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Jan 2008

Volume 15, Issue 1, Articles (01xxxx)

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Phys. Plasmas 15, 013109 (2008); http://dx.doi.org/10.1063/1.2825663 (15 pages)

L. Yin, B. J. Albright, K. J. Bowers, W. Daughton, and H. A. Rose
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back to top Basic Plasma Phenomena, Waves, Instabilities

Neutrino induced charge in a superdense two-electron Fermi plasma

L. A. Rios and P. K. Shukla

Phys. Plasmas 15, 012101 (2008); http://dx.doi.org/10.1063/1.2826438 (5 pages) | Cited 5 times

Online Publication Date: 2 January 2008

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Using plasma physics methods, the effective neutrino charge in a superdense two-electron Fermi plasma is determined. The Fermi plasma has distinct groups of hot and cold electrons. Accounting for the quantum statistical pressure for the hot electron component and the quantum force associated with the quantum Bohm potential, the neutrino induced charge produced by the neutrino driving force is estimated. The influence of the quantum-mechanical effects on the neutrino effective electric charge has been investigated.
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52.40.-w Plasma interactions (nonlaser)

Growth of resistive instabilities in E×B plasma discharge simulations

E. Fernandez, M. K. Scharfe, C. A. Thomas, N. Gascon, and M. A. Cappelli

Phys. Plasmas 15, 012102 (2008); http://dx.doi.org/10.1063/1.2823033 (10 pages) | Cited 7 times

Online Publication Date: 8 January 2008

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Two-dimensional hybrid numerical simulations of E×B discharges used in Hall thruster propulsion point to the presence of strong fluctuations attributable to resistive instabilities in the frequency range of f ≈ 0.1–10 MHz and the wavenumber range of λ−1 ≈ 10–500 m−1. Analytical analyses confirm that these resistive modes are of the convective type, become increasingly unstable at low electron mobility, and are particularly intense at high voltage. The simulations, which model cross-field electron flow via an experimentally measured mobility, exhibit large fluctuation power in a region corresponding to a strong electron transport barrier. The analysis gives an electron mobility (μe) -dependent growth rate (γ) scaling as γ ∼ μe−1/2. The predicted phase velocity of these waves is close to the ion velocity, somewhat lower than that seen in the simulations. Including the electron pressure contribution lowers the growth rate at high frequencies, and introduces a phase velocity that is shifted by ± the ion acoustic speed for the stable and unstable branch, respectively. Surprisingly, the phase velocity of the strong disturbances at high frequency seen in the simulations is found to be in agreement with that of the initially stable branch. Finite ionization/particle wall recombination does not change the overall conclusions at high frequencies. However, at lower f or larger λ, the growth rate of the instability is dominated by the ionization rate, and the disturbances are better described as “ionization” instabilities. The transition/competition between ionization, electron pressure, and resistive behavior gives rise to a “quiescent frequency band” where the growth rate is found to be small, consistent with what is seen in the numerical experiments. While simple linear analysis captures much of the observed simulation behavior, comparison with limited experimental data at low frequency suggests that other effects, in particular azimuthal dynamics, are very important, and further motivate extending the hybrid simulation models to three dimensions.
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52.80.-s Electric discharges
52.65.-y Plasma simulation
52.25.Fi Transport properties

Spectral gap of shear Alfvén waves in a periodic array of magnetic mirrors

Yang Zhang, W. W. Heidbrink, H. Boehmer, R. McWilliams, Guangye Chen, B. N. Breizman, S. Vincena, T. Carter, D. Leneman, W. Gekelman, P. Pribyl, and B. Brugman

Phys. Plasmas 15, 012103 (2008); http://dx.doi.org/10.1063/1.2827518 (14 pages) | Cited 12 times

Online Publication Date: 8 January 2008

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A multiple magnetic mirror array is formed at the Large Plasma Device (LAPD) [ W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991) ] to study axial periodicity-influenced Alfvén spectra. Shear Alfvén waves (SAW) are launched by antennas inserted in the LAPD plasma and diagnosed by B-dot probes at many axial locations. Alfvén wave spectral gaps and continua are formed similar to wave propagation in other periodic media due to the Bragg effect. The measured width of the propagation gap increases with the modulation amplitude as predicted by the solutions to Mathieu’s equation. A two-dimensional finite-difference code modeling SAW in a mirror array configuration shows similar spectral features. Machine end-reflection conditions and damping mechanisms including electron-ion Coulomb collision and electron Landau damping are important for simulation.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.70.-m Plasma diagnostic techniques and instrumentation
52.75.-d Plasma devices

Ions motion effects on the full unstable spectrum in relativistic electron beam plasma interaction

A. Bret and M. E. Dieckmann

Phys. Plasmas 15, 012104 (2008); http://dx.doi.org/10.1063/1.2828607 (13 pages) | Cited 7 times

Online Publication Date: 9 January 2008

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A relativistic fluid model is implemented to assess the role of the ions motion in the linear phase of relativistic beam plasma electromagnetic instabilities. The all unstable wave vector spectrum is investigated, allowing us to assess how ion motions modify the competition between every possible instability. Beam densities up to the plasma one are considered. Due to the fluid approach, the temperatures must remain small, i.e., nonrelativistic. In the cold limit, ions motion affect the most unstable mode when the beam gamma factor γb≳αM/mZi, α being the beam to plasma density ratio, Zi the ion charge, M their mass, and m the electrons. The return current plays an important role by prompting Buneman-type instabilities which remain in the nonrelativistic regime up to high beam densities. Nonrelativistic temperatures only slightly affect these conclusions, except in the diluted beam regime where they can stabilize the Buneman modes.
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52.40.Mj Particle beam interactions in plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Jm Ionization of plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.27.Ny Relativistic plasmas

Drift mode in a bounded plasma having two-ion species

Ali Ahmad, M. Sajid, and H. Saleem

Phys. Plasmas 15, 012105 (2008); http://dx.doi.org/10.1063/1.2826440 (6 pages) | Cited 3 times

Online Publication Date: 10 January 2008

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The drift wave is investigated in a two-ion species plasma in several different cases. The global drift mode is studied in a plasma bounded in a cylinder having Gaussian density profile corresponding to different poloidal wavenumbers. The frequency of the mode becomes a little larger when it is investigated without including the ion cyclotron wave dynamics. The effect of magnetic shear on the wave propagation along the density gradient is studied in a Cartesian geometry assuming absorbing boundary. It is found that the wave amplitude is reduced when two-ion species are present (with the same concentration) compared to pure electron-ion plasma.
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52.25.-b Plasma properties
52.35.Kt Drift waves
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.27.Cm Multicomponent and negative-ion plasmas

Creation of finely focused particle beams from single-component plasmas

T. R. Weber, J. R. Danielson, and C. M. Surko

Phys. Plasmas 15, 012106 (2008); http://dx.doi.org/10.1063/1.2817967 (10 pages) | Cited 5 times

Online Publication Date: 16 January 2008

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In a recent communication [ Danielson et al., Appl. Phys. Lett. 90, 081503 (2007) ], a nondestructive technique was described to create finely focused beams of electron-mass, charged particles (i.e., electrons or positrons) from single-component plasmas confined in a Penning–Malmberg trap. This paper amplifies and expands upon those results, providing a more complete study of this method of beam formation. A simple model for beam extraction is presented, and an expression for a Gaussian beam profile is derived when the number of extracted beam particles is small. This expression gives a minimum beam diameter of four Debye lengths (full width to 1/e) and is verified using electron plasmas over a broad range of plasma temperatures and densities. Numerical procedures are outlined to predict the profiles of beams with large numbers of extracted particles. Measured profiles of large beams are found in fair agreement with these predictions. The extraction of over 50% of a trapped plasma into a train of nearly identical beams is demonstrated. Applications and extensions of this technique to create state-of-the-art positron beams are discussed.
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52.27.Jt Nonneutral plasmas
41.75.Fr Electron and positron beams
07.77.Ka Charged-particle beam sources and detectors

Self-gravitational instability of rotating anisotropic heat-conducting plasma

R. P. Prajapati, A. K. Parihar, and R. K. Chhajlani

Phys. Plasmas 15, 012107 (2008); http://dx.doi.org/10.1063/1.2828074 (8 pages) | Cited 4 times

Online Publication Date: 18 January 2008

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The self-gravitational instability of rotating anisotropic heat-conducting plasma with modified Chew–Goldberger–Low equations is investigated. The general dispersion relation is obtained using normal mode analysis by constructing the linearized set of equations. This dispersion relation is further reduced for propagation parallel and perpendicular to the direction of magnetic field. These conditions are discussed for axis of rotation along and perpendicular to the magnetic field. It is found that the heat flux vector does not influence the transverse mode of propagation for both cases of rotation and Jeans condition remains unchanged. In case of propagation parallel to the magnetic field with axis of rotation perpendicular to the magnetic field, we get the dispersion relation, which shows the joint effect of rotation and heat flux vector. The two separate modes of propagation are obtained in terms of rotation and heat flux vector for rotation parallel to the magnetic field. It is demonstrated that the Alfvén wave and the associated firehose instability are not affected by the presence of heat flux corrections and rotation also. The numerical analysis is performed to show the effect of rotation, pressure anisotropy, and heat flux parameter on the condition of instability in the spiral arms of galaxy. The Jeans condition of gravitational instability is obtained for both the cases of propagation.
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95.30.Qd Magnetohydrodynamics and plasmas
98.58.-w Interstellar medium (ISM) and nebulae in external galaxies
98.62.-g Characteristics and properties of external galaxies and extragalactic objects

Nonlinear filamentation of a current-carrying plasma

A. R. Niknam and B. Shokri

Phys. Plasmas 15, 012108 (2008); http://dx.doi.org/10.1063/1.2833595 (4 pages) | Cited 7 times

Online Publication Date: 22 January 2008

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The nonlinear filamentation in a nonrelativistic collisional current-carrying plasma in the diffusion frequency region is investigated. It is shown that by using the two-fluid plasma equations and Ampere’s law and assuming that the plasma is nonisothermal and inhomogeneous, the spatial evolution of the magnetic field in a plasma is described by the Lienard nonlinear differential equation. Also, it is shown that a transverse filamentation and density steepening can occur in the static limit. Furthermore, the profiles of magnetic field and the electron density variation have a nonsinusoidal shape in the nonlinear regime. Moreover it is shown that the shape of the transverse filamentation varies due to the nonlinear effect in the static limit.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
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.)

Debye-shielding potential in the presence of pair correlations

Anirban Bose and M. S. Janaki

Phys. Plasmas 15, 012109 (2008); http://dx.doi.org/10.1063/1.2832682 (5 pages)

Online Publication Date: 24 January 2008

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The first-order kinetic equation of the Bogoliubov–Born–Green–Kirkwood–Yvon hierarchy of equations for an equilibrium inhomogeneous plasma is shown to contain an effective force resulting from pair correlations that depends on the gradient of the average electric field modulus. Such a kinetic equation is utilized to obtain a Boltzmann distribution that includes the effects of correlations. For an electron-ion plasma with stationary ions and finite electron-electron correlations, the nature of the Debye-screening potential is investigated.
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52.25.Dg Plasma kinetic equations
05.20.-y Classical statistical mechanics

Quantum effects on Rayleigh–Taylor instability in magnetized plasma

Jintao Cao, Haijun Ren, Zhengwei Wu, and Paul K. Chu

Phys. Plasmas 15, 012110 (2008); http://dx.doi.org/10.1063/1.2833588 (6 pages) | Cited 10 times

Online Publication Date: 24 January 2008

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The effects of the quantum mechanism and magnetic field on Rayleigh–Taylor (RT) instability in an ideal incompressible plasma are investigated. The explicit expression of the linear growth rate is obtained in the presence of fixed boundary conditions. It is shown that the magnetic field has a stabilizing effect on RT instability similar to the behavior in classical plasmas and RT instability is affected significantly by quantum effects. Quantum effects are also shown to suppress RT instability with the appropriate physical quantities. Some astrophysical parameters are discussed as an example to investigate the new effects.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

The instabilities induced by electrostatic fields and gradients in a plasma shock front

Yong He, Xiwei Hu, Zhonghe Jiang, and Jianhong Lü

Phys. Plasmas 15, 012111 (2008); http://dx.doi.org/10.1063/1.2834726 (4 pages) | Cited 2 times

Online Publication Date: 29 January 2008

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The linear instabilities induced by the electrostatic fields and gradients of equilibrium parameters in a plasma shock front are analyzed for the plasma shock structure. Small perturbations as well as the steady-state shock structure are described by a set of coupled two-fluid and Poisson equations. The dispersion relations are obtained at high frequency in two cases, in which the wave vectors are, respectively, parallel and perpendicular to the shock propagation direction. The imaginary parts of the frequency (growth rates) of the instabilities are dependent on the fields and the gradients.
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52.35.Tc Shock waves and discontinuities
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

On the magnetohydrodynamic load and the magnetohydrodynamic metage

Sagar Chakraborty and Partha Guha

Phys. Plasmas 15, 012112 (2008); http://dx.doi.org/10.1063/1.2836617 (7 pages)

Online Publication Date: 30 January 2008

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In analogy with the load and the metage in hydrodynamics, this paper defines magnetohydrodynamic load and magnetohydrodynamic metage in the case of magnetofluids. They can be used to write the magnetic field in MHD in Clebsch’s form. It has been shown herein how these two concepts can be utilized to derive the magnetic analog of the Ertel’s theorem and also, how in the presence of nontrivial topology of the magnetic field in the magnetofluid one may associate the linking number of the magnetic field lines with the invariant MHD loads. The paper illustrates that the symmetry translation of the MHD metage in the corresponding label space generates the conservation of cross helicity.
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47.65.Cb Magnetic fluids and ferrofluids
75.50.Mm Magnetic liquids

Nonresonant power transfer in plasma-surface interactions via two-surface wave decay

Yu. A. Akimov and K. Ostrikov

Phys. Plasmas 15, 012113 (2008); http://dx.doi.org/10.1063/1.2836621 (7 pages)

Online Publication Date: 31 January 2008

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The excitation of pairs of electron surface waves via nonresonant decay of plasma waves incident onto a solid surface is studied in the context of controlling the interaction of pulsed electromagnetic radiation with plasma-exposed solid surfaces. The role of the plasma-exposed surfaces in nonlinear heating of the plasma edge and related power transfer is discussed. It is shown that the maximum efficiency of the power transfer at solid surfaces with dielectric permittivity εd<3 corresponds to the resonant two-surface wave decay. On the other hand, for solids with εd>3 the maximum power transfer efficiency is achieved through nonresonant excitation of the quasistatic surface waves. In this case the plasma waves generated by external radiation dissipate their energy into the plasma periphery most effectively.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.50.-b Plasma production and heating
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