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Idomura, Yasuhiro
Europhysics Conference Abstracts (Internet), 45A, 4 Pages, 2021/06
This work presents the impacts of the hydrogen isotope mass and the normalized plasma size on confinement of hydrogen (H) and deuterium (D) plasmas dominated by ion temperature gradient driven turbulence. Numerical experiments of H and D plasmas with ion and electron heating conditions were conducted using the Gyrokinetic Toroidal 5D full- f Eulerian code GT5D. The energy confinement time in the ion heated numerical experiments was almost independent of isotope mass, and the energy confinement was determined mainly by the normalized plasma size or the plasma size divided by the ion gyro radius, indicating an impact of non-local transport. On the other hand, the electron heated numerical experiments showed a clear isotope mass dependency. In addition to the plasma size effect, the isotope mass dependency of the collisional energy transfer from electrons to ions changes the ion heat flux and the turbulence intensity, leading to the degradation of confinement in H plasmas. These results qualitatively agree with the hydrogen isotope scaling in experiments.
Idomura, Yasuhiro; Ina, Takuya*; Ali, Y.*; Imamura, Toshiyuki*
Proceedings of International Conference for High Performance Computing, Networking, Storage, and Analysis (SC 2020) (Internet), p.1318 - 1330, 2020/11
Times Cited Count：1 Percentile：36.4(Computer Science, Information Systems)The multi-scale full-
simulation of the next generation experimental fusion reactor ITER based on a five dimensional (5D) gyrokinetic model is one of the most computationally demanding problems in fusion science. In this work, a Gyrokinetic Toroidal 5D Eulerian code (GT5D) is accelerated by a new mixed-precision communication-avoiding (CA) Krylov method. The bottleneck of global collective communication on accelerated computing platforms is resolved using a CA Krylov method. In addition, a new FP16 preconditioner, which is designed using the new support for FP16 SIMD operations on A64FX, reduces both the number of iterations (halo data communication) and the computational cost. The performance of the proposed method for ITER size simulations with 0.1 trillion grids on 1,440 CPUs/GPUs on Fugaku and Summit shows 2.8x and 1.9x speedups respectively from the conventional non-CA Krylov method, and excellent strong scaling is obtained up to 5,760 CPUs/GPUs.
Asahi, Yuichi*; Grandgirard, V.*; Sarazin, Y.*; Donnel, P.*; Garbet, X.*; Idomura, Yasuhiro; Dif-Pradalier, G.*; Latu, G.*
Plasma Physics and Controlled Fusion, 61(6), p.065015_1 - 065015_15, 2019/05
Times Cited Count：4 Percentile：26.6(Physics, Fluids & Plasmas)The role of poloidal convective cells on transport processes is studied with the full-F gyrokinetic code GYSELA. For this purpose, we apply a numerical filter to convective cells and compare the simulation results with and without the filter. The energy flux driven by the magnetic drifts turns out to be reduced by a factor of about 2 once the numerical filter is applied. A careful analysis reveals that the frequency spectrum of the convective cells is well-correlated with that of the turbulent Reynolds stress tensor, giving credit to their turbulence-driven origin. The impact of convective cells can be interpreted as a synergy between turbulence and neoclassical dynamics.
Asahi, Yuichi*; Latu, G.*; Ina, Takuya; Idomura, Yasuhiro; Grandgirard, V.*; Garbet, X.*
IEEE Transactions on Parallel and Distributed Systems, 28(7), p.1974 - 1988, 2017/07
Times Cited Count：7 Percentile：55.15(Computer Science, Theory & Methods)High-dimensional stencil computation from fusion plasma turbulence codes involving complex memory access patterns, the indirect memory access in a Semi-Lagrangian scheme and the strided memory access in a Finite-Difference scheme, are optimized on accelerators such as GPGPUs and Xeon Phi coprocessors. On both devices, the Array of Structure of Array (AoSoA) data layout is preferable for contiguous memory accesses. It is shown that the effective local cache usage by improving spatial and temporal data locality is critical on Xeon Phi. On GPGPU, the texture memory usage improves the performance of the indirect memory accesses in the Semi-Lagrangian scheme. Thanks to these optimizations, the fusion kernels on accelerators become 1.4x - 8.1x faster than those on Sandy Bridge (CPU).
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
Nuclear Fusion, 45(12), p.1571 - 1581, 2005/12
Times Cited Count：39 Percentile：74.86(Physics, Fluids & Plasmas)Using a global gyrokinetic toroidal particle code, the toroidal electron temperature gradient driven (ETG) turbulence is studied in positive and reversed shear tokamaks. In the nolinear turbulent state, the ETG turbulence in the positive and reversed shear configurations show quite different structure formations. In the positive shear configuration, the ETG turbulence is dominated by streamers which have a ballooning type structure, and the electron temperature 
profile is quickly relaxed to the marginally stable state in a turbulent time scale. In the reversed shear configuration, quasi-steady zonal flows are produced in the regative shear region, while the positive shear region is characterized by streamers. Accordingly, the electron thermal diffusivity 
has a gap structure across the 
surface, and the gradinet is sustained above the marginal value for a long time in the quasi-steady phase. The results suggest a stiffness of the profile in positive shear tokamaks, and a possibility of the Te transport barrier in reversed shear tokamaks.
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.
Bottino, A.*; Angelino, P.*; Allfrey, S. J.*; Brunner, S.*; Hatzky, R.*; Idomura, Yasuhiro; Jolliet, S.*; Sauter, O.*; Tran, T. M.*; Villard, L.*
Theory of Fusion Plasmas, ISPP21, p.75 - 86, 2004/00
The global nonlinear electrostatic PIC code ORB5 solves the gyrokinetic Vlasov-Poisson system assuming adiabatic electrons in realistic tokamak magnetohydrodynamic (MHD) equilibria. The present version of ORB5 shows remarkable particle and energy conservation properties and can be used for physics studies in toroidal geometry. In particular, the optimized tracer loading method has been adapted to tokamak geometry and implemented in ORB5 together with a new adaptive gyro-average algorithm. Basic physical conservation properties (energy and particle number) are used as indicators of the quality of the numerical simulations. In this paper we present the first nonlinear results of electrostatic collisionless microinstabilities of realistic MHD shaped equilibria, provided by the MHD equilibrium code CHEASE, including the toroidicity induced geometrical coupling of the zonal ExB flow and the parallel velocity nonlinearlity.
Jolliet, S.*; Angelino, P.*; Bottino, A.*; Idomura, Yasuhiro; Villard, L.*
Theory of Fusion Plasmas, ISPP21, p.345 - 351, 2004/00
Global particle-in-cell (PIC) simulations are a very useful tool for studying the time evolution of turbulence induced by ion-temperature-gradient (ITG) instabilities. Unfortunately, the linear code LORB5 and its non-linear version ORB5 require high computational power. In order to study more sophisticated models, we need to optimize these codes. We will focus on LORB5, which uses a cylindrical grid (r,z) for solving the Vlasov equation and a (s,
) grid for the Poisson equation. The approach presented in this work consists of implementing the gyrokinetic model using a single (s,
) grid. Here is the straight-field-line poloidal coordinate. A method to avoid the singularity at the magnetic axis is presented, and a benchmark with the CYCLONE case is shown.
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
Nuclear Fusion, 43(4), p.234 - 243, 2003/04
Times Cited Count：119 Percentile：94.96(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
Idomura, Yasuhiro
no journal, ,
Gyrokinetics gives first principles based descriptions of multi-scale phenomena in fusion plasmas ranging from micro-scale plasma turbulence to macro-scale plasma profiles. The development of supercomputers enabled full-f gyrokinetic simulations, which directly compute the multi-scale problem, which conventional 
f simulation realized low cost simulations by avoiding the multi-scale problem under scale separation between them. Moreover, recent development of a kinetic electron model enabled more realistic numerical experiments including electron turbulence, and experimental observations, in which electron turbulence plays a critical role, have been analyzed. In this invited talk, the progress of full-f gyrokinetic simulations leading to the latest electron turbulence simulation is reviewed.
Idomura, Yasuhiro; Matsuoka, Seikichi; Ina, Takuya; Garbet, X.*; Brunner, S.*; Villard, L.*; Kawai, Chika*
no journal, ,
This talk reviews outcomes from GT5DISO projects, which was conducted for FY2014-2016. In this project, isotope effects on turbulent transport have been studied using the gyrokinetic toroidal five dimensional full-f Eulerian code GT5D. In FY2014, it was shown that the ion temperature gradient driven (ITG) turbulence with adiabatic electrons does not show isotope effects, and the trapped electron mode (TEM) driven by kinetic trapped electrons is essential for this issue. In FY2015, a new hybrid kinetic electron model was developed in GT5D, and its verification tests for ITG-TEM turbulence simulations were conducted. In FY2016, the kinetic electron model was validated against electron heating modulation experiments, in which the TEM turbulence plays key roles in particle and momentum transport. Finally, we performed isotope scan of ITG-TEM turbulence simulations, which tend to indicate difference of confinement between hydrogen and deuterium plasmas.
Asahi, Yuichi*; Grandgirard, V.*; Idomura, Yasuhiro; Sarazin, Y.*; Latu, G.*; Garbet, X.*
no journal, ,
This talk reviews outcomes from BMTFF projects, which was conducted for FY2015-2016. In this project, in order to establish a firm basis of full-f gyrokinetic models, two major full-f gyrokinetic codes in EU and Japan, GYSELA and GT5D, were benchmarked. In FY2015, all the numerical implementations were examined, and boundary conditions were fixed to be the same. With this correction, collisional transport, linear zonal flow damping, and linear stability of the ion temperature gradient driven (ITG) mode were successfully benchmarked. In FY2016, the same source and sink models were implemented in both codes, and nonlinear turbulence simulations were benchmarked. Decaying ITG turbulence simulations without heat sources showed similar profile relaxation processes, and nonlinear critical temperature gradients agreed quantitatively with each other. On the other hand, driven ITG turbulence simulations with heat sources showed intermittent bursts of avalanche like transport, which indicate similar 1/f type frequency spectra.
Idomura, Yasuhiro
no journal, ,
This talk reviews the development of the gyrokinetic toroidal five dimensional full-f Eulerian code GT5D, and its application to plasma turbulence research, which have been conducted on the Helios supercomputer and the K-computer during the IFERC-CSC project. In the former half period, computing techniques were developed towards larger scale ion temperature gradient driven turbulence simulations, and strong scaling over the full system of the K-computer was achieved by advanced communication overlap techniques. In the latter half period, a new kinetic electron model was developed towards trapped electron mode turbulence simulations, and a mechanism of momentum transport in electron heating modulation experiments was clarified.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The use of tungsten in plasma facing components inevitably leads to the pollution of the fusion plasma by heavy impurities and their accumulation at the core. Although heavy impurity transport has been estimated by the neoclassical transport theory, recent studies exhibited differences between global gyrokinetic simulations and the Hirshman-Sigmar (HS) moment approach, a commonly employed local theory. We performed a thorough benchmark for neoclassical particle transport of various impurities using the newly upgraded multi-species linear Fokker-Plank collision operator of our gyrokinetic full-f Eulerian simulation code GT5D. While good agreement was obtained in the case of flat temperature profiles, the dependence on the temperature gradient was found to be much weaker than the H-S theory in small machine sizes. Good agreement between GT5D and the H-S theory was recovered only for the case of large machine sizes, similar to ITER but beyond that of most current fusion devices.
Obrejan, K.; Idomura, Yasuhiro; Honda, Mitsuru*
no journal, ,
The use of tungsten in plasma facing components inevitably leads to the pollution of the fusion plasma by heavy impurities and their accumulation at the core, and this phenomenon is not yet fully understood. In this study, we performed a thorough comparison of the impurity particle fluxes between the global gyrokinetic full-f Eulerian code GT5D and local collisional transport theory called as the Hirshman-Sigmar moment approach. It is found that the simulation and the theory agree only in flat temperature profile cases or in large device sizes comparable to ITER. The cause of their discrepancy at the current device sizes is investigated in detail by comparing flows, which drive collisional impurity transport.
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
no journal, ,
The Gyrokinetic Toroidal 5D full-f Eulerian code GT5D is based on a semi-implicit finite difference scheme, in which a stiff linear 4D convection operator is subject to implicit time integration, and the implicit finite difference solver for fast kinetic electrons occupies more than 80% of the total computing cost. The implicit solver was originally developed using a Krylov subspace method, in which global collective communications and halo data communications were becoming bottlenecks on the latest accelerator based platforms. To resolve this issue, the convergence property is improved by using a new FP16 preconditioner, and an order of magnitude reduction of the number of iterations and thus, communications was achieved. A communication-avoiding (CA) solver based on the FP16 preconditioner was developed by utilizing the new support for FP16 SIMD operations on FUGAKU, and was ported also on Summit. The new CA solver showed significant speedups both on FUGAKU and SUMMIT, and its performance portability was demonstrated.
Watanabe, Tomohiko*; Idomura, Yasuhiro; Todo, Yasushi*; Honda, Mitsuru*
no journal, ,
During the initial start-up phase of the supercomputer Fugaku, we have launched a simulation project to explore physics of burning plasma confinement, that is, turbulent transport of particles, momentum, energy, impurity ions and hydrogen isotopes, and confinement of energetic particles, in collaboration with data science approaches. In prior to the project, we have upgraded and optimized three major fusion plasma simulation codes, GKV, GT5D and MEGA, which solve the kinetic plasma dynamics on multi-dimensional phase space, achieving the high computational performance on Fugaku. The flux tube gyrokinetic code, GKV, is applied to simulations of the multi-scale turbulence in multiple ion species plasma and the turbulent transport of heavy impurity ions. The global full-f gyrokinetic code, GT5D, is employed to explore non-local turbulent transport and intrinsic plasma rotation. The kinetic-MHD hybrid code, MEGA, is used for studying confinement of energetic ions, and has also been extended to introduce kinetic dynamics of bulk ions. In the project, data science approaches are also promoted to improve transport modeling and efficiency of the simulation research.
Idomura, Yasuhiro; Dif-Pradalier, G.*; Garbet, X.*; Sarazin, Y.*; Tore Supra Teams*
no journal, ,
LOC-SOC (linear and saturated ohmic confinement) transition phenomena in ohmic plasmas on ToreSupra tokamak were analyzed using full-f gyrokinetic simulations on Fugaku, and transition from trapped electron mode turbulence to ion temperature gradient driven turbulence was confirmed between LOC phase (low density, high Zeff) and SOC phase (high density, low Zeff). Numerical experiments qualitatively recovered experimental observations such as changes in energy confinement times and intrinsic rotation profiles, and exhaust of carbon impurity ions.
