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論文

Parallel filtering in global gyrokinetic simulations

Jolliet, S.; McMillan, B. F.*; Villard, L.*; Vernay, T.*; Angelino, P.*; Tran, T. M.*; Brunner, S.*; Bottino, A.*; 井戸村 泰宏

Journal of Computational Physics, 231(3), p.745 - 758, 2012/02

 被引用回数:13 パーセンタイル:61.19(Computer Science, Interdisciplinary Applications)

In this work, a Fourier solver is implemented in the global Eulerian gyrokinetic code GT5D and in the global Particle-In-Cell code ORB5 in order to reduce the memory of the matrix associated with the field equation. This scheme is verified with linear and nonlinear simulations of turbulence. It is demonstrated that the straight-field-line angle is the coordinate that optimizes the Fourier solver, that both linear and nonlinear turbulent states are unaffected by the parallel filtering, and that the $$k_parallel$$ spectrum is independent of plasma size at fixed normalized poloidal wave number.

論文

Transport and turbulence with innovative plasma shapes in the TCV tokamak

Labit, B.*; Pochelon, A.*; Rancic, M.*; Piras, F.*; Bencze, A.*; Bottino, A.*; Brunner, S.*; Camenen, Y.*; Chattopadhyay, P. K.*; Coda, S.*; et al.

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

We present recent results on turbulence measurements in TCV L-mode plasmas. The transport reduction at negative triangularity (compared to positive triangularity) is reflected in the reduction of the temperature fluctuation level, in the low frequency part of the spectrum (30-150 kHz), measured by correlation ECE in the outer equatorial plane. The TEM induced transport computed from nonlinear gyrokinetic simulations is shown to decrease with decreasing triangularity and increasing collisionality. First results of an experimental scenario to reach the H-mode regime at negative triangularity in TCV are presented. Then, we report on an innovative divertor magnetic configuration: the snowflake (SF) divertor as opposed to the classical single-null (SN) divertor. For ELMy SF plasmas, the strike-point properties (density, temperature, fluctuation level,...) are studied with Langmuir probes (LPs) and compared with those of a SN configuration obtained within the same discharge.

論文

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

 被引用回数:18 パーセンタイル:56.65(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 $$rho^*$$) 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 $$rho^*$$ $$rightarrow$$ 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.

論文

System size effects on gyrokinetic turbulence

McMillan, B. F.*; Lapillonne, X.*; Brunner, S.*; Villard, L.*; Jolliet, S.; Bottino, A.*; G$"o$rler, T.*; Jenko, F.*

Physical Review Letters, 105(15), p.155001_1 - 155001_4, 2010/10

 被引用回数:98 パーセンタイル:93.44(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.

論文

Global nonlinear electromagnetic simulations of tokamak turbulence

Bottino, A.*; Scott, B. D.*; Brunner, S.*; McMillan, B. F.*; Tran, T. M.*; Vernay, T.*; Villard, L.*; Jolliet, S.; Hatzky, R.*; Peeters, A. G.*

IEEE Transactions on Plasma Science, 38(9), p.2129 - 2135, 2010/09

 被引用回数:26 パーセンタイル:69.61(Physics, Fluids & Plasmas)

The particle-in-cell code ORB5 is a global gyrokinetic turbulence simulation code in tokamak geometry. It solves the gyrokinetic equation in the whole plasma core, including the magnetic axis. A field-aligned filtering procedure and sophisticated noise/control and heating operators allow for accurate simulations. Recently, the code ORB5 has been extended to include self-consistent perpendicular magnetic field perturbations. The inclusion of magnetic perturbations allows for a comprehensive study of finite $$beta$$ effects on microinstability. In this paper, we present the first linear and nonlinear code results concerning electromagnetic effects on tokamak microinstabilities.

論文

A Global collisionless PIC code in magnetic coordinates

Jolliet, S.*; Bottino, A.*; Angelino, P.*; Hatzky, R.*; Tran, T. M.*; McMillan, B. F.*; Sauter, O.*; Appert, K.*; 井戸村 泰宏; Villard, L.*

Computer Physics Communications, 177(5), p.409 - 425, 2007/09

 被引用回数:175 パーセンタイル:98.47(Computer Science, Interdisciplinary Applications)

グローバルプラズマ乱流シミュレーションコードORB5について報告する。コードの大きな特徴は、直線磁力線座標を用い磁力線に沿ったフーリエフィルターを適用することによる数値ノイズ低減や時間ステップ幅の伸長により、処理性能を大幅に向上させたことである。また、もう一つの特徴は任意の軸対称理想MHD平衡配位を取り扱えることである。帯状流の解析解、及び、ほかのコードとの線形及び非線形テストにおいてコードの妥当性を検証した。

口頭

Gyrokinetic PIC simulation of trapped electron mode turbulence

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。

口頭

Global nonlinear particle-in-cell simulations of trapped-electron-mode turbulence

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].

口頭

Collisions in global gyrokinetic particle-in-cell code ORB5

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.

口頭

System size and shear flow effects on ITG turbulence

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.

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