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Title: Zonal flow dynamics in the double tearing mode with antisymmetric shear flows

Abstract

The generation dynamics and the structural characteristics of zonal flows are investigated in the double tearing mode (DTM) with antisymmetric shear flows. Two kinds of zonal flow oscillations are revealed based on reduced resistive magnetohydrodynamics simulations, which depend on the shear flow amplitudes corresponding to different DTM eigen mode states, elaborated by Mao et al. [Phys. Plasmas 20, 022114 (2013)]. For the weak shear flows below an amplitude threshold, v{sub c}, at which two DTM eigen states with antisymmetric or symmetric magnetic island structure are degenerated, the zonal flows grow oscillatorily in the Rutherford regime during the nonlinear evolution of the DTMs. It is identified that the oscillation mechanism results from the nonlinear interaction between the distorted islands and the zonal flows through the modification of shear flows. However, for the medium shear flows above v{sub c} but below the critical threshold of the Kelvin-Helmholtz instability, an oscillatory growing zonal flow occurs in the linear phase of the DTM evolution. It is demonstrated that the zonal flow oscillation originates from the three-wave mode coupling or a modulation instability pumped by two DTM eigen modes with the same frequency but opposite propagating direction. With the shear flows increasing, the amplitude ofmore » zonal flow oscillation increases first and then decreases, whilst the oscillation frequency as twice of the Doppler frequency shift increases. Furthermore, impacts of the oscillatory zonal flows on the nonlinear evolution of DTM islands and the global reconnection are also discussed briefly.« less

Authors:
 [1];  [2];  [3];  [1];  [3];  [2]
  1. School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
  2. (Japan)
  3. Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011 (Japan)
Publication Date:
OSTI Identifier:
22252889
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DOPPLER EFFECT; EVOLUTION; HELMHOLTZ INSTABILITY; MAGNETIC ISLANDS; MAGNETOHYDRODYNAMICS; NONLINEAR PROBLEMS; OSCILLATIONS; SHEAR; SIMULATION; SYMMETRY; TEARING INSTABILITY

Citation Formats

Mao, Aohua, Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011, Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp, Liu, Jinyuan, E-mail: jyliu@dlut.edu.cn, Kishimoto, Yasuaki, and Institude of Advanced Energy, Kyoto University, Uji, Kyoto 6110011. Zonal flow dynamics in the double tearing mode with antisymmetric shear flows. United States: N. p., 2014. Web. doi:10.1063/1.4875729.
Mao, Aohua, Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011, Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp, Liu, Jinyuan, E-mail: jyliu@dlut.edu.cn, Kishimoto, Yasuaki, & Institude of Advanced Energy, Kyoto University, Uji, Kyoto 6110011. Zonal flow dynamics in the double tearing mode with antisymmetric shear flows. United States. doi:10.1063/1.4875729.
Mao, Aohua, Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011, Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp, Liu, Jinyuan, E-mail: jyliu@dlut.edu.cn, Kishimoto, Yasuaki, and Institude of Advanced Energy, Kyoto University, Uji, Kyoto 6110011. 2014. "Zonal flow dynamics in the double tearing mode with antisymmetric shear flows". United States. doi:10.1063/1.4875729.
@article{osti_22252889,
title = {Zonal flow dynamics in the double tearing mode with antisymmetric shear flows},
author = {Mao, Aohua and Graduate School of Energy Science, Kyoto University, Uji, Kyoto 6110011 and Li, Jiquan, E-mail: lijq@energy.kyoto-u.ac.jp and Liu, Jinyuan, E-mail: jyliu@dlut.edu.cn and Kishimoto, Yasuaki and Institude of Advanced Energy, Kyoto University, Uji, Kyoto 6110011},
abstractNote = {The generation dynamics and the structural characteristics of zonal flows are investigated in the double tearing mode (DTM) with antisymmetric shear flows. Two kinds of zonal flow oscillations are revealed based on reduced resistive magnetohydrodynamics simulations, which depend on the shear flow amplitudes corresponding to different DTM eigen mode states, elaborated by Mao et al. [Phys. Plasmas 20, 022114 (2013)]. For the weak shear flows below an amplitude threshold, v{sub c}, at which two DTM eigen states with antisymmetric or symmetric magnetic island structure are degenerated, the zonal flows grow oscillatorily in the Rutherford regime during the nonlinear evolution of the DTMs. It is identified that the oscillation mechanism results from the nonlinear interaction between the distorted islands and the zonal flows through the modification of shear flows. However, for the medium shear flows above v{sub c} but below the critical threshold of the Kelvin-Helmholtz instability, an oscillatory growing zonal flow occurs in the linear phase of the DTM evolution. It is demonstrated that the zonal flow oscillation originates from the three-wave mode coupling or a modulation instability pumped by two DTM eigen modes with the same frequency but opposite propagating direction. With the shear flows increasing, the amplitude of zonal flow oscillation increases first and then decreases, whilst the oscillation frequency as twice of the Doppler frequency shift increases. Furthermore, impacts of the oscillatory zonal flows on the nonlinear evolution of DTM islands and the global reconnection are also discussed briefly.},
doi = {10.1063/1.4875729},
journal = {Physics of Plasmas},
number = 5,
volume = 21,
place = {United States},
year = 2014,
month = 5
}
  • The effect of zonal flow shear on the double tearing mode is investigated by solving the linear reduced two-fluid equations for the equilibrium including zonal flow. The zonal flow caused by microturbulence is obtained from nonlinear simulation results presented by A. Ishizawa and N. Nakajima [Phys. Plasmas 14, 040702 (2007)]. There is no clear evidence that could indicate whether the double tearing mode is stabilized or destabilized by the zonal flow.
  • The double tearing mode (DTM) is characterized by two eigen states with antisymmetric or symmetric magnetic island structure, referred to as the even or odd DTM. In this work, we systematically revisit the DTM instabilities in the presence of an antisymmetric shear flow with a focus on eigenmode characteristics as well as the stabilization or destabilization mechanism in a wide parameter region. Both initial value simulation and eigenvalue analysis are performed based on reduced resistive MHD model in slab geometry. A degenerated eigen state is found at a critical flow amplitude v{sub c}. The even (or odd) DTM is stabilizedmore » (or destabilized) by weak shear flow below v{sub c} through the distortion of magnetic islands mainly due to the global effect of shear flow rather than the local flow shear. The distortion can be quantified by the phase angles of the perturbed flux, showing a perfect correspondence to the growth rates. As the shear flow increases above v{sub c}, the degenerated eigen state bifurcates into two eigen modes with the same growth rate but opposite propagating direction, resulting in an oscillatory growth of fluctuation energy. It is identified that two eigen modes show the single tearing mode structure due to the Alfven resonance (AR) occurring on one current sheet. Most importantly, the AR can destabilize the DTMs through enhancing the plasma flow exerting on the remaining island. Meanwhile, the local flow shear plays a remarkable stabilizing role in this region. In addition, the eigenmode characteristic of the electromagnetic Kelvin-Helmholtz instability is also discussed.« less
  • Long-distance toroidal correlations of potential and density fluctuations have been investigated at the TEXTOR tokamak [H. Soltwisch et al., Plasma Phys. Controlled Fusion 26, 23 (1984)] in edge electrode-biasing experiments. During the biasing-induced H-mode, the dc ExB shear flow triggers a zonal flow structure and hence long-distance correlation in potential fluctuations, whereas for density fluctuations there is nearly no correlation. These results indicate an intimate interaction between the mean and zonal flows, and the significance of long range correlations in improved-confinement regimes.
  • We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was foundmore » that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.« less
  • The dynamics of global reconnection in the presence of a poloidal shear flow located in between magnetic islands is investigated. Different linear and nonlinear regimes are identified depending on the resistivity, the equilibrium velocity amplitude, and the distance between the low-order resonant surfaces. It is found that nonlinearly, the shear flow can significantly delay DTM generation and global reconnection. It is shown that this delay is linked to a symmetry breaking imposed by the shear flow and the generation of mean poloidal flows in the resistive layers. It is also found that turbulence can be generated by Kelvin-Helmholtz instability inmore » between the resonance layers and enhance magnetic reconnection processes.« less