bluuebunny/crossref_metadata_2025 huggingface dataset:
On the re-connexion of magnetic lines of force
Authors: Fukao Shoichiro , Tsuda Takao
Published: March 2009

The magnetic field and flow with an X-type neutral point or stagnation point are studied numerically for the steady state of incompressible, finitely conducting, viscous fluid in two dimensions. There appear two transition layers connecting smoothly the regions on either side, each of which contains almost uniform magnetic field and flow. The electric currents are concentrated in the vicinity of the neutral point and along the transition layers. The magnetic field is regarded as almost frozen in the fluid in other current-free regions, even in the case of moderate conductivities. The current-core over the neutral point is accompanied by a remarkable shear of currents, which may contribute to reducing the local electrical conductivity effectively. Thus the re-connexion of magnetic lines of force may be possible even in very highly conducting fluids. It is shown that the re-connexion is not essentially influenced by dissipations due to finite electrical conductivity or viscosity, but definitely by external conditions such as the applied electric field in the magnetic field and flow.
Radiation and ionization by relativistic electron beams
Authors: Benford Gregory
Published: March 2009

The electromagnetic streaming instability yields substantial growth for propagation at large angles to the beam. Transverse Landau damping suppression of the mode is calculated for a variety of beam parameters. The saturated stage of the instability (bunching in position space) can produce large electric fields oscillating at the plasma frequency in the vicinity of the beam. These fields can cause further ionization, and define the final channel radius. Comparison with experiment is satisfactory.
On the stability of nonlinear cold plasma waves. Part 2
Authors: Infeld E. , Rowlands G.
Published: March 2009

In part 1 (Infeld 1972), it was shown that a nonlinear stationary wave in a cold plasma is marginally stable to all perturbations that are functions of the spatial direction parallel to the direction of propagation only. The stability analysis is extended here in part 2 to include general spatial variations. Within the limitations of the treatment, it is found that, for wave amplitudes up to maximal value (onset of trapping), the wave is marginally stable. Hence one would expect these large-amplitude cold plasma waves to exist in practice.

The one-dimensional analysis of part 1 is also extended to include waves with relativistic velocities, and such waves are again found to be marginally stable.
Ambipolar diffusion as a singular perturbation problem
Authors: Giles M. J.
Published: March 2009

The effect of a magnetic field on the diffusion of a cylindrical column of ionization, having an initial electron density much greater than that of the ambient weakly ionized plasma in which it is embedded, is examined for the case in which the electron gyro-frequency is much greater than the electron neutral collision frequency Ve. The nonlinear diffusion equations are solved by means of a perturbation expansion based on their exact solution for the case Ve = 0. This approach leads to a singular perturbation problem, and shows that, when the column is not closely aligned with the field the distribution of plasma differs appreciably from that obtained from an ordinary anisotropic diffusion equation.
On the stability of nonlinear magneto-sonic waves in a collisionless plasma
Authors: Demchenko V. V. , Hussein A. M.
Published: March 2009

The stability of a magneto-sonic wave of small (but finite) amplitude, propagating in a low- β plasma across a magnetic field, is investigated. It is shown that such a wave is unstable with respect to parametric splitting into many satellite waves. Wavenumbers of the satellite waves differ from that of the original magneto-sonic wave. Thus, the sateffite waves leave an interaction space, and form oscillating ‘tails ’ in front of and behind the initial pulse.
Effects of lithium and heavier ions on electromagnetic proton cyclotron instability
Authors: Cuperman S. , Gomberoff L. , Sternlieb A.
Published: March 2009

The effects of lithium and heavier ions (i.e. having specific charge Zj e/mj smaller than the proton's), on the electromagnetic cyclotron instability in warm anisotropic (bi-maxwellian) proton plasmas, are analytically and numerically investigated. It is found that the occurrence of resonances for modes with ωr = Ωj (ωr, real wave frequency; Ωj, ion gyrofrequency), which produce a cut-off in the phase velocity, leads to the possible existence of two different situations. (i) If the proton thermal anisotropy is smaller than a critical value A pc (which depends on the ion specific charge), the resonance and therefore the ‘stop band’ occurs outside the unstable range. The maximum growth rate, as well as the instability range in k space, may increase with the relative ion concentration ion and warm proton particle densities, respectively. There is an optimum value of η for maximum enhancement of the instability. (ii) If Ap > Apc, the unstable spectrum in Wr space is divided by the ‘stop band’ into two distinct regions. In the higher-frequency region, the maximum growth rate, as well as the width of the unstable spectrum, decrease with increasing relative ion concentration. For η > ηc, the instability is completely suppressed. In the lower-frequency region, however, the maximum growth rate and the extension in k space may increase with η.
Magnetohydrodynamic combustion waves in aligned fields
Authors: Asano N.
Published: March 2009

Steady magnetohydrodynamic combustion waves for a perfectly conducting, electrically neutral perfect gas in an aligned field are examined in phase space, taking into account the effects of viscosity and the thermal conduction as transport processes. Steady defiagration does not exist. Conditions to be satisfied by the initial and final states of detonation waves are derived, which may include an extension of the evolutionarity condition and the Taniuti—Resler relation to shock waves with finite width and energy release. A constraint on the shock wave is given in a conservation form. The exact solution of the final state is also given in such a way that it depends linearly on the energy supply, and may be classified completely by means of the parameters of the solution itself.
Hydrodynamical description of one-component weakly coupled plasmas
Authors: Rozmus W.
Published: March 2009

Starting from the Vlasov–Landau kinetic equation, linearized around the global equilibrium state and assuming the finite dimensional approximation to the non-hydrodynamical subspace, we derive the hydrodynamical equations for a weakly coupled, one-component plasma. Explicit expressions are given for the transport coefficients and frequencies of the hydrodynamical modes. These results describe the influence of the plasma oscillations on the hydrodynamical behaviour of the system. Certain differences are obtained compared with the standard phenomenological approach. Also the real part of the frequency for the plasma mode in our model is in agreement with the Bohm–Gross dispersion relation.
An analytical local approach to flux-conserving tokamak equilibrium
Authors: Ramos J. J
Published: March 2009

A solution to the Grad–Shafranov equation is obtained by expanding the MHD equilibrium functions in half-integer powers of the poloidal flux, about the magnetic axis. The poloidal angle dependence of the expansion coefficients is solved for, from a sequence of ordinary linear differential equations with constant coefficients. Flux conservation is achieved after calculating the inverse rotational transform, by requiring it to be invariant during the pressure rise.
Convection of a weakly ionized plasma in a strong magnetic field: non-axisymmetric waves
Authors: Shivamoggi Bhimsen K. , Uberoi Mahinder S.
Published: March 2009

Convective instability of a weakly ionized plasma contained in a narrow gap between two metal cylinders is studied considering non-axisymmetric waves. The case with the applied magnetic field in the azimuthal direction due to a central electrode is treated. The results show that the non-axisymmetric waves are more stable than their axisymmetric counterparts.
The resistive evolution of force-free magnetic fields. Part 3. Cylindrical geometry
Authors: Reid J. , Laing E. W.
Published: March 2009

Equations describing the resistive evolution of a cylindrically symmetric magnetic field through force-free states enable us to study its response to externally applied electric fields. The process is relaxational, and, under certain conditions, the final state is a reversed field configuration. We show, moreover, that the non-standard nature of the equations leads to a non-trivial (adiabatic) evolution in the case of vanishing resistivity.
Magnetoacoustic oscillations in a finite-beta current carrying plasma column
Authors: Sawley M. L.
Published: March 2009

Forced magnetoacoustic oscillations in a fully ionized, non-uniform, current carrying plasma column of finite beta are treated theoretically. The results of numerical calculations are given for the specific case of diffuse pinch equilibrium configurations. It is found that, for these configurations, the amplitude of the axial component of the oscillating magnetic field is enhanced and the frequency at which magnetoacoustic resonance occurs is raised. It is also found that the presence of an equilibrium axial current produces a substantial azimuthal component, in addition to the axial component, of the oscillating magnetic field.
Method for predicting the properties of cyclotron harmonic waves from the perpendicular dispersion relation
Authors: Lembège B.
Published: March 2009

A theoretical method is proposed for predicting the properties of the backward propagating cyclotron harmonic waves from the simple dispersion curve for perpendicular propagation. This method is illustrated for the frequency range 1 ω÷ωc ω 2, where ω and ωc, are, respectively, the wave and electron cyclotron frequencies, and is applicable from very low to infinite plasma densities. The behaviour of the backward propagating cyclotron harmonic wave in the whole propagation space and then in the real space can be easily deduced. The method can be extended to any dispersion branch of backward cyclotron harmonic waves.
Finite-Larmor-radius effects on anisotropy-driven electromagnetic modes in high-beta plasmas
Authors: Goedert J. , Mondt J. P.
Published: March 2009

From hybrid-kinetic theory an eigenvalue equation for electromagnetic perturbations with ω ≈ ωci in collisionless theta-pinches with anisotropic ion energy was recently derived. This equation is presently reduced to two ordinary second-order linear differential equations by an expansion in the thermal ion Larmor radius. The leading-order correction terms contain Cherenkov resonances absent in the homogeneous case, which are reached for speeds ≈ υ| β|-½ and wave-numbers typical for unstable modes in the homogeneous case, indicating the importance of Cherenkov resonance on the stability of modes driven by ion energy anisotropy. These equations are supplemented by appropriate boundary conditions for the case when the plasma is surrounded by a cylindrical, perfectly conducting wall. For weak inhomogeneities a local dispersion equation is obtained. The physical mechanism underlying the influence of Cherenkov resonance parallel to the confining magnetic field as a FLR effect on stability behaviour is illustrated.
Excitation of high-frequency waves with mixed polarization by streaming energetic electrons
Authors: Lee L. C. , Wu C. S. , Freund H. P. , Dillenburg D. , Goedert J.
Published: March 2009

The excitation of the slow extraordinary and electron whistler modes with frequencies in the vicinity of the electron plasma frequency is investigated for a plasma which is composed of thermal and suprathermal electrons. Ion dynamics are ignored. The suprathermal electrons are assumed to comprise a long, anisotropic tail parallel to the ambient magnetic field. Instability is found to occur via a relativistic, anomalous gyroresonance with the suprathermal electrons, and to excite waves with frequencies above and below the electron plasma frequency. Landau and cyclotron damping due to the thermal background is included in the treatment.
Parametric decay of non-ducted whistler-mode signal
Authors: Nenovski P. , Shukla P. K. , Tagare S. G. , Zhelyazkov I.
Published: March 2009

It is shown that a whistler-mode signal propagating obliquely to the external magnetic field can parametrically decay into a daughter wave and an ion cyclotron wave. A dispersion relation involving a three-wave decay process is derived. Application of our results in space plasma is pointed out.
Stationary states of two-dimensional magnetohydrodynamic turbulence: non-dissipative limit
Authors: Calinon Ronald , Merlini Danilo
Published: March 2009

A class of exact stationary statistical states for the inviscid magnetohydrodynamic equations in two dimensions and in various geometries is found and the corresponding fluctuation spectra are calculated. Some solutions agree with previous computations in the canonical ensemble while other solutions are found. In particular, the Navier—Stokes limit is recovered and maximum cross helicity solutions exist in two dimensions. The difficulty of proving existence and uniqueness of statistical solutions for non-dissipative two-dimensional turbulence is quoted in terms of rugged constants and associated Gibbs measure.
The effect of current shear on the tearing instability
Authors: Barker R. J. , Buneman O.
Published: March 2009

A fully relativistic stream superposition model is employed to conduct a linear numerical simulation of a self-consistently confined sheet of collisionless, neutral plasma. This multi-stream model employs a novel variable termed the ‘canonical momentum potential’ (or ‘action function’) to follow the ion and electron dynamics. For the classic, unsheared sheet pinch, growth rates obtained for the tearing instability are in reasonable agreement with previous estimates using an approximate Vlasov approach. Current shear is then introduced into the sheet and growth rates are again measured. Stabilization of the shorter wavelength modes is observed.
Corrigendum
Authors: Infeld E. , Rowlands G.
Published: March 2009

In this note we investigate the stability of large-amplitude longitudinal relativistic plasma waves. We find that they are secularly stable, that is, small perturbations grow in time proportional to time but not exponentially with time. Similar results have recently been obtained for transverse waves by Romeiras (1978)
Modulational instability of electrostatic ion cyclotron wave in a two-electron-temperature plasma
Authors: Lisak M.
Published: March 2009

A three-dimensional nonlinear Schrüdinger equation for an electrostatic ion cyclotron wave coupled to an ion-acoustic wave in a collision-free plasma consisting of cold ions and two-temperature electrons is derived using the reductive perturbation method. It is shown that a range of wavenumbers corresponding to the instability of a plane electrostatic ion cyclotron wave against a two-dimensional modulation depends on the ratio of temperature of hot and cold electron components.
Convective instability of a plasma slab in a magnetic field
Authors: Bhimsen K. , Shivamoggi  , Mahinder  , Uberoi S.
Published: March 2009

Convective instability of a plasma slab (contained between two metal walls) subject to a longitudinal external magnetic field is studied. The results show that (i) increase in the ionization rate Z causes a reduction in the stability of the plasma; (ii) the instability persists in the limit k ⇒ 0.
Functional calculus in strong plasma turbulence
Authors: Ahmadi Goodarz , Hirose Akira
Published: March 2009

The theory of electrostatic plasma turbulence is considered. The basic equations for the dynamics of the hierarchy of the moment equations are derived and the difficulty of the closure problem for strong plasma turbulence is discussed. The characteristic functional in phase space is introduced and its relations to the correlation functions are described. The Hopf functional equation for dynamics of the characteristic functional is derived, and its equivalence to the hierarchy of the moment equations is established. Similar formulations were carried out in velocity-wave vector space. characteristic functional are considered and their relationships are studied. An approximate solution for Hopf's equation for the nearly normal turbulence is obtained which is shown to predict diffusion of the mean distribution function in velocity space.
Effects of toroidal field ripple on suprathermal ions in tokamak plasmas
Authors: Goldston R. J. , Towner H. H.
Published: March 2009

Analytic calculations of three important effects of toroidal field ripple on suprathermal ions in tokamak plasmas are presented. In the first process, collisional ripple-trapping, ions become trapped in local magnetic wells near their banana tips owing to pitch-angle scattering as they traverse the ripple on barely unripple-trapped orbits. In the second process, collisionless ripple-trapping, ions are captured (again near a banana tip) owing to their finite orbits, which carry them out into regions of higher ripple. In the third process, banana-drift diffusion, fast-ion banana orbits fail to close precisely, due to a ripple-induced ‘variable lingering period’ near the banana tips. These three mechanisms lead to substantial radial transport of banana-trapped, neutral-beam-injected ions when the quantity α*≡ε|τ|/Nqδ is of order unity or smaller.
Marginal stability and critical thickness of strong double layers
Authors: Wahlberg Christer
Published: March 2009

Previous investigations of the stability, in particular the critical thickness for marginal stability, of an electron configuration of double-layer type are extended in order to include effects of (i) unequal plasma densities in the field-free regions, and (ii) finite values of the parameter eΔø/kTe. The results obtained are compared with the corresponding quantities in various experiments, and a striking coincidence is found.
Reciprocity relations between currents and fields in plane-stratified magnetoplasmas
Authors: Schatzberg A , Altman C.
Published: March 2009

The dyadic Green's function, relating currents and fields in transverse-k space, is determined for a homogeneous magnetoplasma, and then extended to a plane- stratified system by means of the reflexion and transmission matrices of the medium, taking into account multiple reflexions at the source and observation points. A conjugate problem is next considered, in which the propagation eigenvectors have a certain mirror symmetry with respect to those in the original problem and, by relating the scattering matrices in the two cases, a Lorentz-type reciprocity theorem is derived relating currents and fields in the original problem with the mirrored currents and their associated wave fields which characterize the conjugate problem.
Production of plasma vortices by lower-hybrid waves
Authors: Yu M. Y. , Shukla P. K. , Rahman H. U.
Published: March 2009

Nonlinear excitation of electrostatic and magnetostatic zero-frequency modes by finite-amplitude lower-hybrid waves is considered. It is found that modulational instabilities can give rise to enhanced plasma vortices. Dispersion relations, as well as analytical expressions for the growth rates, are obtained. The enhanced vortices may cause anomalous cross-field diffusion which can affect plasma confinement in tokamak devices when lower-hybrid waves are used for plasma heating or current drive. We found that magnetic fluctuations associated with the parametrically driven magnetostatic mode are of particular importance in tokamak plasmas.
Nonlinear theta-pinch equilibria
Authors: Abraham-Shrauner B.
Published: March 2009

Analytic solutions for cylindrical, rigid-drift equilibria were searched for by checking the invariance of the second-order, nonlinear differential equations of the line density and particle density under one-parameter Lie groups. No invariance was found for the cylindrical screw-pinch for the polytrope index γ ╪ 2 of the pressure equation of state. For the Z-pinch, the differential equation for the line density for arbitrary γ is invariant under one group and reduces by Euler's method to an intractable first-order, nonlinear differential equation. In the case of a θ-pinch, the nonlinear differential equations for the particle density and line density are invariant at least under the translation group. The particle density is found as an implicit function of the radial distance r, involving incomplete beta functions of the γth power of the particle density.
Stability of Doublet III plasmas against axisymmetric resistive MHD modes
Authors: McLain Fred W. , Jensen Torkil H.
Published: March 2009

Stability of doublet plasmas in the Doublet III device against resistive axisymmetric MHD modes has been studied. The real characteristics of the device were modelled as accurately as possible. Thus, for example, the actual toroidal geometry was used, the field shaping coils (F-coils) which surround the plasma were included, and the location of real limiters was incorporated for determination of the plasma surface. We have used two parameters to model the plasma current distribution and the equilibrium boundary conditions: one describes the flatness of the current profile, the other describes the fraction of the poloidal plasma flux contained within the separatrix. Thus we have determined stability as a function of these two parameters. If the fluxes at the F-coils are kept fixed, there are stable as well as unstable regimes in this two-dimensional parameter space. If the F-coil fluxes are controlled to imitate the presence of virtual F-coils with fixed fluxes located closer to the plasma, it is possible to stabilize the plasma. This stabilization is discussed in the paper and numerical examples are given. Finally, the relationship between the results of this paper and experimental observations from Doublet III is discussed.
Nonlinear equilibrium and stability analysis of rippled, partially neutralized, magnetically focused electron beams
Authors: Cuperman S. , Petran F.
Published: March 2009

In the first part of this work a higher-order solution of the anharmonic oscillator equation describing the nonlinear rippled equilibrium state of magnetically focused, partially neutralized electron beams is given. Thus, using the method of harmonic balance, we derive a ripple-&litude solution of the form

where ø=ω1t+β0,ω1 being the nonlinear proper frequency and β0 a phase shift depending on the initial conditions. In the second part of the work we carry out a stability analysis of the nonlinear equilibrium state found in the first part with respect to long- and short-wavelength surface space-charge perturbations. In the framework of a local approximation the wave equation for the rippled beam is found to be a Hill type of equation which contains harmonic terms up to cos 3kSz (ks is the wavenumber of the ripple). This equation is solved by a resonant-mode coupling method; coupling of fast-fast, slow-slow and slow-fast waves is considered. The growth rates and band widths for different possible wave couplings are derived and compared.
Kinetic theory for a short-wavelength lasing plasma
Authors: Heffernan Daniel M. , Liboff Richard L.
Published: March 2009

A kinetic analysis is made of a reacting plasma dominated by three-body recombination and ionization, together with collisional and radiative excitation and de-excitation of atomic states. The plasma includes excited atoms, ions, electrons and photons. The kinetic theory yields rate equations for these species, together with explicit expressions for relevant rate coefficients. In the limit of spatial homogeneity and assuming atom and electron densities are close to equilibrium, an explicit form is obtained for the radiation absorption coefficient per unit length. A criterion is then constructed for population inversion. Application to a helium-like active medium (e.g. Al+11) and hydrogen-like passive medium (e.g. A1+12), at electron temperature of 300 eV, reveals that population inversion ensues at electron densities in excess of 1020 cm−3. Algebraic solution of atomic state rate equations demonstrates that the absorption coefficient grows insensitive to photon-atom interactions with increasing electron density.
The effect of plasma compressibility on the Kelvin-Helmholtz instability
Authors: Prialnik Dina , Eviatar Aharon , Ershkovich Alexander I.
Published: March 2009

The Kelvin-Helmholtz (KH) instability of a tangential discontinuity between two compressible plasmas in relative motion is investigated, by solving the dispersion equation for two cases. In the first, neutrals are excluded; in the second, collisions between neutrals and ions are introduced in the form of a drag force in the momentum equation. The velocity of neutrals is assumed to be perpendicular to the interface. In both cases the growth rate of the KH instability is obtained as a function of the density jump between the plasmas. Although it has often been remarked that compressibility should, in general, stabilize a plasma, it is found that this ceases to be true when allowance is made for a significant density jump at the interface. Thus, for a large density jump and a large velocity shear, the instability growth rate in a compressible plasma may considerably exceed the growth rate obtained when incompressibility is assumed. Collisions, it is shown, may either stabilize or destabilize a tangential discontinuity, depending on the change in the product of density and collision frequency (pv), as one moves with the neutrals across the interface; when pv decreases, the instability is enhanced (and vice versa).
Spherically symmetric high-velocity plasma expansions into background gases
Authors: Tan Tai-Ho , Borovsky Joseph E.
Published: March 2009

Spherically symmetric plasmas with high expansion velocities have been produced by irradiating targets with eight beams from the Helios CO2 laser in the presence of gases at various pressures. Attention was given to the properties of the target-emitted ions in order to obtain information about the ion acceleration mechanisms in plasma expansions. Photo-ionization of the ambient gases by the soft X-ray emission from the laser-irradiated targets produced background plasmas, permitting plasma counterstreaming experiments to be performed in spherical geometry. Successful laser-target coupling in the presence of background gases is obtained, modification of the ion acceleration in accordance with isothermal-expansion models is observed, and an absence of collective coupling between collisionless counterstreaming plasmas is found.
Covariant ponderomotive Hamiltonian
Authors: Achterberg A.
Published: March 2009

A covariant formulation for the ponderomotive Hamiltonian is developed using Lie-transform perturbation theory. The case of unmagnetized as well as magnetized particles is discussed.
Relaxation of magnetic field in a plasma via the tearing mode
Authors: Auluck S. K. H.
Published: March 2009

A simple argument based on energetics is presented to bring out the similarities between diverse plasmas which undergo current filamentation. The predictions of this argument are found to be in agreement with more detailed theoretical results and experimental data.
Collisional transfer of energy and momentum between drifting tri-Maxwellians
Authors: Hernández R. , Marsch E.
Published: March 2009

The collisional transfer tensor for energy and transfer vector for momentum exchange between drifting tri-Maxwellians for an arbitrary central interaction force between neutral and/or ionized particles are evaluated. We introduce the new concept of a generalized Rosenbluth potential whereby the heat and momentum exchange rates can be written in a concise form. We also discuss the associated time-scales which depend on the masses, densities, temperatures, and drift velocities of the two colliding species.
A comparative measurement of the neutral density and particle confinement time in EBT-S
Authors: Glowienka John C. , Richards Roger K.
Published: March 2009

The neutral density and particle confinement time in the ELMO Bumpy Torus-Scale Experiment (EBT-S) have been determined by two different techniques. These involve a spectroscopic measurement of molecular and atomic hydrogen emissions and a time-decay measurement of a fast-ion population using a diagnostic neutral beam. The results from both diagnostics exhibit identical trends for either estimate, although the absolute values differ by a factor of 2 to 3. The observed variations with fill gas pressure and microwave power from either technique are consistent with measurements of electron density and temperature. In this paper, the measurement techniques are discussed, and the results are compared in the context of consistency with independently observed plasma behaviour.
A comparative study of the instabilities of two classes of nonlinear waves in cold plasmas
Authors: Romeiras F. J. , Rowlands G.
Published: March 2009

Results are presented of the stability analysis against small parallel perturbations of two classes of nonlinear waves in cold unmagnetized electron plasmas emphasizing similarities and differences. The first class is a stationary longitudinal wave set up by two counter-streaming cold electron beams; the second class is a mixed transverse-longitudinal standing wave in a relativistic plasma with a circularly polarized transverse electric field whose amplitude is periodically modulated in the longitudinal direction. The perturbation dispersion relations are discussed for all perturbation wavenumbers and all nonlinear wave amplitudes. Particular attention is given to the appearance of gaps in those dispersion relations.
Kinematic and temperature restrictions on the electron cyclotron maser instability
Authors: Robinson P. A.
Published: March 2009

The ranges of temperature T, harmonic number s and wave propagation angle θ in which the loss-cone-driven electron cyclotron instability can exist are found to be limited by opposing contributions to the growth rate from adjacent harmonics. For waves with refractive index n ⋍ 1 it is found that instability is possible only if T and s satisfy saT ≲ C with a = 2 − 2·5 and where the constant C is determined by θ and the form of the distribution function. It is argued that the corresponding restrictions for waves with very large or very small n are less severe. Instability is found to be forbidden for waves propagating outside a range |θ − 90°| < φ(s), except if θ ⋍ 0, where π(s) is independent of temperature and sin2φ(s) ⋍ s−1; this restriction limits the range of potentially unstable frequencies at a given harmonic.
Self-interaction of compressional hydromagnetic waves in a cylindrical plasma-filled waveguide
Authors: Ghosh B. , Das K. P.
Published: March 2009

Nonlinear behaviour of azimuthally symmetric compressional hydromagnetic waves propagating along a cylindrical cold magnetized plasma-filled waveguide is investigated. A nonlinear Schrödinger equation describing the nonlinear evolution of such waves is derived. Numerical evaluation of the dispersive and nonlinear terms reveals that such waves are modulationally stable in the fundamental radial mode of propagation. Calculations are presented for the amplitude dependent frequency and wavenumber shifts.
Effect of ion temperature on ion-acoustic solitons in a two-ion warm plasma with adiabatic positive and negative ions and isothermal electrons
Authors: Tagare S. G.
Published: March 2009

Ion-acoustic solitons in a collisionless plasma with adiabatic positive and negative ions with equal ion temperature and isothermal electrons are studied by using the reductive perturbation method. The basic set of fluid equations is reduced for the fast ion-acoustic wave to the Korteweg–de Vries and modified Korteweg–de Vries equation and for the slow ion-acoustic wave to the Korteweg–de Vries equation. Stationary solutions of these equations are obtained and the effect of ion temperature on fast and slow ion-acoustic solitons is investigated.
Collisionless evolution of ion distributions in the presence of ion cyclotron resonance heating
Authors: Anderson D. , Eriksson L.-G. , Lisak M.
Published: March 2009

Explicit analytical solutions are given for the collisionless time evolution of the distribution function for ions absorbing RF wave power through ion cyclotron resonance heating in a tokamak. Two different scenarios are considered: (i) conventional ICRH and (ii) combined neutral beam heating and ICRH with the RF wave frequency tuned to the ion cyclotron resonance frequency of the injected ions. Finally, the effect of particle trapping on the time development of the distribution function is also analysed.
Local analysis of extraordinary-mode stability properties for relativistic non-neutral electron flow in a planar diode
Authors: Davidson Ronald C. , Uhm Han S.
Published: March 2009

The extraordinary-mode eigenvalue equation is used to investigate the local stability properties of relativistic, non-neutral electron flow in a planar diode. The local stability analysis assumes gentle equilibrium gradients and short perturbation wavelengths. The lowest-order local dispersion relation is derived assuming that localized solutions for the eigenfunction exist, and stability properties are investigated numerically over a wide range of System parameters for perturbations with frequency small in comparison with the electron cyclotron frequency. It is found that the local dispersion relation supports three solutions in this frequency regime. One of the solutions corresponds to a stable diocotron mode driven by the local density gradient. The other two branches are found to exhibit instability over a wide range of electron density. These modes are electromagnetic in nature and require relativistic electron flow with velocity shear in order for instability to exist. Moreover, the growth rate of the unstable electromagnetic mode can be substantial (a few per cent of the electron cyclotron frequency).
An approximate theory of electromagnetic wave propagation in a weakly relativistic plasma
Authors: Sazhin S. S.
Published: March 2009

An approximate analysis of different types of electromagnetic wave propagation in a weakly relativistic electron plasma is presented. The particular case of wave propagation near the cold plasma cut-offs is considered, and possible applications of the results to diagnostics of magnetospheric parameters are discussed. It is pointed out that wave propagation near plasma resonances in some cases requires relativistic consideration, especially for extraordinary waves. Almost parallel right- and left-hand polarized waves as well as almost perpendicular ordinary and extraordinary wave propagation are considered in detail. It is shown that, in the vicinity of certain frequencies, relativistic effects on the refractive index of these waves cannot be disregarded even when the electron energy is quite small. The problem of wave energy focusing along and perpendicular to the magnetic field is considered with relativistic effects taken into account.
Effect of ion temperature on ion-acoustic solitons in a two-ion warm plasma with adiabatic positive and negative ions and isothermal electrons
Authors: Tagare S. G.
Published: March 2009

In the above mentioned paper, table 1 is incorrect and the correct version is given below. Thus the result which was there obtained, namely that the coefficient of the nonlinear term of the modified KdV equation becomes negative, is not correct and, in fact, the coefficient is always positive.
Two-stream and filamentation instabilities for a light ion beam—plasma system
Authors: Okada Toshio , Schmidt Winfried
Published: March 2009

Electrostatic two-stream and electromagnetic filamentation instabilities for a light ion beam penetrating a plasma are investigated. The dispersion relations of these instabilities including the effect of plasma heating by the ion beam are solved analytically and numerically. Stability conditions are derived for propagation through a plasma. Attention is paid to the finite size effects of beams with small diameters of the order 0·1 cm typical for pinched gas discharges. The results are illustrated by plotting stability boundaries for a 100 keV proton beam propagating through a plasma.
Transport properties of the two-component strongly coupled plasma
Authors: Cauble R. , Rozmus W.
Published: March 2009

The systematic derivation of transport coefficients for the semi-classical two-component strongly coupled plasma is presented. Starting from a detailed kinetic memory function formulation, a hydrodynamic projection operator method is applied to find a transport model equivalent to the two-Sonine polynomial approximation. The electron thermal conductivity K, d.c. electrical conductivity σ, and the thermoelectric power coefficient are expressed in terms of exact static correlation functions, which are calculated in the hypernetted chain approximation. Numerical values of k and σ are given and comparisons are made with other theories and molecular dynamics simulations of strongly coupled hydrogen. Predictions of σ and k for strongly coupled carbon are also presented.
Nonlinear stage of the modulational instability of a whistler wave. Part 1
Authors: Karpman V. I. , Shagalov A. G.
Published: March 2009

The development of the modulational instability of a whistler wave is investigated in the linear and subsequent nonlinear stages. It is shown that some predictions of the linear theory remain valid up to the tirne when the wave amplitude modulation rate is of the order of unity.
Kinetic theory of the high-frequency part of the slow electromagnetic mode in weakly ionized gas-discharge argon plasma with inelastic collisions
Authors: Žigman V. J. , Milić B. S.
Published: March 2009

The spectral characteristics of the high-frequency part of the slow electromagnetic mode, specific for plasmas placed in an external d.c. electric field, as well as the features of the corresponding instability, are analysed for weakly ionized argon gas-discharge plasmas with E/n ranging from 25 to 150 Td, and with electron temperatures between 60000 and 70000 K. The analysis is based on the linear theory of perturbation, and the dynamics of the electrons is described by appropriately modified kinetic equations for the one-particle distribution function. Attention is focused on the collisional processes between electrons and neutrals, and both elastic and excitational collisions are taken into account. Apart from the ‘indirect’ collision effects (modifications of the form of the electron steady-state distribution function, evaluated here analytically, with the thermal motion of the neutrals included), their ‘direct’ influence (arising from perturbations of the collision integrals) is also significant in the electron temperature range considered. As a consequence of the ‘direct’ influence of inelastic collisions, in particular, the mode studied was found to exist in two distinctly separate wavelength ranges. The instability was found to develop only in the one corresponding to shorter wavelengths (below some 30 cm).
Containment forces in low energy states of plasmoids
Authors: Wells Daniel R. , Hawkins Lawrence Carl
Published: March 2009

The application of Hamilton's principle to the problem of the determination of the structure of low free energy state plasmoids is discussed. It is shown that Clebsch representations of the vector fields and representations involving side conditions on the functional result in the same sets of Euler–Lagrange equations. The relationship of these representations to the problem of containment forces in vortex structures (plasmoids) is considered. It is demonstrated that the lowest free energy state of an incompressible plasma is always Lorentz force and Magnus force free. For a compressible plasma obeying the adiabatic gas laws, the Magnus force is finite. Introduction of conservation of angular momentum as an additional side condition also results in finite containment forces.
A general solution condition for collisionless sheaths
Authors: Main Geoffrey L. , Lam S. H.
Published: March 2009

A general solution condition for collisionless sheaths is developed. Previous work has assumed that the Bohm criterion or the generalized Bohm criterion ensures a self-consistent sheath solution. This paper shows that for nonmonotonic collisionless sheath structures, such as double sheaths containing trapped ions, the generalized Bohm criterion is a necessary but not a sufficient condition. The general solution condition developed is always sufficient and the generalized Bohm criterion is shown to be special case of it. The general solution condition is applied to a double emitter sheath containing trapped ions. First, it is shown that the low-energy part of the plasma ion distribution coming into the sheath cannot be neglected as claimed in some analyses, because the shift in mean ion velocity through the pre-sheath (generalized Bohm speed) depends strongly on low-energy ions. Second, it is shown that the presence of trapped ions moves the point of critical self-consistency away from the collisionless sheath-neutral plasma asymptotic match and into the collisionless sheath. Consequently, both the sheath structure and the generalized Bohm speed depend on the amount of trapped ions. Thus collisional effects may dominate the structure of a presumably collisionless sheath through the trapping mechanism and the collisional pre-sheath which determines the low-energy ion component entering the collisionless sheath.
Hydrodynamic analogy of nonlinear plasma flows
Authors: Bazdenkov S. V. , Pogutse O. P.
Published: March 2009

Some new aspects of an analogy between plasma in a magnetic field and a rotating shallow liquid are considered. Effects of gyroscopic screening and resonant wave excitation are studied. The results of numerical simulations of the nonlinear evolution of sheared flows in rotating shallow water are presented.
Thermodynamic derivation of Saha's equation for a multi-temperature plasma
Authors: Morro Angelo , Romeo Maurizio
Published: March 2009

The ionization equilibrium between the constituents of a multi-temperature plasma is investigated within the thermodynamics of fluid mixtures. As a result, a law of mass action is derived that, in the approximation of ideal gases for the constituents, leads to a direct generalization of Saha's equation. The main properties of this generalization are discussed, and contrasted with those of other equations which have appeared in the literature.
Electrostatic Rossby-type ion plasma waves
Authors: McKenzie J. F. , Dougherty M. K.
Published: March 2009

It is shown that a plasma in which the background magnetic field varies in a direction perpendicular to its line of action can support ‘Rossby-type’ electrostatic waves at frequencies very much less than the ion gyrofrequency. The intrinsic wave propagation mechanism at work is structurally similar to that in the atmospheric Rossby wave, which comes about from fluid perturbations being in quasi-geostrophic equilibrium (i.e. the Coriolis force nearly balances the pressure gradient) and the latitudinal variation of the vertical component of rotational frequency vector (the β-effect) so that the time rate of change of the vertical component of the fluid vorticity is equal to the northward transport of the planetary vorticity. In a plasma this ‘geostrophic balance’ arises from the near-vanishing of the Lorentz force on the ion motion while the β-effect is provided by the transverse spatial variation of the ambient magnetic field. Unlike the atmosphere, however, such a magnetized plasma is capable of supporting two distinct types of Rossby wave. The interesting dispersive and anisotropic features of these waves are revealed by the properties of their wave operators and described in terms of the geometry of their wavenumber surfaces. Since these surfaces intersect, inhomogeneity or nonlinearity will give rise to strong mode-mode coupling in regions where the phases of both modes nearly match.
Mean-field magnetohydrodynamics associated with random Alfvén waves in a plasma with weak magnetic diffusion
Authors: Hamabata Hiromitsu , Namikawa Tomikazu
Published: March 2009

Using first-order smoothing theory, Fourier analysis and perturbation methods, a new equation is derived governing the evolution of the spectrum tensor (including the energy and helicity spectrum functions) of the random velocity field as well as the ponderomotive and mean electromotive forces generated by random Alfvén waves in a plasma with weak magnetic diffusion. The ponderomotive and mean electromotive forces are expressed as series involving spatial derivatives of mean magnetic and velocity fields whose coefficients are associated with the helicity spectrum function of the random velocity field. The effect of microscale random Alfvén waves, through ponderomotive and mean electromotive forces generated by them, on the propagation of large-scale Alfvén waves is also investigated by solving the mean-field equations, including the transport equation of the helicity spectrum function.
Properties of waves in an ion-beam plasma system
Authors: Zank G. P. , McKenzie J. F.
Published: March 2009

In this paper a multi-fluid approach is used to describe electrostatic interactions in an ion-beam plasma system. The structure of the wave equation governing the system exhibits the anisotropic and dispersive nature of the waves, whose properties are analysed in terms of the dispersion relation. The main purpose of this paper is to classify the different waves that can arise in an ion-beam plasma system in a systematic fashion. The classification is facilitated by introducing a three-parameter CMA diagram that illustrates the topological changes in not only the wavenumber, or refractive-index, surface but also the ray-velocity surface. Furthermore, an analytic expression governing wave amplification in an ion-beam plasma is incorporated within the framework of a generalized CMA diagram. Such a description provides a simple interpretation for the onset of wave amplification in terms of a topological change in the refractive-index surface. It is hoped that by collating the wave properties in a unified form, many of the complicated wave features observed in an experiment may be interpreted more easily.
Some particular cases of oblique whistler-mode propagation in a hot anisotropic plasma
Authors: Sazhin S. S. , Sazhina E. M.
Published: March 2009

Explicit formulae for the refractive index describing oblique whistler-mode propagation at frequencies corresponding to ξ1 = −φ ≡ −0·924 (but |ξn| ≫ 1 when n ≠ 1), ξ0 = φ (but |ξn| ≫ 1 when n ≠ 0) and ξ0 = −ξ1 = φ (where ξn ≡ (ω − nΩ)/k‖w‖ are the arguments of the plasma dispersion function) are derived and analysed for two limiting cases of quasi-longitudinal and quasi-electrostatic propagation of the waves.
Effect of electron temperature gradient on the modulational instability of drift waves and anomalous transport due to drift-wave turbulence
Authors: Majumdar D.
Published: March 2009

A nonlinear drift-mode equation including the effect of an electron-temperature gradient has been derived. To discuss modulational instability, we have obtained a nonlinear evolution equation for the drift mode from a third-order secularity-elimination condition using a multiple time- and space-scales technique. The effect of localized structure on the transport process has been investigated.
On nonlinear circularly polarized Alfvén waves
Authors: Mann G.
Published: March 2009

Finite-amplitude circularly polarized Alfvén waves propagating along the ambient magnetic field are described by a derivative nonlinear Schrödinger-type equation. It leads to stationary, solitary and periodic solutions with phase modulations. The amplitude–width relation for these solitons is shown to be an inequality. The relevance of the results is briefly discussed for particular phenomena in the solar wind.