.1082 - 1088, 2011/09
Times Cited Count：11 Percentile：52.23(Metallurgy & Metallurgical Engineering)Accumulation and recovery of radiation-induced damage with swift heavy ions instoichiometric magnesium aluminate spinel, MgAlO, has been investigated. Microstructural change and atomic disordering was examined through transmission electron microscopy (TEM) techniques, with bright-field (BF) and high-resolution (HR) TEM images, and high angular resolution electron channelling X-ray spectroscopy (HARECXS), for single crystal MgAlO irradiated with 200 MeV Xe, and 340 or 350 MeV Au ions. The density of core damage region, detected by BFTEM with Fresnelcontrast, increased proportionally with ion fluence at the early stage of accumulation. This result is discussed with a balance between the formation and recovery of the core damage region under irradiation, and the influence region to induce the recovery was evaluated to be 7-9 nm in radius. The structure of the core damage region is found from HR and BFTEM images to be a columnar vacancy-rich region with a low atomic density.
Kawaguchi, Kazuhiro; Saito, Masahiro*; Takahiro, Katsumi*; Yamamoto, Shunya; Yoshikawa, Masahito
Plasmonics, 6(3), p.535 - 539, 2011/09
Times Cited Count：8 Percentile：28.2(Chemistry, Physical)Silver nanoparticles (Ag NPs) have optical absorption bands due to localized surface plasmon resonance (LSPR) in visible range. The LSPR of Ag-NPs is being used for optical gas sensors. However, there have been differences in LSPR absorption band between most of the experimental data and calculations. We have demonstrated that plasma treatments for Ag NPs to clear the effect of contamination on surface of Ag NPs for LSPR absorption band. The results show that Ar plasma treatments to Ag NPs bring blue-shift and narrowing in their LSPR absorption band. Raman scattering analysis result that hydrocarbons adsorbed on silver surfaces were removed effectively by plasma exposure. It was found that the decrease in Raman line intensity for hydrocarbons was correlated well with the blue-shift. Our findings indicate that one of the most important factors for difference in LSPR absorption band between the experimental data and calculations is due to the impurity adsorption on silver surfaces.
Kashiwagi, Mieko; Taniguchi, Masaki; Kojima, Atsushi; Dairaku, Masayuki; Hanada, Masaya; Hemsworth, R. S.*; Mizuno, Takatoshi*; Takemoto, Jumpei; Tanaka, Masanobu*; Tanaka, Yutaka*; et al.
Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03
At JAEA, a multi-aperture multi-grid accelerator has been developed for the ITER neutral beam system. A target is H
ion beam acceleration of 0.5 A (200 A/m) at 1 MeV. In real accelerators, it was found that the voltage holding was about a half of that obtained in an ideal small electrode. After applying necessary gap length and radii of edges of grid supports to lower local electric field concentrations, the accelerator succeeded in sustaining 1 MV for 4000 s. As a result, beam parameters were increased to 879 keV, 0.36 A (157 A/m) at perveance matched condition from 796 kV, 0.32 A (140 A/m) reported in FEC2008. In the beam acceleration, the beamlet deflections due to magnetic field and space charge repulsion caused direct interceptions, that resulted in limitations in the beam energy and current. Compensation of these beamlet deflections has been tested applying aperture offset and field shaping plate, which were examined in a three-dimensional beam analysis.
Hakoda, Teruyuki; Yamamoto, Shunya; Kawaguchi, Kazuhiro; Yamaki, Tetsuya; Kobayashi, Tomohiro*; Yoshikawa, Masahito
Applied Surface Science, 257(5), p.1556 - 1561, 2010/12
Times Cited Count：13 Percentile：50.83(Chemistry, Physical)Carbon-based films having nitrogen species on their surface were prepared on a glassy-carbon (GC) substrate as a non-platinum cathode catalyst for polymer electrolyte fuel cells by depositing cobalt and carbon in the presence of N gas using a pulse laser deposition method and then removing metal Co by HCl-washing treatment. The oxygen reduction reaction (ORR) activity was electrochemically determined using a rotating disk electrode system where the film samples on the GC substrate were replaceable. The ORR activity increased with elevating temperature of the GC substrate during the deposition. A carbon-based film prepared at 600C in the presence of 66.7 Pa N showed the highest ORR activity among the tested samples; its ORR potential was 0.66 V (vs. NHE). This film was composed of amorphous carbons doped with pyridine-type nitrogen atoms on its surface.
Yamamoto, Masanori; Watanabe, Kazuhiro; Yamanaka, Haruhiko; Takemoto, Jumpei; Yamashita, Yasuo*; Inoue, Takashi
JAEA-Technology 2010-029, 60 Pages, 2010/08
JAEA-Technology-2010-029.pdf:10.49MB
A power supply for the ITER Neutral Beam Injector (NBI) is a DC ultra-high voltage (UHV) power supply to accelerate negative ion beams of 40 A up to an energy of 1 MeV. Japan Atomic Energy Agency as the Japan Domestic Agency for ITER contributes procurement of dc -1 MV main components such as step-up -1 MV transformers rectifiers, a high voltage deck 2, a -1 MV insulating transformer, a transmission line, a surge reduction system and equipments for site test. Design of the surge suppression in the NBI power supply is one of the key issues to obtain the stable injector performance. This report describes the design study using EMTDC code on the surge suppression by optimizing the core snubber and additional elements in the -1 MV power supply. The results show that the input energy from the stray capacitance to the accelerator at the breakdown can be reduced to about 25 J that is smaller than the design criteria of 50 J for the ITER NBI.
Bigi, M.*; De Lorenzi, A.*; Grando, L.*; Watanabe, Kazuhiro; Yamamoto, Masanori
Fusion Engineering and Design, 84(2-6), p.446 - 450, 2009/06
Times Cited Count：16 Percentile：70.97(Nuclear Science & Technology)The ITER NBI requires a five stage -1 MV power supply system under strict load protection for electric breakdowns. A circuit model of the power supply with MAMuG accelerator has been developed for the simulation of fast transients related to the accelerator breakdowns. The complex inductive and capacitive couplings were assessed by calculations with finite element techniques. The circuit model, developed to address a number of design issues requiring simulations at system level, is now ready for use - the optimization of passive protections being the most significant application.
Watanabe, Kazuhiro; Yamamoto, Masanori; Takemoto, Jumpei; Yamashita, Yasuo*; Dairaku, Masayuki; Kashiwagi, Mieko; Taniguchi, Masaki; Tobari, Hiroyuki; Umeda, Naotaka; Sakamoto, Keishi; et al.
Nuclear Fusion, 49(5), p.055022_1 - 055022_5, 2009/05
Times Cited Count：28 Percentile：70.93(Physics, Fluids & Plasmas)Japan Atomic Energy Agency as the Japan Domestic Agency (JADA) for ITER contributes procurement of dc -1 MV ultra-high voltage (UHV) components such as a dc -1 MV generator, a transmission line and a -1 MV insulating transformer for the ITER NBI power supply. Inverter frequency of 150 Hz in the -1 MV power supply and major circuit parameters have been proposed and adopted in the ITER NBI. The dc UHV insulation at the multi-layer insulation structure of the transformer for a long pulse up to 3600 s has been designed with electric field simulation. Based on the simulation overall dimensions of the dc UHV components have been finalized. The JADA contributes to provide an effective surge suppression system composed of core snubbers and resistors. Input energy into the accelerator from the power supply can be reduced to about 20 J which satisfies the design criteria of the total 50 J at -1 MV breakdown.
Dairaku, Masayuki; Watanabe, Kazuhiro; Tobari, Hiroyuki; Kashiwagi, Mieko; Inoue, Takashi; Sakamoto, Keishi; Hanada, Masaya; Akino, Noboru; Ikeda, Yoshitaka; Yamamoto, Takumi*
JAEA-Technology 2008-091, 23 Pages, 2009/03
JAEA-Technology-2008-091.pdf:5.82MB
A plasma generator whose inner dimensions are 25 cm in width, 59 cm in length, and 31 cm in depth for a high power and long pulse ion source in neutral beam injector has been designed and fabricated. The plasma generator has a beam extraction area of 12 cm in width and 46 cm in length. A target of the output beam using the plasma generator is to produce deuterium positive ion beams up to 120 keV, 65 A for longer than 200 s pulses. Arrangement of the permanent magnets and filaments has been designed by using an electron trajectory simulation code to produce uniform and high density plasma with high proton yield. Cooling channels have been also designed to operate the long pulse plasma generation with a 100 kW arc discharge power.
Watanabe, Kazuhiro; Yamamoto, Masanori; Takemoto, Jumpei; Yamashita, Yasuo*; Dairaku, Masayuki; Kashiwagi, Mieko; Taniguchi, Masaki; Tobari, Hiroyuki; Umeda, Naotaka; Sakamoto, Keishi; et al.
Proceedings of 22nd IAEA Fusion Energy Conference (FEC 2008) (CD-ROM), 7 Pages, 2008/10
The JADA contributes procurement of DC -1 MV ultra-high voltage (UHV) components such as a -1 MV DC generator, a transmission line and a -1 MV insulating transformer. The DC UHV insulation has been carefully analyzed since DC long pulse insulation is quite different from conventional AC insulation. The insulation structure has been designed and the overall dimensions of the DC UHV components have been finalized. The JADA contributes to provide an effective surge suppression system composed of core snubbers and resistors. Input energy into the accelerator from the power supply can be reduced to about 20 J which satisfies the design criteria of the total 50 J at -1 MV breakdown. From these studies, major technical issues were considered and the functional technical specifications of the UHV components have been developed for the procurement by the JADA.
Aihara, Jun; Hojo, Kiichi; Furuno, Shigemi*; Hojo, Tomohiro; Sawa, Kazuhiro; Yamamoto, Hiroyuki; Motohashi, Yoshinobu*
Materials Transactions, 48(7), p.1896 - 1900, 2007/07
Times Cited Count：0 Percentile：0.01(Materials Science, Multidisciplinary)Silicon carbide(SiC) TEM specimens were annealed, in-situ, at 1273K for 30 minutes after amorphization with 30keV Ne
irradiation to the fluence of 1.9 or 2.310
Ne/m at 573K or about 98K. The crystal nucleation and bubble coalescence accompanied by recrystallization were observed in both specimens with the annealing after the irradiations. 2.310Ne/m irradiations in both specimens. The Debye-Sherrer rings of the nucleated crystals well fitted the net pattern of the matrix, even though no ring corresponding to (200) of 
-SiC appeared. Dependence of the crystal nucleation behavior on irradiation temperature was not observed within the present experimental range.
O-yttria stabilized ZrO composite material irradiated with Ne ions at high temperaturesHojo, Tomohiro*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi
Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.123 - 127, 2006/09
Times Cited Count：2 Percentile：21.09(Instruments & Instrumentation)Spinel and yttria stabilized zirconia (YSZ) are candidates for fuel materials for use in nuclear reactors and the optical and insulating materials for fusion reactors. In the present study, the damage evolution process of polycrystalline spinel-YSZ composite materials has been studied by in situ transmission electron microscope observation during ion irradiation. The irradiation was performed with 30 keV Ne at a flux of 5 10
ions/cm per second at 923 K and 1473 K, respectively. At 923 K, defect clusters and bubbles were formed homogeneously in YSZ grains. On the other hand, at 1473 K, only bubble formation was observed. The bubbles grew remarkably with increasing ion fluence in both grains. Even though the growth of the bubbles was observed in both grains, the average diameter of grown bubbles in spinel grains was larger than those in YSZ ones. The bubbles tended to form along the grain boundary at both temperatures.
