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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：2 Percentile：13.82(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.
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：10.37(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.
Kawai, Chika; Idomura, Yasuhiro; Maeyama, Shinya; Ogawa, Yuichi*
no journal, ,
In estimating confinement properties of fusion plasmas, it is a critical issue to understand structures of turbulent spectra, leading to turbulent transport. In this study, self-organization processes, which produce zonal flows from electron turbulence, are analyzed in detail via a highly accurate gyrokinetic Eulerian code, and structures of turbulent spectra leading to zonal flow generation are clarified.
Kawai, Chika; Maeyama, Shinya; Idomura, Yasuhiro; Ogawa, Yuichi*
no journal, ,
Self organization through inverse energy cascade in quasi two dimensional turbulence spectra is considered as a mechanism of the formation of zonal flow structure in magnetized plasma. However, relation between turbulence energy spectra and formation of zonal flow structure has not been clarified in first-principles based plasma turbulence simulations. In this study, we examine relations between turbulent energy spectra and structure formations due to self-organization, which are derived from a fluid description of plasma turbulence, the Hasegawa-Mima equation, using gyrokinetic Vlasov simulations of electron turbulence.
Kawai, Chika; Idomura, Yasuhiro; Maeyama, Shinya*; Ogawa, Yuichi*
no journal, ,
To investigate relations between self-organization and flow structure formation in magnetized plasmas, energy spectrum structures of electron turbulence are estimated by gyrokinetic simulations. It is found that the existence of zonal flow formation is affected by the plasma density and the temperature ratio between ions and electrons, which change wave dispersion induced by diamagnetic rotation. Depending on saturation amplitudes of turbulence, zonal flow formation processes are varied from an inverse energy cascade due to self-organization to a modulational instability due to direct mode coupling. These results suggest that structures of electron turbulence are significantly changed by macroscopic plasma parameters.
Kawai, Chika; Idomura, Yasuhiro; Maeyama, Shinya*; Ogawa, Yuichi*
no journal, ,
To investigate relation between the formation of zonal flows in magnetized plasmas and self-organization phenomena, energy spectrum structures of electron scale turbulence is evaluated using gyrokinetic simulations. It is verified that the inverse energy cascade, which is a characteristic of the self-organization in quasi-2D systems, and the formation of anisotropic turbulent spectra in a long wavelength region due to linear dispersion of drift waves induced by diamagnetic plasma rotation contribute to the formation of zonal flows in kinetic plasma turbulence. It is also clarified that plasma parameters such as the temperature ratio of ions to electrons and fluctuation amplitudes change the turbulence structure by modulating the linear dispersion of drift waves.
Idomura, Yasuhiro; Matsuoka, Seikichi; Ina, Takuya; Garbet, X.*; Brunner, S.*; Villard, L.*; Kawai, Chika*
no journal, ,
This talk reviews outcomes from GT5DISO projects, which was conducted for FY2014-2016. In this project, isotope effects on turbulent transport have been studied using the gyrokinetic toroidal five dimensional full-f Eulerian code GT5D. In FY2014, it was shown that the ion temperature gradient driven (ITG) turbulence with adiabatic electrons does not show isotope effects, and the trapped electron mode (TEM) driven by kinetic trapped electrons is essential for this issue. In FY2015, a new hybrid kinetic electron model was developed in GT5D, and its verification tests for ITG-TEM turbulence simulations were conducted. In FY2016, the kinetic electron model was validated against electron heating modulation experiments, in which the TEM turbulence plays key roles in particle and momentum transport. Finally, we performed isotope scan of ITG-TEM turbulence simulations, which tend to indicate difference of confinement between hydrogen and deuterium plasmas.
Kawai, Chika; Maeyama, Shinya; Idomura, Yasuhiro; Ogawa, Yuichi*
no journal, ,
Self-organization through inverse cascades of energy in a turbulent spectrum is considered as one of the paths to formation of zonal flow structures in magnetized plasma. Despite the theoretical suggestion, relations between the turbulence energy spectrum and the formation of zonal flow structures have not been rigorously investigated in terms of numerical simulation studies based on a first-principle model. In this study, spectrum structures of electron scale plasma turbulence are obtained from high-resolution Vlasov simulations. The long wave length region of the spectrum is investigated in relation with self-organization.
