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Journal Articles

Compressing the time series of five dimensional distribution function data from gyrokinetic simulation using principal component analysis

Asahi, Yuichi; Fujii, Keisuke*; Heim, D. M.*; Maeyama, Shinya*; Garbet, X.*; Grandgirard, V.*; Sarazin, Y.*; Dif-Pradalier, G.*; Idomura, Yasuhiro; Yagi, Masatoshi*

Physics of Plasmas, 28(1), p.012304_1 - 012304_21, 2021/01

This article demonstrates a data compression technique for the time series of five dimensional distribution function data based on Principal Component Analysis (PCA). Phase space bases and corresponding coefficients are constructed by PCA in order to reduce the data size and the dimensionality. It is shown that about 83% of the variance of the original five dimensional distribution can be expressed with 64 components. This leads to the compression of the degrees of freedom from $$1.3times 10^{12}$$ to $$1.4times 10^{9}$$. One of the important findings - resulting from the detailed analysis of the contribution of each principal component to the energy flux - deals with avalanche events, which are found to be mostly driven by coherent structures in the phase space, indicating the key role of resonant particles.

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:3 Percentile:40.69(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:7 Percentile:74.25(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:3 Percentile:23.72(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:4 Percentile:50.79(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:8 Percentile:38.12(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:29 Percentile:76.96(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:17 Percentile:59.53(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:221 Percentile:74.19(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:37 Percentile:82.41(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:259 Percentile:76.74(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:83 Percentile:92.45(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, , 

31 (Records 1-20 displayed on this page)