bluuebunny/crossref_metadata_2025 huggingface dataset:
Phenomenology of hydromagnetic turbulence in a uniformly expanding medium
Authors: Matthaeus William H. , Zank Gary P. , Oughton Sean
Published: March 2009

A simple phenomenology is developed for the decay and transport of turbulence in a constant-speed, uniformly expanding medium. The fluctuations are assumed to be locally incompressible, and either of the hydrodynamic or non-Alfvénic magnetohydrodynamic (MHD) type. In order to represent local effects of nonlinearities, a simple model of the Kaármá-Dryden type for locally homogeneous turbulent decay is adopted. A detailed discussion of the parameters of this familiar one-point hydrodynamic closure is given, which has been shown recently to be applicable to non-Alfvénic MHD as well. The effects of the large-scale flow and expansion are incorporated using a two-scale approach, in which assumptions of particular turbulence symmetries provide simplifications. The derived model is tractable and provides a basis for understanding turbulence in the outer heliosphere, as well as in other astrophysical applications.
A Hamiltonian formulation in the electrodynamics of charged moving fluids
Authors: Merches I.
Published: March 2009

By using the concept of combined field, we present a simple and symmetric Hamiltonian formulation for an infinitely conducting fluid, moving in an electromagnetic field. The definition of the combined field potentials makes it possible to replace the interaction between the electromagnetic field and charges by an interaction between two fields. Some applications are made, to prove the theory (e.g. the Hamiltonian of a point charge, Fourier representation).
Drift instabilities in anti-loss-cone plasmas
Authors: Buti B.
Published: March 2009

The paper investigates the stability of electrostatic waves in non-uniform magnetoplasmas, governed by anti-loss-cone distributions. A new high- frequency anti-loss-cone instability occurs if ρ > ρc. (ρ is the parameter charactensing the strength of the anti-loss-cone.) An increase in ρ increases the growth rates for this instability, but stabilizes the low-frequency instability that exists even in the absence of the anti-loss cone. The growth rates can be of order 0.1Ωe.
Current-driven Alfvén instability
Authors: Hollweg Joseph V. , Smith Dean F.
Published: March 2009

The current-driven Alfvén instability is discussed analytically. The instability is driven by the resonant Landau and transit-time terms for propagation not parallel to B0. The critical current for instability is slightly less than the corresponding one for the ‘k-like’instability; thus, the instability discussed in this paper may be the more important for the parameter range in which our approximations are valid. The effect of current flow on the magnetosonic mode is also discussed, but no instability is found.
Like-particle collisional interactions in an inhomogeneous plasma
Authors: Santini F. , Engelmann F.
Published: March 2009

A like-particle collision operator is derived for an inhomogeneous plasma with a periodic equilibrium potential which traps part of the particle population. The derivation is made in the guiding centre approximation (one-dimensional orbits along a strong magnetic field), and only resonant interactions are considered. The effect of the particle bouncing replaces that of the three-dimensional orbits in this limit. For resonances between different harmonics of the bounce motion the operator does not vanish as happens in the classical one-dimensional case. A discussion of the general equations describing this effect is presented together with some estimates.
The generation of interpenetrating plasma flows in an expanding discharge
Authors: Davis H. A. , Mahdavi M. A. , Lovberg R. H.
Published: March 2009

We report on an experiment designed to study collisionless shock waves in an inverse pinch discharge using argon. A magnetic disturbance was generated which propagated ahead of the driving field at twice the piston speed. Measurements of the magnetic and electric field structures, electron density and temperature, as well as ion velocities revealed that the disturbance was produced by a beam of plasma moving through the ionized ambient plasma rather than by a true shock wave. Calculations of ion trajectories using measured electric fields demonstrated that the beam originated at small radii and early times, and was not the result of a steady specular reflexion from the piston field. It is concluded that the ions comprising this stream, which were collisionless relative to the ambient ions, did not couple to the background plasma even though a strong magnetic field was applied.
High-frequency ion electrostatic instabilities in mixed warm–cold plasma
Authors: Gomberoff L. , Cuperman S.
Published: March 2009

It is shown that an ion loss cone distribution function with m ≥ 1 becomes unstable against electrostatic waves with ω ≫ Ωp and k0 = 0 in the presence of a cold plasma population, in contrast with pure warm systems, which require m ≥ 3 for instability. This result is an extension to high frequencies, ω ≫ Ω of similar conclusions reached by Pearlstein et al. (1966) and Farr & Budwine (1968), for ω-values equal to the first few harmonics of the proton gyrofrequency.
Relativistic nonlinear plasma waves in a magnetic field
Authors: Kennel C. F. , Pellat R.
Published: March 2009

We study five relativistic plane nonlinear waves: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfvén waves, linearly polarized transverse waves propagating in zero magnetic field, and finally the relativistic analogue of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an ‘electron–positron’ plasma guides us to equations which have the form of a one dimensional potential well. Our solutions indicate that a large-amplitude super luminous wave determines the average plasma properties, and not vice versa. For example, linearly polarized waves impose a plasma number flux equal to the relativistic addition of Nc/β and NVE, where N is the density, c the speed of light, β (>1) the ratio of the phase speed to c and VE the E × B speed measured in the frame moving with speed c/β with respect to the frame in which the phase speed is measured. The implications for cosmic ray acceleration in pulsar magnetospheres are considered.
Linear stability analysis of a class of solutions of the filament model for a stationary field electron ring accelerator
Authors: Chen Techien , Ehrman J. B.
Published: March 2009

The stability of two of the short time scale solutions obtained in the filament model for a stationary field electron ring accelerator is studied by means of a linearized perturbation on the electron and ion distribution functions. The Vlasov equations for the electrons and ions are coupled. The coupling of these equations results in a Fredholm integral equation which can be converted into an infinite system of linear equations. A stability criterion is then obtained from the zeros of the truncated determinants of the coefficients of the infinite system. One of the equilibrium solutions, for which the ion density in phase space is a monotonic non-increasing function of the unperturbed ion Hamiltonian, is entirely stable. The other solution, for which this monotonicity does not hold, may be unstable, but turns out to be stable provided that both the non-monotonicity parameter ∈ and the ratio of the ion period to the electron period are not too large. In the nonmonotonic case, the ion density in physical space also does not drop off to zero monotonically from the centre of the ring. For the unstable cases, the instability is driven by a ‘spike’ in the phase-space ion density located at the maximum value of the unperturbed ion Hamiltonian.
Kinetic theory of surface wave propagation along a hot plasma column
Authors: Atanassov V. , Zhelyazkov I. , Shivarova A. , Genchev Zh.
Published: March 2009

In this paper we propose an exact solution of Vlasov and Maxwell's equations for a bounded hot plasma in order to derive the dispersion relation of the axially-symmetric surface waves propagating along a plasma column. Assuming specular reflexion of plasma particles from the boundary, expressions for the components of the electric displacement vector are obtained on the basis of the Vlasov equation. Their substitution in Maxwell's equations, neglecting the spatial dispersion in the transverse plasma dielectric function, allows us to determine the plasma impedance. The equating of plasma and dielectric impedances gives the wave dispersion relation which, in different limiting cases, coincides with the well-known results.
Electromagnetic instabilities in high-β anti-loss-cone plasmas
Authors: Buti B.
Published: March 2009

The stability of electromagnetic drift waves in high-β anti-loss-cone plasmas is investigated. These waves with propagation transverse to the external magnetic field are found to be unstable provided ρ > ρc, where ρ is the parameter which characterizes the strength of the anti-loss-cone. The growth rates associated with this instability (which may be called the anti-loss-cone drift instability) are ˜ 0·1Ωe and they increase with the strength of the anti-loss-cone.
Macroscopic plasmadynamical modes in a complete two-fluid description
Authors: Balescu R. , Paiva-Veretennicoff I.
Published: March 2009

The paper contains an analysis of the linearized plasma-dynamical equations, including the energy conservation equations, and accounting completely for all the dissipative mechanisms, in the absence of external fields. The eigenvalues of the 14 plasmadynamical modes are obtained systematically in terms of the transport coefficients of the plasma.
Energetic ion distribution resulting from neutral beam injection in tokamaks
Authors: Gaffey John D.
Published: March 2009

The Fokker-Planck equation is studied for an energetic ion beam injected into a magnetized plasma consisting of Maxwellian ions and electrons with υthi ≪υb≪ υthe. The time evolution of the fast ion distribution is given in terms of an infinite sum of Legendre polynomials for distributions that are axisymmetric about the magnetic field. The effect of charge exchange is included. The resulting ion distribution is somewhat isotropic for velocities much less than the injection velocity, however, the distribution is sharply peaked in both energy and pitch angle for velocities near the injection velocity. Approximate asymptotic expressions are given for the distribution in the vicinity of the injected beam and for velocities greater than the injection velocity. The effect of a weak parallel electric field is also given.
Modification of a turbulent spectrum through the injection of a monochronatic wave. Part 1. The evolution equation
Authors: Brinca Armando L.
Published: March 2009

Analysis of the influence of an injected monochromatic wave on a turbulent spectrum shows that the evolution equation of the ensemble average distribution function is significantly different from the classical diffusion equation in velocity space. The average turbulent collision operator involves the usual spatial and temporal autocorrelation of the stochastic field, together with the correlation of this field with its spatial gradient, and the velocity derivatives are complemented by spatial derivatives
Ray tracing in weakly nonlinear moving media
Authors: Censor Dan
Published: March 2009

Electromagnetic ray propagation is discussed for weakly nonlinear dispersive media. Specialization to periodic waves justifies the use of a self-excitation model and facilitates the construction of a complete system of ray equations. The solution describes the evolution of frequencies, propagation vectors and amplitudes along the ray path. The formalism may be extended to include the case where a velocity field exists. This is based on special relativity and the Minkowski model for the electrodynamics of moving media. It is assumed that the velocity field varies slowly in space and time. The results are relevant to propagation problems in weakly nonlinear plasmas and optical media.
Nonlinear interaction between three ordinary electromagnetic modes
Authors: Muñoz P. , Dagach S.
Published: March 2009

In this paper we consider the resonant interaction between three modified ordinary electromagnetic waves, which propagate perpendicular to a constant magnetic field. We show that for the modified mode to be a normal mode we must have the unperturbed current equal to zero. Using the averaged Lagrangian method, we calculate the coupling coefficient for the resonant interaction between three of these modes. It is proportional only to the cube of the drift velocity, as expected from the vanishing of the unperturbed current.
Low-frequency instabilities of a warm plasma in a magnetic field: Part 1. Instabilities driven by field-aligned currents
Authors: Smith Dean F. , Hollweg Joseph V.
Published: March 2009

The marginal stability of a plasma carrying current along the static magnetic field with isotropic Maxwellian ions and isotropic Maxwellian electrons drifting relative to the ions is investigated. The complete electromagnetic dispersion relation is studied using numerical techniques; the electron sums are restricted to three terms which limits the analysis to frequencies much less than the electron gyro-frequency, but includes frequencies somewhat above the ion gyro-frequency. A ‘kink-like’ instability and an instability of the Alfvén mode are found to have the lowest threshold drift velocities in most cases. In fact the threshold drift for the kink-like instability can be significantly less than the ion thermal speed. Electrostatic and electromagnetic ion-cyclotron instabilities are also found as well as the electro-static ion-acoustic instability. No instability of the fast magnetosonic mode was found. The stability analysis provides only threshold drift velocities and gives no information about growth rates.
Ion and electron heating in the earth's bow shock region
Authors: Revathy P. , Lakhina G. S.
Published: March 2009

Ion and electron heating in the earth's bow shock region is studied in terms of the modified two stream instability by treating the electron's response to be electromagnetic and that of ions to be electrostatic. The modified two stream flute mode, driven unstable by the density and temperature gradients, can heat the ions to about 50 times their upstream temperature. However, the electrons are heated mainly by the non-flute mode and their temperature can be increased by a factor of 1·5 or more. Consequently the ions will be hotter than the electrons downstream of the shock, as observed by satellites.
Electromagnetic radiation from line sources embedded in a moving bounded magnetoplasma sheath
Authors: Mukherjee P. K.
Published: March 2009

The problem of electromagnetic radiation from electric and magnetic line sources embedded in a moving bounded magrietoplasma sheath situated over a perfectly conducting plane is studied. The radiation fields due to the line sources consist of both E and H modes, excited simultaneously in the moving sheath. However, when the magnetic field lies parallel to the line source and is oriented normal to the direction of the sheath motion, the modes become decoupled. The far-zone radiation fields for both the electric and the magnetic line sources have been obtained, using the method of saddle-point approximation. The corresponding radiation patterns are also obtained and their variation studied as a function of the magnetic field, the location of the line source, the thickness and the velocity of the moving plasma sheath. It is found that the fields radiated by an electric line source remain unaffected by the presence of an ambient magnetic field and that, in the presence of a sufficiently intense magnetizing field, the magnetic line source over a perfectly conducting plane radiates as though surrounded by vacuum.
Theoretical cross-spectrum of the microfield measured by two small dipoles in a warm isotropic plasma
Authors: Pottelette R. , Chauliaguet C. , Storey L. R. O.
Published: March 2009

We suggest that the electron density and temperature of a plasma could be determined by immersing two small dipole antennae in it, and by measuring, as a function of frequency, the cross-spectrum of the random signals that they receive. When the plasma is in thermal equilibrium, this spectrum is related simply, by Nyquist's theorem, to the real part of the mutual impedance of the two antennae. We have studied the case where, in addition, the plasma is collisionless and no magnetic field is present. The spectrum has a main resonance peak slightly above the plasma frequency, while for still higher frequencies it exhibits oscillations, the amplitudes of which decrease as one moves away from the plasma frequency. The main resonance peak becomes sharper, but smaller, as the distance between the antennae becomes large compared with the Debye length.
Stability of cylindrical rotating plasmas to axisymmetric electrostatic perturbations
Authors: Barston E. M.
Published: March 2009

Necessary and sufficient conditions for the exponential stability of an N-component, warm or cold, rotating cylindrical plasma to axisymmetric electrostatic perturbations are obtained. The plasma is immersed in an axial magnetic field B0(r), where r is the radial co-ordinate, and the equilibrium quantities are permitted to be arbitrary functions of r consistent with the 0-order equations. The maximal growth rate of an unstable system is shown to be determined by a maximum principle.
Finite amplitude effects in the propagation and interaction of m =0 torsional hydromagnetic waves
Authors: Jones I. R. , Cheetham A. D.
Published: March 2009

In this paper the nonlinear behaviour of the m = 0 torsional hydromagnetic wave is analyzed. Two cases have been considered: the nonlinear self-interaction of a single torsional wave and the nonlinear interaction of two identical, oppositely propagating torsional waves. In the first case the nonlinear terms in Ohm's law and the equation of motion generate a second order perturbation which accompanies the primary wave and has two components: a steady component and an oscillatory component having twice the frequency of the primary torsional wave. In the second case studied the self and cross-interactions of the two waves again generate a second order perturbation field. The existence of certain critical wavelengths, at which geometric resonances of the perturbation occur, is established.
Approximate theory of large-amplitude wave propagation
Authors: Kim H.
Published: March 2009

An orbit perturbation procedure is applied to the description of monochromatic, large-amplitude, electrostatic plasma wave propagation. In the lowest-order approximation, untrapped electrons are assumed to follow constant-velocity orbits and trapped electrons are assumed to execute simple harmonic motion. The deviations of these orbits from the actual orbits are regarded as perturbations. The nonlinear damping rate and frequency shift are then obtained in terms of simple functions. The results are in good agreement with previous less approximate analyses. A significant feature of the analysis is that it treats a single wave by techniques previously applied to turbulent spectra. The analysis can consequently be extended to the case of a large-amplitude wave interacting with a lower-amplitude spectrum of waves.
The effect of a high-frequency potential of the reflexion of p-polarized electromagnetic waves from the plasma layer
Authors: Dolgopolov V. V. , El-Shereif R. N. , Hussein A. M.
Published: March 2009

It is shown that, in the case of incidence of p−olarized waves onto a plane- parallel plasma layer, the wave field pressure can cause the electromagnetic field to penetrate into the plasma, which is opaque in the linear approximation for the given waves. The plasma density average over the region of the electromagnetic field does not change.
Time asymptotic statistics of the Vlasov equation
Authors: Knorr Georg
Published: March 2009

A statistical description of the Vlasov equation is made possible by truncation of phase space in the velocity co-ordinates and writing the equation in terms of Fourier components in configuration and velocity space. Invariants of the resulting nonlinear turbulence equations are discussed. Expectation values and in particular an electric field spectrum of the form (β+ ακ2)-1are derived.αandβare constants;αis always positive;βmay be negative, depending on the initial conditions of the plasma. The spectrum is in reasonable agreement with available experiments and simulations.
Resistive instability of a low-beta plasma cylinder without assumed mode localization
Authors: Wright R. J.
Published: March 2009

Resistive instabilities in a low-β incompressible cylindrical model are investigated in a weakly sheared magnetic field. No boundary layer assumptions are made. Previous analytic results are found to fail badly when resistivity becomes too large, causing peaking in the growth rate dependence upon resistivity, and when the resonant surface approaches the axis, causing stabilization. The m = 1 tearing mode is investigated and found to lack the cut-off of higher m numbers. Finite Larmor radius effects have expected stabilizing properties, but produce a new, delocalized instability.
Resistive effects on Alfvén wave heating
Authors: Kappraff J. M. , Tataronis J. A.
Published: March 2009

We consider the effects of resistive dissipation on energy absorption by spatially localized Alfvén waves which form a part of the continuous spectrum of ideal magnetohydrodynamics (MHD). We demonstrate that the strong absorption rate found in ideal MHD is unaltered for plasma resistivities of the order found in tokamaks, thus implying the possibility of effective heating of these machines by Alfvén waves.
Larmor radius effects on the gravitational instability of a two-component plasma
Authors: Chhonkar R. P. S. , Bhatia P. K.
Published: March 2009

The gravitational instability of a two-component plasma has been studied here to include simultaneously the effects of neutral gas friction, finite ion Larmor radius, magnetic resistivity and Hall currents. The viscosities of the two components of the plasma have also been taken into account. The mode of the transverse as well as the longitudinal wave propagation have been discussed. The dispersion relations have been obtained for both these cases and numerical calculations have been performed to obtain the dependence of the growth rate of the gravitationally unstable mode on the various physical parameters involved. For the transverse mode of propagation, it is found that the growth rate of the unstable mode increases with magnetic resistivity and with the ratio of the densities of two components. The influence of the magnetic resistivity is, therefore, destabilizing on this mode of wave propagation. The viscosities of the two components are found to have a stabilizing influence on the growth rate in this case since it is found that the increase of hte viscosity effects reduces the growth rate. For the longitudinal mode also it is found that the effects of viscosities as well as that of neutral gas friction are stabilizing. The magnetic resistivity does not affect the growth rate since the equation determining the growth rate is found to be independent of this effect.
Hydromagnetic stability of a jet of very high compressibility
Authors: Iyengar H. K. S. , Chakraborty B. B.
Published: March 2009

This paper studies the hydromagnetic stability of a cylindrical jet of a perfectly conducting and inviscid fluid of very high compressibility. The fluid velocities and magnetic fields, inside and outside the jet, are uniform and in the axial direction, with possible cliscontinuities in their values across the jet surface. In the limit of infinite compressibifity, the jet is stable against axisymmetric disturbances, but instability is present for asymmetric disturbances when the magnetic field is sufficiently small. For these disturbances the infinitely compressible jet behaves like an incompressible one when the wavenumber of disturbances is small. The effect of (infinite) compressibility becomes more evident as the wavenumber of disturbances increases and the jet becomes stable when the wavelength tends to vanish.
A note on the Lagrangian method for nonlinear dispersive waves
Authors: Kawahara T.
Published: March 2009

This paper makes a few remarks on the method of the averaged Lagrangian developed by Whitham to describe slow variations of nonlinear wave trains. The concept of multiple scales is incorporated into the variational formalism, and a consistent development to higher approximation is suggested as a formal perturbation based on the variational principle. The propagation of weakly dispersive long waves is also reconsidered in relation to the Lagrangian method. It is demonstrated that the nonlinear Schrodinger equation and the Korteweg–de Vries equation can be derived from the Euler–Lagrange equations of the perturbed Lagrangian.
Wall stabilization in a collisionless bumpy theta-pinch
Authors: Vahala George , Vahala Linda
Published: March 2009

Finite wavelength guiding centre plasma stability of the bumpy θ-pinch is examined by a normal mode analysis. It is shown that previous bumpy θ-pinch calculations are recoverable as special cases of this analysis. The ideal magnetohydrodynamic and guiding centre plasma growth rates are compared for various pressure anisotropies and for various wavenumbers of the field line bumpiness. The well-posedness conditions on the guiding centre plasma equations are shown to give upper and lower bounds on the permissible pressure anisotropy which corresponds to the Aifvén continuum staying on the stable side of the spectrum and to the particle mirror force not having a singularity. It is also found that the higher azimuthal m ≥ 2 modes have growth rates larger than the m = 1 mode.
Fine diagnostic of laser-created plasmas by induced Compton scattering
Authors: Montes Carlos , Peyraud Jean
Published: March 2009

Laser-created plasmas are characterized by high photon occupation numbers. Analysis of the induced Compton scattering of an auxiliary laser beam, tunable in frequency and incident angle, is used as a fine diagnostic mechanism for measuring the subcritical plasma distribution function.
Theory of a parametric instability excited by two pump waves
Authors: Fejer J. A. , Cragin B. L , Showen R. L.
Published: March 2009

The threshold of a parametric instability in which the frequency of the excited Langmuir waves is exactly the arithmetic mean of two pump frequencies, is calculated. The kinetic equation is used to describe the ion dynamics. The threshold is infinitely high when the difference between the two pump frequencies is exactly double the frequency of ion-acoustic waves if pump waves of equal intensity are assumed. For very large values of Te/Ti the threshold reaches its lowest values when the difference frequency is slightly more or slightly less than twice the resonant frequency of the ion-acoustic waves.
Observation of nonlinear effects in the propagation of m=0 torsional hydromagnetic waves
Authors: Brennan M. H. , Cheetham A. D. , Jones I. R. , Sawley M. L.
Published: March 2009

This paper reports on the observation of nonlinear effects in the propagation of axisymmetric (m = 0) torsional hydromagnetic waves in a partially ionized helium afterglow plasma. In accordance with the predictions of a weakly nonlinear theory, magnetic field perturbations oscillating at twice the frequency of the primary wave have been observed. Good quantitative agreement between the experimental data and theoretical calculations is obtained for moderate primary wave amplitudes.
Three-component non-symmetric counter-streaming instabilities: oblique propagation case
Authors: Cuperman S. , Gomberoff L. , Roth I.
Published: March 2009

The effects of the background plasma as well as of the non-resonant plasma-cyclotron and cyclotron–cyclotron interactions on the oblique unstable electrostatic waves generated by resonant plasma–cyclotron (P–C) and cyclotron–cyclotron (C–C) interactions in magnetized non-symmetric two-stream plus background plasma systems are theoretically investigated. Two main effects are reported: (a) preferential increase or decrease of the maximum growth rates of certain m−modes for appropriate plasma parameters and (b) an additional contribution to the frequency shift from the integer multiple values of half the cyclotron frequency. Closed analytical expressions for the maximum growth rates and frequency shifts of both plasma-cyclotron and cyclotron–cyclotron unstable interactions are presented and discussed. The theoretical results obtained in this paper are supported by recent experimental results on electron counter-streaming instabilities in the presence of significant background plasma concentrations in which dominant electric field emissions at 3Ωe/2 have been observed to occur.
Damping of nonlinear magneto-acoustic waves
Authors: Kalra G. L. , Bhatia V. B.
Published: March 2009

Nonlinear magneto-acoustic waves in a turbulent plasma are simulated by collisional MHD equations. Damping of these waves due to electrical conductivity arising from micro-instabilities and collisional viscosity are analyzed. Numerical investigation of competing effects due to non-linearity and dissipation has been carried out. It is found that finite amplitude perturbation leads to the formation of a shock in both the slow and the fast mode propagation. Collisional viscosity plays an important role in the damping of nonlinear magneto-acoustic waves in the astrophysical and space plasmas.
Excitation of Alfvén waves by fast particles in a finite pressure plasma of adiabatic traps
Authors: Meerson B. I. , Mikhallovskii A. B. , Pokhotelov O. A.
Published: March 2009

Resonant excitation of Alfvén waves by fast particles in a finite pressure plasma in a non-uniform magnetic field is studied. Plasma compressibility in the wave field is determined both by the curvature of the magnetic lines of force and finite Larmor radius of fast particles. A general expression for the instability growth rate is obtained and analyzed; the applicability of the results obtained in the previous paper has also been studied. The finite pressure stabilization of the trapped particles instability has been found. The bounce-resonance effects are analyzed.
Anomalous transport coefficients in a turbulent plasma
Authors: Balescu R. , Paiva-Veretennicoff I.
Published: March 2009

A general self-consistent framework is developed for the calculation of transport coefficients in a collisionless, weakly turbulent plasma. These coefficients characterize the response to a perturbation away from a quasi-steady turbulent state, which is assumed to exist as a result of the stabilization of the linear instabilities. It is shown that a purely hydrodynamical description does not exist for plasmas: the macroscopic picture must include non-conserved quantities, which lead to the plasmadynamical (or ‘two-fluid’) picture of the system. The number of independent transport coefficients, necessary for the macroscopic characterization of the plasma, is correspondingly increased as compared with a two- component mixture of two ordinary fluids. The typical turbulent contributions to the transport coefficients are clearly exhibited.
Small amplitude waves in a hot relativistic two-fluid plasma
Authors: Hyun S. , Kennel C. F.
Published: March 2009

Using the two-fluid approximation, we summarize properties of linear waves in an unbounded magnetized relativistic plasma by a parameter-space diagram of wave phase velocity: a relativistic plasma pond.
Production of high energy ions in a tokamak during neutral injection heating
Authors: Peyraud Nelly
Published: March 2009

The kinetics of ions in a tokamak is analyzed on the basis of the Balescu – Lenard equation. We show that the injection of a neutral beam (acting through charge exchange with the plasma) produces a population of high energy ions. The global energy increase is evaluated.
Two-dimensional magnetohydrodynamic turbulence: cylindrical, non-dissipative model
Authors: Montgomery David , Vahala George
Published: March 2009

Incompressible magnetohydrodynamic turbulence is treated in the presence of cylindrical boundaries which are perfectly conducting and rigidly smooth. The model treated is non-dissipative and two-dimensional, the variation of all quantities in the axial direction beingignored. Equilibrium Gibbs ensemble predictions are explored assuming the constraint of constant axial current (appropriate to tokamak operation). No small-amplitude approximations are made. The expectation value of the turbulent kinetic energy is found to approach zero for the state of maximum mean-square vector potential to energy ratio. These are the only states for which large velocity fluctuations are not expected.
Plan MHD flows in a hyperbolic magnetic field: implications for the problem of magnetic field line reconnexion
Authors: Habbal Shadia Rifai , Tuan Tai-Fu
Published: March 2009

This paper examines the nature of plane, steady, incompressible MHD flow in a purely hyperbolic magnetic field. It is shown that in such a magnetic field the MHD equations can yield exact analytic solutions for the plasma flow. The flow has the following properties. In the far region where the conductivity is assumed to be sufficiently high so that the plasma is effectively ‘ frozen ’ to the magnetic field, the flow pattern is radial. The plasma motion is directed towards the neutral line in the incident ‘ sectors ’ and away from it in the outgoing ‘ sectors ’ with a consequent reversal in direction across the magnetic separatrices where the solution becomes singular. The plasma pressure and density in this flow are calculated and it is shown that the latter remains constant along a streamline. It is further shown that a uniform finite conductivity is not compatible with a stagnation point at the magnetic null point. However, for a parabolic increase of conductivity with increasing distance from that point, plasma flow with uniform density along hyperbolic streamlines is shown to be possible. The relevance of these flows to the magnetic field merging problem is discussed.
Temporal evolution of magnetic recomiexion in the vicinity of a magnetic neutral line
Authors: Forbes T. G. , speiser T.W.
Published: March 2009

Following Dungey's original magnetohydrodynamic formulation, a solution is obtained for the nonlinear evolution of a current discharge in the vicinity of a magnetic neutral line. For an ideal gas with constant conductivity and uniform mass density we obtain a particular exact solution in the limit of an initial, nearly sheet-like configuration. This particular solution implies special boundary conditions for the pressure and electric field at the surface of the conductor. If These conditions are not met, then the solution eventually breaks down before the current density becomes infinite. The time required for complete breakdown is determined by the wave propagation times from the surface of the fluid to the neutral line and by the diffusion time for the magnetic field through the fluid. For large conductivity and a small sound speed, the maximum current density achieved at the time of the solution's complete breakdown depends upon the ratio of the characteristic diffusion time to the Alfvén wave propagation time. In the limit of infinite conductivity or infinite extension of the fluid, the current density along the neutral line becomes infinite at π/23/2 times the Alfvénic scale time. At this same time the inflow Alfvenic Mach number approaches 21/2i while the outflow Alfvenic Mach number approaches infinity.
Current driven electromagnetic ion cyclotron instability
Authors: Forslund D. W. , Kindel J. M. , Stroscio M. A.
Published: March 2009

When an electron distribution drifts relative to the ions along a d.c. magnetic field, it is known that, above some critical drift velocity, a nearly field-aligned electromagnetic ion cyclotron instability may be excited. We extend the study of this instability over wide variations in plasma parameters, ion β in particular, and beyond marginal stability.Above threshold the most unstable waves propagate very obliquely to the ambient d.c. magnetic field at wavenumbers of the order of an inverse ion Larmor radius. At low ion β the critical electron drift normalized to the ion thermal velocity scales inversely as β i- ½ while, for β i>10-2, the critical drift scales as the ion thermal velocity. For the Te≈Tielectromagnetic ion cyclotron instabifity begins to have a lower threshold than the corresponding electrostatic instability at β i≈me/Mi. In a moderately high β i, homogeneous, collisionless plasma the electromagnetic ion cyclotron instability appears to have the lowest threshold of any current driven instability.
On self-consistent waves and their stability in warm plasma. Part 1.Construction of the self-consistent waves
Authors: Lee M. A. , Lerche I.
Published: March 2009

Following a prescription invoked by Clemmow for cold plasma, we show how the method can be extended for a warm plasma so that self-consistent, large-amplitude, nonlinear waves can be obtained in an otherwise homogeneous, stationary system. Results are given for situations in the presence of an imbedded constant magnetic field. The relationship of phase and amplitude for such waves is more complex than in the cold plasma since the resultsobtained depend to a surprising degree on the form of the distribution functions invoked for the warm plasma, as we demonstrate by specffic example. We have pursued this problem for two reasons: first, Clemmow has noted that the need has arisen for a detailed investigation of the behaviour of large amplitude waves in plasma; secondly, the self- consistent, large-amplitude waves catalogued by Clemmow in the case of a cold plasma, have recently been shown to be highly unstable. The question then arises of a possible stabilizing influence in the case of a warm plasma. In this paper we investigate the first part of this problem: construction of self-consistent waves in warm plasma.
Modulational instability of two transverse waves in a cold plasma
Authors: Das K. P. , Sihi S.
Published: March 2009

By Whitham's method of averaged Lagrangian developed by Dysthe, two coupled nonlinear Schrödiriger equations are obtained for the evolution of the amplitude of two plane polarized transverse waves in a cold plasma, both propagating in the same direction. Relativistic corrections are included and amplitude-dependent frequency shifts are derived. It is found that two transverse waves are modulationally unstable. The relativistic terms play an important part in this instability.
Acoustic instabilities and plasma heating resulting from energetic ion beam injection
Authors: Da Jornada E. H. , Gaffey J. D. , Caponi M. Zales
Published: March 2009

Electrostatic instabilities excited by an energetic ion beam are examined as a possible plasma heating mechanism. The dielectric properties of electrostatic waves in a uniform magnetized plasma are studied for a warm ion beam propagating at an arbitrary angle with respect to the magnetic field. The instability threshold and growth rate are calculated for the resonant ion-beam and ion- acoustic modes. The quasi-linear moment equations are used to follow the self-consistent evolution of the macroscopic plasma properties. A comparison is made with the collisional slowing-down rate of the beam. For the fastest growing modes it is found that the quasi-linear slowing-down time is significantly shorter than the coffisional slowing-down time.
Two-dimensional plasma equilibria
Authors: Shercliff J. A.
Published: March 2009

Complex-variable, hodograph methods are used to solve the free-boundary problem of a plasma confined by its own skin currents and the field due to two parallel external conductors. In one extreme case the external field is a quadrupole field in the vicinity of the plasma; another extreme case describes the local perturbation of a large plasma by a single, nearby conductor.
Reply to the comments by G. Schmidt
Authors: Hirose A.
Published: March 2009

The points raised by Schmidt (1979) are irrelevant and do not invalidate my paper (Hirose 1978). He has overlooked the beam deceleration and consequent obvious relationship, where V (t) is the beam drift velocity at arbitrary time, V(0) is the initial beam velocity, nb1, is the perturbed beam density and vb1 is the perturbed beam velocity. It is obvious that V(t) < V(0) due to beam deceleration caused by the instability as shown by Shapiro (1963) and also in the subject paper (Hirose 1978).
Finite ion Larmor radius modifications to the firehose and mirror instabilities
Authors: Hall A. N.
Published: March 2009

We examine the effect of finite ion Larmor radius on the hydromagnetic growth rates of the firehose and mirror instabilities. We perturb an infinite, collisionless, magnetized plasma which is initially uniform, and we do not restrict the direction of the wave vector, k.
Anomalous resistivity of a turbulent plasma in a strong electric field
Authors: Kiwamoto Y. , Kuwahaara H. , Tanaca H.
Published: March 2009

The enhanced effective collision frequency in a turbulent plasma produced by a strong electric field is studied using a small toroidal device. The collision frequency is presented as a function of the electric field E and the average electron drift velocity. Two collision frequency regimes are identified. In the regime I where v ∝ E½, the current driven ion-acoustic turbulence is considered responsible.
Padé approximants and nonlinear waves
Authors: Romerias F. J. , Dougherty J. P.
Published: March 2009

The perturbation solution of the ordinary differential equations that describe exact nonlinear travelling plane waves leads to asymptotic expansions in powers of the (small) wave amplitude for both the proffle and the frequency of the waves. This paper shows how the Padé approximant method can be used to extend the validity of those expansions to larger amplitudes. The method is applied to the Duffing equation and to two types of nonlinear waves in a cold electron plasma: longitudinal oscillations and coupled transverse–longitudinal relativistic waves.
Hybrid-kinetic stability properties of high-beta plasmas
Authors: Mondt J. P. , Davidson R. C.
Published: March 2009

A hybrid-kinetic model (Vlasov ions and drift-kinetic electrons) is used to investigate the equilibrium and stability properties of collisionless linear screw-pinch configurations, assuming low-frequency perturbations (|ω|≲ωci) but making no a priori assumptions regarding the size of the ion Larmor radius (arbitrary rLi/L⊥). A general eigenvalue equation is derived for perturbations about a general equilibrium characterized by density profile N(r), isotropic ion equilibrium f0i(H), and locally Maxwellian electrons. This eigenvalue equation clearly exhibits the importance of finite electron temperature and electron kinetic effects parallel to the magnetic field direction, and reduces to the Vlasov-fluid eigenvalue equation of Freidberg in the limit of zero electron temperature.
A relativistically covariant formulation in the theory of plasma stability
Authors: Merches I.
Published: March 2009

The definition of the ‘combined field’ and the ‘combined field potentials’ allows one to formulate a constrained minimum energy problem. The constraints can be put in a relativistically covariant form. The equations of stable equilibrium, for a non-rotating charged fluid, are obtained. If the physical conditions are suitably chosen, a special kind of Alfvén-like velocity may exist.
Dual propagation and absorption in a warm plasma half-space
Authors: Dorchak Edwin J. , Liboff Richard L.
Published: March 2009

The relativistic Vlasov equation together with Maxwell's equations are used in a study of p-polarized electromagnetic waves incident on a warm plasma halfspace. The domain for dual propagation of longitudinal and transverse waves is derived as a function of density, temperature and incident angle at a given frequency. Expressions for the reflection and absorption coefficients are obtained in the non-relativistic limit. It is found that maximum absorption occurs at an angle dependent on the density and temperature of the plasma, above which dual propagation will not occur. It is inferred that the density–temperature space available for dual propagation diminishes with the growth of the maximum angle for such propagation.
Classical Vlasov plasma description through quantum numerical methods
Authors: Bertrand P. , van Tuan Nguyen , Gros M. , Izrar B. , Feix M. , Gutierrez J.
Published: March 2009

The Schrödinger equation describes the motion of a particle in a statistical sense. It consequently possesses the two main properties of the Vlasov equation (dynamic and statistic) and can replace this last equation provided we take sophisticated initial conditions. The scheme must be considered as a new attempt to discretize intelligently the amount of information contained in the phase space distribution and to stop, without destroying it, the flow of information which usually goes to high wavenumbers in velocity space. The method is applied to the breaking of highly nonlinear waves in a cold plasma (usually treated by the Lagrangian method) and to double beam instability. It is shown that such an Eulerian scheme works quite well with a much smaller number of discretized functions than are required in the regular Fourier—Fourier or Fourier-Hermite methods. The central point is the introduction of the phase space Wigner distribution function which is a useful mathematical tool in spite of its poor physical properties.
Numerical model of plasma double layers using the Vlasov equation
Authors: Johnson Lloyd E.
Published: March 2009

The one-dimensional plasma double layer is modelled by numerically integrating the time-dependent Vlasov and Poisson equations. A constant magnetic field at an arbitrary angle with respect to the layer is included. The model shows that such a plasma region can generate as well as reflect Langmuir waves and shows how RF emission may arise. An axial magnetic field does not inhibit the formation of a double layer, although a non-axial field may do so.
The stability properties of cylindrical force-free fields: effect of an external potential field
Authors: Chiuderi C. , Einaudi G. , Ma S. S. , van Hoven G.
Published: March 2009

A large-scale potential field with an embedded smaller-scale force-free structure (∇ × B = αB) is studied in cylindrical geometry. We consider cases in which α goes continuously from a constant value α0 on the axis to zero at large r. Such a choice of α(r) produces fields which are realistic (few field reversals) but not completely stable. The MHD-unstable wavenumber regime is found. Since the considered equilibrium field exhibits a certain amount of magnetic shear, resistive instabilities can arise. The growth rates of the tearing mode in the limited MHD-stable region of º space are calculated, showing time-scales much shorter than the resistive decay time.
A generalization of kinetic ponderomotive effects
Authors: Schamel Hans , Schmidt George
Published: March 2009

The plasma response to electrostatic travelling wave packets with a slowly varying envelope is investigated, including dynamical friction between electrons and ions. A kinetic diffusion equation and, therefrom, a new set of macroscopic equations is derived which includes current and magnetic field generation due to friction and wave momentum transfer.