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Dec 2012

Volume 19, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 19, 122305 (2012); http://dx.doi.org/10.1063/1.4769029 (11 pages)

T. Tatsuno (龍野 智哉), G. G. Plunk, M. Barnes, W. Dorland, G. G. Howes, and R. Numata (沼田 龍介)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Gas breakdown driven by L band short-pulse high-power microwave

Yi-Ming Yang (杨一明), Cheng-Wei Yuan (袁成卫), and Bao-Liang Qian (钱宝良)

Phys. Plasmas 19, 122101 (2012); http://dx.doi.org/10.1063/1.4768220 (5 pages)

Online Publication Date: 4 December 2012

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High power microwave (HPM) driven gas breakdown is a major factor in limiting the radiation and transmission of HPM. A method that HPM driven gas breakdown could be obtained by changing the aperture of horn antenna is studied in this paper. Changing the effective aperture of horn antenna can adjust the electric field in near field zone, leading to gas breakdown. With this method, measurements of air and SF6 breakdowns are carried out on a magnetically insulated transmission-line oscillators, which is capable of generating HPM with pulse duration of 30 ns, and frequency of 1.74 GHz. The typical breakdown waveforms of air and SF6 are presented. Besides, the breakdown field strengths of the two gases are derived at different pressures. It is found that the effects of air and SF6 breakdown on the transmission of HPM are different: air breakdown mainly shortens the pulse width of HPM while SF6 breakdown mainly reduces the peak output power of HPM. The electric field threshold of SF6 is about 2.4 times larger than that of air. These differences suggest that gas properties have a great effect on the transmission characteristic of HPM in gases.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.Pi High-frequency and RF discharges
52.70.Gw Radio-frequency and microwave measurements

Magnetic instability in a dilute circular rarefaction wave

M. E. Dieckmann, G. Sarri, and M. Borghesi

Phys. Plasmas 19, 122102 (2012); http://dx.doi.org/10.1063/1.4769128 (7 pages)

Online Publication Date: 4 December 2012

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The growth of magnetic fields in the density gradient of a rarefaction wave has been observed in simulations and in laboratory experiments. The thermal anisotropy of the electrons, which gives rise to the magnetic instability, is maintained by the ambipolar electric field. This simple mechanism could be important for the magnetic field amplification in astrophysical jets or in the interstellar medium ahead of supernova remnant shocks. The acceleration of protons and the generation of a magnetic field by the rarefaction wave, which is fed by an expanding circular plasma cloud, is examined here in form of a 2D particle-in-cell simulation. The core of the plasma cloud is modeled by immobile charges, and the mobile protons form a small ring close to the cloud's surface. The number density of mobile protons is thus less than that of the electrons. The protons of the rarefaction wave are accelerated to 1/10 of the electron thermal speed, and the acceleration results in a thermal anisotropy of the electron distribution in the entire plasma cloud. The instability in the rarefaction wave is outrun by a TM wave, which grows in the dense core distribution, and its magnetic field expands into the rarefaction wave. This expansion drives a secondary TE wave.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.Rr Particle-in-cell method

Photonic band gaps in one-dimensional magnetized plasma photonic crystals with arbitrary magnetic declination

Hai-Feng Zhang, Shao-Bin Liu, and Xiang-Kun Kong

Phys. Plasmas 19, 122103 (2012); http://dx.doi.org/10.1063/1.4766474 (13 pages) | Cited 3 times

Online Publication Date: 4 December 2012

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In this paper, the properties of photonic band gaps and dispersion relations of one-dimensional magnetized plasma photonic crystals composed of dielectric and magnetized plasma layers with arbitrary magnetic declination are theoretically investigated for TM polarized wave based on transfer matrix method. As TM wave propagates in one-dimensional magnetized plasma photonic crystals, the electromagnetic wave can be divided into two modes due to the influence of Lorentz force. The equations for effective dielectric functions of such two modes are theoretically deduced, and the transfer matrix equation and dispersion relations for TM wave are calculated. The influences of relative dielectric constant, plasma collision frequency, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency on transmission, and dispersion relation are investigated, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that plasma collision frequency cannot change the locations of photonic band gaps for both modes, and also does not affect the reflection and transmission magnitudes. The characteristics of photonic band gaps for both modes can be obviously tuned by relative dielectric constant, incidence angle, plasma filling factor, the angle between external magnetic field and +z axis, external magnetic field and plasma frequency, respectively. These results would provide theoretical instructions for designing filters, microcavities, and fibers, etc.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
02.10.Yn Matrix theory
02.60.-x Numerical approximation and analysis
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Mq Dielectric properties

Global gyrokinetic particle-in-cell simulations of internal kink instabilities

Alexey Mishchenko and Alessandro Zocco

Phys. Plasmas 19, 122104 (2012); http://dx.doi.org/10.1063/1.4769379 (9 pages)

Online Publication Date: 5 December 2012

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Internal kink instabilities have been studied in straight tokamak geometry employing an electromagnetic gyrokinetic particle-in-cell (PIC) code. The ideal-MHD internal kink mode and the collisionless m = 1 tearing mode have been successfully simulated with the PIC code. Diamagnetic effects on the internal kink modes have also been investigated.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.65.Rr Particle-in-cell method
52.65.Tt Gyrofluid and gyrokinetic simulations

Effect of viscosity and shear flow on the nonlinear two fluid interfacial structures

Rahul Banerjee, Labakanta Mandal, M. Khan, and M. R. Gupta

Phys. Plasmas 19, 122105 (2012); http://dx.doi.org/10.1063/1.4769728 (6 pages)

Online Publication Date: 6 December 2012

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A nonlinear formulation is presented to deal with the combined action of Rayleigh-Taylor and Kelvin-Helmholtz instabilities as well as combined Ricthmyer-Meshkov and Kelvin-Helmholtz instabilities at the two fluid interface under the influence of viscosity and consequent shear flow. Using Layzer's model, the development of the interfacial structures like bubbles is investigated analytically and numerically. It is found that the growth and normal velocity of the structures are dependent on the relative velocity shear and the kinematic coefficient of viscosity of both the fluids. Both the bubble growth and growth rate are reduced significantly for fluids of higher viscosity coefficient with small velocity shear difference. It is also observed that, for viscous fluids, the transverse velocity of the perturbed interface becomes slower under certain conditions.
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47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
47.55.dd Bubble dynamics
83.60.Fg Shear rate dependent viscosity

Study of second harmonic generation by high power laser beam in magneto plasma

Prerana Sharma and R. P. Sharma

Phys. Plasmas 19, 122106 (2012); http://dx.doi.org/10.1063/1.4759014 (10 pages)

Online Publication Date: 11 December 2012

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This paper examines the problem of nonlinear generation of second harmonic of a high power laser pulse propagating in magnetized plasma. The propagation of strong laser beam is proposed in the direction perpendicular to a relatively weak static magnetic field. The laser pulse is taken to be linearly polarized, with the orientation of its electric field that corresponds to an ordinary electromagnetic wave. Besides the standard ponderomotive nonlinearity, the appropriate wave equation also contains the nonlinearity that arises from the relativistic electron jitter velocities. During its propagation, the laser beam gets filamented on account of relativistic and pondermotive nonlinearities present in the plasma. The generated plasma wave gets coupled into the filamentary structures of the pump beam. Due to the expected presence of the beam filamentation, the work has been carried out by considering modified paraxial approximation (i.e., beyond the standard paraxial approximation of a very broad beam). It is found that the power of the plasma wave is significantly affected by the magnetic field strength in the presence of both relativistic and pondermotive nonlinearities. It is investigated that the second harmonic generation is also considerably modified by altering the strength of magnetic field. To see the effect of static magnetic field on the harmonic generation, a key parameter, i.e., the ratio of the cyclotron frequency ωc = eB0/mc over the laser frequency ω0 has been used, where c is the velocity of light, m and e are the mass and charge of the electron and B0 is the externally applied magnetic field.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Modulation instability of an intense laser beam in the hot magnetized electron-positron plasma in the quasi-neutral limit

N. Sepehri Javan

Phys. Plasmas 19, 122107 (2012); http://dx.doi.org/10.1063/1.4771596 (7 pages) | Cited 1 time

Online Publication Date: 13 December 2012

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The aim of the present study is to investigate the problem of modulation instability of an intense laser beam in the hot magnetized electron-positron plasma. Propagation of the intense circularly polarized laser beam along the external magnetic field is studied using a relativistic fluid model. A nonlinear equation describing the interaction of the laser pulse with the magnetized hot pair plasma is derived based on the quasi-neutral approximation, which is valid for the hot plasma. Also, the nonlinear dispersion equation for the hot plasma is obtained. The growth rate of the instability is calculated and its dependence on temperature and external magnetic field are considered.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.38.Kd Laser-plasma acceleration of electrons and ions
02.30.Hq Ordinary differential equations
52.25.Xz Magnetized plasmas
52.27.Ny Relativistic plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Spontaneous electromagnetic fluctuations in unmagnetized plasmas. III. Generalized Kappa distributions

M. Lazar, P. H. Yoon, and R. Schlickeiser

Phys. Plasmas 19, 122108 (2012); http://dx.doi.org/10.1063/1.4769308 (8 pages) | Cited 1 time

Online Publication Date: 17 December 2012

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In the first two papers of this series, the general expressions for the spontaneous fluctuations spectra (electric and magnetic field, charge and current densities) from uncorrelated plasma particles are derived and illustrated for a Maxwellian (relativistic or nonrelativistic) plasma close to thermal equilibrium. In this paper, the results are illustrated for the nonideal case of a plasma out of thermal equilibrium and described by the generalized Kappa (power-law) particle distribution function in the nonrelativistic limit. The suprathermal fluctuations of weakly amplified modes and aperiodic modes are provided. Thus, it is shown for the first time the existing finite level of noncollective fluctuations, which are particularly important in the context of plasma fluctuations (collective or noncollective) as the best agent in the energy dissipation and transfer to suprathermal populations. The results obtained in the first paper for an equilibrium plasma are recovered only in the limit of a very large power index κ→∞.
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52.25.Gj Fluctuation and chaos phenomena
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties

Electron temperature anisotropy instabilities represented by superposition of streams

A. Inglebert, A. Ghizzo, T. Reveille, P. Bertrand, and F. Califano

Phys. Plasmas 19, 122109 (2012); http://dx.doi.org/10.1063/1.4772770 (12 pages)

Online Publication Date: 19 December 2012

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The generation of magnetic field, together with the electrostatic activity met in the saturation regime of the Weibel instability (WI), is investigated by means of an analytical multi-stream model in a Hamiltonian framework. Taking advantage from the invariance of the generalized canonical momentum, the model allows to reduce the full kinetic 1D2V Vlasov equation into several 1D1V equations while keeping its kinetic character. The multi-stream model provides a more complete and accurate picture of the Weibel instability, because it is possible to separate the specific contribution of each stream during the development of the Weibel instability. An interesting result for the multi-stream mode is a lower cost in the perpendicular treatment of the py momentum component since no differential operator associated with some approximate numerical scheme has to be carried out on this variable. Indeed, a small number of streams or particle classes are sufficient to correctly describe the magnetic field generation and the mixed electrostatic- electromagnetic nature of the instability.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Ff Fokker-Planck and Vlasov equation
52.25.Dg Plasma kinetic equations

Power loss of an oscillating electric dipole in a quantum plasma

L. Ghaderipoor and A. Mehramiz

Phys. Plasmas 19, 122110 (2012); http://dx.doi.org/10.1063/1.4769034 (5 pages)

Online Publication Date: 19 December 2012

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A system of linearized quantum plasma equations (quantum hydrodynamic model) has been used for investigating the dispersion equation for electrostatic waves in the plasma. Furthermore, dispersion relations and their modifications due to quantum effects are used for calculating the power loss of an oscillating electric dipole. Finally, the results are compared in quantum and classical regimes.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.-y Plasma simulation
02.10.-v Logic, set theory, and algebra

A computational approach to continuum damping of Alfvén waves in two and three-dimensional geometry

Axel Könies and Ralf Kleiber

Phys. Plasmas 19, 122111 (2012); http://dx.doi.org/10.1063/1.4769115 (8 pages)

Online Publication Date: 19 December 2012

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While the usual way of calculating continuum damping of global Alfvén modes is the introduction of a small artificial resistivity, we present a computational approach to the problem based on a suitable path of integration in the complex plane. This approach is implemented by the Riccati shooting method and it is shown that it can be transferred to the Galerkin method used in three-dimensional ideal magneto-hydrodynamics (MHD) codes. The new approach turns out to be less expensive with respect to resolution and computation time than the usual one. We present an application to large aspect ratio tokamak and stellarator equilibria retaining a few Fourier harmonics only and calculate eigenfunctions and continuum damping rates. These may serve as an input for kinetic MHD hybrid models making it possible to bypass the problem of having singularities on the path of integration on one hand and considering continuum damping on the other.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Kj Magnetohydrodynamic and fluid equation
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Tn Ideal and resistive MHD modes; kinetic modes

The stability and the growth rate of the electron acoustic traveling wave under transverse perturbations in a magnetized quantum plasma

Dong-Ning Gao, Cang-Long Wang, Xue Yang, Wen-Shan Duan, and Lei Yang

Phys. Plasmas 19, 122112 (2012); http://dx.doi.org/10.1063/1.4773216 (5 pages)

Online Publication Date: 26 December 2012

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Theoretical and numerical studies are carried out for the stability of the electron acoustic waves under the transverse perturbation in a magnetized quantum plasma. The Zakharov-Kuznetsov (ZK) equation of the electron-acoustic waves (EAWs) is given by using the reductive perturbation technique. The cut-off frequency is obtained by applying a transverse sinusoidal perturbation to the plane soliton solution of the ZK equation. The propagation velocity of solitary waves, the real cut-off frequency, as well as the growth rate of the higher order perturbation to the traveling solitary wave are obtained.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
52.65.Vv Perturbative methods
52.25.Xz Magnetized plasmas

Nonlocal theory of electromagnetic wave decay into two electromagnetic waves in a rippled density plasma channel

Priti Sati and V. K. Tripathi

Phys. Plasmas 19, 122113 (2012); http://dx.doi.org/10.1063/1.4773029 (5 pages)

Online Publication Date: 27 December 2012

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Parametric decay of a large amplitude electromagnetic wave into two electromagnetic modes in a rippled density plasma channel is investigated. The channel is taken to possess step density profile besides a density ripple of axial wave vector. The density ripple accounts for the momentum mismatch between the interacting waves and facilitates nonlinear coupling. For a given pump wave frequency, the requisite ripple wave number varies only a little w.r.t. the frequency of the low frequency decay wave. The radial localization of electromagnetic wave reduces the growth rate of the parametric instability. The growth rate decreases with the frequency of low frequency electromagnetic wave.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
94.20.Fg Plasma temperature and density
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Group velocity of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects

Chunhua Li, Zhengwei Wu, Haijun Ren, Weihong Yang, and Paul K. Chu

Phys. Plasmas 19, 122114 (2012); http://dx.doi.org/10.1063/1.4773046 (7 pages)

Online Publication Date: 27 December 2012

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Based on the one component plasma model, a new dispersion relation and group velocity of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The group velocity of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.
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52.25.Fi Transport properties
52.25.Xz Magnetized plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
95.30.Qd Magnetohydrodynamics and plasmas

The modulational instability in the extended Hasegawa-Mima equation with a finite Larmor radius

S. Gallagher, B. Hnat, C. Connaughton, S. Nazarenko, and G. Rowlands

Phys. Plasmas 19, 122115 (2012); http://dx.doi.org/10.1063/1.4773050 (10 pages)

Online Publication Date: 27 December 2012

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The effects of the finite Larmor radius on the generation of zonal flows by the four-wave modulational instability are investigated using an extended form of the Hasegawa-Mima equation. Growth rates of the zonal mode are quantified using analytical predictions from a four-mode truncated model, as well as from direct numerical simulation of the nonlinear extended Hasegawa-Mima equation. We not only consider purely zonal flows but also examine the generic oblique case and show that, for small Larmor radii, off-axis modes may become dominant. We find a key parameter Mρ which characterises the behaviour of the system due to changes in the Larmor radius. We find that, similarly to previous results obtained by changing the driving wave amplitude, two separate dynamical regimes can be accessed. These correspond to oscillatory energy transfer between zonal flows and a driving wave and the fully saturated zonal flow.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Development of high-power gyrotrons with gradually tapered cavity

Lei Chaojun, Yu Sheng, Niu Xinjian, Liu Yinghui, Li Hongfu, and Li Xiang

Phys. Plasmas 19, 122116 (2012); http://dx.doi.org/10.1063/1.4773290 (6 pages)

Online Publication Date: 27 December 2012

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In high power gyrotrons, the parasitic modes coupled with the operating mode cannot be avoided in the beam-wave interaction. These parasitic modes will decrease the efficiency of the gyrotrons. The purity of the operating mode affected by different tapers should be carefully studied. The steady-state self-consistent nonlinear theory for gyrotron with gradually tapered cavity is developed in this paper. A steady-state calculation code including “cold cavity” and “hot cavity” is designed. By comparison, a time-domain model analysis of gyrotron operation is also studied by particle-in-cell (PIC). It is found that the tapers of gyrotron have different influences on the modes coupling between the operating mode and the parasitic modes. During the study, an example of 94 GHz gyrotron with pure operating mode TE03 has been designed. The purity of the operating mode in the optimized cavity is up to −77 dB, and in output waveguide of the cavity is up to −76 dB. At the same time, the beam-wave interaction in the designed cavity has been simulated, too. An output power of 120 kW, corresponding to 41.6% efficiency and an oscillation frequency of 94.099 GHz have been achieved with a 50 kV, 6 A helical electron beam at a guiding magnetic field of 3.5485 T. The results show that the power in spurious modes of the optimized cavity may be kept far below than that of the traditional tapered cavity.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Mj Particle beam interactions in plasmas
52.65.Rr Particle-in-cell method
back to top Nonlinear Phenomena, Turbulence, Transport

Existence domains of arbitrary amplitude nonlinear structures in two-electron temperature space plasmas. II. High-frequency electron-acoustic solitons

S. K. Maharaj, R. Bharuthram, S. V. Singh, and G. S. Lakhina

Phys. Plasmas 19, 122301 (2012); http://dx.doi.org/10.1063/1.4769174 (9 pages)

Online Publication Date: 5 December 2012

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A three-component plasma model composed of ions, cool electrons, and hot electrons is adopted to investigate the existence of large amplitude electron-acoustic solitons not only for the model for which inertia and pressure are retained for all plasma species which are assumed to be adiabatic but also neglecting inertial effects of the hot electrons. Using the Sagdeev potential formalism, the Mach number ranges supporting the existence of large amplitude electron-acoustic solitons are presented. The limitations on the attainable amplitudes of electron-acoustic solitons having negative potentials are attributed to a number of different physical reasons, such as the number density of either the cool electrons or hot electrons ceases to be real valued beyond the upper Mach number limit, or, alternatively, a negative potential double layer occurs. Electron-acoustic solitons having positive potentials are found to be supported only if inertial effects of the hot electrons are retained and these are found to be limited only by positive potential double layers.
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52.35.Sb Solitons; BGK modes
52.25.Fi Transport properties
52.27.Cm Multicomponent and negative-ion plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.-y Plasma simulation
52.40.Kh Plasma sheaths

On physical interpretation of two dimensional time-correlations regarding time delay velocities and eddy shaping

N. Fedorczak, P. Manz, S. C. Thakur, M. Xu, G. R. Tynan, G. S. Xu, and S. C. Liu

Phys. Plasmas 19, 122302 (2012); http://dx.doi.org/10.1063/1.4769849 (9 pages)

Online Publication Date: 6 December 2012

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Time delay estimation (TDE) techniques are frequently used to estimate the flow velocity from fluctuating measurements. Tilted structures carried by the flow lead to misinterpretation of the time delays in terms of velocity direction and amplitude. It affects TDE measurements from probes, and is also intrinsically important for beam emission spectroscopy and gas puff imaging measurements. Local eddy shapes estimated from 2D fluctuating field are necessary to gain a more accurate flow estimate from TDE, as illustrated by Langmuir probe array measurements. A least square regression approach is proposed to estimate both flow field and shaping parameters. The technique is applied to a test case built from numerical simulation of interchange fluctuations. The local eddy shape does not only provide corrections for the velocity field but also quantitative information about the statistical interaction mechanisms between local eddies and E×B flow shear. The technique is then tested on gaz puff imaging data collected at the edge of EAST tokamak plasmas. It is shown that poloidal asymmetries of the fluctuation fields—velocity and eddy shape—are consistent at least qualitatively with a ballooning type of turbulence immersed in a radially sheared equilibrium flow.
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52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation

Plasma turbulence driven by transversely large-scale standing shear Alfvén waves

Nagendra Singh and Sathyanarayan Rao

Phys. Plasmas 19, 122303 (2012); http://dx.doi.org/10.1063/1.4769851 (9 pages)

Online Publication Date: 6 December 2012

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Using two-dimensional particle-in-cell simulations, we study generation of turbulence consisting of transversely small-scale dispersive Alfvén and electrostatic waves when plasma is driven by a large-scale standing shear Alfvén wave (LS-SAW). The standing wave is set up by reflecting a propagating LS-SAW. The ponderomotive force of the standing wave generates transversely large-scale density modifications consisting of density cavities and enhancements. The drifts of the charged particles driven by the ponderomotive force and those directly caused by the fields of the standing LS-SAW generate non-thermal features in the plasma. Parametric instabilities driven by the inherent plasma nonlinearities associated with the LS-SAW in combination with the non-thermal features generate small-scale electromagnetic and electrostatic waves, yielding a broad frequency spectrum ranging from below the source frequency of the LS-SAW to ion cyclotron and lower hybrid frequencies and beyond. The power spectrum of the turbulence has peaks at distinct perpendicular wave numbers (k⊥) lying in the range de−1-6de−1, de being the electron inertial length, suggesting non-local parametric decay from small to large k⊥. The turbulence spectrum encompassing both electromagnetic and electrostatic fluctuations is also broadband in parallel wave number (k||). In a standing-wave supported density cavity, the ratio of the perpendicular electric to magnetic field amplitude is R(k⊥) = |E⊥(k⊥)/|B⊥(k⊥)| ≪ VA for k⊥de < 0.5, where VA is the Alfvén velocity. The characteristic features of the broadband plasma turbulence are compared with those available from satellite observations in space plasmas.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Ra Plasma turbulence
52.65.Rr Particle-in-cell method
52.25.-b Plasma properties

Magnetic turbulence suppression by a helical mode in a cylindrical geometry

J.-H. Kim and P. W. Terry

Phys. Plasmas 19, 122304 (2012); http://dx.doi.org/10.1063/1.4769369 (11 pages) | Cited 1 time

Online Publication Date: 7 December 2012

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To study processes involved in a helical structure formation in reversed field pinch devices, the scaling of a turbulent boundary layer width associated with a vortex structure having large shears of magnetic field and flow is obtained for reduced magnetohydrodynamics. The coherent vortex, with its flow and magnetic shears, interacts with Alfvén turbulence, forming a turbulent boundary layer at the edge of the vortex. The layer arises from the balance between turbulence diffusion rates and shearing rates and suppresses the turbulence in the structure. The suppression of turbulence impedes relaxation of the coherent vortex profiles, leading to long coherence times. The scaling of the boundary layer width reveals that both magnetic shear and flow shear can effectively suppress magnetic turbulence.
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52.35.Ra Plasma turbulence
52.35.We Plasma vorticity
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Ez Theta pinch
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
FREE

Freely decaying turbulence in two-dimensional electrostatic gyrokinetics

T. Tatsuno (龍野 智哉), G. G. Plunk, M. Barnes, W. Dorland, G. G. Howes, and R. Numata (沼田 龍介)

Phys. Plasmas 19, 122305 (2012); http://dx.doi.org/10.1063/1.4769029 (11 pages)

Online Publication Date: 11 December 2012

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In magnetized plasmas, a turbulent cascade occurs in phase space at scales smaller than the thermal Larmor radius (“sub-Larmor scales”) [Tatsuno et al., Phys. Rev. Lett. 103, 015003 (2009)]. When the turbulence is restricted to two spatial dimensions perpendicular to the background magnetic field, two independent cascades may take place simultaneously because of the presence of two collisionless invariants. In the present work, freely decaying turbulence of two-dimensional electrostatic gyrokinetics is investigated by means of phenomenological theory and direct numerical simulations. A dual cascade (forward and inverse cascades) is observed in velocity space as well as in position space, which we diagnose by means of nonlinear transfer functions for the collisionless invariants. We find that the turbulence tends to a time-asymptotic state, dominated by a single scale that grows in time. A theory of this asymptotic state is derived in the form of decay laws. Each case that we study falls into one of three regimes (weakly collisional, marginal, and strongly collisional), determined by a dimensionless number D*, a quantity analogous to the Reynolds number. The marginal state is marked by a critical number D* = D0 that is preserved in time. Turbulence initialized above this value become increasingly inertial in time, evolving toward larger and larger D*; turbulence initialized below D0 become more and more collisional, decaying to progressively smaller D*.
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52.35.Ra Plasma turbulence
52.65.Tt Gyrofluid and gyrokinetic simulations
02.60.Cb Numerical simulation; solution of equations
52.25.Xz Magnetized plasmas
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.)

Gyrokinetic studies of the effect of β on drift-wave stability in the National Compact Stellarator Experiment

J. A. Baumgaertel, G. W. Hammett, D. R. Mikkelsen, M. Nunami, and P. Xanthopoulos

Phys. Plasmas 19, 122306 (2012); http://dx.doi.org/10.1063/1.4771587 (9 pages) | Cited 1 time

Online Publication Date: 12 December 2012

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The gyrokinetic turbulence code GS2 was used to investigate the effects of plasma β on linear, collisionless ion temperature gradient (ITG) modes and trapped electron modes (TEM) in National Compact Stellarator Experiment (NCSX) geometry. Plasma β affects stability in two ways: through the equilibrium and through magnetic fluctuations. The first was studied here by comparing ITG and TEM stability in two NCSX equilibria of differing β values, revealing that the high β equilibrium was marginally more stable than the low β equilibrium in the adiabatic-electron ITG mode case. However, the high β case had a lower kinetic-electron ITG mode critical gradient. Electrostatic and electromagnetic ITG and TEM mode growth rate dependencies on temperature gradient and density gradient were qualitatively similar. The second β effect is demonstrated via electromagnetic ITG growth rates' dependency on GS2's β input parameter. A linear benchmark with gyrokinetic codes GENE and GKV-X is also presented.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Jd Magnetic mirrors, gas dynamic traps
52.65.Tt Gyrofluid and gyrokinetic simulations
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Kt Drift waves

Boundary conditions for plasma fluid models at the magnetic presheath entrance

J. Loizu, P. Ricci, F. D. Halpern, and S. Jolliet

Phys. Plasmas 19, 122307 (2012); http://dx.doi.org/10.1063/1.4771573 (10 pages) | Cited 1 time

Online Publication Date: 13 December 2012

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The proper boundary conditions at the magnetic presheath entrance for plasma fluid turbulence models based on the drift approximation are derived, focusing on a weakly collisional plasma sheath with Ti≪Te and a magnetic field oblique to a totally absorbing wall. First, the location of the magnetic presheath entrance is rigorously derived. Then boundary conditions at the magnetic presheath entrance are analytically deduced for v||i, v||e, n, ϕ, Te, and for the vorticity ω = ∇⊥2ϕ. The effects of E × B and diamagnetic drifts on the boundary conditions are also investigated. Kinetic simulations are performed that confirm the analytical results. Finally, the new set of boundary conditions is implemented in a three-dimensional global fluid code for the simulation of plasma turbulence and, as an example, the results of a tokamak scrape-off layer simulation are discussed. The framework presented can be generalized to obtain boundary conditions at the magnetic presheath entrance in more complex scenarios.
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52.40.Kh Plasma sheaths
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Ra Plasma turbulence

Low frequency solitons and double layers in a magnetized plasma with two temperature electrons

O. R. Rufai, R. Bharuthram, S. V. Singh, and G. S. Lakhina

Phys. Plasmas 19, 122308 (2012); http://dx.doi.org/10.1063/1.4771574 (5 pages)

Online Publication Date: 14 December 2012

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Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.
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52.35.Sb Solitons; BGK modes
94.05.Fg Solitons and solitary waves
94.20.Ac Auroral ionosphere
94.20.wf Plasma waves and instabilities
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Reactive and internal contributions to the thermal conductivity of local thermodynamic equilibrium nitrogen plasma: The effect of electronically excited states

D. Bruno, G. Colonna, A. Laricchiuta, and M. Capitelli

Phys. Plasmas 19, 122309 (2012); http://dx.doi.org/10.1063/1.4771689 (8 pages) | Cited 1 time

Online Publication Date: 17 December 2012

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Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n> 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.
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52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
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