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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 
is reduced, zonal flows in a minimum 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 region may trigger the formation of ion transport barriers.
Miyato, Naoaki; Kishimoto, Yasuaki; Li, J.*
Plasma Physics and Controlled Fusion, 48(5A), p.A335 - A340, 2006/05
Times Cited Count：26 Percentile：64.63(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 () region. The other is oscillatory ones appearing in a high 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 
, where 
is an ion Larmor radius and 
is a minor radius of a torus. In this research effects of on the nonlocal behaviour of the zonal flows are investigated by global Landau fluid ITG simulations.
Miyato, Naoaki; Li, J. Q.*; Kishimoto, Yasuaki
Nuclear Fusion, 45(6), p.425 - 430, 2005/06
Times Cited Count：25 Percentile：61.9(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 (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 almost 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; Kishimoto, Yasuaki; Tokuda, Shinji
Europhysics Conference Abstracts (CD-ROM), 29C, 4 Pages, 2005/00
A gyrokinetic simulation is an essential tool to study anomalous turbulent transport in tokamak plasmas. Although a delta-f PIC code or a particle approach has been a standard method, it has difficulty in implementing non-conservative effects such as a heat source and collisions, which are important for a realistic long time turbulence simulation. On the other hand, a Vlasov code or a mesh approach is much more flexible to simulate these non-conservative effects. In this work, a new gyrokinetic Vlasov code is developed based on the CIP method, which is one of recent advanced CFD schemes. Numerical properties and computational costs of the gyrokinetic PIC and CIP codes are compared in ITG turbulence simulations.
Miyato, Naoaki; Kishimoto, Yasuaki; Li, J.
Physics of Plasmas, 11(12), p.5557 - 5564, 2004/12
Times Cited Count：116 Percentile：94.97(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 . In a low 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 region. Energy transfer from the oscillatory zonal flows to the turbulence via the poloidally asymmetric pressure perturbations is identified. Therefore in the high 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 region where the stationary zonal flows are dominant 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 
. In a low 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 region. Also we identify energy transfer from the zonal flows to the turbulence via the poloidally asymmetric pressure perturbations in the high region. Therefore in the high region the zonal flows cannot quench the turbulet transport completely.
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.
Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki
New Journal of Physics (Internet), 4(1), p.101.1 - 101.13, 2002/12
The ion temperature gradient driven (ITG) mode in reversed shear tokamaks is analyzed using a gyrokinetic toroidal particle code. It is found that the ITG mode in the reversed shear configuration shows a coupled mode structure between the slab and toroidal ITG modes. Especially in the 
region, a slab like feature due to the reversed shear slab ITG mode becomes strong. This coupled eigenmode structure is changed from a slab mode to a toroidal mode depending on 
and 
. Results show that in reversed shear tokamaks, the ITG mode is determined from a competition between the slab and toroidal ITG modes.
Li, J.; Kishimoto, Yasuaki
Physical Review Letters, 89(11), p.115002_1 - 115002_4, 2002/09
Times Cited Count：32 Percentile：77.28(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.
Kishimoto, Yasuaki; J.Y.Kim*; W.Horlon*; T.Tajima*; LeBrun, M. J.*; Shirai, Hiroshi
Plasma Physics and Controlled Fusion, 40(Suppl.3A), p.A663 - A677, 1999/03
no abstracts in English
Yamagiwa, Mitsuru; Hirose, A*; Elia, M.*
PPL-163, 22 Pages, 1997/01
no abstracts in English
Kishimoto, Yasuaki; J.Y.Kim*; Fukuda, Takeshi; Ishida, Shinichi; Fujita, Takaaki; Tajima, Toshiki*; W.Horton*; J.Furnish*; LeBrun, M. J.*
Fusion Energy 1996, Vol.2, p.581 - 591, 1997/00
no abstracts in English
Yamagiwa, Mitsuru; Hirose, A*; Elia, M.*
Plasma Physics and Controlled Fusion, 39(3), p.531 - 540, 1997/00
Times Cited Count：6 Percentile：24.39(Physics, Fluids & Plasmas)no abstracts in English
J.Y.Kim*; Kishimoto, Yasuaki; Wakatani, Masahiro*; Tajima, Toshiki*
Physics of Plasmas, 3(10), p.3689 - 3695, 1996/10
Times Cited Count：52 Percentile：82.07(Physics, Fluids & Plasmas)no abstracts in English
Kishimoto, Yasuaki; Tajima, Toshiki*; W.Horton*; LeBrun, M. J.*; J.Y.Kim*
Physics of Plasmas, 3(4), p.1289 - 1307, 1996/04
Times Cited Count：79 Percentile：89.74(Physics, Fluids & Plasmas)no abstracts in English
Kishimoto, Yasuaki; Tajima, Toshiki*; LeBrun, M. J.*; W.Horton*; J.Y.Kim*; J.Q.Dong*; F.L.Waelbroeck*; Tokuda, Shinji; *; Fukuda, Takeshi
IAEA-CN-60/D-10, 0, p.299 - 307, 1996/00
no abstracts in English
