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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

 Percentile:100

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

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

 Percentile:100(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.

Journal Articles

Optimization of fusion kernels on accelerators with indirect or strided memory access patterns

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).

Journal Articles

Core transport properties in JT-60U and JET identity plasmas

Litaudon, X.*; Sakamoto, Yoshiteru; de Vries, P. C.*; Salmi, A.*; Tala, T.*; Angioni, C.*; Benkadda, S.*; Beurskens, M. N. A.*; Bourdelle, C.*; Brix, M.*; et al.

Nuclear Fusion, 51(7), p.073020_1 - 073020_13, 2011/07

 Times Cited Count:7 Percentile:59.42(Physics, Fluids & Plasmas)

A variety of triggering mechanisms and structures of internal transport barrier (ITB) has been observed in various devices or depending on operation scenarios. Thus identity experiments on ITB in JT-60U and JET have been performed to shed light on the physics behind ITBs. Because of their similar size, the dimensionless parameters between both devices are the same. These experiments were performed with near identical magnetic configurations, heating waveforms and normalized quantities such as safety factor, magnetic shear, normalized Larmor radius, normalized collision frequency, beta, temperatures ratio. Similarities of the ITB triggering mechanism and the ITB strength have been observed when a proper match is achieved of the most relevant profiles of the normalized quantities. This paper will report on the detail comparison of transport properties of ITBs obtained in these JET/JT-60U identity experiments.

Journal Articles

Estimation of kinetic parameters based on chirping Alfv$'e$n Eigenmodes

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

Alfv$'e$n Eigenmodes (AEs) with frequency sweeping (chirping AEs) are analyzed based on the so-called Berk-Breizman (BB) model. Kinetic parameter regimes with chirping nonlinear solutions are delimited, and a new quasi-periodic chirping regime is found, where the quasi-period of chirping events depends on the linear growth rate. Fundamental kinetic parameters such as the linear drive and the external damping rate are estimated by fitting nonlinear chirping characteristics between the experiment and the BB model. This approach is applied to Toroidicity-induced AEs on JT-60U, which suggests the existence of modes far from marginal stability. Two collision models are considered, and it is shown that dynamical friction and velocity-space diffusion are essential to reproduce nonlinear features observed in experiments. The results are validated by recovering measured growth and decay of perturbation amplitude, and by estimating collision frequencies from experimental equilibrium data.

Journal Articles

Spectroscopic determination of kinetic parameters for frequency sweeping Alfv$'e$n eigenmodes

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*; JT-60 Team

Physics of Plasmas, 17(12), p.122311_1 - 122311_9, 2010/12

 Times Cited Count:25 Percentile:20.88(Physics, Fluids & Plasmas)

Journal Articles

Gyrokinetic simulations of turbulent transport; Size scaling and chaotic behaviour

Villard, L.*; Bottino, A.*; Brunner, S.*; Casati, A.*; Chowdhury, J.*; Dannert, T.*; Ganesh, R.*; Garbet, X.*; G$"o$rler, T.*; Grandgirard, V.*; et al.

Plasma Physics and Controlled Fusion, 52(12), p.124038_1 - 124038_18, 2010/11

 Times Cited Count:14 Percentile:40.39(Physics, Fluids & Plasmas)

Journal Articles

Gyrokinetic simulations of turbulent transport

Garbet, X.*; Idomura, Yasuhiro; Villard, L.*; Watanabe, Tomohiko*

Nuclear Fusion, 50(4), p.043002_1 - 043002_30, 2010/04

 Times Cited Count:173 Percentile:28.33(Physics, Fluids & Plasmas)

This overview is an assessment of the gyrokinetic framework and simulations to compute the turbulent transport in fusion plasmas. It covers an introduction to the gyrokinetic theory, the principal numerical techniques which are being used to solve the gyrokinetic equations, fundamentals in gyrokinetic turbulence and the main results which have been brought by simulations with regard to transport in fusion devices and actuation measurements.

Journal Articles

Fully nonlinear features of the energetic beam-driven instability

Lesur, M.*; Idomura, Yasuhiro; Garbet, X.*

Physics of Plasmas, 16(9), p.092305_1 - 092305_12, 2009/09

 Times Cited Count:33 Percentile:15.61(Physics, Fluids & Plasmas)

Journal Articles

Progress in the ITER physics basis, 2; Plasma confinement and transport

Doyle, E. J.*; Houlberg, W. A.*; Kamada, Yutaka; Mukhovatov, V.*; Osborne, T. H.*; Polevoi, A.*; Bateman, G.*; Connor, J. W.*; Cordey, J. G.*; Fujita, Takaaki; et al.

Nuclear Fusion, 47(6), p.S18 - S127, 2007/06

no abstracts in English

Journal Articles

A Review of internal transport barrier physics for steady-state operation of tokamaks

Connor, J. W.*; Fukuda, Takeshi*; Garbet, X.*; Gormezano, C.*; Mukhovatov, V.*; Wakatani, Masahiro*; ITB Database Group; ITPA Topical Group on Transport and Internal Barrier Physics*

Nuclear Fusion, 44(4), p.R1 - R49, 2004/04

 Times Cited Count:235 Percentile:23.26(Physics, Fluids & Plasmas)

This paper first reviews the present state of theoretical and experimental knowledge regarding the formation and characteristics of ITBs in tokamaks. Specifically, the current status of theoretical modeling of ITBs is presented; then, an international ITB database based on experimental information extracted from some nine tokamaks is described and used to draw some general conclusions concerning the necessary conditions for ITBs to appear, comparing these with the theoretical models. The experimental situation regarding the steady-state, or at least quasi-steady-state, operation of tokamaks is reviewed and finally the issues and prospects for achieving such operational modes in ITER are discussed.

Journal Articles

Edge localized mode physics and operational aspects in tokamaks

B$'e$coulet, M.*; Huysmans, G.*; Sarazin, Y.*; Garbet, X.*; Ghendrih, P.*; Rimini, F.*; Joffrin, E.*; Litaudon, X.*; Monier-Garbet, P.*; An$'e$, J.-M.*; et al.

Plasma Physics and Controlled Fusion, 45(12A), p.A93 - A113, 2003/12

 Times Cited Count:77 Percentile:6.88(Physics, Fluids & Plasmas)

no abstracts in English

Oral presentation

Nonlinear features of the energetic beam-driven instability

Lesur, M.*; Idomura, Yasuhiro; Garbet, X.*

no journal, , 

no abstracts in English

Oral presentation

Nonlinear features of the energy beam-driven instability

Lesur, M.*; Idomura, Yasuhiro; Garbet, X.*

no journal, , 

Oral presentation

The Energetic beam-driven instability, kinetic nonlinearities and subcritical instability in JT-60U

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

no journal, , 

Oral presentation

Reduced model analysis of chirping Alfv$'e$n eigenmodes; Application to MAST

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

no journal, , 

Oral presentation

Estimation of kinetic parameters based on chirping Alf$'v$en eigenmodes

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

no journal, , 

Oral presentation

Estimation of kinetic parameters based on chirping Alfven eigenmodes

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

no journal, , 

Oral presentation

Spectroscopic determination of kinetic parameters for frequency sweeping Alfv$'e$n eigenmodes

Lesur, M.*; Idomura, Yasuhiro; Shinohara, Koji; Garbet, X.*

no journal, , 

Oral presentation

Optimization of fusion plasma codes

Asahi, Yuichi; Latu, G.*; Ina, Takuya; Idomura, Yasuhiro; Virginie, G.*; Garbet, X.*

no journal, , 

We present the optimization of kernels from fusion plasma codes, GYSELA and GT5D, on Tera-flops many-core architecturesincluding accelerators (Xeon Phi, GPU), and a multi-core CPUs (FX100). GYSELA kernel is based on a semi-Lagrangian scheme with high arithmetic intensity. Through the optimization of GYSELA kernel on Xeon Phi, we show the importance of the vectorization on Xeon Phi. For GT5D kernel, which is based on a finite difference scheme, a sophisticated memory access is necessary for high performance. Through the optimization of GT5D kernel on GPUs, we show the effective optimization for memory access on GPUs.

26 (Records 1-20 displayed on this page)