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  • 1
    Electronic Resource
    Electronic Resource
    Numerical study of the nonlinear evolution of toroidicity-induced Alfvén eigenmodes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 226-237 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simulation code for the nonlinear evolution of the toroidicity-induced Alfvén eigenmodes (TAE) is implemented based on a collisional δf simulation method [Phys. Plasmas 4, 3591 (1997)] and a Hamiltonian formulation of the guiding-center motion [Phys. Fluids 27, 2455 (1984)]. The nonlinear behavior of TAE in the regime of weak damping is studied numerically and compared with the predictions of theoretical analysis. The theoretical prediction for the scaling of the saturation amplitude with the linear growth rate and the collision rate is well confirmed. The enhancement of the saturation level due to resonance overlapping when there are multiple modes is observed and analyzed. The simulation code is applied to the alpha-driven TAE's in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)]. An estimate of the background damping rate is obtained from the simulation result. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873275
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  • 2
    Electronic Resource
    Electronic Resource
    Collisional δf method (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3591-3598 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general method for including various collisional effects, such as the drag and diffusion of test particles due to background plasmas, the effect of particle source and sink, and the like-particle Coloumb collisions, is presented. The marker density g is generally unknown along the particle trajectory, and its evaluation depends on the way particles are initially loaded and new particles are injected into the simulation. The method is demonstrated for the problem of the nonlinear evolution of the toroidicity induced Alfvén eigenmode, driven by energetic α particles. The saturation amplitude is found to scale with the collision rate in a way as predicted by theory.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872254
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo approach to collisional transport (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2603-2613 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linearized discretization approach is proposed for the numerical investigation of the gyrokinetic equation describing the dynamics of a strongly rotating plasma in a toroidally axisymmetric configuration. The discretization scheme allows the numerical evaluation of the neoclassical transport matrix in terms of a suitably discretized distribution function. A basic feature of the discretization scheme here developed is that it permits the introduction of Monte Carlo collision operators to advance in time the gyrokinetic state of a suitable set of test particles. Such operators, which apply to general non-normal gyrokinetic coordinates, are constructed in such a way as to conserve exactly the collisional invariants. A fundamental consequence is that the neoclassical transport coefficients determined in this way fulfill exactly both Onsager's symmetry relations and the condition of strict ambipolarity for the particle-flux transport coefficients. Such properties are proven to be satisfied independently of the number of test particles used in the discretization scheme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870587
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  • 4
    Electronic Resource
    Electronic Resource
    Self-consistent study of the alpha-particle-driven toroidicity-induced Alfvén eigenmode (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2733-2740 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of high energy particles with an Alfvén eigenmode is investigated self-consistently by using a kinetic dispersion relation. All important poloidal mode numbers and their radial mode profiles as calculated with the nova−k code [C. Z. Cheng, Phys. Rep. 211, 1 (1992)] are included. A Hamiltonian guiding center code is used to simulate the alpha particle motion. The numerical simulations include particle orbit width, nonlinear particle dynamics, and the effects of the modes on the particles. Modification of the particle distribution leading to mode saturation is observed. Particle loss depends on the radial extent of the mode and the ratio of the alpha particle gyroradius to the minor radius.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870508
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  • 5
    Electronic Resource
    Electronic Resource
    Probabilistic approach to Monte Carlo operators (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2591-2602 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general method for constructing Monte Carlo collision operators is formulated based on the introduction of a stochastic Liouville equation. The approach is applied to the investigation of a suitable discretized gyrokinetic equation describing the dynamics of a strongly rotating multispecies plasma, in a toroidally axisymmetric configuration. Improved expressions are obtained for the Monte Carlo collision operators for general non-normal (in v space) coordinate systems. As an application, the important case of the bounce-averaged gyrokinetic equation is discussed, in various cases of interest. Finally, using an approximate collision operator, the friction coefficients are evaluated and expressed in terms of energy and momentum restoring coefficients, thus yielding for the Monte Carlo operators a representation convenient for their numerical implementation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870586
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  • 6
    Electronic Resource
    Electronic Resource
    Construction of Monte Carlo operators in collisional transport theory (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 951-959 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Monte Carlo approach for investigating the dynamics of quiescent collisional magnetoplasmas is presented, based on the discretization of the gyrokinetic equation. The theory applies to a strongly rotating multispecies plasma, in a toroidally axisymmetric configuration. Expressions of the Monte Carlo collision operators are obtained for general v-space nonorthogonal coordinates systems, in terms of approximate solutions of the discretized gyrokinetic equation. Basic features of the Monte Carlo operators are that they fullfill all the required conservation laws, i.e., linear momentum and kinetic energy conservation, and in addition that they take into account correctly also off-diagonal diffusion coefficients. The present operators are thus potentially useful for describing the dynamics of a multispecies toroidal magnetoplasma. In particular, strict ambipolarity of particle fluxes is ensured automatically in the limit of small departures of the unperturbed particle trajectories from some initial axisymmetric toroidal magnetic surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870754
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of α-particle redistribution due to sawteeth on the Tokamak Fusion Test Reactor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1103-1109 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In recent deuterium–tritium experiments on the Tokamak Fusion Test Reactor (TFTR), both the pellet charge exchange (PCX) [Phys. Rev. Lett. 75, 846 (1995); Nucl. Fusion 35, 1437 (1995)] and the alpha charge exchange recombination spectroscopy (α-CHERS) [Phys. Rev. Lett. 75, 649 (1995)] diagnostics indicate that sawtooth oscillations can cause significant broadening of the fusion alpha radial density profile. Investigation of this sawtooth mixing phenomenon was performed by applying a Hamiltonian guiding center approach. A model of time evolution of the Kadomtsev-type sawtooth [Sov. J. Plasma Phys. 1, 389 (1976)] is constructed. The presence of more than one mode in the nonlinear stage of the sawtooth crash is necessary to cause significant broadening of the alpha density profile. Use of numerical equilibria allows us to perform detailed comparisons with TFTR experimental data. The simulation results are in reasonable agreement with α-CHERS and show a broadening of alpha particles similar to that seen in PCX measurements. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872198
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  • 8
    Electronic Resource
    Electronic Resource
    Rapid guiding center calculations (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2915-2919 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pseudo-Cartesian coordinates are used to represent the magnetic field and toroidal ripple magnitudes in a Hamiltonian guiding center formalism. The resulting code ORBITX is three to eight times as fast as previous guiding center codes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871191
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  • 9
    Electronic Resource
    Electronic Resource
    Nonlinear evolution of the alpha-particle-driven toroidicity-induced Alfvén eigenmode (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4555-4562 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fast and efficient numerical algorithm using energy conservation is developed to study the interaction of high-energy particles with a toroidicity-induced Alfvén eigenmode (TAE). A Hamiltonian guiding center code is used to simulate the alpha particle motion and a nonlinear δf scheme is employed to calculate the wave-particle energy exchange. The code is benchmarked using the bump-on-tail problem and simulation results agree with analytical estimates. For a single TAE mode, the particle radial excursion is much less than the spacing between the resonances produced by the poloidal harmonics for International Thermonuclear Experimental Reactor parameters. Resonant particles that lose their energy to the wave can become trapped poloidally, but transfer to a loss orbit through this mechanism does not occur. Modification of the particle distribution leading to mode saturation is observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871013
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of runaway collisional transport (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3942-3960 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The purpose of this paper is to formulate the transport problem for a multispecies rotating toroidal magnetoplasma in the so-called runaway regime, which is defined by an appropriate ordering of relevant characteristic frequencies, in particular, the Larmor frequency, the characteristic acceleration frequency due to the applied electric field and the effective collision frequency, all evaluated at some characteristic speed v0. A suitable form of the gyrokinetic equation is obtained to describe the time-dependent, multispecies plasma response to an applied electric field, in toroidal geometry and for a strongly rotating, quiescent, and collisional plasma. Its moment equations are proven to imply the reduction of the energy equation to Joule's law, as well as consequences on the form of Ohm's law and of the Grad–Shafranov equation. To construct an approximate solution of the gyrokinetic equation and to evaluate all relevant fluxes, appearing in the moment equations, a general variational solution method is developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860615
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