bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear propagation of the extraordinary mode in a hot magnetoplasma
Authors: Khiet Tu , Furutani Y , Ichikawa Y. H.
Published: March 2009

Kinetic theory for the nonlinear propagation of quasi-monochromatic extraordinary waves is presented. It reveals that propagation of an envelope of the extraordinary carriers is described by the nonlinear Schrödinger equation. In the cold plasma limit, a detailed analysis is carried out of the behaviour of the envelope of the upper- and the lower-hybrid waves at their respective resonant frequency ranges.
Nonlinear theory of the Weibel instability
Authors: Lemons Don S. , Winske D. , Gary S. Peter
Published: March 2009

A canonical distribution function is proposed to describe the instantaneous state of a single nonlinear wave–plasma system as it evolves quasi-statically in time. This function is based on two single particle constants of motion for a charged particle in a zero-frequency transverse magnetic wave and determines a wavenumber condition and two system energy constants. In the case of a onecomponent bi-Maxwellian plasma with T⊥/T‖>1, these relations are particularly simple and yield expressions for the energy in the magnetic wave field, the wavenumber, the temperatures, and the entropy of the system in terms of one unknown parameter, chosen to be the instantaneous temperature ratio, T⊥/T‖ The maximum value of the field energy is expressed in terms of only the initial temperature anisotropy, and is shown to be always less than of the system's total energy. The results are in good agreement with computer simulations of the electron Weibel instability.
Kinetic equation for an electron gas (non-neutral plasma) in strong fields and inhomogeneities
Authors: Øien Alf H.
Published: March 2009

The first two equations of the BBGKY hierarchy are discussed and solved in order to derive a kinetic equation for an electron gas (non-neutral plasma) where strong electric and magnetic fields as well as inhomogeneities are taken into account on scales relevant for collisions between particles. The gyrotropic assumption is not made. The magnetic field and the inhomogeneities are shown to have special effects on the collision terms. A strong magnetic field approximation is then made in order to simplify the collision term, and a new, proper collision term has been found when a strong magnetic field is present.
Turbulent heating of tokamak plasmas by runaway electron beam– plasma instability
Authors: Jones R.
Published: March 2009

Low ‘Ohmic’ voltages are adequate for establishing intense runaway electron beams in toroidal devices. These beams do not destroy conventional tokamak equilibrium and stability but still prove sufficient for turbulent heating by beam–plasma interaction.
Magnetic field-line reconnexion by localized enhancement of resistivity. Part 3. Controlling factors
Authors: Ugai Masayuki , Tsuda Takao
Published: March 2009

The previous companion papers have shown the important effect of a local increase in resistivity upon the fast-reconnexion configuration. The present paper exaniines another significant situation where the injection rate of magnetic flux into the reconnexion region is strongly constrained by some external agency. It is shown that as long as a local resistivity enhancement is retained, stationary configurations can ultimately be established which depend on the imposed boundary values in each case. The rate of magnetic field line reconnexion in the stationary configuration is indeed closely controlled by the boundary values. However, the reconnexion rate (measured by the local Mach number at a distance from the neutral point as in the ordinary theoretical treatments) is scarcely influenced by them. Also, it is shown that without the local resistivity enhancement the large-scale X-type field configuration, which should be required for any fast reconnexion process, can no longer be sustained.
The resistive evolution of force-free magnetic fields. Part 1. Slab geometry
Authors: Reid J. , Laing E. W.
Published: March 2009

The resistive evolution of a magnetic field through force-free states is discussed, and some unusual features described.
A variational principle in relativistic magnetofluid dynamics
Authors: Merches I.
Published: March 2009

The definition of the generalized antipotential four-vector makes it possible to give a relativistically covariant variational formulation in the dynamics of ideal charged fluids. A special relativistically covariant form of Maxwell's equation is given. The antipotential four-vector does not explicitly appear in the Lagrangian density. The derivation of the equation of motion of a single charged particle is given, to illustrate the theory.
Structure of shock waves at re-entry speeds
Authors: Shanmugasundaram V. , Murty S. S. R.
Published: March 2009

The unified structure of steady, one-dimensional shock waves in argon, in the absence of an external electric or magnetic field, is investigated. The analysis is based on a two-temperature, three-fluid continuum approach, using the Navier—Stokes equations as a model and including non-equilibrium collisional as well as radiative ionization phenomena. Quasi charge neutrality and zero velocity slip are assumed. The integral nature of the radiative terms is reduced to analytical forms through suitable spectral and directional approximations. The analysis is based on the method of matched asymptotic expansions. With respect to a suitably chosen small parameter, which is the ratio of atom-atom elastic collisional mean free-path to photon mean free-path, the following shock morphology emerges: within the radiation and electron thermal conduction dominated outer layer occurs an optically transparent discontinuity which consists of a chemically frozen heavy particle (atoms and ions) shock and a collisional ionization relaxation layer. Solutions are obtained for the first order with respect to the small parameter of the problem for two cases: (i) including electron thermal conduction and (ii) neglecting it in the analysis of the outer layer. It has been found that the influence of electron thermal conduction on the shock structure is substantial. Results for various free-stream conditions are presented in the form of tables and figures.
Nonlinear propagation of elliptically shaped Gaussian laser beams
Authors: Anderson D. , Bonnedal M. , Lisak M.
Published: March 2009

An analytic investigation is made of the nonlinear propagation characteristics of laser beams with elliptically shaped Gaussian intensity cross-sections. Explicit analytic criteria, in terms of inital conditions, are given, which determine the dynamical behaviour of the transverse dimensions of the beam, i.e. its self- focusing and defocusing properties. Approximate analytic solutions are also given, which display the characteristic features of the general variation of beam width with distance of propagation.
Corrigendum
Authors: Lemons Don S. , Gary S. Peter , Winske D.
Published: March 2009

It has been called to our attention that our paper on the nonlinear evolution of a temperature anisotropic plasma (T⊥ > T¶) in the absence of an external magnetic field (Lemons, Winske & Gary 1979) did not make reference to several relevant and previously published works. Specifically, the linear theory of this unstable plasma has been explored by Kalman, Montes & Quemada (1968), the quasi-linear theory by Smith (1969) and Montes, Coste & Diener (1970) while additional thermodynamic considerations were given by Montes & Peyraud (1972). We regret this oversight.
Effective coffision frequency and electron temperature in a weakly ionized argon plasma
Authors: Schneider C. P.
Published: March 2009

Herein is described a calculation of the effective coffision frequency νeffof a low- density, shock-heated argon plasma under the influence of a weak electric field which oscillates harmonically with angular frequency ω. It is shown that, for the high frequency case ω >whereis the collision frequency in a Maxwellian gas plasma, one has νeff⋍ 2, provided that the imaginary part of the argon plasma conductivity is negligibly small in comparison to the real part. The influence of the theoretical model used to calculate νeffon the values of the electron temperatureTederived from measurements is compared with the results obtained in a data reduction for which the hard-sphere model for particle encounters was utilized.
Electromagnetic instability and stopping power of plasma for relativistic electron beams
Authors: Okada Toshio , Niu Keishiro
Published: March 2009

The stopping power of a plasma for a relativistic electron beam (REB) is derived by taking a Weibel-type electromagnetic instability into account in a collisionless plasma. A quasi-linear theory is developed to derive the stopping power of the plasma due to the electromagnetic instability. The wave–particle interaction by use of the renormalization theory leads to a saturation level of instability. Thus the purely growing electromagnetic instability, including the effect of the beam temperature, decides an effective stopping length of the REB in the plasma.
Parametric instabilities in a turbulent plasma
Authors: Galin E.
Published: March 2009

We make some investigations regarding the anomalous energy absorption in a turbulent plasma through high-frequency parametric instabilities. We establish the optimum threshold conditions with respect to the pump frequency. The influence of the turbulence spectrum on the parametric phenomena is investigated.
Re-ionization of a partially ionized plasma by an Alfvén wave of moderate amplitude
Authors: Brennan M. H. , Sawley M. L.
Published: March 2009

This paper reports on the use of forced magneto-acoustic oscillations to investigate the effect of a torsional hydromagnetic (Alfvén) wave pulse of moderate amplitude on the properties of a partially ionized afterglow helium plasma. Observations of the magnetic flux associated with the oscillations, measured at a number of frequencies, are used to determine radial density proffles and to provide estimates of plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. The torsional wave is shown to cause significant re-ionization of the plasma with no corresponding increase in the plasma temperature. However, the presence of a number of energetic particles is evidenced by the production of a significant number of doubly charged helium ions.
Solitary Alfvén waveguide structures in a magnetized plasma
Authors: Sheerin J. P. , Ong R. S. B.
Published: March 2009

A nonlinear Alfvén wave structure with axial symmetry about the line of force of an ambient magnetic field is presented. The solitary wave forms a ‘ring’ shaped waveguide along the magnetic field line.
Nonlinear electron-acoustic waves in a multi-species plasma
Authors: Buti B.
Published: March 2009

Propagation of electron-acoustic waves in a strongly nonlinear magnetoplasma with two ion species is investigated. The presence of the second ion component affects the dynamics of these solitary waves in a variety of ways. Besides solitons, supersonic holes (density depressions) are produced by sufficiently large- amplitude perturbations. Heavier and hotter ions are more favourable to the holes. Applications of the present investigations to space plasmas are pointed out.
Longitudinal electron modes in plasma
Authors: Bydder E. L. , Liley B. S.
Published: March 2009

Propagation of longitudinal electron modes in Maxwellian plasma is discussed using both the Vlasov equation and the 13-moment equations. Both methods are shown to be consistent and in addition both methods are shown to predict a second (heavily damped) mode which propagates below as well as above the plasma frequency. The results are in excellent agreement with earlier experiments for near-equilibrium plasmas.
Scattering from electron density irregularities in a compressible anisotropic plasma
Authors: Okuzawa T. , Nguyen T. H.
Published: March 2009

The cold-plasma model of the radio wave scattering from spatially random fluctuations of electron density in an anisotropic plasma is extended to the warmplasma model, in which the effect of electron pressure is taken into account. Since the medium is compressible as well as anisotropic, there is the additional possibility of mode conversion from an incident electromagnetic wave to a scattered electron plasma wave. Some numerical results are also included.
Langinuir probe measurements of double-layers in a pulsed discharge
Authors: Levine J. S. , Crawford F. W.
Published: March 2009

Langmuir probe measurements have been carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double- layer. Supplementary evidence, obtained from d.c. and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers is discussed, and directions for future work are suggested.
Magnetic field reconnexion in a sheared field
Authors: Ugai Masayuki
Published: March 2009

The present paper numerically studies a nonlinear development of the Petschek mode in a sheared magnetic field where there is a field component Bz along an X line. It is found that finite-amplitude intermediate waves, adjacent to the slow shock, may eventually stand in the quasi-steady configuration; on the other hand, the fundamental characteristics of the Petschek-mode development are scarcely influenced, either qualitatively or quantitatively, by the Bz field.
Three electrostatic temperature drift instabilities
Authors: Gary S. Peter , Abraham-Shrauner Barbara
Published: March 2009

This paper considers temperature drift instabilities, modes which can be driven unstable solely by a temperature gradient perpendicular to a magnetic field. The linear electrostatic dispersion relation for a Vlasov plasma in a uniform magnetic field is used and propagation is assumed to be in the plane perpendicular to the gradient. Three temperature drift instabilities have been found. The ion temperature drift instability arises at frequencies much below the ion cyclotron frequency, the electron temperature drift instability propagates somewhat below that frequency and the lower-hybrid temperature drift instability has frequencies above the lower-hybrid frequency. The first of these modes is driven by an ion temperature gradient and is enhanced by increasing Te/Ti. The latter two modes are driven by an electron temperature gradient and are enhanced by a decreasing Te/Ti. Density gradients are considered as an additional source of free energy, and comparisons of temperature drift with density drift instabilities are made.
Excitation of an ion-acoustic wave by two whistlers in a collisionless magnetoplasma
Authors: Sodha M. S. , Singh Tarsem , Singh D. P. , Sharma R. P.
Published: March 2009

This paper presents an investigation of the excitation of an ion-acoustic wave in a collisionless hot magnetoplasma by two whistlers. On account of the interaction of the two whistlers, of frequencies ω1 and ω2, ponderomotive force at frequency △ ω(= ω1 – ω2) leads to the generation of an ion-acoustic wave. When the two whistlers have initially Gaussian intensity distributions, a d.c. component of the ponderomotive force leads to the redistribution of the background electron/ion density, and cross-focusing of the whistlers occurs. The power of the generated ion-acoustic wave, being dependent on the background ion density and powers of the whistlers, is further modified. The ion-acoustic wave power also changes drastically with the strength of the static magnetic field.
Electrostatic instabilities in anti-loss-cone plasma
Authors: Bhatia K. G. , Lakhina G. S.
Published: March 2009

It is shown that both lower hybrid and modified electron acoustic instabilities can be excited in a hot anti-loss-cone plasma co-existing with a rarefied cold plasma, provided the anti-loss-cone factor, ρ, exceeds a value Tm/Tt, where Tm and Tt are the parallel temperatures of missing and trapped electrons respectively. These instabilities are excited in a bounded range of wavenumbers and the growth rates are enhanced with the increase of cold plasma density. For

Tm/Tt < ρ > (Tm/Tt)½

both the instabilities are of resonant type whereas for ρ > (Tm/Tt)½ both may be converted into non-resonant types. These instabilities are expected to give rise to the heating of protons as well as electrons in the magnetosphere beyond the plasmapause.
Ion beam excitation of ion-cyclotron waves and ion heating in plasmas with drifting ions
Authors: Hauck J. P. , Böhmer H. , Rynn N. , Benford Gregory
Published: March 2009

Ion-cyclotron waves are excited by cesium and potassium ion beams in cesium and potassium Q-machine plasmas. The ion beams are injected along the magnetic field with care to avoid beam transverse velocities. The observed ion-cyclotron mode frequencies are below those driven by electron currents. These resonant instabilities are convective in character with small spatial growth rates ki/kr ≃ 0.05. Plasma ion heating is observed and is consistent with a model in which mode amplitudes are saturated by diffusion effects.
Electromagnetic effects on the electrostatic ion-cyclotron instability
Authors: Gomberoff L.
Published: March 2009

One possible mechanism for ring current proton losses is the electrostatic ioncyclotron instability. Since typical ring-current parameters involve values of β of the order of one, the electron response must be treated electromagnetically. To this end, the effect of electromagnetic corrections on the electrostatic ioncyclotron instability is discussed. It is shown that the electromagnetic response of the electrons has been only partially included in previous studies. A relatively simple expression for the growth rate, including all relevant corrections, is derived. On the basis of this expression, growth rates for typical ring-current parameters are calculated and compared with previous results. Flute-like modes are shown not to be affected by these corrections.
Filamentation of a laser beam in a strongly ionized magnetoplasma
Authors: Pitale L. A.
Published: March 2009

On a time-scale of the order of the energy relaxation time, a high power laser beam, propagating in a strongly ionized magnetoplasma is shown to be unstable for small scale fluctuations. In the domain r0 < [mi/m]½ λm. v2/[ω2c + v2] (r0, λm, v, ωc, and m being respectively the spatial scale of the perturbation, electron mean free path, collision frequency, cyclotron frequency and mass and mi being the ion mass) the main loss of excess electron energy is due to thermal conduction; in the other limit collisional loss dominates. It is shown that for small scale fluctuations the growth rate increases with (i) increasing magnetic field and (ii) increasing r0. For large scale fluctuations the magnetic field does not show any effect; the growth rate, however, diminishes with increasing spatial scale. A maximum growth rate is obtained both for some optimum value of scale length and for intensity of the main beam.
Stability of aligned magnetoatmospheric flow
Authors: Adam J. A.
Published: March 2009

Using the stationary equilibrium energy principle a sufficient condition is obtained for the stability of a compressible stratified fluid with a non-uniform horizontal magnetic field, with an aligned shear flow. The condition is used to provide a simple generalization of a known result for a specific atmospheric model.
Beat Hamiltonians and generalized ponderomotive forces in hot magnetized plasma
Authors: Johnston Shayne , Kaufman Allan N. , Johnston George L.
Published: March 2009

A novel approach to the theory of nonlinear mode coupling in hot magnetized plasma is presented. The formulation retains the conceptual simplicity of the familiar ponderomotive-scalar-potential method, but removes the approximations. The essence of the approach is a canonical transformation of the single-particle Hamiltonian, designed to eliminate those interaction terms which are linear in the fields. The new entity (the ‘oscillation centre’) then has no first-order uttering motion, and generalized ponderomotive forces appear as nonlinear terms in the transformed Hamiltonian. This viewpoint is applied to derive a compact symmetric formula for the general three-wave coupling coefficient in hot uniform magnetized plasma, and to extend the conventional ponderomotive-scalar-potential method to the domain of strongly magnetized plasma.
Parallel solitary Alfvén waves in warm multi-species beam-plasma systems. Part 2. Anisotropic pressures
Authors: Verheest Frank
Published: March 2009

A nonlinear treatment is given for MHD waves that propagate parallel to the external magnetic field in warm multi-species plasmas with anisotropic pressures and different equilibrium drifts. Both the wave electric and magnetic fields obey a derivative nonlinear Schrödinger equation. Soliton solutions are discussed, in particular for plasmas with two ion species.
The transformation of plasma equations to normal form in mode conversion theory
Authors: Sabzevari Bijan
Published: March 2009

Field variables in a slowly varying plasma are solutions of a system of differential and integral equations. To solve these equations, the fields are expanded in the eigenvectors of an algebraic plasma tensor, and the plasma equations can be transformed into a system of transport equations. The expansion becomes singular when eigenvalues coincide (for example in the case of mode conversion). It is shown how this problem can be resolved for an arbitrary system of Maxwell and/or fluid equations in arbitrary dimensions and for every kind of medium. The method is applied to horizontal stratified media as a simple example.
Relativistic and non-relativistic analysis of whistler-mode waves in a hot anisotropic plasma
Authors: Sazhin S. S. , Sumner A. E. , Temme N. M.
Published: March 2009

The dispersion equation for parallel whistler-mode propagation in a hot anisotropic plasma is analysed numerically in both weakly relativistic and nonrelativistic approximations under the assumption that wave growth or damping does not influence the wave refractive index. The results of this analysis are compared with the results of an asymptotic analysis of the same equation, and the range of applicability of the latter results is specified. It is pointed out that relativistic effects lead to a decrease in the range of frequencies for which instability occurs. For a moderately anisotropic plasma (T⊥/T‖ = 2) relativistic effects lead to an increase in the maximum value of the increment of instability.
Long, nonlinear, non-axisymmetric surface-wave propagation in a magnetic tube
Authors: Ruderman M. S.
Published: March 2009

The propagation of long, nonlinear, non-axisymmetric surface waves in a magnetic cylinder is considered. It is supposed that the electrical conductivity is infinite, the fluid is incompressible and there is no magnetic field outside the cylinder. The nonlinear integro-differential equation governing the wave propagation is derived using the reductive perturbation method. The interesting and important point is that this equation governs the evolution of all nonaxisymmetric modes simultaneously. This is because the phase velocities of all non-axisymmetric modes are equal to the kink speed in the linear, infinitely long-wavelength approximation, and as a result all non-axisymmetric modes interact strongly in the nonlinear case. Solutions of the governing equation in the form of periodic helical waves of permanent form are obtained numerically.
Classical free-electron lasing in an undulating electrostatic field in the axial direction
Authors: Kim S. H.
Published: March 2009

It is shown that the phase of the electromagnetic wave emitted through stimulated emission is intrinsically random. The insensitivity of the phase of the laser field to any disturbance in the laser cavity parameter derives from the fact that stimulated and spontaneous emissions take place concurrently at the same wave vector, the phases of spontaneous emission are mildly bunched, and the central limit theorem can be applied to the phase of the laser field. The two spectral lines observed in the Smith-Purcell free-electron laser experiment show that both classical and quantum-mechanical free-electron lasings, in which the wigglers behave as classical waves and wiggler quanta respectively, take place concurrently at different laser wavelengths in the case of the electric wiggler. It is shown that the coherence of the classical free-electron laser is achieved through modulation of the relativistic electron mass by the electric wiggler. The classical free-electron lasing is calculated using the quantum-augmented classical theory. In this, the probability of stimulated emission is first evaluated by interpreting the classically derived energy exchange between an electron and the laser field from a quantum-mechanical viewpoint. Then the laser gain is obtained from this probability by using a relationship between the two quantities derived by quantum kinetics. The wavelength of the fundamental line of classical free-electron lasing is twice the wavelength of the fundamental line of the free-electron two-quantum Stark emission, which is the quantum free-electron lasing in the electric wiggler. The gain of the classical free-electron lasing appears to scale as λ3w/γ3, where γ is the Lorentz factor of the electron beam and λw is the wavelength of the wiggler.
Wave propagation in equal-mass plasmas
Authors: Stewart G. A. , Laing E. W.
Published: March 2009

We study linear wave propagation in the case of equal-mass plasmas. We show that the special symmetry of such plasmas simplifies the problem and causes the disappearance of well-known phenomena such as Faraday rotation and whistler wave modes. We exploit the Symmetry of the problem to derive analytical expressions for wave propagation for various fluid models of the plasma. We also find which distribution functions will retain the symmetry properties of the fluid models.
Effects of neutral gas friction and ion viscosity on the Rayleigh-Taylor instability of a stratified plasma in the presence of Hall currents
Authors: Bhatia P. K.
Published: March 2009

The effects of neutral gas friction, on the Rayleigh–Taylor instability of an infinitely conducting plasma of variable density, with ion viscosity and Hall currents, are investigated. For an ambient horizontal magnetic field, it is shown that the solution is characterized by a variational principle. Making use of the existence of this, proper solutions are obtained for a semi-infinite plasma, in which the density is stratified exponentially along the vertical, confined between two planes. In the simultaneous presence of the effects of ion viscosity and Hall currents, it is found that the potentially unstable stratification is unstable for all wavenumber perturbations, irrespective of whether or not the effects of neutral gas friction are included. Further, it is found that the growth rate increases with both Hall currents and neutral gas friction, and decreases with ion viscosity. The influence of the Hall currents and the neutral gas friction, therefore, is destabilizing, while that of ion viscosity is stabilizing. In the absence of Hall currents, it is found that the viscous plasma is stable, even for a potentially unstable stratification, for perturbations confined to a cone about the magnetic field vector. The angle of the cone of stable propagation of an inviscid plasma,. however, decreases with both Hall currents and effects of neutral gas friction.
Extension of Doughterty's model Fokker–Planck equation for a plasma
Authors: Papa Robert J.
Published: March 2009

A generalization of the Appleton–Hartree equation is made to include the effects of energy-dependent electron-neutron collisions, Coulomb encounters and spatial dispersion. The frequency of electromagnetic waves propagating in a magneto-plasma is sufficiently high that the ion motion may be neglected compared with the electron motion. The present analysis extends Dougherty (1963, 1964) to include the simultaneous effect on wave propagation of Coulomb forces, spatial dispersion and energy-dependent electron-neutral collisions, where one or more of these effects can have a significant influence on circularly polarized waves propagating at frequencies near electron cyclotron resonance. The electrical conductivity tensor is expressible in terms of appropriate velocity moments of the electron distribution function. The electron velocity distribution function is determined by expanding the inverse of the differential operator of the linearized kinetic equation in a small parameter ε2', where in one case ε2 is the ratio of Coulomb collision frequency to signal frequency, and in the second case ε2 is the ratio of electron-neutral collision frequency to signal frequency. For wave propagation along the magnetic field, the dispersion relations for right-hand and left-hand circularly polarized waves, and also the dispersion relation for longitudinal waves, are solved numerically, and graphs are presented to show the effects of collisionless damping, velocity dependent electron-neutral collisions and Coulomb collisions.
Absorption coefficients of a hydrogen plasma for laser radiation
Authors: Stallcop James R.
Published: March 2009

The formalism for the calculation of the absorption of radiation by a hydrogen plasma at common laboratory conditions is summarized. The hydrogen plasma absorption coefficient for laser radiation has been computed for a wide range of electron densities (1015- 1018 cm-3) and temperatures (10 000–40 000 °K). The results of this computation are presented in a graphical form that permits a determination of the absorption coefficient for the following laser wavelengths: 0.176, 0.325, 0.337, 0.442, 0.488, 0.51, 0.633, 0.694, 1.06, 1.15, 2.36, 3.39, 5.40 and 10.6 Μm. The application of these results and laser radiation absorption measurements to plasma diagnostics is discussed briefly.
Phase and signal velocities of eigenwaves in a binary dissipative plasma
Authors: Kranyš M. , Teichmann J.
Published: March 2009

The signal and phase velocities of the possible waves (eigenwaves) in a dissipative binary plasma have been studied on the basis of the linearized thirteenmoment theory. The complete set of eigenmodes for the given system is formed using approximations in the range of frequencies high compared with typical collision or plasma frequencies. There are twenty non-trivial propagation modes. Four of them are modes with signal-front speed c associated with the induced electromagnetic wave. Eight modes belong to each of the gas constituents, among them two longitudinal diffusion modes (±WI), four transverse viscosity modespolarized respectively along two transverse axes ±W⊥ in the direction x1 and ±W⊥ in the direction x2) and two longitudinal thermal modes (±WII). The signalfront speed of all eigenwaves is lower than the speed of light, so that the system is hyperbolic. The ultra-relativistic plasma is also briefly discussed. In this case, all the mixture constituents will have the same set of signal-front speeds as a single gas, irrespective of the bulk viscosity. Comparison is made of the present theory and results with other theories (for some special cases).
Fractional harmonics in a plasma
Authors: Lewak G. J. , Lee H. J.
Published: March 2009

The most common approach to the study of plasma nonlinearities is by a form of perturbation theory which first studies the linearized equations, then evaluates effects of nonlinearities in terms of these linear solutions. Such an approach is probably justifiable for the effect of weak nonlinearities, but will almost certainly miss features that are exclusively nonlinear in nature (i.e. effects which cannot be described by modifying linear theory, or effects which are present only when e.g. a source of disturbances in a plasma reaches a certain threshold amplitude). It is the object of this paper to investigate one possible such nonlinear effect.
Oscillations of a plasma confined by the magnetic field of a line multipole
Authors: Burghes David N.
Published: March 2009

The problem of confinement and stability of a plasma enveloped by the magnetic field of a line multipole is considered. An energy method is used to find the increment in potential energy when the configuration is given a small displacement. The frequency and modes of oscillation are found in a particular example.
Field line reconnexion and magnetic energy release
Authors: Yeh Tyan
Published: March 2009

It is shown that an equilibrium of a magnetoplasma with a small separatrix angle at the magnetic neutral point possesses a greater magnetic energy than its corresponding equilibrium with a large separatrix angle. Hence, it is energetically possible for a configuration with two oppositely directed magnetic fields in contact to proceed to a potential field through the process of field line reconnexion. The excessive magnetic energy would be released into kinetic and thermal energies.
An electron thermal instability in a resistive non-equilibrium fully ionised plasma
Authors: Haines M. G.
Published: March 2009

An electron thermal instability is proposed, which could explain the occurrence of the break-up of a plasma shell into separated current elements during the early history of a discharge. Inclusion of electron thermal conduction and Faraday's law leads to an optimum wavelength for growth, in good agreement with recent results on a θ pinch at NRL, Washington. Finally, the addition of ion motion leads to a modification of the stability criterion. The non-convective instability exists only at low temperature and high density; but a convective instability now appears, which persists at high temperature, and could be relevant to fusion conditions.
Thermal relaxation of a two-dimensional plasma in a d.c. magnetic field. Part 2. Numerical simulation
Authors: Hsu Jang-Yu , Joyce Glenn , Montgomery David
Published: March 2009

The thermal relaxation process for a spatially uniform two-dimensional plasma in a uniform d.c. magnetic field is simulated numerically. Thermal relaxation times are defined in terms of the time necessary for the numerically computed Boltzmann H function to decrease through a given part of the distance to its minimum value. Dependence of relaxation time on two parameters is studied: number of particles per Debye square n0 λ2D and ratio of gyrofrequency to plasma frequency Ω/ωp. When Ω2/ω2p becomes ≫[ln (L/2πλD)]−½, where L is the linear dimension of the system, it is found that the relaxation time varies to a good approximation as (n0 λ2D)½ and Ω/ωp.
Surface waves at a vacuum—plasma interface
Authors: Clemmow P. C. , Elgin J.
Published: March 2009

It is emphasized that the dispersion relation for surface waves at a vacuum—plasma interface can be obtained by setting the reflexion coefficient to zero The relations for warm, collisional and hot, collisionless plasmas are derived in this way, and shown to be inagreement with previous results. The former relation is expressed explicitly as a cubic equation for y = 2c2k12/ω2p, as a function of x = 2ω2/ω2p − 1, where k1 is thecomponent of the wave vector along the interface, a is the frequency and w the plasma frequency; and the nature of the three branches of the y(x) curve is analyzed in detail. The rotation of the vacuum wave vector as the frequency runs from 0 to ∞ is displayed, and it is established that one and only one branch corresponds, in the collisionlesscase, to pure surface waves.
The ray tracing treatment of the oblique echo model for the topside upper hybrid resonance
Authors: Parkes E. J.
Published: March 2009

The oblique echo model for the resonance near the local upper hybrid frequency fT observed by topside sounders involves the propagation of slow waves away from the sounder, which later return as echoes after refiexion due to an electron density gradient. The model is investigated by using ray tracing techniques. Use of Poeverlein constructions gives some idea as to the qualitative nature of the rays which contribute to the resonance. A quantitative description requires the use of ray-trajectory equations. By using a simple approximate warm electromagnetic dispersion relation (which, nevertheless, retains all the important features of the exact dispersion relation), the ray-trajectory equations are integrated analytically for the case of a stratified plasma with a linear density gradient. These equations are used to investigate the behaviour of the frequency of the received echoes as a function of delay time. The resonance exhibits strikingly different characteristics for fT<2fH and fT>2fH respectively, where fH is the electron gyrofrequency. For fT<2fH the resonance is ‘strong’, the receiver observing a continuous response consisting of two echoes which interfere to give a fringe pattern. Some typical ray paths are illustrated. For fT<2fH the resonance is ‘weak’ and without fringes. A condition is derived for the existence of intercepting ray paths and for the maximum time delay that occurs when they do exist.
An experimental investigation of parallel and oblique shock waves in a magnetized plasma
Authors: Craig A. D.
Published: March 2009

The Charybdis apparatus is designed to produce parallel and oblique shock waves in a magnetized plasma. An initial hydrogen plasma (nel 7 × 1020 m-3, T1 ˜ 1.3 eV) is produced in a Pyrex chamber (0.46 m cia., 1 2 m long) containing an axial magnetic field (B1 up to 0.2 T). A diffuse current front is produced in a fast-rising radial discharge between a central electrode and an annular outer electrode at one end of the chamber. The Lorentz force on the current sheet causes axial motion, and a quasisteady shock proffle propagates ahead. A clear shock separation is achieved across almost the complete radial extent for a wide range of initial parameters. The shock propagation angle to the initial field ranges from 0Ú to 40Ú. The Alfvén Mach number MA of the flow is varied by changing the initial field strength. Switch-on shock behaviour is demonstrated at a point of parallel propagation for low MA. For higher MA cases, no separated point of parallel propagation occurs in the shock profile.
The effect of wave reflection on induced Raman scattering in an inhomogeneous plasma
Authors: Cairns R. A.
Published: March 2009

We consider the Raman back-scatter instability produced by an electromagnetic wave in a plasma whose density increases in the direction of propagation. It is shown that, when reflexion of the waves involved in the interaction is taken into account, it may be possible to obtain, in the linear approximation, normal modes that grow exponentially in time. This is in contrast to the theory that neglects refiexion, and focuses attention only on the region of resonant interaction, which predicts only spatial amplification.
On the Dupree–Weinstock turbulence theory
Authors: Peyraud Nelly , Coste Jean
Published: March 2009

We give a necessary criterion of validity for the Dupree–Weinstock theory of turbulence. In this connexion, we analyze two specific cases of high-frequency (HF) and low-frequency (LF) turbulence. In the HF case, we show that an appreciable modification of the growth rate of unstable modes cannot occur before trapping.
On the possibility of magnetic fields and fluid flows parallel to the X-line in a re-connexion geometry
Authors: Cowley S. W. H.
Published: March 2009

We consider the possibility of modifying the Sonnerup solution for incompressible fluid flow about an X-type re-connexion line, to include fields and flows parallel to the X line. We find that such fields and flows may change across the discontinuities of the Sonnerup solution. By considering the requirements imposed by a proper matching across the various regions of flow, and by the integral conservation properties of the diffusion region, we seek to find the restrictions that are imposed on this parallel field and flow, and on the arrangement of the discontinuity planes around the diffusion region. We find that four types of such arrangements are possible, each corresponding to a different set of restrictions on the parallel field and flow. In one case, where all the discontinuity planes intersect at a common line, the ‘ parallel’ parameters of the in-flow and out-flow regions may be arbitrarily and independently chosen. Of the remaining three cases, one contains solutions with uniform parallel fields ad flows, while the other two depend for their existence on large fluid flow or magnetic field shears across the two in-flow regions.
Monatomic plasma-thermal radiation interaction: a weakly-ionized kinetic model
Authors: Phillips Warren F. , Arpaci Vedat S.
Published: March 2009

A model for the kinetic formulation of a weakly-ionized monatomic gas, which interacts with thermal radiation, is proposed. The collision terms for particle-initiated ionization, developed in terms of a non-equilibrium degree of ionization, and the collision terms for photon-initiated ionization, developed by assuming particles remain in local equilibrium during photon relaxation, all satisfy the usual conservation principles. It is also shown that the proposed model leads to an H theorem.
The expansion of a plasma from a spherical source into a vacuum Part 1. Fully-ionized flow
Authors: Goldfinch Judith , Pack D. C.
Published: March 2009

Hamel & Willis (1966) first showed that anisotropy in temperature could be predicted theoretically in the expansion of a spherical source of gas into a vacuum, thus explaining anisotropies observed to occur in rarefied gas jets. Chou & Talbot (1967) carried out numerical calculations based on similai ideas for a plasma consisting of electrons, ions and neutral particles. These showed that the electron temperature remains isotropic, and little anisotropy occurring among the ions within the (rather extensive) calculations. Here, in the first of two papers, an analytic treatment is applied to the expansion of a fully ionized plasma source, with the particles interacting according to the Coulomb law.
The expansion of a plasma from a spherical source into a vacuum Part 2. Partially-ionized flow
Authors: Goldfinch Judith
Published: March 2009

This paper introduces the effects of partial ionization and recombination into the steady supersonic spherical source expansion of a plasma. It presents an analytical solution for a problem previously solved only numerically, using moment equations derived directly from the Boltzmann equation under the assumption of an ellipsoidal distribution function. The recombination is assumed collisionalradiative, as considered by Bates, Kingston & MeWhirter (1962a, b) and an approximate rate constant is derived from their results. The plasma is taken to be optically thick. The results show that, in a highly ionized plasma, the species maintain equal isotropic temperatures for the main part of the flow, with the degree of ionization tending to a finite limit. Recombinations, however, remain sufficiently frequent to keep the temperature above that in an expansion with no recombination. In a weakly ionized plasma the temperature of the heavy particles is almost unaffected by recombinations and falls adiabatically, although the electron temperature remains high. The analytical results are compared with the numerical results of Chou & Talbot (1967).
Stability of a plasma stream in a magnetic field
Authors: Lamont A. , Taylor J. C. , Laing E. W.
Published: March 2009

The system studied is a plasma streaming parallel to a uniform magnetic field with a velocity which varies in a transverse direction. The flow is bounded at y =± a by perfectly conducting planes.

The Poisson-Vlasov equations are used to derive an integro-differential equation for ø the Fourier transform of the electrostatic potential. The kernel of this equation is expanded using a small Larmor radius expansion for ø and for the equilibrium distribution function f0.
A note on the formation of Debye potential well in current-carrying plasmas
Authors: Kan J. R.
Published: March 2009

The field of a test charge at rest in a plasma is known to be shielded via the collective interaction between the test charge and the particles of the plasma. In a thermal equilibrium plasma, the shielded potential has a spatial variation of the Debye form exp (— r)/r. In this note we will show that, in a collisionless current-carrying plasma, the potential profile along the radial direction parallel to the current changes from the Debye form to a potential well form, and causes a reversal of the ele ctric field of the test charge. The formation of the Debye potential well is attributed to the resonant interaction between the particles and the waves stationary in the test charge frame when the net flux of charged particles is different from zero. This is the same type of resonant interaction which leads to the well-known Landau damping (Landau 1946).
The role of energy and momentum conservation in nonlinear beam–plasma interaction
Authors: Jungwirth K.
Published: March 2009

Theoretical and numerical results concerning the nonlinear interaction of an initially cold beam with a single wave (ω ≈ k∥ vb) in either magnetized or field- free plasma are presented and discussed. By using the energy and momentum conservation laws, the equations describing the development of the wave amplitude and phase, both in the temporal and spatial problem, are derived and then solved numerically together with the equations of motion of the beam particles. The fundamental role of an absorption (or transformation) of the wave in its interaction with a beam modulated at a frequency belonging to the upper branch of the electron plasma oscillation is recognized in two model situations.
Analytic BGK modes and their modulational instability
Authors: Schamel Hans
Published: March 2009

Physically acceptable solutions of the time-independent Vlasov–Poisson system are found by applying a method which is analogous to the soliton method in Korteweg–de Vries theory. Cnoidal wave solutions for small-amplitude Langmuir and ion acoustic waves are derived, in which the nonlinearity is determined by trapped electrons. The class of weakly distorted waves is shown to be modulational unstable.
Absolute maxmum growth rates and enhancement of unstable electromagnetic ion–cyclotron waves in mixed warm–cold plasmas
Authors: Cuperman S. , Gomberoff L. , Sternlieb A.
Published: March 2009

We calculated relative and absolute maximum linear growth rates of the electromagnetic ion–cyclotron instability produced by the addition of cold plasma to an infinite uniform anisotropic plasma. In this, both accurate numerical solution of the linearized dispersion relation, and approximate analytic calculations, were carried out, and the results were compared critically.

Qualitatively, results similar to those obtained in the past for the right-hand polarized electron–cyclotron electromagnetic (whistler) waves (Cuperman & Landau 1974) are found also for the left-hand polarized waves considered in this paper. Specifically, the electromagnetic ion–cyclotron instability in a warm, anisotropic proton plasma, characterized by Pp ≡ βP,A2p(Ap + 1) ≲ 1, may be significantly enhanced by addition of cold plasma.
Ordinary electromagnetic mode instability
Authors: Cheng Chio-Zong
Published: March 2009

The instability of the ordinary electromagnetic mode, propagating perpendicular to an external magnetic field, is studied for a single-species plasma with ring velocity distribution. The marginal instability boundaries for both the purely growing mode and the propagating growing modes are calculated from the instability criteria. The dispersion characteristics for various sets of plasma parameters are also given. The frequency bands of the propagating growing modes are centered at about (η +½)ωc, where η = 1, 2,…, and the typical growth rates are of the order of the cyclotron frequency and enhanced by increasing fluβ1.