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Journal Articles

Synergy of turbulent and neoclassical transport through poloidal convective cells

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:27.54(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.

Journal Articles

Turbulent generation of poloidal asymmetries of the electric potential in a tokamak

Donnel, P.*; Garbet, X.*; Sarazin, Y.*; Asahi, Yuichi; Wilczynski, F.*; Caschera, E.*; Dif-Pradalier, G.*; Ghendrih, P.*; Gillot, C.*

Plasma Physics and Controlled Fusion, 61(1), p.014003_1 - 014003_11, 2019/01

 Times Cited Count:12 Percentile:68.03(Physics, Fluids & Plasmas)

Poloidal asymmetries of the $$E times B$$ plasma flow are known to play a role in neoclassical transport. According to conventional neoclassical theory, the level of poloidal asymmetry of the electric potential is expected to be very small. In the present work, a general framework for the generation of axisymmetric structures of potential by turbulence is presented. Zonal flows, geodesic acoustic modes and convective cells are described by a single model. This is done by solving the gyrokinetic equation coupled to the quasi-neutrality equation. This calculation provides a predictive calculation of the frequency spectrum of flows given a specified forcing due to turbulence. It also shows that the dominant mechanism comes from zonal flow compression at intermediate frequencies, while ballooning of the turbulence Reynolds stress appears to be the main drive at low frequency.

Journal Articles

Benchmarking of flux-driven full-F gyrokinetic simulations

Asahi, Yuichi*; Grandgirard, V.*; Idomura, Yasuhiro; Garbet, X.*; Latu, G.*; Sarazin, Y.*; Dif-Pradalier, G.*; Donnel, P.*; Ehrlacher, C.*

Physics of Plasmas, 24(10), p.102515_1 - 102515_17, 2017/10

AA2017-0418.pdf:4.26MB

 Times Cited Count:7 Percentile:37.85(Physics, Fluids & Plasmas)

Two full-F global gyrokinetic codes are benchmarked to compute flux-driven ion temperature gradient turbulence in tokamak plasmas. For this purpose, the Semi-Lagrangian code GYSELA and the Eulerian code GT5D are employed, which solve the full-F gyrokinetic equation with a realistic fixed flux condition. Using the appropriate settings for the boundary and initial conditions, flux-driven ITG turbulence simulations are carried out. The avalanche-like transport is assessed with a focus on spatio-temporal properties. A statistical analysis is performed to discuss this self-organized criticality (SOC) like behaviors, where we found $$1/f$$ spectra and a transition to $$1/f^3$$ spectra at high-frequency side in both codes. Based on these benchmarks, it is verified that the SOC-like behavior is robust and not dependent on numerics.

Oral presentation

Benchmarking of global full-f gyrokinetic codes

Asahi, Yuichi*; Garbet, X.*; Idomura, Yasuhiro; Grandgirard, V.*; Latu, G.*; Sarazin, Y.*; Dif-Pradalier, G.*; Donnel, P.*; Ehrlacher, C.*; Passeron, Ch.*

no journal, , 

Two global full-f gyrokinetic codes, which have been developed at CEA and JAEA, are benchmarked. Quantitative agreements between two codes are obtained regarding linear processes such as the linear stability of ion temperature gradient driven modes, the linear damping of zonal flows, and the collisional transport. Preliminary benchmarks on nonlinear turbulence simulations show some differences of calculation results, which arise due to differences in calculation models such as boundary conditions and heat source models, and the remaining issues towards quantitative nonlinear benchmarks are clarified.

Oral presentation

How to prepare the GYSELA-X code to future exascale edge-core simulations

Grandgirard, V.*; Asahi, Yuichi; Bigot, J.*; Bourne, E.*; Dif-Pradalier, G.*; Donnel, P.*; Garbet, X.*; Ghendrih, P.*

no journal, , 

Core transport modelling in tokamak plasmas has now reached maturity with non-linear 5D gyrokinetic codes in the world available to address this issue. However, despite numerous successes, their predictive capabilities are still challenged, especially for optimized discharges. Bridging this gap requires extending gyrokinetic modelling in the edge and close to the material boundaries, preferably addressing edge and core transport on an equal footing. This is one of the long term challenges for the petascale code GYSELA [V. Grandgirard et al., CPC 2017 (35)]. Edge-core turbulent plasma simulations with kinetic electrons will require exascale HPC capabilities. We present here the different strategies that we are currently exploring to target the disruptive use of billions of computing cores expected in exascale-class supercomputer as OpenMP4.5 tasks for overlapping computations and MPI communications, KOKKOS for performant portability programming and code refactoring.

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