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Villard, L.*; Bottino, A.*; Brunner, S.*; Casati, A.*; Chowdhury, J.*; Dannert, T.*; Ganesh, R.*; Garbet, X.*; G
rler, T.*; Grandgirard, V.*; et al.
Plasma Physics and Controlled Fusion, 52(12), p.124038_1 - 124038_18, 2010/11
被引用回数：18 パーセンタイル：56.51(Physics, Fluids & Plasmas)This paper presents some of the main recent advances in gyrokinetic theory and computing of turbulence. A past controversy regarding the finite size (finite 
) effect in ITG turbulence has now been resolved. Now, both Eulerian and Lagrangian global codes are shown to agree and to converge to the flux-tube result in the 
0 limit. It is found, however, that an appropriate treatment of geometrical terms is necessary. Turbulent processes are characterized by a chaotic behavior, often accompanied by bursts and avalanches. Performing ensemble averages of statistically independent simulations, starting from different initial conditions, is presented as a way to assess the intrinsic variability of turbulent fluxes and obtain reliable estimates of the standard deviation.
McMillan, B. F.*; Lapillonne, X.*; Brunner, S.*; Villard, L.*; Jolliet, S.; Bottino, A.*; Grler, T.*; Jenko, F.*
Physical Review Letters, 105(15), p.155001_1 - 155001_4, 2010/10
被引用回数：100 パーセンタイル：93.39(Physics, Multidisciplinary)The scaling of turbulence-driven heat transport with system size in magnetically confined plasmas is re-examined using first-principles based numerical simulations. Two very different numerical methods are applied to this problem, in order to resolve a long-standing quantitative disagreement, which may have arisen due to inconsistencies in the geometrical approximation. System size effects are further explored by modifying the width of the strong gradient region at fixed system size. The finite width of the strong gradient region in gyroradius units, rather than the finite overall system size, is found to induce the diffusivity reduction seen in global gyrokinetic simulations.
Jolliet, S.*; Villard, L.*; 井戸村 泰宏; McMillan, B. F.*; Bottino, A.*; Lapillonne, X.*
no journal, ,
トカマクプラズマにおける電子乱流輸送の主要機構となっている捕捉電子駆動乱流のジャイロ運動論的PICシミュレーションを行い、従来のイオン温度勾配駆動乱流との比較からその輸送特性や帯状流の性質を議論した。
Jolliet, S.; McMillan, B. F.*; Bottino, A.*; Angelino, P.*; Lapillonne, X.*; Vernay, T.*; 井戸村 泰宏; Villard, L.*
no journal, ,
The global Particle-In-Cell ORB5 code [Jolliet, CPC, 2007] has been extended to include the kinetic response of trapped electrons. The gyrokinetic model is explained and a linear benchmark is presented. Nonlinear simulations show that, for the set of parameters considered, the influence of the zonal flows on Trapped-Electron-Mode turbulence is weak. These results are in agreement with previous results obtained with the flux-tube PIC code GEM [Lang, POP, 2008].
Vernay, T.*; Brunner, S.*; Villard, L.*; Jolliet, S.; McMillan, B. F.*; Lapillonne, X.*
no journal, ,
In this work, a Lorentz collision operator using a random walk over the pitch angle, as well as a full, linearized self-collision operator including a random walk in velocity space and a background reaction acting on the weights, are implemented in a simple 1D Particle-In-Cell (PIC) code simulating Langmuir waves with a 2 weights scheme. The crucial conservation properties of the discretized collision operators are explained. In a second step, the implementations of the 2 weights scheme and such operators in the global gyrokinetic PIC code ORB5 are presented. Some results concerning the effects of collisions on micro-instabilities and neoclassical transport are studied.
McMillan, B. F.*; Jolliet, S.; Tran, T. M.*; Bottino, A.*; Lapillonne, X.*; Villard, L.*
no journal, ,
In this work, the role of system size (rhostar scaling) and shear flow levels on ion temperature gradient (ITG) turbulence in gyrokinetic simulations is explored using the ORB5 code. Firstly, the scaling of heat flux level versus system size in plasmas with zero initial flow shear is reexamined. Secondly, the effect of poloidal shear flow on ITG turbulence is examined. Even at flow levels many times smaller than the supression threshold, nonlinear turbulence is only seen in the simulation if the initial perturbation is large: the system manifests subcritical turbulence. Inward or outward propagating avalanches and inward and outward shifted diffusivity profiles are seen according to the sign of the flow shear. In cases with strong flow shear almost all the flux is associated with avalanches, which propagate across the entire region with strong pressure gradient.
