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Dec 2010

Volume 17, Issue 12, Articles (12xxxx)

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Phys. Plasmas 17, 120501 (2010); http://dx.doi.org/10.1063/1.3514586 (36 pages)

A. Bret, L. Gremillet, and M. E. Dieckmann
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Multidimensional electron beam-plasma instabilities in the relativistic regime

A. Bret, L. Gremillet, and M. E. Dieckmann

Phys. Plasmas 17, 120501 (2010); http://dx.doi.org/10.1063/1.3514586 (36 pages)

Online Publication Date: 28 December 2010

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The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.27.Ny Relativistic plasmas
52.25.Mq Dielectric properties
52.25.Dg Plasma kinetic equations
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
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Measurements of impulsive reconnection driven by nonlinear Hall dynamics

T. D. Tharp, A. F. Almagri, M. C. Miller, V. V. Mirnov, S. C. Prager, J. S. Sarff, and C. C. Kim

Phys. Plasmas 17, 120701 (2010); http://dx.doi.org/10.1063/1.3521336 (4 pages) | Cited 2 times

Online Publication Date: 10 December 2010

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The magnetic fields associated with reconnection in the edge of the reversed field pinch configuration have been measured in the Madison Symmetric Torus. The measured magnetic field structure is compared with theoretical predictions computed in both toroidal and cylindrical geometries. The summation of multiple modes has been accomplished to reveal a complex but still coherent edge structure. Key terms of relevant Ohm’s law are accessible from magnetic field measurement and reveal the ordering [(1/ne)J×B⪢E>ηJ], which implies that two fluid effects are important in the physics governing this reconnection. Further, it is seen that the nonlinear three-wave coupling of the Hall term acts as a driving mechanism for this linearly stable mode.
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52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Transient growth in stable linearized Vlasov–Maxwell plasmas

J. J. Podesta

Phys. Plasmas 17, 122101 (2010); http://dx.doi.org/10.1063/1.3525092 (9 pages) | Cited 1 time

Online Publication Date: 9 December 2010

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Large amplitude transient growth of kinetic scale perturbations in stable collisionless magnetized plasmas has recently been demonstrated using a linearized Landau fluid model. Initial perturbations with lengthscales of the order of the ion gyroradius were shown to have transient timescales that in some cases were long compared to the ion gyroperiod, Ωit⪢1. Moreover, it was suggested that such perturbations are not rare but instead form a large class within the set of all possible initial conditions. For collisionless plasmas, the Vlasov–Maxwell equations provide a more complete description of kinetic physics and the existence of transient growth of solutions for the linearized Vlasov–Maxwell system is an interesting question. The existence of transient growth of solutions is demonstrated here for a special case of the Vlasov–Maxwell equations, namely, the one dimensional Vlasov–Poisson system. The analysis is different from the standard approach of nonmodal analysis since the initial value problem is described by a Volterra integral equation of the second kind, reflecting the fact that the time evolution of the system depends on the memory of the state from time zero through time t. For the case of a thermal equilibrium plasma, it is shown how initial conditions may be constructed to obtain solutions that grow linearly in time; the duration of this growth is the time required for a thermal electron to traverse the wavelength of the initial perturbation, a timescale that can last for many plasma periods 2π/ωpe, thus demonstrating the existence of transient growth of solutions for the linearized Vlasov–Poisson system. The results suggest that the phenomenon of transient growth may be a common feature of the linearized Vlasov–Maxwell system as well as for Landau fluid models.
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52.40.Mj Particle beam interactions in plasmas
52.65.Ff Fokker-Planck and Vlasov equation
52.25.Tx Emission, absorption, and scattering of particles
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.-y Plasma simulation

Model of electron pressure anisotropy in the electron diffusion region of collisionless magnetic reconnection

A. Divin, S. Markidis, G. Lapenta, V. S. Semenov, N. V. Erkaev, and H. K. Biernat

Phys. Plasmas 17, 122102 (2010); http://dx.doi.org/10.1063/1.3521576 (9 pages) | Cited 2 times

Online Publication Date: 15 December 2010

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A new model of the electron pressure anisotropy in the electron diffusion region in collisionless magnetic reconnection is presented for the case of antiparallel configuration of magnetic fields. The plasma anisotropy is investigated as source of collisionless dissipation. By separating electrons in the vicinity of the neutral line into two broad classes of inflowing and accelerating populations, it is possible to derive a simple closure for the off-diagonal electron pressure component. The appearance of these two electron populations near the neutral line is responsible for the anisotropy and collisionless dissipation in the magnetic reconnection. Particle-in-cell simulations verify the proposed model, confirming first the presence of two particle populations and second the analytical results for the off-diagonal electron pressure component. Furthermore, test-particle calculations are performed to compare our approach with the model of electron pressure anisotropy in the inner electron diffusion region by Fujimoto and Sydora [Phys. Plasmas 16, 112309 (2009)] .
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52.35.Vd Magnetic reconnection
52.65.Rr Particle-in-cell method
94.30.cp Magnetic reconnection

Plasma dispersion function for a Fermi–Dirac distribution

D. B. Melrose and A. Mushtaq

Phys. Plasmas 17, 122103 (2010); http://dx.doi.org/10.1063/1.3528272 (7 pages)

Online Publication Date: 15 December 2010

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A plasma dispersion function (PDF) is defined for a nonrelativistic Fermi–Dirac distribution and its properties are explored. The degree of degeneracy is described by a parameter ξ = eμe/Te, for electrons, with μe/Te large and negative in the nondegenerate limit, and large and positive in the completely degenerate limit. The PDF is denoted Z(y,ξ), where the variable y = ω/mathkVe, is the argument of the conventional PDF, Z(y) = Z(y,0), for a Maxwellian distribution. In the completely degenerate limit, Z(y,ξ) approaches a logarithmic function that depends on the Fermi temperature and is independent of Te. Analytic approximations to Z(y,ξ) are derived in terms of polylogarithmic functions for y2⪢1 and for y2⪡1.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.50.-r Probability theory, stochastic processes, and statistics
52.35.Dm Sound waves

Dynamics of charged particles in spatially chaotic magnetic fields

Abhay K. Ram and Brahmananda Dasgupta

Phys. Plasmas 17, 122104 (2010); http://dx.doi.org/10.1063/1.3529366 (7 pages)

Online Publication Date: 17 December 2010

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The spatial topology of magnetic field lines can be chaotic for fields generated by simple current configurations. This is illustrated for a system consisting of a circular current loop and a straight current wire. An asymmetric configuration of the current system leads to three-dimensional spatially chaotic magnetic fields. The motion of charged particles in these fields is not necessarily chaotic and exhibits intriguing dynamical properties. Particles having initial velocities closely aligned with the direction of the local magnetic field are likely to follow chaotic orbits in phase space. Other particles follow coherent and periodic orbits; these orbits being the same as in the symmetric current configuration for which the field lines are not chaotic. An important feature of particles with chaotic motion is that they undergo spatial transport across magnetic field lines. The cross-field diffusion is of interest in a variety of magnetized plasmas including laboratory and astrophysical plasmas.
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52.20.Dq Particle orbits
52.65.Cc Particle orbit and trajectory

Excitation of surface plasma waves by a density-modulated electron beam in a magnetized plasma cylinder

Ruby Gupta, Suresh C. Sharma, and Ved Prakash

Phys. Plasmas 17, 122105 (2010); http://dx.doi.org/10.1063/1.3528438 (6 pages) | Cited 2 times

Online Publication Date: 21 December 2010

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A density-modulated electron beam propagating through a plasma cylinder excites surface plasma waves (SPWs) via Cerenkov and fast cyclotron interaction. A nonlocal theory of this process has been developed. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The growth rate γ (in rad/s) of the unstable wave instability increases with the modulation index Δ and has the largest value for Δ ∼ 1 in addition to when the frequency and wave number of the modulation are comparable to that of the unstable wave. For Δ = 0, γ turns out to be ∼ 6.06×109 rad/s for Cerenkov interaction and ∼ 5.47×109 rad/s for fast cyclotron interaction. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The real part of the frequency of the unstable wave increases as almost the square root of the beam voltage. The results of the theory are applied to explain some of the experimental observations.
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52.25.Mq Dielectric properties
52.25.Vy Impurities in plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Shear Alfvén wave continuous spectrum within magnetic islands

Alessandro Biancalani, Liu Chen, Francesco Pegoraro, and Fulvio Zonca

Phys. Plasmas 17, 122106 (2010); http://dx.doi.org/10.1063/1.3531689 (8 pages)

Online Publication Date: 30 December 2010

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The radial structure of the continuous spectrum of shear Alfvén waves is calculated in this paper within the separatrix of a magnetic island. Geometrical effects due to the noncircularity of the flux surface’s cross section are retained to all orders. On the other hand, only curvature effects responsible for the beta-induced gap in the low-frequency part of the continuous spectrum are kept. Modes with different helicity from that of the magnetic island are considered. The main result is that, inside a magnetic island, there is a continuous spectrum very similar to that of tokamak plasmas, where a generalized safety factor q can be defined and where a wide frequency gap is formed, analogous to the ellipticity induced Alfvén eigenmode gap in tokamaks. The presence of this gap is due to the strong eccentricity of the island cross section. The importance of the existence of such a gap is recognized in potentially hosting magnetic island induced Alfvén eigenmodes (MiAE). Due to the frequency dependence of the shear Alfvén wave continuum on the magnetic island size, the possibility of utilizing MiAE frequency scalings as a novel magnetic island diagnostic is also discussed.
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52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
back to top Nonlinear Phenomena, Turbulence, Transport

Neoclassical equilibria as starting point for global gyrokinetic microturbulence simulations

T. Vernay, S. Brunner, L. Villard, B. F. McMillan, S. Jolliet, T. M. Tran, A. Bottino, and J. P. Graves

Phys. Plasmas 17, 122301 (2010); http://dx.doi.org/10.1063/1.3519513 (21 pages) | Cited 2 times

Online Publication Date: 1 December 2010

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The implementation of linearized operators describing inter- and like-species collisions in the global gyrokinetic particle-in-cell code ORB5 [ S. Jolliet, Comput. Phys. Commun. 177, 409 (2007) ] is presented. A neoclassical axisymmetric equilibrium with self-consistent electric field can be obtained with no assumption made on the radial width of the particle trajectories. The formulation thus makes it possible to study collisional transport in regions where the neoclassical approximation breaks down such as near the magnetic axis. The numerical model is validated against both analytical results as well as other simulation codes. The effects of the poloidally asymmetric Fourier modes of the electric field are discussed, and the contribution of collisional kinetic electrons is studied. In view of subsequent gyrokinetic simulations of turbulence started from a neoclassical equilibrium, the problem of numerical noise inherent to the particle-in-cell approach is addressed. A novel algorithm for collisional gyrokinetic simulation switching between a local and a canonical Maxwellian background for, respectively, carrying out the collisional and collisionless dynamics is proposed, and its beneficial effects together with a coarse graining procedure [ Y. Chen and S. E. Parker, Phys. Plasmas 14, 082301 (2007) ] on noise and weight spreading reduction are discussed.
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52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.20.-j Elementary processes in plasmas
52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Rr Particle-in-cell method

Acoustic solitons in inhomogeneous pair-ion plasmas

Asif Shah, S. Mahmood, and Q. Haque

Phys. Plasmas 17, 122302 (2010); http://dx.doi.org/10.1063/1.3512937 (7 pages) | Cited 3 times

Online Publication Date: 1 December 2010

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The acoustic solitons are investigated in inhomogeneous unmagnetized pair ion plasmas. The Korteweg–de Vries (KdV) like equation with an additional term due to density gradients is deduced by employing reductive perturbation technique. It is noticed that pair-ion plasma system is conducive for the propagation of compressive as well as rarefactive solitons. The increase in the temperature ratio causes the amplitude of the rarefactive soliton to decrease. However, the amplitude of the compressive solitons is found to be increased as the temperature ratio of ions is enhanced. The amplitude of both compressive and rarefactive solitons is found to be increased as the density gradient parameter is increased. The equlibrium density profile is assumed to be exponential. The numerical results are shown for illustration.
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52.35.Sb Solitons; BGK modes
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.-b Plasma properties

Spatial and temporal evolution of filamentation instability in a current-carrying plasma

B. Mohammadhosseini, A. R. Niknam, and B. Shokri

Phys. Plasmas 17, 122303 (2010); http://dx.doi.org/10.1063/1.3524558 (6 pages) | Cited 2 times

Online Publication Date: 3 December 2010

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The spatial and temporal evolution of the electric and magnetic fields in a current-carrying plasma is investigated in the nonlinear regime. Using the magnetohydrodynamic equations, a nonlinear diffusion equation for the magnetic field in the plasma is obtained. This nonlinear equation is numerically solved and the spatiotemporal evolution of the electric and magnetic fields and the electron density distribution are plotted. It is shown that as the time passes, the profile of the electric and magnetic fields changes from a sinusoidal shape to a saw-tooth one and the electron density distribution becomes very steepened. Also, the mechanism of the filament formation is then discussed. Furthermore, the effects of the thermal motion, collisions, and ion mass on growth rate of filaments as well as the saturation time are argued. Finally, it is found that the energy dissipation is associated with the aforementioned effects and strong plasma density gradient.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Imaging of turbulent structures and tomographic reconstruction of TORPEX plasma emissivity

D. Iraji, I. Furno, A. Fasoli, and C. Theiler

Phys. Plasmas 17, 122304 (2010); http://dx.doi.org/10.1063/1.3523052 (8 pages) | Cited 2 times

Online Publication Date: 8 December 2010

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In the TORPEX [ A. Fasoli et al., Phys. Plasmas 13, 055902 (2006) ], a simple magnetized plasma device, low frequency electrostatic fluctuations associated with interchange waves, are routinely measured by means of extensive sets of Langmuir probes. To complement the electrostatic probe measurements of plasma turbulence and study of plasma structures smaller than the spatial resolution of probes array, a nonperturbative direct imaging system has been developed on TORPEX, including a fast framing Photron-APX-RS camera and an image intensifier unit. From the line-integrated camera images, we compute the poloidal emissivity profile of the plasma by applying a tomographic reconstruction technique using a pixel method and solving an overdetermined set of equations by singular value decomposition. This allows comparing statistical, spectral, and spatial properties of visible light radiation with electrostatic fluctuations. The shape and position of the time-averaged reconstructed plasma emissivity are observed to be similar to those of the ion saturation current profile. In the core plasma, excluding the electron cyclotron and upper hybrid resonant layers, the mean value of the plasma emissivity is observed to vary with (Te)α(ne)β, in which α = 0.25–0.7 and β = 0.8–1.4, in agreement with collisional radiative model. The tomographic reconstruction is applied to the fast camera movie acquired with 50 kframes/s rate and 2 μs of exposure time to obtain the temporal evolutions of the emissivity fluctuations. Conditional average sampling is also applied to visualize and measure sizes of structures associated with the interchange mode. The ω-time and the two-dimensional k-space Fourier analysis of the reconstructed emissivity fluctuations show the same interchange mode that is detected in the ω and k spectra of the ion saturation current fluctuations measured by probes. Small scale turbulent plasma structures can be detected and tracked in the reconstructed emissivity movies with the spatial resolution down to 2 cm, well beyond the spatial resolution of the probe array.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Ra Plasma turbulence

Electron acoustic solitary waves and double layers with superthermal hot electrons

Biswajit Sahu

Phys. Plasmas 17, 122305 (2010); http://dx.doi.org/10.1063/1.3527988 (6 pages) | Cited 11 times

Online Publication Date: 10 December 2010

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The problem of arbitrary amplitude electron acoustic solitary waves (EASWs) are discussed using Sagdeev’s pseudopotential technique for a plasma comprising cold electrons, superthermal hot electrons, and stationary ions. The standard normal-mode analysis is used to study the dispersion relation for linear waves. It is found that the present plasma model supports EASWs having negative potential. The influence of superthermal hot electrons on the present plasma model is investigated for the existence of solitary waves. The investigation shows that the solitary structure ceases to exist when the parameter κ crosses a certain limit. It is also found that the small amplitude double layer solution can exist in such a plasma system in some parametric regions. It is shown that solitary structures and double layers are affected by superthermality, as well as by relevant plasma parameters.
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52.35.Sb Solitons; BGK modes
52.40.Kh Plasma sheaths
52.65.-y Plasma simulation

Generation of wakefields by whistlers in spin quantum magnetoplasmas

A. P. Misra, G. Brodin, M. Marklund, and P. K. Shukla

Phys. Plasmas 17, 122306 (2010); http://dx.doi.org/10.1063/1.3527995 (7 pages) | Cited 7 times

Online Publication Date: 10 December 2010

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The excitation of electrostatic wakefields in a magnetized spin quantum plasma by the classical and the spin-induced ponderomotive force (CPF and SPF, respectively) due to whistler waves is reported. The nonlinear dynamics of the whistlers and the wakefields is shown to be governed by a coupled set of nonlinear Schrödinger and driven Boussinesq-like equations. It is found that the quantum force associated with the Bohm potential introduces two characteristic length scales, which lead to the excitation of multiple wakefields in a strongly magnetized dense plasma (with a typical magnetic field strength B0≳109 T and particle density n0≳1036 m−3), where the SPF strongly dominates over the CPF. In other regimes, namely, B0≲108 T and n0≲1035 m−3, where the SPF is comparable to the CPF, a plasma wakefield can also be excited self-consistently with one characteristic length scale. Numerical results reveal that the wakefield amplitude is enhanced by the quantum tunneling effect; however, it is lowered by the external magnetic field. Under appropriate conditions, the wakefields can maintain high coherence over multiple plasma wavelengths and thereby accelerate electrons to extremely high energies. The results could be useful for particle acceleration at short scales, i.e., at nanometer and micrometer scales, in magnetized dense plasmas where the driver is the whistler wave instead of a laser or a particle beam.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Xz Magnetized plasmas

Gyrokinetic statistical absolute equilibrium and turbulence

Jian-Zhou Zhu (朱建州) and Gregory W. Hammett (哈米特)

Phys. Plasmas 17, 122307 (2010); http://dx.doi.org/10.1063/1.3514141 (13 pages) | Cited 2 times

Online Publication Date: 13 December 2010

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A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence [ T.-D. Lee, Q. Appl. Math. 10, 69 (1952) ] is taken to study gyrokinetic plasma turbulence: a finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N+1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney–Hasegawa–Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
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52.35.Ra Plasma turbulence
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
02.70.Dh Finite-element and Galerkin methods
52.25.Dg Plasma kinetic equations

Formation of large-scale structures in ablative Kelvin–Helmholtz instability

L. F. Wang, W. H. Ye, Wai-Sun Don, Z. M. Sheng, Y. J. Li, and X. T. He

Phys. Plasmas 17, 122308 (2010); http://dx.doi.org/10.1063/1.3524550 (9 pages) | Cited 2 times

Online Publication Date: 15 December 2010

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In this research, we studied numerically nonlinear evolutions of the Kelvin–Helmholtz instability (KHI) with and without thermal conduction, aka, the ablative KHI (AKHI) and the classical KHI (CKHI). The second order thermal conduction term with a variable thermal conductivity coefficient is added to the energy equation in the Euler equations in the AKHI to investigate the effect of thermal conduction on the evolution of large and small scale structures within the shear layer which separate the fluids with different velocities. The inviscid hyperbolic flux of Euler equation is computed via the classical fifth order weighted essentially nonoscillatory finite difference scheme and the temperature is solved by an implicit fourth order finite difference scheme with variable coefficients in the second order parabolic term to avoid severe time step restriction imposed by the stability of the numerical scheme. As opposed to the CKHI, fine scale structures such as the vortical structures are suppressed from forming in the AKHI due to the dissipative nature of the second order thermal conduction term. With a single-mode sinusoidal interface perturbation, the results of simulations show that the growth of higher harmonics is effectively suppressed and the flow is stabilized by the thermal conduction. With a two-mode sinusoidal interface perturbation, the vortex pairing is strengthened by the thermal conduction which would allow the formation of large-scale structures and enhance the mixing of materials. In summary, our numerical studies show that thermal conduction can have strong influence on the nonlinear evolutions of the KHI. Thus, it should be included in applications where thermal conduction plays an important role, such as the formation of large-scale structures in the high energy density physics and astrophysics.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Electron collisions in the trapped gyro-Landau fluid transport model

G. M. Staebler and J. E. Kinsey

Phys. Plasmas 17, 122309 (2010); http://dx.doi.org/10.1063/1.3505308 (10 pages) | Cited 2 times

Online Publication Date: 16 December 2010

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Accurately modeling electron collisions in the trapped gyro-Landau fluid (TGLF) equations has been a major challenge. Insights gained from numerically solving the gyrokinetic equation have lead to a significant improvement of the low order TGLF model. The theoretical motivation and verification of this model with the velocity-space gyrokinetic code GYRO [ J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003) ] will be presented. The improvement in the fidelity of TGLF to GYRO is shown to also lead to better prediction of experimental temperature profiles by TGLF for a dedicated collision frequency scan.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Fi Transport properties
52.35.Kt Drift waves

Electromagnetic effects on toroidal momentum transport

M. Ansar Mahmood, A. Eriksson, and J. Weiland

Phys. Plasmas 17, 122310 (2010); http://dx.doi.org/10.1063/1.3511441 (7 pages) | Cited 3 times

Online Publication Date: 16 December 2010

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A parametric study of electromagnetic effects on toroidal momentum transport has been performed. The work is based on a new version of the Weiland model where symmetry breaking toroidicity effects derived from the stress tensor have been taken into account. The model includes a self-consistent calculation of the toroidal momentum diffusivity, which contains both diagonal and off-diagonal contributions to the momentum flux. It is found that electromagnetic effects considerably increase the toroidal momentum pinch. They are sometimes strong enough to make the total toroidal momentum flux inward.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Fa Tokamaks, spherical tokamaks

Spectroscopic determination of kinetic parameters for frequency sweeping Alfvén eigenmodes

M. Lesur, Y. Idomura, K. Shinohara, X. Garbet, and the JT-60 Team

Phys. Plasmas 17, 122311 (2010); http://dx.doi.org/10.1063/1.3500224 (9 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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A method for analyzing fundamental kinetic plasma parameters, such as linear drive and external damping rate, based on experimental observations of chirping Alfvén eigenmodes, is presented. The method, which relies on new semiempirical laws for nonlinear chirping characteristics, consists of fitting procedures between the so-called Berk–Breizman model and the experiment in a quasiperiodic chirping regime. This approach is applied to the toroidicity induced Alfvén eigenmode (TAE) on JT-60 Upgrade (JT-60U) [ N. Oyama et al., Nucl. Fusion 49, 104007 (2009) ], which yields an estimation of the kinetic parameters and suggests the existence of TAEs far from marginal stability. Two collision models are considered, and it is shown that dynamical friction and velocity-space diffusion are essential to reproduce nonlinear features observed in experiments. The results are validated by recovering measured growth and decay of perturbation amplitude and by estimating collision frequencies from experimental equilibrium data.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Vv Perturbative methods

Modeling of plasma turbulence and transport in the Large Plasma Device

P. Popovich, M. V. Umansky, T. A. Carter, and B. Friedman

Phys. Plasmas 17, 122312 (2010); http://dx.doi.org/10.1063/1.3527987 (11 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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Numerical simulation of plasma turbulence in the Large Plasma Device (LAPD) [ W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991) ] is presented. The model, implemented in the BOUndary Turbulence code [ M. Umansky, X. Xu, B. Dudson et al., Contrib. Plasma Phys. 180, 887 (2009) ], includes three-dimensional (3D) collisional fluid equations for plasma density, electron parallel momentum, and current continuity, and also includes the effects of ion-neutral collisions. In nonlinear simulations using measured LAPD density profiles but assuming constant temperature profile for simplicity, self-consistent evolution of instabilities and nonlinearly generated zonal flows results in a saturated turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good qualitative and reasonable quantitative agreement, in particular in frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. For comparison with LAPD measurements, the plasma density profile in simulations is maintained either by direct azimuthal averaging on each time step, or by adding particle source/sink function. The inferred source/sink values are consistent with the estimated ionization source and parallel losses in LAPD. These simulations lay the groundwork for more a comprehensive effort to test fluid turbulence simulation against LAPD data.
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52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Kt Drift waves
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Ra Plasma turbulence
52.25.Fi Transport properties

On the widespread use of the Corrsin hypothesis in diffusion theories

R. C. Tautz and A. Shalchi

Phys. Plasmas 17, 122313 (2010); http://dx.doi.org/10.1063/1.3530185 (8 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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In the past four decades, several nonlinear theories have been developed to describe (i) the motion of charged test particles through a turbulent magnetized plasma and (ii) the random walk of magnetic field lines. In many such theories, the so-called Corrsin independence hypothesis has been applied to enforce analytical tractability. In this note, it is shown that the Corrsin hypothesis is part of most nonlinear diffusion theories. In some cases, the Corrsin approximation is somewhat hidden, while in other cases a different name is used for the same approach. It is shown that even the researchers who criticized the application of this hypothesis have used it in their nonlinear diffusion theories. It is hoped that the present article will eliminate the recently caused confusion about the applicability and validity of the Corrsin hypothesis.
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52.25.Xz Magnetized plasmas
52.65.-y Plasma simulation
96.50.Tf MHD waves; plasma waves, turbulence

Head-on collision of ion acoustic solitary waves in an electron-positron-ion plasma with superthermal electrons

Prasanta Chatterjee, Uday narayan Ghosh, Kaushik Roy, S. V. Muniandy, C. S. Wong, and Biswajit Sahu

Phys. Plasmas 17, 122314 (2010); http://dx.doi.org/10.1063/1.3528544 (6 pages) | Cited 8 times

Online Publication Date: 21 December 2010

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The head-on collision of ion acoustic solitary waves in a three-component unmagnetized plasma with cold ions, Boltzmann distributed positrons, and superthermal electrons is investigated using the extended Poincaré–Lighthill–Kuo method. The effects of the ratio of electron temperature to positron temperature, the spectral index, κ, of the electron kappa distribution, and fractional concentration of positron component (p) on the phase shift are studied. It is found that the presence of superthermal electrons play a significant role on the collision of ion acoustic solitary waves.
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52.35.Sb Solitons; BGK modes
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.-b Plasma properties
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.27.Cm Multicomponent and negative-ion plasmas

Trapped gyro-Landau-fluid transport modeling of DIII-D hybrid discharges

J. E. Kinsey, G. M. Staebler, and C. C. Petty

Phys. Plasmas 17, 122315 (2010); http://dx.doi.org/10.1063/1.3523058 (12 pages)

Online Publication Date: 22 December 2010

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Previous work has summarized the physics and first results of benchmarking the trapped gyro-Landau-fluid (TGLF) model for turbulent transport driven by trapped ion and electron modes, ion and electron temperature gradient (ETG) modes, and electromagnetic kinetic ballooning modes including the effects of shaped geometry. Recently, an improved collision model was implemented which provides a more accurate fit to a transport database of nonlinear collisional GYRO [ J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003) ] simulations of long wavelength driftwave turbulence. The impact of the new collision model on TGLF modeling results was unknown. Using the improved TGLF model we obtain excellent agreement with the ion and electron temperature profiles from 30 DIII-D [ A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005) ] hybrid discharges. The transport results show that the electron energy transport tends to be dominated by short wavelength ETG modes in cases where the ion energy transport approaches neoclassical levels. The hybrid regime has significant energy confinement improvement from E×B velocity shear which is well predicted by TGLF. Weak magnetic shear and low safety factor are also shown to enhance the hybrid regime energy confinement. In high normalized β hybrids, we find that finite β effects noticably reduce the predicted electron energy transport and improve agreement with the measured electron temperature profiles.
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52.65.-y Plasma simulation
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks

Wavenumber spectrum of whistler turbulence: Particle-in-cell simulation

S. Saito, S. Peter Gary, and Y. Narita

Phys. Plasmas 17, 122316 (2010); http://dx.doi.org/10.1063/1.3526602 (7 pages) | Cited 2 times

Online Publication Date: 28 December 2010

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The forward cascade of decaying whistler turbulence is studied in low beta plasma to understand essential properties of the energy spectrum at electron scales, by using a two-dimensional electromagnetic particle-in-cell (PIC) simulation. This simulation demonstrates turbulence in which the energy cascade rate is greater than the dissipation rate at the electron inertial length. The PIC simulation shows that the magnetic energy spectrum of forward-cascaded whistler turbulence at electron inertial scales is anisotropic and develops a very steep power-law spectrum which is consistent with recent solar wind observations. A comparison of the simulated spectrum with that predicted by a phenomenological turbulence scaling model suggests that the energy cascade at the electron inertial scale depends on both magnetic fluctuations and electron velocity fluctuations, as well as on the whistler dispersion relation. Thus, not only kinetic Alfvén turbulence but also whistler turbulence may explain recent solar wind observations of very steep magnetic spectra at short scales.
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52.35.Ra Plasma turbulence
52.65.Rr Particle-in-cell method
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations

Spatially autoresonant stimulated Raman scattering in inhomogeneous plasmas in the kinetic regime

T. Chapman, S. Hüller, P. E. Masson-Laborde, W. Rozmus, and D. Pesme

Phys. Plasmas 17, 122317 (2010); http://dx.doi.org/10.1063/1.3529362 (8 pages) | Cited 2 times

Online Publication Date: 28 December 2010

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The impact of spatial autoresonance on backward stimulated Raman scattering in inhomogeneous plasmas is investigated in the regime where the dominant nonlinear frequency shift of the Langmuir wave is due to kinetic effects. By numerically solving the coupled mode equations, the spatial growth of the Langmuir wave is observed to self-adjust so as to cancel the detuning from resonance due to inhomogeneity, giving rise to phase-locked solutions to the electron plasma wave equation. For a single resonant point in a linear density profile, the envelope of the electron plasma wave is characterized by a growth that begins at the resonant point and is proportional to the square of distance propagated. In the more physical case where the scattered light is seeded with a broadband noise, autoresonance may lead to a reflectivity well above the level predicted by the usual Rosenbluth gain factor [ M. N. Rosenbluth, Phys. Rev. Lett. 29, 565 (1972) ].
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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