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Kawai, Chika*; Idomura, Yasuhiro; Ogawa, Yuichi*; Yamada, Hiroshi*

Physics of Plasmas, 27(8), p.082302_1 - 082302_11, 2020/08

Times Cited Count：1 Percentile：27.66(Physics, Fluids & Plasmas)Self-organization in the toroidal electron temperature gradient driven (ETG) turbulence is investigated based on a global gyrokinetic model in a weak magnetic shear configuration. Because of global profile effects, toroidal ETG modes with higher toroidal mode number n are excited at the outer magnetic surfaces, leading to strong linear wave dispersion. The resulting anisotropic wave turbulence boundary and the inverse energy cascade generate the self-organization of zonal flows, which is the unique mechanism in the global gyrokinetic model. The self-organization is confirmed both in the decaying turbulence initialized by random noises and in the toroidal ETG turbulence. It is also shown that the self-organization process generates zonal flows and isotropic eddies depending on a criterion parameter, which is determined by the ion to electron temperature ratio and the turbulence intensity.

Idomura, Yasuhiro

Physics of Plasmas, 26(12), p.120703_1 - 120703_5, 2019/12

Times Cited Count：2 Percentile：27.41(Physics, Fluids & Plasmas)This Letter presents the impacts of the hydrogen isotope mass and the normalized gyroradius on L-mode like hydrogen (H) and deuterium (D) plasmas dominated by ion temperature gradient driven (ITG) turbulence using global full-f gyrokinetic simulations. In ion heated numerical experiments with adiabatic electrons, the energy confinement time shows almost no isotope mass dependency, and is determined by Bohm like scaling. Electron heated numerical experiments with kinetic electrons show clear isotope mass dependency caused by the isotope effect on the collisional energy transfer from electrons to ions, and the H and D plasmas show similar ion and electron temperature profiles at an H to D heating power ratio of . The normalized collisionless ion gyrokinetic equations for H and D plasmas become identical at the same , and collisions weakly affect ITG turbulence. Therefore, the isotope mass dependency is mainly contributed by the scaling and the heating sources.

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

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 spectra and a transition to 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.

Kawai, Chika*; Idomura, Yasuhiro; Maeyama, Shinya*; Ogawa, Yuichi*

Physics of Plasmas, 24(4), p.042303_1 - 042303_13, 2017/04

Times Cited Count：2 Percentile：15.91(Physics, Fluids & Plasmas)Self-organization in the slab electron temperature gradient driven (ETG) turbulence is investigated based on gyrokinetic simulations and the Hasegawa-Mima (HM) equation. The scale and the anisotropy of self-organized turbulent structures vary depending on the Rhines scale and the characteristic scale given by the adiabatic response term in the HM equation. The former is determined by competition between the linear wave dispersion and the nonlinear turbulent cascade, while the latter is given as the scale, at which the turbulent cascade is impeded. These scales are controlled by plasma parameters such as the density and temperature gradient, and the temperature ratio of ion to electron. It is found that depending on the plasma parameters, the ETG turbulence shows either isotropic turbulence or zonal flows, which give significantly different transport levels. Although the modulational instability excites zonal modes regardless of the plasma parameters, the final turbulent structure is determined by the self-organization process.

Idomura, Yasuhiro

Plasma and Fusion Research (Internet), 11, p.2403006_1 - 2403006_5, 2016/02

In this work, we address saturation mechanisms of decaying turbulence induced by the ion temperature gradient driven trapped electron mode. In the simulation, turbulent transport is quenched in the nonlinear quasi-steady phase, where temperature profiles exceeding linear critical temperature gradient parameters are formed. This kind of nonlinear critical temperature gradient is sustained by radial electric fields with strong shear, which is generated by corrugated density profiles. It is found that the density profile structure is related to electrons transport near low order mode rational surfaces, where non-adiabatic response of passing electrons becomes important.

Idomura, Yasuhiro

Purazuma, Kaku Yugo Gakkai-Shi, 81(8), p.581 - 592, 2005/08

A gyrokinetic particle simulation is a powerful tool in studying tokamak microturbulence. A method, which is a standard method in recent gyrokinetic particle simulations, dramatically improved an efficiency of a particle simulation by reducing a particle noise, and full torus turbulence simulations are enabled. In this paper, the method is reviewed, and issues in full torus gyrokinetic particle simulations are discussed.

Miyato, Naoaki; Li, J. Q.*; Kishimoto, Yasuaki

IAEA-CN-116/TH/8-5Rb (CD-ROM), 8 Pages, 2004/11

Using a global Landau fluid code in toroidal geometry, an electromagnetic ion temperature gradient (ITG) driven turbulence-zonal mode system is investigated. Two different types of zonal flows, i.e. stationary zonal flows in a low (safety factor) region and oscillatory ones in a high region which are called geodesic acoustic modes (GAM), are found to be simultaneously excited in a torus. The stationary flows efficiently suppress turbulent transport, while the oscillatory ones weakly affect the turbulence due to their time varying nature. Therefore in the low region where the zonal flows are stationary, the zonal flows are dominant over the turbulence. On the other hand, the turbulence is still active in the high region where the zonal flows are oscillatory.

Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki

Journal of Plasma and Fusion Research SERIES, Vol.6, p.17 - 72, 2004/00

A global gyrokinetic toroidal particle code for a 3D nonlinear simulation (GT3D) has been developed for a comprehensive study of the ion and electron anomalous transport arising from the ion temperature gradient driven - trapped electron mode (ITG-TEM) turbulence in tokamak plasmas. In the preliminary linear ITG-TEM calculations, basic properties of ITG-TEM modes are confirmed. Adding trapped electrons not only increases the growth rate of the ITG mode, but also produces another unstable electron mode, the TEM mode, which is unstable even at . The dominant mode changes from the ITG mode to the TEM mode depending on and . In linear benchmark calculations using Cyclone base case parameters, eigenfrequencies obtained from GT3D, GTC(PPPL-UCI) and FULL(PPPL) show reasonable quantitative agreement.

Jolliet, S.*; Angelino, P.*; Bottino, A.*; Idomura, Yasuhiro; Villard, L.*

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

Global particle-in-cell (PIC) simulations are a very useful tool for studying the time evolution of turbulence induced by ion-temperature-gradient (ITG) instabilities. Unfortunately, the linear code LORB5 and its non-linear version ORB5 require high computational power. In order to study more sophisticated models, we need to optimize these codes. We will focus on LORB5, which uses a cylindrical grid (r,z) for solving the Vlasov equation and a (s,) grid for the Poisson equation. The approach presented in this work consists of implementing the gyrokinetic model using a single (s,) grid. Here is the straight-field-line poloidal coordinate. A method to avoid the singularity at the magnetic axis is presented, and a benchmark with the CYCLONE case is shown.

Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki

Nuclear Fusion, 43(4), p.234 - 243, 2003/04

Times Cited Count：112 Percentile：95.35(Physics, Fluids & Plasmas)no abstracts in English

Hirayama, Toshio; Shirai, Hiroshi; Yagi, Masatoshi; Shimizu, Katsuhiro; Koide, Yoshihiko; Kikuchi, Mitsuru; Azumi, Masafumi

Nuclear Fusion, 32(1), p.89 - 106, 1992/00

Times Cited Count：7 Percentile：33.61(Physics, Fluids & Plasmas)no abstracts in English

; *

Journal of the Physical Society of Japan, 51(5), p.1639 - 1643, 1982/00

Times Cited Count：0 Percentile：0.01(Physics, Multidisciplinary)no abstracts in English

; Ichikawa, Michio

Journal of Nuclear Science and Technology, 6(2), p.55 - 62, 1969/00

no abstracts in English

Ioka, Ikuo; Kato, Hitoshi; Ogawa, Hiroaki

no journal, ,

When the function of cooling system for a spent fuel pool is lost, the spent fuel pin is exposed to steam and air environment. In addition, oxidation behavior of the cladding may be changed due to axial temperature gradient and induced stress gradient during the process of dry out of the spent fuel pool. The oxidation behavior of the Zircaloy-2 cladding under axial temperature gradient was investigated in this study. The axial temperature gradients was about 100 C/cm. The oxidation test was carried out at 600 C in the saturated steam flow with Ar of 0.5 l/min as a career gas. Little difference was seen in the configuration of the surface cracks and the oxide thickness of specimens oxidized with different temperature gradients. Consequently, the high-temperature oxidation of Zircaloy-2 cladding was hardly changed by the steep axial temperature gradient of about 100 C/cm in this study.

Idomura, Yasuhiro

no journal, ,

Decaying turbulence simulations of ion temperature gradient driven (ITG) turbulence with adiabatic electrons and ion temperature gradient driven trapped electron mode (ITG-TEM) turbulence with kinetic electrons are performed using a full-f gyrokinetic code. Nonlinear critical temperature gradients exceeding linear critical temperature gradients are observed in both simulations, and mechanisms to sustain them are investigated. It is found that unlike zonal flows in the ITG turbulence, the ITG-TEM turbulence produces corrugated electron density profiles, which form radial electric fields with strong shear following a force balance relation.

Idomura, Yasuhiro

no journal, ,

We develop a kinetic electron model for electrostatic ion temperature gradient driven trapped electron mode (ITG-TEM) turbulence simulations in the Gyrokinetic Toroidal 5D full-f Eulerian code, GT5D. In the model, a full kinetic electron model is used for computing collisional processes and radial electric fields, while turbulent fluctuations are computed by kinetic response of trapped electrons only in order to avoid a high frequency mode, which appear as the electrostatic limit of kinetic Alfvn waves. By using this model, we compare full-f gyrokinetic simulations of ITG turbulence with adiabatic and kinetic electron models, and discuss influences of kinetic electrons on ion turbulent transport.

Idomura, Yasuhiro

no journal, ,

To analyze electrostatic turbulence including trapped electron modes (TEMs), a kinetic electron model is developed in the gyrokinetic full-f Eulerian code GT5D. This model computes turbulent fields by assuming kinetic trapped electrons responses and adiabatic passing electrons, and describes collisional processes of the ion-electron system using multi-species Fokker-Planck operator. Linear growth rates of ITG-TEMs and ion-electron neoclassical transport are successfully reproduced, and a nonlinear critical temperature gradient is found by decaying turbulence simulations.

Asahi, Yuichi*; Garbet, X.*; Idomura, Yasuhiro; Grandgirard, V.*; Latu, G.*; Sarazin, Y.*; Dif-Pradalier, G.*; Donnel, P.*; Ehrlacher, C.*; Passeron, Ch.*

no journal, ,

Two global full-f gyrokinetic codes, which have been developed at CEA and JAEA, are benchmarked. Quantitative agreements between two codes are obtained regarding linear processes such as the linear stability of ion temperature gradient driven modes, the linear damping of zonal flows, and the collisional transport. Preliminary benchmarks on nonlinear turbulence simulations show some differences of calculation results, which arise due to differences in calculation models such as boundary conditions and heat source models, and the remaining issues towards quantitative nonlinear benchmarks are clarified.

Idomura, Yasuhiro

no journal, ,

Gyrokinetics gives first principles based descriptions of multi-scale phenomena in fusion plasmas ranging from micro-scale plasma turbulence to macro-scale plasma profiles. The development of supercomputers enabled full-f gyrokinetic simulations, which directly compute the multi-scale problem, which conventional f simulation realized low cost simulations by avoiding the multi-scale problem under scale separation between them. Moreover, recent development of a kinetic electron model enabled more realistic numerical experiments including electron turbulence, and experimental observations, in which electron turbulence plays a critical role, have been analyzed. In this invited talk, the progress of full-f gyrokinetic simulations leading to the latest electron turbulence simulation is reviewed.

Idomura, Yasuhiro

no journal, ,

Numerical experiments of hydrogen (H) and deuterium (D) plasmas with ion and electron heating conditions were conducted using the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. The energy confinement time in the ion heated numerical experiments was almost independent of isotope mass, and the plasma size scaling gives Bohm scaling. On the other hand, the electron heated numerical experiments showed a clear isotope effect. In this case, in addition to the plasma size scaling, the isotope dependency of the collisional energy transfer from electrons to ions contributed to the total isotope scaling by enhancing the ion heat transport channel. Systematic electron heating power scans for the H and D plasmas showed similar ion and electron temperature profiles at an H to D heating power ratio of 1.4. These results qualitatively agree with the isotope scaling in L-mode experiments with ion and electron heating conditions.