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Journal Articles

Self-organization of zonal flows and isotropic eddies in toroidal electron temperature gradient driven turbulence

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.

Journal Articles

Zonal flow and GAM dynamics and associated transport characteristics in reversed shear tokamaks

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

Journal of Plasma Physics, 72(6), p.821 - 824, 2006/12

 Times Cited Count:0 Percentile:0.01(Physics, Fluids & Plasmas)

Zonal flow behaviour and its effect on turbulent transport in reversed shear tokamaks are investigated by global nonlinear simulation of ion temperature gradient driven turbulence. When safety factor $$q$$ is reduced, zonal flows in a minimum $$q$$ region change from oscillatory ones to stationary ones and suppress the turbulent transport effectively. This result indicates that the change of zonal flow behaviour in the minimum $$q$$ region may trigger the formation of ion transport barriers.

Journal Articles

Observation of the interaction between the geodesic acoustic mode and ambient fluctuation in the JFT-2M tokamak

Ido, Takeshi*; Miura, Yukitoshi; Hoshino, Katsumichi; Kamiya, Kensaku; Hamada, Yasuji*; Nishizawa, Akimitsu*; Kawasumi, Yoshiaki*; Ogawa, Hiroaki; Nagashima, Yoshihiko*; Shinohara, Koji; et al.

Nuclear Fusion, 46(5), p.512 - 520, 2006/05

 Times Cited Count:80 Percentile:93.3(Physics, Fluids & Plasmas)

The electrostatic fluctuation spectrum and the fluctuation-induced particle flux of the JFT-2M tokamak were estimated using the hevy ion beam probe (HIBP) measurement. A geodesic acoustic mode (GAM) of the frequency about15kHz was identified in the L-mode. The GAM has its peak at about 3cm inside of the separatrix with the electric field of about 1.4kV/m. The estimated turbulent particle flux is found to be intermittent. It is found that the density fluctuation is modulated by the GAM in the wide frequency range and the coherence analysis shows that the flucruation-induced particle flux is partially contributed by the GAM. In the H-mode the GAM disappears and the fluctuation and the flux is much decreased.The mechanism of the large burst-like flux in the L-mode is not understood yet and left as the future problem.

Journal Articles

Nonlocal behaviour of zonal flows in tokamak plasmas

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

Plasma Physics and Controlled Fusion, 48(5A), p.A335 - A340, 2006/05

 Times Cited Count:22 Percentile:60.16(Physics, Fluids & Plasmas)

It is well known that drift wave turbulence such as ion temperature gradient (ITG) driven turbulence and zonal flows nonlinearly generated from it play an important role in anomalous transport in tokamak plasmas. The zonal flows can regulate turbulent transport and trigger formation of transport barriers. In toroidal plasmas there are two kinds of zonal flows. One is stationary zonal flow which is dominant in a low safety factor ($$q$$) region. The other is oscillatory ones appearing in a high $$q$$ region. Global ITG turbulence simulations have shown that the frequencies of the oscillatory zonal flows do not vary continuously with a radius, but the oscillatory zonal flows have the same frequency over a certain radial region. It is considered that the nonlocal behaviour becomes weak for small $$rho_i/a$$, where $$rho_i$$ is an ion Larmor radius and $$a$$ is a minor radius of a torus. In this research effects of $$rho_i/a$$ on the nonlocal behaviour of the zonal flows are investigated by global Landau fluid ITG simulations.

Journal Articles

Bispectral analysis applied to coherent floating potential fluctuations obtained in the edge plasmas on JFT-2M

Nagashima, Yoshihiko*; Ito, Kimitaka*; Ito, Sanae*; Fujisawa, Akihide*; Hoshino, Katsumichi; Takase, Yuichi*; Yagi, Masatoshi*; Ejiri, Akira*; Ida, Katsumi*; Shinohara, Koji; et al.

Plasma Physics and Controlled Fusion, 48(4), p.S1 - S15, 2006/04

 Times Cited Count:33 Percentile:75.73(Physics, Fluids & Plasmas)

This paper presents the results of bispectral analysis of floating potential fluctuations in the edge region of ohmically heated plasmas in the JFT-2M tokamak. Inside of the outermost magnetic surface,coherent modes were observed around the frequency of geodesic acoustic mode which is a kind of the zonal flow. The squared bicoherence shows significant nonlinear couplings between the coherent fluctuations and the background fluctuations (which are likely to contain drift wave turbulent fluctuations). The experimental results that the total bicoherence is proportional to the squared amplitude of the coherent fluctuation, and that the biphase of the coherent modes localizes around a constant value $$pi$$, are consistent with the theoretical prediction on the drift wave - zonal flow systems based on the Hasegawa-Mima model.

Journal Articles

Geodesic-acoustic-mode in JFT-2M tokamak plasmas

Ido, Takeshi*; Miura, Yukitoshi; Kamiya, Kensaku; Hamada, Yasuji*; Hoshino, Katsumichi; Fujisawa, Akihide*; Ito, Kimitaka*; Ito, Sanae*; Nishizawa, Akimitsu*; Ogawa, Hiroaki; et al.

Plasma Physics and Controlled Fusion, 48(4), p.S41 - S50, 2006/04

 Times Cited Count:119 Percentile:96.8(Physics, Fluids & Plasmas)

The potential and density fluctuations of Geodesic-Acoustic-Mode (GAM) were investigated through the direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe(HIBP). It was found that the amplitude of the fluctuation has a maximum inside of the plasma boundary and that it has an almost constant frequency. It was also found that the mode propagates in the radial direction and that the GAM affects the background turbulence. The influence to the background turbulence was found to be in consistent with a theoretical prediction.

Journal Articles

Global profile effects and structure formations in toroidal electron temperature gradient driven turbulence

Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki

Nuclear Fusion, 45(12), p.1571 - 1581, 2005/12

 Times Cited Count:38 Percentile:76.55(Physics, Fluids & Plasmas)

Using a global gyrokinetic toroidal particle code, the toroidal electron temperature gradient driven (ETG) turbulence is studied in positive and reversed shear tokamaks. In the nolinear turbulent state, the ETG turbulence in the positive and reversed shear configurations show quite different structure formations. In the positive shear configuration, the ETG turbulence is dominated by streamers which have a ballooning type structure, and the electron temperature $$T_e$$ profile is quickly relaxed to the marginally stable state in a turbulent time scale. In the reversed shear configuration, quasi-steady zonal flows are produced in the regative shear region, while the positive shear region is characterized by streamers. Accordingly, the electron thermal diffusivity $$chi_e$$ has a gap structure across the $$q_{min}$$ surface, and the $$T_e$$ gradinet is sustained above the marginal value for a long time in the quasi-steady phase. The results suggest a stiffness of the $$T_e$$ profile in positive shear tokamaks, and a possibility of the Te transport barrier in reversed shear tokamaks.

Journal Articles

Study of a drift wave-zonal mode system based on global electromagnetic landau-fluid ITG simulation in toroidal plasmas

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

Nuclear Fusion, 45(6), p.425 - 430, 2005/06

 Times Cited Count:22 Percentile:60.74(Physics, Fluids & Plasmas)

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 $$q$$ (safety factor) region and oscillatory ones in a high $$q$$ 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 $$q$$ region where the zonal flows are almost stationary, the zonal flows are dominant over the turbulence. On the other hand, the turbulence is still active in the high $$q$$ region where the zonal flows are oscillatory.

Journal Articles

Global structure of zonal flow and electromagnetic ion temperature gradient driven turbulence in tokamak plasmas

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

Physics of Plasmas, 11(12), p.5557 - 5564, 2004/12

 Times Cited Count:106 Percentile:95.18(Physics, Fluids & Plasmas)

Global characteristics of the coupled system of zonal flows and electromagnetic ion temperature gradient driven turbulence in tokamak plasmas are investigated using a global electromagnetic Landau fluid code. Zonal flow behavior changes with the safety factor $$q$$. In a low $$q$$ region stationary zonal flows are excited and suppress the turbulence effectively. Coupling between zonal flows and poloidally asymmetric pressure perturbations due to a geodesic curvature makes the zonal flows oscillatory in a high $$q$$ region. Energy transfer from the oscillatory zonal flows to the turbulence via the poloidally asymmetric pressure perturbations is identified. Therefore in the high $$q$$ region where the zonal flows are oscillatory, the zonal flows cannot quench the turbulence and turbulent transport is not suppressed completely. As for the zonal flow behavior, it is favorable for confinement improvement to make the low $$q$$ region where the stationary zonal flows are dominant in tokamak plasmas.

Journal Articles

Study of drift wave-zonal mode system based on global electromagnetic landau-fluid ITG simulation in toroidal plasmas

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 $$q$$ (safety factor) region and oscillatory ones in a high $$q$$ 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 $$q$$ 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 $$q$$ region where the zonal flows are oscillatory.

JAEA Reports

Global characteristics of zonal flows generated by ion temperature gradient driven turbulence in tokamak plasmas

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

JAERI-Research 2004-010, 18 Pages, 2004/08

JAERI-Research-2004-010.pdf:4.55MB

Global structure of zonal flows driven by ion temperature gradient driven turbulence in tokamak plasmas is investigated using a global electromagnetic Landau fluid code. Characteristics of the coupled system of the zonal flows and the turbulence change with the safety factor ${it q}$. In a low ${it q}$ region stationary zonal flows are excited and suppress the turbulence effectively. Coupling between zonal flows and poloidally asymmetric pressure perturbations via a geodesic curvature makes the zonal flows oscillatory in a high ${it q}$ region. Also we identify energy transfer from the zonal flows to the turbulence via the poloidally asymmetric pressure perturbations in the high ${it q}$ region. Therefore in the high ${it q}$ region the zonal flows cannot quench the turbulet transport completely.

Journal Articles

Advances in plasma and fusion simulation and prospects for the future; From a viewpoint of magnetically confined fusion

Kishimoto, Yasuaki

Purazuma, Kaku Yugo Gakkai-Shi, 80(5), p.390 - 395, 2004/05

High performance magnetically confined plasma is realized by having structures in plasmas, where different elementary processes with different time and spatial scales are deeply contributing with each other. A research based on large scale simulation is then essential to understand such hierarchical complex plasmas. We discuss the underlying physical process of the structural plasma and present a prospect for future numerical simulations covering a wide dynamical range.

Journal Articles

Numerical study of zonal flow dynamics and electron transport in electron temperature gradient driven turbulence

Li, J.; Kishimoto, Yasuaki

Physics of Plasmas, 11(4), p.1493 - 1510, 2004/04

 Times Cited Count:57 Percentile:87.05(Physics, Fluids & Plasmas)

The electron temperature gradient (ETG) driven turbulence in tokamak core plasmas is numerically investigated based on three-dimensional gyrofluid model with adiabatic ion response. Attentions are focused on the zonal flow dynamics in ETG fluctuations and the resultant electron heat transport. A high electron energy confinement mode is found in the weak magnetic shear regime, which is closely relevant with self-organization behavior of turbulence through the enhanced zonal flow dynamics rather than the weak shear stabilization of ETG fluctuations. It is demonstrated that the weak shear is favorable for the enhancement of zonal flows in ETG turbulence.

Journal Articles

Saturation of zonal flow in gyrofluid simulations of electron temperature gradient driven turbulence

Li, J.; Kishimoto, Yasuaki; Idomura, Yasuhiro; Miyato, Naoaki; Matsumoto, Taro

Journal of Plasma and Fusion Research SERIES, Vol.6, p.585 - 588, 2004/00

An enhanced zonal flow is observed in collisionless electron temperature gradient (ETG) driven turbulence with weak magnetic shears. The Kelvin-Helmholtz (KH) instability is proposed as a primary damping mechanism of such flow. Some considerable evidences for the KH mode excitation are presented. Results seem to suggest a possibility of turbulence transition from the ETG-dominated one to the KH-dominated one due to the zonal flow dynamics in weak shear plasmas.

Journal Articles

Electromagnetic effect on turbulent transport in tokamak based on Landau fluid global simulation

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

Journal of Plasma and Fusion Research SERIES, Vol.6, p.581 - 584, 2004/00

Electromagnetic effect on ion temperature gradient driven turbulence and zonal flow generated from the turbulence is investigated based on global electromagnetic Landau fluid simulations in tokamak plasmas. Turbulent transport decreases by increasing beta in a low beta regime. Two types of zonal flow are observed. One is almost stationary flow formed in a low safety factor (q) region, which is weaker at higher beta. The other is flow oscillating coherently at the geodesic acoustic mode (GAM) frequency.

Journal Articles

Prospect for "multiple-hierarchical complex plasma" where turbulent and laminar flow fluctuations are mixed

Kishimoto, Yasuaki; Idomura, Yasuhiro; Li, J.

Purazuma, Kaku Yugo Gakkai-Shi, 79(5), p.478 - 488, 2003/05

This is a collection of review article related to the "Multiple Time and Spatial Scale Plasma Simulation" of various fields including fundamental research area of self-organization, magnetic and laser fusion field, space and astrophysics field where a plasma plays an essential roles.

Journal Articles

Global gyrokinetic simulation of ion temperature gradient driven turbulence in plasmas using a canonical Maxwellian distribution

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

Journal Articles

Interaction between small-scale zonal flows and large-scale turbulence; A Theory for ion transport intermittency in tokamak plasmas

Li, J.; Kishimoto, Yasuaki

Physical Review Letters, 89(11), p.115002_1 - 115002_4, 2002/09

 Times Cited Count:31 Percentile:78.24(Physics, Multidisciplinary)

Interaction between small-scale zonal flows and large-scale turbulence is investigated. The key mechanism is identified as radially non-local mode coupling. Fluctuating energy can be non-locally transferred from the unstable longer to stable or damped shorter wavelength region, so that turbulence spectrum is seriously deformed and deviated from the nonlinear power law structure. Three-dimensional gyro-fluid ion temperature gradient (ITG) turbulence simulations show that an ion transport bursting behavior is consistently linked to the spectral deformity with the causal role of ITG-generated zonal flows in tokamak plasmas.

Journal Articles

Zonal flows in gyrofluid simulations of slab electron temperature gradient turbulence

Li, J.; Kishimoto, Yasuaki

Physics of Plasmas, 9(4), p.1241 - 1254, 2002/04

 Times Cited Count:35 Percentile:73.62(Physics, Fluids & Plasmas)

Zonal flows can be generated by drift wave turbulence through the nonlinear interactions. 3-D gyrofluid simulations show that in a turbulent system driven by electrostatic sheared slab electron temperature gradient(ETG) modes, the excitation of zonal flows is a slower process that indicates the amplitudes grow up approximately proportionally to time. The zonal flows are very weak comparing with the background turbulence and hardly work for suppressing the turbulent electron heat transport. The dynamics of zonal flows is numerically explored through starting zonal flow component in the quasi-steady state.

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