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論文

Progress of full-f gyrokinetic simulation toward reactor relevant numerical experiments

井戸村 泰宏; 仲田 資季; Jolliet, S.*

Plasma and Fusion Research (Internet), 9(Sp.2), p.3503028_1 - 3503028_7, 2014/04

Full-fジャイロ運動論シミュレーションは乱流輸送と分布形成の両方を実験と同様の一定の加熱、運動量、および、粒子入力条件のもとで計算する。シミュレーションの時間スケールがエネルギー、運動量、および、粒子のバランス条件を成立するのに十分長ければ、この手法はプラズマ分布を決定することができる。近年のペタスケール計算機によってそのような長時間スケールシミュレーションが可能となり、full-fジャイロ運動論シミュレーションが核融合炉の数値実験に適用されるようになった。本論文ではジャイロ運動論的full-fオイラーコードGT5Dの物理モデル、数値手法、および、精度検証についてまとめ、さらに乱流輸送のプラズマサイズおよび加熱パワーに関する輸送スケーリング研究に関する最近の応用事例を概説する。

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:11 パーセンタイル:60.56(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

Plasma size scaling of avalanche-like heat transport in tokamaks

Jolliet, S.; 井戸村 泰宏

Nuclear Fusion, 52(2), p.023026_1 - 023026_14, 2012/02

The influence of plasma size on global Ion Temperature Gradient turbulence is studied with the full-$$f$$ Eulerian code GT5D. Plasma sizes from $$rho^*=1/100$$ to $$rho^*=1/225$$ are studied by scaling the minor radius $$a$$ and the input power. For the first time, worse-than-Bohm scaling is observed in experimentally realistic conditions. Global effects are investigated by looking at the force balance relation and the avalanches dynamics. It is found that the parallel momentum and radial electric field profiles are coupled. A low shearing rate region is induced in the large plasma size simulation and enhances heat transport. In this region, the dynamics of avalanches is altered. GT5D simulations therefore highlight avalanches as a non-local mechanism for broken gyro-Bohm scaling and point out the importance of the yet unknown plasma size effects on momentum transport.

論文

Performance evaluations of gyrokinetic Eulerian code GT5D on massively parallel multi-core platforms

井戸村 泰宏; Jolliet, S.*

Proceedings of International Conference for High Performance Computing, Networking, Storage and Analysis (SC '11) (USB Flash Drive), 9 Pages, 2011/11

核融合プラズマの第一原理モデルである5次元ジャイロ運動論方程式に基づくプラズマ乱流シミュレーションは乱流輸送現象を評価する標準的手法となっているが、ITER装置規模の5次元乱流計算は膨大な計算となるため、超並列計算機の効率的利用が核融合分野の計算科学における重要課題となっている。原子力機構で開発した5次元格子コードGT5Dでは方程式系の物理的特性や対称性に基づいて5次元空間の階層的な多次元領域分割を行う。これを複数のMPIコミュニケータとSMPを組合せた階層的通信構造によって実装することにより高いスケーラビリティを実現し、BX900システム16384コアを用いて実効性能19.4TFlopsを達成した。

論文

Simulating plasma turbulence with the global Eulerian gyrokinetic code GT5D

Jolliet, S.; 井戸村 泰宏

Progress in Nuclear Science and Technology (Internet), 2, p.85 - 89, 2011/10

In this talk, the numerical implementation of the global Eulerian gyrokinetic code GT5D will be presented. GT5D solves the vlasov-maxwell system (including coulomb collisions and a heat source and sink operator) in 5D, which requires huge CPU ressources. In particular, the implementation of a straight-field-line solver, reducing the memory of the field equation matrix by orders of magnitude, will be detailed. This scheme takes advantage of the alignment of the turbulence with the magnetic field lines to suppress small parallel wavelengths with a fourier filter. In addition, weak and strong scalings, as well as a plasma size scaling will be presented.

論文

Performance evaluations of advanced massively parallel platforms based on gyrokinetic toroidal five-dimensional eulerian code GT5D

井戸村 泰宏; Jolliet, S.

Progress in Nuclear Science and Technology (Internet), 2, p.620 - 627, 2011/10

A fusion plasma is an extremely complex physical system consisting of multiple fluids (an electron fluid and other ion fluids) coupled through electromagnetic fields and weak coulomb collisions. Because of its complexities, a direct numerical simulation (DNS) is becoming important not only as a complementary approach to obtain physical understanding but also as an essential tool for predicting turbulent transport in the experiment. In the presentation, an introductive review of simulation models and numerical approaches are given, and a progress in turbulent fusion plasma simulations is presented based on recent verification and validation studies.

論文

Consequences of profile shearing on toroidal momentum transport

Camenen, Y.*; 井戸村 泰宏; Jolliet, S.; Peeters, A. G.*

Nuclear Fusion, 51(7), p.073039_1 - 073039_11, 2011/07

 被引用回数:80 パーセンタイル:96.91(Physics, Fluids & Plasmas)

Turbulent transport of toroidal momentum is investigated in global linear gyrokinetic simulations. The poloidal tilt of the global mode structure arising from the radial variation of the equilibrium (profile shearing) is shown to induce non-diagonal non-pinch momentum transport (residual stress). Local simulations performed at finite radial wave vector show that the effect is mainly due to the antisymmetric radial component of the magnetic drift. The residual stress resulting from profile shearing enhances co-current rotation for ion temperature gradient turbulence and counter-current rotation for trapped electron mode turbulence (for positive magnetic shear).

論文

Impact of toroidal rotation and safety factor on ion turbulent transport in tokamaks

井戸村 泰宏; Jolliet, S.; 吉田 麻衣子; 浦野 創

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

大域的ジャイロ運動論的トロイダル5次元オイラーコードGT5Dを用いてイオン温度勾配駆動(ITG)乱流におけるトロイダル回転と安全係数qの影響を調べた。回転スキャン数値実験ではトロイダル回転に依存して径電場Erが変化する。Er分布によって局所的な輸送レベルは影響を受けるが、そのシア率が平均的に同程度であれば大域的な輸送特性は変化しない。qスキャン数値実験では大きなqにおいて乱流輸送が大きく増大する。ここで、qが大きいとErシアによる線形ITGモードの安定化効果が弱まることがわかった。イオン熱輸送と非拡散的な運動量輸送の両方が増大する。前者によりイオン温度勾配が低下するのに対し、後者はより大きな内側への運動量束、および、プラズマ炉心の電流方向の自発回転をもたらす。

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

Plasma size scaling of avalanche-like heat transport in tokamaks

Jolliet, S.*; 井戸村 泰宏

Nuclear Fusion, 52(2), p.023026_1 - 023026_14, 2011/02

 被引用回数:35 パーセンタイル:86.18(Physics, Fluids & Plasmas)

The influence of plasma size on global ion temperature Gradient turbulence is studied with the full-$$f$$ Eulerian code GT5D. The gyrokinetic model includes a consistent neoclassical electric field as well as a fixed-power source operator, enabling long-time simulations with self-consistent turbulent transport and equilibrium profiles. The effects of plasma size are studied by scaling the minor radius $$a$$ and the input power. For the first time, worse-than-Bohm scaling is observed in experimentally realistic conditions. For all plasma sizes, avalanches propagate over significant radii but their propagation depends on the radial electric shear. It is found that this quantity does not scales with the size due to the building up of intrinsic momentum. These simulations therefore suggest that intrinsic momentum reduces heat transport.

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:17 パーセンタイル:59.53(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:84 パーセンタイル:93.18(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:24 パーセンタイル:71.36(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:159 パーセンタイル:98.57(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。

論文

Recent advances in nonlinear gyrokinetic PIC simulations in tokamak geometry

Bottino, A.*; Angelino, P.*; Allfrey, S. J.*; Brunner, S.*; Hatzky, R.*; 井戸村 泰宏; Jolliet, S.*; Sauter, O.*; Tran, T. M.*; Villard, L.*

Theory of Fusion Plasmas, ISPP21, p.75 - 86, 2004/00

非線形静電的グローバルPICコードORB5は実MHD平衡において、断熱的電子応答を仮定してジャイロ運動論的Vlasov-Poisson系を解析する。最適化粒子配分法と適応幅ジャイロ平均アルゴリズムの実装により、現バージョンのコードは非常に優れて粒子・エネルギー保存特性を有する。この基本的な保存特性は数値シミュレーションの質を測る量として重要である。論文ではExB帯状流と平行速度非線形性を含めた静電的無衝突微視的不安定性のシミュレーション結果をCHEASEコードから得られた実MHD並行配位において初めて示す。

論文

A Linear gyrokinetic model in magnetic coordinates

Jolliet, S.*; Angelino, P.*; Bottino, A.*; 井戸村 泰宏; Villard, L.*

Theory of Fusion Plasmas, ISPP21, p.345 - 351, 2004/00

グローバル粒子シミュレーションはイオン系乱流の時間発展を解析するうえで非常に有効な手法であるが、非常に計算コストが高い。このため、より洗練されたシミュレーションを実現するためには、さらにコードを最適化する必要がある。論文ではVlasov方程式を円柱座標(r,z)で解き、Poisson方程式を磁束座標(r,$$theta$$)で解くLORB5コードに関して、どちらの方程式も単一の磁束座標(s,$$theta_*$$)で取り扱うモデルを提案する。ここで、$$theta_*$$はstraight-field-lineポロイダル座標を示す。磁気軸での特異性を避ける手法、Cycloneパラメータを用いたベンチマークについても報告する。

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

Parallel filtering in global Vlasov simulations

Jolliet, S.; 井戸村 泰宏

no journal, , 

In this work, a new field solver is implemented in the global Eulerian code GT5D, which drastically reduces memory. The idea is to filter high parallel components of the perturbed density and potential consistently with the gyrokinetic ordering. In addition, the gyroaverage operator has been parallelized to further reduce memory. This new solver is tested in linear and neoclassical simulations. Then, this new scheme is applied to nonlinear simulations. It is shown that the filtering procedure decreases the ion diffusivity and removes spurious components of the spectrum produced by aliasing. As a result, simulations of plasma with sizes comparable to JT60U are now possible.

口頭

Properties of avalanches and momentum transport in driven ITG turbulence

井戸村 泰宏; Jolliet, S.

no journal, , 

駆動ITG(イオン温度勾配)乱流の第一原理トカマク乱流シミュレーションにおいて運動量入力を変化させる数値実験を実施した。その結果、プラズマ回転分布の変化に伴い、運動量の釣り合い条件を通して径方向電場が変化することがわかった。径電場シアによるイオン熱輸送の雪崩現象に対する影響の評価を行い、径電場シアが弱まるプラズマ回転分布において熱輸送が増大することを発見した。また、異なる回転分布における運動量輸送特性の解析によって、運動量輸送の拡散,ピンチ,残留応力の評価を行った。

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