bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion curves for the generalized Bernstein modes
Authors: Puri S. , Leuterer F. , Tutter M.
Published: March 2009

Dispersion curves are plotted for the extraordinary branch of the electron- and ion-cyclotron harmonic waves propagating perpendicularly to the static magnetic field in a non-relativistic, hot Maxwellian plasma, without invoking the electrostatic approximation. It is found that, except in the vicinity of the cyclotron harmonics and the hybrid resonances, either the cold-plasma or the electrostatic approximation are accurate representations of the exact solution. The hybrid resonances of the cold-plasma model become monotonically shrinking regions of low group velocity as the temperature is increased, till all discernible evidence of these resonances disappears as the parameters corresponding to the thermonuclear plasmas are approached.
Some Properties of large-amplitude electrostatic waves (Allis modes)
Authors: Neel W. W. , Flynn R. W.
Published: March 2009

Allis modes are large-ampliturde, undamped electrostatic plasma waves, in which the trapped electron distribution is the analytic continuation of the untrapped distribution. Allis modes can be pulse-like, as well as periodic. As the amplitude of the periodic solutions increases, the frequency decrsases and the wavelength increases, leading finally to solitary pulse solutions as a limiting case, reached when an appreciable number of electrons are trapped by the wave. These pluse-like solutions imply a maximum amplitude to Allis modes, and a maximum d.c. current they can drive. A simple approximate expression gives the non-linear properties of Allis modes in terms of the linear properties and the maximum amplitude.
A unified picture of the parallel whistler mode instability
Authors: Landau Ronald W. , Cuperman Sami
Published: March 2009

A parametric investigation of parallel right-hand electromagnetic waves below the electron cyclotron frequency has been carried out; this wave is unstable for anisotropic temperatures if T⊥ <T1. Simple analytic expressions for the maximum growth rate have been obtained for the full range of the parameters β1, _ and A_ ≡ (T⊥/T1)_ -1 as they range from zero to infinity. It is shown that the parameter P ≡ β1_A_(A_+1)2 has an important role: (i) for P ≪1, the results of Kennel & Petschek (1966), for large resonant velocities, hold; (ii) for P ≫ 1, the results of Sudan (1963, 1965) for small resonant velocities are recovered; (iii) for P ≫ 1 and A ≫ 1, the growth rate approaches an upper limit (near the plasma frequency for hot plasmas) identical to the zero field instability of Weibel (1959). For the case P ≫ l and moderate A values (i.e. Sudan's regime), analytic expressions for the rates of growth are calculated without restriction on their magnitude.
Comparison of electron and electronic temperatures in recombining nozzle flow of ionized nitrogen–hydrogen mixture. Part 2. Experiment
Authors: Park Chul
Published: March 2009

This is part 2 of a two-part paper. In this part, visible and infrared line radiations from nitrogen and hydrogen are measured with a spectrograph in an ionized flow expanding through a supersonic nozzle, wherein the hydrogen content is less than 0·1 %. The geometry and stagnation conditions are those for which the calculations were made in part 1. The experiment confirms quantitatively the predictions of part 1 that the electronic excitation temperatures of hydrogen aud (3P) core states of nitrogen are higher than the electron temperature, and that (3P) excitation temperatures exhibit maxima within the nozzle. The measured excitation temperatures of states with (1D) core are found to agree with the calculated electron temperatures.
Nonlinear development and Fourier analysis of the whistler mode instability
Authors: Cuperman S. , Salu Y.
Published: March 2009

The results of the nonlinear computer investigationof the whistler mode instability with the aid of particle-in-cell simulation methods are presented. The electron plasma considered is hot (kT‖ = 20 keV), anisothermal (T⊥/T‖ ≃ 2) and embedded in a static magnetic field such that β‖ = 0.8. A detailed Fourier analysis of the electromagnetic activity developed under the above stated conditions is carried out: the waves are shown to be electron-like and excellent agreement with the linear stability analysis for the first stages of evolution is found. The feed-back effect of the waves on the particles is shown to result in a continuous decrease of the thermal anisotropy ratio T⊥/T‖ corresponding changes in the Fourier spectra of the electromagnetic activity are observed; additional changes in the wave spectrum are introduced by the interaction between various instability modes. At the end of the run (ωpt ⋍600), the state of the system resembles a quasi-stable equilibrium, in which the electromagnetic energy achieves its maximum value: in this state, unlike the equilibrium one usually considered in the linear stability analysis, a thermally anisotropic plasma with T⊥/T‖⋍1·35 appears to be quasi-stable against the whistler mode instability. This last result is relevant for the geostationary magnetospheric conditions (in the equatorial region) where quasi-stationary states with T⊥/T‖ about 1·3 are observed.
Shielding of moving test particles in warm, isotropic plasma
Authors: Chen Liu , Landon A. Bruce , Lieberman M. A.
Published: March 2009

Shielding of test charges in warm, isotropic electron and electron–ion (Te ≫ Ti) plasmas is studied analytically and numerically. For a plasma with hot Maxwellian electrons and cold mobile ions, the potential due to a charge moving faster than the ion acoustic velocity has an ion acoustic Cerenkov cone. Ahead of the particle, the shielding is the usual electron Debye type with a modified longer shielding length. Potential wells with γ−1 dependence exists inside the cone. The potential falls off as along the cone surface. Outside the cone, the potential decays exponentially. A charge moving slower than the ion acoustic velocity also creates a cone, with potential decay as γ−3 outside the cone, potential wells decaying as γ−1 inside the cone, and potential wells falling off as along the cone surface. In both cases a radial logarithmic singularity exists along the trailing axis. Using a mono-energetic ion distribution, the singularity is removed and an ion thermal Cerenkov cone appears. For a monoenergetic electron plasma, assuming immobile ions, a test charge moving faster than the electron thermal velocity excites a thermal Cerenkov cone. Outside the cone, the far-field potential falls off in quadrupole form as γ−3. Inside the cone, potential wells decay as γ−1.
A modified Korteweg-de Vries equation for ion acoustic wavess due to resonant electrons
Authors: Schamel Hans
Published: March 2009

The dependence of the asymptotic behaviour of small ion-acoustic waves on the number of resonant electrons is investigated by assuming an electron equation of state corresponding to the observed flat-topped electron distribution functions. The result is a modified Korteweg-de Vries equation with a stronger nonlinearity.
Negative temperature states for the two-dimensional guiding-centre plasma
Authors: Joyce Glenn , Montgomery David
Published: March 2009

Theoretical development and numerical simulation of the two-dimensional electrostatic guiding-centre plasma with positive total interaction energy are presented. Equilibrium statistical mechanics predicts that no spatially homogeneous thermal equilibrium state exists for this system. This non-existence is associated with the phenomenon of ‘negative temperatures’. Quasi-stable, spatially inhomogeneous states are shown to form, and are characterized by macroscopic spatially-separated vortex structures.
Approximations to the plasma dispersion function
Authors: Brinca A. L.
Published: March 2009

The two-pole and resonance distribution approximations to the plasma dispersion function are discussed and compared.
Fast charged particle reactions in a plasma
Authors: Brueckner Keith A. , Brysk Henry
Published: March 2009

The probability that a fast charged particle slowing down in a plasma will react with an ambient ion prior to thermalization is calculated, as is the probability that an ambient ion scattered by the incident particle will similarly react. Results are given for an α particle from the DT reaction in a DT plasma.
Non-turbulent electric fields in soliton and shock-like structures in magnetized plasmas
Authors: Mendel C. W. , Wright T. P.
Published: March 2009

A new treatment of soliton and laminar shock-like structures in single ion species and counter-streaming plasmas in perpendicular magnetic fields is presented. Charge separation effects are treated exactly, and may become important for high Alfvén Mach number flows. The theory contains the familiar quasi-neutrality theory in the limitB20≪ Μ0nmec2and the Longmire theory in the limitB20≫ Μ0nmec2. The introduction of the potential ψ as the primary dependent variable, instead of the magnetic fieldB, clarifies the role of ion dynamics. New pseudo-potential functions are defined which generate classes of solutions for single ion species, rigid piston problems, and multispecies problems. They also provide information about the evolution of particle piston solutions. Results include the fact that a small amount of resistivity allows shock solutions for very large Mach numbers, and for zero dissipation the parameter

does not affect the solutions except in the scale length.
A theory of the amplitude modulation of quasi-monochromatic nonlinear plasma waves
Authors: Ichikawa Yoshi H. , Suzuki Takehiko , Fried Burton D.
Published: March 2009

A theory of the amplitude modulation of plasma waves is developed by applying the Karpman-Krushkal theory of quasi-monochromatic wave propagation analysis of the nonlinear wave-particle resonant effect leads to the modified nonlinear Schrüdinger equation with a non-local nonlinear term, which has been independently derived by Ichikawa & Taniuti on the basis of a reductive perturbation approach. The effect of the non-local nonlinear term is described explicity by investigating the modulation instability of an ion plasma wave.
H theorem and kinetic equations for a reacting gas
Authors: Fang Ta-Ming
Published: March 2009

A previously developed set of kinetic model equations for a chemically-reacting gas is modified. By examining closely the H theorem, a new set of constraints is obtained. These conditions are then used to determine the inelastic collision parameters proposed in the model. The kinetic equations so obtained are able to produce exactly the same rate equations as prescribed by the actual chemical reactions.
Ion rarefaction waves in cylindrical and spherical geometries
Authors: Prewett P. D. , Allen J. E.
Published: March 2009

A similarity technique is used to solve the problem of the ion rarefaction wave associated with a sheath growing at constant speed from a cylindrical or spherical probe into an infinite plasma.
Theory of the mutual impedance of two small dipoles in a warm isotropic plasma
Authors: Pottelette R. , Rooy B. , Fiala V.
Published: March 2009

We show theoretically that the electron density and temperature of a plasma could be deduced from the measurements of the transfer impedance between two small dipole antennae, each much shorter than a Debye length, separated by a distance of ten or more Debye lengths. In contrast to the quadripole probe, this ‘double-dipole probe’ relies on not producing perturbations in the plasma, rather than on minimizing their effects. The plasma is assumed to be warm and isotropic, and the motion of the ions is neglected. First, it is shown that, in a Maxwellian plasma, the frequency response of a double-dipole probe is easier to interpret than that of a quadripole probe with the customary square layout. Then, in a second step, the transfer impedance of the former probe is calculated in a Cauchy plasma, and the results are compared with those previously obtained in a Maxwellian plasma. By so doing, we show that, for large distances between the dipoles, the real part of the transfer impedance is sensitive to the form of the tail of the distribution function.
Surface Waves at the boundary of a magneto-active plasma
Authors: Elgin J. N.
Published: March 2009

Dispersion relations are obtained for surface waves propagating along plasma—vacuum and plasma—plasma interfaces in a direction perpendicular to a uniform magneto-static field (that lying parallel to the interface), by setting to zero reflexion coefficient for an incident plane wave. Complete solutions to the dispersion relations are presented for both cases and the results are displayed diagrammatically. Comparisons are made with the work of other authors.
Some comments on magnetic field reconnection
Authors: Priest E. R. , Cowley S. W. H.
Published: March 2009

Some comments are made about how to determine the speed with which magnetic flux is carried towards an X-type neutral point and reconnected. Conditions in the diffusion region near the neutral point are also investigated, with the conclusion that the streamlines and magnetic field lines cannot both be locally hyperbolic. Instead, two distinct modes may be possible. In the first, the magnetic field lines are straight, and the diffusion region does not differ greatly from that described by Parker (1963). In the second, the fluid velocity components increase cubically away from the neutral point with the result that, for a given reconnection rate, the diffusion region is typically five times greater than in the Parker model.
Resistive MHD stagnation-point flows at a current sheet
Authors: Sonnerup B. U. Ö. , Priest E. R.
Published: March 2009

A family of exact solutions to the MHD equations is presented for steady incompressible two- and three-dimensional flow in the vicinity of the stagnation point, which forms in a current sheet separating two colliding plasma streams. The magnetic field in each plasma is strictly parallel to the current sheet, but can have different magnitudes and directions. Resistive and viscous effects are accounted for. These flows are of considerable interest in connexion with the magnetic field merging process. They represent the limit of resistive field annihilation with zero reconnexion.
Switch-shock wave structure in a magnetized partly-ionized gas
Authors: Cramer N. F.
Published: March 2009

The effect of the interaction of plasma and neutral gas on the structure of switchtype shock waves propagating in a partly-ionized gas is studied. These shocks, in which the magnetic field is perpendicular to the shock front either upstream or downstream, exhibit a spiralling behaviour of the magnetic field in the shock transition region, if the Hall term is important in the Ohm's law. Observation of this behaviour for shocks propagating into a plasma with a residual neutral content of ~ 15 % has implied an anomalously high resistivity of the plasma. We show that this can be partly explained by considering the collisions of ions with the neutral atoms in a magnetic field. We show that the extra dissipation due to the increase in resistivity goes primarily to the ions and neutrals. Thus even in the absence of viscous dissipation within each species, the heavy particles can be appreciably heated in a shock propagating into a partly-ionized gas in a magnetic field.
Nonlinear decay of a large-ampitude ion-acoustic wave
Authors: Hung Nguyen The
Published: March 2009

This paper studies the nonlinear coupling between an ion—acoustic wave and two Alfvén waves. On the basis of the MHD equations, this three-wave interaction is described within the coupled normal-mode theory. It is shown that a largeamplitude acoustic wave can decay into a pair of Alfvén waves in a high-β plasma. Calculations of the threshold condition and the maximum growth rate suggest that this decay process may occur both in the laboratory and in the ionosphere.
The use of magneto-acoustic oscillations as a plama diagnostic technique
Authors: Frommelt J. J. B. , Jones Ieuan R.
Published: March 2009

A theoretical and experimental investigation of the forced radial magnetoacoustic oscillations of a magnetized plasma column is presented in this paper. Forced magneto-acoustic oscillations of a magnetized argon afterglow plasma are generated continuously by passing an RF current through a solenoid wrapped around the discharge tube. The radial variation of the amplitude of the magnetic
field disturbance [bz(r)] associated with these oscillations is measured at various times during the decay of the afterglow plasma. A theoretical description of these oscillations is developed in which the collision frequencies between the various plasma constituents are treated as free parameters. The values of these free parameters at any given instant during the decay of the plasma are determined by fitting computed bz{r) radial profiles to the measured ones. The electron temperature Te, and the ion-neutral cross section for momentum transfer QD are deduced from these collision frequencies. The reliability of this plasma diagnostic technique is demonstrated by its ability to yield values for Te and QD which compare favourably with the results obtained by other workers.
On the maximum rate of magnetic-field reconnexion for Petschek's mechanism
Authors: Roberts† B. , Priest E. R.
Published: March 2009

The standard model for fast magnetic-field reconnexion (Petschek 1964) is qualitatively valid, despite numerous criticisms of its quantitative details. It contains four slow magnetohydrodynamic shock waves, which radiate from a central diffusion region. On the basis of Petschek's rough analysis, it is generally stated that, for large values of the magnetic Reynolds number Rm, reconnexion can occur at a rate no faster than a fraction π/(4 log Rm) of the Alfvén speed. Alternative models of the region outside that of diffusion have been put forward by Yeh & Axford (1970), whose general solutions Vasyliusnas (1975) proved invalid, and by Sonnerup (1970), whose model is mathematically useful, but of limited practical applicability. But their results suggest that reconnexion can occur at any rate whatsoever, with the diffusion-region dimensions responding accordingly. The present paper analyses the external region for Petschek's mechanism in greater detail than hitherto, with the object of deciding whether or not there is a maximum rate. The inclinations of the shock waves are calculated as a function of the fluid speed ve at large distances, which is taken as a measure of the reconnexion rate. It is found that, in agreement with Petschek's rough analysis, there is indeed an upper limit on the allowable rate of magnetic-field reconnexion. Its variation with Rm is calculated, and it is shown, for log10 Rm ≫1, to be approximately 20% of Petschek's value. Typical values are 0·10vAe for Rm = 10·2 and 0·02vAe for Rm = 106. (vAe is the Alfvén speed at large distances from the diffusion region.)
Nonlinear, periodic waves in a cold plasma: a quantitative analysis
Authors: Chian A. C.-L. , Clemmow P. C.
Published: March 2009

The exact theory of a wave of fixed profile travelling with speed c/n (0 < n < 1) through a uniform, cold, collisionless, unmagnetized plasma is investigated for the case in which the electric field has a non-zero transverse component, which lies in a fixed direction. The governing equations, referred to the frame of reference in which there is no space dependence, are studied analytically in each limit n→0, n→1. and by computation for other values of n. It is shown that, for each value of n, there is, in general, just one periodic solution of an arbitrarily given amplitude; and a quantitative description of these periodic solutions is provided in graphical form. A simple ‘dispersion relation’ is obtained for large- amplitude waves.
Magnetic field-line reconnexion by localized enhancement of resistivity. Part 4. Dependence on the magnitude of resistivity
Authors: Ugai Masayuki , Tsuda Takao
Published: March 2009

The present paper quantitatively examines how the process of fast reconnexion depends on the magnitude of the local resistivity enhanced in the vicinity of the magnetic neutral point. It is shown that quasi-steady Petschek-type configurations are set up, one for each of the variously imposed local resistivity enhancements. The fundamental structure of the quasi-steady configuration is largely controlled by the initially indented value of locally enhanced resistivity. It is especially remarked that the width of the diffusion region becomes smaller as the locally enhanced resistivity becomes smaller. We find that each of the quasi-steady configurations presents nothing other than the Petschek-type configuration that corresponds to the allowable maximum reconnexion rate for the relevant magnetic Reynolds number. We also see that the magnitude of fast reconnexion rate has a weak dependence on the local resistivity in the diffusion region. All our numerical results are very consistent with previous theoretical work on the fast reconnexion problem, once the problem is reconsidered from another angle. We hence suggest that the process of fast reconnexion should be viewed as a gross instability, inherent to the current sheet system itself, that can be triggered by some local onset of anomalous resistivity.
The resistive evolution of force-free magnetic fields. Part 2. Relation to anisotropic diffusion
Authors: Reid J. , Laing E. W.
Published: March 2009

We consider the diffusion of a magnetic field in a stationary medium where the electrical conductivity along field lines (σ∥) differs from that across them (σ⊥), and by showing that in the limit σ⊥/σ∥ → 0 the fields remain force-free, some unusual features of force-free evolution are clarified.
Free expansion of a plasma with two electron temperatures
Authors: Wickens L. M. , Allen J. E.
Published: March 2009

A theory for the free expansion of a plasma with two electron temperatures is presented. It is shown that in the case of a laser-produced plasma expansion the ions separate into a fast and a slow component, and that the number of fast ions is particularly sensitive to the hot to cold electron temperature ratio. If the electron temperature ratio is ≳ 10 then the quasi-neutral self-similar solution breaks down. The regions in the rarefaction expansion where the quasi-neutrality assumption fails are discussed.
Compressible magnetic-field reconnexion
Authors: Hameiri Eliezer
Published: March 2009

The Sonnerup solution for reconnexion about an X-type magnetic null point is modified to involve only stable shocks. However, the reconnexion process described does not originate at the line breaking point but is engineered by precise boundary conditions in the inflow region. Our solution is also valid in the compressible case. The limit on the reconnexion rate (in Mach number units) is about 1·5. A non-uniqueness of the solution raises the possibility of viewing flare phenomena as abrupt jumps to different branches of the solution.
On the existence and stability of trapped Langmuir modes in a double layer
Authors: Wahlberg Christer
Published: March 2009

The stability problem of the double layer (electrostatic shock) is investigated using a simple model of the plasma. It is shown that local Penrose-stability in general is insufficient for global stability, owing to the existence of linerly unstable trapped Langmuir modes in the density cavity. An additional requirement for stability is that the thickness of the layer must be smaller than a critical value, which in the case of a strong layer (eΔπ/κTe ≫ 1). and for the particular model being used, is of the order (eΔπ/κTe)½ λD. Various qualitative features of the instability mechanism are discussed in terms of normal mode coupling, and quantitative results, such as mode frequencies, growth rates etc., are obtained by means of a conventional perturbation approach, which, in addition to the results expected from coupled mode theory, also shows the existence of two purely decaying modes, appearing for a sufficiently thin, stable layer. The double layer formation process is briefly commented on, and some distinguishing features of the instability in this regard are pointed out.
Energy equilibria in the diffuse pinch. Part 1. Classical scalar conductivity and neo-classical models
Authors: Tommiura A. , Haines M. G.
Published: March 2009

Numerical solutions of the momentum and energy equilibria in a two-temperature diffuse pinch show that it is possible for the electron temperature to have a radially oscillating component with a wavelength of the order of ae(mi/me)1/2, where ae is the electron Larmor radius. This is also the order of magnitude of the optimum wavelength for growth of an electro-thermal instability in a homogeneous plasma (studied in part 3 of this series) and suggests this kind of instability as a possible primary source of a current filamentation in the plasma. It has also been revealed both analytically and computationally in this strictly steady state model that the pressure of one species (ions or electrons) is finite at the wall boundary; the same study carried out on a neo-classical model shows, however, that strict confinement is possible provided some restrictions are imposed upon its free parameters. This is also found with a model employing classical tensor conductivity (studied in part 2).
Formation of percursor whistler mode plasma turbulence in parallel shock waves
Authors: Jackson B. W. , Golden K. I.
Published: March 2009

The beam-whistler and ion cyclotron instabilities are proposed as principal mechanisms for the generation of precursor turbulence in shock waves propagating along the constant magnetic field. The beam is formed from ions which are reflected from a potential barrier whose existence inside the shock layer is assumed. We find that these reflected beam particles drive unstable a spatial continuum of zero group velocity (with respect to the shock front) precursor whistler waves.
Reflexion of a plane wave at a plasma slab
Authors: Elgin J. N.
Published: March 2009

The problem of a monochromatic plane electromagnetic wave incident from a vacuum onto a plasma slab is considered. The method of solution is based on the representation of the disturbance in the plasma layer as that generated by an appropriate current source in the complementary regions into which, for the purpose of the representation, the plasma is conceived to extend. The normal incidence case is treated first for both the specular reflexion and the absorption boundary conditions, with the extension to oblique incidence following in a later section of the paper.
The microinstabilities of a high-β plasma flow with a non-uniform velocity profile
Authors: Mikhailovskii A. B. , Klimenko V. A.
Published: March 2009

The microinstabilities of a high-pressure plasma moving along a magnetic field with a non-uniform velocity profile are investigated. A similar problem was studied earlier by Dobrowolny on the basis of hydromagnetic equations with an oblique viscosity tensor. The present paper, unlike Dobrowolny's work, gives a kinetic analysis. Perturbations with transverse wavelength both larger and smaller than the ion Larmor radius are considered. The analysis indicates that there is a large family of microinstabilities of the ‘drift’ type whose mechanism differs from the classical Kelvin–Helmholtz instability.
Effect of collisions on the relativistic electromagnetic instability
Authors: Okada Toshio , Niu Keishiro
Published: March 2009

The electromagnetic instability of a relativistic electron beam penetrating an infinite plasma is analyzed. The purpose of this paper is to determine the effect of collisions within the plasma upon the growth rate of the Weibel-type electromagnetic instability. The dispersion relation including the effect of collisions is solved analytically and numerically. It is found that collisions can enhance the growth rate of the electromagnetic instability in the case of low plasma temperature.
The only three classes of symmetric MHD equilibria
Authors: Edenstrasser J. W.
Published: March 2009

Ideal MHD equilibria with an ignorable space variable are investigated. It is shown thatonlythree classes of these symmetric equilibria exist: the systems with a straight, a (cylindric) helical, and a circular magnetic axis.
Self-induced magnetic force of a toroidal current
Authors: Yeh Tyan
Published: March 2009

A class of magnetostatic solutions is obtained for the magnetic field and current in a toroid. The solutions are characterized by nested toroidal flux surfaces whose cross-sections are concentric circles. The model distribution of the magnetic field and current allows a correct calculation of the typical self-induced magnetic force exerted by a current interacting with its own magnetic field in a toroidal configuration.
A.C. conductivity in a homogeneous plasma from a convergent collision integral
Authors: Mondt J. P. , Guernsey R. L.
Published: March 2009

Recently a spatially uniform expression for the time asymptotic binary correlation function of a Landau-stable plasma was derived from the BBGKY hierarchy equations. In this paper, the high-frequency (Vei ≪ ‖w‖ ≪ ωpe) electrical conductivity of a spatially homogeneous, unmagnetized Lorentz plasma

is calculated from this expression; the result is compared with those obtained from other convergent collision integrals.
Self-similar state of a weakly turbulent plasma
Authors: Balescu R.
Published: March 2009

The models of Vekshtein, Ryutov & Sagdeev (VRS), describing a marginally stable turbulent plasma sustaining an electric current, are shown to be incomplete by their neglect of the equations determining the spectral densities of the driving modes. An exhaustive study of these models including a detailed determination of the frequencies, spectral densities and turbulent energy densities, shows that, strictly speaking, there exists no self-similar turbulent state (SSTS). However, an approximate SSTS can be constructed, based on the finding that the tail of the spectral densities behaves self-similarly.
Studies of strong laboratory double layers and comparison with computer simulation
Authors: Baker K. D. , Singh N. , Block L. P. , Kist R. , Kampa W. , Thiemann H.
Published: March 2009

Strong electrostatic double layers were produced with a triple plasma configuration in the large plasma chamber (5 m long, 2·5 m diameter) at IPM in Freiburg, Federal Republic of Germany. Owing to relatively low densities (1011 1012m−3), Debye lengths of a few centimetres and layer thicknesses of the order of a metre were obtained. Layers both with and without magnetic fields were studied. Analysis of particle spectra prove that wave-particle interactions play a minor role in maintaining the strong electric field. The three-dimensional potential distribution is measured and is qualitatively discussed in terms of particle budget. For cases with a magnetic field it tends to agree with observations above the aurora. Comparisons are made with double-layer theory and computer experiments, and general agreement is found as far as the available results allow.
Influence of relaxation processes on the structure of a thermal boundary layer in partially ionized argon
Authors: Dongen M. E. H. Van , Van R. B. , Van Eck P. , Hagebeuk H. J. L. , Hirschberg A. , Hutten-Mansfeld A. C. B. , Jager H. J. , Willems J. F. H.
Published: March 2009

A model for the unsteady thermal boundary-layer development at the end wall of a shock tube, in partially ionized atmospheric argon, is proposed. Consideration is given to ionization and thermal relaxation processes. In order to obtain some insight into the influence of the relaxation processes on the structure of the boundary layer, a study of the frozen and equilibrium limits has been carried out. The transition from a near-equilibrium situation in the outer part of the boundary layer towards a frozen situation near the wall has been determined numerically. Experimental data on the electron and atom density profiles obtained from laser schlieren and absorption measurements are presented. A quantitative agreement between theory and experiment is found for a moderate degree of ionization (3 %). At a higher degree of ionization the structure of the boundary layer is dominated by the influence of radiation cooling, which has been neglected in the model.
A generalized treatment of the electrostatic instability of rippled non-neutral magnetically focused electron beams
Authors: Cuperman S. , Petran F.
Published: March 2009

A generalization of the stability analysis of rippled non-neutral electron beams is presented. The treatment covers regimes ranging between those known as ‘Brillouin flow’ (ωpe = ωc/2½) and ‘immersed flow’ (ωpe≪ωc). It considers electrostatic surface waves with azimuthal symmetry (l = 0) as well as harmonic modes (l≠0). Both long-wavelength and short-wavelength domains are analysed. A general discussion of instability is given in terms of the solution of the Mathieu-Hill equation. New unstable modes are found and their growth rates are derived and compared.
Feedback stabilization of tokamaks against slow axisymmetric MHD instabilities
Authors: Jensen Torkil H.
Published: March 2009

Single axis tokamaks as well as doublets may be unstable toward axisymmetric MHD instabilities. Such instabilities may, for the case of a single-axis tokamak, be slow when the plasma is surrounded by a relatively close fitting conducting wall, such as a vacuum chamber; the growth rate may be proportional to the resistivity of the wall material. For the case of doublets, slowly growing instabilities with growth rates proportional to the plasma resistivity exist. Such slow instabilities can be stabilized by feedback control of the currents through coils surrounding the plasma; since it is only required that the amplifiers used in the circuits respond fast compared with the growth time of the slow instabilities, this feedback stabilization is not technologically demanding. This paper describes a formalism for the stability analysis of such a system consisting of the plasma, surrounded by a conducting wall or vacuum chamber and coils with their control system.
A numerical study of the generation of an azimuthal current in a plasma cylinder using a transverse rotating magnetic field
Authors: Hugrass W. N. , Grimm R. C.
Published: March 2009

The generation of a steady azimuthal current in a cylindrical plasma column using a rotating magnetic field is numerically investigated. The mixed initial-boundary-value problem is solved using a finite difference method. It is shown that substantial azimuthal current can be driven provided that the amplitude of the rotating magnetic field is greater than a certain threshold value which depends on the plasma resistivity.
Resonant generation of electromagnetic surface wave by inhomogeneous relativistic electron stream
Authors: Čadež V. M. , Vuković S. , Frolov V. V. , Kyrie A. Yu.
Published: March 2009

Generation of electromagnetic surface waves by relativistic inhomogeneous particle flows is investigated for plane and cylindrical geometries. The basic excitation mechanisms are shown to be the induced anomalous Doppler effect and the hydrodynamic Čerenkov effect. The relevant maximal growth rates may differ significantly from those derived for monoenergetic beams.
The relaxation zone behind normal shock waves in a reacting dusty gas. Part 1. Monatomic gases
Authors: Ben-Dor G. , Igra O.
Published: March 2009

The conservation equations for a suspension composed of an ionized gas and small solid dust particles are formulated and solved numerically. Such flows can be found downstream of strong normal shock waves propagating into dusty gases. The solution indicates that the presence of the dust has a significant effect on the post-shock flow field. Owing to the dust, the relaxation zone will be longer than in the pure plasma case; the equilibrium values for the suspension pressure and density will be higher than in the dust-free case, while the obtained values for the temperature, degree of ionization and velocity will be lower. The numerical solution was executed for shock Mach numbers ranging from 10 to 17. It was found that the thermal relaxation length for the plasma decreases rapidly with increasing shock Mach number, while the thermal relaxation length for the suspension mildly increases with increasing M. The kinematic relaxation length passes through a pronounced maximum at i M = 12·5. Throughout the investigated range of Mach numbers, the kinematic relaxation is longer than the suspension thermal relaxation length.
Implosion of a uniform current sheet in a low-beta plasma
Authors: Forbes T. G.
Published: March 2009

Using ideal, one-dimensional MHD equations, numerical and analytic solutions are presented which describe the nonlinear behaviour of an imploding current sheet in a low-fl plasma. Initially the current density is uniformly distributed in asheet of finite thickness, and the Lorentz force tending to pinch the plasma together is unopposed by any fluid pressure force. As the implosion develops the current density in the sheet is concentrated into a thin layer at the centre of the sheet, and both the current density and the current in this layer become infinite in a finite time if β = 0. At the moment this occurs, fast-mode shocks are produced which propagate outward from the centre of the current sheet, and as the shocks move away an infinitely thin current sheet is left behind. Although the solutions are related to electric discharges, they are also closely related to a problem posed by Dungey concerning the evolution of a uniformly distributed current in the vicinity of an X-type magnetic neutral line. The implications of these solutions for Dungey's problemare discussed.
Second harmonic interference patterns of ion-acoustic waves
Authors: Schott L.
Published: March 2009

The interaction of two weakly nonlinear sinusoidal ion-acoustic waves produces mainly a fundamental and a second harmonic diffraction pattern. The former is similar to the double slit pattern well known from physical optics, while it is found that the latter resembles a linear pattern generated by the superposition of three waves. The third wave is formed by mutual nonlinear interaction of the two fundamental waves. The intensity of the second harmonic pattern is modulated by the recurrence effect and it depends also on the angle between the local wave vectors.
Removable background inhomogeneity and non-steadiness in the evolution of the envelopes of nonlinear waves
Authors: Taranov V. B.
Published: March 2009

Lie group transformations are found which allow the removal of background inhomogeneity and non-steadiness from the nonlinear Schrödinger equation for the envelopes of HF waves. Background profiles are determined for which this removal can be realized.
Electrical a.c. conductivity for hot isotropic collisional plasmas
Authors: Hebenstreit Helmut , Suchy Kurt
Published: March 2009

With an infinite system of balance equations, derived from the Boltzmann equation, conductivity expressions are obtained in the form of three-term recurrence relations leading to continued fractions. Without collisions, only Landau damping causes attenuation. Its modification by collisions is illustrated for some simple collision models.
Effect of higher-order nonlinearity on propagation of nonlinear ion-acoustic waves in a collisionless plasma consisting of negative ions
Authors: Tagare S. G. , Reddy R. Virupakshi
Published: March 2009

The combined effects of negative ions and higher-order nonlinearity on ionacoustic solitons are studied using the reductive perturbation method. The basic set of fluid equations for a plasma consisting of negative cold ions, positive cold ions and hot electrons (non-isothermal and isothermal) reduces to the modified Korteweg-de Vries equation and the Korteweg-de Vries equation for the first-order potential, and to the linear inhomogeneous equation for the second-order potential. Stationary solutions of the coupled equations are obtained in the case of negative ions, retaining terms up to the third order in the usual reductive perturbation method.
Infinite contraction in force-free magnetic field evolution in cylindrical geometry
Authors: Watterson Peter A.
Published: March 2009

This paper provides a new formulation of the resistive force-free evolution of cylindrically symmetric magnetic fields subject to purely radial motions. It is shown analytically that the evolution bounded by a perfect conductor ceases to exist after a finite time if the initial field has total axial flux of opposite sign to the field on the axis of symmetry. A numerical solution indicates that the evolution ceases to exist owing to the unlimited contraction of the field profile producing a line of infinite current density. The asymptotic form of this ‘blow-up’ is identified as the particular self-similar contraction for which the field direction is exactly reversed in the limit of large radius. Possible applications to solar flares and the reversed-field pinch are discussed.
On the generation of quasi-electrostatic half-electron-gyrofrequency VLF emissions in the magnetosphere
Authors: Ohmi Norichika , Hayakawa Masashi
Published: March 2009

A theoretical study is made of the generation mechanism of quasi-electrostatic VLF emissions observed in the distant magnetosphere, with frequency greater than half the electron gyrofrequency and with wave normal around the cold plasma oblique resonance cone. The two-component plasma is treated, composed of cold electrons and hot electrons with bi-Maxwellian and loss-cone distribution functions. The effects of various plasma parameters on the instability characteristics are examined in order to estimate their relative importance in determining the properties of unstable waves. It is found that both types of hot plasma distribution function can account for quasi-electrostatic half-gyrofrequency emissions. The frequency where the maximum growth rate occurs is mainly determined by the temperature anisotropy of the hot plasma, and the wave normal angle where maximum growth is expected is determined by the temperature of the hot plasma and the ratio of the cold to hot plasma densities. These theoretical considerations form the basis of a suggested plasma model which is able to explain our experimental direction-finding results.
Three-wave coupling coefficient in a drifting bi-Maxwellian plasma
Authors: Bergmann Rachelle
Published: March 2009

A general electrostatic coupling coefficient which satisfies the Manley-Rowe relations is used to derive an explicit expression for the resonant three-wave coupling coefficient between electrostatic normal modes of a uniformly magnetized, infinite, homogeneous plasma with species described by drifting bi-Maxwellian distribution functions. The limit of this expression is taken when the phase velocities of the three waves are much larger than a species thermal speed, and also when the phase velocities are much smaller than the thermal speed. These are fluid limits and are applicable to the three-wave interaction between some low-frequency electrostatic waves, such as ion acoustic and ion cyclotron modes, in a plasma where Te ≫ Ti.
Quantum-kinetic theory of free electron lasing in a spatially periodic longitudinal electrostatic field by a relativistic electron beam
Authors: Kim S. H.
Published: March 2009

The lasing by stimulated bremsstrahlung of a relativistic dilute electron beam passing through a spatially periodic longitudinal electrostatic field is investigated by means of the quantum-kinetic method. It is shown that the energy transfer from the electrons to the radiation field by the Lorentz force of the radiation field can be neglected compared with that by the force due to net stimulated bremsstrahlung (the emission by stimulated bremsstrahlung minus the absorption by inverse bremsstrahlung). The gain per unit length in the intensity of the laser light and the force acting on the electron due to free electron lasing are explicitly expressed as a function of the relevant parameters of the laser light and the electron beam.
The orbits of electrons and ions in the fields of the rotamak
Authors: Hugrass W. N. , Turley M.
Published: March 2009

The motion of electrons and ions in the self-consistent fields of a compact toroidal equilibrium maintained by means of a rotating magnetic field is studied. It is found that the particles are confined although the lines of the instantaneous magnetic field are open. The results are compared with those obtained in an earlier study of the motion of charged particles in the self-consistent fields appropriate to cylindrical plasma equilibrium maintained by means of rotating magnetic fields.
The ion-ion acoustic instability
Authors: Gary S. Peter , Omidi Nojan
Published: March 2009

This paper considers the linear theory of ion-acoustic-like instabilities in a homogeneous Vlasov plasma with two ion components, a less dense beam and a more dense core, with a relative drift velocity. Numerical solutions of the full electrostatic dispersion equation are presented, and the properties of the ion–ion acoustic instability are studied in detail. The following properties are demonstrated: (i) At relatively cold beam temperatures, the instability is fluid-like, but it becomes a beam resonant kinetic instability as the beam temperature becomes of the order of the core temperature; (ii) if the mode is unstable, its threshold lies well below the threshold of the electron–ion acoustic instability; (iii) an electron temperature anisotropy T⊥/T‖e > 1 enhances the instability and (iv) at sufficiently large beam-core relative drift speeds, electron magnetization can either detract from or enhance the instability. If field-aligned ion beams are to drive the ion-acoustic-like enhanced fluctuations observed upstream of the Earth's bow shock, the effective beam temperature must be much smaller than values quoted in the literature.
Modified convective cells in plasmas
Authors: Jovanović D. , Pécseli H. L. , Rasmussen J. Juul , Thomsen K.
Published: March 2009

Two coupled equations describing the nonlinear evolution of modified convective cells with a finite but small wavenumber parallel to the external magnetic field B are derived. It is found that, for oblique propagation, the electrostatic and magnetostatic convective mode do not decouple as in the strictly perpen-dicular case. Various aspects of the governing equations are investigated. In the weakly nonlinear lirait, a three-wave interaction study shows the possibility of dual energy cascading, or of cascading to larger wavenumbers only, depending on the direction of the parallel wavenumber component of the pump wave. Furthermore, solitary wave solutions in the form of double vortices are considered.
Self-focusing of nonlinear ion-acoustic waves and solitons in magnetized plasmas. Part 2. Numerical simulations, two-soliton collisions
Authors: Infeld E. , Frycz P.
Published: March 2009

Nonlinear waves and solitons satisfying the Zakharov-Kuznetsov equation for a dilute plasma immersed in a strong magnetic field are studied numerically. Growth rates of perpendicular instabilities, found theoretically in part 1, are confirmed and extended to arbitrary wavelengths of the perturbations (the calculations of part 1 were limited to long-wave perturbations). The effects of instabilities on nonlinear waves and solitons are illustrated graphically. Pre-vious, approximate results of other authors on the perpendicular growth rates for solitons are improved on. Similar results for perturbed nonlinear waves are presented. The effects of two-soliton collisions on instabilities are investigated. Rather surprisingly, we find that the growth of instabilities can be retarded by collisions. Instabilities can also be transferred from one soliton to another in a collision. This paper can be read independently of part 1.