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  • 1
    Electronic Resource
    Electronic Resource
    Gyrokinetic particle-in-cell simulation of Alfvénic ion-temperature-gradient modes in tokamak plasma (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 861-868 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linearized gyrokinetic particle-in-cell code is developed to study the excitations of electromagnetic instabilities due to finite ion temperature gradients in tokamak plasmas. The code employs the δf scheme to solve the gyrokinetic equations for ion dynamics; while electrons are modeled as massless fluid. The instability threshold condition of the Alfvénic ion-temperature-gradient (ITG) mode as well as the finite β stablization of electrostatic ITG mode are studied. Here β=8πp/B2 is the ratio between the plasma and magnetic pressure. In the β→0 limit, our code recovers the electrostatic results. As β increases, the destablization of kinetic ballooning mode due to finite ion temperature gradient is observed. The simulation results also reveal two possible critical values of ηi, where ηi=d ln Ti/d ln n is the ratio between the density scale length to the temperature scale length; one of the critical values is for the predominantly electrostatic ITG mode and one for the Alfvénic ITG mode, where ηi,cAITG〈ηi,cESITG. The transition domain between the Alfvénic ITG mode and the ITG mode, meanwhile, is found to depend on β and ηi. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1454124
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  • 2
    Electronic Resource
    Electronic Resource
    On resonant heating below the cyclotron frequency (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4713-4716 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resonant heating of particles by electrostatic and Alfvén waves propagating in a confining uniform magnetic field is examined. It is shown that, with a sufficiently large wave amplitude, significant perpendicular stochastic heating can be obtained with wave frequency at a fraction of the cyclotron frequency. This result may have relevance for the heating of ions in the solar corona, and is a generic phenomenon, independent of the type of wave considered. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1406939
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  • 3
    Electronic Resource
    Electronic Resource
    Gyrokinetic-magnetohydrodynamic hybrid simulation of the transition from toroidal Alfvén eigenmodes to kinetic ballooning modes in tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2349-2352 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A gyrokinetic-magnetohydrodynamic (MHD) hybrid simulation code has been developed in order to study high-n (where n is the toroidal mode number) MHD instabilities driven by energetic particles in finite-β tokamaks. Here β is the ratio between plasma and magnetic pressures. Specifically, it is observed that as the core plasma β value increases, there is a corresponding transition from the toroidal Alfvén eigenmode (TAE) to the kinetic ballooning mode (KBM). The energetic particle mode (EPM) branches of both the toroidal Alfvén mode (TAM) and KBM are shown to be important in this transition. KBM are preferentially excited when the energetic particle velocity is small compared to the Alfvén velocity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871918
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  • 4
    Electronic Resource
    Electronic Resource
    Theory of magnetohydrodynamic instabilities excited by energetic particles in tokamaksf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1519-1522 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The resonant excitations of high-n magnetohydrodynamic instabilities by the energetic ions/alpha particles in tokamaks are theoretically analyzed. Here, n is the toroidal mode number. The magnetohydrodynamic eigenmodes, typically, consist of two-scale structures; one corresponds to the singular ("inertial'') region and the other the regular (ideal) region. Due to the finite-size orbits, the energetic particle contributions in the singular region are suppressed. Analytical dispersion relations can be derived via the asymptotic matching analysis. The dispersion relations have the generic form of the "fishbone'' dispersion relation [Phys. Rev. Lett. 52, 1122 (1984)] and demonstrate, in particular, the existence of two types of modes; that is, the discrete gap mode and the energetic-particle continuum mode. Specific expressions are given for both the kinetic ballooning modes and the toroidal Alfvén modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870702
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  • 5
    Electronic Resource
    Electronic Resource
    Excitation of zonal flow by drift waves in toroidal plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3129-3132 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical dispersion relation is derived which shows that, in toroidal plasmas, zonal flows can be spontaneously excited via modulations in the radial envelope of a single-n coherent drift wave, with n the toroidal mode number. Predicted instability features are verified by three-dimensional global gyrokinetic simulations of the ion-temperature-gradient mode. Nonlinear equations for mode amplitudes demonstrate saturation of the linearly unstable pump wave and nonlinear oscillations of the drift-wave intensity and zonal flows, with a parameter-dependent period doubling route to chaos. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874222
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical simulations of toroidal Alfvén instabilities excited by trapped energetic ions (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2469-2476 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extensive magnetohydrodynamic–gyrokinetic hybrid simulations have been carried out to study the excitations of Alfvén instabilities by trapped energetic ions in tokamak plasmas. Depending on the parameters, the most unstable mode can be either the toroidal Alfvén eigenmode (TAE) or the energetic-particle mode (EPM). In both cases, the dominant instability driving mechanism is the resonance with the trapped-particle magnetic precessional drifts. The mode frequencies of the most unstable modes, meanwhile, tend to be near the toroidal frequency gap in order to minimize the continuum damping. It is also demonstrated that the instabilities can be quenched by reversing the magnetic precessional drifts via either negative magnetic shear or locating the magnetic turning points in the inner (strong B) side of the torus. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874086
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  • 7
    Electronic Resource
    Electronic Resource
    Existence of ion temperature gradient driven shear Alfvén instabilities in tokamaks : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1917-1924 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The existence of unstable ion temperature gradient driven Alfvén eigenmodes (AITG) is demonstrated in tokamak plasmas, which are ideally stable with respect to magnetohydrodynamics (MHD). Conditions for the destabilization of such modes are quantitatively discussed on the basis of numerical solutions of a set of one-dimensional integral equations along the ballooning coordinate (quasi-neutrality and parallel Ampère's law). Furthermore, theoretical analyses of the eigenmode dispersion relation, which is given in a compact analytical form in the small ion orbit width limit (compared to the radial wavelength), provide a basis for explaining the general properties of the modes. It is emphasized that instability requires both sufficiently strong thermal ion temperature gradients and that the plasma be not too far away from ideal MHD marginal stability. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873449
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  • 8
    Electronic Resource
    Electronic Resource
    Plasma compressibility induced toroidal Alfvén eigenmode (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 444-449 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For circular tokamaks, it is demonstrated, both analytically and numerically, that there exists a new frequency gap within the shear Alfvén continuous spectrum around the Alfvén frequency, ωA=vA/qR, due to the ion compressibility effect. Here, vA denotes the Alfvén speed, q is the safety factor, and R the major radius. The frequency gap width, meanwhile, is proportional to the core ion beta, βi (ratio between core ion and magnetic pressures), and, correspondingly, the new discrete toroidal Alfvén eigenmode (TAE) inside the gap is referred to as βTAE. Collective excitations of the βTAE by energetic ions are also analyzed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872728
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetic toroidal Alfvén eigenmodes in finite-β tokamak plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1056-1061 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Kinetic toroidal Alfvén eigenmodes (KTAEs) in finite-β circular tokamak plasmas are investigated. Here, β is the ratio between plasma and magnetic pressures, and, formally, β∼O(r/Rq2), with q being the safety factor, r and R denoting, respectively, minor and major radii. A new effect associated with finite parallel electric field effect due to the ion magnetic drift (IMD) is discovered, which is of the same order as that due to the well-known effect associated with the finite ion Larmor radii. The IMD-induced parallel electric field effect is shown to contribute to potential wells for the eigenmodes. Therefore, the IMD-induced parallel electric field effect can discretize the lower Alfvén continuum along the real eigenfrequency. Subsequently, this new branch of KTAEs could be readily destabilized by the energetic ions. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872635
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of toroidal Alfvén modes excited by energetic particles in tokamaks (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 323-343 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general analytical theory for the two-dimensional eigenmode structures and stability of high toroidal-mode-number (high-n) shear Alfvén modes in axisymmetric tokamaks is presented. This theory, thus, further generalizes the previous work on the high-n toroidal Alfvén eigenmode (TAE) [Phys. Fluids B 5, 3668 (1993)] by including, nonperturbatively, plasma kinetic effects and resonant excitations by energetic particles. Specifically, in addition to recovering the known theoretical predictions on TAE, we have derived new results on global radial structures, as well as stability properties of kinetic toroidal Alfvén eigenmodes (KTAE) and energetic-particle modes (EPM). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871857
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