Saito, Hiroyuki*; Machida, Akihiko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*
Physica B; Physics of Condensed Matter, 587, p.412153_1 - 412153_6, 2020/06
The site occupancy of deuterium (D) atoms in face-centered-cubic nickel (fcc Ni) was measured along a cooling path from 1073 to 300 K at an initial pressure of 3.36 GPa via in situ neutron powder diffraction. Deuterium atoms predominantly occupy the octahedral (O) sites and slightly occupy the tetrahedral (T) sites of the fcc metal lattice. The O-site occupancy increases from 0.4 to 0.85 as the temperature is lowered from 1073 to 300 K. Meanwhile, the T-site occupancy remains c.a. 0.02. The temperature-independent behavior of the T-site occupancy is unusual, and its process is not yet understood. From the linear relation between the expanded lattice volume and D content, a D-induced volume expansion of 2.09(13) /D atom was obtained. This value is in agreement with the values of 2.14-2.2 /D atom previously reported for Ni and Ni Fe alloy.
Meigo, Shinichiro; Oi, Motoki; Fujimori, Hiroshi*
Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06
As hadron accelerators for such as the ADS and spallation neutron source achieve increasing beam power, damage to targets is becoming increasingly severe. To mitigate this damage, nonlinear beam optics based on octupole magnets is attractive. Nonlinear optics can decrease the beam-focusing hazard due to failure of the rastering magnet. As a side effect of nonlinear optics, the beam size is known to expand drastically compared with linear optics. Nonlinear effects have been studied via a simplified filament model that ignores beam-divergence spread at the octupole magnet. In this study, a new generalized model is proposed for application to an octupole magnet, regardless of the filament-model approximation. It is found that the transverse distribution obtained by beam tracking can be specified by the introduction of only two parameters, namely the normalized octupole strength of and the of the phase advance. To achieve the two antagonistic requirements of reduction of the beam-peak density and minimization of the beam loss, the transverse distribution is surveyed for a large range of beam position. It is found that a bell-shaped distribution with 1 and 3 can satisfy requirements. This result is applied to beam transport in the spallation neutron source at J-PARC. The calculation result given by the present model shows good agreement with the experimental data, and the peak current density is reduced by 50% compared with the linear-optics case.
Bao, S.*; Cai, Z.*; Si, W.*; Wang, W.*; Wang, X.*; Shangguan, Y.*; Ma, Z.*; Dong, Z.-Y.*; Kajimoto, Ryoichi; Ikeuchi, Kazuhiko*; et al.
Physical Review B, 101(21), p.214419_1 - 214419_8, 2020/06
Saito, Hiroyuki*; Machida, Akihiko*; Iizuka, Riko*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Sato, Toyoto*; Orimo, Shinichi*; Aoki, Katsutoshi*
Scientific Reports (Internet), 10, p.9934_1 - 9934_8, 2020/06
Neutron powder diffraction profiles were collected for iron deuteride (FeDx) while the temperature decreased from 1023 to 300 K for a pressure range of 4-6 GPa. The ' deuteride with a double hexagonal close-packed (dhcp) structure, which coexisted with other stable or metastable deutrides at each temperature and pressure condition, formed solid solutions with a composition of FeD at 673 K and 6.1 GPa and FeD at 603 K and 4.8 GPa. Upon stepwise cooling to 300 K, the D-content x increased to a stoichiometric value of 1.0 to form monodeuteride FeD. In the dhcp FeD at 300 K and 4.2 GPa, dissolved D atoms fully occupied the octahedral interstitial sites, slightly displaced from the octahedral centers in the dhcp metal lattice, and the dhcp sequence of close-packed Fe planes contained hcp-stacking faults at 12%. Magnetic moments with 2.11 0.06 B/Fe-atom aligned ferromagnetically in parallel on the Fe planes.
Ito, Takashi; Higemoto, Wataru; Shimomura, Koichiro*
Journal of the Physical Society of Japan, 89(5), p.051007_1 - 051007_8, 2020/05
Iida, Kazuki*; Kofu, Maiko; Suzuki, Katsuhiro*; Murai, Naoki; Kawamura, Seiko; Kajimoto, Ryoichi; Inamura, Yasuhiro; Ishikado, Motoyuki*; Hasegawa, Shunsuke*; Masuda, Takatsugu*; et al.
Journal of the Physical Society of Japan, 89(5), p.053702_1 - 053702_5, 2020/05
Harjo, S.; Aizawa, Kazuya; Gong, W.*; Kawasaki, Takuro
Materials Transactions, 61(5), p.828 - 832, 2020/04
Shinohara, Takenao; Kai, Tetsuya; Oikawa, Kenichi; Nakatani, Takeshi; Segawa, Mariko; Hiroi, Kosuke; Su, Y.; Oi, Motoki; Harada, Masahide; Iikura, Hiroshi; et al.
Review of Scientific Instruments, 91(4), p.043302_1 - 043302_20, 2020/04
Komatsu, Kazuki*; Klotz, S.*; Machida, Shinichi*; Sano, Asami; Hattori, Takanori; Kagi, Hiroyuki*
Proceedings of the National Academy of Sciences of the United States of America, 117(12), p.6356 - 6361, 2020/03
Above 2 GPa the phase diagram of water simplifies considerably and exhibits only two solid phases up to 60 GPa, ice VII and ice VIII. The two phases are related to each other by hydrogen ordering, with the oxygen sub-lattice being essentially the same. Here we present neutron diffraction data to 15 GPa which reveal that the rate of hydrogen-ordering at the ice VII-VIII transition decreases strongly with pressure to reach time scales of minutes at 10 GPa. Surprisingly, the ordering process becomes more rapid again upon further compression. We show that such an unusual change in transition rate can be explained by a slowing-down of the rotational dynamics of water molecules with a simultaneous increase of translational motion of hydrogen under pressure, as previously suspected. The observed crossover in the hydrogen dynamics in ice is likely the origin of various hitherto unexplained anomalies of ice VII in the 10-15 GPa range reported by Raman spectroscopy, X-ray diffraction, and proton conductivity.
Takahashi, Osamu*; Shibui, Yohei*; Xu, P. G.; Harjo, S.; Suzuki, Tetsuya*; Tomota, Yo*
Quantum Beam Science (Internet), 4(1), p.16_1 - 16_15, 2020/03
Yamashita, Takayuki; Morooka, Satoshi; Harjo, S.; Kawasaki, Takuro; Koga, Norimitsu*; Umezawa, Osamu*
Scripta Materialia, 177, p.6 - 10, 2020/03
Hamon, 30(1), p.45 - 50, 2020/02
no abstracts in English
Komatsu, Kazuki*; Klotz, S.*; Nakano, Satoshi*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Yamashita, Keishiro*; Irifune, Tetsuo*
High Pressure Research, 40(1), p.184 - 193, 2020/02
A new high pressure cells for neutron diffraction experiments using nano-polycrystalline anvil is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to 82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of FeO at ambient conditions using this cell and discuss the current limitation and future developments.
Naoe, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Wakui, Takashi; Wakai, Eiichi; Haga, Katsuhiro; Takada, Hiroshi
JPS Conference Proceedings (Internet), 28, p.081004_1 - 081004_6, 2020/02
The beam window of the mercury target vessel in J-PARC is severely damaged by the cavitation. The cavitation damage is a crucial factor to limit lifetime of the target because it increases with the beam power. Therefore, mitigating cavitation damage is an important issue to operate the target stably for long time at 1 MW. At J-PARC, to mitigate the cavitation damage: gas microbubbles are injected into mercury for suppressing pressure waves, and double-walled structure with a narrow channel of 2 mm in width to form high-speed mercury flow (4m/s) has been adopted. After operation, the beam window was cut to inspect the effect of the cavitation damage mitigation on inner wall. We optimized cutting conditions through the cold cutting tests, succeeding in cutting the target No.2 (without damage mitigation technologies) smoothly in 2017, and target No.8 with damage mitigation technologies. In the workshop, progress of cavitation damage observation for the target vessel will be presented.
Naoe, Takashi; Harjo, S.; Kawasaki, Takuro; Xiong, Z.*; Futakawa, Masatoshi
JPS Conference Proceedings (Internet), 28, p.061009_1 - 061009_6, 2020/02
At the J-PARC, a mercury target vessel made of 316L SS suffers proton and neutron radiation environment. The target vessel also suffers cyclic impact stress caused by the proton beam-induced pressure waves. The vessel suffers higher than 4.510 cyclic loading during the expected service life of 5000 h. We have investigated fatigue strength 316L SS up to gigacycle in the previous studies. The cyclic hardening and softening behavior were observed. In this study, to evaluate the cyclic hardening/softening behavior, the dislocation densities of specimens were measured using the neutron diffraction method at the MLF BL-19. The result showed that the dislocation density of a 316L SS was increased with increasing the number of loading cycles. By contrast, in the case of cold-rolled 316L SS, annihilation and re-accumulation of dislocation by cyclic loading were observed. In the workshop, result of neutron diffraction measurement will be introduced with the progress of fatigue test.
Meigo, Shinichiro; Matsuda, Hiroki; Iwamoto, Yosuke; Yoshida, Makoto*; Hasegawa, Shoichi; Maekawa, Fujio; Iwamoto, Hiroki; Nakamoto, Tatsushi*; Ishida, Taku*; Makimura, Shunsuke*
JPS Conference Proceedings (Internet), 28, p.061004_1 - 061004_6, 2020/02
no abstracts in English
Takada, Hiroshi; Haga, Katsuhiro
JPS Conference Proceedings (Internet), 28, p.081003_1 - 081003_7, 2020/02
At the Japan Proton Accelerator Research Complex (J-PARC), the pulsed spallation neutron source has been in operation with a redesigned mercury target vessel from October 2017 to July 2018, during which the operational beam power was restored to 500 kW and the operation with a 1-MW equivalent beam was demonstrated for one hour. The target vessel includes a gas-micro-bubbles injector and a 2-mm-wide narrow mercury flow channel at the front end as measures to suppress the cavitation damage. After the operating period, it was observed that the cavitation damage at the 3-mm-thick front end of the target vessel could be suppressed less than 17.5 m.
Kai, Tetsuya; Shinohara, Takenao; Matsumoto, Yoshihiro*
Kensa Gijutsu, 25(2), p.1 - 5, 2020/02
no abstracts in English
Oikawa, Kenichi; Kiyanagi, Yoshiaki*; Sato, Hirotaka*; Omae, Kazuma*; Pham, A.*; Watanabe, Kenichi*; Matsumoto, Yoshihiro*; Shinohara, Takenao; Kai, Tetsuya; Harjo, S.; et al.
Materials Research Proceedings, Vol.15, p.207 - 213, 2020/02
Kai, Tetsuya; Hiroi, Kosuke; Su, Y.; Segawa, Mariko; Shinohara, Takenao; Matsumoto, Yoshihiro*; Parker, J. D.*; Hayashida, Hirotoshi*; Oikawa, Kenichi
Materials Research Proceedings, Vol.15, p.149 - 153, 2020/02