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Idomura, Yasuhiro
no journal, ,
The research plan and the current status of fusion plasma code development in the Post-K priority issue 6 "Development of Innovative Clean Energy" [Core Design of Fusion Reactor] are reviewed. This project develops first principles based plasma analysis codes on plasma turbulence phenomena and MHD phenomena, which are taken into account in the design of operation scenarios of fusion reactors. Because of the spatio-temporal scales in ITER core plasmas and the complexity of their physics models including multi-species ions and burning processes, these fusion plasma analysis codes require new simulation techniques. In this talk, we discuss the development of Exa-scale computating technologies such as many-core optimization, and new physics and numerical models to enable long time scale simulations.
Idomura, Yasuhiro
no journal, ,
A communication-avoiding generalized minimal residual (CA-GMRES) method is applied to the gyrokinetic toroidal five dimensional Eulerian code GT5D, and its performance is compared against the original code with a generalized conjugate residual (GCR) method on the Oakforest-PACS (KNL). The CA-GMRES method has less memory access and collective communications than the GCR method, and thus, is suitable for future Exa-scale architectures with limited memory and network bandwidths. It is shown that compared with the original GCR version, the CA-GMRES version is accelerated by 1.32x, and the cost of data reduction communication is reduced from ~13% to ~1% of the total cost at 1,280 nodes.
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
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, ,
A gyrokinetic toroidal 5D Eulerien code GT5D resolves global torus plasma using 5D grids, and core plasma simulations of ITER require exascale computing on Fugaku. To this end, we developed a new communication avoiding (CA) Krylov solver with FP16 preconditioning for implicit finite difference computation, which occupies more than 80% of the total computing cost in GT5D. In this solver, a bottleneck of global collective communication is resolved using a CA Krylov subspace method. In addition, halo communication is reduced by improving the convergence property with FP16 preconditioning. The FP16 preconditioner was designed based on physics properties of the operator, and was implemented using FP16 SIMD operations. Compared with the conventional solver, the new solver improved the performance of ITER size simulations with ~100 billion grids by ~3.5x, and a good strong scaling was achieved up to 5,760 nodes.
Idomura, Yasuhiro
no journal, ,
Thanks to new technologies such as KNL and MCDRAM, Oakforest-PACS (OfP) achieved significantly high computing power and memory bandwidths against the conventional multi-core platforms, and played an important role as a prototype of exascale supercomputers. We developed extreme scale nuclear CFD simulations on OfP, where an important issue was to resolve communication bottlenecks revealed by accelerated computation. This issue was resolved by developing communication-avoiding (CA) matrix solvers based on CA Krylov subspace methods and CA multigrid methods, and high performance CFD simulations were enabled by using the full system size on OfP. In this talk, we review CA matrix solvers developed for the five dimensional plasma simulation code GT5D and the three dimensional multi-phase multi-component thermal-hydraulic code JUPITER.