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Journal Articles

Development of spin correlations in the geometrically frustrated triangular-lattice Heisenberg antiferromagnet CuCrO$$_2$$

Kajimoto, Ryoichi; Tomiyasu, Keisuke*; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 84(7), p.074708_1 - 074708_6, 2015/07

 Times Cited Count:8 Percentile:58.5(Physics, Multidisciplinary)

Journal Articles

Piezoluminescence and liquid crystallinity of 4,4'-(9,10-Anthracenediyl)bispyridinium salts

Komoto, Shigeo*; Chuko, Tomotaka*; Hisamatsu, Shugo; Okuda, Yasuhiro*; Masu, Hyuma*; Takahashi, Masahiro*; Kishikawa, Keiki*

Crystal Growth & Design, 15(6), p.2723 - 2731, 2015/05

 Times Cited Count:9 Percentile:64.62(Chemistry, Multidisciplinary)

Piezoluminescence and liquid crystallinity of anthracene-based bispyridinium salts were investigated in stimulus responsive luminescent organic crystals and luminescent ionic liquid crystals. The salts possess an anthracene moiety as a fluorophore in their center, and the pyridiniums attached to the anthracene moiety are substituted with trialkoxybenzyl groups. Single crystals of the salts bearing two trimethoxybenzyl groups were obtained as solvates. Ethyl acetate, acetone, and dioxane solvates of the chlorides have almost the same crystal structures with one-dimensional channels. Grinding of the solvated crystals caused the extrusion of the included solvent molecules, which resulted in the red shifts of their fluorescence in the solid state. Tris(octyloxy)benzyl and tris(dodecyloxy)benzyl derivatives exhibited rectangular columnar liquid crystals upon being heated for their bromide and tetrafluoroborate salts and upon being cooled for their hexafluorophosphate salts.

Journal Articles

Low-energy spin fluctuations in CuCrO$$_{2}$$ and Cu$$_{0.85}$$Ag$$_{0.15}$$CrO$$_{2}$$ studied by inelastic neutron scattering

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Okuda, Tetsuji*; Tomiyasu, Keisuke*

JPS Conference Proceedings (Internet), 3, p.014018_1 - 014018_5, 2014/06

Journal Articles

Effects of Mg, Ag, and Al substitutions on magnetic excitations in the triangular-lattice antiferromagnet CuCrO$$_{2}$$

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Kakurai, Kazuhisa; Hokazono, Takahisa*; Ozono, Akira*; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 82(5), p.054702_1 - 054702_6, 2013/05

 Times Cited Count:4 Percentile:36.94(Physics, Multidisciplinary)

Journal Articles

Temperature and Ag doping effect on magnetic excitations in the quasi-two-dimensional triangular lattice antiferromagnet CuCrO$$_2$$ studied by inelastic neutron scattering

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Kakurai, Kazuhisa; Arai, Masatoshi; Hokazono, Takahisa*; Ozono, Akira*; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 79(12), p.123705_1 - 123705_4, 2010/12

 Times Cited Count:21 Percentile:74(Physics, Multidisciplinary)

Journal Articles

Study of ion turbulent transport and profile formations using global gyrokinetic full-$$f$$ Vlasov simulation

Idomura, Yasuhiro; Urano, Hajime; Aiba, Nobuyuki; Tokuda, Shinji

Nuclear Fusion, 49(6), p.065029_1 - 065029_14, 2009/06

 Times Cited Count:108 Percentile:97.41(Physics, Fluids & Plasmas)

Key features of ion turbulent transport in a normal shear tokamak with on-axis heating are clarified using a global gyrokinetic full-$$f$$ Vlasov simulation with sources and collisions. It is found that stiff ion temperature $$T_i$$ profiles are sustained with globally constant gradient scale length $$L_{ti}equiv |T_i/T'_i|$$ near a critical value, and a significant part of the heat flux is carried by avalanches with $$1/f$$ type spectra, which suggest a self-organized criticality. The directions of avalanche propagation and the momentum flux are strongly affected by the shear of the equilibrium radial electric field $$E_r$$, which is determined by a parallel momentum balance. Nondiffusive momentum transport due to the $$E_r$$ shear stress is observed and a non-zero (intrinsic) toroidal rotation is formed without momentum input near the axis.

Journal Articles

Conservative global gyrokinetic toroidal full-$$f$$ 5D Vlasov simulation

Idomura, Yasuhiro; Tokuda, Shinji; Aiba, Nobuyuki; Urano, Hajime

Proceedings of 22nd IAEA Fusion Energy Conference (FEC 2008) (CD-ROM), 8 Pages, 2008/10

A new global gyrokinetic toroidal full-$$f$$ five dimensional Vlasov simulation GT5D is developed based on the gyrokinetic theory and the linear Fokker-Planck collision operator. In a normal shear tokamak, source driven ion temperature gradient turbulence simulations are performed, and turbulent transport and profile evolutions are evolved over a collision time. It is found that a significant part of the heat flux is carried by avalanches in source free regions, where stiff temperature profiles are sustained. In this region, the equilibrium radial electric field $$E_r$$ becomes significantly larger than the neoclassical level, and its shear strongly affects the directions of the avalanche propagation and the momentum flux. A non-diffusive momentum flux due to the $$E_r$$ shear is observed and non-zero (intrinsic) toroidal rotation is sustained without momentum input near the axis.

Journal Articles

Conservative global gyrokinetic toroidal full-$$f$$ five-dimensional Vlasov simulation

Idomura, Yasuhiro; Ida, Masato; Kano, Takuma; Aiba, Nobuyuki; Tokuda, Shinji

Computer Physics Communications, 179(6), p.391 - 403, 2008/09

 Times Cited Count:72 Percentile:95.62(Computer Science, Interdisciplinary Applications)

A new conservative global gyrokinetic toroidal full-$$f$$ five-dimensional Vlasov simulation (GT5D) is developed using a novel non-dissipative conservative finite difference scheme. The scheme guarantees numerical stability by satisfying relevant first principles in the modern gyrokinetic theory, and enables robust and accurate simulations of tokamak micro-turbulence. GT5D is verified through comparisons of zonal flow damping tests, linear analyses of ion temperature gradient driven (ITG) modes, and nonlinear ITG turbulence simulations against a global gyrokinetic toroidal $$delta f$$ particle code. In the comparison, global solutions of the ITG turbulence are identified quantitatively by using two gyrokinetic codes based on particle and mesh approaches.

Journal Articles

Numerical matching scheme for linear magnetohydrodynamic stability analysis

Kagei, Yasuhiro; Tokuda, Shinji

Plasma and Fusion Research (Internet), 3, p.039_1 - 039_5, 2008/07

JAEA Reports

Examination on small-sized cogeneration HTGR for developing countries

Sakaba, Nariaki; Tachibana, Yukio; Shimakawa, Satoshi; Ohashi, Hirofumi; Sato, Hiroyuki; Yan, X.; Murakami, Tomoyuki; Ohashi, Kazutaka; Nakagawa, Shigeaki; Goto, Minoru; et al.

JAEA-Technology 2008-019, 57 Pages, 2008/03

JAEA-Technology-2008-019.pdf:8.59MB

The small-sized and safe cogeneration High Temperature Gas-cooled Reactor (HTGR) that can be used not only for electric power generation but also for hydrogen production and district heating is considered one of the most promising nuclear reactors for developing countries where sufficient infrastructure such as power grids is not provided. Thus, the small-sized cogeneration HTGR, named High Temperature Reactor 50-Cogeneration (HTR50C), was studied assuming that it should be constructed in developing countries. Specification, equipment configuration, etc. of the HTR50C were determined, and economical evaluation was made. As a result, it was shown that the HTR50C is economically competitive with small-sized light water reactors.

Journal Articles

Conservative gyrokinetic Vlasov simulation

Idomura, Yasuhiro; Ida, Masato; Tokuda, Shinji

Communications in Nonlinear Science and Numerical Simulation, 13(1), p.227 - 233, 2008/02

 Times Cited Count:5 Percentile:42.31(Mathematics, Applied)

A new conservative gyrokinetic Vlasov code is developed using a finite difference operator which conserves both the L1 and L2 norms. The growth of numerical oscillations is suppressed by conserving the L2 norm, and the code is numerically stable and robust in a long time micro-turbulence simulation. In the slab ion temperature gradient driven (ITG) turbulence simulation, numerical properties of the new code are discussed, and the results are benchmarked against a conventional $$delta$$$$f$$ particle-in-cell (PIC) code.

Journal Articles

New conservative gyrokinetic full-$$f$$ Vlasov code and its comparison to gyrokinetic $$delta f$$ particle-in-cell code

Idomura, Yasuhiro; Ida, Masato; Tokuda, Shinji; Villard, L.*

Journal of Computational Physics, 226(1), p.244 - 262, 2007/09

 Times Cited Count:30 Percentile:79.83(Computer Science, Interdisciplinary Applications)

A new conservative gyrokinetic full-$$f$$ Vlasov code is developed using a finite difference operator which conserves both the $$L1$$ and $$L2$$ norms. The growth of numerical oscillations is suppressed by conserving the $$L2$$ norm, and the code is numerically stable and robust in a long time simulation. In the slab ion temperature gradient driven (ITG) turbulence simulation, the energy conservation and the entropy balance relation are confirmed, and solutions are benchmarked against a conventional $$delta f$$ particle-in-cell (PIC) code. The results show that the exact particle number conservation and the good energy conservation in the conservative Vlasov simulation are advantageous for a long time micro-turbulence simulation. In the comparison, physical and numerical effects of the $$v_parallel$$ nonlinearity are clarified for the Vlasov and PIC simulations.

Journal Articles

Gyrokinetic simulation of fusion plasma turbulence, 1; Modelling and numerical methods

Ida, Masato; Idomura, Yasuhiro; Tokuda, Shinji

Nihon Ryutai Rikigakkai Nenkai 2007 Koen Rombunshu (CD-ROM), 5 Pages, 2007/08

A numerical code for fusion plasma turbulence has been developed based on a conservative finite difference method for neutral fluids. The theoretical model used in the code is the gyrokinetic equation, and the present finite difference formula is based on the one proposed by Morinishi, which is known to conserve not only the dependent variable but also its squared value. Numerical tests based on ITG turbulence simulations have demonstrated excellent properties of the present code. The conservation error in total energy of the present code, for example, is more than ten times smaller than that of existing codes.

Journal Articles

Gyrokinetic simulation of fusion plasma turbulence, 2; Self-organization of zonal flows in electron turbulence

Idomura, Yasuhiro; Ida, Masato; Tokuda, Shinji

Nihon Ryutai Rikigakkai Nenkai 2007 Koen Rombunshu (CD-ROM), 4 Pages, 2007/08

Electron temperature gradient driven (ETG) turbulence is considered as one of relevant mechanisms of the electron thermal transport in tokamak plasmas. Recent simulation studies disclosed various turbulent structures in the ETG turbulence, and in particular, the formation of zonal flows, which lead to suppression of heat transport, is attracting great attention. In the talk, first principle gyrokinetic simulations of the ETG turbulence are shown, and zonal flows observed in the reversed shear tokamak configuration are discussed. Self-organization mechanisms of zonal flows are clarified from the viewpoint of similarities between zonal flows in the ETG turbulence and zonal jets in the Rossby wave turbulence in the planetary atmosphere.

Journal Articles

Magnetic and superconducting properties of LaIrSi$$_3$$ and CeIrSi$$_3$$ with the non-centrosymmetric crystal structure

Okuda, Yusuke*; Miyauchi, Yuichiro*; Ida, Yuki*; Takeda, Yuji*; Tonohiro, Chie*; Ozuchi, Yasuhiro*; Yamada, Tsutomu*; Nguyen, D.; Matsuda, Tatsuma; Haga, Yoshinori; et al.

Journal of the Physical Society of Japan, 76(4), p.044708_1 - 044708_11, 2007/04

 Times Cited Count:78 Percentile:91.73(Physics, Multidisciplinary)

Single crystals of LaIrSi$$_3$$ and CeIrSi$$_3$$ were grown by the Czochralski pulling method in a tetra-arc furnace and the magnetic and superconducting properties, together with super- conductivity in CeIr$$_{1-x}$$Co$$_x$$Si$$_3$$, were clarified by measuring the electrical resistivity, specific heat, magnetic susceptibility, magnetization and de Haas-van Alphen (dHvA) effect. From the results of the dHvA experiment for LaIrSi$$_3$$, the Fermi surface is found to split into two Fermi surfaces due to the spin-orbit interaction arising from the non-centrosymmetric crystal structure. The electronic state of CeIrSi$$_3$$ is tuned from the antiferro- magnetic state to the superconducting state by applying pressure. The upper critical field H$$_{c2}$$(0) at a pressure of 2.65 GPa is found to be highly anisotropic. Large magnitude and anisotropy of H$$_{c2}$$(0) in CeIrSi$$_3$$ are consistent with the theoretical prediction for superconductivity in the non-centrosymmetric crystal structure.

Journal Articles

New conservative gyrokinetic Vlasov code and its application to fusion plasma turbulence

Ida, Masato; Idomura, Yasuhiro; Tokuda, Shinji

Dai-22-Kai Seiken TSFD Shimpojiumu Koen Rombunshu, p.88 - 95, 2007/03

no abstracts in English

JAEA Reports

Kinetic simulations of electrostatic plasma waves using Cubic-Interpolated-Propagation scheme

Lesur, M.*; Idomura, Yasuhiro; Tokuda, Shinji

JAEA-Research 2006-089, 29 Pages, 2007/01

JAEA-Research-2006-089.pdf:1.67MB

Kinetic properties of small amplitude waves in an electron plasma are studied using analytic and numerical calculations based on the Vlasov-Poisson system. The dispersion relation of plasma waves in a Maxwellian plasma is solved using Laplace-Fourier transform, and it is shown that waves decay in time by Landau damping. A simulation code for solving the Vlasov-Poisson system in phase space is developed using the Cubic-Interpolated-Propagation (CIP) scheme, and Landau damping is successfully calculated numerically. Finally, the stability of an electron plasma with a beam component is discussed by applying these analytic and numerical approaches.

Journal Articles

Gyrokinetic toroidal full-$$f$$ 5D Vlasov code GT5D

Idomura, Yasuhiro; Ida, Masato; Tokuda, Shinji

Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00

A conservative gyrokinetic toroidal five dimensional Vlasov code GT5D is developed. A conservative finite difference scheme is extended to generalized curvilinear coordinates, and a discretization method is developed so that it exactly satisfies the phase space volume conservation, which is an important feature of the gyrokinetic equaion. In the code, highly accurate and robust long time scale tokamak turbulence simulations in a torus configuration are enabled by these techniques. The code is verified through linear benchmark tests against a toroidal particle code. It is also confirmed that first principles such as the particle number conservation and the energy conservation, which was critical issues in the conventional particle code, are satisfied at high presition.

Journal Articles

Swift heavy ion irradiation effects in nanocrystalline gold

Chimi, Yasuhiro; Iwase, Akihiro*; Ishikawa, Norito; Kobiyama, Mamoru*; Inami, Takashi*; Kambara, Tadashi*; Okuda, Shigeo*

Nuclear Instruments and Methods in Physics Research B, 245(1), p.171 - 175, 2006/04

 Times Cited Count:14 Percentile:68.77(Instruments & Instrumentation)

We have studied effects of irradiation with energetic particles on defect accumulation in nanocrystalline gold (nano-Au). The specimens of nano-Au foil (3-5 $$mu$$m thickness) with various grain sizes (23-156 nm) are prepared by the gas deposition method and subsequent thermal annealings. Irradiations of the specimens with 60-MeV $$^{12}$$C ions, 3.54-GeV $$^{136}$$Xe ions or 2.0-MeV electrons are performed at low temperature. The defect accumulation behavior is observed by measuring the electrical resistivity change during irradiation. Through an analysis of defect accumulation behavior, cross-sections for defect production, $$sigma$$$$_{d}$$, and annihilation, $$sigma$$$$_{r}$$, in nano-Au increase monotonically as the grain size decreases. These results are considered to be caused by the existence of a large volume fraction of the regions near grain boundaries in nano-Au where the threshold energy for atomic displacements, E$$_{d}$$, becomes lower than in polycrystalline gold. The possibility of electronic excitation effects in nano-Au is also discussed.

Journal Articles

Conservative gyrokinetic Vlasov simulation using Morinishi scheme

Idomura, Yasuhiro; Ida, Masato; Tokuda, Shinji; Villard, L.*

Europhysics Conference Abstracts (CD-ROM), 30I, 4 Pages, 2006/00

A gyrokinetic simulation is an essential tool to study turbulent anomalous transport in tokamak plasmas, and a long time global simulation of driven turbulence in open system is highly desirable towards estimation and prediction of turbulent transport. However, poor conservation properties in conventional gyrokinetic simulations were problematic in such a long time simulation. To overcome this difficulty, a new conservative gyrokinetic code is developed using Morinishi scheme, which was originally developed for conservative simulations of neutral fluid turbulence. In the new code, in addition to the exact particle number conservation, the energy conservation is dramatically improved, and the scheme is robust in a long time simulation. In slab ion temperature gradient driven turbulence simulations, comparisons of the new code and a conventional particle code are presented.

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