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Journal Articles

Dimensional reduction by geometrical frustration in a cubic antiferromagnet composed of tetrahedral clusters

Okuma, Ryutaro*; Kofu, Maiko; Asai, Shinichiro*; Avdeev, M.*; Koda, Akihiro*; Okabe, Hirotaka*; Hiraishi, Masatoshi*; Takeshita, Soshi*; Kojima, Kenji*; Kadono, Ryosuke*; et al.

Nature Communications (Internet), 12(1), p.4382_1 - 4382_7, 2021/07

 Times Cited Count:0 Percentile:0(Multidisciplinary Sciences)

Journal Articles

Quantum dynamics of hydrogen in the iron-based superconductor LaFeAsO$$_{0.9}$$D$$_{0.1}$$ measured with inelastic neutron spectroscopy

Yamaura, Junichi*; Hiraka, Haruhiro*; Iimura, Soshi*; Muraba, Yoshinori*; Bang, J.*; Ikeuchi, Kazuhiko*; Nakamura, Mitsutaka; Inamura, Yasuhiro; Honda, Takashi*; Hiraishi, Masatoshi*; et al.

Physical Review B, 99(22), p.220505_1 - 220505_6, 2019/06

AA2019-0126.pdf:0.9MB

 Times Cited Count:1 Percentile:10.83(Materials Science, Multidisciplinary)

Inelastic neutron scattering was performed for an iron-based superconductor, where most of D (deuterium) replaces oxygen, while a tiny amount goes into interstitial sites. By first-principle calculation, we characterize the interstitial sites for D (and for H slightly mixed) with four equivalent potential minima. Below the superconducting transition temperature Tc = 26 K, new excitations emerge in the range 5-15 meV, while they are absent in the reference system LaFeAsO$$_{0.9}$$F$$_{0.1}$$. The strong excitations at 14.5 meV and 11.1 meV broaden rapidly around 15 K and 20 K, respectively, where each energy becomes comparable to twice of the superconducting gap. The strong excitations are ascribed to a quantum rattling, or a band motion of hydrogen, which arises only if the number of potential minima is larger than two.

Journal Articles

Effects of centrifugal modification of magnetohydrodynamic equilibrium on resistive wall mode stability

Shiraishi, Junya; Aiba, Nobuyuki; Miyato, Naoaki; Yagi, Masatoshi

Nuclear Fusion, 54(8), p.083008_1 - 083008_8, 2014/08

 Times Cited Count:8 Percentile:44.28(Physics, Fluids & Plasmas)

Toroidal rotation effects are self-consistently taken into account not only in the linear magnetohydrodynamic (MHD) stability analysis but also in the equilibrium calculation. The MHD equilibrium computation is affected by centrifugal force due to the toroidal rotation. To study the toroidal rotation effects on resistive wall modes (RWMs), a new code has been developed. The RWMaC modules, which solve the electromagnetic dynamics in vacuum and the resistive wall, have been implemented in the MINERVA code, which solves the Frieman-Rotenberg equation that describes the linear ideal MHD dynamics in a rotating plasma. It is shown that modification of MHD equilibrium by the centrifugal force significantly reduces growth rates of RWMs. Moreover, it can open a stable window which does not exist under the assumption that the rotation affects only the linear dynamics.

Journal Articles

Bipartite magnetic parent phases in the iron oxypnictide superconductor

Hiraishi, Masatoshi*; Iimura, Soshi*; Kojima, Kenji*; Yamaura, Junichi*; Hiraka, Haruhiro*; Ikeda, Kazutaka*; Miao, P.*; Ishikawa, Yoshihisa*; Torii, Shuki*; Miyazaki, Masanori*; et al.

Nature Physics, 10(4), p.300 - 303, 2014/04

 Times Cited Count:94 Percentile:96.38(Physics, Multidisciplinary)

Journal Articles

Stabilization of resistive wall modes by magnetohydrodynamic equilibrium change induced by plasma toroidal rotation

Shiraishi, Junya; Aiba, Nobuyuki; Miyato, Naoaki; Yagi, Masatoshi

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2013/03

Effects of plasma toroidal rotation are self-consistently taken into account not only in the magnetohydrodynamic (MHD) stability analysis but also in the equilibrium calculation. To study the effects of toroidal rotation on resistive wall modes (RWMs), a new code has been developed. The RWMaC modules, which solve the electromagnetic dynamics in vacuum and the resistive wall, have been implemented in the MINERVA code, which solves the Frieman-Rotenberg equation that describes the linear ideal MHD in a rotating plasma. It is shown for the first time that MHD equilibrium change induced by toroidal rotation significantly reduces the growth rates of RWMs. Moreover, it can open the stable window which does not exist under the assumption that the rotation affects only the linear dynamics. The rotation modifies the equilibrium pressure, current density, and mass density profiles, which results in the change of the potential energy including rotational effects.

Journal Articles

J-PARC decay muon channel construction status

Strasser, P.*; Shimomura, Koichiro*; Koda, Akihiro*; Kawamura, Naritoshi*; Fujimori, Hiroshi*; Makimura, Shunsuke*; Kobayashi, Yasuo*; Nakahara, Kazutaka*; Kato, Mineo*; Takeshita, Soshi*; et al.

Journal of Physics; Conference Series, 225, p.012050_1 - 012050_8, 2010/06

 Times Cited Count:11 Percentile:95.51

Journal Articles

Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi$$_{1.75}$$Pb$$_{0.35}$$Sr$$_{1.90}$$CuO$$_{6+z}$$

Hiraka, Haruhiro*; Hayashi, Yoichiro*; Wakimoto, Shuichi; Takeda, Masayasu; Kakurai, Kazuhisa; Adachi, Tadashi*; Koike, Yoji*; Yamada, Ikuya*; Miyazaki, Masanori*; Hiraishi, Masatoshi*; et al.

Physical Review B, 81(14), p.144501_1 - 144501_6, 2010/04

 Times Cited Count:15 Percentile:57.93(Materials Science, Multidisciplinary)

Oral presentation

Recent activity of the JAEA theory group towards a better understanding of the effects of flows and energetic particles on the stability of MHD modes

Aiba, Nobuyuki; Ishii, Yasutomo; Bierwage, A.; Hirota, Makoto; Shiraishi, Junya; Yagi, Masatoshi

no journal, , 

Recently, the MHD researchers in JAEA theory group pay attention to the effects of the "plasma flow" and the "energetic particles" on the MHD stability, and achieve many results about them. These parameters are thought as important to understand not only the experimental results in existing devices but also the physics of MHD stability that will be destabilized in ITER. In this workshop, we introduce the recent results of JAEA theory group about these effects on MHD stability to Korean researchers; in particular, we report in detail the results about the rotation effect on the edge localized MHD mode and the application for JT-60U experimental analysis.

Oral presentation

Theory and simulation for resistive wall modes in rotating plasmas

Shiraishi, Junya; Aiba, Nobuyuki; Tokuda, Shinji*; Yagi, Masatoshi*

no journal, , 

no abstracts in English

Oral presentation

Effect of poloidal rotation on ELM and RWM in tokamaks

Aiba, Nobuyuki; Shiraishi, Junya; Tokuda, Shinji*; Yagi, Masatoshi

no journal, , 

Numerical analysis is performed for identifying the poloidal rotation effect on the stability of edge localized MHD mode, which relates to the type-I ELM, and that of the resistive wall mode (RWM), which sometimes causes a disruption. This analysis clarifies that the poloidal rotation observed experimentally can destabilize the edge localized MHD mode but stabilize RWM. Furthermore, when the plasma rotates in both the toroidal and the poloidal directions, MHD stability depends on the direction of the toroidal rotation. This dependence is qualitatively consistent with the experimental result of the relation between ELM phenomena and the toroidal rotation direction in JT-60U. Though this dependence of RWM is not discussed until now, this result suggests that we need to confirm whether or not this dependence can be observed experimentally to stabilize RWM in JT-60SA and ITER.

Oral presentation

Effect of poloidal rotation on ELM and RWM in toroidally rotating tokamaks

Aiba, Nobuyuki; Shiraishi, Junya; Tokuda, Shinji*; Yagi, Masatoshi

no journal, , 

Numerical analysis is performed for identifying the poloidal rotation effect on the stability of edge localized MHD mode, which relates to the type-I ELM, and that of the resistive wall mode (RWM), which sometimes causes a disruption. This analysis clarifies that the poloidal rotation observed experimentally can destabilize the edge localized MHD mode but stabilize RWM. Furthermore, when the plasma rotates in both the toroidal and the poloidal directions, MHD stability depends on the direction of the toroidal rotation. This dependence is qualitatively consistent with the experimental result of the relation between ELM phenomena and the toroidal rotation direction in JT-60U. Though this dependence of RWM is not discussed until now, this result suggests that we need to confirm whether or not this dependence can be observed experimentally to stabilize RWM in JT-60SA and ITER.

Oral presentation

Development of resistive wall mode analysis code for rotating plasmas and its application to JT-60SA

Shiraishi, Junya; Aiba, Nobuyuki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Stabilization of resistive wall modes by toroidal rotation shear

Shiraishi, Junya; Aiba, Nobuyuki; Miyato, Naoaki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Development of resistive wall mode analysis code for rotating plasmas

Shiraishi, Junya; Aiba, Nobuyuki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Development of resistive wall mode analysis code for rotating tokamaks; Analysis of high-$$beta$$ plasma in JT-60SA

Shiraishi, Junya; Aiba, Nobuyuki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Stabilization of resistive wall modes by MHD equilibrium change induced by plasma toroidal rotation

Shiraishi, Junya; Aiba, Nobuyuki; Miyato, Naoaki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Impact of Centrifugal Modification of Magnetohydrodynamic Equilibrium on Resistive Wall Mode Stability

Shiraishi, Junya; Aiba, Nobuyuki; Miyato, Naoaki; Yagi, Masatoshi

no journal, , 

no abstracts in English

Oral presentation

Status of the ITER plasma modeling activities in JAEA

Shiraishi, Junya; Honda, Mitsuru; Hayashi, Nobuhiko; Aiba, Nobuyuki; Toma, Mitsunori; Matsuyama, Akinobu; Naito, Osamu; Miyata, Yoshiaki; Inoue, Shizuo; Narita, Emi; et al.

no journal, , 

no abstracts in English

18 (Records 1-18 displayed on this page)
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