bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport equations on different time scales for intermediately and strongly collisional regimes
Authors: Edenstrasser J. W. , Kassab M. M. M.
Published: March 2009

The plasma transport equations for a weakly collisional plasma have previously been derived for four different time scales. This paper is devoted to the derivation of the plasma transport equations for the two other complementary regimes: the intermediately collisional regime (ICR) (i.e. for the case where the transit time w1 is of the same order as the collision timeis of the same order as the collision time), and the strongly collisional regime (SCR) (i.e. for the case of) for different time scales. It is shown that the lowest-order gyromotion is unperturbed by collisions. On the Alfvén time scale, one merely obtains for both the intermediately collisional case and the strongly collisional case the single-fluid ideal MHD equations, if certain additional requirements are satisfied. On the MHD-collision time scale, one arrives at the full set of transport equations, where in both cases, contrary to the weakly collisional case, no turbulent terms are found. On the resistive diffusion timescale, one ends up with the known transport equations, with the addition of turbulent contributions.
Collective effects in bremsstrahlung in plasmas
Authors: Tsytovich V. N. , Bingham R. , de Angelis U. , Forlani A.
Published: March 2009

The results of recent developments in the theory of fluctuations in plasmas show that the previously used theory of bremsstrahlung is incomplete and the exact expressions for bremsstrahlung should include transition bremsstrahlung. The collective effects in bremsstrahlung known previously as Debye screening are changed to a qualitatively different structure, which removes the effect of ion polarization in bremsstrahlung and introduces a new effective polarization which depends on an effective ion charge and electron velocity. The results may be relevant for applications in plasmas when the wavelength is greater than the Debye length. It is shown that for the problem of photon transport in the solar interior the correct collective corrections to the bremsstrahlung change the opacity by only about −0·35%, which is less than was calculated previously when collective effects in bremsstrahlung where estimated without taking recent results of plasma fluctuation theory into account.
Stability of solitary waves in a magnetized non-thermal plasma
Authors: Mamun A. A. , Cairns R. A.
Published: March 2009

A theoretical investigations is made of the stability of electrostatic waves in a magnetized non-thermal plasma. The Zakharov-Kuznetsov equation (or Korteweg-de Vries equation in three dimensionas) for these solitary waves in this plasma system is derived, and their three-dimensional stability is studied by the small-k (long wavelength plane-wave) perturbation expansion method. The instability criterion and its growth rate depending on the magnetic field and the propagation directions of the solitary wave and its perturbation mode are discussed.
Modelling of a solar coronal loop
Authors: Krishan V.
Published: March 2009

Montgomery and co-workers have developed a framework to describe the steady state of a turbulent magnetofluid, without the usual recourse to linearization. Thus the magnetic and velocity fields emerge in their fully nonlinear form as a consequence of the selective decays of the invariants of the system. Using this statistical theory of magnetohydrodynamic turbulence, the pressure, magnetic and flow fields of a solar coronal loop have been determined. The spatial and time profiles of the loop pressure are derived. A comparison with the observed properties of the loops is made, whenever possible.
Coherent drift-wave structures in toroidal plasmas
Authors: Horton W. , Tajima T. , Kim J.-Y. , Kishimoto Y. , Ottaviani M.
Published: March 2009

Using the ion-temperature-gradient-driven drift waves as a paradigm for drift-wave anomalous transport, we explore the structure of the linear and nonlinear modes. Two phases of transport are shown to exist: (i) Bohm-like transport for parameters close to marginal stability; (ii) gyro-Bohm transport for turbulent convection cells in systems driven away from marginal stability. Nonlinear relaxation to large-scale coherent convective structures is observed in three-dimensional toroidal particle simulations.
Ion parallel viscosity and anisotropy in MHD turbulence
Authors: Oughton Sean
Published: March 2009

We report on results from direct numerical simulation of the incompressible three- dimensional magnetohydrodynamic (MHD) equations, modified to incorporate viscous dissipation via the strongly anisotropic ion-parallel viscosity term. Both linear and nonlinear cases are considered, all with a strong background magnetic field. It is found that spectral anisotropy develops in almost all cases, but that the contribution from effects associated with the ion-parallel viscosity is relatively weak compared with the previously reported nonlinear process. Furthermore, and in contrast to this earlier work, it is suggested that when B0 is large, the anisotropy will develop and persist for many large-scale turnover times even for non-dissipative runs. Resistive dissipation is found to dominate over viscous even when the resistivity is several orders of magnitude smaller than the ion parallel viscosity. A variance anisotropy effect and anisotropy dependence on the polarization of the fluctuations are also observed.
Instability of magnetic modons and analogous Euler flows
Authors: Chui A. Y. K. , Moffatt H. K.
Published: March 2009

We construct numerical examples of a ‘modon’ (counter-rotating vortices) in an Euler flow by exploiting the analogy between steady Euler flows and magnetostatic equilibria in a perfectly conducting fluid. A numerical modon solution can be found by determining its corresponding magnetostatic equilibrium, which we refer to as a ‘magnetic moclon’. Such an equilibrium is obtained numerically by a relaxation procedure that conserves the topology of the relaxing field. Our numerical results show how the shape of a magnetic modon depends on its ‘signature’ (magnetic flux profile), and that these magnetic modons are unexpectedly unstable to non-symmetric perturbations. Diffusion can change the topology of the field through a reconnection process and separate the two magnetic eddies. We further show that the analogous Euler flow (or modon) behaves similar to a perturbed Hill's vortex.
General stability analysis of force-free magnetic fields. Part 2. Application to continuous and discrete spectra of α
Authors: Krüger Jan
Published: March 2009

Theorems and criteria on stability of force-free fields, developed in part 1 (Krüger 1976) are illustrated for continuous, as well as discontinuous, spectra of α. Previous and new results are understood from a unified viewpoint.
Multiple spatial scaling and the weak-coupling approximation. Part 1. General formulation and equilibrium theory
Authors: Kleinsmith Paul E.
Published: March 2009

Multiple spatial scaling is incorporated in a modified form of the Bogoliubov plasma cluster expansion; then this proposed reformulation of the plasma weak- coupling approximation is used to derive, from the BBGKY Hierarchy, a decoupled set of equations for the one- and two-particle distribution functions in the limit as the plasma parameter goes to zero. Because the reformulated cluster expansion permits retention of essential two-particle collisional information in the limiting equations, while simultaneously retaining the well-established Debye-scale relative ordering of the correlation functions, decoupling of the Hierarchy is accomplished without introduction of the divergence problems encountered in the Bogoliubov theory, as is indicated by an exact solution of the limiting equations for the equilibrium case. To establish additional links with existing plasma equilibrium theories, the two-particle equilibrium correlation function is used to calculate the interaction energy and the equation of state. The limiting equation for the equilibrium three-particle correlation function is then developed, and a formal solution is obtained.
Nonlinear development of the plasma-beam instability in a magnetized plasma
Authors: Yamamoto Takashi
Published: March 2009

The nonlinear development of a plasma-mean system immersed in a static magnetic field B0 is investigated. The beam electrons are assumed to be streaming parallel to the direction of B0 and have a spread in the perpendicular component of the velocity. We restrict our consideration to the P instabilities which result in growing whistler waves aligned in a direction parallel to that of B0. Scaled equations describing the time evolution of these instabilities are derived under the assumptions that the beam density is small and that the resulting whistler wave is nearly sinusoidal. The perturbation of the perpendicular component of the electron velocity during the interaction can be excluded from the equation determining the wave dynamics, and then these scaled equations can be reduced to the simpler ones amenable to numerical solution which depends analytically on all the basic parameters of the problem. This solution shows that the amplitude of an unstable whistler wave first increases at the linear growth rate until the electrons are trapped and then, after overshooting, it approaches a steady state. The time evolution of the amplitude does not show an oscillation with a constant period; this results from the phase mixing enhanced by the spread in perpendicular velocities of the beam electrons.
Electrostatic ion cyclotron waves: Plasma heating, frequency shifts and linewidths
Authors: Benford Gregory
Published: March 2009

Ion cyclotron waves cannot be quasilinearly stabilized in Q-machine experiments because the electron distribution function does not have time to flatten while electrons pass through the plasma volume. We invoke a turbulently dissipative (or ‘resonance broadening’) model to explain the observed steady-state mode saturation. We give a qualitative picture of the important nonlinear features and their implications for plasma heating experiments. We extend the turbulently dissipative model to give nonlinear frequency shifts and a description of the mode linewidths in steady-state experiments. Turbulent resistivity is calculated and found to be unobservably small compared to the classical value. Implications for further experiments are discussed.
Propagation of electronic longitudinal modes in a truncated maxwellian plasma
Authors: Treguier J. P. , Henry D.
Published: March 2009

This paper is a theoretical and experimental study of the propagation of longitudinal electron waves in a collisionless, homogeneous, isotropic plasma, whose velocity distribution function is a truncated Maxwellian. Using the method of residues and numerical calculation, the behaviour of the electric field is found to be in good agreement with experimental results. The plasma parameters can be deduced from the theoretical dispersion curves matching the experimental points; they are found to agree well with those measured by electrostatic probes. In conclusion, a pragmatic approach to the resolution of the plasma inverse problem is discussed.
Enhanced fluctuations in a magnetized plasma due to the presence of an electromagnetic wave
Authors: Larsson J. , Stenflo L. , Tegeback R.
Published: March 2009

We calculate the electric field fluctuation spectrum in a magnetized plasma considering the influence of a finite amplitude pump wave.
Shock wave focusing by curved walls and staging of beam induced thermonuclear microexplosions
Authors: Winterberg F.
Published: March 2009

Because of the technical difficulties associated with the production of ultrashort beam pulses, the efforts to release energy from thermonuclear microexplosions are mainly directed at present towards confinement in a high-Z material solid wall, as in the original proposal by the author for relativistic electron beam induced fusion. The most common approach today is by the implosion of a solid high-Z material shell, for example, with an intense relativistic electron beam. We will show that better utilization of the beam energy may be possible with beam bombardment of a curved concave wall, setting off a shock wave which can be focused precisely onto the thermonuclear target. In addition, by a proper variation of the atomic weight and density in the layer of the wall material to be ablated by the energy deposition of the beam, the pulse length of the shock wave can be made substantially shorter than the pulse length of the beam.
Nonlinear resonant interaction of three longitudinal waves in a magnetized plasma
Authors: Das K. P. , Banerjee D.
Published: March 2009

Resonant nonlinear interaction among three longitudinal waves propagating along any arbitrary angle to a uniform magnetic field in a plasma is investigated by a quantum-mechanical method. The coupled mode equations and coupling coefficients are derived.
Nonlinear oscillations in warm plasmas with initial velocity perturbations
Authors: Cuperman S. , Mond M.
Published: March 2009

The Vlasov equation is solved by a phase-space boundary integration method in order to investigate the nonlinear frequency of an electron plasma mode. Unlike the familiar discrete particle simulation codes in which a limited number of particles may be considered, the present model represents a more realistic plasma case in which a very large number (practically unlimited) of plasma particles evolving in their self-consistent collective field is investigated. The unperturbed collisionless one-dimensional plasma system consists of warm electrons having a water-bag distribution to simulate equilibrium, and of static ions. The initial perturbation is introduced by changing the boundaries of the electron plasma such that υu = υ0 (1 + α.sin kx) and υl = − υ0(1 − α sin kx), υu and υl representing the upper and the lower boundaries, respectively. This corresponds to a standing wave perturbation. The results obtained for different wavelength perturbations λ ≡ 2π/k, and for several perturbation amplitudes α, are presented and discussed.
High-beta turbulence in two-dimensional magnetohydrodynamics
Authors: Fyfe David , Montgomery David
Published: March 2009

Incompressible turbulent flows are investigated in the framework of ideal magnetohydrodynamics. All the field quantities vary with only two spatial dimensions. Equilibrium canonical distributions are determined in a phase space whose co-ordinates are the real and imaginary parts of the Fourier coefficients for the field variables. In the geometry considered, the magnetic field and fluid velocity have variable x and y components, and all field quantities are independent of z. Three constants of the motion are found (one of them new) which survive the truncation in Fourier space and permit the construction of canonical distributions with three independent temperatures. Spectral densities are calculated. One of the more novel physical effects is the appearance of macroscopic structures involving long wavelength, self-generated, magnetic fields (‘magnetic islands’) for a wide range of initial parameters. Current filaments show a tendency toward consolidation in much the same way that vorticity filaments do in the guiding-centre plasma case. In the presence of finite dissipation, energy cascades to higher wavenumbers can be accompanied by vector potential cascades to lower wavenumbers, in much the same way as, in the fluid dynamic (Navier-Stokes) case, energy cascades to lower wavenumbers accompany enstrophy cascades to higher wavenumbers. It is suggested that the techniques may be relevant to theories of the magnetic dynamo problem and to the generation of megagauss magnetic fields when pellets are irradiated by lasers.
Statistical theory of frequency-dependent transport coefficients. Part 1. A two-fluid plasma in a magnetic field
Authors: Vasu G.
Published: March 2009

The statistical theory of the transport coefficients which was formulated in a previous paper (Vasu, 1976) is exemplified here by the case of a two-fluid plasma in a magnetic field. In addition, a general method is given which allows us to calculate frequency dependent transport coefficients; this method is a natural extension of the paper mentioned above. In the static limit, the transport coefficients obtained for the two-fluid plasma in a magnetic field are similar to those reported by Braginsky (1963) although there are some numerical differences. The frequency dependent transport coefficients obtained here include important resonant and time lag effects.
The m = 1 motion of a screw pinch measured by external magnetic probes
Authors: Pochelon A. , Keller R.
Published: March 2009

Measurements of the m = 1 growing mode of a linear screw pinch, by external dipole probes, are compared with the recorded plasma motion on streak photographs. Good agreement is found up to a maximum amplitude which depends on plasma density and growth rate.
Purely-growing parametric instabilities in plasmas at near-critical densities
Authors: Cassedy E. S.
Published: March 2009

The oscillating-two-stream instability (OTSI) is shown to be a zero-frequency absolute instability of the backward-wave parametric type. The instability is shown to be distinct from the concurrent parametric-decay-instability (PDI), even for sub-critical pump frequencies very near the critical value. The analogous ‘purely-growing Brissllouin instability’ (POBI) is shown not to exist, in a collinear interaction, with a travelling-wave pump. In fact we conclude that no such backward-wave, zero frequency, absolute instability could occur in any case where the two interacting, frequency shifted waves are on the same mode of propagation as the travelling-wave pump. Finally, the possibility of a PGBI by means of a standing-wave pump, as suggested earlier by Lashmore-Davies, is confirmed for a collinear interaction, through the identification on the Brilbum diagram of a zero-frequency, back-wave parametric interaction resulting from the coupling of Stokes and anti-Stokes light waves by the standing-wave pumb light wave.
A general dispersion relation for non-uniform magnetized plasmas
Authors: All'an W.
Published: March 2009

A general dispersion relation is derived for linear waves in a non-uniform, magnetized plasma using the polarized co-ordinate system. An equilibrium distribution function with general gradients in density and temperature (and differing parallel and perpendicular temperatures) is proposed using polarized tensors. A compact conductivity tensor is derived in terms of tensor quantities, including certain tensor moment integrals whose elements may be evaluated separately from a given problem. This is of importance in computational applications. The derivation is under the restrictions (a) small gradients, (b) the local approximation of Krall & Rosenbluth, and (c) β⊥ ≪ 1. Conditions for coupling of electrostatic and electro-magnetic modes are investigated.
Influence of a high frequency pump on trapped particle modes
Authors: Sundaram A. K. , Sen A.
Published: March 2009

We investigate the influence of a lower hybrid pump field on the dispersion characteristics of various trapped particle modes and delineate the conditions for their excitation or suppression. Our calculations also reveal the existence of certain new instabilities driven by the pump.
Statistical mechanics of a guiding centre plasma
Authors: Williamson J. H.
Published: March 2009

The equilibrium configurations of a one-species guiding centre plasma are circularly symmetric. Unlike results obtained for systems with artificial periodicity, the profiles depend uniquely on the energy and mean square radius. The random phase approximation is shown to be invalid.
Propagation of the higher-order Landau modes of electron plasma wave
Authors: Ikezawa S. , Kawai Y. , Hara T. , Nakamura Y. , Itoh T. , Kawabe T.
Published: March 2009

Propagation of electrostatic electron waves whose frequency is smaller than the electron plasma frequency in a large unmagnetized plasma is investigated both experimentally and theoretically. When a receiver is close to a transmitter, free-streaming electrons are detected owing to their large capacity for excitation. When the distance between the receiver and the transmitter becomes large, the third-order Landau mode is observed due to its smaller damping than that of free-streaming electrons. Finally, a dip in amplitude of the wave, caused by interference by the higher-order Landau modes, is seen. The results are in reasonable agreement with numerical calculation assuming a dipole excitation for the wave.
Magnetic dynamo action in two-dimensional turbulent magneto-hydrodynamics
Authors: Fyfe David , Joyce Glenn , Montgomery David
Published: March 2009

Two-dimensional magnetohydrodynamic turbulence is explored by means of numerical simulation. Previous analytical theory, based on non-dissipative constants of the motion in a truncated Fourier representation, is verified by following the evolution of highly non-equilibrium initial conditions numerically. Dynamo action (conversion of a significant fraction of turbulent kinetic energy into long-wavelength magnetic field energy) is observed. It is conjectured that in the presence of dissipation and external forcing; a dual cascade will be observed for zero-helicity situations. Energy will cascade to higher wavenumbers simultaneously with a cascade of mean square vector potential to lower wavenumbers, leading to an omni-directional magnetic energy spectrum which varies ask-⅓at lower wavenumbers, simultaneously with a build-up of magnetic excitation at the lowest wavenumber of the system. Equipartition of kinetic and magnetic energies is expected at the highest wavenumbers in the system.
Multiple spatial scaling and the weak coupling approximation. Part 2. Homogeneous kinetic equation
Authors: Kleinsmith P. E.
Published: March 2009

A modified form of the Bogoliubov plasma cluster expansion is applied to the derivation of a divergence-free kinetic equation from the BBGKY hierarchy. Special attention is given to the conditions under which the Landau kinetic equation may be derived from this more general formulation.
The test charge problem in the theory of bounded plasmas
Authors: Tegeback R. , Usenko A. S. , Yakimenko I. P. , Zagorodny A. G.
Published: March 2009

The test charge problem for a semi-infinite plasma is formulated. Expressions for the far field potential are derived for stationary and slowly moving test charges. By applying the superposition principle for uncorrelated dressed test particles we calculate the dynamic form factor as well as the energy spectrum of the spontaneous radiation field.
Solitary electrostatic ion cyclotron waves
Authors: Yu M. Y.
Published: March 2009

It is shown that solitary electrostatic ion cyclotron waves exist. An explicit solution is presented for the case of propagation near the ion-acoustic speed.
Self-generated magnetic fields in plasmas
Authors: Pert G. J.
Published: March 2009

The generation of magnetic fields by currents driven by the electron pressure gradient in non-uniform plasmas is considered. The equations for field generation and energy balance are derived under the MHD approximation. It is shown that there exists a class of waves, thermal magnetic waves, which propagate along surfaces of constant density. The properties of such waves are examined. In addition, a class of self-similar solutions are presented. These represent an unstable growth of magnetic field in localized plasma regions, i.e. magnetic hot spots.
Magnetic field aligned electric fields in an adiabatic plasma
Authors: Hruška A.
Published: March 2009

A stationary collisionless and neutral plasma flowing along magnetic lines of force (B-lines) is considered and the variation of electric potential along the B-lines is described. A steep magnetic field aligned gradient of electric potential is generated at a certain location whenever plasma moves along the lines of force.
Self-focusing of electormagnetic waves as a result of relativistic electron-mass variation
Authors: Spatschek Karl H.
Published: March 2009

Relativistic electron-mass variations due to the presence of intense electromagnetic radiation in the plasma cause a nonlinear refractive index. Using a variational principle the latter is obtained up to fourth order in the electric field amplitude and it is shown that nonlinear effects of the second order lead to self-focusing of a beam of radiation. By nonlinear optics considerations, the self- focusing length of an axially symmetric beam is obtained. Including higher- order dispersive effects it is shown that within the thin-beam approximation thecomplex electric field envelope obeys a cubic nonlinear Schrödinger equation with an attractive self-consistent potential. The cylindrically symmetric nonlinear Schrödinger equation predicts collapse of the radiation at the self-focusing distance. The nature of the self-focusing singularity is analysed and it is shown that higher-order nonlinearities saturate the amplitude. Then oscillations of beam radius along the axial direction occur.
Temperature effects in non-symmetric three-component counter-streaming electron plasmas: theory and computer simulation experiments
Authors: Cuperman S. , Mond M. , Roth I. , Gomberoff L.
Published: March 2009

Temperature effects on the electrostatic instability of non-symmetric electron plasma systems consisting of two warm counter-streaming beams and of warm background particles are investigated linearly (analytically and numerically) and nonlinearly (by computer simulation experiments) for the case of Heaviside and moderately warm Maxwellian particle distribution functions. The non-symmetry is due to unequal temperatures, streaming velocities and particle densities in the beams. Other variable parameters investigated are the relative thermal velocities of the beams and background as well as the relative background particle concentration. When the beam temperatures are unequal, unstable waves with Re ω > 0 and propagating in the direction of the beam with lower temperature occur; this is in contrast to the equal temperature symmetric two-stream case, in which the unstable waves have Re ω = 0 (standing waves) and the temperature effect is only to decrease the growth rate. When three warm components are present in the system, the following results hold: (i) the beam temperatures have the effect of decreasing the importance of the unstable standing waves with Re ω > 0 (and growth rate yB) relative to the waves with Re w = 0 (growth rate yA) which occur in cold three-component symmetric systems; in addition to this, both γA, max and γB, max decrease with increasing temperature; (ii) the background temperature has the general effect of reducing the absolute maximum growth rate. For relative background temperatures above a certain critical value, a separation (in k and ω spaces) of regions B and A occurs; γA, max increases and γB, max decreases with increasing relative background temperature.
Solitary surface waves
Authors: Yu M. Y. , Zhelyazkov I.
Published: March 2009

We consider nonlinear surface waves on a cold plasma half-space. It is found that for a certain region of the wavenumber spectrum, supersonic envelope surface wave solitons exist.
Optimization of plasma quiescence
Authors: Jones R.
Published: March 2009

A procedure is outlined for obtaining a high degree of quiescence in a magneto- plasma.
A model for precursor structure in supercritical perpendicular, collisionless shock waves
Authors: Sherwell D. , Cairns R. A.
Published: March 2009

Magnetosonic solitons may be given smooth increasing profiles by assuming the presence within the wave of a current distribution Jy(x) of trapped ions perpendicular to Bz(x) and the wave velocity Vx. Suitable ions are found immediately upstream of perpendicular, collisionless shock waves and these are coincident with the often observed ‘foot’ in magnetic field profiles of moderately supercritical shocks. By modelling Jy(x) we apply the theory to previous experiments where Jy(x) is observed, and are able to reproduce reasonably, and thus explain, the profiles in the foot. Insight into a number of features of fast shocks is obtained.
Excitation of an upper hybrid wave by a Gaussian electromagnetic beam in ordinary mode
Authors: Sodha M. S. , Tewari D. P. , Patheja B. L. , Sharma R. P.
Published: March 2009

This paper presents an investigation of the excitation of an upper hybrid wave in a hot collisionless magnetoplasma by a Gaussian EM beamm propagation perpendicular to the static magnetic field and having its electric vector polarized along the direction of the static magnetic field (ordinary mode). On account of the Gaussian intensity distribution of the EM beam the ponderomotive force becomes finite and the electorns are redistributed. The amplitude of the upper hybrid wave, which depends on the background electron concentration, is thus nonlinearly coupled with the EM wave. When the initial power of the EM wave is between the two critical powers Pcr1 and Pcr2 (Pcr1 < Pcr2) self-focusing occurs. On the other hand, for very low powers (P < Pcrl) and high powers (P > Pcr2), monotonic and oscillatory defocusing of the EM wave occurs. The dynamics of the excitation of the upper hybrid wave in these different power domains of the pump wave is accordingly modified. Moreover it is seen that the effect of changing the strength of the static magnetic field on the nonlinear coupling, and hence on the dynamics of the excitation of the upper hybrid wave, is significant.
Minimum non-spherical implosion velocity for inertial confinement fusion
Authors: Winterberg F.
Published: March 2009

For a non-spherical ellipsoidal or conical implosion with an eccentricity of ε≃10 the minimum implosion velocity is computed to be less than 100km sec−1.
A phenomenological theory of drift wave type plasma turbulence
Authors: Sen Amiya K.
Published: March 2009

A phenomenological theory of drift type turbulence in inhomogeneous magnetized plasma is developed in the spirit of the Kolmogorov spectrum of hydrodynamic turbulence. We model the spectrum in terms of subspectra: production, equilibrium and dissipation. Different nonlinearities and either weak or strong turbulence characterize different subspectra.
Conductivity tensors of all orders in a collisionless plasma
Authors: Larsson J.
Published: March 2009

Expressions for the conductivity tensors of all orders are obtained, for both relativistic and unrelativistic magnetized Vlasov–Maxwell plasmas, closely related to the well-known formula for the linear conductivity tensor. Thus the unperturbed orbit integrations and the ø-integration in velocity space have been performed and each conductivity tensor is expressed as an infinite series with terms involving ordinary Bessel functions. Jα(K⊥V⊥/ωc) and denominators of type ω–KzVz–αωc for integers.α a. The symmetries related to the Manley-Rowe relations are explicitly seen in the formulae presented. These conductivity tensor formulae provide a much better starting point than the basic equations for many nonlinear investigations.
Determination of wave growth from measured distribution functions and transport theory
Authors: Dum C. T. , Marsch E. , Pilipp W.
Published: March 2009

A stability analysis which directly uses particle distribution functions determined from experiments or transport theory, rather than model distributions, is carried out. The features of distribution functions relevant to whistlers, ion cyclotron waves, including their low-frequency extensions for propagation along the magnetic field, and to ion-acoustic waves are analyzed in detail. The dependence of wave growth on the precise shape of the distributions and the numerical feasibility of the method is demonstrated by the use of measured solar wind distributions.
Parametric decay of extraordinary electromagnetic waves into two upper hybrid plasmons
Authors: Grebogi Celso , Liu C. S.
Published: March 2009

The effects of a self-generated magnetic field in a laser produced plasma on the parametric decay of an extraordinary electromagnetic wave into two upper hybrid plasmons is examined for arbitrary magnetic field intensity and arbitrary ratio k/k0. Owing to the presence of magnetic field, the linear Landau damping is greatly reduced and the spectrum of unstable modes is significantly modified for kλD≳ 0·2.
Statistical thermodynamics of temperature anisotropy driven Weibel instabilities
Authors: Lemons Don S. , Winske D.
Published: March 2009

A statistical theory of one- and two-dimensional temperature anisotropy driven Weibel instabilities is proposed. The theory is based on a two-temperature canonical distribution and the mean field approximation. It applies to a nonlinear, periodic, charge-neutralized, and collisionless system. Using a partition function formalism, equations of state are derived which predict upper bounds on the magnetic field energy produced by a quasi-static evolution of these instabilities. Theoretical predictions are in good agreement with results from numerical simulations.
Exact electron-acoustic solitary waves
Authors: Buti B. , Mohan M. , Shukla P. K.
Published: March 2009

Nonlinear propagation of an electron-acoustic wave in a magnetoplasma is considered. Accounting for the exact electron and ion nonlinearities, we show that the equations governing the dynamics of these waves can be written in terms of the energy integral of a classical particle. A careful analysis of the potential reveals the existence of exact planar solitary waves. Application of our investigation to space plasmas is pointed out.
Self-consistent profile modification in the underdense region of laser-produced plasmas
Authors: Sanmartín J. R. , Montañes J. L.
Published: March 2009

Profile modification in the underdense region of laser-plasmas with spatially uniform temperature Te, is studied. A multiple scale method is used to describe self-consistently the plasma flow and the wave field, in (i) the scale of the field wavelength, and (ii) the overall expansion scale. For Te∝ taordinary differential equations with definite boundary conditions are obtained. For a = 0 and weak fields, we explicitly solve the equations and relate the field in the critical layer to the incident field.
Nonlinear Landau damping of large-amplitude Langmuir waves and formation of standing nonlinear waves
Authors: Pavlenko V. P.
Published: March 2009

The interaction of nonlinear Langmuir wave packets corresponding to periodic solutions of the nonlinear Schrödinger equation with thermal plasma particles is considered. The mechanism of interaction is nonlinear Landau damping. The wave packets are slowed down owing to interaction but their amplitudes remain essentially unchanged. The characteristic scale lengths of the slowing down are determined.
Generation of whistler-mode signals in the presence of enhanced fluctuations in plasmas
Authors: Nambu M. , Bujarbarua S. , Shukla P. K. , Spatschek K. H.
Published: March 2009

Acceleration of an electron by the electrostatic field of ion wave fluctuations is considered including the external magnetic field. It is found that an accelerated electron can emit unstable electromagnetic waves which propagate along the guide magnetic field. As an example, we discuss the generation of right-handed circularly polarized whistler waves. Application of our result to laboratory and space plasmas is examined.
Hall effects on MHD flow past an accelerated plate
Authors: Soundalgekar V. M. , Ravi S. , Hiremath S. B.
Published: March 2009

An exact solution of the MHD flow of an incompressible, electrically conducting, viscous fluid past a uniformly accelerated infinite plate has been presented. The velocity profiles are shown graphically and the numerical values of axial and transverse components of skin friction are tabulated. At high values of the Hall parameter, wt, the velocity is found to be oscillatory near the plate.
Oscillating two-stream instabifity of upper-hybrid laser radiation in a plasma
Authors: Sharma R. R.
Published: March 2009

In the vicinity of a turning point, a high-power laser radiation (in the upper- hybrid mode) is unstable for short wavelength, purely growing perturbations, viz, oscillating two-stream instability. The nonlinearity in the low-frequency response arises through the parallel pondermotive force whereas in the high- frequency response it arises through the equation of continuity. In the limits of long and short perpendicular wavelengths, κ┴ρe< 1 and κ┴ρe > 1, the growth rates are found to be γ∞ │κ┴.V0┴│2, where ρe and V0┴ are the electron Larmor radius and oscillatory drift velocity.
Fluid instabifities of a uniformly imploding ablatively driven shell
Authors: Book David L. , Bernstein Ira B.
Published: March 2009

The linear stability of a uniformly imploding shell, modelled as an ideal polytropic fluid, is investigated. Two types of unstable modes are found: incompressible irrotational perturbations localized at the outer surface, ascribable to Rayleigh—Taylor instability, and compressible modes, associated with convective instabiiity. Kidder's result for the Rayleigh—Taylor modes is shown to hold independently of the form of the shell density profile. By means of a variational principle it is shown that the criterion for convective instability is the existence of a region within which d(pp-γ)/dr> 0. Analytic solutions for both spatial and temporal dependence of the perturbations are presented, and the results applied to pellets imploded by the action of a laser or charged-particle beam.
Generation of an electrostatic pulse by two electromagnetic pulses in a plasma
Authors: Thakur Alok , Sharma R. P.
Published: March 2009

This paper presents an investigation of the excitation of an electrostatic pulse in a hot collisionless plasma by two Gaussian EM pulses at the difference frequency w1–w2, w1 and w2being the angular frequencies of two EM pulses. When the EM pulses have intensity distributions which are uniform in space and Gaussian in time, the generated electrostatic pulse is Gaussian in time with pulse width [t210 t220/ (t210+ t220)]½, where t10 and t20 are the EM pulse widths. When. the two EM pulses have Gaussian distributions in a plane transverse to the direction of propagation, the generation phenomena are considerably modified as a result of the cross-focusing of the two EM pulses.
Nonlinear phenomena in plasma with relativistic high-frequency electron motion
Authors: Berezhiani V. I. , Tsintsadze N. L. , Tskhakaya D. D.
Published: March 2009

Considering the influence of relativistic effects on the plasma motion in a HF field, we show that even small relativistic terms qualitatively change the propagation character of nonlinear longitudinal and transverse waves. We also find new regions and branches for the modulational instability.
Nonlinear coupling of five waves in non-uniform streaming plasma
Authors: Pramanik G. C.
Published: March 2009

In this paper, nonlinear interaction of five monochromatic waves in a hot nonuniform streaming electron plasma has been presented. The method of formulation of the problem is based on the coupled mode theory. The wave–wave interaction phenomena have been analysed in the case of three longitudinal and two transverse waves. Furthermore, the presence of a stream velocity and its uniform gradient offers a generalization of the nonlinear interaction of an earlier work.
Transverse MHD shock waves in a partly ionized plasma. Part 1. Structure equations and topology
Authors: Mathers C. D.
Published: March 2009

The structure of transverse MHD shock waves in an initially partly ionized plasma is studied using a three-fluid model with collisional transport coefficients. This model includes the effects of non-equilibrium ionization and of ion velocity slip. A closed set of structure equations is obtained and it is shown that they have a saddle-point – saddle-point topology which prohibits direct integration. In distinction from previous MHD shock structure studies, it is not possible to reduce the number of variables in a realistic manner to allow direct integration, nor is it possible to use the method of matched asymptotic expansions. An iterative solution method is presented in this paper, based on a detailed analysis of the integral curve topology.
Transverse MHD shock waves in a partly ionized plasma. Part 2. Shock structure in hydrogen
Authors: Mathers C. D.
Published: March 2009

The structure of transverse MHD shock waves in a partly ionized hydrogen plasma is studied using a three-fluid model with collisional transport coefficients developed in Part 1. The morphology of the various sublayers in the shock front is analyzed in detail and it is shown that strong shock waves have a characteristic viscous structure. Weak to moderate strength shock waves display a resistive structure in which the enhanced transverse resistivity due to ion-slip plays a significant role, leading to a pronounced peak in the ion temperature profile. Calculated shock structure profiles are also compared with experimental temperature data. Results in the form of tables and figures are presented for shock waves with fast Mach number ranging from 1–10 in hydrogen plasma with initial degree of ionization ranging from 5–100%.
Nonlinear cylindrical or spherical converging ion-acoustic pulses
Authors: Okutsu E.
Published: March 2009

The Korteweg–de Vries equation which describes cylindrical or spherical converging ion-acoustic waves is solved numerically. Soliton-like structures are shown to be generated not only from compressive but also from rarefactive and mixed initial pulses. The velocity of the soliton-like structures is dependent on the initial pulse shape.
On the kinetic instabilities of uniform magnetized plasmas with generalized loss-cone distribution functions
Authors: Gomberoff L. , Cuperman S.
Published: March 2009

A general proof is given that in uniform magnetized plasmas described by generalized loss-cone distribution functions (loss-cone index l, thermal velocity α∥, and perpendicular spread α⊥), electromagnetic, electrostatic, or coupled-mode instabilities are insensitive to the separate values of l and (α⊥/α∥); they depend rather, on the effective thermal anisotropy Aeff ≡ (T⊥/T∥)eff-1, where (T⊥/T∥)eff ≡ (l + 1) (α2⊥/α2∥). In the case of parallel propagation this statement is limited only by the linearization assumption; in the oblique propagation case, the additional condition λ⊥/rL ≫ 1 is required (λ⊥ = 1/k⊥, where k⊥ is the wave vector perpendicular to the external magnetic field, and rL is the Larmor radius). Thus, dispersion relations and their solutions obtained by using simple bi-Maxwellian distribution functions can be used directly for the complex case of generalized loss-cone distribution functions by simply replacing the anisotropy factor, A ≡α2⊥/α2∥-1, by Aeff defined above. This result explains earlier conclusions that the growth rate of the whistler instability is independent of the explicit value of the loss-cone index l, for a given thermal anisotropy.
Low-frequency heating of doublets
Authors: Jensen T. H. , McClain F. W. , Grad H.
Published: March 2009

Heating of a doublet plasma by driving an axisymmetric mode at low frequency may be an attractive means for auxiliary heating. The attractiveness of the method stems from (1) the low technology required for low-frequency power sources, (2) the fact that the field-shaping coils required for doublets may also be used as the antennae for transmitting the power, (3) the possibility of transmitting the power through a resistive vacuum wall, (4) the insensitivity to the plasma temperature and density and (5) the relative simplicity of the physical model. The utility of the concept depends on the existence of a special axisymmetric eigenmode in the resistive M.HD approximation which is used. This mode has nodes through the elliptic axes of the doublet equilibrium and an antinode at the hyperbolic axis. It is remarkable that the dissipation per cycle of this mode remains large at low plasma resistivity. This paper describes a linear theory for such heating.
Dispersion and energy conservation relations of surface waves in semi-infinite plasma
Authors: Atanssov V.
Published: March 2009

The hydrodynamic theory of surface wave propagation in semi-infinite homogeneous isotropic plasma is considered. Explicit linear surface wave solutions are given for the electric and magnetic fields, charge and current densities. These solutions are used to obtain the well-known dispersion relations and, together with the general energy conservation equation, to find appropriate definitions for the energy and the energy flow densities of surface waves. These densities are associated with the dispersion relation and the group velocity by formulae similar to those for bulk waves in infinite plasmas. Both cases of high-frequency (HF) and low-frequency (LF) surface waves are considered.
Ion beam excitation of ion-cyclotron waves and ion heating in plasmas with drifting electrons
Authors: Hauck J. P. , Böhmer H. , Rynn N. , Benford Gregory
Published: March 2009

Ion-cyclotron waves are excited by a cesium ion beam in a cesium Q-machine plasma with drifting plasma electrons. These interactions differ significantly from those in the case of drifting ions in that the drifting electrons play an active role in the instability mechanism. The observed mode frequencies are slightly below those of the electron current driven modes. These waves can be convectively or absolutely unstable, depending on the ion beam velocity. For low beam velocities the instabifities are convective in character with large spatial growth rates ki/kr ∼ 0.2. For larger beam velocities the instabilities are absolute in character with temporal growth rates 0.04. The absolute instabilities are similar to two-stream instabilities. Plasma ion heating is observed and is consistent with a model in which mode amplitudes are saturated by diffusion effects.
Measurement of non-Maxwellian electron velocity distributions in a reflex discharge
Authors: Phipps C. R. , Bershader D.
Published: March 2009

Thomson scattering was used to determine space- and time-resolved electron velocity distribution components parallel and transverse to the magnetic field direction in a Penning-type reflex discharge in hydrogen. Electron densities were of the order 1013 cm-3, and temperatures about 3eV. For magnetic field strengths less than about 200 G, Maxwellian distributions were obtained over an energy range six times the thermal energy. Temperatures were in excellent agreement with Langmuir probe data. However, for fields of about 4500 G chaotic plasma potentials were observed with the Langmuir probe. In this regime, in which the plasma was unstable, Thomson scattering showed electron velocity distributions having central temperatures of about 2eV and wing temperatures of 15–20 eV. The experiment design employed led to extremely low stray light levels permitting clean measurements at the laser wavelength and detection of scattered signals as faint as two photons.
Stimulated Raman backscattering in a magnetized plasma
Authors: Willett Joseph E. , Maraghechi Behrooz
Published: March 2009

The parametric decay of an intense electromagnetic (pump) wave into a back-scattered electromagnetic wave and an electron plasma wave is considered. The dispersion relation for a homogeneous magnetized plasma in the presence of the pump wave is developed in the cold-plasma approximation with the pump frequency large compared to the cyclotron and plasma frequencies. Formulae are derived for the growth rate γ and threshold power PT associated with the instability. The effects of the magnitude and direction of the static magnetic field on γ and PT are studied numerically.
Ion-acoustic solitons in an electromagnetically irradiated magnetoplasma
Authors: Patel L. A.
Published: March 2009

We have investigated how the presence of an electromagnetic beam and a static magnetic field influences the ion-acoustic solitons in a plasma. A modified KdV equation is derived in which the electromagnetic field plays the role of a source term. By using the perturbation analysis technique, it is shown that a homogeneous electromagnetic beam does not destabilize the ion-acoustic solitons; it reduces the amplitude, but not the velocity, of the solitons. However, any inhomogeneity in the electromagnetic field intensity does destabilize the ion-acoustic solitons; albeit not to an appreciable extent for typical cases.