Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Watanabe, Tomohiko*; Idomura, Yasuhiro; Todo, Yasushi*; Honda, Mitsuru*
Nihon Genshiryoku Gakkai-Shi ATOMO
, 64(3), p.152 - 156, 2022/03
Understanding of physical processes of particle, momentum, and thermal transports is essential for predicting the confinement performance of burning plasmas in ITER, which is targeting the scientific demonstration of magnetic confinement fusion. First principles based simulations on Fugaku disclosed physical mechanisms such as complex transport processes of multi-scale turbulence in deuterium-tritium plasmas and kinetic effects in energetic particle transport due to electromagnetic fluctuations. We promote further research and development of first principles based simulations towards the performance prediction of burning plasmas.
Idomura, Yasuhiro; Ina, Takuya*; Ali, Y.*; Imamura, Toshiyuki*
Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.225 - 230, 2020/10
A new communication avoiding (CA) Krylov solver with a FP16 (half precision) preconditioner is developed for a semi-implicit finite difference solver in the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. In the solver, the bottleneck of global collective communication is resolved using a CA-Krylov subspace method, while the number of halo data communication is reduced by improving the convergence property using the FP16 preconditioner. The FP16 preconditioner is designed based on the physics properties of the operator and is implemented using the new support for FP16 SIMD operations on A64FX. The solver is ported on Fugaku (A64FX) and Summit (V100), which respectively show 
63x and 29x speedups in socket performance compared to the conventional non-CA Krylov solver on JAEA-ICEX (Haswell).
Idomura, Yasuhiro
no journal, ,
We review the development of global full-f gyrokinetic simulation GT5D and recent simulation studies on Fugaku. Towards exascale simulations on Fugaku, a new matrix solver was developed using half precision computation, which was newly supported on A64FX, and an implicit finite difference solver for kinetic electrons was accelerated by ~3.5x compared to the conventional solver. This enabled global turbulence simulations with kinetic electrons at the real mass ratio. By using this code, the linear and saturated ohmic confinement (LOC/SOC) transition in ohmic L-mode discharges on the Tore Supra device was analyzed. The simulation reproduced the exhaust of carbon impurity ions, the change of intrinsic plasma rotation, and the change of energy confinement time, which are observed during the LOC/SOC transition, and their physical mechanisms were clarified.
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.
