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Matsumoto, Taro; Kishimoto, Yasuaki; Miyato, Naoaki; Li, J.*
Journal of Plasma Physics, 72(6), p.1183 - 1187, 2006/12
Times Cited Count：6 Percentile：21.5(Physics, Fluids & Plasmas)no abstracts in English
Kawai, Chika; Maeyama, Shinya; Idomura, Yasuhiro; Ogawa, Yuichi*
no journal, ,
Self organization through inverse energy cascade in quasi two dimensional turbulence spectra is considered as a mechanism of the formation of zonal flow structure in magnetized plasma. However, relation between turbulence energy spectra and formation of zonal flow structure has not been clarified in first-principles based plasma turbulence simulations. In this study, we examine relations between turbulent energy spectra and structure formations due to self-organization, which are derived from a fluid description of plasma turbulence, the Hasegawa-Mima equation, using gyrokinetic Vlasov simulations of electron turbulence.
Asahi, Yuichi; Ishizawa, Akihiro*; Watanabe, Tomohiko*; Sugama, Hideo*; Tsutsui, Hiroaki*; Iio, Shunji*
no journal, ,
Turbulent transport driven by electron temperature gradient (ETG) modes and trapped electron modes (TEMs) is investigated by means of gyrokinetic simulations. It is found that ETG turbulence can be suppressed by zonal flows driven by TEMs. Then, the mechanism of the regulation of ETG turbulence by zonal flows is investigated by nonlinear entropy transfer analysis. Firstly, it is confirmed that the entropy is transferred from TEMs to zonal flow. Secondly, it is found that the zonal flows in the steady state meditate the entropy transfer of the ETG modes from low to high radial wavenumber regions. In short, it is quantitatively shown that the zonal flows is driven by TEMs and the ETG turbulence is regulated by the TEM-driven zonal flows.
Idomura, Yasuhiro; Maeyama, Shinya*; Nakata, Motoki*; Nunami, Masanori*; Ishizawa, Akihiro*; Watanabe, Tomohiko*
no journal, ,
A novel parallel optimization technique for extreme scale CFD simulations is developed on the K-computer, and strong scaling of finite difference and spectral fusion plasma turbulence codes is improved toward million-core regimes. The optimization technique consists of a multi-dimensional and multi-layer domain decomposition, optimized process mapping on a three dimensional (3D) torus network, and overlap of computations and communications using communication threads. The improved strong scaling dramatically expanded capabilities of the fusion plasma turbulence codes both in problem sizes and time-scales, and enabled us to study critical issues in ITER such as the plasma size scaling of ion turbulent heat transport, and the electron heat transport induced by multi-scale electron turbulence.
Idomura, Yasuhiro
no journal, ,
Transient plasma responses due to modulated electron heating are investigated in numerical experiments of ion temperature gradient driven trapped electron mode turbulence using gyrokinetic full-f Eulerian code GT5D. It is found that even with electron heating without particle and momentum sources such as electron cyclotron resonance heating, dominant turbulence is changed from ion turbulence to electron turbulence due to changes of the electron temperature gradient and the temperature ratio, and the resulting turbulent transport produces responses of density and rotation profiles.
Idomura, Yasuhiro
no journal, ,
Turbulent transport is one of key issues in fusion science. To address this issue via a five dimensional (5D) gyrokinetic model, the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed. On the K-computer, inter-node parallelization techniques such as multi-dimensional/-layer domain decomposition and communication-computation overlap were developed, and strong scaling of GT5D was improved up to 
million cores. This computing power enabled us to study ITER relevant issues such as the plasma size scaling of turbulent transport. However, extensions of GT5D towards burning plasmas including kinetic electrons and multi-species ions require exascale computing. Under the post-K project, we have developed computing techniques for the next generation computing platforms based on many core processors. In this talk, we discuss computational challenges related to complicated intra-processor memory hierarchy and limited inter-node communication performance compared with accelerated computation.
Idomura, Yasuhiro
no journal, ,
Under the Post-K project, a Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed towards exascale burning plasma simulations on the Post-K machine. In this talk, we review the present status on new computational techniques on GT5D, in which Krylov based sparse matrix solvers for a semi-implicit time integration method occupy the most of computational cost. Recently, we introduced communication-avoiding (CA) Krylov methods, and improved the scalability of GT5D on the latest many-core platforms. We also ported the CA-Krylov solver on the latest GPU platforms, and achieved speedup by more than an order of magnitude.
Idomura, Yasuhiro
no journal, ,
Under the Post-K project, a Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed towards exascale burning plasma simulations on the Post-K machine. In this talk, firstly, we review petascale computing techniques on current petascale machines such as the K-computer and their impacts on the progress of full-f gyrokinetic simulations. Secondly, we discuss extensions of simulation models towards burning plasma simulations and systematic experimental data analyses. Thirdly, we present new exascale computing techniques towards the Post-K machine, and demonstrate their computational performance on the latest many core platforms.
Idomura, Yasuhiro; Obrejan, K.
no journal, ,
A gyrokinetic full-f Eulerian code GT5D is extended for multiple ion species. Multi-species collision operators between high Z impurities and bulk ions or electrons become multi-scale problems in velocity space, and thus, are numerically difficult problems. This issue is resolved by introducing a filter to suppress the divergence of collisional coefficients at lower energy and an implicit collision operator, and analyses of high Z impurities such as tungsten are realized. We present verification results on neoclassical transport with multiple ion species, and discuss impurity transport properties in nonlinear turbulence simulations.
Idomura, Yasuhiro
no journal, ,
This lecture aims to overview progress in gyrokinetic simulations of turbulent fusion plasmas. Firstly, theoretical frameworks of physical models from the 6D Vlasov equation to the 5D gyrokinetic equation are presented, and then, simulation models to treat multi-scale physics in the 5D gyrokinetic equation are discussed. Secondly, properties of numerical approaches, namely, Lagrangian and Eulerian approaches are described, and a role of numerical dissipation in collisionless plasma turbulence simulations is discussed. Thirdly, recent advances in gyrokinetic simulations are reviewed focusing on multi-scale simulations such as numerical experiments using full-f gyrokinetic models and ion-electron multi-scale electron turbulence simulations.
Idomura, Yasuhiro
no journal, ,
We review gyrokinetic simulations of turbulent fusion plasmas. First, the five dimensional (5D) gyrokinetic model is presented, and its numerical approaches, namely, Lagrangian and Eulerian approaches are explained. Second, the gyrokinetic toroidal 5D Eulerian code GT5D is presented, and novel exascale computing techniques on the latest many core and GPU platforms are discussed. Third, the current petascale numerical experiments on ion temperature gradient turbulence are presented, and the target issues in the future exascale numerical experiments on FUGAKU are discussed.
Idomura, Yasuhiro
no journal, ,
In this lecture, we provide an overview of the high-performance computing techniques for the global full-f gyrokinetic simulation code GT5D on the Fugaku supercomputer, and discuss the results of numerical experiments conducted using it. Exascale supercomputers such as Fugaku have revealed communication performance bottlenecks due to the improvement in computational performance, particularly in the 16-bit operations provided for machine learning. In this research, we resolved this issue by employing communication-avoiding algorithms that leverage 16-bit operations, leading to a significant acceleration of GT5D. Through numerical experiments on Fugaku, we analyzed the transition phenomena of fusion plasma turbulence, reproduced the complex transport properties of heat, particles, and momentum, and elucidated their underlying physical mechanisms.
