bluuebunny/crossref_metadata_2025 huggingface dataset:
Unified geometric and analytical treatment of magneto– gasdynamic shocks. Part 2. The shock polars
Authors: A. Bertram Lee
Published: March 2009

Previously derived shock solutions for a perfectly conducting perfect gas are used to compute shock polars for the one-dimensional unsteady and two- dimensional non-aligned shock representations. A new special-case shock solution, having a downstream particle velocity relative to the shock equal to upstream Alfvén velocity, is obtained, in addition to exhaustive analytical classification schemes for the shock polars. Eight classes of one-dimensional polars and twelve classes of two-dimensional polars are identified.
On re-normalization in the theory of weak turbulence in plasmas
Authors: Vaclavik Jan
Published: March 2009

The paper compares the methods of re-normalization introduced by the Dupree—Weinstock theory of turbulence with those in the theories of Kadomtsev, Rudakov and Tsytovich. It is shown to what extent they are equivalent.
Charge transfer from low-lying excited states: effects on reactive thermal conductivity
Authors: Capitelli M.
Published: March 2009

Charge transfer and diffusion cross-sections of low-lying excited states are calculated usingab initioquantum-mechanical potential-energy curves. These data are used to calculate the reactive thermal conductivity λRof an atmospheric nitrogen plasma. Differences of up to 20 % are found between the present values of λRand the corresponding values obtained by increasing the cross-sections of excited states by a factor of 2. These differences propagate, to a minor extent (10 %), in the total thermal conductivity.
Propagation of electromagnetic waves parallel to a magnetic field in a cold plasma between conducting planes: asymmetric model
Authors: Weber Helmut N.
Published: March 2009

A small-signal analysis is carried out for a geometry consisting of two parallel conducting planes, with a magnetized plasma resting on the one plane, and a vacuum gap between the plasma and the other. Each of the solutions found to fit the boundary conditions consists of a superposition of two ‘transverse’ wave-functions with one and the same longitudinal propagation constant. Numerical solution of the dispersion relations yields the following. (i) A set of slow waves, in good agreement with the well-known quasi-static approximation. (ii) Fast waves, which approximate TM waves (Hz ≐ 0) propagating only at relatively high frequencies. (iii) Fast waves propagating in the same frequency range as the TM waves, but with negligible longitudinal electric field component Ez, thus resembling TE waves. (iv) A set of waves with a dispersion which resembles that obtained from coupling between fast forward and slow backward modes of propagation. (v) A single wave, not obtainable from the slow-wave approximation which resembles the helicon wave of the one-dimensional case, with the frequency approaching the cyclotron frequency at small wavelengths, provided the magnetic field is relatively strong (ωc < ωp), the spacing between the conducting planes not too narrow and the fill-factor not too small. For relatively weak magnetic fields (ωc < ωp), this wave appears as a surface wave with frequency approaching the lower hybrid frequency at small wavelengths.
Interaction of a test particle with a magnetized plasma
Authors: Liang E. W. , Gibson A. L.
Published: March 2009

In the presence of a sufficiently strong magnetic field, the shielding of a test particle in a two-dimensional Vlasov plasma disappears. An intermediate regime is investigated, for both a stationary and a moving test particle, in which the plasma frequency ωp and the cyclotron frequency ωc are of the same order of magnitude. In the case of a stationary test particle, this intermediate regime is approximately in the range ½ ≤ a ≤ 2, where a = ωp/ωc. For a < ½, only partial shielding occurs, the potential retaining its vacuum logarithmic dependence. For a < 2, the potential approximates to the field-free case, and falls off exponentially. For a test particle moving at electron thermal speed, the typical bow wave and wake phenomenon, associated with an unmagnetized plasma, is no longer present. We find, instead, that the potential possesses upstream—downstream symmetry.
A composite solution of field-line reconnexion
Authors: Yeh Tyan
Published: March 2009

A solution of the Mhd equations is presented, which describes field-line reconnexion by stagnant diffusion in the middle of a piecewise-uniform convective hydromagnetic flow. This composite solution demonstrates that the diffusion region adjusts its shape and size in accommodation to the incident merging fluids.
Three-wave interaction in a magnetized Vlasov plasma
Authors: Larsson J.
Published: March 2009

The resonant interaction of three waves in a uniform hot magnetized plasma is examined. The coupling coefficients are obtained in a symmetric form from the Vlasov-Maxwell equations.
Magnetic field-line reconnection in a highly-conducting incompressible fluid: properties of the diffusion region
Authors: Cowley S. W. H.
Published: March 2009

The properties of the field and flow near a two-dimensional X-type magnetic neutral line are considered for an incompressible, inviscid, conducting fluid in the steady state. In this region the magnetic field is not ‘frozen’ into the plasma, and finite conductivity effects must be considered. In the region surrounding the X line, it has hitherto been assumed that the field lines to lowest order form systems of hyperbolae (the field components increasing linearly with distance from the null), while the fluid flow lines form systems of rectangular hyperbolae with fluid flow perpendicular to the field on the axes of symmetry of the field lines. The assumption of such a configuration was based upon a somewhat cursary consideration of the governing equations, a detailed examination never having been carried out. We present the results of such an examination, which reveal that the above configuration is not a valid solution of the MHD equations, and that, for the case studied, the field to lowest order must form a neutral sheet. The properties of the field and flow parallel to the plane of symmetry are also considered. It is found that non-uniform fields and flows may exist within the diffusion region, in support of recent convection-region studies. This work shows clearly the need for more detailed and careful consideration of such systems.
Fluctuation spectrum in turbulent plasma
Authors: Pelletier Guy , Pomot Claude
Published: March 2009

A nonlinear fluctuation—dissipation theorem is derived for a turbulent plasma. The method of dressed test particles is generalized to a nonlinearly stable plasma; the turbulent state is described by the Dupree—Weinstock formalism. A comparison with the Cook—Taylor theory is discussed.
Dispersion formulae for waves in a relativistic plasma
Authors: Misra P.
Published: March 2009

We derive dispersion formulae for the transverse and longitudinal waves propagating through a Vlassov plasma, valid for relativistic as well as non-relativistic temperatures, and compare them with those of earlier workers. We discuss wave propagation under various limiting conditions of temperature.
Nonlinear theory of a whistler wave
Authors: Yamamoto Takashi
Published: March 2009

Using the Dupree—Weinstock perturbed-orbit model of plasma turbulence, we obtain the diffusion equation describing the evolution of the average one-particle distribution function for whistler mode turbulence. The numerical result for electron pitch-angle diffusion within this scheme leads us to conclude that the effect of the resonance broadening due to perturbed orbits on the pitch-angle diffusion coefficient is not large compared with that evaluated by the unperturbed orbit in the whistler mode spectrum with a finite width. Based on the explicitly evaluated resonance function, the effects of this broadening on the growth rate for the whistler wave are also discussed.
Corrigendum
Authors: Bhatia P. K.
Published: March 2009

‘On effects of neutral gas friction and ion viscosity on the Rayleigh-Taylor instability of a stratified plasma in the presence of Hall currents’

By P. K. Bhatia,

J. Plasma Phys. vol. 11, 1974, pp. 1–10

Bhatia (1974) investigated the effects of neutral gas friction and ion viscosity on the dynamical stability of a composite plasma of variable density in the presence of the effects of Hall currents.
Corrigendum
Authors: Bhatia P. K.
Published: March 2009

Index to Volume13, 1975

It is regretted that the following was omitted:

Landatj, R. W. New, almost electrostatic, anisotropy instability, 377
Instability of ion–ion hybrid waves in current-carrying collisional plasmas with two ion species
Authors: Lee Kai Fong
Published: March 2009

The stability of electrostatic waves propagating at large angles with respect to the background magnetic field is studied in collisional, fully ionized plasmas with two types of ion species and carrying a field-aligned current. By considering plasmas with ma/mb ≪ Nb/Na ≪ mb/ma where m and N denote mass and density respectively and subscripts a and b refer to the two ion species, a complicated dispersion relation is reduced to two simple equations for the determination of the real and imaginary parts of the frequency. It is found that, under appropriate conditions, an instability occurs at frequencies slightly above but very close to the ion–ion hybrid frequency. The growth rate scales directly as the electron–ion collisional frequency.
The spectrum of second harmonic emission from a laser-produced plasma
Authors: Cairns R. A.
Published: March 2009

Observations show a second harmonic spectrum which is broadened and shifted towards the low-frequency side of the true harmonic. A theoretical description of this effect is given based on the assumption that plasma waves generated by resonant absorption at the critical surface are coupled to a series of side-bands via an ion sound wave, and the resultant broadening of the plasma wave spectrum is reflected in the second harmonic emission. If the ion sound wave is propagating outwards, it is shown that, for suitable parameters, a large number of side-bands on the low-frequency side can be excited, giving a spectrum in good agreement with experimental results.
Stability of relativistic transverse cold plasma waves. Part 2. Linearly polarized waves
Authors: Romeiras F. J.
Published: March 2009

This is part 2 of a paper concerned with the stability against small perturbations of a certain class of nonlinear wave solutions of the equations that describe a cold unmagnetized plasma. It refers to transverse linearly polarized waves in an electron-positron plasma. A numerical method, based on Floquet's theory of linear differential equations with periodic coefficients, is used to solve the perturbation equations and obtain the instability growth rates. All the three possible types of perturbations are discussed for a typical value of the (large) amplitude of the nonlinear wave: electrically longitudinal slightly unstable modes (with maximum growth rate γ approximately equal to 0·07ω0, where ω0is the frequency of the nonlinear wave); purely transverse moderately unstable modes (with γ ≃ 0·26ω0); and highly unstable electrically transverse modes (with γ ≃ l·5ω0).
Soliton formation at critical density in laser-irradiated plasmas
Authors: Anderson D. , Bondeson A. , Lisak M.
Published: March 2009

The generation of Langmuir solitons at the resonance layer in a plasma irradiated by a strong high-frequency pump is investigated. The process is modelled by the nonlinear Schrödinger equation including an external pump, a density gradient and linear damping. The evolution equation is reformulated as an exact variational principle and the one-soliton generation process is studied by substituting various trial solutions. The applicability conditions for the nonlinear Schrödinger equation are re-examined and found to be more restrictive than previously stated.
Energy equilibria in the diffuse pinch. Part 2. A tensor conductivity model
Authors: Tomimura A. , Haines M. G.
Published: March 2009

A tensor conductivity model for a fully ionized, two-temperature, cylindrical and diffuse pinch is constructed and its properties analyzed under energy and momentum equilibria conditions. The set of Braginskii's classical two-temperature tensor transport equations are solved for the strict steady state and the radial equilibria profiles of the relevant parameters produced. Unlike the scalar conductivity model (part 1 of this series) tensor coefficients yield profiles with the appropriate ideal boundary conditions, namely zero pressure and temperatures at the plasma radius. Furthermore, spatial oscillations of the electron temperature only occur for extreme values of the free parameters.
Test charge potential in the presence of trapped electrons
Authors: Nambu M. , Spatschek K. H. , Akama H.
Published: March 2009

Using a test particle approach, the potential of a trapped electron is calculated outside the Debye sphere in the electrostatic limit. The potential strongly depends on some characteristic parameters, such as bounce frequencies of the test and background trapped particles, the total number of trapped particles, etc. In some cases, the potential falls off as the inverse of the distance r. The model is limited to the single-wave case; possible generalizations to the many-wave situation in a turbulent plasma are discussed.
Transition layer between two magnetized plasmas
Authors: Lee L. C. , Kan J. R.
Published: March 2009

Structures of the current layer between two magnetized anisothermal plasmas are studied on the basis of a kinetic formulation. It is shown that the structure of the current layer is dominantly controlled by the hotter species of the plasmas. The thickness is characterized by the ion gyroradius if the ion temperature is much greater than the electron temperature. The structure is, in general, insensitive to the asymptotic potential difference and the relative flow velocity between plasmas on the two sides.
Dispersion formulae for waves in a magneto-active relativistic plasma
Authors: Misra P. , Mohanty J. N.
Published: March 2009

We derive dispersion formulae for the transverse waves propagating through a collisionless magneto-active plasma in the direction of the magnetic field valid for relativistic as well as non-relativistic temperatures, and compare them with those of earlier works. Wave propagation under various limiting conditions of temperatures and magnetic field are discussed.
Langmuir turbulence as a critical phenomenon. Part 2. Application of the dynamical renormalization group method
Authors: Pelletier Guy
Published: March 2009

In part 1 of this work, we have found a ‘critical curve’ which separates the unstable self-modulation regime from the stable one for a Gibbs ensemble of interacting modes. On this critical curve, the correlation length diverges and scaling invariance occurs; in particular, the Langmuir correlation spectrum is proportional to k-2. Simple laws have been derived for the neighbourhood of the critical curve. However these derivations are based on equilibrium statistical mechanics and the results are obtained with a Hartree approximation which has not been checked. So, in this second part, we elaborate a direct statistical theory of Zakharov's equations completed by excitation sources and dissipations. In spite of infra-red divergences and a large fluctuation level, large-scale properties are derived in the neighbourhood of the critical curve, by the renormalization group method. The laws obtained in part 1 are slightly modified; however, the same spectrum is obtained.
A unified approach to some integral formulae for reflexion processes in an isotropic plasma
Authors: Heading John
Published: March 2009

Many different problems, associated with the propagation of electromagnetic waves in an inhomogeneous isotropic plasma and governed by second-order differential equations, are reformulated so as to be brought within the scope of a common analytical procedure. Refiexion coefficients, energy considerations, approximation procedures, slab refiexion, and other theorems are considered, the investigations of different physical processes all being attributable to one underlying mathematical method involving integrals, whose integrands contain quadratic products of the field variables and their derivatives in two different arrangements.
The theory of inoizing shock waves in a magnetic field. Part 1. Skew and oblique shock waves, boundary conditions and ionization stability
Authors: Liberman M. A. , Velikovich A. L.
Published: March 2009

The general theory of ionizing shock waves in a magnetic field has been constructed. The theory takes into account precursor ionization of a neutral gas ahead of the shock wave front, caused by photo-ionization, as well as by the impact ionization with electrons accelerated by a transverse electric field induced by the shock front in the incident flow of a neutral gas. The concept of shock wave ionization stability, being basic in the theory of ionizing shock waves in a magnetic field, is introduced. An additional equation for the electric field in the shock wave is obtained. This equation, together with the investigation of the singular point in the downstream flow behind the shock wave front, provides all the information required for solving the problem. For example, this provides two additional boundary conditions for the shock waves of type 2, determining the value and direction of the electric field in the incident flow. One additional boundary condition determines a relation between the value and direction of the electric field for supersonic shock waves of type 3. There are no additional boundary conditions for supersonic shock waves of type 4. The electric field ahead of the shock front has two degrees of freedom. As well as for shocks of other types, its value is less than that of the transverse electric field at which an ionization wave could be emitted by the shock wave front (the ionization stability condition). The additional relationship for supersonic waves of type 4 determines the onset of an isomagnetic (viscous) jump in the structure of the shock wave front. The boundary conditions and ionizing shock wave structures, considered earlier by the authors of the present paper in the ‘limit of electrostatic breakdown’, as well as the structural determination of the electric field, considered earlier by Leonard, are limiting cases in the theory developed here. The ionizing shock wave structures are shown to transform from the GD regime at a low shock velocity to the MHD regime at an enhanced intensity of the shock wave. The abruptness of such a transition (e.g. the transition width on the Mach number scale) is determined by precursor photo-ionization.
The effect of electron temperature anisotropy on the propagation of whistler waves
Authors: Namikawa Tomikazu , Hamabata Hiromitsu , Tanabe Kazuhiko
Published: March 2009

The first-order Chew, Goldberger & Low (GGL) equations for electrons including the effect of finite Larmor radius are applied to the whistler wave. The zerothorder velocity distribution function for electrons in the GGL expansion is assumed to be an anisotropic Maxwellian. The effect of electron thermal motion on the propagation of whistler waves is analysed by use of a dispersion relation and properties of the refractive index surface. It is shown that the electron thermal motion intensifies the tendency of whistler waves to follow the lines of force of the earth's magnetic field at appropriate values of electron temperature anisotropy.
Propagation of hydromagnetic waves through a collisionless, heat-conducting plasma
Authors: Namikawa Tomikazu , Hamabata Hiromitsu
Published: March 2009

The propagation of small-amplitude hydromagnetic waves in a collisionless, heat-conducting plasma is investigated using the first-order Chew-Goldberger- Low (CGL) fluid equations including the effect of finite Larmor radius of the ion. The first-order heat flux equations are derived by use of Macmahon's technique. The zeroth-order velocity distribution function of the ion in the CGL expansion is assumed to be a heat-flux-bearing distribution function. The effect of heat flux on the propagation of hydromagnetic waves is analysed by use of phase speed and refractive index surfaces and the amplitude relation between the density perturbation and the magnetic field perturbation. It is shown that the hydromagnetic wave propagation characteristics are asymmetric with respect to the direction of external magnetic field to zeroth order and first order for magneto- acoustic and Alfvén waves, respectively, and the garden hose instability criterion is modified by the heat flux anisotropy.
Eigenmode analysis of resistive MHD stability by matrix shooting
Authors: Freidberg J. P. , Hewett D. W.
Published: March 2009

A fast and efficient numerical procedure has been developed to solve the exact linearized stability equations of resistive magnetohydrodynamics.
Nonlinear interaction of electrostatic surface waves in a semi-infinite plasma. Part 1. Derivation of the coupled mode equations
Authors: Atanassov V. , Mateev R. , Zhelyazkov I.
Published: March 2009

We have derived a set of coupled mode equations which govern the nonlinear interaction of three high-frequency electrostatic surface waves through a low-frequency density perturbation produced by them. The set is compared with that obtained when a similar problem is solved for bulk waves in an infinite plasma. Some differences are shown to exist caused by the specific features of surface waves such as the amplitude attenuation normal to the interface and their hybrid nature.
Nonlinear interaction of electrostatic surface waves in a semi-infinite plasma. Part 2. Time-dependent solutions to the coupled mode equations
Authors: Atanassov V. , Mateev E. , Zhelyazkov I.
Published: March 2009

The coupled mode equations which govern the nonlinear interaction of three electrostatic high-frequency surface waves and a low-frequency density perturbation are analysed considering time-dependent solutions only. We show the existence of a filamentation instability in the static limit for the low-frequency density perturbation. In the opposite case (density perturbation close to the lowfrequency surface wave resonance) we arrive at a decay instability where only surface waves take part. The parametric approximation (growth rate and threshold) as well as the nonlinear evolution of both types of instabilities are studied.
Langmuir solitons in a two-temperature plasma
Authors: Buti B. , Yu M. Y.
Published: March 2009

The existence of finite-amplitude Langnwir solitary waves in a two-electron-temperature plastia is investigated. A now type of soliton, in which the density depression and the electric field amplitude scale in the same manner, and which travels at the effective sound speed, has been found.
Resistive instability of interchange modes due to anomalous diffusion
Authors: Pavlenko V. P. , Weiland J.
Published: March 2009

It is found that convective cell diffusion leads to a kind of resistive instability for negative energy interchange modes.
The plasma wake of mesosonic conducting bodies. Part 2. An experimental parametric study of the mid-wake ion density peak
Authors: Stone Nobie H.
Published: March 2009

An experimental investigation of the disturbed flow field created by conducting bodies in a mesosonic, collisionless plasma stream is reported. Part 1 dealt with ion focusing by the body's plasma sheath and the subsequent filling of the near-wake void region. In part 2, the mid-wake region is investigated, where, for bodies of the order of a Debye length in size, the focused ion streams converge to form a significant current density peak on the wake axis. A parametric description is obtained of the behaviour of the amplitude, width, and position of this peak. The results also indicate that portions of the axial ion peak are created by additional mechanisms and that body geometry affects the mid-wake structure only when the sheath is sufficiently thin to conform to the shape of the body.
An experimental investigation of current production by means of rotating magnetic fields
Authors: Hugrass W. N. , Jones I. R. , Phillips M. G. R.
Published: March 2009

An investigation of current production by means of a rotating magnetic field is made in an experiment in which the technique is used to generate a theta-pinch- like distribution of field and plasma. Detailed measurements are made of both the generated unidirectional azimuthal electron current and the penetration of the rotating field into the plasma. The experimental results support the theoretical prediction that a threshold value of the amplitude of the applied rotating field exists for setting the electrons into rotation.
Equilibrium and stability of collisionless systems in the paraxial limit
Authors: Newcomb William A.
Published: March 2009

A study is made of the equilibrium and stability of a magnetically confined collisionless plasma in the paraxial or ‘long, thin’ limit. The main field is poloidalaxisymmetric, and a stabilizing quadrupole field is superimposed.
A steady-state model of current filamentation caused by the electrothermal instability in a fully ionized magnetized plasma
Authors: Haines M. G. , Marsh F.
Published: March 2009

A magnetically confined two-fluid plasma is considered in which the Ohmic heating of the electrons by a current driven parallel to an applied magnetic field is balanced by bremsstrahlung and equipartition to the ions. It is found that for a steady state the applied electric field must be below a critical value which in absence of bremsstrahlung is given by where the electrical conductivity is and the total pressure is p. Under this condition it is found that there are two /Futions for Te/Ti which satisfy the steady electron energy balance equation in a homogeneous, fully ionized plasma. One of these /Futions always has values above the critical value of Te/Ti (= 132 in absence of bremsstrahlung) for the onset of the electrothermal instability in a fully ionized gas. Inclusion of electron thermal conduction transverse to the magnetic field (with Hall parameter ) yields a wavelength for maximum growth of the instability of about , where ae is the electron Larmor radius. The steady non linear profiles showing current filamentation have been calculated. Runaway electrons and ion-acoustic instabilities can occur in the spatial maximum of the current density and electron temperature. Inclusion of bremsstrahlung loss reduces the value of Te/Ti for the onset of the instability, and at Te = Ti yields a maximum ion temperature obtainable by Ohmic heating in a stable plasma.
Relativistic dielectric tensor of a Maxwellian plasma for electron cyclotron waves at arbitrary propagation angles
Authors: Airoldi A. C. , Orefice A.
Published: March 2009

The relativistic dielectric tensor of a magnetized Maxwellian plasma is obtained in a general way, for electron cyclotron waves at arbitrary incident angle. A new expression is provided for the computation of the relativistic (Shkarofsky) dispersion functions.
Alfvén wave heating of a cylindrical plasma using axisymmetric waves. Part 2. Kinetic theory
Authors: Donnelly I. J. , Clancy B. E. , Cramer N. F.
Published: March 2009

Kinetic theory, including ion Larmor radius effects, is used to analyse the Alfvén wave heating of cylindrical plasmas using axisymmetric waves excited by an antenna at frequencies up to the ion cyclotron frequency. At the Alfvén resonance position, the compressional wave is mode converted to a quasi-electrostatic wave (QEW) which propagates towards the plasma centre or edge depending on whether the plasma is hot or warm. The energy absorbed by the plasma agrees with the MHD theory predictions provided the QEW is heavily damped before reaching the plasma centre or edge; if it is not, then QEW resonances may occur with a consequent increase in antenna resistance. The relation between ion cyclotron wave resonances and QEW resonances in a hot plasma is shown. The behaviour described above is demonstrated by numerical solution of the wave equations for small and large tokamak-like plasmas. WKB theory has been used to derive useful expressions which quantify the QEW behaviour.
Frequency doubling of extraordinary wave
Authors: Čadež V. M. , Jovanović D.
Published: March 2009

Second-harmonic generation of an extraordinary wave is investigated in the domain of phase synchronism with the pump wave. The conversion efficiency parameter is calculated for various values of the magnetic field, electron plasma density, angle of propagation and slab thickness.
Finite-amplitude solitary Alfvén waves in a low-beta plasma
Authors: Kalita M. K. , Kalita B. C.
Published: March 2009

An exact nonlinear Alfvén wave in a low-β plasma is investigated. Both super-and sub-Alfvénic rarefactive solitons are found to exist depending upon the angle of inclination of the propagation vector to the magnetic field.
New representations of dielectric tensor elements in magnetized plasma
Authors: Shkarofsky I. P.
Published: March 2009

Each of the dielectric tensor elements in a Maxwellian magnetoplasma is expressed in terms of various derivatives of a single functional expression. The relationships for all the elements are given, first for the general case of a relativistic plasma, then for the slightly relativistic case, and finally for the non-relativistic case, when the perpendicular wavenumber is either large or small. We also derive new relations useful for the computation of the slightly relativistic plasma dispersion function.
Low-frequency drift-induced instabilities in a magnetized two-ion plasma
Authors: Bharuthram R. , Hellberg M. A.
Published: March 2009

Numerical solutions of a dispersion relation for low-frequency electrostatic waves in a current-carrying, cold, weakly collisional, magnetized two-ion plasma are used to discuss the two-stream and resistive natures of the ion-ion hybrid instability. An instability with analogous behaviour is found to be associated with the light ion cyclotron frequency. Analytical results explain the behaviour. A numerically derived transition diagram summarizes the parameter values for which transitions between different modes take place.
Hamiltonian theory of guiding centre motion revisited
Authors: Weyssow B. , Balescu R.
Published: March 2009

The classical problem of the motion of a charged particle in a slowly varying electromagnetic field is reconsidered in the framework of ‘pseudo-canonical transformations’ in a Hamiltonian formalism. As compared with Littlejohn's important recent work, we develop a method which we believe to be more transparent. It consists, in essence, of exploiting directly the requirement that the Lie brackets of the guiding centre variables be independent of the (new) gyrophase. By using this method, we construct explicitly the complete set of functional relationships between the guiding centre variables and the particle variables, up to second order in the drift parameter є These expressions are valid for magnetic and electric fields of arbitrary geometry (within the drift approximation), which may be slowly varying in time.
Suprathermal drift through a warm collisional plasma: evolutional solution
Authors: Chee-Seng Lim
Published: March 2009

Evolutional drift-theory representations are used to consider suprathermal drift of a switched-on electron through a warm collisional plasma. The general suprathermal solution for an arbitrarily time-varying electron is made up of two nontrivial constituents. One of these exists in the interiorR2of an expanding thermal front Г. The other exists in a drifting-extending regionR1enclosed by part of Г, together with a sheet that diverges downstream from the suprathermal electron (outside Г) and terminates tangentially at Г. The solution vanishes identically beyondR1,R2and their boundaries. Two- and three-dimensional closed forms of an exact solution are next extracted inR1for the pulsating electron with complex frequency. Furthermore, two-dimensional near-ultimate state results are asymptotically derived deep withinR2for a real electron frequency and a collisionless plasma. Hyperbolic/hyperboloidal attenuation normally affects space-time dissipation.
The intrinsic electromagnetic solitary vortices in magnetized plasma
Authors: Liu Jixing , Horton Wendell
Published: March 2009

Several Rossby-type vortex solutions constructed for electromagnetic perturbations in magnetized plasma encounter the difficulty that the perturbed magnetic field and the parallel current are not continuous on the boundary between two regions. We find that fourth-order differential equations must be solved to remove this discontinuity. Special solutions for two types of boundary value problem for the fourth-order partial differential equations are presented. By applying these solutions to different nonlinear equations in magnetized plasma, the intrinsic electromagnetic solitary drift-Alfvén vortex (along with solitary Alfvén vortex) and the intrinsic electromagnetic solitary electron vortex (along with short-wavelength drift vortex) are constructed. While still keeping a localized dipole structure, these new vortices have more complicated radial structures in the inner and outer regions than the usual Rossby-wave vortex. The new type of vortex guarantees the continuity of the perturbed magnetic field δB⊥ and the parallel current j‖ on the boundary between inner and outer regions of the vortex. The allowed regions of propagation speeds for these vortices are analysed, and we find that the complementary relation between the vortex propagating speeds and the corresponding phase velocities of the linear modes no longer exists.
On the formation of periodic and solitary whistler envelopes
Authors: Mann G.
Published: March 2009

The nonlinear interaction of whistler waves with the background plasma via the ponderomotive force gives rise to the formation of both periodic and solitary whistler envelopes. This is described in terms of the Lagrange formalism which allows us to define conserved quantities which determine, together with the parameters of the background plasma and the whistler frequency, the particular form of the envelope.
Stimulated Raman scattering from a fully focused relativistic electron beam in a waveguide
Authors: Schill Robert A. , Seshadri S. R.
Published: March 2009

Stimulated Raman scattering from a fully focused relativistically drifting electron plasma in a parallel-plate waveguide is studied. A set of internally consistent transport relations governing the three-wave interactions is developed. These transport relations lead to the proper conservation of energy and momentum. Including small wall and bulk plasma losses, parametric and nonlinear characteristics are investigated theoretically and numerically. It is found that in an unbounded medium the saturation period of the signal wave is considerably smaller than in a bounded medium. The signal energy comes from the plasma stream through the idler wave with small depletion of the pump wave amplitude.
Nonlinear surface waves on a thin plasma layer
Authors: Zhelyazkov I. , Vodenicharova T. , Yu M. Y.
Published: March 2009

The propagation of nonlinear high-frequency TM antisymmetric surface waves on a thin un magnetized plasma slab bounded by vacuum has been studied. It is found that smooth surface wave solitons due to the modulation of finite-amplitude electron surface waves by slow ion-acoustic motion exist. When the high-frequency wave propagation is modified by a purely electronic slow motion, the governing equation is a derivative nonlinear Schröd inger equation with a cusped-soliton solution.
Theory of thermal solitary vortices in current-carrying edge plasmas
Authors: Mondt J. P. , Liu J.
Published: March 2009

It is shown that the nonlinear dynamics of current-convective excitations in current-carrying edge plasmas allows for the existence of solitary vortices despite the effects of magnetic shear and dissipation in the form of parallel electron thermal conductivity. The potential importance of this finding with regard to heat balance is pointed out.
Reactive and resistive nonlinear instabilities
Authors: Melrose D. B.
Published: March 2009

It is argued that familiar nonlinear instabilities, such as three-wave decay instabilities and scattering off quasi-modes, have reactive and resistive versions. In appropriate limits these versions correspond to fixed-phase parametric instabilities and to random phase growth in weak turbulence theory, respectively. Using a simplified model it is shown that the reactive version passes over into the resistive version when the band-width of the pump is comparable with the growth rate.
Thermodynamic approach to transport scalings in tokamaks
Authors: Yamagishi T.
Published: March 2009

The cross-field plasma diffusion coefficient is expressed in terms of the perturbed potential energy W by making use of the nonlinearity of orbit diffusion. The thermodynamic bound of the energy W for a current-carrying collisionless plasma has been determined consistently with four constraints: the invariance of averaged Hamiltonian, angular momentum, entropy and density. It is found that with momentum invariance the major contribution from the plasma current cancels, and the lowest upper bound of W is determined by the high-order toroidal effect coupled with the plasma current, which yields the neo-Alcator (TFTR) scaling for the energy confinement time. When neoclassical deformation is allowed in the plasma distribution, the thermodynamic bound has additional terms which come from the neoclassical source of free energy due to the bootstrap current. When the poloidal beta is larger than a certain critical value, the energy confinement time shows the effect of density saturation, and becomes proportional to the plasma current.
Collisional transport for a superthermal ion species in magnetized plasma
Authors: Cozzani F. , Horton W.
Published: March 2009

The transport theory of a high-energy ion species injected isotropically in a magnetized plasma is considered for arbitrary ratios of the high-energy ion cyclotron frequency to the collisional slowing down time. The assumptions of (i) low fractional density of the high-energy species and (ii) average ion speed faster than the thermal ions and slower than the electrons are used to decouple the kinetic equation for the high-energy species from the kinetic equations for background ions and electrons. The kinetic equation is solved by a Chapman–Enskog expansion in the strength of the gradients; an equation for the first correction to the lowest-order distribution function is obtained without scaling a priori the collision frequency with respect to the gyrofrequency. Various transport coefficients are explicitly calculated for the two cases of a weakly and a strongly magnetized plasma.
Relationship between directions of wave and energy propagation for cold plasma waves
Authors: Musielak Zdzislaw E.
Published: March 2009

The dispersion relation for plasma waves is considered in the ‘cold’ plasma approximation. General formulae for the dependence of the phase and group velocities on the direction of wave propagation with respect to the local magnetic field are obtained for a cold magnetized plasma. The principal cold plasma resonances and cut-off frequencies are defined for an arbitrary angle and are used to establish basic regimes of frequency where the cold plasma waves can propagate or can be evanescent. The relationship between direction of wave and energy propagation, for cold plasma waves in hydrogen atmosphere, is presented in the form of angle diagrams (angle between group velocity and magnetic field versus angle between phase velocity and magnetic field) and polar diagrams (also referred to as ‘Friedrich's diagrams’ ) for different directions of wave propagation. Morphological features of the diagrams as well as some critical angles of propagation are discussed.
On the propagation of half-gyrofrequency whistler-mode waves in the magnetospheric plasma
Authors: Ohmi N. , Hayakawa M.
Published: March 2009

The propagation of whistler-mode waves at frequencies above one half the electron gyrofrequency has been investigated for a magnetospheric two-component plasma (cold and lower energy hot electrons) by use of the properties of refractive index surfaces. The presence of hot plasma is found to enhance the tendency towards field-aligned focusing of half-gyrofrequency whistler-mode propagation at large wave normal angles close to the oblique resonance angle of the whistler-mode propagation in the corresponding cold plasma.
Electromagnetic modulations of electron whistlers in plasmas
Authors: Stenflo L. , Yu M. Y. , Shukla P. K.
Published: March 2009

This paper presents a formulation of the nonlinear coupling of the electron whistler mode radiation with generalized (including higher frequencies than allowed by the magnetohydrodynamic model) magnetosonic fluctuations. A coupled set of nonlinear equations describing the interaction of the whistler wave electric field with the density and the field-aligned magnetic fluctuations of the generalized magnetosonic waves is derived and the problem of modula-tional instability is discussed. Our results have relevance to the non-thermal magnetic field fluctuations which lead to supplementary plasma heating.
Electron hole and electron wave excitation in a plasma with transverse effects
Authors: Iizuka Satoru , Tanaca Hiroshi
Published: March 2009

Excitation of electron holes and electron wave pulses is investigated numerically in a single-ended plasma by computer simulation using a particle model. The transverse effects are taken into account by introducing the perpendicular wavenumber in the Poisson equation. Increase in the plasma potential in front of a plasma source, resulting from propagation of the rarefaction pulse from an end boundary, gives rise to the excitation of electron holes, while the rarefaction pulse reflects back as the compression pulse toward the boundary. The qualitative properties are in good agreement with experiment.
Nonlinear evolution of a wave packet propagating along a hot magnetoplasma column
Authors: Ghosh B. , Das K. P.
Published: March 2009

The method of multiple scales is used to derive a nonlinear Schrödinger equation, which describes the nonlinear evolution of electron plasma ‘slow waves’ propagating along a hot cylindrical plasma column, surrounded by a dielectric medium and immersed in an essentially infinite axial magnetic field. The temperature is included as well as mobile ion effects for ail possible modes of propagation along the magnetic field. From this equation the condition for modulational instability for a uniform plasma wave train is determined.
Instability and saturation of drift-convective modes in an inhomogeneous plasma
Authors: Balescu R. , Bessenrodt H. , Shukla P. K. , Spatschek K. H.
Published: March 2009

It is found that the inclusion of the electron inertia effect (parallel to an external magnetic field) can provide a linear coupling between the electrostatic drift and the convective modes in a non-uniform plasma. This coupling leads to new branches of rapidly growing modes, which are calculated in the kinetic as well as in the hydrodynamic regimes. To study the saturation of the linear unstable modes, we account for the mode coupling and derive a set of model nonlinear fluid equations. A perturbation technique is employed to obtain a nonlinear evolution equation. In the steady state, the latter yields the saturated electric potential. It is argued that the enhanced low-frequency fluctuations can cause anomalous particle transport in a magnetoplasma.
The interaction of a conducting object with a supersonic plasma flow: ion deflection near a negatively charged obstacle
Authors: Merlino R. L. , D'Angelo N.
Published: March 2009

An experimental study of the interaction of a conducting object with a flowing plasma is described. Particular attention is given to the deflection of ions in the sheath of a negatively charged body. The experiments were conducted in a double plasma device in which a relatively weak longitudinal magnetic field may also be present. For the particular conditions used in these experiments, it was found that ion deflection occurs primarily near the edge of the body. A simple physical model is discussed which accounts for the observed dependences of the convergence of ion streams on the body potential and ion beam velocity. A density rarefaction wave is also observed in the wake region, which propagates into the ambient plasma at roughly the ion acoustic Mach angle. Finally, some preliminary observations of the spatial distribution of plasma noise in the wake region are presented.
The Zakharov equations: a derivation using kinetic theory
Authors: Melrose D. B.
Published: March 2009

The Zakharov equations are derived using the weak turbulence expansion with approximate forms of the nonlinear response tensors from kinetic theory. The method is used to generalize the equations to the magnetized case. The range of validity of the Zakharov model is discussed briefly.
A model of an isolated magnetic flux tube in a stratified atmosphere
Authors: Hu Wen-Rui
Published: March 2009

A two-dimensional model of a magnetic flux tube confined in a gravitational stratified atmosphere is discussed. The magnetic field in the flux tube is assumed to be force-free. By using the approximation of large scale height, the problem of a free boundary with nonlinear conditions may be reduced to one involving a fixed boundary. The two-dimensional features are obtained by applying the perturbation method and adopting the Lüst–Schlüter model as the basic state. The results show that the configuration of a flux tube confined in a gravitational stratified atmosphere is divergent, and the more twisted the magnetic field, the more divergent is the flux tube.
Ripple transport in ‘transport-optimized’ stellarators
Authors: Hitchon W. N. G. , Mynick H. E.
Published: March 2009

Transport in ‘transport-optimized’ stellarators at low collision frequencies has been studied using a numerical method of solution of the bounce-averaged Fokker–Planck equation which describes both ripple-trapped and non-ripple-trapped particles in a stellarator. Diffusion rates in ‘transport-optimized’ stellarators had not previously been calculated at collision frequencies which are low enough for the effects of a radial electric field to be important. It was found that the configurations which were optimized for transport at the highest collision frequencies at which ripple-trapped particles exist give improved transport at all lower collision frequencies of interest, and also at higher collision frequencies. Standard stellarators have also been studied since in these cases the results can be compared with existing analytic theories and the transport mechanisms have been clarified as a result. Comparisons with Monte Carlo calculations show excellent agreement, and, although existing analytic methods of solution can strictly only be applied in rather few cases, some extensions of analytic results are discussed which enable us to explain quantitatively the behaviour observed.
The effect of a steady azimuthal field on rotating magnetic field current drive
Authors: Bertram W. K.
Published: March 2009

The method of generating steady azimuthal currents in a cylindrical plasma column by means of a rotating magnetic field is investigated numerically and analytically for the case where an external steady azimuthal magnetic field is applied to the plasma. For a plasma of low resistivity, the effect of imposing a strong azimuthal field is a substantial reduction in the amount of current that can be driven. For a resistive plasma the effect is more complicated. In some cases the azimuthal field enhances current drive as has been observed in recent experiments.