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  • 1
    Electronic Resource
    Electronic Resource
    Kinetic effects in tokamak scrape-off layer plasmas : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1672-1680 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The short mean-free path expansion used in fluid modeling of scrape-off layer plasmas is often violated for typical discharge parameters, especially by the superthermal particles, which carry most of the heat flux. Thus, the tail of the distribution function can strongly depart from Maxwellian due to nonlocal mean-free path effects, which can modify plasma transport, impurity radiation, and plasma–neutral gas interactions. These nonlocal effects become particularly pronounced for detached plasma conditions that are characterized by sharp gradients in the plasma parameters along the magnetic field. These problems are being addressed by developing one spatial dimension and two velocity variables, fully kinetic, collisional, and time-dependent particle-in-cell code, W1 [Contrib. Plasma Phys. 34, 436 (1994)], and its parallel-computer version, PW1 [Contrib. Plasma Phys. 34, 424 (1996)]. Comparisons are made with the Fokker–Planck code ALLA [Phys. Plasmas 3, 1634 (1996)] and with experimental results. Kinetic effects on probe measurement interpretation, impurity radiation, and parallel heat conductivity due to non-Maxwellian features in scrape-off layer plasmas are considered. Heat conductivity is compared with ad hoc heat flux limit models. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872280
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of impurity ions on the charge separation and velocity shear at a plasma edge (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1401-1404 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The problem of the formation of charge separation in a plasma in the presence of a steep density gradient, the self-consistent electric field and the associated E×B velocity, are studied using a two-dimensional (2D) gyro-kinetic Vlasov code for the ions, with electrons following an adiabatic law. The code shows the formation of a one-dimensional (1D) equilibrium charge at the plasma edge. It is also shown that the presence of a small fraction of impurity ions at the plasma edge can have a significant effect in increasing the effective charge separation and the associated electric field. The present results show that only a kinetic code can solve the problem of the equilibrium electric field in the presence of a density gradient, and point to the important role played by the ions' gyro-radius in establishing a charge separation at a plasma edge. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873486
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  • 3
    Electronic Resource
    Electronic Resource
    Comments on "Electron acoustic surface waves in a two-electron component plasma'' [Phys. Fluids B 5, 4502 (1993)] (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3716-3717 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transverse attenuation coefficient for the transverse surface electromagnetic wave is derived. This Comment shows that the result derived in Ref. [Phys. Fluids B 5, 4502 (1993)] for this transverse attenuation coefficient is incorrect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870908
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  • 4
    Electronic Resource
    Electronic Resource
    Comment on "Surface wave propagation in a magnetized dusty plasma with charge fluctuation" [Phys. Plasmas 6, 3765 (1999)] (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3116-3118 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dispersion relation of surface waves at the interface of a semi-infinite magnetized drifting plasma was recently derived with the assumption that the tangential component of the wave magnetic field at the beam surface is continuous. It is the purpose of the present note to show that this assumption is incorrect. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874169
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  • 5
    Electronic Resource
    Electronic Resource
    Charge separation at a plasma edge in the presence of a density gradient (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2517-2525 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fully kinetic code for ions [one dimensional (1-D) in space, and using the three velocity dimensions in velocity space] is used to study the problem of the formation of a charge separation with the self-consistent electric field in a plasma in the presence of a density gradient. Electrons are treated using an adiabatic law. Graphical results are presented which follow the formation of a 1-D steady state showing the formation of an oscillating positive potential bump toward the edge of the plasma. These oscillations are closely associated with the gyration of the ions. It is also shown that the presence of a small fraction of impurity ions at the plasma edge can have a significant effect on the rapid buildup of the potential at the edge, and in increasing the charge separation and the associated electric field at the edge, in comparison to the case when no impurity ions are included. The present results show the importance of a kinetic solution to the problem of the equilibrium electric field and charge separation in the presence of a density gradient, and point to the important role played by the finite ions' gyroradius and the important contribution of impurity ions in this case. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874091
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  • 6
    Electronic Resource
    Electronic Resource
    Vlasov gyrokinetic simulations of ion-temperature-gradient driven instabilities (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 202-217 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Eulerian code that solves the gyrokinetic Vlasov equation in slab geometry is presented. It takes into account the E×B and polarization drifts in the plane perpendicular to the magnetic field, and kinetic effects in the parallel direction. The finite Larmor radius is modelled by a convolution operator. The relation is established between this model and others proposed previously, and they are shown to be equivalent in the limit of long wavelengths and small Larmor radii. The code is applied to investigate ion-temperature-gradient modes in the quasi-neutral regime, with adiabatic electrons. Numerical results are reported for a wide range of parameters, including density and temperature profiles, magnetic field strength, and ion to electron temperature ratio. Normally the plasma evolves towards long wavelength structures, although in some cases (when Landau damping is very weak) more strongly turbulent regimes are observed. Test particles are used to compute diffusion coefficients both in real space and velocity space. For the most strongly turbulent regimes, particle diffusion coefficients are of order 20 m2 s−1. The saturation mechanism is also investigated. Many previous numerical results obtained with particle codes are confirmed, but the Vlasov Eulerian technique allows a much finer resolution of structures both in real space and velocity space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871846
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  • 7
    Electronic Resource
    Electronic Resource
    A kinetic model of transient effects in tokamak edge plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1634-1639 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fluid descriptions are not adequate for edge plasma studies when the high collision frequency assumption fails in the presence of rapid transient processes. The results of analytic and numerical modeling of some of the non-Maxwellian features of edge plasma transport associated with transient heating and cooling phenomena in the scrape-off layer are presented. It is found that kinetic effects alter the heat conduction coefficient and lead to interesting critical behavior of the distribution function. The numerics are performed with the recently developed time-dependent Fokker–Planck code ALLA. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872023
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  • 8
    Electronic Resource
    Electronic Resource
    A hybrid Eulerian Vlasov code. I. Study of high-frequency beatwave experiment and Manley–Rowe action evolution in a finite causal system (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 650-668 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the first time, beatwave simulations relevant to the UCLA experiment (University of California at Los Angeles) [see Clayton et al., Phys. Rev. Lett. 70, 37 (1993), and also Phys. Plasmas 1, 1753 (1994)] have been made with a relativistic Eulerian Hilbert–Vlasov code for a realistically high ratio of driver frequency to plasma wave frequency (ω0/ωp≈30). Some of the more striking features that have emerged from the Hilbert–Vlasov simulations are discussed in this paper, with particular emphasis on particle dynamics in phase space with beam injection, and action transfer results obtained from the derivation of the integrated Manley–Rowe relations derived for a finite causal system. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871892
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  • 9
    Electronic Resource
    Electronic Resource
    Two-stage electron acceleration by simultaneous stimulated Raman backward and forward scattering (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3115-3129 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coexistence of stimulated Raman forward and backward scattering of intense electromagnetic radiation, which can occur, for instance, in laser fusion plasmas, is investigated. The simultaneous Raman forward and backward scattering is shown to create an electrostatic field structure which is exceptionally efficient in producing highly relativistic electrons. The mechanism of the electron acceleration is analyzed both by Vlasov–Maxwell simulations with self-consistent fields and by test particle calculations with prescribed electrostatic fields. The Vlasov–Maxwell simulations reveal that the two plasma waves generated by the backward and forward scattering are spatially separated, and thus form a two-stage electron "accelerator.'' © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871144
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  • 10
    Electronic Resource
    Electronic Resource
    Simulations of wave–particle interactions in stimulated Raman forward scattering in a magnetized plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3590-3607 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated Raman forward scattering in a high-temperature, magnetized plasma is investigated with relativistic Vlasov–Maxwell simulations and with envelope and test particle calculations. The parameters correspond to Raman current drive by free-electron lasers in reactor grade tokamak plasmas. The phase velocity of the Raman excited plasma wave is large, and therefore the Landau damping is initially weak. The electron plasma wave grows to a large amplitude and accelerates electrons to high energies. Simultaneous pump depletion weakens the driving ponderomotive force, which leads to a collapse of the plasma wave if the number of the interacting electrons is large enough. Spatially the wave–particle interaction takes place in a distance of a few wavelengths of the plasma wave. The electron energies can largely exceed the kinetic energy at the phase velocity of the electron plasma wave. Short-wavelength amplitude modulations of the plasma wave appear at high amplitudes. Efficient generation of the nonresonant anti-Stokes wave and of the second Stokes wave are also observed. Analytical growth rates and envelope calculations explain well the early evolution of the Raman process. Later on, nonlinear wave–particle interactions and relativistic effects start to dominate, and the system is not satisfactorily described by simple envelope equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860368
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