bluuebunny/crossref_metadata_2025 huggingface dataset:
A manifestly gauge-invariant Hamiltonian theory of the oscillation-centre dynamics
Authors: Weyssow B. , Balescu R.
Published: March 2009

The theory of the slow reaction of charged particles in the presence of a high-frequency electromagnetic field (oscillation-centre motion) is developed by using a Hamiltonian formalism with non-canonical variables and pseudo-canonical transformations. The flexibility introduced by the latter features allows us to construct a theory which is manifestly gauge-invariant and involves only physical concepts (electromagnetic fields and particle velocities instead of potentials and canonical momenta). A complete description of the oscillation-centre dynamics is derived. The known expressions of the ponderomotive force are derived as special cases of our theory.
The effect of the ion temperature on the ion acoustic solitary waves in a collisionless relativistic plasma
Authors: Nejoh Yasunori
Published: March 2009

The effect of the ion temperature on ion acoustic solitary waves in a collisionless relativistic plasma is discussed using the Korteweg–de Vries equation. The phase velocity of the ion acoustic waves decreases as the relativistic effect increases, and increases as the ion temperature increases. Only a compressional soliton of the ion acoustic wave is formed in this system. Since its amplitude increases for the lower ion temperature as the relativistic effect increases, we deduce the formation of a precursor by the presence of the streaming ions. In contrast, for the higher ion temperature, the amplitude decreases slowly. Furthermore, it is shown that the oscillatory solution of the Korteweg–de Vries equation smoothly links with the nonlinear Schrödinger equation in a relativistic plasma.
Generalized Budden resonance tunnelling, with application to linear conversion nearly parallel to magnetic field
Authors: Mjølhus Einar
Published: March 2009

A model of linear wave conversion problems is formulated, which forms a natural generalization of the Budden resonance tunnelling model. The structure of the model is such as to conserve energy flux, and also is such as to allow explicit solution in terms of contour integrais. An arbitrary number of wave modes may participate. Explicit expressions for the conversion coefficients in terms of quantities derivable from the dispersion relations are obtained. A standard way of extending the model, by which resonant absorption is retrieved as conversion into an additional short wave mode, is included. The formulae obtained, are shown to include a complete solution to the problem of linear conversion in a magnetized plasma when the waves are nearly parallel to the magnetic field.
Effect of toroidicity during lower-hybrid mode conversion
Authors: Riyopoulos S. , Mahajan S. M.
Published: March 2009

The effect of toroidicity during lower-hybrid mode conversion is examined by treating the wave propagation in an inhomogeneous medium as an eigenvalue problem for ω2 (m, n), m, n poloidal and toroidal wavenumbers. Since the fre-quency regime near ω = ω2LH is an accumulation point for the eigenvalue spectrum, the degenerate perturbation technique must be applied. The toroidal eigenmodes are constructed by a zeroth-order superposition of monochromatic solutions with different poloidal dependence m; thus they generically exhibit a wide spectrum in k‖ for given fixed ω2 even for small inverse aspect ratio є. When the average 〈k‖〉 is in the neighbourhood of kmin, the minimum wave-number for accessibility of the mode conversion regime, it is possible that excitation of toroidal modes rather than geometrie optics may determine the wave coupling to the plasma. Our results are not changed significantly by a small amount of dissipation. The level of density fluctuations in modem tokamaks, on the other hand, may cause enough k‖ scattering to mask the toroidicity effects. Nevertheless, it is shown that a wide k‖ spectrum excited by a monochromatic pump will persist even with vanishing fluctuation level.
Geometrical effects in X-mode scattering
Authors: Bretz N.
Published: March 2009

One technique to extend microwave scattering as a probe of long-wavelength density fluctuations in magnetically confined plasmas is to consider the launching and scattering of extraordinary (X-mode) waves nearly perpendicular to the field. When the incident frequency is less than the electron cyclotron frequency, this mode can penetrate beyond the ordinary mode cut-off at the plasma frequency and avoid significant distortions from density gradients typical of tokamak plasmas. In the more familiar case, where the incident and scattered waves are ordinary, the scattering is isotropic perpendicular to the field. However, because the X-mode polarization depends on the frequency ratios and the ray angle to the magnetic field, the coupling between the incident and scattered waves is complicated. This geometrical form factor must be unfolded from the observed scattering in order to interpret the scattering due to density fluctuations alone. The geometrical factor is calculated here for the special case of scattering perpendicular to the magnetic field. For frequencies above the ordinary-mode cut-off the scattering is relatively isotropic, while below cut-off there are minima in the forward and backward directions which go to zero at approximately half the ordinary-mode cut-off density.
A plasma-optical System modelled using particles
Authors: Hitchon W. N. G.
Published: March 2009

A ‘particle’ model of plasma behaviour, suitable for application to the study of plasma-optical Systems, has been developed. A plasma-optical System which removes macroscopic droplets from a neutralized beam of ions and electrons, produced by an arc, has been modelled and its performance has been analysed. The particle model employs an extremely efficient treatment of the electron motion through a background gas, which in this case consists of neutral particles. The distribution of distances travelled by electrons in the course of many collisions with the neutral background is generated using a Monte Carlo method and samples from the distribution are used to determine the electron motion at each integration step. In sheath regions, for instance, direct integration is still necessary, but for most electrons the simulation is very fast, largely removing the numerical ‘stiffness’ of the particle method. This method will be equally effective for time-dependent fields such as occur in RF discharges used in ‘plasma processing’. The variation in ion current to a substrate, where the ions deposit as a thin film, has been studied. The objective is to maximize the deposition rate whilst preventing macroscopic particles which arise at the are from striking the film. An alternative System whose calculated transmittal rate from source to target is higher, for long mean-free-paths, is also examined.
Toroidal plasma configuration with anisotropic pressure
Authors: Rizk Hussain M.
Published: March 2009

The relation between various surface quantities required in hydrodynamic calculations, and the relation between the parallel and perpendicular currents in an arbitrary magnetic toroidal plasma configuration with scalar pressure, are generalized to the case of anisotropic pressure. Magnetic co-ordinates for hydrodynamic equilibria in this configuration are defined. A general expression for the mean velocity of diffusion through a magnetic surface, on the basis of the one-fluid magnetohydrodynamic equation with anisotropic pressure, is derived.
Asymptotic approximation for the dispersion relation of a hot magnetized plasma
Authors: Bravo-Ortega A. , Swanson D. G. , Glasser A. H.
Published: March 2009

An asymptotic expression for the dielectric tensor e of a hot magnetized plasma is obtained employing the steepest descents method, via the transformation of the components of ε into their integral representation. The electrostatic Bernstein dispersion relation for oblique and perpendicular propagation is discussed under this treatment. It is shown that with this procedure the computation of the dispersion relation is up to 20 times faster when it is compared with the original expression, and the relative accuracy is usually as good as O·l% for a typical case.
Particle paths and phase plane for time-dependent similarity solutions of the one-dimensional Vlasov-Maxwell equations
Authors: Roberts Dana Aaron , Abraham-Shrauner Barbara
Published: March 2009

Lie group point transformations applied to the one-dimensional Vlasov– Maxwell equations yield general similarity forms for the dependent and independent variables. One class of such solutions is seemingly like Bern-stein-Greene-Kruskal solutions in allowing a relatively free choice of electric field, but with a more complex time dependence. The phase trajectories of the particles are found here for both temporally damped and (possibly unphysical) growing electric fields in this class by numerical integration in the original and in transformed co-ordinates. The analysis, which includes an analytic consideration of phase-plane fixed (critical) points, shows the advantages of the new co-ordinates, and reveals qualitative features of the distribution function.
Dispersion ion-drift hydrodynamics
Authors: Lakhin V. P. , Makurin S. V. , Mikhailovskii A. B. , Onishchenko O. G.
Published: March 2009

The set of hydrodynamic equations for the ion component of a magnetized low-pressure plasma, including the nonlinear ion drift and waves related to it, taking into account dispersion effects of order k2⊥ρ2i (k⊥is the characteristic transverse wavenumber and ρi is the ion Larmor radius), is obtained. The reduction of these equations using the standard assumptions of vortex theory is given. The problem of the integrals of motion of the simplified equations is discussed. Account is taken of the gravitational force (which models curvature of the magnetic field lines), the three-dimensionality of the perturbations (drift-Alfvén effects) and plasma rotation. It is suggested that the ion-drift hydrodynamics discussed here should be the basis for the analysis of the ion drift and the vortices related to it, as well as for the theory of decay processes with participation of the ion-drift waves.
Vortices of ion-drift and related waves
Authors: Lakhin V. P. , Makurin S. V. , Mikhailovskii A. B. , Onishchenko O. G.
Published: March 2009

The problem of vortices of ion-drift and related flute-drift, balloon-drift and drift-Alfvén waves is analysed, taking into account the finiteness of the Larmor radius of the ions. It is shown that the structure of the stationary ion-drift vortices is similar to that of the Alfvén waves. It is found that the stationary ion-drift vortices in a plasma confined in a curvilinear magnetic field are characterized, generally speaking, by two different spatial scales. The role of plasma rotation in the vortex problem is investigated.
Observation of large-amplitude ion acoustic solitary waves in a plasma
Authors: Nakamura Yoshiharu
Published: March 2009

Propagation of nonlinear ion acoustic waves in a multi-component plasma with negative ions is investigated in a double-plasma device. When the density of negative ions is larger than a critical value, a broad negative pulse evolves to rarefactive solitons, and a positive pulse whose amplitude is less than a certain threshold value becomes a subsonic wave train. In the same plasma, a positive pulse whose amplitude is larger than the threshold develops into a solitary wave. The critical amplitude is measured as a function of the density of negative ions and compared with predictions of the pseudo-potential method. The energy distribution of electrons in the solitary wave is also measured.
Probability-maximization theory for a highly turbulent beam-plasma system
Authors: Nakamura Tadas , Yamamoto Takashi
Published: March 2009

A new approach to the theoretical study of turbulent behaviour of a collisionless plasma is developed. This approach is based upon the concept or probability maximization originally applied to collisional gases by Boltzmann. The probability-maximization theory deals with stochastic processes in a steady turbulent plasma by solving for the most-probable distribution. Our theory as applied to counter-streaming electron beams can quantitatively predict beam retardation, i.e. a decrease in the mean velocity of electrons injected from the system boundary. This is also in agreement with the results of a one-dimensional numerical experiment performed for such a beam-plasma system.
Stability of short-axial-wavelength internal kink modes of an anisotropic plasma
Authors: Faghihi M. , Scheffel J.
Published: March 2009

The double adiabatic equations are used to study the stability of a cylindrical Z-pinch with respect to small axial wavelength, internal kink (m ≥ 1) modes. It is found that marginally (ideally) unstable, isotropic equilibria are stabilized. Also, constant-current-density equilibria can be stabilized for P⊥ > P∥ and large β⊥
Relativistic theory of absorption and emission of electron cyclotron waves in anisotropic plasmas
Authors: Orefice A.
Published: March 2009

The weakly relativistic theory of absorption and emission of electron cyclotron waves in hot magnetized plasmas is developed for a large class of anisotropic electron distribution functions. The results are expressed in terms of the weakly relativistic plasma dispersion functions, and therefore of the well-known plasma Z-function. The particular case of a loss-cone electron distribution function is presented as a simple example.
Three-wave coupling coefficients for MHD plasmas
Authors: Brodin G. , Stenflo L.
Published: March 2009

By reconsidering the general theory for the resonant interaction of three waves in a plasma, we find explicit expressions for the coupling coefficients for three MHD waves. In particular we demonstrate that the interaction between two magnetosonic waves and one Alfvén wave, as well as the interaction between two Alfvén waves and one magnetosonic wave, can be described by very simple formulae for the coupling coefficients.
Measurements of the oscillating fields and the time-averaged forces in rotating magnetic field current drive
Authors: Collins G. A. , Durance G. , Tendys J.
Published: March 2009

Measurement of the RF (radio-frequency) magnetic field about the equatorial plane of the rotamak has enabled the distribution of the oscillating currents to be derived. The time-averaged forces, produced by the interaction of these currents with the oscillating field, have been estimated. In the standard field-reversed configuration there is a radial force, which helps to confine the plasma pressure, and a toroidal force, which drives the equilibrium current. In compact tokamak configurations there is an additional poloidal force, which produces a diamagnetic current. As the toroidal field increases, penetration of the RF fields improves owing to the excitation of a whistler wave mode. The connection between the rotating magnetic field technique and fast wave current drive is explained.
Higher-order corrections to the ion-acoustic waves in a relativistic plasma (isothermal case)
Authors: Pakira Gobinda Pada , Chowdhury A. Roy , Paul S. N.
Published: March 2009

As a continuation of our earlier work, we have analysed the higher-order perturbative corrections to the formation of (ion-acoustic) solitary waves in a relativistic plasma. It is found that the relativistic considerations affect the amplitude and width variation - as conjectured in our previous paper. Our analysis employs a higher-order singular perturbation technique, with the elimination of secular terms in stages. In this way we arrive at an inhomogeneous KdV-type equation, which is then solved exactly. At this point a new phenomena arises at a critical value of the phase velocity at which the coefficient of the nonlinear term in the KdV equation vanishes. A new set of stretched co-ordinate is then used to derive a modified KdV equation. In both cases we have numerically computed the specific physical profile of the new solitary wave and its width.
Effects of higher-order nonlinearity and finite geometry on the propagation of KdV solitons
Authors: Ghosh B. , Das K. P.
Published: March 2009

Using reductive perturbation theory and a planar waveguide geometry, the effects of higher-order nonlinearity and finite boundaries on the propagation of electron plasma and ion-acoustic KdV solitons are investigated by taking into account finite electron and ion temperatures. For an electron plasma wave, the higher-order nonlinearity is found to increase the amplitude of the soliton and slightly decrease the width of the soliton compared with that predicted by the first-order theory. For an ion-acoustic wave the higher-order-nonlinearity and finite-boundary effects give rise to a W-shaped soliton.
Ion-acoustic solitary waves in an inhomogeneous plasma
Authors: Shivamoggi Bhimsen K.
Published: March 2009

Despite extensive theoretical investigation of the problem of ion-acoustic solitary waves in an inhomogeneous plasma, a fully satisfactory account has so far not been given. This paper provides a critical account of the shortcomings of the previous theoretical approaches and then describes a fully self-consistent treatment of the problem.
Resonance absorption of energy by a cold inhomogeneous plasma
Authors: Sedláček Z. , Roberts B.
Published: March 2009

The active and reactive power resonantly absorbed by a linear passive system is calculated in terms of its continuum eigenfunctions and the spatial–temporal spectral density of the external force. An application to the resonance absorption of electromagnetic radiation by a cold inhomogeneous plasma is given.
The effect of light filamentation on uniformity of energy deposition in laser plasmas
Authors: Nicholas D. J. , Sajjadi S. G.
Published: March 2009

The detailed behaviour of a beam of light propagating through a fully ionized plasma is studied near the critical density. Transient effects in the laser beam and plasma are included by taking into account, in a self-consistent manner, the proper motion of the plasma in an intense electromagnetic field. Parameters of the laser beam and plasma conditions are studied that prove most beneficial in providing a uniform deposition of energy. The behaviour of the light beams near the critical density at the three wavelengths 1054 nm, 527 nm and 351 nm are compared.
Acoustic-like modes in a two-ion quasi-neutral plasma: linear and nonlinear analysis
Authors: Dwivedi C. B. , Tiwari R. S. , Sayal V. K. , Sharma S. R.
Published: March 2009

A theoretical analysis of acoustic-like modes in a plasma consisting of two kinds of ions with different temperatures has been performed using fluid equations. The electrons are assumed to form a dynamic neutralizing background, and their perturbation has been neglected – which is permissible for k2λ2De ≫ 1. The analysis shows that an acoustic-like mode appears to propagate as a normal mode when the hotter ion concentration is very large compared with that of the colder ions.
Nonlinear magnetic electron drift waves in magnetized plasmas
Authors: Murtaza G. , Shukla P. K. , Yu M. Y. , Stenflo L.
Published: March 2009

This paper presents a derivation of the nonlinear equations governing the space–time evolution of magnetic electron drift waves in an inhomogeneous magnetoplasma. The equilibrium electron pressure gradient is maintained by the gradient of an external magnetic field. An oscillatory instability is shown to arise. The existence of magnetic electron drift vortices is discussed and the limitation on the vortex speed due to the external magnetic field is pointed out.
Arbitrary-amplitude theory of ion-acoustic solitons in warm multi-fluid plasmas
Authors: Baboolal S. , Bharuthram R. , Hellberg M. A.
Published: March 2009

A recently described numerical theory for obtaining the Sagdeev and real potential profiles of stationary wave forms in a plasma consisting of double-Maxwellian electrons and two or more species of warm ions is used for the study of solitons in such a plasma. The effects of ion temperature and light-ion concentration on rarefactive ion-acoustic soliton profiles in a double-ion plasma obtained with this large-amplitude theory are compared with those predicted from a Korteweg–de Vries equation. Application of the theory to the work of Nakamura and co-workers is discussed, and we draw attention to ion thermal effects.
Stochastic acceleration and heating of ions by a non-sinusoidal magnetosonic wave
Authors: Varvoglis H. , Basios V.
Published: March 2009

The stochastic non-resonant energization of ions in non-sinusoidal coherent plane-polarized magnetosonic waves is investigated. It is found that, as in the case of sinusoidal magnetosonic waves, the process does not follow quasi-linear theory, i.e. it is a diffusion in velocity space, but with a diffusion coefficient D ∝ ν–α, α ≈ 1, instead of D ∝ ν–3. Moreover, it is found that the presence of strong harmonics lowers the stochasticity threshold of the wave amplitude by as much as one order of magnitude (depending on the form of the power spectrum), but at the same time it suppresses the diffusion rate of the ions in velocity space. Our results indicate that waves with a saw-tooth wave form are the most efficient for ion energization.
Exact dielectric tensor for relativistic magnetized plasma with loss-cone and field-aligned drift
Authors: Yoon Peter H. , Chang Tom
Published: March 2009

An exact form of the dielectric tensor for a wide variety of relativistic magnetized plasmas is derived from the fully relativistic linearized Vlasov-Maxwell equations. The equilibrium function chosen incorporates a loss-cone in perpendicular momentum space, and a net drift along the external field-line. This choice of distribution function is fully relativistic, and the resulting form of the dielectric tensor is valid for arbitrary value of temperature, arbitrary degrees of loss-cone, and arbitrary drift velocity along the field-line. The exact result is simplified in several limiting cases relevant to various physical applications.
On self-similar motions in Z-pinch dynamics
Authors: Bud'ko A. B. , Liberman M. A.
Published: March 2009

New self-similar solutions of the MHD equations for the dynamics of a high-density plasma in a linear Z-pinch are derived, taking into account the finite electric conductivity of the plasma. In a number of particular cases the self-similar solutions obtained are expressed in simple analytic form. Radial distributions of the MHD variables in the self-similar profiles show that during current heating and plasma expansion regimes with essential plasma heating on the pinch boundary are possible both with decrease and concentration of the current density on the outer pinch boundary.
Effects of plasma dielectric properties on Thomson scattering of millimetre waves in tokamak plasmas
Authors: Hughes T. P. , Smith S. R. P.
Published: March 2009

Thomson scattering from a magnetized plasma is considered, taking into account the dielectric properties of the plasma. General results for the geometrical form factor are given in explicit form. The scattered power detectable by a heterodyne receiver is discussed and some numerical calculations are presented. The results are applied to the scattering of millimetre waves in tokamak plasmas near the electron-plasma and electron-cyclotron frequencies.
Turbulent excitation of spontaneous reconnection
Authors: Deeds D. , Van Hoven G.
Published: March 2009

We explore the long-term nonlinear evolution of a tearing-mode-unstable sheared-field plasma in a turbulent environment. Two different physical configurations are modeled, and a different computational system is used for each. Results of both sets of calculations show that magnetic tearing arises spontaneously provided that the initial turbulence energy level is below the natural saturation level of the tearing instability.

We discuss briefly the relationship between our results and those of previous calculations, concluding that there are no significant unexplainable disagreements.
MHD intermediate shock discontinuities. Part 1. Rankine—Hugoniot conditions
Authors: Kennel C. F. , Blandford R. D. , Coppi P.
Published: March 2009

Recent numerical investigations have focused attention once more on the role of intermediate shocks in MHD. Four types of intermediate shock are identified using a graphical representation of the MHD Rankine-Hugoniot conditions. This same representation can be used to exhibit the close relationship of intermediate shocks to switch-on shocks and rotational discontinuities. The conditions under which intermediate discontinuities can be found are elucidated. The variations in velocity, pressure, entropy and magnetic-field jumps with upstream parameters in intermediate shocks are exhibited graphically. The evolutionary arguments traditionally advanced against intermediate shocks may fail because the equations of classical MHD are not strictly hyperbolic.
The effect of random Alfvén waves on the propagation of hydromagnetic waves in a finite-beta plasma
Authors: Hamabata Hiromitsu , Namikawa Tomikazu
Published: March 2009

Using first-order smoothing theory, Fourier analysis and perturbation methods, we obtain the evolution equation of the wave spectrum as well as the nonlinear forces generated by random Alfvén waves in a finite-β plasma with phenomenological Landau-damping effects. The effect of microscale random Alfvén waves on the propagation of large-scale hydromagnetic waves is also investigated by solving the mean-field equations. It is shown that parallel-propagating random Alfvén waves are modulationally stable and that obliquely propagating random Alfvén waves can be modulationally unstable when the energy of random waves is converted to slow magneto-acoustic waves that can be Landau-damped, providing a dissipation mechanism for the Alfvén waves.
Motion of a single charged particle in electromagnetic fields with cyclotron resonances
Authors: Weyssow Boris
Published: March 2009

The general Hamiltonian-averaging transformation developed to study the motion of a charged particle in a strong magnetic field and various electromagnetic perturbations permits a clear definition of the dynamics of the guiding centre. In the case of a high-frequency electromagnetic perturbation, the equations of evolution of the phase-space co-ordinates are sums of guiding-centre terms, resonant terms at any of the cyclotron resonance frequencies n(r‖k‖–ω)+lΩ≈0(l and n are integers) and ponderomotive terms. In this paper we consider the n = 1 resonances giving a contribution one order stronger than the ponderomotive terms to the equations of motion. The guiding-centre transformation therefore suffices to derive the leading terms of the averaged dynamics. A simple case of isolated resonance is then considered for which, depending on the value of the external parameters (initial particle energy, amplitude of the perturbation), the phase space may possess one or two trapping regions. Even in the latter situation, the particle trajectories can be described analytically by the set of 12 Jacobian elliptic functions.
Excitation of surface waves in magnetohydrodynamics
Authors: Shivamoggi Bhimsen K.
Published: March 2009

A study is made of the transient development of two-dimensional linearized surface waves generated by a localized steady pressure distribution on the interface between a uniformly streaming, semi-infinite, infinitely conducting plasma subjected to a gravitational field and the confining vacuum magnetic field. The linearized equations associated with an initial-value problem are used to obtain the large-time asymptotic behaviour of the disturbance in the far field.
Quasi-static evolution of a dissipative plasma column in vacuum
Authors: Surdo C. Lo
Published: March 2009

We consider the following problem: how far, in what sense and with what practical applications might the analysis of the quasi-static evolution of a (strictly) dissipative plasma column in vacuum be carried out independently of computational means (however necessary at a later stage) in the framework of a conveniently simplified, yet significant, mathematical model. We show that the the (two-region) evolution problem of concern can be reduced to the (numerical) solution of just three nonlinear non-autonomous evolution equations in three unknowns, sayẊ=Ẋ(X,t), withX≡ (X1,X2,X3), where the corresponding mapping (X,t)↣Ẋcan be made effective at the cost of inverting a non-canonical Fredholm operator of the second kind that is completely defined for the givenX=X(t) andt. The assumption of sufficiently slow evolution allows us to work with the static-equilibrium momentum equation. Under axial (or cylindrical) symmetry, we know that the ‘radial’ equilibrium condition leads to a semi-linear elliptic equation in the meridional (or (x, y)) plane. The Fredholm operator arises from the inversion of the Laplacian appearing in that equation.
Inhomogeneity effects on the absorption of electromagnetic high-frequency waves by magnetized Maxwellian plasmas
Authors: Fo R. A. Caldela , Schneider R. S. , Ziebell L. F.
Published: March 2009

Inhomogeneity effects on the absorption of high-frequency electromagnetic waves by magnetized Maxwellian plasmas are considered, and in particular the propagation and absorption of the ordinary and extraordinary modes propagating perpendicularly to the magnetic field are analysed. We show that, for small values of the ratio of the electron plasma frequency to the electron-cyclotron frequency, the inhomogeneity effects are more important for the ordinary mode, and that for values of this ratio close to or greater than unity the effects become pronounced for the extraordinary mode. It is also shown that, for a given value of this ratio, and for a fixed value of the ratio of electron-cyclotron frequency to wave frequency, the inhomogeneity effects tend to increase as the ambient magnetic field decreases. The temperature dependence of the effect, the dependence on the direction of propagation l'elative to the inhomogeneity, the influence of temperature anisotropy, and the isolated contribution of the gradients of different plasma parameters are investigated. Several circumstances in which instabilities may occur are mentioned.
Parametric decay in a two-electron-temperature plasma
Authors: Guha S. , Asthana Meenu
Published: March 2009

Nonlinear decay of an ordinary electromagnetic pump wave into an electro-acoustic wave and an upper-hybrid wave in a two-electron-temperature plasma has been investigated analytically. In contrast with the work of Sharma, Ramamurthy & Yu (1984), it is found that the decay can take place in the absence of the restrictive condition Ti ≫ Te and the plasma be magnetized. Using a hydrodynamical model of the plasma, the nonlinear dispersion relation and growth rate are obtained. A comparison of the present investigation is made with earlier work, and its possible application to the ELMO bumpy torus is discussed.
Exact nonlinear wave solutions of the incompressible magnetohydrodynamic equations in a sheared magnetic field
Authors: Hamabata Hiromitsu
Published: March 2009

Exact wave solutions of the nonlinear jnagnetohydrodynamic equations for a highly conducting incompressible fluid are obtained for the cases where the physical quantities are independent of one Cartesian co-ordina.te and for where they vary three-dimensionally but both the streamlines and magnetic field lines lie in parallel planes. It is shown that there is a class of exact wave solutions with large amplitude propagating in a straight but non-uniform magnetic field with constant or non-uniform velocity.
Solitons in an ion-beam plasma
Authors: Huibin Lan , Kelin Wang
Published: March 2009

In this paper the exact solution in a function-series form is given of the multi-fluid ion-beam plasma model proposed by Zank & McKenzie. The general condition necessary for the existence of finite-amplitude solitons propagating in the system is obtained and the upper bound on the velocity of solitary wave is found.
Effects of repeated interactions and correlational disintegration on kinetic and transport properties of a non-neutral plasma in strong fields
Authors: Øien Alf H.
Published: March 2009

Collisions in a cylindrically symmetric non-neutral (electron) plasma, where the Larmor radius is much smaller than the Debye length, and the consequent particle transport, are studied. The plasma is confined radially by a strong axial magnetic field and axially by electric potentials. Hence two particles may interact repeatedly. Eventually they drift too far away from each other poloidally to interact any more, owing to shear in the E × B drift. The consequent build-up of correlation is limited by correlational disintegration due to collisions with ‘third particles’ between the repeated interactions. A kinetic equation including these effects is derived, and the cross-field particle transport along the density gradient is found. An associated equilibration time is shown to scale as B and to be in good agreement with the experimentally obtained values of Briscoli, Malmberg and Fine.
Higher-order corrections to solitary waves in a non-isothermal relativistic plasma with cold ions and two-temperature electrons
Authors: Chowdhury A. Roy , Pakira Gobinda , Paul S. N. , Chowdhury K. Roy
Published: March 2009

A critical analysis of nonlinear waves in a non-isothermal relativistic plasma is performed using reductive perturbation theory. The plasma is assumed to contain two-temperature electrons. Higher-order corrections to the solitary wave are also computed, and the variations of the profile with respect to v/c, the two temperatures of the electrons, and the parameters bl, and bn characterising the non-isothermal nature are depicted graphically and com-pared with previous results.
Electrostatic surface waves on a plasma with non-uniform boundary
Authors: Stenflo L. , Gradov O. M.
Published: March 2009

A new analytical method is introduced to consider electrostatic surface waves propagating on a cold plasma. A very simple dispersion relation is derived for a plasma bounded by two dielectrics. Previous theory for solitary surface waves is also generalized.
Nonlinear magnetic reconnection models with separatrix jets
Authors: Priest E. R. , Lee L. C.
Published: March 2009

A new theory for fast steady-state magnetic reconnection is proposed that includes many features of recent numerical experiments. The inflow region differs from that in the classical model of Petschek (1964) and the unified linear solutions of Priest & Forbes (1986) in possessing highly curved magnetic field lines rather than ones that are almost straight. A separatrix jet of plasma is ejected from the central diffusion region along the magnetic separatrix. Two types of outflow are studied, the simplest possessing an outflow magnetic field that is potential. The other contains weak standing shock waves attached to the ends of the diffusion region and either slowing down the flow (fast-mode shock) after it crosses the separatrix jet or speeding it up (slow-mode), depending on the downstream boundary conditions. A spike of reversed current slows down the plasma that emerges rapidly from the diffusion region into the more slowly moving downstream region, and diverts most of it along the separatrix jets. In the simplest case the outflow possesses no vorticity over most of the downstream region. The models demonstrate that both upstream and downstream boundary conditions are important in determining which regime of reconnection is produced from a wide variety of possibilities.
On the existence of compressional MHD oscillations in an inhomogeneous magnetoplasma
Authors: Wright Andrew N.
Published: March 2009

In a cold plasma the wave equation for solely compressional magnetic field perturbations appears to decouple in any surface orthogonal to the background magnetic field. However, the compressional fields in any two of these surfaces are related to each other by the condition that the perturbation field b be divergence-free. Hence the wave equations in these surfaces are not truly decoupled from one another. If the two solutions happen to be ‘matched’ (i.e. V.b = 0) then the medium may execute a solely compressional oscillation. If the two solutions are unmatched then transverse fields must evolve. We consider two classes of compressional solutions and derive a set of criteria for when the medium will be able to support pure compressional field oscillations. These criteria relate to the geometry of the magnetic field and the plasma density distribution. We present the conditions in such a manner that it is easy to see if a given magnetoplasma is able to executive either of the compressional solutions we investigate.
Adiabatic theory of nonlinear electron-cyclotron resonance heating
Authors: Kotel'nikov I. A. , Stupakov G. V.
Published: March 2009

Plasma heating at the electron-cyclotron frequency by an ordinary wave propagating at right-angles to a unidirectional magnetic field is considered. The injected microwave power is assumed to be sufficiently large that the relativistic change in electron gyrofrequency during one flight through the wave beam is much greater than inverse time of flight. The electron motion in the wave field is described using the Hamiltonian formalism in the adiabatic approximation. It is shown that energy coupling from the wave to electrons is due to a bifurcation of the electron trajectory, which results in a jump in the adiabatic invariant. The probability of a bifurcational transition from one trajectory to another is calculated analytically and used for the estimation of the beam power absorbed in the plasma.
Effect of a weak ambipolar field on non-local heat transport using the non-diffusive approximation
Authors: Murtaza G. , Mirza Arshad M. , Qaisar M. S.
Published: March 2009

We investigate the effect of a weak ambipolar field on non-local heat transport by solving the reduced Fokker-Planck equation in the non-diffusive approximation for the electron distribution function. It turns out that for a moderately high-Z plasma with steep gradients the maximum-heat-flow expression is modified and the ensuing results compare favourably with the experimental values. However, in the gentle-gradient limit the classical Spitzer-Härm heat flux expression is unaltered.
Velocity-space diffusion due to resonant wave–wave scattering of electromagnetic and electrostatic waves in a plasma
Authors: Sugaya Reiji
Published: March 2009

The velocity-space diffusion equation describing distortion of the velocity distribution function due to resonant wave-wave scattering of electromagnetic and electrostatic waves in an unmagnetized plasma is derived from the Vlasov-Maxwell equations by perturbation theory. The conservation laws for total energy and momentum densities of waves and particles are verified, and the time evolutions of the energy and momentum densities of particles are given in terms of the nonlinear wave-wave coupling coefficient in the kinetic wave equation.
Reconstruction of global micropulsations in the magnetosphere
Authors: Whang M. H. , Kuo S. P. , Lee M. C.
Published: March 2009

The coupling of hydromagnetic Alfvén waves is studied numerically in a dipolc-field model of the magnetosphere. The two coupled hydromagnetic equations derived by Radoski are solved as an implicit boundary-value problem, namely the boundary conditions at the magnetopause are determined self-consistently. Thus the calculated wave-field distribution inside the magnetosphere can match all known linear characteristic features of the stormtime Pc5 waves observed on 14/15 November 1979 from satellites. A set of proper boundary conditions is found, excellent agreement between the numerical results and observations is demonstrated. Based on the very limited spatial coverage (L ≈ 6·6 and within a latitudinal region ( −10°, 10°)), of the data provided by the satellites, the theoretical model can successfully reconstruct the global micropulsations in the magnetosphere and identify the source regions of hydromagnetic waves.
Excitation of thermonuclear cone instabilities by toroidal equilibrium distributions of high-energy alpha particles in tokamaks
Authors: Lisak M. , Hamnén H. , Anderson D.
Published: March 2009

The possibility of a new set of thermonuclear cone instabilities in tokamaks is demonstrated. These instabilities are caused by an inherent anisotropy existing in the alpha-particle velocity distribution function owing to the finite width of the particle orbits in combination with a spatially varying particle source. The conditions for the excitation of shear Alfvén waves by well-trapped alpha particles are studied.
Computer modelling of three-dimensional dynamics of fast reconnection
Authors: Ugai M.
Published: March 2009

Computer simulations are used to investigate the basic three-dimensional structure of the fast reconnection mechanism spontaneously developing from a long current sheet. It is shown that if three-dimensional effects (∂sol;∂z ≠ 0) are not so strong, a locally enhanced resistivity results in current-sheet thinning, and a fast reconnection process, involving switch-off shocks, is eventually set up in a region limited in the z direction. The fast reconnection process near the z = 0 plane becomes quasi-steady and two-dimensional (∂/∂z = 0), so that the well-known Petschek mechanism is fully applicable. Distinct plasma rarefaction occurs inside the fast reconnection region, so that fast-mode expansion may propagate in the z direction, and the resulting inflow velocity uz takes the magnetic field into the fast reconnection region and contracts the latter. The global current system undergoes drastic changes during the fast-reconnection development. The current flow, initially directed in the z direction, first converges towards the neutral line, and is then largely deflected away from this line in the inner reconnection region.
Relativistic charge currents in oblique electric and magnetic fields
Authors: Melia Fulvio , Fatuzzo Marco
Published: March 2009

Runaway processes on neutron stars leading to the sudden release of large quantities of energy (up to of order 1040 erg) on time scales as short as a fraction of a second involve plasma heating and particle acceleration in superstrong magnetic fields H (of order 1012 G). These transient events are interesting from a theoretical standpoint because they require knowledge of particle transport properties in low-density plasmas (εe ≲ 1025 cm−3) threaded by both electric (E) and magnetic fields. The evaluation of matrix elements involving solutions to the Dirac equation for such a field configuration is often difficult and sometimes impossible, since no completely normalized wave function has yet been found. Here it is shown that, in the special case of E/H ≲ 10−4, a simplification of the overlap integrals permits an analytical integration that yields explicit expressions for the relativistic charge currents needed in the computation of the anisotropic conductivity tensor when E.H ≠ 0. The application of these results to the evaluation of the conductivity is briefly discussed. Among other things, this work is relevant to a theory of resistive magnetic tearing instabilities in a quantizing field.
Electron-acoustic instability driven by a field-aligned hot electron beam
Authors: Bharuthram R.
Published: March 2009

Using kinetic theory, the electron-acoustic instability is investigated in a three-component plasma consisting of a hot electron beam and stationary cool electrons and ions. In the model considered here both the electrons and ions are magnetized, with the beam drift along the external magnetic field. The dependence of the growth rate on plasma parameters, such as electron-beam density, electron-beam speed, magnetic field strength and propagation angle, is studied. In addition, the effects of anisotropies in the velocity distributions of the hot electron beam and the cool electrons on the instability growth rate are examined.
Weyl's theorem for magnetohydrodynamics
Authors: Zank G. P.
Published: March 2009

Weyl's well-known theorem describing the behaviour of the entropy on the Hugoniot for gasdynamics is extended to magnetohydrodynamics. In so doing, it is pointed out why similar thermodynamical arguments are not easily established for more complicated reacting fluids such as the gasdynamical equations with mass-loading.
Nonlinear surface Alfvén waves
Authors: Cramer N. F.
Published: March 2009

The problem of nonlinear surface Alfvén waves propagating on an interface between a plasma and a vacuum is discussed, with dispersion provided by the finite-frequency effect, i.e. the finite ratio of the frequency to the ion-cyclotron frequency. A set of simplified nonlinear wave equations is derived using the method of stretched co-ordinates, and another approach uses the generation of a second-harmonic wave and its interaction with the first harmonic to obtain a nonlinear dispersion relation. A nonlinear Schrödinger equation is then derived, and soliton solutions found that propagate as solitary pulses in directions close to parallel and antiparallel to the background magnetic field.
Magnetic field intensification and formation of field-aligned current in a non-uniform magnetic field
Authors: Murata H.
Published: March 2009

A study is made of the induction of a direct field-aligned current due to Alfvén waves excited through an initial–boundary condition for an incompressible fluid with high conductivity in a non-uniform magnetic field. A simple but exact case is considered in which the direction of inhomogeneity of the magnetic field is perpendicular to that of the shear fluid motion at the boundary, and the fluid moves across the magnetic field. The boundary does not satisfy the frozen-flux condition, but has a large Lundquist number. The conductivity of the fluid held between the two boundaries is high, and the frozen-flux condition is approximately satisfied there. A preflare stage of the sun is investigated, and a reasonable magnetic field intensity and d.c. field-aligned current in the magnetic arcade are obtained for a given horizontal shear motion that is antisymmetric at both boundaries of the arcade foot points, taking account of the observed horizontal fluid motion.
Theory of nonlinear interaction of particles and waves in an inverse plasma maser. Part 1. Collision integral
Authors: Krivitsky Victor S. , Vladimirov Sergey V.
Published: March 2009

An expression is obtained for the collision integral describing the simultaneous interaction of plasma particles with resonant and non-resonant waves. It is shown that this collision integral is determined by two processes: a ‘direct’ nonlinear interaction of particles and waves, and the influence of the non-stationarity of the system. The expression for the nonlinear collision integral is found to be quite different from the expression for a quasi-linear collision integral; in particular, the nonlinear integral contains higher-order derivatives of the distribution function with respect to momentum than the quasi-linear one.
Plasma maser theory of the extraordinary mode in the presence of Langmuir turbulence
Authors: Sarma S. N. , Sarma K. K. , Nambu M.
Published: March 2009

The emission of extraordinary mode radiation in a plasma with Langmuir turbulence driven by an electron beam is considered. The process of emission considered in this paper is the plasma maser effect, which is essentially an energy up-conversion process. The energy necessary for the growth of the extraordinary mode is derived from the Langmuir turbulence. The nonlinear dispersion relation of the extraordinary mode in the presence of Langmuir turbulence is obtained and its growth rate calculated. The scope of application of the results to space-plasma observation is then stressed.