bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionization waves in plasma columns detected by microwaves
Authors: Cicconi G. , Rosatelli C. , Molinari V.
Published: March 2009

Ionization wave frequency spectra and their spatial distribution along argon and neon plasma positive columns are detected by microwaves in the 8–18 GHz frequency band. The plasmas are created at medium pressure by d.c. discharges in narrow tubes. Detection takes place in a rectangular waveguide on the microwave fields reflected and transmitted by plasma columns which are placed transversely across the waveguide in different positions and at several values of the discharge current. The frequency of the microwaves is adjusted for a parametric resonance condition with respect to Langmuir's electron frequency. The properties and dispersion relations of these waves are derived from a linear theory developed by K. W. Gentle, in which, for discharge operation below the Pupp limit, metastables are also included in the ionization and species conservation equations. An estimate of the total collision frequency is derived from a simplified two-fluid model valid essentially near the Pupp equilibrium limit.
Effect of finite ion Larmor radius on the Kelvin–Helmholtz instability
Authors: Nagano Hirosh
Published: March 2009

The effect of finite ion Larmor radius on the Kelvin–Helmholtz instability is investigated in the cases of an incompressible and a compressible plasma. When a wave vector is perpendicular to a uniform magnetic field, the effect of finite Larmor radius (FLR) stabilizes perturbations with a wavenumber exceeding a critical value, while there exists another case that the FLR effect destabilizes still more than the usual MHD approximation. The difference between these cases is decided from the configuration of flow velocity and magnetic field. When a wave vector is parallel to a magnetic field, the FLR effect tends to stabilize perturbations with a larger wavenumber.
Nonlinear propagation of lower-hybrid waves in an inhomogeneous plasma
Authors: Yu M. Y. , Shukla P. K. , Spatschek K. H.
Published: March 2009

We investigate the problem of spatial depletion of propagating lower-hybrid waves in an inhomogeneous plasma. In particular, we consider the nonlinear evolution of a lower-hybrid pump which is coupled to a daughter lower-hybrid decay wave excited by low-frequency density perturbations. Our results show that pump depletion occurs when three-dimensional effects are included. This phenomenon competes with the filamentation of the pump caused by self- interaction. Implications to lower-hybrid heating experiments are discussed.
Stability of the solar wind against the whistler mode
Authors: Revathy P.
Published: March 2009

The stability of the solar wind against the whistler mode is analyzed. It is shown that the solar wind can become unstable owing to this mode after a distance of 100 R from the sun. The minimum value of the relative velocity (Ur) between ∝-particles and protons for the excitation of this instability is the proton thermal velocity αi. The maximum growth rate at 200 R occurs for the values of the parameters kρi = 0·3,(T┤/T∥)i = 0·3 and Ur/αi = 0·5.
Nonlinear interaction of a magnetized overdense plasma with relativistically strong electromagnetic waves
Authors: Shih L. Y.
Published: March 2009

In this paper we consider relativistic interaction of an overdense plasma with very intense electromagnetic waves. Nonlinear coupling of dispersive waves in the presence of an ambient magnetic field is investigated. Lorentz transformation together with rotations of the co-ordinate system are employed to obtain analytic solutions. Two cases with variable gamma factors are treated in detail: in one case the magnitude of the electric field remains constant in the transformed frame; in the other no restriction is made to the electric field, but the total stream velocity vanishes in the transformed frame. Numerical illustrations of various modes for these two cases are depicted graphically.
Ray-tracing in the electron-cyclotron frequency region
Authors: de Luca F. , Maroli C.
Published: March 2009

The tracing of the geometrical optics rays in toroidal geometry and in the electron-cyclotron frequency range has been done numerically. The results presented are relevant to the extraordinary-mode propagation and conversion at the upper-hybrid resonance layer. High-density regime refraction effects, together with strong bending of the warm Bernstein rays along the toroidal direction and resonance-cone structure generation, are the main features of the numerical output.
Ion beam expansion due to ion cyclotron wave interactions
Authors: Hauck J. P. , Benford Gregory
Published: March 2009

We observe radial expansion of an ion beam propagating along a homogeneous guide magnetic field. The beam spreading appears to arise from interactions with beam-excited resonant ion cyclotron waves. Magnitude and scaling of the expansion agree with a theory based on a resonant diffusion process.
On the nonlinear development of the Langmuit modulational instability
Authors: Bingham R. , Lashmore C. N.
Published: March 2009

We consider the nonlinear development of a long-wavelength finite-amplitude Langmuir wave. The wavenumber k0 of the initial Langmuir wave is chosen such that the three-wave decay is forbidden. We then describe the coupling of the initial Langmuir wave to Stokes and anti-Stokes Langmuir perturbations (with wavenumbers k0 ∓ ks) due to the presence of a low-frequency density perturbation of wavenumber ks. We then show that for a wide range of experimental conditions, the Stokes and anti-Stokes Langmuir waves are generated with wavenumbers well separated from k0. In order to describe the nonlinear evolution of these perturbations and the pump wave we make the static approximation for the ions and describe the high-frequency waves by three distinct wave envelopes. These coupled nonlinear differential equations are then solved exactly for a number of special cases. For the temporal evolution, we obtain periodic solutions and, when damping is included, we find a slow exponential decay of the amplitudes with a corresponding increase in the nonlinear period of oscillation. The stationary spatially varying solutions are shown to include four basic types of behaviour: periodic, solitary wave, phase jump and shock-like profiles. These latter solutions are of interest since they are obtained for zero dissipation and for a coherent wave interaction.
The effects of ionization on the jump conditions for MHD and transverse ionizing shock waves
Authors: Cross R. C. , Mathers C. D.
Published: March 2009

The jump conditions for MHD shock waves in partly ionized gases and for transverse ionizing shock waves in neutral gases are obtained in explicit forms suitable for calculation. The fractional ionization behind the shook front is determined by assuming the plasma reaches Saha ionizational equilibrium. Solutions to the MHD jump equations are calculated for geometries ranging from transverse to switch-on. Switch-on shock jump solutions are compared with experimental observations of switch-on shock waves in partly ionized hydrogen plasmas. Numerical solutions are presented for transverse ionising shock waves in hydrogen, using the pre-shock electric field as a variable parameter, and the modes of propagation of such shook waves are examined in detail. Ionization is found to play a significant role in medium shock speed behaviour, particularly in determining the density jump.
Some uniqueness theorems for the ideal MHD equilibrium of a cylindrical tokamak
Authors: Thomas C.LL.
Published: March 2009

The cylindrical MHD equilibrium equation is formulated in a manner suitable for numerical computations which require the application of a constraint. In this formulation a uniqueness theorem is proved for a free boundary equilibrium with a specified total current. Uniqueness is independent of the details of the current density and merely requires that the total current is compatible with the current density. Two uniqueness theorems for diffuse plasmas are also presented. Four free boundary examples are studied with a variety of constraints applied.
Most probable states in magnetohydrodynamics
Authors: Montgomery David , Turner Leaf , Vahala George
Published: March 2009

We discuss the possible magnetohydrodynamic configurations that can be realized as ‘most probable’ states compatible with the existence of certain constraints. These constraints can be either experimentally imposed constraints such as constant total electric current or magnetic flux, or constants of the motion, or both.
Merging tokamaks
Authors: Ohyabu N. , Hsieh C. L. , Jensen T. H.
Published: March 2009

The concept of merging tokamak plasmas is proposed. It has potential applications for solving the problems of pseudo steady-state tokamak operation, refuelling, impurity removal and plasma heating. The currents in the two merging tokamak plasmas are in the same direction so that the columns attract each other. A model for the merging process is given.
Transverse instability of soliton solutions to nonlinear Schrödinger equations
Authors: Anderson D. , Bondeson A. , Lisak M.
Published: March 2009

An inverstigation is made of the transverse instability of plane soliton solutions of the nonlinear Schrödinger equation, including the case of an exponential nonlinearity. The analysis is based on a variational method, where specific trial functions are applied for the perturbations. Explicit expressions for the growth rates are given, showing good agreement with numerical results.
Low-frequency waves in inhomogeneous magnetic fields
Authors: Hruška A.
Published: March 2009

Propagation of waves in inhomogeneous, hot, isotropic plasma is described, assuming that the wavelength is much smaller than the scale-length of the plasma. The effect of the magnetic field topology on properties of waves is discussed in some detail. Coupling between the modes of oscillations is always present in an inhomogeneous ‘hot’ plasma. It is particularly strong for magneto- dynamic and sound waves propagating essentially along the fleidlines in the vicinity of a point where the phase velocities of the two modes are equal.
On Dupree's resonance function
Authors: Rolland P.
Published: March 2009

It is shown that Dupree's resonance function has a negative real asymptotic tail, so that the dispersion relation of the renormalized weak turbulence theory leads to unstable high phase velocity waves, even when the average distribution is a Gaussian. A possible explanation of this paradox is proposed.
A second-order theory for the ion-acoustic heat flux instability
Authors: Gary S. Peter
Published: March 2009

A second-order theory for electrostatic instabilities driven by the free energy in the relative drifts of plasma components in an infinite homogeneous, Vlasov plasma is constructed. General expressions for the wave–particle exchange rates of momentum, energy and heat flux are derived. Under the boundary condition of constant current, new terms arise which significantly modify the conventional quasi-liner results. The theory is applied to the B = 0 ion-acoustic heat flux instability, and exchange rates are obtained which are suitable for inclusion in electron fluid models of thermal transport.
Comments on the paper ‘On energy of non-resonanlty growing plasma waves’ by A. Hirose
Authors: Schmidt G.
Published: March 2009

This paper (Hirose 1978) appears to contain an error. The space averaged beam kinetic energy density is, to second order where n and V are the space averaged beam density and velocity, ñ and V are the oscillating quantities. The last term is significant, as will be shown, but it has been omitted by Hirose.
Energy equilibria in the diffuse pinch. Part 3. The electrothermal stability analysis with wave vector othogonal to magnetic field
Authors: Tomimura A. , Haines M. G.
Published: March 2009

A stability analysis is presented of the electrothermal modes of perturbation of a spatially homogeneous, two-temperature and fully ionized plasma with wave-vector K perpendicular to the magmetic field. It is found that the wavelength of the fastest growing unstable, non-convective mode is of the order of (mi/ me)½ ae, with maximum growth rate of the order of (me/ mi) vei, where ae and vei are the electron Larmor radius and electorn-ion collision frequency respectively. Depending on the values of ωτ and β, this analysis also shows the presence of a convective mode which persists in the limit of long wavelengths. This theory has been consistently examined with homogeneous equilibrium plasma models constructed under the assumption of either a scalar or a tensor electric conductivity. A comparison of these results with the previous steady-state profiles obtained in parts 1 and 2 of this series indicates that current filamentation can take place as a result of electrothermal instabilities in the plasma.
The half subharmonic excitation of ionization waves in positive columns of glow discharges
Authors: Ohe Kazuyuki , Takeda Susumu
Published: March 2009

The ½ subharmonic excitation is studied for the ionization wave in a positive column glow discharge. When an oscillation with about twice the frequency (and twice the wavenumber) of the resonant one is applied by modulating the discharge current, the ½ subharmonic is excited if the applied voltage exceeds a certain critical value. However, the excitation phenomenon differs from that of the ion-acoustic wave, since the ionization wave has a backward wave property in contrast to the forward one. Such an excitation mechanism is theoretically explained by the Van der Pol equation.
Electromagnetic drift wave turbulence and convective cell formation
Authors: Sanuki H. , Weiland J.
Published: March 2009

A model equation for nonlinear drift Alfvén waves in the region where they do not couple to the electrostatic drift wave branch is derived. Two conservation relations are derived and the results are compared to that of the Hasegawa—Mima equation. The spectrum is found to cascade to both smaller and larger k. The convective cell formation is studied for two different orderings of the parameters. The relation between characteristic scale lengths parallel and perpendicular to the drift flow for the onset of cell formation has been found.
Nonlinear waves in a magnetized plasma: periodicity analysis
Authors: Clemmow P. C. , Harding R. D.
Published: March 2009

The propagation of a superluminous plane wave of fixed profile through a cold electron plasma, in a direction perpendicular to the ambient magnetostatic field, is considered. The polarization is such that the electric vector has no component parallel to the magnetostatic field. The analysis is referred to the frame of reference in which all the field quantities are uniform in space, and the exact governing equations are cast into the form of an autonomous system of four nonlinear, first-order, coupled differential equations. The equations contain the parameter n that specifies the wave speed, c/n, in the laboratory frame, and inspection reveals that the limiting case n = 0 admits two exact solutions, which are monochromatic, of arbitrary amplitude, and recover the standard solutions of linear theory in the small-amplitude limit. The possibility of the existence of corresponding period solutions for the case n ≫ 1 is then investigated by a perturbation treatment. I t is found that the analysis can be carried through explicitly, and, to the first order in n, the outcome confirms the existence of periodic solutions, and yields the dependence of the period'on an amplitude parameter. The results are checked against a direct numerical integration procedure that incorporates a method of searching for periodic solutions, and close quantitative agreement is found for sufficiently small values of n.
Nonlinear scattering of whistlers by lower hybrid and ion Bernstein modes
Authors: Sodha M. S. , Sharma R. R. , Tripathi V. K.
Published: March 2009

Following the fluid model for the response of electrons, it is shown that a high-power whistler wave decays efficiently into a lower hybrid or a Bernstein mode and a scattered whistler wave in a homogeneous plasma. The thresholds for these channels of stimulated scattering are generally low. However, the channel of scattering involving lower hybrid waves is possible only for scattering angles exceeding ¼π. The other channel involving Bernstein modes is possible at shorter scattering angles but the growth rate is relatively small and the threshold is high.
Derivation of CGL theory with finite Larmor radius corrections
Authors: Chhajlani R. K. , Bhand S. C.
Published: March 2009

A method has been developed for the derivation of Chew–Goldberger–Low (CGL) theory for a collisionless plasma in the presence of a strong magnetic field. The pressure tensor in the pressure tensor equation is expanded in the inverse power of Larmor frequency. In the zeroth order, CGL equations are obtained and, the higher order, finite Larmor radius corrections to CGL equations are derived.
A fluid description of plasma double-layers
Authors: Levine J. S. , Crawford F. W.
Published: March 2009

This paper describes the space-charge double-layer that forms between two plasmas with different densities and thermal energies. Three progressively more realistic models are treated by fluid theory, taking into account four species of particles: electrons and ions reflected by the double-layer, and electrons and ions transmitted through it. First, the two plasmas are assumed to be cold, and the self-consistent potential, electric field and space-charge distributions within the double-layer are determined. Second, the effects of thermal velocities are taken into account for the reflected particles, and the modifications to the cold plasma solutions are established. Third, the further modifications due to thermal velocities of the transmitted particles are examined. The applicability of a one-dimensional fluid description, rather than plasma kinetic theory, is discussed. One valuable product of this description is the potential difference across the double- layer in terms of the parameters of the two plasmas which it separates. A useful length parameter is defined characterizing the distance over which most of this potential is dropped. Comparisons are then made between theoretical predictions, and double-layer potentials and lengths deduced from laboratory and space plasma experiments.
Instability of lower-hybrid waves in collisional plasmas with a field-aligned current
Authors: Lee Kai Fong
Published: March 2009

A study is presented for electrostatic waves propagating at large angles with respect to the background magnetic field in collisional, fully ionized plasmas carrying a field-aligned current. In addition to a mode at the usual lower-hybrid frequency, it is found that the presence of electron drift velocity introduces two more modes of oscillation at several times the lower-hybrid frequency. Under appropriate conditions, a resistive instabifity, with frequency very close to the lower-hybrid frequency and growth rate proportional to the electron–ion collisional frequency, can occur. A necessary condition is that the parallel phase velocity of the wave be smaller than the electron drift velocity. A numerical example is given to illustrate the essential features of the instability.
Wave propagation in a temperate multi-species plasma around the ion cyclotron frequency range
Authors: Janzen G.
Published: March 2009

Plane wave propagation in temperate plasmas consisting of n ion species is calculated analytically for collisionless plasmas of arbitrary composition. Numerical results are given for the complex refractive index of plasmas including collisions between particles of any kind and at arbitrary angles of propagation. There are two waves propagating at all angles other than 90°, one wave showing resonances at each of the n cyclotron frequencies of the ions involved. High ion-ion collision frequencies combine the motions of the ions to give new mass and composition weighted hybrid ion cyclotron resonances. At right angles to the external magnetic field one wave will propagate in the ion cyclotron range showing n – 1 ion-ion hybrid resonances and n – 1 hybrid cut-offs. The ion-ion hybrid resonances can be traced down to propagation at angles smaller than 90°, disappearing for parallel propagation. The hybrid resonance frequencies are close to the cyclotron frequencies of the ions with small relative concentrations. Damping of the waves in the neighbourhood of the ion-ion hybrid resonances is strongly affected by ion-ion collisions.
Stability properties of cold mantle systems for current-driven modes
Authors: Ohlsson D.
Published: March 2009

The stability problem of the boundary regions of cold blanket systems with induced currents parallel to the lines of force is formulated. Particular interest is focused on two types of mode: first electrostatic modes driven by the combined effects of a transverse resistivity gradient due to a spatially non-uniform electron temperature and a longitudinal current, second electromagnetic kink-like modes driven by the torque arising from a transverse current density gradient and magnetic field perturbations. It is found that the combination of various dissipative and neutral gas effects introduces strong stabilizing effects within specific parameter ranges. For particular steady-state models investigated it is shown that these effects become of importance in laboratory plasmas at relatively high densities, low temperatures and moderate magnetic field strengths. Stability diagrams based on specific steady-state cold plasma blanket models will be presented.
A calculation with respect to momentum transfer by the electron–neutral collisions and a new approach to the Boltzmami coffision integral
Authors: Nagata M.
Published: March 2009

A calculation with respect to momentum transfer by the electron–neutral collisions is carried out, based on an idea that collision phenomena should be characterized by mean free path rather than by the collision time, and correction terms are derived for the previous equation of momentum conservation and the previous approach to the Boltzmann collision integral.
The statistical mechanics of vortex—acoustic ion wave turbulence
Authors: Giles M. J.
Published: March 2009

The equilibrium statistical mechanics of electrostatic ion wave turbulence is studied within the framework of a continuum ion flow with adiabatic electrons. Attention is drawn to the fact that the wave field consists in general of two components, namely ion-acoustic and ion vortex modes. It is shown that the latter can significantly affect the equilibria on accoant of their ability both to emit and to scatter ion sound. Exact equilibria for the vortex—acoustic wave field are given in terms of a canonical distribution and the correlation functions are expressed in terms of a generating functional. A nonlinear transformation of the wave field, which removes the vortex-acoustic interaction energy to lowest order in the strength of the coupling, while preserving the phase space volume element, is then introduced. This enables the Feynman-Hibbs variational principle to be used to obtain an approximate generating functional based on a ‘trial’ energy functional, which is a quadratic in the new variables. Detailed calculations are carried out for the case in which the dominant coupling is an indirect interaction of the vortex modes mediated by the sound field. An equation for the spectrum of the vortex modes is obtained for this case, which is shown to possess a simple exact solution. This solution shows that the spectrum of fluctuations changes considerably as the total energy increases. At low levels of excitation the solution reduces to equipartition of energy. At higher levels the indirect interaction becomes significant and the formation of a condensed vortex state is possible when the mean energy exceeds the electron thermal energy. It is suggested that condensed vortex states could occur in the plasma sheet of the earth's magnetosphere and it is shown that the predicted ratio of the mean ion energy to the mean electron energy is consistent with the trend of observed values.
Super-ion-beam accelerator for the ignition of thermonuclear reactions
Authors: Winterberg F.
Published: March 2009

A pulsed, multi-stage, high-voltage accelerator is proposed which should be capable of producing intense ion beams of many million amperes and many million volts. Super ion beams produced by this type of accelerator can exceed the limiting Aifvén current for light ions, typically 107 A, at which beam pinching occurs. The beam pinching of these super-beams permits them to be precisely focused onto a thermonuclear target. With such an accelerator it seems to be possible to reach a beam voltage of 108 V with a beam current of 107 A. The resulting beam power of 1015 W should be more than sufficient to ignite a DT thermonuclear microexplosion. By the formation of a stable ion beam superpinch within a thermonuclear target, such a large beam power in conjunction with the strong self-magnetic field of the beam may even lead to the ignition of the DD and perhaps HB11 thermonuclear reactions.
Parametric instability driven by density modulation in velocity space
Authors: Sherwell D. , Cairns R. A.
Published: March 2009

Any ion distribution f;i =(θ—ώit) is an exact solution of the Vlasov equation for a uniformly magnetized plasma. Here θ is the phase angle in velocity space and ώi is the Larmor frequency. Then fi rotates rigidly in velocity space with frequency ώ;i about an axis along a magnetic field line. If fi has anisotropy in the perpendicular velocity plane of the form fi(V, t) = fi(V) [1+A cos 2(θ— ώit)], then it represents a density modulation of frequency 2ώ;i which is confined to velocity space. This non-Maxwellian distribution is an oscillating source of free energy (a pump) which may stimulate certain ion Bernstein modes, their frequencies being near harmonics of Ωi. We here investigate the linear kinetic theory of the system. Linearization implies the parametric approximation of a strong constant pump. Application of the theory may be found in the earth's bow shock.
Resonance cones and guided wave modes
Authors: Grabbe Crockett L.
Published: March 2009

A brief review of resonance cones in magnetized plasmas and their relationship with guided wave modes in bounded plasmas is given. It is shown that these two concepts are related mathematically by a Watson transformation, and physically by being complementary descriptions of waves in a warm bounded plasma. A detailed summary of the complementary nature of these two wave descriptions is given.
Kelvin–Helmholtz problem in a rotating Hall plasma
Authors: Granik A. T.
Published: March 2009

The Kelvin–Helmholtz problem in a Hall plasma, including the effects of rotation, is studied. In contrast to previous results, it is shown that if the angular velocity is normal to the wave vector that describes perturbations of the interface, the rotation does not affect the stability of a shear plane. The special case of very small angular velocity is studied and it is shown that the rotation has either a stabilizing or a destabilizing effect, according as the gravitational speed is greater or less than the Alfvén speed.
Plasmadynamical description of two-component weakly coupled plasma
Authors: Rozmus W.
Published: March 2009

Plasmadynamical equations for a two-component plasma are obtained starting from the linearized Vlasov–Landau kinetic equation. Explicit formulae are given for the frequency dependent transport coefficients. Eigenvalues of ten plasmadynamical modes are also discussed.
Unified treatment of symmetric MHD equilibria
Authors: Edenstrasser Johann W.
Published: March 2009

Under the assumption of a general symmetry (dependency on two space variables only), a generalized Grad–Shafranov equilibrium equation is derived and discussed. An elementary formulation of the boundary conditions is given and the existence of solutions is investigated. It emerges that from the equilibrium requirements almost no restrictions follow for the two arbitrary functions appearing in the equilibrium equation.
Theory of double resonance parametric excitation in plasmas. Part 2
Authors: Fried Burton D. , Adler Allen , Bingham Robert
Published: March 2009

Using a simpler formalism than in the original paper on this subject, we verify the earlier result that, for a pump frequency separation Δ approximately equal to twice the ion acoustic frequency Ω, the use of two long-wavelength pumps can reduce the threshold for parametric excitation of ion-acoustic waves when, andonlywhen, the Langmuir wave damping rate γ is much larger than Ω. The threshold is then reduced by a factor of order Ω/Ω, the optimum value of t being ▵ 2Ω –Γ for equal pump amplitudes, where Γ is the ion-acoustic wave damping rate and Γ ≪ Ω. The analysis presented in a recent paper is shown to be valid only for γ ≪ Ω, where the threshold reduction is quite small, vanishing in the limit of weak ion-acoustic wave damping (Te/Ti≫ 1).
Surface wave instability in bounded magnetized plasma with inhomogeneous particle stream
Authors: Jovanović D. , Vuković S.
Published: March 2009

The instability of surface wave modes in a semi infinite magnetoactive plasma with a non-homogeneous particle stream is studied. The existence of two possible mechanisms for the development of the instability: induced anomalous Doppler effect and induced Cherenkov effect is demonstrated. Related growth-rates and stability criteria are calculated.
Parametric instabilities with well separated frequencies in magnetized plasmas
Authors: Chou Yu-Mei , Tsai Shih-Tung
Published: March 2009

A nonlinear dispersion relation is derived for a homogeneous, magnetized plasma by the conventional ‘ponderomotive force’ method. By using this dispersion relation, various parametric instabilities (stimulated anomalous absorptions and scatterings) are discussed. The results are compared in detail with those obtained by other authors. In the validity region of this model the results derived by previous authors can be recovered. In addition to obtaining a few instabilities which have not been published in the literature, we also find that in general (i) the ‘dipole approximation’ can give the right results for the stimulated anomalous absorption problems and (ii) the ambient magnetic field may enhance the plasma stability.
Stability of weakly nonlinear ion sound waves with finite ion temperature
Authors: Infeld E. , Rowlands G.
Published: March 2009

The modulation instability of small-amplitude ion-acoustic waves is investigated in three dimensions for Ti<0 (ion temperature non-zero). Relevance of results to an experiment of Watanabe is discussed. Instabilities present in this experiment are seen to be due to three-dimensional rather than thermal effects and would also appear for Ti = 0.
Hall current effects on tearing modes in rotating reverse field plasmas
Authors: Kappraff Jay , Grossman William , Kress Michael
Published: March 2009

It has been experimentally observed for some time that certain tearing modes in plasmas may be suppressed if the plasma rotates in a preferred direction. In this paper we treat the m = 0, finite-wavelength tearing mode in cylindrical geometry for a reversed-field plasma equilibrium and show that by generalizing Ohm's law to include Hall current terms, we are able to explain this effect of rotation on tearing modes. Our results agree qualitatively with earlier analysis and numerical simulations. We also show that our results are sensitive to the position of the outer conducting wall, and for wall positions sufficiently close to the plasma-vacuum interface, tearing modes may be quenched when the rotation reaches a critical value. These results follow from a boundary-layer analysis and numerical integration of the boundary-layer equations.
The plasma capacitor problem
Authors: Elgin J. N.
Published: March 2009

The problem of the penetration of a longitudinal electric field into a bounded plasma layer is considered. The method of solution is based on the representation of the disturbance in the plasma layer as that generated by an appropriate charge source in the complementary regions into which, for the purpose of the representation, the plasma is conceived to extend. The problem is solved for each of the three boundary conditions in common use: these are the specular refiexion, the absorption and the diffuse scattering boundary conditions.
Debye shielding of a moving test charge in plasma
Authors: Wang Chong-Lung , Joyce Glenn , Nicholson D. R.
Published: March 2009

Equipotential contours for a moving test charge in isotropic Maxwellian plasma are determined numerically for a wide range of test charge speeds.
Electrostatic waves potential at the plasma and upper-hybrid resonances
Authors: Thiel J. , Debrie R.
Published: March 2009

The potential created by an infinitesimal alternating dipole in a Maxwellian magnetoplasma is computed numerically at the plasma and upper-hybrid resonance frequencies when the latter extends from one to three times the electron cyclotron frequency. A linear full kinetic theory is used for a homogeneous magnetoplasma for which the forced ion motion and the collisions are neglected. The integral which gives the potential is evaluated by using the least-damping- roots (LDR) approximation, i.e. by neglecting the higher-order roots of the dispersion equation for electrostatic waves. Some characteristic potential patterns of dipoles parallel and perpendicular to the magnetic field are computed and comparisons with analytical results previously published are made. The numerical and analytical patterns are similar only at the plasma frequency when the dipole is parallel to the magnetic field.
Rapid collapse of antiparallel magnetic field system of finite width by fast reconnexion
Authors: Ugai Masayuki
Published: March 2009

The present computer experiment studies an explosive magnetic energy conversion in an antiparallel-fleid system of finite width where sheet current flows in the middle of the system and return current flows on both sides of the system. It is demonstrated that, initiated by local onset of anomalous resistivity, the global plasma flow grows so as to bring about the so-called fast reconnexion process that provides rapid magnetic flux transfer as well as rapid magnetic energy release. In the resulting configuration of fast reconnexion, the plasma flow drastically reverses its direction across the magnetic- field region, and the effective width of the magnetic-field region becomes rapidly reduced with time. It is found that the fast reconnexion suddenly decays when the front tip of the return-current region has just arrived at the field-reversal region.
Active and passive methods for the study of non-equilibrium plasmas using electrostatic waves
Authors: Pottelette R. , Storey L. R. O.
Published: March 2009

We study the possibility of measuring the properties of a non-equilibrium plasma by means of a double-dipole radio-frequency probe, consisting of two small dipoles immersed in the plasma, and separated by a distance one or two orders of magnitude greater than the Debye length. This type of probe can be used either in an active or in a passive mode. The theory of both modes is presented, taking the example of an isotropic plasma in which the electrons have a biMaxwellian distribution function; the first Maxwellian represents the major population of thermal electrons, and the second a minor population of suprathermal electrons. In the active mode, one dipole emits artificial signals which the other receives; thus we study the propagation of electrostatic waves between the two dipoles. In the passive mode both dipoles are used to receive random signals induced by the natural electric microfield in the plasma, and we compute the cross-spectrum of these signals. By combining the active and passive techniques, it is possible to measure the electron density and temperature of the thermal electrons, and also to get some information about the distribution function of the suprathermal electrons.
On the emission of radiation from a localized current source in a magnetoplasma
Authors: Giles M. J.
Published: March 2009

A new approach to the problem of the radiation emitted from a localized external current source embedded in a magnetoplasma is described. It is argued that the calculation of the fields in the radiation zone can be substantially simplified by adopting at the outset a suitable parametrization of the dispersion surface. We illustrate the approach by calculating the far fields using the full expression for the dielectric tensor of a warm magnetized electron gas. In this case one can take the angle of rotation about the external magnetic field and the square of the refractive index as the curvilinear co-ordinates of the dispersion surface. The form of the surfaces of constant phase and the amplitudes of the emitted waves are described for each topologically different region of parameter space and their structures are related to the shapes of the refractive index surfaces. Attention is also drawn to the existence of locally cylindrical waves that can produce beams which are highly collimated in the direction of the external magnetic field.
Excitation of lower hybrid waves by electron beams in finite geometry plasmas. Part 2. Surface waves
Authors: Gagné Réal R. J. , Shoucri Magdi M.
Published: March 2009

The dispersion relations for the quasi-static lower hybrid surface waves are derived. Conditions for their existence and their linear excitation by a small density electron beam are discussed. Instabilities appearing in low-frequency surface waves are also discussed.
Self-focusing of a laser pulse in a transient plasma
Authors: Sodha M. S. , Tewari D. P. , Patel L. A.
Published: March 2009

Following Akhmanov's approach, self-focusing of a laser pulse in a transient plasma has been studied. The beamwidth parameter and hence the laser intensity and the frequency shift (time derivative of the phase) have been evaluated as a function of time and the distance of propagation. It is seen that the time dependence of the axial intensity changes appreciably as the pulse propagates. The present investigation is restricted to a pulse whose incident intensity has Gaussian radial dependence.
Nonlinear propagation of the ordinary mode in a hot magnetoplasma
Authors: Khiet Tu , Furutani Y. , Ichikawa Y. H.
Published: March 2009

Kinetic theory of the self-modulation of a quasi-monochromatic ordinary wave propagating across an external magnetic field is presented. Explicit expressions of the dispersion and the nonlinear coupling coefficients are given for a Maxwellian plasma. In the limit of zero-temperature, a Karpman–Kruskal linear stability of the O-mode envelope is discussed.
Acceleration of trapped particles by a Langmuir wave in an inhomogeneous plasma
Authors: Dysthe K. B. , Gudmestad O. T.
Published: March 2009

The acceleration of trapped particles by a Langmuir wave in an inhomogeneous plasma is investigated for different density profiles. In particular the important case of a wave moving towards its refiexion point is considered both analytically and numerically. To obtain estimates of the energy gain of the trapped particles, their stability is investigated. Our findings differ from those of previous authors. The effect of wave damping, and a slowly varying frequency (whistler-like phenomena), on the stability of trapping is estimated.
On nonlinear axisymmetric equilibria in the magnetohydrodynamic approximation
Authors: Woolley M. L.
Published: March 2009

The second order elliptic differential equation which describes the static equilibrium of an axisymmetric ideally conducting plasma toroid, in the magnetohydrodynamic approximation, may be transformed into an equivalent equation which admits at least one class of exact analytic solutions for which the original equation is essentially nonlinear. Necessary and sufficient conditions are given for the existence of systems in this category having closed toroidal flux surfaces and a result is proved which gives some insight into the mathematics by which the spatial variation of the hydrodynamic pressure can be represented by families of nested closed curves.
Effect of self-focusing on parametric back-scattering and absorptive instabilities in a plasma
Authors: Sodha M. S. , Kaushik S. C. , Sharma R. P.
Published: March 2009

This paper presents an investigation of the effect of self-focusing on the absolute growth rates of parametric back-scattering (e.g. stimulated Raman and Brillouin scatterings) and absorptive instabilities (e.g. two-plasmon decay and ion–plasmon decay) in a homogeneous and collisionless plasma. Gaussian intensity distribution of the pump laser beam causes the redistribution of carriers in the plane transverse to the beam propagation on account of the ponderomotive force, and leads the beam to propagate in an oscillatory wave guide mode. The modifications in plasma frequency and intensity of the beam cause the growth rates of the above parametric instabilities to show an oscillatory behaviour with the distance of propagation.
Plasma heating by a relativistic electron beam with secondary instabilities
Authors: Tajima T.
Published: March 2009

Relativistic electron beam heating of a dense plasma through the two-stream instability is studied. A large amplitude beam-plasma wave excited by the instability induces waves of wide wavenumber spectrum at low phase velocities through secondary parametric instability processes. In some cases such a complicated mode coupling of the beam-plasma wave into low phase velocity waves and their saturation may be described in terms of soliton formation. A beam stopping length associated with this process is obtained.
On the propagation of energetic ion beams through a fusion target chamber
Authors: Jorna S. , Thompson W. B.
Published: March 2009

This article treats some aspects of the propagation of a highly energetic heavy ion beam through a fusion target chamber. The stability of this beam to various perturbations is especially emphasized, first for vacuum propagation, and then for propagation through a background plasma. The results are illustrated by detailed calculations for a beam carrying 3 kA of current and consisting of 70GeV, singly ionized uranium ions. We find that such a beam will propagate stably through the target chamber. As a second example we have applied some of our results to the recently proposed I53+ concept in which up to a hundred beams of 40GeV iodine ions each carrying 4.2 kA of current are directed to the target. Our conclusions for this case are less optimistic, as such beams are likely to be subject to space-charge problems due to the increased value of v/γ and are prone to instabilities of the two-stream type.
Self-similar solutions for Vlasov and water-bag models
Authors: Burgan J. R. , Gutierrez J. , Fijalkow E. , Navet M. , Feix M. R.
Published: March 2009

Using finite group theory, self-similar solutions for the one-dimensional Vlasov– Poisson system are considered, both for electron plasmas, with a fixed ion background, and for a single species beam. Difficulties arising from the Poisson equation are pointed out and handled by using an exponential group of transformations. Introducing, for the beam, a water-bag model, we find that the boundary condition problem, imposed by self-similarity, can be solved through the introduction of a ‘virtual particle’ concept. In order to test the analytical solution obtained, we perform a numerical simulation using a particle code. Complete agreement is found.
Kinetic theory of binary correlations in turbulent plasmas
Authors: Misguich J. H. , Balescu R.
Published: March 2009

The two-particle correlations in a turbulent plasma are analyzed on a quite general basis by using the modern methods of non-equilibrium statistical mechanics. It is shown that the binary correlations can be split (in a time in- variant way) into a part which decays quickly by ballistic motion, and a long- living part: ‘the natural correlations’. The latter are continuously regenerated from the one-particle distribution function by the internal interactions, even in the absence of true collisions. The general theory can be made operational by using approximation schemes, among which the ‘RQL2’ method, which generalizes the renormalized quasi-linear approximation, leads to results comparable to, but more general than, those developed by previous authors. The explicit relation of the long-living enhanced correlations to the concept of ‘clumps’ will be developed in a forthcoming paper.
Collisional absorption of two laser beams in plasma
Authors: Mohan Man , Acharya Rama
Published: March 2009

The collisional absorption of two laser beams is considered by solving the kinetic equation for the plasma electron. Results show that the simultaneous effects of two laser beams on the heating rate is greater as compared with the individual contribution of each laser beam when the two laser beams have a difference of frequencies equal to the plasma frequency.
Clebsch representations in the theory of minimum energy equilibrium solutions in magnetohydrodynamics
Authors: Rund Hanno , Wells Daniel R. , Hawkins Lawrence Carl
Published: March 2009

The introduction of Clebsch representations allows one to formulate the problem of finding minimum energy solutions for a magneto-fluid as a well-posed problem in the calculus of variations of multiple integrals. When the latter is subjected to integral constraints, the Euler–Lagrange equations of the resulting isoperimetric problem imply that the fluid velocities are collinear with the magnetic field. If, in particular, one constraint is abolished, Alfvén velocities are obtained. In view of the idealized nature of the model treated here, further investigations of more sophisticated structures by means of Clebsch representations are anticipated. Preliminary results of a similar calculation utilizing a modified two fluid model are discussed.
Anomalous ion beam scattering by shear Kelvin—Helmholtz wave interactions
Authors: Hauck J. P. , Benford Gregory
Published: March 2009

We inject a fast ion beam across a magnetic field, through a cylindrical 5 cm diameter plasma. Shear Kelvin–Helmholtz waves, already present in the plasma, are considerably amplified. The ion beam is rapidly slowed and scattered. The observed stopping power exceeds the classical power by over two orders of magnitude. A simple theoretical estimate, ascribing beam energy loss to driving of the waves, agrees qualitatively with observations.
Nonlinear saturation of trapped electron instability
Authors: Sen Amiya K.
Published: March 2009

We consider the effect of trapped electron instability turbulence on the dynamics of a typical mode. We find its effects are turbulence induced additional collision frequencies for the trapped electrons which are stabilizing. The resulting saturation level is found to be considerably smaller than previous estimates.
Multiple water-bag model and nonlinear plasma oscillations: appearance of a new pole
Authors: Gros M. , Bertrand P. , Baumann G.
Published: March 2009

The complete second-order theory of the multiple water-bag model is developed for one-dimensional collisionless electrostatic waves, in terms of the initial value problem. Nonlinear frequency spectra are obtained in Van Kampen's formulation, and a new pole, already predicted by R. W. B. Best, appears for hot plasmas. This theory is successfully checked by a full numerical experiment of the Vlasov–Poisson system.