Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Maeyama, Shinya*; Watanabe, Tomohiko*; Nakata, Motoki*; Nunami, Masanori*; Asahi, Yuichi; Ishizawa, Akihiro*
Nature Communications (Internet), 13, p.3166_1 - 3166_8, 2022/06
Times Cited Count：22 Percentile：96.13(Multidisciplinary Sciences)Turbulent transport is a key physics process for confining magnetic fusion plasma. Recent theoretical and experimental studies of existing fusion experimental devices revealed the existence of cross-scale interactions between small (electron)-scale and large (ion)-scale turbulence. Since conventional turbulent transport modelling lacks cross-scale interactions, it should be clarified whether cross-scale interactions are needed to be considered in future experiments on burning plasma, whose high electron temperature is sustained with fusion-born alpha particle heating. Here, we present supercomputer simulations showing that electron scale turbulence in high electron temperature plasma can affect the turbulent transport of not only electrons but also fuels and ash. Electron-scale turbulence disturbs the trajectories of resonant electrons responsible for ion-scale micro-instability and suppresses large-scale turbulent fluctuations. Simultaneously, ion-scale turbulent eddies also suppress electron-scale turbulence. These results indicate a mutually exclusive nature of turbulence with disparate scales. We demonstrate the possibility of reduced heat flux via cross-scale interactions.
Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Nunami, Masanori*
Computer Physics Communications, 235, p.9 - 15, 2019/02
Times Cited Count：6 Percentile：47.14(Computer Science, Interdisciplinary Applications)We have implemented the Sugama collision operator in the gyrokinetic Vlasov simulation code, GKV, with an implicit time-integration scheme. The new method is versatile and independent of the details of the linearized collision operator, by means of an operator splitting, an implicit time integrator, and an iterative Krylov subspace solver. Numerical tests demonstrate stable computation over the time step size restricted by the collision term. An efficient implementation for parallel computation on distributed memory systems is realized by using the data transpose communication, which makes the iterative solver free from inter-node communications during iteration. Consequently, the present approach achieves enhancement of computational efficiency and reduction of computational time to solution simultaneously, and significantly accelerates the total performance of the application.
Kanno, Ryutaro*; Nunami, Masanori*; Satake, Shinsuke*; Matsuoka, Seikichi; Takamaru, Hisanori*
Nuclear Fusion, 58(1), p.016033_1 - 016033_7, 2018/01
Times Cited Count：0 Percentile：0.00(Physics, Fluids & Plasmas)The electron heat transport in a torus plasma which involves a radially-bounded ergodic region, where flux surfaces are partially destroyed by perturbative magnetic fields, is studied. In this paper, we have demonstrated that the radial heat conduction by the particles' parallel motion is reduced by trapped particles.
Maeyama, Shinya*; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki*; Ishizawa, Akihiro*; Nunami, Masanori*
Nuclear Fusion, 57(6), p.066036_1 - 066036_10, 2017/05
Times Cited Count：18 Percentile：68.37(Physics, Fluids & Plasmas)Multi-scale plasma turbulence including electron and ion temperature gradient (ETG/ITG) modes has been investigated by means of electromagnetic gyrokinetic simulations. Triad transfer analyses on nonlinear mode coupling reveal cross-scale interactions between electron and ion scales. One of the interactions is suppression of electron-scale turbulence by ion- scale turbulence, where ITG-driven short-wavelength eddies act like shear flows and suppress ETG turbulence. Another cross-scale interaction is enhancement of ion-scale turbulence in the presence of electron-scale turbulence. This is caused via short-wavelength zonal flows, which are created by the response of passing kinetic electrons in ITG turbulence, suppress ITG turbulence by their shearing, and are damped by ETG turbulence. In both cases, sub-ion-scale structures between electron and ion scales play important roles in the cross-scale interactions.
Kanno, Ryutaro*; Nunami, Masanori*; Satake, Shinsuke*; Matsuoka, Seikichi; Takamaru, Hisanori*
Contributions to Plasma Physics, 56(6-8), p.592 - 597, 2016/08
Times Cited Count：2 Percentile：10.75(Physics, Fluids & Plasmas)A drift-kinetic 
simulation code is developed for estimating collisional transport in quasi-steady state of toroidal plasma affected by resonant magnetic perturbations and radial electric field. In this paper, validity of the code is confirmed through several test calculations. It is found that radial electron flux is reduced by positive radial-electric field, although radial diffusion of electron is strongly affected by chaotic field-lines under an assumption of zero electric field.
Ishizawa, Akihiro*; Idomura, Yasuhiro; Imadera, Kenji*; Kasuya, Naohiro*; Kanno, Ryutaro*; Satake, Shinsuke*; Tatsuno, Tomoya*; Nakata, Motoki*; Nunami, Masanori*; Maeyama, Shinya*; et al.
Purazuma, Kaku Yugo Gakkai-Shi, 92(3), p.157 - 210, 2016/03
The high-performance computer system Helios which is located at The Computational Simulation Centre (CSC) in The International Fusion Energy Research Centre (IFERC) started its operation in January 2012 under the Broader Approach (BA) agreement between Japan and the EU. The Helios system has been used for magnetised fusion related simulation studies in the EU and Japan and has kept high average usage rate. As a result, the Helios system has contributed to many research products in a wide range of research areas from core plasma physics to reactor material and reactor engineering. This project review gives a short catalogue of domestic simulation research projects. First, we outline the IFERC-CSC project. After that, shown are objectives of the research projects, numerical schemes used in simulation codes, obtained results and necessary computations in future.
Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*
Parallel Computing, 49, p.1 - 12, 2015/11
Times Cited Count：7 Percentile：51.11(Computer Science, Theory & Methods)Maeyama, Shinya*; Idomura, Yasuhiro; Watanabe, Tomohiko*; Nakata, Motoki*; Yagi, Masatoshi; Miyato, Naoaki; Ishizawa, Akihiro*; Nunami, Masanori*
Physical Review Letters, 114(25), p.255002_1 - 255002_5, 2015/06
Times Cited Count：99 Percentile：95.12(Physics, Multidisciplinary)Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and 
value are realized for the first time, where the value is given by the ratio of plasma pressure to magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real- mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. When the ion-scale modes are stabilized by finite- effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport.
Watanabe, Tomohiko*; Idomura, Yasuhiro; Maeyama, Shinya; Nakata, Motoki; Sugama, Hideo*; Nunami, Masanori*; Ishizawa, Akihiro*
Journal of Physics; Conference Series, 510, p.012045_1 - 012045_11, 2014/05
Times Cited Count：2 Percentile：66.90(Computer Science, Interdisciplinary Applications)Plasma turbulence accompanied with fluctuations of the distribution function and the electromagnetic fields develops on the phase space composed of the configuration space and the velocity space. Detailed structures of the distribution function in magnetic fusion plasmas are investigated by means of gyrokinetic simulations performed on massively parallel supercomputers. The gyrokinetic simulations of drift wave turbulence have demonstrated entropy transfer in the phase space, zonal flow enhancement by helical fields and the resultant transport reduction. The state-of-the-art high performance computing is utilized for a multi- scale turbulence simulation covering ion- and electron-scales and for a global-scale simulation of turbulent transport in a sub-ITER sized plasma.
Nakata, Motoki; Matsuyama, Akinobu; Aiba, Nobuyuki; Maeyama, Shinya; Nunami, Masanori*; Watanabe, Tomohiko*
Plasma and Fusion Research (Internet), 9, p.1403029_1 - 1403029_12, 2014/04
A local gyrokinetic Vlasov simulation code GKV is extended to incorporate realistic tokamak equilibria including up-down asymmetry, which are produced by a free-boundary 2D Grad-Shafranov equation solver MEUDAS. The developed codes have been verified by a cross-code benchmark test using Cyclone-base-case like MHD equilibrium, where good agreement in the dispersion relation of ion temperature gradient (ITG) driven mode has been confirmed. The extended GKV is applied to two types of shaped plasmas expected in JT-60SA tokamak devices, i.e., ITER-like and highly-shaped plasmas, and ITG-mode stability and residual zonal-flow level are investigated. Through the detailed comparisons, more favorable stability properties against the ITG mode are revealed for the highly-shaped case, where the lower ITG-mode growth rate and higher residual zonal-flow levels compared to the ITER-like case are identified.
Idomura, Yasuhiro; Nakata, Motoki; Yamada, Susumu; Machida, Masahiko; Imamura, Toshiyuki*; Watanabe, Tomohiko*; Nunami, Masanori*; Inoue, Hikaru*; Tsutsumi, Shigenobu*; Miyoshi, Ikuo*; et al.
International Journal of High Performance Computing Applications, 28(1), p.73 - 86, 2014/02
Times Cited Count：17 Percentile：74.78(Computer Science, Hardware & Architecture)Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*
Plasma and Fusion Research (Internet), 8, p.1403150_1 - 1403150_8, 2013/11
flows in helical plasmasWatanabe, Tomohiko*; Nunami, Masanori*; Sugama, Hideo*; Satake, Shinsuke*; Matsuoka, Seikichi*; Ishizawa, Akihiro*; Maeyama, Shinya; Tanaka, Kenji*
Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2012/10
Idomura, Yasuhiro; Nakata, Motoki; Yamada, Susumu; Machida, Masahiko; Imamura, Toshiyuki*; Watanabe, Tomohiko*; Nunami, Masanori*; Inoue, Hikaru*; Tsutsumi, Shigenobu*; Miyoshi, Ikuo*; et al.
Proceedings of 31st JSST Annual Conference; International Conference on Simulation Technology (JSST 2012) (USB Flash Drive), p.234 - 242, 2012/09
Nishihara, Katsunobu*; Sunahara, Atsushi*; Sasaki, Akira; Nunami, Masanori*; Tanuma, Hajime*; Fujioka, Shinsuke*; Shimada, Yoshinori*; Fujima, Kazumi*; Furukawa, Hiroyuki*; Kato, Takako*; et al.
Physics of Plasmas, 15(5), p.056708_1 - 056708_11, 2008/00
Times Cited Count：133 Percentile：97.63(Physics, Fluids & Plasmas)Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*
no journal, ,
Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*
no journal, ,
Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*; Maeyama, Shinya
no journal, ,
Nakata, Motoki; Honda, Mitsuru; Yoshida, Maiko; Urano, Hajime; Maeyama, Shinya; Nunami, Masanori*; Watanabe, Tomohiko*
no journal, ,
First-principle based gyrokinetic simulation is a powerful method for investigating turbulent transport in magnetically confined fusion plasmas, and the quantitative evaluations of the prediction capability through comparisons with existing experiments and the model improvement are important issues. In this study, a local gyrokinetic turbulence code GKV-J is extended to incorporate realistic tokamak equilibria to realize the first principle based turbulent transport simulations on JT-60U tokamak. In addition to clarifications of the micro-stability properties depending on the radial locations, the turbulence simulation results successfully reproduce the experimental results on ion and electron heat diffusivity in the core region, where the conventional fluid-type reduced transport model shows some deviations. Also, the impact of shaping on turbulent transport properties is identified for JT-60SA tokamak.
Maeyama, Shinya; Watanabe, Tomohiko*; Idomura, Yasuhiro; Nakata, Motoki; Nunami, Masanori*; Ishizawa, Akihiro*
no journal, ,
no abstracts in English
