bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulated Brillouin scattering of an electromagnetic wave in a magnetoactive dissipative multi-ion-species plasma
Authors: Bose M.
Published: March 2009

Stimulated Brillouin scattering of an electromagnetic wave is investigated analytically in a dissipative magnetized plasma in the presence of negative ions. With an increase in the number of negative ions (maintaining quasi-neutrality), it is found that the growth rate of ion-acoustic waves decreases very slowly up to 50% concentration (i.e. half of the total ionic contribution) of negative ions. Further increase in the number density of negative ions beyond 50% results in a sharp fall in growth rate.
Solitary waves in an ion-beam-plasma system
Authors: Nakamura Y. , Ohtani K.
Published: March 2009

Solitary waves in an ion-beam-plasma system are investigated theoretically using the pseudo-potential method, including finite temperatures of plasma ions and beam ions. The beam velocity is high enough to avoid ion-ion instability. Three kinds of solitary waves are possible, corresponding to ion- acoustic waves and to fast and slow space-charge waves in the beam. To observe the formation of solitary waves from an initial positive pulse, numerical simulations are performed. For the slow beam mode, a smaller solitary wave appears at the leading part of the pulse, which is a result of negative nonlinearity and anomalous dispersion of the slow mode, and is the opposite behaviour to the cases of the ion-acoustic wave and to the fast beam mode. Overtaking collisions of a solitary wave with a fast-mode solitary wave or with a slow-mode solitary wave are simulated.
Toroidal currents and radial transport driven by ponderomotive forces of fluctuations in a plasma
Authors: Petržílka V. , Balescu B.
Published: March 2009

Non-resonant ponderomotive force theory is applied to fluctuating electromagnetic fields in a plasma. Bootstrap-type relations between the radial transport velocity and the toroidal current driven by fluctuations are also discussed in the case of non-zero ponderomotive forces proportional to d/dr. A special case of fluctuating fields as measured in the SHEILA heliac is discussed.
Microscopic origins and macroscopic uses of plasma rotation
Authors: Montgomery David , Shan Xiaowen
Published: March 2009

We consider the microscopic sources of toroidal and poloidal flow in confined magnetoplasmas and the effects of such flows on macroscopic stability. The central difficulty is satisfactory modelling of kinetic theory effects so as to permit their robust introduction into magnetohydrodynamic (MHD) codes. It is tentatively concluded that poloidal rotation, but not toroidal, is responsible for the computed stabilization and return to axisymmetry.
Macroscopic electric fields driven by lower-hybrid turbulence and acceleration of thermal electrons in the foot of quasi-perpendicular shocks
Authors: Galeev A. A. , Malkov M. A. , Völk H. J.
Published: March 2009

A new mechanism is suggested that draws non-resonant thermal electrons into a higher-velocity range, where they can be effectively accelerated by waves. We argue that the acceleration of a small number of pre-existing resonant particles influences the dynamics of the bulk plasma and results in a macroscopic electric field. The solution for the spatial dependence of this electric field is obtained, and it appears to be a new type of electrostatic shock, which forms only in the presence of background turbulence. This field enriches the region of resonant particles with thermal electrons, which leads to a build-up of an excess of accelerated particles. The number of accelerated particles is calculated. This mechanism appears as a good candidate to explain electron acceleration in the foot of quasi-perpendicular shocks.
Non-stationary resonant Alfvén surface waves in one-dimensional magnetic plasmas
Authors: Ruderman M. S. , Tirry W. , Goossens M.
Published: March 2009

This paper uses incompressible visco-resistive MHD to study the propagation of linear resonant waves in an inhomogeneous plasma. The background density and magnetic field are assumed to depend only on one spartial Cartesian coordinate, and the magnetic field is taken to be unidirectional and perpendicular to the direction of inhomogeneity. The equation that governs the component of the velocity normal to the plane formed by the direction of the inhomogeneity and the magnetic field is derived under the assumption that the coefficients of viscosity and resistivity are sufficiently small that dissipation of energy is confined to a narrow dissipative layer. The solutions to this equation are obtained in the form of decaying normal surface modes with wavelengths much larger than the characteristic scale of the inhomogeneity. The effect of non-stationarity inside the dissipative layer is taken into account, and valid solutions are found even when the ratio of the thickness of the dissipative layer to the inhomogeneity length scale is of the order of or smaller than the ratio of the inhoinogeneity length scale to the wavelength. These solutions are the generalization of the solutions obtained by Mok and Einaudi, which are only valid when the first ratio is much larger than the second. The rate of wave damping is shown to be independent of the values of the viscosity and the resistivity. However, the behaviour of the solutions in the dissipative layer depends strongly on the viscosity and the resistivity. In the case that the effect of dissipation dominates the effect of non-stationarity, the solutions behave in the dissipative layer as found by Mok and Einaudi. When the effect of dissipation is steadily decreased in comparison with the effect of nonstationarity, the solutions become more and more oscillatory, and their amplitudes grow very rapidly in the dissipative layer. Eventually, when nonstationarity dominates dissipation, the amplitudes of the solutions become so large in the dissipative layer in comparison with those outside the dissipative layer that practically all the energy of the perturbations is concentrated in the dissipative layer.
Dynamics of collisional particles in a fluctuating magnetic field
Authors: Spineanu F. , Vlad M.
Published: March 2009

The equations of motion of a test particle in a stochastic magnetic field and interacting through collisions with a plasma are Langevin-type equations. Under reasonable assumptions on the statistical properties of the random processes (field and collisional velocity fluctuations), we perform an analytical calculation of the mean-square displacement (MSD) of the particle. The basic nonlinearity in the problem (Lagrangian argument of the random field) yields complicated averages, which we carry out using a functional formalism. The result is expressed as a series, and we find the conditions for its convergence, i.e. the limits of validity of our approach (essentially, we must restrict attention to non-chaotic regimes). Further, employing realistic bounds (spectral cut-off and limited time of observation), we derive an explicit formula for the MSD. We show that from this unique expression, we can obtain several previously known results.
Dynamic properties of ηi-mode weak turbulence
Authors: Pakyari Alireza , Pavlenko Vladimir P.
Published: March 2009

The turbulence of the toroidal ηi mode has a forward spectral cascade. This means that most of the energy initially placed in the low-wavenumber region (the linear instability region) will be spread out towards high-wavenumber modes. Therefore the linear instability may be reduced by this energy cascade. An elementary estimate of the critical amplitude for nonlinear mode coupling to balance the linear growth rate is given. As a consequence of three wave cascade process derivable from the fully toroidal fluid model equations, the formation of zonal flows ηi-mode turbulence is predicted.
Transfer integrals for fully ionized gases
Authors: Fichtner Horst , Sreenivasn S. Ranga , Vormbrock Norbert
Published: March 2009

The general transfer integrals describing the collisional exchange of momentum and energy between the constituents of multicoimponent gases are evaluated for different plasma scenarios characterized by Maxwellian as well as non-Maxwellian distribution functions of the plasma species. Following a brief presentation of the standard approximation frequently employed in the literature, a comparison of numerical evaluations of the transfer integrals for various distribution functions reveals significant differences in the corresponding collisional momentum and energy exchange rates, which are shown to depend mainly on the core structure of the distributions. We demonstrate the inadequacy of the standard approximation and hence the importance of an accurate evaluation of the transfer integrals with an application to the electron proton as well as the helium proton interaction in the solar wind plasma.
Resonant four-wave mixing of finite-amplitude Alfvén waves
Authors: Rauf S. , Tataronis J. A.
Published: March 2009

Using the derivative nonlinear SchrÖdinger equation, resonant four-wave mixing of finite-amplitude Alfvén waves is explored in this paper. The evolution equations governing the amplitudes of the interacting waves and the conservation relations ale derived from the basic equation. These evolution equations are used to study parametric amplification and oscillation of two small-amplitude Alfvén waves due to two large-amplitude pump (Alfvén) waves. It is also shown that three pump waves can mix together to generate a low-frequency Alfven wave in a dissipative plasma.
Beam-plasma instability excited by non-thermal electrons with arbitrary distribution function and comparison with electron-cyclotron master instability
Authors: Huang Guang-Li , Wang De-Yu , Mao Ding-Yi
Published: March 2009

An equation is derived for the growth rates of the beam-plasma instability excited by non-thermal electrons with arbitrary distribution function, and it is shown that the reactive instability does not depend on the assumption of a monoenergetic distribution. Hence the properties of electromagnetic waves are calculated for the hollow beam and loss-cone distribution. Hence the properties of electromagnetic waves are calculated for the hollow beam and loss-cone distribution functions. The general characteristics and structures of the growth rates are similar to the results for the monoenergetic distribution, but there are still some differences in the relation between the growth rates and the relevant parameters, such as the ambient parameter ωpe/Ωe, the angle of propagation θ and the pitch angle a. The main purpose of this paper is to compare the properties of the beam-plasma instability (reactive) and the electron-cyclotron maser instability (kinetic) under similar ambient conditions. The calculations show that both kinds of instabilities are easily excited at larger angles of propagation with respect to the ambient magnetic field, which means that both depend mainly on the free energy of the non-thermal electrons perpendicular to the magnetic field. The magnitudes of the growth rates of the two kinds of instabilities are comparable under the same ambient conditions. However, because the non-resonant wave—particle interaction is taken into consideration for the beam-plasma instability, which makes the resonant peaks broaden and connect with each other, the spectra of the beam-plasma instability are also more complicated than that of the maser instability, and the range of the angle of propagation of the growing waves in the non-resonant case is also larger than that in the resonant case.
Electrostatic solitons in an electron–positron plasma with two distinct groups of positrons
Authors: Srinivas J. , Popel S. I. , Shukla P. K.
Published: March 2009

The existence of novel electrostatic solitary pulses in an electron–positron plasmas with two distinct groups of positrons is demonstrated. It is found that the soliton potential can assume both the rarefactive and compressive polarities. The results might be useful in understanding the properties of localized disturbances in astrophysical plasmas.
Ion dynamics and gravitational instability of a dusty plasma
Authors: Pandey B. P. , Dwivedi C. B.
Published: March 2009

The gravitational instability of a dusty plasma with ion dynamics taken into account is studied. For the range of parameters relevant to planetary rings and interstellar media, we demonstrate that the inclusion of ion dynamics cannot cause additional destabilization of a gravitating dusty plasma system. Streaming of the cold ions, on the other hand, enhances the Jeans condensation of a dusty plasma. Consistency of the results with previous work and new aspects arising owing to consideration of ion dynamics is discussed.
Black-body radiation in plasmas
Authors: Tsintsadze Levan N. , Callebaut Dirk K. , Tsintsadze Nodar L.
Published: March 2009

The theory of black-body radiation in thermal equilibrium with a homogeneous and isotropic plasma is presented. The relevant thermodynamic quantities of the radiation are obtained. The presence of the plasma changes qualitatively and often quantitatively the concept of black-body radiation, essentially through the effect of plasma density.
Large-amplitude ion-acoustic waves in a plasma with a relativistic electron beam
Authors: Nejoh Yasunori
Published: March 2009

Nonlinear wave structures of large-amplitude ion-acoustic waves in a plasma with a relativistic electron beam are studied using the pseudopotential method. The region of existence of large-amplitude ion-acoustic waves is examined, and it is shown that the condition for their existence depends sensitively on parameters such as the relativistic effect of the electron beam, the ion temperature, the electrostatic potential and the electron beam density. It turns out that the region of existence spreads as the relativistic effect (Mach number) increases and the ion temperature decreases. New properties of large-amplitude ion-acoustic waves in a plasma with a relativistic electron beam are predicted.
Nonlinear coupling of a superluminal electromagnetic wave to a relativistic electron beam
Authors: Bisai N. , Sen A. , Jain K. K.
Published: March 2009

The nonlinear propagation of a superluminal, linearly polarized electromagnetic wave in the presence of a relativistic cold electron beam is investigated. At large amplitudes the wave couples to the electron-beam plasma mode owing to two important nonlinear effects, namely the relativistic variation of the electron mass and the excitation of longitudinal space charge fields by strong v × B forces. The nonlinear propagation equations for the coupled electromagnetic and longitudinal waves are derived within the context of a relativistic cold-fluid model. Nonlinear travelling-wave solutions are sought to describe the saturated state of the coupled system. Using Hamiltonian techniques, a wide variety of solutions are obtained and their characteristics discussed.
Magnetohydrodynamic parametric instabilities driven by a standing Alfvén wave in a low-β plasma
Authors: Oliveira L. P. L. , Chian A. C.-L.
Published: March 2009

The stability of a finite-amplitude standing Alfvén wave of circular polarization in a low-β plasma is studied using a set of nonlinearly coupled MHD wave equations. In the presence of a standing Alfvén pump, two distinct gratings associated with the density fluctuations are excited: those due to the ponderomotive beating of the pump magnetic field, and those due the induced magnetic fluctuations. The roles played by the two gratings in the mode coupling are analysed. Both convective and purely growing regimes of the MHD parametric instabilities can be produced by a standing Alfvén wave. In both regimes, the maximum growth rate increases as the pump amplitude increases, and decreases as increases. Tn the presence of the second grating, a new unstable convective regime appears that widens the overall instability bandwidth.
Dissipative instability of the MHD tangential discontinuity in magnetized plasmas with anisotropic viscosity and thermal conductivity
Authors: Ruderman M. S. , Verwichte E. , Erdélyi R. , Goossens M.
Published: March 2009

The stability of the MHD tangential discontinuity is studied in compressible plasmas in the presence of anisotropic viscosity and thermal conductivity. The general dispersion equation is derived, and solutions to this dispersion equation and stability criteria are obtained for the limiting cases of incompressible and cold plasmas. In these two limiting cases the effect of thermal conductivity vanishes, and the solutions are only influenced by viscosity. The stability criteria for viscous plasmas are compared with those for ideal plasmas, where stability is determined by the Kelvin—Helmholtz velocity VKH as a threshold for the difference in the equilibrium velocities. Viscosity turns out to have a destabilizing influence when the viscosity coefficient takes different values at the two sides of the discontinuity. Viscosity lowers the threshold velocity V below the ideal Kelvin—Helmholtz velocity VKH, so that there is a range of velocities between V and VKH where the overstability is of a dissipative nature.
Plasma physics: a personal perspective
Authors: Montgomery David
Published: March 2009

At a college where I taught, there was a ‘Last Lecture’ series, in which the faculty took turns giving a public lecture that would be the lecture they would give if it were to be their very last one. The invitation to contribute a few nontechnical pages to this issue of Journal of Plasma Physics has a somewhat similar valedictory ring, and inspires mixed feelings.
Vortex dynamics in perfect fluids
Authors: Pomeau Yves
Published: March 2009

I review the current status of a problem, relevant to both plasma physics and ordinary fluid mechanics, namely the long-time behaviour of solutions of the perfect fluid equations. In two space dimensions, thanks in particular to the work of D. Montgomery, the situation is now quite clear, since one expects the formation at long times of large vortices in a background of potential flow. In three dimensions, the situation is blurred, although its understanding is a central issue for fully developped turbulence. I present some new estimates for a possible scenario of self-similar blow up of solutions of 3D Euler. That turns out to be a rather subtle question, if one tries to stay consistent with the conservation of circulation and of energy.
The theory of nonlinear ion-acoustic waves revisited
Authors: Malfliet W. , Wieërs E.
Published: March 2009

The basic set of equations describing nonlinear ion-acoustic waves in a cold collisionless plasma, in the limit of long wavelengths, is reconsidered. First, a travelling-wave solution is found up to third order by means of a straightforward perturbation approach based on the smallness of the wavenumber. As a result, a positive dressed solitary wave shows up, which is larger, taller and faster than the KdV soliton, the first-order result. Furthermore, the accuracy of this approach is tested and compared with previous result. Secondly, the reductive perturbation techique to study higher-order corrections is revised and adapted to the present problem.
Inverse cascades in incompressible fluid and magnetofluid turbulence
Authors: Hossain Murshed
Published: March 2009

Absolute equilibrium statistical theory and numerical simulations are reviewed in the context of inverse cascades in two- and three-dimensional incompressible fluid and magnetofluid turbulence. Turbulent fluctuations of physically interesting quantities undergo inverse cascade to larger spatial scales, leading to self-organization under certain circumstances. In particular, most systems with more than one quadratic ideal invariant, or, having some kind of imposed anisotropy, exhibit inverse cascades. Anisotropic fluid turbulence in the presence of a uniform rotation and magnetofluid turbulence in the presence of a uniform magnetic field are considered.
Bifurcations of magnetic topology by the creation or annihilation of null points
Authors: Priest E. R. , Lonie D. P. , Titov V. S.
Published: March 2009

Linear null points of a magnetic field may come together and coalesce at a secondorder null, or vice versa a second-order null may form and split, giving birth to a pair of linear nulls. Such local bifurcations lead to global changes of magnetic topology and in some cases release of magnetic energy. In two dimensions the null points are of X or O type and the flux function is a Hamiltonian; the magnetic field may undergo addle-centre, pitchfork or degenerate resonant bifurcations. In three dimensions the null points and their creation or annihilation by bifurcations are considerably more complex. The nulls possess a skeleton consisting of a spine curve and a fan surface and are of radial-type (proper or improper) or spiral-type; the type of null and the inclination of spine and fan depend on the magnitudes of the current components along and normal to the spine. In cylindrically symmetric fields a comprehensive treatment is given of the various types of saddle-node, Hopf and saddle-node—Hopfbifurcations. In fully three-dimensional situations examples are given of saddle-node and degenerate bifurcations, in which generically two nulls are created or destroyed and are joined by a separator field line, which is the intersection of the two fans. Furthermore, global bifurcations can create chaotic field lines that could perhaps trigger energy release in, for example, solar flares.
States of minimum dissipation in magnetohydrodynamics: a review
Authors: Phillips Lee
Published: March 2009

The hypothesis that the steady, or statistically steady, states of a magnetofluid can be predicted by minimizing the integral of the total energy dissipation is discussed in relation to theorems in fluid dynamics. A survey is made of the recent literature wherein the hypothesis is used to predict magnetofluid behaviour and some related work. A detailed discussion of boundary conditions is provided, and we close with a brief summary of the current state of research.
General stability analysis of force-free magnetic fields. Part 1. General theory
Authors: Krüger Jan
Published: March 2009

We formulate, in the framework of MHD, a simple eigenvalue problem, capable of treating the stability of force-free magnetic fields curl B = αB in different geometries. We prove that a force-free field surrounded by a rigid wall is stable, if the eigenvalue α corresponds to the lowest value ofcompatible with the geometry considered. We extend this result to the case where α is a function of position; and we recliscuss it from the viewpoint of the first-order variation. We give various theorems and criteria for stability, for continuous as well as for admissible discontinuous or infinite displacements. A general upper limit for the growth rate is, where andand are respectively the maximum values ofand υAthe Alfvén velocity inthe plasma volume.
Temperature anisotropy instabilities in a plasma of two ion components
Authors: Lemons Don S. , Gary S. Peter
Published: March 2009

This paper studies the linear dispersion properties of ion temperature anisotropy instabilities in an infinite, homogeneous Vlasov plasma containing a second, cooler-ion component. The cooler component enhances the T‖>T⊥ firehose instability, as well as the T⊥>T‖, ion-cyclotron instability, by making the waves more resonant with the ions. The effect of various parameters on this enhancement is studied numerically.
Nonlinear interaction between two electrostatic harmonics in a plasma
Authors: Verheest Frank , Lewak G. J.
Published: March 2009

The problem of harmonic and subharmonic generation of electrostatic waves in a general collisionless plasma, or in some other electromagnetic medium, is treated anew, using coupled-mode theory based on two time scales. A novel feature is that one of the two interacting waves may be a negative energy wave. Furthermore, the model describing the medium need not be specified, only a general linear and nonlinear conductivity or an equivalent description is required. Just by invoking wave energy conservation, the coupled-mode equations are obtained in such a way that unequivocal conclusions can be drawn.

When both waves have positive energy, they exchange part of it in a periodic fashion, provided they both have some energy initially. If initially all the energy is in the fundamental, then all of it will eventually end up (irreversibly) in thesecond harmonic. If, on the other hand, all the energy is in the harmonic initially, then no generation of the fundamental (or subharmonic) will take place. If one of the two waves is a negative-energy wave, however, an explosive instability develops, and this regardless of initial values. For comparable conditions, the instability time depends on whether the negative energy wave is in the fundamental or in the upper harmonic.
Electromagnetic and electrostatic wavesin a multi-component plasma near the lower hybrid frequency
Authors: Hamelin M. , Beghin C.
Published: March 2009

In propagation perpendicular to the magnetic field, the lower hybrid frequency is the transition between long electromagnetic and short electrostatic waves. Cold, warm and hot plasma theories are applied to the case of a plasma composed of different ion species. For cold and warm (adiabatic) theories, the dispersion curves are not qualitatively different from the single-ion case. In the hot microscopic theory, the dispersion curves, the so-called ‘Bernstein modes’, have a structure mainly related to the lightest ion gyroharmonics, even in concentration as low as 1 %. The theoretical results can explain the ray structure observed in the ISIS II and Electron Echo 1 experiments.
Nonlinear Rayleigh–Taylor instability in hydromagnetics
Authors: Kalra G. L. , Kathuria S. N.
Published: March 2009

Nonlinear theory of Rayleigh—Taylor instability in plasma supported by a vacuum magnetic field shows that the growth rate of the mode, unstable in the linear theory, increases if the wavelength of perturbation π lies between

and 2πcrit. This might have an important bearing on the proposed thermonuclear MHD power generation experiments.
Electrostatic plasma turbulence Part 1. Turbulent plasma diffusion across a magnetic field
Authors: Barr H. C. , Boyd T. J. M.
Published: March 2009

The turbulent diffusion of plasma across a magnetic field is studied theoretically using a three-dimensional model which includes the full dynamics of the diffusing particles and which is valid for arbitrary magnetic field strengths. The theory is confined to perpendicular turbulence, i.e. where the build-up of the fluctuations lies primarily in the plane perpendicular to the magnetic field (although it is more generally applicable). A single expression for the diffusion is derived in terms of the fluctuation spectrum, particle energy, the dispersion characteristics of the excited modes and the magnetic field. Earlier results for equilibrium plasmas are confirmed. We demonstrate the continuous transition from anomalous (1/B) diffusion in regimes of low fluctuation levels (or strong magnetic fields) to classical (1/B2) diffusion in regimes where the fluctuation level destroys the coherence sustained by the magnetic field. In this latter regime, the particles behave as if unmagnetized except for a turbulent drift which appears in the presence of anisotropic spectra.
Theory and computer simulation of electron beam-plasma interactions in unbounded systems
Authors: Cuperman S. , Roth I. , Bernstein W.
Published: March 2009

Computer simulation experiments of linear and nonlinear collisionless interactions between electron beams and background plasmas, for conditions relevant to active magnetospheric experiments, were carried out. Both electrostatic and electromagnetic interactions were simultaneously considered. The beam-plasma systems were infinite and homogeneous.

The relative beam concentrations considered were ε ≡ nb/np, = 1, 0·1 and 0·01. In all cases, the background plasma (1 eV thermal energy) was penetrated by an electron beam of 1 keV streaming energy and 5 % thermal spread in the streaming direction.

The paper presents a full description of the results and a brief discussion of their relevance to magnetospheric active experiments.

The off-angle propagation case in unmagnetized plasmas is also briefly discussed.
Propagation of magnetodynamic waves into a collisionless current layer
Authors: Hruška A.
Published: March 2009

In a layer of magnetic field aligned current, waves corresonding to the slow mode in the limit of no current are absorbed and/or reflected as soon as they enter the layer, while, under certain conditions, the waves corresponding to the fast mode do propagate through the layer.
Nonlinear development of the ion-cyclotron electromagnetic instability
Authors: Cuperman S. , Sternlieb A. , Williams D. J.
Published: March 2009

Cornwall et al. (1970) suggested that if the ring current protons penetrated the plasmapause, intense resonant electromagnetic ion cyclotron turbulence would lead to their rapid precipitation loss. IN this paper we present a computer simulation study of the electromagnetic ion-cyclotron instability in a homogeneous plasma consisting of protons and electrons embedded in a static magnetic field, B0x. The plasma parameters used are and Effects such as sources and losses or space non-uniformities are not considered here. The predictions of the linear theory for the fast build-up of unstable left-hand (proton-like) electromagnetic ion-cyclotron waves are fully confirmed.
Kinetic theory of the evolution of collective plasma excitations in an external electric field
Authors: Balescu R. , Paiva-Veretennicoff I.
Published: March 2009

The kinetic theory of a plasma is developed on the basis of a normal mode analysis-In the absence of any external field, the system approaches a ‘plasmadynamical (PD) state’, described by fourteen amplitudes of the PD modes. The corresponding eigenvalues and eigenvectors are constructed explicitly. When an external time-dependent electric field is switched on, transitions between these modes determine the evolution of the plasma. Assuming that a PD regime is valid, the kinetic equations reduce to a set of equations describing parametric effects and nonlinear mode-mode couplings. A new source term, arising from the interference between collisions and external field, also appears. Some qualitative implications are discussed.
On the stability of the screw pinch in the CGL model
Authors: Srivastava Krishna M. , Waelbroeck F.
Published: March 2009

We have investigated the stability of the screw pinch with the help of the double adiabatic (CGL) equations including the finite Larmor radius effects through the anisotropic pressure tensor. The calculations are approximate, with FLR treated as a first-order correction to the ideal plasma equations. The dispersion relation has been solved for various values of R2 = p∥/p⊥ and α for the rale and imaginary part of the frequency (ω = ωR ± iωI) in three particular cases: (a) μ = 0, the θ-pinch, (b) μ = ∞, the Z-pinch, (c) μ = -α/m, field distubances parallel to the equilibrium field. Here μ is the pitch of the magnetic field in the pressureless plasma surrounding the main column, α is the wave number, m is the azimuthal number, p∥ and p⊥ are plasma pressures along and perpendicular to the magnetic field.
On the modulational instability of hydromagnetic waves parallel to the magnetic field
Authors: Mjølhus Einar
Published: March 2009

The stability of circularly polarized waves of finite amplitude propagating parallel to the magnetic field is studied. A set of equations for slowly varying waves of arbitrary amplitude is obtained. A discussion of the stability of the waces is based on this set of equations. Earlier results are confirmed; in addition we find that finite amplitude always promotes stability. An amplitude dependent stability condition for long waves, previously obtained by the author, is confirmed.
The zero-mode instability: a new parametric decay instability of a plasma in an external field
Authors: Balescu R. , Paiva-Veretennicoff I.
Published: March 2009

The parametric resonances involving the coupling of an external harmonic electric field to the plasmadynamical (PD) modes are studied. Particular attention is devoted to the resonant triplets involving purely dissipative PD modes of zero frequency. It is shown that a new type of instability exists in this class of processes.
On the theory of Langmuir solitons
Authors: Gibbons J. , Thornhill S. G. , Wardrop M. J. , Haar D. Ter
Published: March 2009

We find a Lagrangian density from which the equations of motion for the Lang-muir solitons follow in the usual way. We show how this Lagrangian leads to the usual conservation laws. For the one-dimensional case we discuss how a consideration of these conservation laws can help us to understand some of the results obtained in numerical experiments on the behaviour of a strongly turbulent plasma. We point out that the situation in the three-dimensional case may be fundamentally different, and we discuss near-sonic perturbations and Karpman's treatment of these.
Finite amplitude E × B oscillations in bounded plasmas
Authors: Holter Øivin
Published: March 2009

A semi-infinite plasma slab with a density gradient and an externally applied electric field normal to an applied magnetic field is considered. Stable finite amplitude density and potential oscillations are investigated for parameters favourable for the E × B instability. Explicit expressions for the oscillation amplitudes, frequency, and wavelength are derived in the limit of a weak density gradient. The calculations are performed with a closed set of zero and first harmonic equations. It is shown that second harmonic contributions are small in the case considered.
Locally excited magnethohydrodynamic waves in a uniform cylindrical plasma waveguide
Authors: Sy W. N-C.
Published: March 2009

The guided modes of Woods' magnetohydrodynamic waveguide for a uniform, cylindrical plasma are shown to satisfy a homogeneous wave equation whose differential operator is the product of eight Helmholtz operators. The propagation constants of the Helmholtz operators are the characteristic roots of an 8 × 8 matrix which is derived and written down explicitly. This reformulated theory is extended to include localized sources which excite the guided modes. For certain cases, the Green's functions for the differential operators can be represented by Dini expansions in terms of modal eigenfunctions, which manifestly satisfy the boundary conditions. For the case of MHD waves excited by an azimuthally symmetric current source in a resistive, pressureless, inviscid, fully ionized plasma, a detailed solution is obtained which is in good qualitative agreement with experiments.
Dissipative, forced turbulence in two-dimensional magnetohydrodynamics
Authors: Fyfe David , Montgomery David , Joyce Glenn
Published: March 2009

The equations of motion for turbulent two-dimensional magnetohydrodynamic flows are solved in the presence of finite viscosity and resistivity, for the case in which external forces (mechanical and/or magnetic) act on the fluid. The goal is to verify the existence of a magnetohydrodynamic dynamo effect which is represented mathematically by a substantial back-transfer of mean square vector potential to the longest allowed Fourier wavelengths. External forces consisting of a random part plus a fraction of the value at the previous time step are employed, after the manner of Lilly for the Navier–Stokes case. The regime explored is that for which the mechanical and magnetic Reynolds numbers are in the region of 100 to 1000. The conclusions are that mechanical forcing terms alone cannot lead to dynamo action, but that dynamo action can result from either magnetic forcing terms or from both mechanical and magnetic forcing terms simultaneously. Most real physical cases seem most accurately modelled by the third situation. The spatial resolution of the 32 × 32 calculation is not adequate to test accurately the predictions of the spectral power laws previously arrived at on the basis of the assumption of simultaneous cascades of energy and vector potential. Some speculations are offered concerning possible relations between turbulent cascades and the ‘disruptive instability’.
Cyclotron instabilities of a magnetized electron plasma with anisotropic temperatures
Authors: Chiuderi C. , Einaudi G. , Giachetti R.
Published: March 2009

The dispersion relation for an electron plasma in a magnetic field is investigated for a bi-Maxwellian distribution function. A new set of solutions for non-perpendicular propagation is found. The linear growth rates are computed and the instability regions in the (k, cos θ) plane are determined. An approximate analytical treatment of the problem is also given for certain ranges of the parameters.
Electrostatic plasma turbulence Part 2. The nonlinear dispersion relation and fluctuation spectrum
Authors: Barr H. C. , Boyd T. J. M.
Published: March 2009

This paper complements an earlier one in which we considered the diffusion and drift across a magnetic field induced by a turbulent spectrum of fluctuations. We examine here the effects of these on the propagation of an unstable spectrum of modes. In the first paper a nonlinear dispersion relation is derived in a general closed form. This is then examined in the limint of short wavelengths (i.e.wavelengths much less than the gyroradii) and results of other authors are retrieved. In particular it is found that modes supported by the magnetic field are quashed whenever a particle may diffuse a wavelength per gyroperiod. For instance, in the context of current-driven instabilities (current across the magnetic field), electron cyclotron instabilities are quashed but not the ion-acoustic. The dispersion characteristics of the latter are unchanged except in that the drift which sustains the instability is altered by the presence of a turbulent (E × B) type drift. Depending on the level of fluctuations and magnetic field strength, this may amount simply to a rotation of the cone of unstable modes or may form a countercurrent which in turn suppresses the original current driving the instability.

In the second half of the paper the problem of calculating the fluctuation spectrum of the electric field is addressed since this is essential for a self-consistent computation of the diffusion tensor and turbulent drift appearing in the nonlinear dispersion relation.
Renormalization method and singularities in the theory of Langmuir turbulence
Authors: Pelletier G.
Published: March 2009

The method of renormalization, using propagators and diagrams, is recalled with enough mathematical details to be read and used by a non-specialist. The Markovian models are discussed and applied to plasma turbulence. The physical meaning of the diagrams is exhibited. In addition to the usual resonance broadening, an improved renormalization is set out, including broadening of the nonlinear resonance with a beat wave by induced scattering. We emphasize this improved renormalization. In the case of Langmuir turbulence, it removes difficulties arising at the group velocity, and enhances large-scale induced-scattering diffusion.
Modifications in the maximum convective growth rate of the electromagnetic proton cyclotron instability due to the presence of thermal ions
Authors: Gomberoff L. , Cuperman S.
Published: March 2009

The effect of thermal ions on the convective properties of the electromagnetic proton cyclotron instability is investigated. It is shown that when Ap < 1, where Ap is the proton anisotropy, cold ions, with relative specific charge mj/Zj mp ≥ 1, stabilize the convective growth of the instability. When Ap >1, the effect of thermal ions is to enhance the convective growth of the instabifity in the range where the real part of the frequency, ωr, is smaller than the ion gyrofrequency, Ωj. The maximum enhancement, corresponding to an optimum concentration of heavy ions, is shown to be a constant independent of the species. However, for each species, even for Ap > 1 (except for protons), there is always a range of values of Ap such that the species will stabilize the system. Heavier ions are shown to be more effective in enhancing the convective growth of the instability, in the sense that, the heavier they are, smaller relative concentrations are required to reach the constant value mentioned above. For sufficiently heavy species, the required concentration to optimize the convective growth, is independent of the species.
Determination of plasma density and temperature profiles using magneto-acoustic oscillations
Authors: Brennan M. H. , Jessup B. L. , Jones I. R.
Published: March 2009

This paper reports on theoretical and experimental refinements in the use of forced radial magneto-acoustic oscillations of a magnetized plasma as a diagnostic technique. The theory of such oscillations is extended to include radial variations in electron number density, neutral atom density and plasma temperature. In experiments carried out in an argon afterglow plasma, observations of the radial variation of the oscillation amplitude, and of the total flux in the plasma, are combined with theory to yield radial density and temperature profiles. These profiles are in good agreement with independent measurements made using laser interferometry and spectroscopic techniques.
A quantum field theoretical approach to plasmas
Authors: Gomberoff L.
Published: March 2009

By making use of the Feynman–Schwinger formalism of quantum electrodynamics, the classical dispersion relation for electrostatic and electromagnetic waves in a homogeneous plasma is derived. It is then argued that such techniques can be helpful in dealing with quasi-linear and nonlinear problems in plasmas.
Modulation of randomly phased whistler wave packets by kinetic Alfvén and ion quasi-modes in a magnetized plasma
Authors: Shukla P. K.
Published: March 2009

We consider the nonlinear coupling of stationary whistler wave turbulence with low-frequency kinetic Alfvén and ion quasi-modes in a magnetized plasma. It is found that such couplings lead to instabilities. The influence of various plasma parameters on the linear growth rates of the instabilities is obtained. Our results may be useful to the understanding of numerous phenomena associated with electron whistler waves in space and laboratory plasmas.
Two-dimensional self-modulation of a whistler wave propagating along the magnetic field in a plasma
Authors: Karpman V. I. , Washimi H.
Published: March 2009

Two-dimensional nonlinear self-modulations of a high-frequency whistler wave propagating along an applied magnetic field in a plasma are investigated. We derive new, fairly broad, regions of modulational instabilities in directions oblique to the initial wave propagation with growth rates much greater than in the case of ‘parallel’ self-modulation. The largest growth rate appears to be for the angles corresponding to the parametric instabilities. Nonlinear solutions describing the envelope solitons propagating obliquely to the initial wave are also discussed. Our results are in qualitative agreement with recent experiments.
Overlooked perturbations and completeness
Authors: Krüger J. G.
Published: March 2009

An important class of overlooked MHD perturbations which are necessary to satisfy arbitrary initial conditions is discussed.
Drift waves in a turbulent plasma
Authors: Mendonça I. , Mendonça J. T.
Published: March 2009

We study the dispersion equation of drift waves in the presence of electron- plasma turbulence in a plasma with magnetic shear. We show that the shear stabilization can be cancelled out by a hot turbulent spectrum, even for a low level of turbulence, W/n0Te≪ 1.
Profile modifications at critical density of laser-produced plasmas
Authors: Shukla P. K. , Spatschek K. H.
Published: March 2009

Profile modification by the ponderomotive force of the mode-converted Langmuir waves at critical density of a laser-irradiated plasma is investigated. A nonlinear Schrödinger equation governing the interaction of Langmuir waves with slow plasma motion is obtained taking into account the plasma inhomogeneity, dissipation, and a driver. The initial value problem is solved by means of the inverse scattering method. The soliton formation and self-consistent density steepemng at the critical layer are investigated.
Nonlinear interaction between longitudinal waves in a magnetized plasma
Authors: Selim A. A.
Published: March 2009

Quantum field theory is used to investigate the resonant nonlinear interaction between three longitudinal waves propagating at any arbitrary angle to a uniform magnetic field in a plasma. The coupled mode equations, coupling coefficient and a formula for the growth rates are derived.
Merging of magnetic fields with field-aligned plasma flow components
Authors: Mitchell H. G. , Kan J. R.
Published: March 2009

The Sonnerup merging model for an incompressible plasma is extended to allow a flow component along the field lines in the inflow regions. Solutions are found to exist as long as the difference between the quantities B. V for the two inflow regions does not exceed a critical magnitude dependent on the inflow field magnitudes and plasma densities. All such solutions satisfy Vasyliunas' definition of merging, but some classes of solution have radically altered geometries, i.e. geometries in which the inflow regions are much smaller than the outflow regions. The necessary but not sufficient condition for these unusual geometries is that the field-aligned flow component in at least one inflow region be super Alfvénic. A solution for the case of a vacuum field in one inflow region is obtained in which any flow velocity is allowed in the non-vacuum inflow region, although super-Alfvénic flow can still result in an unusual geometry. For symmetric configurations, the usual geometry, that of Petschek and Sonnerup, is retained as long as both field-aligned flow components in the inflow regions are less than twice the inflow Alfvén speed. For the case of a vacuum field on one side and fields approximating the boundary between the solar wind and the earth's dayside magnetosphere, the usual geometry is retained for flow less than about 2·5 times the local Alfvén speed.
Electrostatic heat flux instabilities
Authors: Gary S. Peter
Published: March 2009

The linear Vlasov dispersion relation for electrostatic waves in a homogeneous plasma is studied for instabilities driven by an electron heat flux. A two Maxwellian model of the electron distribution function gives rise to three unstable modes: the electron beam, ion-acoustic and ion cyclotron heat flux instabilities. At large Te/Ti the ion-acoustic instability has the lowest threshold; at small Te/Ti the electron beam instability is dominant; and at intermediate values of Te/Ti the ion cyclotron mode is the first to go unstable. The presence of a high energy tail on the electron distribution function raises the value of the dimensionless heat flux qe/(nemev3e) at the ion-acoustic threshold, but increasing atomic number of the ions decreases this value.
Derivation of the quasi-linear equation in a magnetic field
Authors: Berk H. L.
Published: March 2009

A formal derivation of the quasi-linear equation of a plasma in a magnetic field is presented. The theory accounts for spatial inhomogeneity in one direction and for bounce motion of particles confined in a mirror magnetic field.
Stimulated backscattering of electromagnetic ordinary waves from extraordinary waves below the upper hybrid frequency
Authors: Maraghechi Behrooz , Willett Joseph E.
Published: March 2009

The parametric decay of an intense electromagnetic ordinary wave, propagating perpendicular to a uniform static magnetic field, into an extraordinary wave and a backscattered ordinary wave is investigated. Formulae are derived for the growth rate and threshold power associated with the instability in a homogeneous plasma. An analysis of the spatial amplification of the decay waves in an inhomogeneous plasma is presented. The effects of the uniform static magnetic field on the backscattering in both homogeneous and inhomogeneous plasmas are studied numerically.