Spatial distribution and preferred orientation of crystalline microstructure of lead-bismuth eutectic

Ito, Daisuke*; Sato, Hirotaka*; Odaira, Naoya*; Saito, Yasushi*; Parker, J. D.*; Shinohara, Takenao; Kai, Tetsuya; Oikawa, Kenichi

Journal of Nuclear Materials, 569, p.153921_1 - 153921_6, 2022/10

https://doi.org/10.1016/j.jnucmat.2022.153921

Neutron transmission spectrum of liquid lead bismuth eutectic

Oba, Yojiro; Ito, Daisuke*; Saito, Yasushi*; Onodera, Yohei*; Parker, J. D.*; Shinohara, Takenao; Oikawa, Kenichi

Materials Research Proceedings, Vol.15, p.160 - 164, 2020/02

https://doi.org/10.21741/9781644900574-25

Lead Bismuth eutectic (LBE) is a promising candidate of the coolant for accelerator driven system (ADS) and fast breeder reactor. Neutron transmission imaging is a powerful technique to investigate the LBE in flow channel. However, previous studies have focused on the analysis of the neutron transmission spectra due to Bragg diffraction (Bragg edge transmission) from the solid phase of the LBE. If the neutron transmission spectra due to the diffraction from a liquid phase can be observed, it is useful to study the behavior of the molten LBE in the flow channel. Therefore, the energy-resolved neutron transmission imaging measurements of the molten LBE was carried out. The observed neutron transmission spectra can be explained by those calculated from the scattering profiles of the molten LBE. This indicates that the structure of the molten LBE can be characterized and mapped using the neutron transmission imaging.

Reduced-shifted conjugate-gradient method for a Green's function; Efficient numerical approach in a nano-structured superconductor

Nagai, Yuki; Shinohara, Yasushi*; Futamura, Yasunori*; Sakurai, Tetsuya*

Journal of the Physical Society of Japan, 86(1), p.014708_1 - 014708_9, 2017/01

https://doi.org/10.7566/JPSJ.86.014708

no abstracts in English

Time-dependent density functional theory of high-intensity short-pulse laser irradiation on insulators

Sato, Shunsuke*; Yabana, Kazuhiro*; Shinohara, Yasushi*; Otobe, Tomohito; Lee, K.-M.*; Bertsch, G. F.*

Physical Review B, 92(20), p.205413_1 - 205413_6, 2015/11

https://doi.org/10.1103/PhysRevB.92.205413

We calculate the energy deposition by very short laser pulses in SiO (-quartz) with a view to establishing systematics for predicting damage and nanoparticle production. The theoretical framework is time-dependent density functional theory, implemented by the real-time method in a multiscale representation. We find that the deposited energy in the medium can be accurately modeled as a function of the local electromagnetic pulse fluence. The energy deposition function can in turn be quite well fitted to the strong-field Keldysh formula. We find reasonable agreement between the damage threshold and the energy required to melt the substrate. The ablation threshold estimated by the energy to convert the substrate to an atomic fluid is higher than the measurement, indicating significance of nonthermal nature of the process. A fair agreement is found for the depth of the ablation.

Dynamics of low- shear Alfvn modes driven by energetic N-NB ions in JT-60U

Bierwage, A.; Todo, Yasushi*; Aiba, Nobuyuki; Shinohara, Koji

Nuclear Fusion, 54(10), p.104001_1 - 104001_14, 2014/10

https://doi.org/10.1088/0029-5515/54/10/104001

First-principles simulation of the optical response of bulk and thin-film -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

https://doi.org/10.1063/1.4864662

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.

Numerical construction of a low-energy effective Hamiltonian in a self-consistent Bogoliubov-de Gennes approach of superconductivity

Nagai, Yuki; Shinohara, Yasushi*; Futamura, Yasunori*; Ota, Yukihiro*; Sakurai, Tetsuya*

Journal of the Physical Society of Japan, 82(9), p.094701_1 - 094701_10, 2013/09

https://doi.org/10.7566/JPSJ.82.094701

no abstracts in English

First-principles calculation to explore mechanisms of coherent phonon generation

Shinohara, Yasushi*; Otobe, Tomohito; Iwata, Junichi*; Yabana, Kazuhiro*

Nihon Butsuri Gakkai-Shi, 67(10), p.685 - 689, 2012/10

https://doi.org/10.11316/butsuri.67.10_685

Coherent phonon is the macroscopic coherent oscillation of atoms in a solid state generating under the ultrafast laser pulse which is shorter than the frequency of the phonon. Some physical processes for the coherent phonon have been proposed. We are studying the computational method describing the dynamics of the electron and atom employing the time-dependent density functional theory. Our computational results show the origine of the coherent phonon in Si quantitatively.

Nonadiabatic generation of coherent phonons

Shinohara, Yasushi*; Sato, Shunsuke*; Yabana, Kazuhiro*; Iwata, Junichi*; Otobe, Tomohito; Bertsch, G. F.*

Journal of Chemical Physics, 137(22), p.22A527_1 - 22A527_8, 2012/08

https://doi.org/10.1063/1.4739844

The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling and optical phonon of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonon.

Development of polarized Xe gas target for neutron experiment at J-PARC

Sakai, Kenji; Oku, Takayuki; Shinohara, Takenao; Kira, Hiroshi; Oi, Motoki; Maekawa, Fujio; Kakurai, Kazuhisa; Ino, Takashi*; Arimoto, Yasushi*; Shimizu, Hirohiko*; et al.

Journal of Physics; Conference Series, 340, p.012037_1 - 012037_7, 2012/02

https://doi.org/10.1088/1742-6596/340/1/012037

At the Materials and Life science experimental Facility (MLF) in J-PARC, an experiment of detecting a neutron polarizing ability caused by a neutron-nuclear (n-N) spin correlation term at a resonant peak of Xe is planned. The Xe gas having a high polarization under low magnetic field and room temperature by a spin exchange optical pumping (SEOP) technique is expected to become a suitable target for verification of the neutron optical theorem (NOPT). We evaluated measurable quantities based on the NOPT, developed a polarized Xe gas system, and carried out a feasibility test of our apparatus. This paper reports on the present status of the experiment.