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Matsuoka, Seikichi*; Sugama, Hideo*; Idomura, Yasuhiro
Physics of Plasmas, 28(6), p.064501_1 - 064501_5, 2021/06
Times Cited Count：4 Percentile：43.17(Physics, Fluids & Plasmas)The improved model collision operator proposed by Sugama et al., which can recover the friction-flow relation of the linearized Landau collision operator, is newly implemented in a global full- f gyrokinetic simulation code, GT5D, and collisional transport simulations of a single ion species plasma in a tokamak are performed over the wide collisionality regime. The improved operator is verified to reproduce the theoretical collisional thermal diffusivity precisely in the high collisionality regime, where the friction-flow relation of higher accuracy is required than in the lower collisional regime. In addition, it is found in all collisionality regimes that the higher accuracy of the collisional thermal diffusivity and the parallel flow coefficient is obtained by the improved operator, demonstrating that collisional processes described by the linearized Landau collision operator is correctly retained.
Asahi, Yuichi*; Latu, G.*; Bigot, J.*; Maeyama, Shinya*; Grandgirard, V.*; Idomura, Yasuhiro
Concurrency and Computation; Practice and Experience, 32(5), p.e5551_1 - e5551_21, 2020/03
Times Cited Count：1 Percentile：14.03(Computer Science, Software Engineering)Two five-dimensional gyrokinetic codes GYSELA and GKV were ported to the modern accelerators, Xeon Phi KNL and Tesla P100 GPU. Serial computing kernels of GYSELA on KNL and GKV on P100 GPU were respectively 1.3x and 7.4x faster than those on a single Skylake processor. Scaling tests of GYSELA and GKV were respectively performed from 16 to 512 KNLs and from 32 to 256 P100 GPUs, and data transpose communications in semi-Lagrangian kernels in GYSELA and in convolution kernels in GKV were found to be main bottlenecks, respectively. In order to mitigate the communication costs, pipeline-based and task-based communication overlapping were implemented in these codes.
Idomura, Yasuhiro
Physics of Plasmas, 24(8), p.080701_1 - 080701_5, 2017/08
Times Cited Count：10 Percentile：46.05(Physics, Fluids & Plasmas)An electron heating modulation numerical experiment based on a global full-f gyrokinetic model shows that transitions from ion temperature gradient driven (ITG) turbulence to trapped electron mode (TEM) turbulence induced by electron heating generate density peaking and rotation changes. Toroidal angular momentum balance during the rotation changes is revealed by direct observation of toroidal angular momentum conservation, in which in addition to ion turbulent stress, ion neoclassical stress, radial currents, and toroidal field stress of ions and electrons are important. Toroidal torque flipping between ITG and TEM phases is found to be related to reversal of the ion radial current that indicates coupling of particle and momentum transport channels. The ion and electron radial currents are balanced to satisfy the ambipolar condition, and the electron radial current is cancelled by the electron toroidal field stress, which indirectly affects toroidal torque.
Idomura, Yasuhiro; Asahi, Yuichi; Ina, Takuya; Matsuoka, Seikichi
Proceedings of 24th International Congress of Theoretical and Applied Mechanics (ICTAM 2016), p.3106 - 3107, 2016/08
Turbulent transport in fusion plasmas is one of key issues in ITER. To address this issue via the five dimensional (5D) gyrokinetic model, a novel computing technique is developed, and strong scaling of the Gyrokinetic Toroidal 5D Eulerian code GT5D is improved up to 
million cores on the K-computer. The computing technique consists of multi-dimensional/multi-layer domain decomposition, overlap of communication and computation, and optimization of computing kernels for multi-core CPUs. The computing power enabled us to study ITER relevant issues such as the plasma size scaling of turbulent transport. Towards the next generation burning plasma turbulence simulations, the physics model is extended including kinetic electrons and multi-species ions, and computing kernels are further optimized for the latest many-core architectures.
Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki*
Nuclear Fusion, 45(11), p.1264 - 1270, 2005/11
Times Cited Count：14 Percentile：43.63(Physics, Fluids & Plasmas)A gyrokinetic particle simulation is executed to clarify the effect of the electron inertia on the MHD phenomena in the reversed shear configuration (RSC) of a cylindrical tokamak plasma. It is found that the collisionless (kinetic) double tearing modes grow up at the Alfv
n time scale, and nonlinearly induce the internal collapse when the helical flux at the magnetic axis is less than that at the outer resonant surface. After the internal collapse, the secondary reconnection is induced by the current concentration due to the 
convective flow. It is also clarified that a nonlinear dynamics accompanied with the elementary processes caused by the flow can generate a new RSC with resonant surfaces. In the presence of the density gradient, after the full reconnection induced by the mode, the radial electric field is found to be generated due to the difference of the 
motion between ions and electrons. However, the intensity of the radial field is not so large as that induced by the collisionless kink mode.
Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki
Physics of Plasmas, 12(9), p.092505_1 - 092505_7, 2005/09
Times Cited Count：2 Percentile：6.86(Physics, Fluids & Plasmas)The behavior of the collisionless magnetohydrodynamics modes is investigated by the gyro-kinetic particle simulation in a cylindrical tokamak plasma in the parameter region where the effects of electron inertia and electron parallel compressibility are competitive for magnetic reconnection. Although the linear growth of the 
internal kink-tearing mode is dominated by the electron inertia, it is found that the growth rate can be nonlinearly accelerated due to the electron parallel compressibility proportional to the ion sound Larmor radius 
. It is also found that, as decreasing the electron skin depth 
, the maximum growth rate before the internal collapse saturates independently of the microscopic scales such as and . The acceleration of growth rate is also observed in the nonlinear phase of the double tearing mode.
simulations of microturbulenceIdomura, Yasuhiro
Purazuma, Kaku Yugo Gakkai-Shi, 81(8), p.581 - 592, 2005/08
A gyrokinetic particle simulation is a powerful tool in studying tokamak microturbulence. A method, which is a standard method in recent gyrokinetic particle simulations, dramatically improved an efficiency of a particle simulation by reducing a particle noise, and full torus turbulence simulations are enabled. In this paper, the method is reviewed, and issues in full torus gyrokinetic particle simulations are discussed.
Villard, L.*; Angelino, P.*; Bottino, A.*; Allfrey, S. J.*; Hatzky, R.*; Idomura, Yasuhiro; Sauter, O.*; Tran, T. M.*
Plasma Physics and Controlled Fusion, 46(12B), p.B51 - B62, 2004/12
Times Cited Count：29 Percentile：67.01(Physics, Fluids & Plasmas)This paper reviews the present status of recent first principles based plasma turbulence simulations, and gives quantitative discussions on influences of the v// nonlinearlity and the geometry effects in the gyrokinetic Poisson equaiton, which are ignored in the conventional approximations, on simulations results. Careful treatments of these effects enable turbulence simulations satisfying the conservation of the energy and the particle number. The new simulation disclosed new phenomena, and it is found that (1) turbulence spreading is induced by avalanche like phnemena consisting of bursty heat transport and local flattening of pressure profiles, and (2) nonlinearly driven E
B flows become global shear flows with scale lengths of about 30 ion gyro radii.
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
Journal of Plasma and Fusion Research SERIES, Vol.6, p.17 - 72, 2004/00
A global gyrokinetic toroidal particle code for a 3D nonlinear simulation (GT3D) has been developed for a comprehensive study of the ion and electron anomalous transport arising from the ion temperature gradient driven - trapped electron mode (ITG-TEM) turbulence in tokamak plasmas. In the preliminary linear ITG-TEM calculations, basic properties of ITG-TEM modes are confirmed. Adding trapped electrons not only increases the growth rate of the ITG mode, but also produces another unstable electron mode, the TEM mode, which is unstable even at 
. The dominant mode changes from the ITG mode to the TEM mode depending on 
and 
. In linear benchmark calculations using Cyclone base case parameters, eigenfrequencies obtained from GT3D, GTC(PPPL-UCI) and FULL(PPPL) show reasonable quantitative agreement.
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
Nuclear Fusion, 43(4), p.234 - 243, 2003/04
Times Cited Count：119 Percentile：94.91(Physics, Fluids & Plasmas)no abstracts in English
Tokuda, Shinji; Naito, Hiroshi*; W.W.Lee*
Purazuma, Kaku Yugo Gakkai-Shi, 74(1), p.44 - 53, 1998/01
no abstracts in English
Kawai, Chika; Idomura, Yasuhiro; Maeyama, Shinya; Ogawa, Yuichi*
no journal, ,
In estimating confinement properties of fusion plasmas, it is a critical issue to understand structures of turbulent spectra, leading to turbulent transport. In this study, self-organization processes, which produce zonal flows from electron turbulence, are analyzed in detail via a highly accurate gyrokinetic Eulerian code, and structures of turbulent spectra leading to zonal flow generation are clarified.
Matsuoka, Seikichi*; Idomura, Yasuhiro; Satake, Shinsuke*
no journal, ,
When non-axisymmetric magnetic perturbations are imposed in axisymmetric tokamaks, broken axisymmetry induces the neoclassical viscosity, and affects momentum transport and resulting plasma rotation profiles. In this work, we estimate the neoclassical toroidal viscosity using full-f gyrokinetic simulations, and verify calculation methods and obtained results. We discuss the parameter dependency of the neoclassical toroidal viscosity in the presence of small resonant magnetic perturbations, based on comparisons against analytic theories and neoclassical transport codes.
Idomura, Yasuhiro
no journal, ,
Full-f gyrokinetic simulations are important tools for estimating confinement properties of fusion plasmas. On Peta-scale machines, capabilities of full-f gyrokinetic simulations have been significantly expanded, and the understanding of ITER-relevant issues such as the plasma size scaling of turbulent transport has been dramatically advanced. On the next generation Exa-scale machines, it is expected that core operation scenario of ITER will be optimized by full-f gyrokinetic simulations of turbulent burning plasmas. In this talk, we discuss physical and computational challenges towards such burning plasma simulations.
Idomura, Yasuhiro
no journal, ,
In this talk, main results from the 4th cycle IFERC-CSC project GT5DISO2 are reviewed. In the 3rd cycle project, it was found that simulations including electron turbulence are needed to reproduce the hydrogen isotope effect. To resolve this issue, in the 4th cycle project, a new kinetic electron model is developed in the plasma turbulence code GT5D, and its accuracy is verified through benchmark calculations of collisional transport phenomena and linear stability analyzes of micro-instabilities. Ion temperature gradient driven turbulence simulations including the new electron model are performed, and a new turbulence saturation mechanism due to kinetic electrons responses is found.
Idomura, Yasuhiro
no journal, ,
Reversal or change of plasma rotation is one of outstanding issues in recent momentum transport tokamak experiments. We address this issue based on numerical experiments using a Gyrokinetic Toroidal 5D full-f Eulerian code GT5D, in which detailed mechanisms of momentum transport and the resulting plasma rotation can be analysed from direct observation of the toroidal angular momentum conservation. In many tokamaks, rotation changes are commonly observed by applying electron cyclotron resonance heating without momentum input. The rotation changes induced by electron heating is reproduced for the first time by the numerical experiment, and it is found that a change of turbulent momentum transport between ion turbulence to electron turbulence plays a critical role.
Idomura, Yasuhiro; Asahi, Yuichi*; Hayashi, Nobuhiko*; Urano, Hajime*
no journal, ,
Full-f gyrokinetic simulations are important tools for analyzing nonlocal turbulent transport, plasma profiles, and the confinement time in fusion plasmas. However, the conventional full-f simulations were limited to ion turbulence with adiabatic electrons. In order to analyze ITER relevant electron turbulence, in this work, we develop a new hybrid electron model for full-f simulations, and verify its accuracy. In the model, passing electrons responses, which induce high frequency noises, are approximated by analytic solutions, and long time scale full-f simulations are enabled by eliminating the high frequency noises. Numerical experiments of electron turbulence using this model clarify new mechanisms for turbulence suppression and momentum transport related to electron turbulence transport. In a validation study, an experimental observation on plasma rotation changes induced by electron heating is successfully reproduced.
Idomura, Yasuhiro
no journal, ,
Turbulent momentum transport, which is considered to dictate plasma rotation in ITER, is one of critical issues in the International Tokamak Physics Activity. In particular, in recent years, plasma rotation changes induced by electron cyclotron heating, which does not have momentum input, have attracted attention as a phenomenon, which indicates transition of turbulent momentum transport. However, its physical mechanism has been open. In this work, we successfully reproduced this phenomena in numerical experiments using a Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. Based on a direct observation of the toroidal angular momentum conservation, it is found that turbulent momentum transport is changed by a transition of dominant turbulence from ion turbulence to electron turbulence induced by electron heating.
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. The main computing part of GT5D is given by Krylov based sparse matrix solvers for a semi-implicit time integration. We have ported computing kernels of these solvers on a prototype machine of FUGAKU and on V100 GPU, and confirmed that almost ideal performance gains are achieved on these state-of-the-art many core and GPU architectures.
Idomura, Yasuhiro; Ali, Y.*; Ina, Takuya*; Imamura, Toshiyuki*
no journal, ,
Implicit finite difference solvers based on Krylov subspace methods occupy dominant computing costs in the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. Under the post-K project, advanced communication avoiding (CA) Krylov subspace methods have been developed for exascale computing platforms, which have limited inter-node communication performance compared with accelerated computation. In this work, we develop a new mixed precision CA-GMRES solver using a FP16 preconditioner, which dramatically reduces the number of iterations, and thus, halo data communications. We port the new solver on FUGAKU and Summit, and compare its performance against conventional solvers on existing muti/many-core processors.
