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Jan 2012

Volume 19, Issue 1, Articles (01xxxx)

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Phys. Plasmas 19, 012105 (2012); http://dx.doi.org/10.1063/1.3672516 (8 pages)

A. Lazarian, Gregory L. Eyink, and E. T. Vishniac
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Chorus wave amplification: A free electron laser in the Earth’s magnetosphere

A. R. Soto-Chavez, A. Bhattacharjee, and C. S. Ng

Phys. Plasmas 19, 010701 (2012); http://dx.doi.org/10.1063/1.3676157 (4 pages)

Online Publication Date: 6 January 2012

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A new theoretical model for whistler-mode chorus amplification in the Earth’s magnetosphere is presented. We derive, based on the free-electron laser mechanism in a high-gain amplifier, a new closed set of self-consistent relativistic equations that couple the Hamiltonian equations for particles with Maxwell’s equations. We demonstrate that these equations predict, through a cubic equation, whistler amplification levels in good agreement with those observed in the Earth’s magnetosphere.
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94.80.+g Instrumentation for space plasma physics, ionosphere, and magnetosphere
41.60.Cr Free-electron lasers
52.27.Ny Relativistic plasmas
94.30.Tz Electromagnetic wave propagation
94.30.Xy Radiation belts

A Maxwell formulation for the equations of a plasma

Richard J. Thompson and Trevor M. Moeller

Phys. Plasmas 19, 010702 (2012); http://dx.doi.org/10.1063/1.3675853 (4 pages)

Online Publication Date: 11 January 2012

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In light of the analogy between the structure of electrodynamics and fluid dynamics, the fluid equations of motion may be reformulated as a set of Maxwell equations. This analogy has been explored in the literature for incompressible turbulent flow and compressible flow but has not been widely explored in relation to plasmas. This letter introduces the analogous fluid Maxwell equations and formulates a set of Maxwell equations for a plasma in terms of the species canonical vorticity and its cross product with the species velocity. The form of the source terms is presented and the magnetohydrodynamic (MHD) limit restores the typical variety of MHD waves.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra Plasma turbulence
52.35.We Plasma vorticity
52.65.Kj Magnetohydrodynamic and fluid equation

Particle beam self-modulation instability in tapered and inhomogeneous plasma

C. B. Schroeder, C. Benedetti, E. Esarey, F. J. Grüner, and W. P. Leemans

Phys. Plasmas 19, 010703 (2012); http://dx.doi.org/10.1063/1.3677358 (4 pages)

Online Publication Date: 23 January 2012

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The particle beam self-modulation instability in tapered and inhomogeneous plasmas is analyzed via an evolution equation for the beam radius. For a sufficiently fast taper, the instability is suppressed, and the condition for growth suppression is derived. The form of the taper to phase lock a trailing witness bunch in the plasma wave driven by a self-modulated beam is determined, which can increase the energy gain by several orders of magnitude. Growth of the instability places stringent constraints on the initial background plasma density fluctuations.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Mj Particle beam interactions in plasmas
52.25.Gj Fluctuation and chaos phenomena
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Poynting vector, energy densities, and pressure of collective transverse electromagnetic fluctuations in unmagnetized plasmas

R. Schlickeiser

Phys. Plasmas 19, 012101 (2012); http://dx.doi.org/10.1063/1.3671965 (11 pages)

Online Publication Date: 5 January 2012

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A systematic calculation of the electromagnetic properties (Poynting vector, electromagnetic energy, and pressure) of the collective transverse fluctuations in unmagnetized plasmas with velocity-anisotropic plasma particle distributions functions is presented. Time-averaged electromagnetic properties for monochromatic weakly damped wave-like fluctuations and space-averaged electromagnetic properties for monochromatic weakly propagating and aperiodic fluctuations are calculated. For aperiodic fluctuations, the Poynting vector as well as the sum of the space-averaged electric and magnetic field energy densities vanish. However, aperiodic fluctuations possess a positive pressure given by its magnetic energy density. This finite pressure density pa of aperiodic fluctuations has important consequences for the dynamics of cosmic unmagnetized plasmas such as the intergalactic medium after reionization. Adopting the standard cosmological evolution model, we show that this additional pressure changes the expansion law of the universe leading to further deceleration. Negative vacuum pressure counterbalances this deceleration to an accelerating universe provided that the negative vacuum pressure is greater than 1.5pa, which we estimate to be of the order 2.1 · 10−16 dyn cm−2.
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52.25.Gj Fluctuation and chaos phenomena
52.25.Mq Dielectric properties
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.)
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Adiabatic nonlinear waves with trapped particles. I. General formalism

I. Y. Dodin and N. J. Fisch

Phys. Plasmas 19, 012102 (2012); http://dx.doi.org/10.1063/1.3654030 (9 pages)

Online Publication Date: 6 January 2012

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A Lagrangian formalism is developed for a general nondissipative quasiperiodic nonlinear wave with trapped particles in collisionless plasma. The adiabatic time-averaged Lagrangian density math is expressed in terms of the single-particle oscillation-center Hamiltonians; once those are found, the complete set of geometrical-optics equations is derived without referring to the Maxwell-Vlasov system. The number of trapped particles is assumed fixed; in particular, those may reside close to the bottom of the wave trapping potential, so they never become untrapped. Then their contributions to the wave momentum and the energy flux depend mainly on the trapped-particle density, as an independent parameter, and the phase velocity rather than on the wave amplitude a explicitly; hence, math acquires a-independent terms. Also, the wave action is generally not conserved, because it can be exchanged with resonant oscillations of the trapped-particle density. The corresponding modification of the wave envelope equation is found explicitly and the new action flow velocity is derived. Applications of these results are left to the other two papers of the series, where specific problems are addressed pertaining to properties and dynamics of waves with trapped particles.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.-b Plasma properties
52.30.-q Plasma dynamics and flow
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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Adiabatic nonlinear waves with trapped particles. II. Wave dispersion

I. Y. Dodin and N. J. Fisch

Phys. Plasmas 19, 012103 (2012); http://dx.doi.org/10.1063/1.3662115 (8 pages)

Online Publication Date: 6 January 2012

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A general nonlinear dispersion relation is derived in a nondifferential form for an adiabatic sinusoidal Langmuir wave in collisionless plasma, allowing for an arbitrary distribution of trapped electrons. The linear dielectric function is generalized, and the nonlinear kinetic frequency shift ωNL is found analytically as a function of the wave amplitude a. Smooth distributions yield ωNL∝math, as usual. However, beam-like distributions of trapped electrons result in different power laws, or even a logarithmic nonlinearity, which are derived as asymptotic limits of the same dispersion relation. Such beams are formed whenever the phase velocity changes, because the trapped distribution is in autoresonance and thus evolves differently from the passing distribution. Hence, even adiabatic ωNL(a) is generally nonlocal.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Dg Plasma kinetic equations
52.25.Mq Dielectric properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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Adiabatic nonlinear waves with trapped particles. III. Wave dynamics

I. Y. Dodin and N. J. Fisch

Phys. Plasmas 19, 012104 (2012); http://dx.doi.org/10.1063/1.3673065 (9 pages)

Online Publication Date: 6 January 2012

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The evolution of adiabatic waves with autoresonant trapped particles is described within the Lagrangian model developed in Paper I, under the assumption that the action distribution of these particles is conserved, and, in particular, that their number within each wavelength is a fixed independent parameter of the problem. One-dimensional nonlinear Langmuir waves with deeply trapped electrons are addressed as a paradigmatic example. For a stationary wave, tunneling into overcritical plasma is explained from the standpoint of the action conservation theorem. For a nonstationary wave, qualitatively different regimes are realized depending on the initial parameter S, which is the ratio of the energy flux carried by trapped particles to that carried by passing particles. At S < 1/2, a wave is stable and exhibits group velocity splitting. At S > 1/2, the trapped-particle modulational instability (TPMI) develops, in contrast with the existing theories of the TPMI yet in agreement with the general sideband instability theory. Remarkably, these effects are not captured by the nonlinear Schrödinger equation, which is traditionally considered as a universal model of wave self-action but misses the trapped-particle oscillation-center inertia.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
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.)
52.25.Fi Transport properties

Relation of astrophysical turbulence and magnetic reconnection

A. Lazarian, Gregory L. Eyink, and E. T. Vishniac

Phys. Plasmas 19, 012105 (2012); http://dx.doi.org/10.1063/1.3672516 (8 pages)

Online Publication Date: 11 January 2012

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Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al. [Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.
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52.35.Ra Plasma turbulence
52.35.Vd Magnetic reconnection
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
95.30.Qd Magnetohydrodynamics and plasmas

Ion acoustic solitons in a plasma with two-temperature kappa-distributed electrons

T. K. Baluku and M. A. Hellberg

Phys. Plasmas 19, 012106 (2012); http://dx.doi.org/10.1063/1.3675866 (10 pages)

Online Publication Date: 12 January 2012

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Existence domains and characteristics of ion acoustic solitons are studied in a two-temperature electron plasma with both electron components being kappa-distributed, as found in Saturn’s magnetosphere. As is the case for double-Boltzmann electrons, solitons of both polarities can exist over restricted ranges of fractional hot electron density ratio for this plasma model. Low κ values, which indicate increased suprathermal particles in the tail of the distribution, yield a smaller domain in the parameter space of hot density fraction and normalized soliton velocity (f, M), over which both soliton polarities are supported for a given plasma composition (the coexistence region). For some density ratios that support coexistence, solitons occur even at the lowest (critical) Mach number (i.e., at the acoustic speed), as found recently for a number of other plasma models. Like Maxwellians, low-κ distributions also support positive potential double layers over a narrow range of low fractional cool electron density (<10%).
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94.30.cq MHD waves, plasma waves, and instabilities
95.30.Qd Magnetohydrodynamics and plasmas
96.30.Mh Saturn
96.50.Tf MHD waves; plasma waves, turbulence
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
94.05.Fg Solitons and solitary waves

Effect of ionization distribution on the low frequency oscillations mode in Hall thrusters

Wei Liqiu, Wang Chunsheng, Han Ke, and Yu Daren

Phys. Plasmas 19, 012107 (2012); http://dx.doi.org/10.1063/1.3676160 (6 pages)

Online Publication Date: 12 January 2012

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It is found that the discharge parameters have notable effects on the mode of discharge current low frequency oscillation in Hall thrusters, but different discharge parameters might form the similar low frequency oscillation mode. In order to study the mechanism of oscillation mode formation, the ionization distribution in the discharge channel was measured experimentally, and one-dimensional quasi-neutrality hydrodynamic model was used to study the relationship between ionization distribution and the oscillation mode. Researches show that the low frequency oscillation with a narrow and condensed ionization distribution has the mode of lower amplitude and scattered frequency. The low frequency oscillation amplitude would become high and have dominative frequency component with the relative wide ionization distribution. Therefore, it can be concluded that the difference of ionization distribution characteristics is the main reason of the oscillation mode variation, and discharge parameters are only the external control parameters of ionization distribution characteristics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.77.-j Plasma applications
52.80.-s Electric discharges
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

A comprehensive study of different gases in inductively coupled plasma torch operating at one atmosphere

Sangeeta B. Punjabi, N. K. Joshi, H. A. Mangalvedekar, B. K. Lande, A. K. Das, and D. C. Kothari

Phys. Plasmas 19, 012108 (2012); http://dx.doi.org/10.1063/1.3676598 (12 pages)

Online Publication Date: 19 January 2012

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A numerical study is done to understand the possible operating regimes of RF-ICP torch (3 MHz, 50 kW) using different gases for plasma formation at atmospheric pressure. A two dimensional numerical simulation of RF-ICP torch using argon, nitrogen, oxygen, and air as plasma gas has been investigated using computational fluid dynamic (CFD) software fluent©. The operating parameters varied here are central gas flow, sheath gas flow, RF-power dissipated in plasma, and plasma gas. The temperature contours, flow field, axial, and radial velocity profiles were investigated under different operating conditions. The plasma resistance, inductance of the torch, and the heat distribution for various plasma gases have also been investigated. The plasma impedance of ICP torch varies with different operating parameters and plays an important role for RF oscillator design and power coupling. These studies will be useful to decide the design criteria for ICP torches required for different material processing applications.
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52.75.Hn Plasma torches
02.60.-x Numerical approximation and analysis
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.40.Kh Plasma sheaths
52.65.-y Plasma simulation

Stimulated Raman scattering coupled to decay instability in a plasma channel

Ranjeet Singh and V. K. Tripathi

Phys. Plasmas 19, 012109 (2012); http://dx.doi.org/10.1063/1.3675851 (9 pages)

Online Publication Date: 20 January 2012

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A non local theory of Stimulated Raman scattering (SRS) coupled to decay instability in a plasma channel is developed. The primary Langmuir wave, produced in the Raman backscattering process, decays into a secondary Langmuir wave of longer wavelength and an ion acoustic wave. This diversion of energy, along with linear Landau damping of the primary Langmuir wave, slows down the Raman process. The nonlocal effects cause further reduction in the growth rate.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Effect of guide field on lower-hybrid drift instabilities in current sheet containing energetic particles

Feng Huang, Yinhua Chen, Yibao Li, and M. Y. Yu

Phys. Plasmas 19, 012110 (2012); http://dx.doi.org/10.1063/1.3676599 (5 pages)

Online Publication Date: 20 January 2012

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The effect of a guide field on the linear lower-hybrid drift instability (LHDI) in a thin current sheet containing energetic particles is investigated using kinetic theory. It is found that the symmetry properties of the LHD modes are destroyed by the guide field. The LHDI growth rate decreases with the strength of the latter, and the perturbed magnetic field is much higher than that of the guide-field free case.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Minimum energy states of the cylindrical plasma pinch in single-fluid and Hall magnetohydrodynamics

I. V. Khalzov, F. Ebrahimi, D. D. Schnack, and V. V. Mirnov

Phys. Plasmas 19, 012111 (2012); http://dx.doi.org/10.1063/1.3676600 (13 pages)

Online Publication Date: 20 January 2012

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Relaxed states of a plasma column are found analytically in single-fluid and Hall magnetohydrodynamics (MHD). We perform complete minimization of the energy with constraints imposed by invariants inherent in the corresponding models. It is shown that the relaxed state in Hall MHD is a force-free magnetic field with uniform axial flow and/or rigid azimuthal rotation. In contrast, the relaxed states in single-fluid MHD are more complex due to the coupling between velocity and magnetic field. Cylindrically and helically symmetric relaxed states are considered for both models. Helical states may be time dependent and analogous to helical waves, propagating on a cylindrically symmetric background. Application of our results to reversed-field pinches (RFP) is discussed. The radial profile of the parallel momentum predicted by the single-fluid MHD relaxation theory is shown to be in reasonable agreement with experimental observation from the Madison symmetric torus RFP experiment.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Fi Transport properties

Landau damping of a driven plasma wave from laser pulses

Zhigang Bu and Peiyong Ji

Phys. Plasmas 19, 012112 (2012); http://dx.doi.org/10.1063/1.3676612 (6 pages)

Online Publication Date: 20 January 2012

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The interaction between a laser pulse and a driven plasma wave with a phase velocity approaching the speed of light is studied, and our investigation is focused on the Gaussian laser pulse. It is demonstrated that when the resonance condition between the plasma wave and the laser pulse is satisfied, the Landau damping phenomenon of the plasma wave originated from the laser pulse will emerge. The dispersion relations for the plasma waves in resonance and non-resonance regions are obtained. It is proved that the Landau damping rate for a driven plasma wave is γ>0 in the resonance region, so the laser pulse can produce an inverse damping effect, namely Landau growth effect, which leads an instability for the plasma wave. The Landau growth means that the energy is transmitted from the laser pulse to the plasma wave, which could be an effective process for enhancing the plasma wave.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.Fi Transport properties

The effect of q-distributed electrons on the head-on collision of ion acoustic solitary waves

Uday Narayan Ghosh, Prasanta Chatterjee, and Rajkumar Roychoudhury

Phys. Plasmas 19, 012113 (2012); http://dx.doi.org/10.1063/1.3675603 (6 pages)

Online Publication Date: 23 January 2012

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The head-on collision of ion acoustic solitary waves (IASWs) in two component plasma comprising nonextensive distributed electrons is investigated. Two opposite directional Kortewg-de-vries (KdV) equations are derived and the phase shift due to collision is obtained using the extended version of Poincaré-Lighthill-Kuo method. Different ranges of nonextensive parameter q are considered and their effects on phase shifts are observed. It is found that the presence of nonextensive distributed electrons plays a significant role on the nature of collision of ion acoustic solitary waves.
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52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes

Effect of dust charging and trapped electrons on nonlinear solitary structures in an inhomogeneous magnetized plasma

Ravinder Kumar, Hitendra K. Malik, and Khushvant Singh

Phys. Plasmas 19, 012114 (2012); http://dx.doi.org/10.1063/1.3671959 (8 pages)

Online Publication Date: 23 January 2012

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Main concerns of the present article are to investigate the effects of dust charging and trapped electrons on the solitary structures evolved in an inhomogeneous magnetized plasma. Such a plasma is found to support two types of waves, namely, fast wave and slow wave. Slow wave propagates in the plasma only when the wave propagation angle θ satisfies the condition θ ≥ tan-1{math}, where v0(u0) is the z- (x-) component of ion drift velocity, σ = Ti/Teff, ndlh = nd0/(nel0 + neh0), and γ1 = -math[math] together with Ti as ion temperature, nel0(neh0) as the density of trapped (isothermal) electrons, Φi0 as the dust grain (density nd0) surface potential relative to zero plasma potential, and Teff = (nelo+neho)TelTeh/(neloTeh+nehoTel), where Tel(Teh) is the temperature of trapped (isothermal) electrons. Both the waves evolve in the form of density hill type structures in the plasma, confirming that these solitary structures are compressive in nature. These structures are found to attain higher amplitude when the charge on the dust grains is fluctuated (in comparison with the case of fixed charge) and also when the dust grains and trapped electrons are more in number; the same is the case with higher temperature of ions and electrons. Slow solitary structures show weak dependence on the dust concentration. Both types of structures are found to become narrower under the application of stronger magnetic field. With regard to the charging of dust grains, it is observed that the charge gets reduced for the higher trapped electron density and temperature of ions and electrons, and dust charging shows weak dependence on the ion temperature.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Sb Solitons; BGK modes
52.25.Xz Magnetized plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Collisionless distribution function for the relativistic force-free Harris sheet

C. R. Stark and T. Neukirch

Phys. Plasmas 19, 012115 (2012); http://dx.doi.org/10.1063/1.3677268 (7 pages)

Online Publication Date: 23 January 2012

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A self-consistent collisionless distribution function for the relativistic analogue of the force-free Harris sheet is presented. This distribution function is the relativistic generalization of the distribution function for the non-relativistic collisionless force-free Harris sheet recently found by Harrison and Neukirch [Phys. Rev. Lett. 102, 135003 (2009)], as it has the same dependence on the particle energy and canonical momenta. We present a detailed calculation which shows that the proposed distribution function generates the required current density profile (and thus magnetic field profile) in a frame of reference in which the electric potential vanishes identically. The connection between the parameters of the distribution function and the macroscopic parameters such as the current sheet thickness is discussed.
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52.27.Ny Relativistic plasmas
52.55.-s Magnetic confinement and equilibrium
52.65.Ff Fokker-Planck and Vlasov equation
52.20.-j Elementary processes in plasmas
52.25.Kn Thermodynamics of plasmas

Sheared-flow induced confinement transition in a linear magnetized plasma

S. Zhou, W. W. Heidbrink, H. Boehmer, R. McWilliams, T. A. Carter, S. Vincena, B. Friedman, and D. Schaffner

Phys. Plasmas 19, 012116 (2012); http://dx.doi.org/10.1063/1.3677361 (12 pages) | Cited 1 time

Online Publication Date: 23 January 2012

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A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn/n~eδφ/kTe~0.5) are observed at the plasma edge, accompanied by a large density gradient (Ln = |∇lnn|-1~2cm) and shearing rate (γ~300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (Vbias) on the obstacle and the axial magnetic field (Bz) strength. In cases with low Vbias and large Bz, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E×B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller Bz, large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m = 1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.-y Plasma simulation
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Propagation of nonlinear coherent structures in a collisional magnetoplasma with nonthermal electrons and finite ion temperature

W. Masood, H. Rizvi, and N. Imtiaz

Phys. Plasmas 19, 012117 (2012); http://dx.doi.org/10.1063/1.3677775 (6 pages)

Online Publication Date: 24 January 2012

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Nonlinear electrostatic waves in dissipative magnetized electron-ion (e-i) plasmas are investigated employing the two fluid model. In this regard, Zakharov Kuznetsov Burgers (ZKB) equation is derived using the small amplitude perturbation expansion method. It is observed that the nonthermal electron population, obliqueness, ion thermal effects, and kinematic viscosity significantly alter the structure of obliquely propagating nonlinear ion acoustic shock waves in dissipative e-i magnetoplasmas. It is observed that the system can admit both compressive and rarefactive shocks. The condition for the formation of both types of shocks is also given. The present study may be useful to understand the nonlinear propagation characteristics of electrostatic shock structures in space environments where the nonthermal electrons have been observed by various satellite missions such as Voyager and Freja.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Tc Shock waves and discontinuities
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Observation of electron plasma waves inside large amplitude electromagnetic pulses in a temporally growing plasma

Shail Pandey, Sudeep Bhattacharjee, and Debaprasad Sahu

Phys. Plasmas 19, 012118 (2012); http://dx.doi.org/10.1063/1.3677363 (8 pages)

Online Publication Date: 26 January 2012

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Observation of electron plasma waves excited inside high power (∼10 kW) short pulse (∼20 μs) electromagnetic (em) waves interacting with a gaseous medium (argon) in the pressure range 0.2–2.5 mTorr is reported. The waves have long wavelength (∼13 cm) and get damped at time scales slower (∼3 μs) than the plasma period (0.1–0.3 μs), the energy conveyed to the medium lead to intense ionization (ion density ni ∼ 1011 cm−3 and electron temperature Te ∼ 6–8 eV) and rapid growth of the plasma (∼105 s−1) beyond the waves. Time frequency analysis of the generated oscillations indicate the presence of two principal frequencies centered around 3.8 MHz and 13.0 MHz with a spread Δf ∼ 4 MHz, representing primarily two population of electrons in the plasma wave. The experimental results are in reasonable agreement with a model that considers spatiotemporal forces of the em wave on the medium, space charges and diffusion.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Two dimensional nonplanar evolution of electrostatic shock waves in pair-ion plasmas

W. Masood and H. Rizvi

Phys. Plasmas 19, 012119 (2012); http://dx.doi.org/10.1063/1.3677779 (8 pages)

Online Publication Date: 26 January 2012

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Electrostatic waves in a two dimensional nonplanar geometry are studied in an unmagnetized, dissipative pair-ion plasma in the presence of weak transverse perturbations. The dissipation in the system is taken into account by incorporating the kinematic viscosity of both positive and negative ions in plasmas. The nonplanar Kadomtsev-Petviashvili-Burgers (KPB) as well as the Burgers Kadomtsev-Petviashvili (Burgers KP) equations are derived using the small amplitude expansion method and the range of applicability of both the equations are discussed. The system under consideration is observed to admit compressive rarefactive shocks. The present study may have relevance to understand the formation of two dimensional nonplanar electrostatic shocks in laboratory plasmas.
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52.35.Tc Shock waves and discontinuities
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
02.30.Jr Partial differential equations

Numerical investigation of the ion temperature effect in magnetized plasma sheath with two species of positive ions

A. K. Shaw, S. Kar, K. S. Goswami, and B. J. Saikia

Phys. Plasmas 19, 012120 (2012); http://dx.doi.org/10.1063/1.3678199 (7 pages)

Online Publication Date: 26 January 2012

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The effect of ion temperature, magnitude of magnetic field and its orientation on a magnetized plasma sheath consisting of electrons and two species of positive ions are investigated. Using three-fluid hydrodynamic model and some dimensionless variables, the dimensionless equations are obtained and solved numerically. It is found that with the increase of the ion temperature and magnetic field strength there is a significant change in ion densities and energies in the sheath. It is also noticed that increase of magnetic field angle enhances the ion density near the sheath edge for a constant ion temperature. With increase in ion temperature and magnetic field angle, the lighter ion density near the sheath edge enhances and reverses for the heavier ion species.
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52.40.Kh Plasma sheaths
02.60.-x Numerical approximation and analysis
52.25.Xz Magnetized plasmas

Magnetized and collimated millimeter scale plasma jets with astrophysical relevance

Parrish C. Brady, Hernan J. Quevedo, Prashant M. Valanju, Roger D. Bengtson, and Todd Ditmire

Phys. Plasmas 19, 012121 (2012); http://dx.doi.org/10.1063/1.3671953 (8 pages)

Online Publication Date: 31 January 2012

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Magnetized collimated plasma jets are created in the laboratory to extend our understanding of plasma jet acceleration and collimation mechanisms with particular connection to astrophysical jets. In this study, plasma collimated jets are formed from supersonic unmagnetized flows, mimicking a stellar wind, subject to currents and magnetohydrodynamic forces. It is found that an external poloidal magnetic field, like the ones found anchored to accretion disks, is essential to stabilize the jets against current-driven instabilities. The maximum jet length before instabilities develop is proportional to the field strength and the length threshold agrees well with Kruskal-Shafranov theory. The plasma evolution is modeled qualitatively using MHD theory of current-carrying flux tubes showing that jet acceleration and collimation arise as a result of electromagnetic forces.
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95.30.Qd Magnetohydrodynamics and plasmas
52.25.Fi Transport properties
52.72.+v Laboratory studies of space- and astrophysical-plasma processes
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Xz Magnetized plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
back to top Nonlinear Phenomena, Turbulence, Transport

Symmetry breaking effects of density gradient on parallel momentum transport: A new ρs* effect

Rameswar Singh, R. Singh, P. Kaw, Ö. D. Gürcan, P. H. Diamond, and H. Nordman

Phys. Plasmas 19, 012301 (2012); http://dx.doi.org/10.1063/1.3672518 (10 pages)

Online Publication Date: 6 January 2012

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See Also: Publisher's Note

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Symmetry breaking effects of density gradient on parallel momentum transport is studied via quasilinear theory. It is shown that finite ρs*( ≡ ρs/Ln), where ρs is ion sound radius and Ln is density scale length, leads to symmetry breaking of the ion temperature gradient (ITG) eigenfunction. This broken symmetry persists even in the absence of mean poloidal (from radial electric field shear) and toroidal flows. This effect, as explained in the text, originates from the divergence of polarization particle current in the ion continuity equation. The form of the eigenfunction allows the microturbulence to generate parallel residual stress via 〈k‖〉 symmetry breaking. Comparison with the math×math shear driven parallel residual stress, parallel polarization stress and turbulence intensity gradient driven parallel residual stress are discussed. It is shown that this ρs* driven parallel residual stress may become comparable to math×math shear driven parallel residual stress in small Ln region. In the regular drift wave ordering, where ρs*≪1, this effect is found to be of the same order as the parallel polarization stress. This ρs* driven parallel residual stress can also overtake the turbulence intensity gradient driven parallel residual stress in strong density gradient region whereas the later one is dominant in the strong profile curvature region. The parallel momentum diffusivity is found to remain undisturbed by this ρs* effect as long as the turbulence intensity inhomogenity is not important.
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52.25.Fi Transport properties
52.35.Kt Drift waves
52.35.Ra Plasma turbulence
02.10.Ud Linear algebra
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