Search Results: Records 1-11 displayed on this page of 11

- 1

Initialising ...

Initialising ...

Initialising ...

Initialising ...

Initialising ...

Initialising ...

Initialising ...

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

Percentile：100The 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：1 Percentile：60.51(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：31 Percentile：23.39(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.

Idomura, 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.

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：101 Percentile：4.26(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.