bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the global availability of misoprostol
Authors: Fernandez Maria M. , Coeytaux Francine , Gomez Ponce de León Rodolfo , Harrison Denise L.
Published: March 2009

Objective

To assess the worldwide availability of misoprostol. Documenting the extent of misoprostol use in obstetrics‐gynecology is difficult because the drug typically is unregistered for such indications.

Methods

Data for 2002–2007 on annual sales (measured in weight) to hospitals and retail pharmacies, plus manufacturer prices per 200‐µg misoprostol, were analyzed for medications containing misoprostol alone or combined with a nonsteroidal anti‐inflammatory drug (NSAID); regional and country‐specific trends were identified. Consumer prices per pill are documented for all formulations of registered medications.

Results

Of the misoprostol sold worldwide, 70% was misoprostol‐NSAID‐combination drugs; of this, 91% was sold in North America and Western Europe. Asia sold the most misoprostol‐only drugs; sales increased dramatically in Bangladesh (by 128%) and India (646%), where various low‐price brands are sold. Misoprostol sales decreased in Latin America but increased in the Middle East‐North Africa and Sub‐Saharan Africa; these regions generally had low amounts sold per population.

Conclusion

Availability is improving in some low‐income regions where misoprostol could significantly reduce maternal deaths due to postpartum hemorrhage and unsafe abortion.
European civil society and citizenship: Complementary or exclusionary concepts?
Authors: Smismans Stijn
Published: March 2009

In the European integration process the two concepts of citizenship and of civil society have been introduced by the EU institutions and policy-makers in order to build support for the new supranational polity. However, the concepts have emerged at different moments in time and have been defined in such a way that they appear nearly exclusionary. Only during the recent constitutional debate has an attempt been made to make “European civil society” and “European citizenship” more complementary.
Computer simulation of synchrotron radiation in two dimensions
Authors: Wang L. T. , Dawson J. M. , Lin A. T. , Menyuk C. R. , Tajima T.
Published: March 2009

Plasma effects on the emission of synchrotron radiation are investigated using a two-dimensional electromagnetic relativistic simulation code. Results are compared with those for a vacuum; it is found that the emission lies between the vacuum emission for nc and nc + 1 where nc is the critical harmonic for EM wave propagation (nc = ωp/Ω0).
A formulation for computation of a class of collision-free plasmas in two dimensions
Authors: Dungey J. W.
Published: March 2009

The restrictions imposed are that the magnetic field is everywhere in the x direction, and that no quantity varies with x, but several interesting instabilities can still occur. After some discussion of objectives, a fluid-like formulation is pursued, in which the pressure anisotropy is retained, but higher moments neglected. It shows a resonance at twice the gyrofrequency, and for electrons the constraint on the time step would be unacceptable, so they should be treated more crudely. Then the dispersion equation shows only two modes, which appear sufficiently harmless for us to proceed to computations.
A study of the mass ratio dependence of the mixed species collision integral
Authors: Garrett A. J. M.
Published: March 2009

This paper is concerned with the Boltzmann collision integral for the one-particle distribution function of a test species of particle undergoing elastic collisions with particles of a second species which is in thermal equilibrium. A previous paper studied this expression as a function of the mass ratio for the two species of particle when the test particle distribution function was isotropic in velocity space; this work generalizes that analysis to anisotropic distribution functions by expanding the distribution function in tensorial spherical harmonics. First the limit of zero mass ratio is considered: this simplifies the calculation dramatically. There is no contribution to the collision integral from the zeroth-order spherical harmonic in this limit. Then the main calculation shows how to find the terms arising from the existence of a finite mass ratio as an ascending power series in this quantity, and evaluates for each spherical harmonic the next term, linear in mass ratio. This is checked for two special cases: that of an isotropic distribution function, when the expression reduces to Davydov's form, and that arising from a cross-section inversely proportional to the collision velocity, when a comparison with the exact solution of the associated eigen problem can be made. As in the isotropic case, an exact representation of the collision integral as an expansion in mass ratio must include some terms non-analytic in this quantity and vanishing more quickly than any positive power: it is shown how these arise in the present formalism. The formulae derived here have applications to the transport theory of electrons and light ions in a predominantly neutral gas as governed by the Boltzmann equation.
The mean electromotive force generated by random Alfvén waves in a collisionless plasma under a non-uniform mean magnetic field
Authors: Namikawa Tomikazu , Hamabata Hiromitsu
Published: March 2009

The mean electromotive force generated by random Alfvén waves in a collision-less plasma is evaluated taking into account mean magnetic field gradients. It is shown that the mean electromotive force associated with a magnetic shear of the mean field and the helicity spectrum function of the random velocity field exists and has a component parallel to the mean magnetic field when it is generated by random waves propagating along the mean magnetic field and by statistically anisotropic random waves propagating in arbitrary directions. The results are applied to the magnetospheric substorms.
Similarity solutions for nonlinear Landau damping of Alfvén waves
Authors: McKenzie J. F.
Published: March 2009

In this paper we develop similarity solutions for the problem of nonlinear Landau damping of Alfvén waves. These solutions which are applicable to power-law wave spectra illustrate not only the basic feature of the damping process, namely that short-wavelength waves decay more rapidly than long-wavelength waves, but also how the damping depends on the initial strength of the power spectrum and its distribution in wavenumber.
The crossfield current-driven ion-acoustic instability in a collisional plasma
Authors: Bharuthram R. , Hellberg M. A. , Lee R. D.
Published: March 2009

Using the Bhatnagar–Gross–Krook collision model, the effects of charge-transfer and elastic ion-neutral collisions on the crossfield beam-driven ion-acoustic instability in a double plasma device are studied. Elastic collisions cause a slowing of the beam, while charge exchange gives rise to an exponential decay in ion beam density. The resultant damping of the instability is calculated and compared with experiment.
The shear Alfvén continuous spectrum of axisymmetric toroidal equilibria in the large aspect ratio limit
Authors: Kieras C. E. , Tataronis J. A.
Published: March 2009

Analytic forms for the MHD continuous spectra in axisymmetric tokamak equilibria are derived using an expansion scheme in powers of the small inverse aspect ratio. Resulting formulae for the shear Alfvén continuum have been evaluated for the shear Alfvén wave heating experiment on the Tokapole II device at the University of Wisconsin-Madison. Mode coupling, induced by toroidicity or non-circularity, is shown to occur, in first order, on and near rational surfaces for particular poloidal and toroidal mode numbers. The coupling is shown to produce gaps in the spectrum, analogous to the gaps which appear in the energy spectrum of a single electron in a periodic potential lattice.
Excitation of electromagnetic quasi-perpendicular ion cyclotron waves in collisional plasmas
Authors: Milić B. S. , Brajušković N. R.
Published: March 2009

The process of spontaneous excitation of electromagnetic (non-potential) and quasi-perpendicular (with respect to the external magnetic field) ion cyclotron waves by electron drift in a weakly ionized plasma is analysed. An infinite plasma placed in mutually parallel d.c. electric and magnetic fields is considered, and its dynamics is described by kinetic equations with BGK model collision integrals. The threshold electron drift necessary for the onset of the corresponding ion cyclotron instability is evaluated. It is shown that the instability sets in first for wavelengths much larger than the electron mean free path, so that the electron collisions, dominant in this range of wavelengths, play a facilitating rather than an impeding role in this process. The results are compared with those for the spontaneous excitation of electrostatic (potential) quasi-perpendicular ion cyclotron waves and, for the same set of plasma parameters, the threshold drift is found to be smaller for the electromagnetic waves.
Theory of runaway electrons in a Lorentz plasma
Authors: Shivamoggi Bhimsen K.
Published: March 2009

A formal method of multiple scales is used to study the effect of a harmonically varying applied uniform electric field, of magnitude much smaller than the Dreicer critical field Ec, on the runaway electrons in a Lorentz plasma.
Stabilization of electrostatic flute mode due to hot electron ring and RF field
Authors: Sanuki H.
Published: March 2009

The dynamic stabilization of electrostatic flute modes by an RF electric field is studied on the basis of the relatively simple model of a smooth cylinder with artificial gravity and an ambipolar field. It is found that the electrostatic flute modes can be effectively stabilized by the RF electric field together with the hot electron ring.
Magnetic and temperature effects on the energy loss rate of test ions
Authors: Hassan M. H. A. , Sakanaka P. H.
Published: March 2009

The energy loss rate, Ė, of test ions injected with velocity V into a Maxwellian electron-ion plasma in the presence of an external magnetic field, is studied. Most of the integrals appearing in the expression for Ė are evaluated analytically and the remaining integrals are evaluated numerically for various values of the parameters η = Ωe / ωe, x = V/ve, r = Te/Ti, and the angle of injection θ. It is shown that the effect of the magnetic field is rather small except for η > 1, the temperature ratio is important for small x (x ≤ 0·2), and the injection angle is not important.
On the cross-field flux of heat in a magnetoplasma
Authors: Woods L. C.
Published: March 2009

A new theory is developed for the transport of energy across a strong magnetic field. The mechanism is micro-convection by sheared fluid elements, and it proves to be much more effective in heat transport than classical conduction. The equivalent thermal conductivity is calculated for the electron gas in a cylindrical plasma carrying an axial current. When the plasma pressure can be neglected, this conductivity is about 400 times greater than the classical value under certain typical conditions.
Two-dimensional toroidal MHD equilibria of arbitrary cross-section
Authors: Cap Ferdinand F.
Published: March 2009

A new approach to the solution of the MHD equilibrium problem is outlined.
Whistler-mode propagation at frequencies near the electron gyrofrequency
Authors: Sazhin S. S.
Published: March 2009

Parallel whistler-mode propagation in a hot anisotropic plasma at frequencies near the electron gyrofrequency is considered by using analytical methods and a simple graphical technique, without any special restrictions on the value of the imaginary part of the plasma dispersion function argument. An exact criterion for the possibility of whistler-mode propagation in the vicinity of the electron gyrofrequency is derived. In particular it is pointed out that whistlers in this frequency interval can propagate only in a very hot and rarefied plasma submerged in a strong magnetic field. These whistlers can only be damped, the modulus of the decrement of the damping cannot exceed 1·1 times the electron plasma frequency. The refractive index remains close to unity.
Electrical conductivity for radio-frequency fields in strongly magnetized plasmas with density fluctuations
Authors: Sayasov Yu. S. , Ritz Ch. P.
Published: March 2009

A general investigation of the electrical conductivity for radio-frequency (RF) fields in strongly magnetized plasmas with small-scale density fluctuations is performed within the cold plasma hydrodynamical approximation. It is shown that in such plasmas an RF phenomenon similar to the Bohm diffusion exists: the presence of stochastic RF electric field in a turbulent plasma can lead to a strong enhancement of the RF currents flowing in the direction of the applied electric field components transverse to the magnetic field. The appearance of these turbulent drift currents favours energy transfer from the RF fields to the plasma and thus leads to their stronger damping. This effect allows us to interpret quantitatively the enhanced damping of the magnetosonic waves observed in several experiments. The magnetized radially inhomogeneous cylindrical plasmas in these experiments are characterized by density fluctuations due to drift instabilities. The theory has also a number of other applications; an example is given of the whistlers damped by the ionospheric density fluctuations.
Propagation of electromagnetic waves in a warm plasma-filled cylindrical waveguide in the presence of an external magnetic field
Authors: Ghosh Sanjay Kumar , Pal S. P.
Published: March 2009

The propagation of electromagnetic waves in a plasma-filled cylindrical waveguide in the presence of a constant external magnetic field is investigated using warm plasma theory. It is found that the waves cannot be separated into transverse magnetic and transverse electric modes; only hybrid modes are propagated. Dispersion relations are derived for zero, finite and infinite magnetic fields. Frequency shifts for the wave propagation in the case of a small magnetic field are calculated.
The thermal self-focusing of a wave beam in an underdense plasma. Part 2. Energy transfer to ions
Authors: Giles M. J.
Published: March 2009

In the second part of this paper devoted to the problem of the thermal self-focusing of an electromagnetic wave in an underdense plasma, we extend the linear theory of part 1 to include the effect of collisional energy transfer from the electrons to the ions. The eigenvalue problem which gives the spectrum of the wave modes that occur in a beam of finite width is formulated and solved for the case of a square beam profile. From the resulting dispersion relation, we derive the unstable wavenumber band and the maximum spatial growth rate. An approximate solution of the dispersion relation is obtained for the case of a thin beam which illustrates how the stabilizing influence of energy transfer to the ions affects the unstable spectrum. In addition, some numerical solutions of the dispersion relation are presented for the cases of ionospheric modification by a power satellite microwave beam and by an ionospheric HF heater.
Weakly relativistic dielectric tensor and dispersion functions of a Maxwellian plasma
Authors: Krivenski V. , Orefice A.
Published: March 2009

In order to study the absorption and emission properties of a magnetized plasma in the electron cyclotron range of frequencies, the weakly relativistic (Shkarofsky) plasma dispersion functions are simply and exactly expressed in terms of the Z function. This gives a useful working form to the dielectric tensor, for any wave vector and harmonic number, covering also the case of electron Maxwellian distributions drifting along the magnetic field.
Stabilizing and destabilizing influence of the Hall effect in aZpinch with a step-like volume current profile
Authors: Schaper Ulrich
Published: March 2009

A dispersion relation is derived for axisymmetric perturbations of an infinitely extended circular incompressibleZpinch with a step-like volume current profile. This profile is characterized by constant but different volume currents in different regions of the plasma and at the step surface there is a sheet current. The stability boundaries are shifted compared with stability limits in ideal MHD theory. For equilibria with no current reversal there is a new stable range whereas for equilibria with current reversal there is a new unstable range. The number of solutions of the dispersion relation depends on the equilibrium. The behaviour of the eigenvalues near the stability boundaries is treated in accordance with bifurcation theory.
Nonlinear Rayleigh-Taylor instability in hydromagnetics
Authors: Chakraborty B. B. , Nayak A. R. , Iyengar H. K. S.
Published: March 2009

Nonlinear Rayleigh-Taylor instability of a heavy, infinitely conducting fluid, supported against gravity by a uniform magnetic field in the vacuum, is studied for three-dimensional disturbances using the method of multiple time-scales. The three-dimensional problem can be reduced to two dimensions as it is found that an instability present for a three-dimensional disturbance of a given wavelength, for a given equilibrium magnetic field, is also present for a two-dimensional disturbance of the same wavelength propagating along an equilibrium magnetic field of lower strength. The instability is studied for both standing and progressive waves. Although in the linear stability problem the instability growth rate for a progressive wave of a given wavelength is equal to that for a stationary wave of the same wavelength, in the nonlinear instability problem studied here these waves are found to have different growth rates. Our results are compared and contrasted with those for the two-dimensional instability problem studied earlier.
On the existence of a free boundary solution of the Grad-Shafranov equation
Authors: Fujii Nobuo , Hirai Masahide
Published: March 2009

The existence of a non-trivial free boundary solution of the nonlinear Grad-Shafranov equation is studied. In the case of axisymmetric toroids, the existence of the solution is proved by the standard variational approach using assumptions which are not physically restrictive. Also, the existence of a cylindrically symmetric solution is proved in the case of straight cylinders with circular cross-section.
Nonlinear coupling of two three-wave systems in plasma
Authors: Basu (De) Shukla , Roychowdhury R. K.
Published: March 2009

The nonlinear interaction of two three-wave systems, including the possibility of negative energy waves in the presence of linear damping or growth and frequency mismatch, is investigated in a plasma, where one system of two transverse and one longitudinal wave interacts with a system of three longitudinal waves, and one of the longitudinal waves introduces coupling between the two subsystems. The solutions are analysed under various initial conditions and it is shown that, if one triplet be explosively unstable by itself, the presence of the second triplet can stabilize the solutions, depending on the relative strength of the coupling factor.
The structure of MHD shock waves
Authors: Badr Omar
Published: March 2009

The MHD equations are used to discuss the formation and structure of shock waves in channel flow of an ionized gas with finite viscosity, thermal and electrical conductivity. The fundamental resulting complicated nonlinear differential equations are solved exactly, and the shock structure is determined completely. A necessary compatibility condition for the evolution of shock waves is obtained in the form:

wherePrandPrmare ordinary and magnetic Prandtl numbers and γ the ratio of specific heats. The flow quantities and parameters are found to depend, in a non-analytical manner, onPrandPrm, so that special cases of interest are to be treated separately. Numerical results are given and discussed.
Nonlinear saturation of resistive modified tearing modes in a toroidal plasma. Part 1. Simon saturation theory in quasi-linear approximation
Authors: Ehrman J. B.
Published: March 2009

The nonlinear saturation of a resistive modified tearing mode in a toroidal plasma is calculated by Simon saturation theory for a weakly linearly unstable (over-stable) regime. The linearly unstable mode is a (1, 1) mode, where the first 1 indicates n, the toroidal mode number about an axisymmetric equilibrium and the second 1 indicates the multiple of the non-zero frequency at which the n = 1 mode oscillates when linearly marginally stable. The saturation amplitude is found to be proportional to (Δ – Δc)½ where Δ, a measure of the driving energy of the instability, is proportional to the difference between the logarithmic derivatives of the radial (i.e. perpendicular to the magnetic surface) perturbation magnetic field in the simplest case, and Δc measures toroidal stabilization due to average magnetic line curvature. To obtain the Simon saturation condition, one must go to third order in the small parameter (Δ –Δc)½. Starting with (1, 1), (1, – 1),( – 1, – 1), and( –1, 1 ) modes in first order in (Δ – Δc)½, the modes (0, 0), (0, 2), (2, 2), (2, 0) are obtained in second order, and these are driven with first-order modes to a third-order (1,1) mode which yields a saturation condition. In the quasi-linear approximation, only the near-zero frequency modes (0, 0) and (2, 0) are considered in the second order. In the present paper, only the axisymmetric perturbation (0,0) is used in second order. This gives a relation between nonlinear saturation amplitude and frequency shift, but does not determine either uniquely because of the undetermined parameter γ in the perturbation solutions. This parameter is determined exactly by the requirement of finiteness of the solutions when the (2, 0) non-axisymmetric near-zero frequency perturbation is taken into account in second order. However, magnetic island width at saturation can still be estimated taking only the (0,0) second order mode because this width depends so insensitively on γ, namely as γ–¼. Under this restriction to (0, 0) in second order, the frequency shift is found to be negative. Its absolute value is proportional to Δ – Δc, while the magnetic island width is proportional to (Δ – Δc)¼ and has a scale determined by t, the thickness of the resistive layer, proportional to η⅓, the cube root of the electrical resistivity.
Fluid theory for fluctuations in cold inhomogeneous plasmas
Authors: Uddholm P.
Published: March 2009

The theory for potential surface wave fluctuation spectra in cold, inhomogeneous, magnetized plasmas is reconsidered, adopting a transition probability approach. A fluctuation dissipation relation is derived, which is valid for general density profiles and which reduces to the familiar fluctuation dissipation theorem for homogeneous plasmas. Significant corrections to previous work are found. Particular spectra are calculated for the special case of a magnetized plasma with a one-dimensional inhomogeneity.
The relaxation zone behind normal shock waves in a dusty reacting gas. Part 2. Diatomic gases
Authors: Igra O. , Ben-Dor G.
Published: March 2009

The propagation of a strong normal shock wave into a quiescent mixture of nitrogen gas seeded with small, spherical inert dust particles is studied. While crossing the shock front, the gaseous phase of the suspension experiences a sudden change in temperature, pressure, density and velocity. (These changes can easily be evaluated using the Rankine-Hugoniot relations.) The solid phase of the suspension (dust) is initially unaffected by the shock wave. As a result, immediately behind the shock front, one phase of the suspension (the nitrogen gas) is in a state of relatively high temperature and low velocity while the other (the dust) is in a state of relatively low temperature and high velocity. Owing to these differences in temperature and velocity, intense heat transfer and viscous interactions between the two phases take place leading eventually to a new state of equilibrium that is reached farther downstream of the shock front. The flow field where these interactions take place, the relaxation zone, is solved numerically. It is shown that the spatial extent of this zone is strongly affected by the mass concentration of the dust in the suspenson and its physical properties (size, density and specific-heat capacity). These parameters also affect the post-shock equilibrium suspension properties. It was found that increasing the dust concentration results in a shorter kinematic relaxation zone, higher post-shock suspension pressure, density and temperature, and lower velocity, as compared to a similar pure-gas case. Increasing the dust particle density or its diameter results in a longer relaxation zone and a higher post-shock equilibrium suspension pressure, density and temperature. Changes in the dust specific-heat capacity affect the extent at the thermal relaxation length and the suspension temperature and density; they do not affect the extent of the kinematic relaxation length or the post-shock suspension pressure and velocity. For the range of dust concentration, size, density, specific-heat capacity and shock-wave Mach number investigated, the kinematic relaxation zone is always longer than the thermal relaxation zone.
Comment on the paper ‘On the influence of the Hall effect on the spectrum of the ideal magnetohydrodynamic cylindrical pinch’ by U. Schaper
Authors: Lifshitz A. , Fedorov E. , Schaper U.
Published: March 2009

General properties of the eigenvalues of Schaper (1983), concerning the continuum of eigenvalues on p. 7, needs correction. The solutions in the distributional sense of the eigenvalue problem (5.3),

will be given for two cases. The first case has been solved by A. Lifshitz and E. Fedorov and concerns continuous eigenvalues. In the second case, the solution for the points of accumulation of discrete eigenvalues is discussed.
Effect of boundary conditions on radial mode structure of whistlers
Authors: Boswell R. W.
Published: March 2009

The dispersion of the radial eigenmodes of a cylindrical m = 1 whistler wave with Ωi; ≪ ω < Ωe ≪ ωpe is investigated for both conducting and insulating boundaries. The effects of electron inertia and resistivity on the modes are discussed.
Excitation of whistler mode instability due to slow cyclotron interaction in an inhomogenous beam–plasma System
Authors: Shah H. A. , Jain V. K.
Published: March 2009

The excitation of whistler wave instability due to slow cyclotron (m = – 1) interaction in an inhomogeneous plasma penetrated by an inhomogeneous beam of electrons is studied. Expressions are obtained for the elements of the plasma and beam dielectric tensors. It is shown that the inhomogeneity in both beam and plasma number densities affects the growth rate of the instability.
Electromagnetic instability supported by a rippled, magnetically focused relativistic electron beam
Authors: Cuperman S. , Petran F. , Gover A.
Published: March 2009

The coupling of volume, long-wavelength TM electromagnetic and longitudinal space charge (electrostatic) waves by the rippling of magnetically focused electron beams is examined analytically. The dispersion relation is obtained and then solved for these types of wave. Instability, with growth rates proportional to the relative ripple amplitude of the beam, is found and discussed.
A numerical solution of the kinetic equations for a spectrum of Langmuir turbulence
Authors: Hayward Denis
Published: March 2009

The main properties of a kinetic wave equation in an isothermal plasma, Te ≈ Ti, are discussed and a quick method of numerical solution based on factorization of the kernel of an integral equation is outlined. As an illustration the method is applied to the problem of plasma heating with a relativistic electron beam and it is shown how the evolution of a spectrum of Langmuir turbulence is the principal contributor to the heating of the plasma. The technique allows an estimate of the error which is present in the stationary solution, and this is made in the final section.
Unified theory of whistler mode instability in the presence of a parallel electric field
Authors: Lal Das Indra Mohan , Singh R. P.
Published: March 2009

The propagation characteristics of right-hand circularly polarized whistler mode waves propagating parallel to the external magnetic field in an anisotropic plasma have been reformulated including the effect of a parallel electric field. Analytical expressions for the real frequency and growth rate have been obtained for the full range of the parameters β (the ratio of particle pressure to magnetic pressure of the hot particles), A (temperature anisotropy) and P ( = βA(A + 1)2) without any restriction on the magnitude of the imaginary part of the wave frequency. The effect of cold plasma injection on the marginal instability has also been studied. Possible application of the present theory to the atmospheres of Earth and Jupiter has been discussed.
Effects of thermal spread on the space charge limit of an electron beam
Authors: Coutsias E. A.
Published: March 2009

An asymptotic analysis is carried out to calculate the effects of a small thermal spread in the injection energy of an electron beam on its space charge limit. It is found that the space charge limit is lowered proportionally to the beam temperature T near T = 0.
Turbulent bremsstrahlung instability of whistler mode in the presence of enhanced ion-acoustic fluctuations
Authors: Sarma S. N. , Nambu M. , Bujarbarua S.
Published: March 2009

In the presence of a low-frequency ion-acoustic turbulence and a high-frequency whistler-mode test wave, a new plasma instability occurs owing to a nonlinear force which originates from the resonant interaction between electrons and modulated nonlinear electric fields. The growth rate of the whistler mode is calculated and compared with observations.
On the Vlasov fluid stability of the m = 0 mode in a pure Z pinch
Authors: Coppins M. , Bond D. J. , Haines M. G.
Published: March 2009

The possibility of using the Vlasov fluid model to describe large ion Larmor radius effects in a Z pinch is discussed. It is shown that the Vlasov fluid formulation can be applied to the m = 0 mode, but the comparison theorem which states that systems which are MHD stable are also Vlasov fluid stable, is shown to be inapplicable in this case.
Pump fluctuation effects on parametric instabilities in plasmas
Authors: Belbachir Ahmed H. , Akcasu A. Ziya
Published: March 2009

In this paper, we consider the effect of stochastic pumps on the parametric instabilities, including the pump band-width effect, the effect of the frequency mismatch and of the plasma temperature fluctuations that are induced by the fluctuations in the pump itself. Contrary to what is found in the literature, the threshold for instability can initially decrease with increasing pump band-width and reach a minimum when these effects are included. We propose a physical explanation of this minimum and point out the relationship between the thresholds for the instability of the mean energy and mean amplitude of the wave. The pump amplitude and the resulting plasma temperature fluctuations compete with the pump band-width and decrease the threshold for instability. Even for large pump band-widths, the threshold for instability for a pump with fluctuating amplitude is always lower than for the coherent one. Our general conclusion is that, in studying the effect of stochastic pumps on parametric instabilities more realistically, one has to include, in addition to the pump band-width, a number of other phenomena like imperfect frequency matching, the fluctuations induced in plasma parameters and the amplitude fluctuations of the pump itself.
Effect of electron thermal anisotropy on the kinetic cross-field streaming instability
Authors: Tsai S. T. , Tanaka M. , Gaffey J. D. , Da Jornada E. H. , Wu C. S. , Ziebell L. F.
Published: March 2009

The investigation of the kinetic cross-field streaming instability, motivated by the research of collisionless shock waves and previously studied by Wu et al., is discussed more fully in the present work. Since, in the ramp region of a quasi-perpendicular shock, electrons can be preferentially heated in the direction transverse to the ambient magnetic field, it is both desirable and necessary to include the effect of the thermal anisotropy on the instability associated with a shock. The present study has found that Te⊥ > Te‖ can significantly enhance the peak growth rate of the cross-field streaming instability when the electron beta is sufficiently high. Furthermore, the present analysis also improves the analytical and numerical solutions previously obtained.
Low aspect-ratio MHD toroidal equilibria
Authors: De Menna Luciano , Martini Stefano
Published: March 2009

In this paper a new approach to the approximate solution of the MHD equilibrium equation is described. The axisymmetric equilibrium equation is first transformed to a time-independent Schrödinger equation and then solved by the Ritz method in a suitable rotational co-ordinate system, the validity of the solution being not limited to large aspect-ratio configurations. The zeroth-order approximation is analytically computed and the relationship between the poloidal beta and the shift of the magnetic axis is derived. To the same order, the adiabatic compression of the plasma ring is studied and a non-dimensional compression chart is obtained. Results of numerical computations of the higher orders are also reported.
Dissipation by thermal forces in quantum plasmas
Authors: Burman R. R. , McClelland D. E.
Published: March 2009

This paper deals with degenerate Fermi–Dirac plasmas in which transport is by quasi-particles that form a dilute gas described by the Boltzmann equation. The off-equilibrium part of the distribution function of each species is estimated by expanding it in terms of the fluid velocity of the species, relative to the plasma, and its relative heat flux vector. Expressions for the frictional forces acting between the species, consisting of a relaxation-model force and a thermal force, are obtained. These are used in a plasma dissipation formalism, yielding, for ternary partially ionized plasmas, a generalized Ohm law and an ambipolar diffusion law. The results are applied to neutron star matter, consisting of thermally ultra-relativistic electrons and non-relativistic protons and neutrons, with the mass density dominated by the neutrons. The dissipation formalism is used to obtain an expression for the magnetic force on this material.
Nonlinear interaction of the surface waves at a narrow inhomogeneous layer of the magnetoactive plasma
Authors: Hussein A. M.
Published: March 2009

Amplitudes of electromagnetic waves with combination frequencies, radiating from a narrow inhomogeneous layer of the magnetoactive plasma due to interaction of the surface waves, are determined. The method used allows for discontinuity of the tangential components of the wave electric field at the combination frequencies at the plasma boundary.
Multi-species kinetic generalization of the Appleton–Hartree dispersion formula
Authors: Garrett A. J. M.
Published: March 2009

This paper calculates, on a kinetic basis, the dispersion relation and field polarization for waves propagating linearly through a homogeneous magnetoplasma when thermal velocities are far less than the phase velocity. Approximations are brought in only as necessary and their physical significance explained. The result is an improved derivation of the Sen–Wyller generalization of the Appleton–Hartree formula for velocity-dependent collision frequency. Further generalization to several charged species is made, and the dispersion relation is also considered in terms of the angle between the ambient magnetic field and the group (rather than phase) propagation direction. Special case reduction to the Appleton-Hartree formula is confirmed. Complications concerning the limit of weak spatial dispersion are discussed. The analysis is restricted to weakly ionized plasmas in which the charge to neutral particle mass ratios are small, collisions are weak, and the wave vector is predominantly real.
The thermodynamics of the Vlasov equilibria
Authors: Minardi E.
Published: March 2009

A statistical procedure is applied for constructing an entropy functional associated with a collective Vlasov equilibrium described by a given coarse-grained current and charge distribution. The functional is not at a maximum if the magnetic or electrostatic equilibrium is not unique. This property connects the principle of maximum entropy with bifurcation theory and marginal stability analysis.
Effects of asymmetries on the collisionless reconnecting instability
Authors: Chike-Obi B.
Published: March 2009

The stability of collisionless reconnecting modes which are driven by a current density gradient is analysed. We consider an inhomogeneous plasma embedded in a sheared magnetic field with finite density and temperature gradients and employ a kinetic description for the inner boundary layer. Appropriate approximations reduce the resulting integro-differential system of equations to a pair of coupled second-order differential equations. In contrast to previous results, the differential operators acting on the field components do not exhibit definite symmetry. Matching is performed numerically to the outer ideal MHD region without regard to symmetry. The asymmetric part of the solution affects the mode frequency and growth rate to the extent that the radial amplitude of the perturbed magnetic field has a significant variation within the singular layer. Stability properties with respect to relevant parameters are investigated.
VLF emission stimulated by parallel electric fields
Authors: Juhl B. , Treumann R. A.
Published: March 2009

We study the influence of a weak quasi-static parallel electric field on the stability of electromagnetic plasma waves. Using an operator calculus to solve the Boltzmann-Maxwell equations we derive a dispersion relation for the electromagnetic waves. Assuming that the electrons have a loss-cone distribution, the real frequency of waves in the whistler band is not changed by the presence of the electric field. Resonant interaction damps the HF waves for propagation parallel to the electric field. In the case of opposite propagation, a new HF excitation is found at frequencies ω ≲ ωce The width of the excitation region depends on the width of the loss cone, field strength and collision frequency. This result is applied to observations of the splitting of VLF emissions under natural conditions in the magnetosphere. It is found that the observed splitting could have been caused by the presence of the weak parallel electric field of a kinetic (shear) Alfvén wave in the emission region, which is quasi-stationary compared with the growth of the observed VLF emission.
Beat-wave excitation of plasma waves
Authors: Mendonça J. T.
Published: March 2009

Nonlinear saturation effects associated with the generation of electron plasma waves by two high-frequency electromagnetic waves, beating at a frequency nearly equal to the electron plasma frequency, are studied. A fluid model including collisions, frequency mismatch and relativistic mass variation is used. It is shown that for large-amplitude driving waves a transition to chaos can occur, leading to plasma wave breakdown. The results may be relevant to the beat-wave current drive in tokamak devices and to beat-wave particle accelerators.
Low-frequency modes in a two-species plasma
Authors: Satya Y. S. , Jain K. M. , Guha S. , Bose Mridul
Published: March 2009

A systematic and comprehensive study of linear and nonlinear analyses of the propagation of low-frequency modes in two-ion-species plasma has been made. Two new non-propagating modes on different ion time-scales are reported. These modes are excited by nonlinear coupling with the external pump. The threshold field of the pump and the growth rates of the various modes above the threshold are also calculated. A comparison of the results with those of single-ion-species plasma shows that the non-propagating mode on the fast ion time-scale excites the oscillating two-stream instability. In addition, the mode corresponding to ωr = 0 on the slow ion time-scale becomes important nonlinearly and excites a new type of instability. It is interesting to note that the threshold electric fields excitation of these instabilities are the same.
Electron dynamics in one-dimensional double layers
Authors: Yamamoto Takashi
Published: March 2009

By numerical simulations, the dynamical behaviour of the electrons in one-dimensional double layers is studied. The simulation results show that at least one third of the electrons emitted at the low-potential boundary of the simulation system are reflected back before passing through the double layers. Such reflexion is due to (i) quasi-linear or nonlinear scattering by plasma oscillations and (ii) ambipolar potentials observed around the potential front of the localized double layer. The whole temporal evolution of the localized double layers are also presented. In particular, we attempt to explain the steepening and collapsing of the localized double layers in terms of the formula for the double-layer thickness.
The electrostatic eigenmodes of a cold plasma with a two-dimensional density non-uniformity
Authors: Näslund E. , Gradov O. M.
Published: March 2009

A new kind of surface oscillation, which can exist when the usual surface waves are absent because of resonant absorption, has been studied for a non-uniform plasma slab. Special attention is paid to the influence of the boundaries on the eigenfrequency spectrum.
Corrigendum
Authors: Forbes T. G. , Priest E. R. , Hood A. W.
Published: March 2009

Numerical solutions were obtained by Forbes, Priest & Hood (1982) for the resistive decay of a current sheet in an MHD fluid. To check the accuracy of the numerical solutions, a linear, analytical solution was also deived for the regime where diffusion is dominant. In a subsequent reinvestigation of this problem an error in the linear, analytical solution has been discovered. For the parameter values used in the numerical solution this error is too small (≲ 2%) to produce any significant change in the previous test comparison between the numerical and analytical solutions. However, for parameter values much different from those used in the numerical solution, the error in the linear solution can be significant.
The structure of quasi-shocks in a collision-free plasma in a magnetic field
Authors: Cordey J. G. , Saffman P. G.
Published: March 2009

A study is made of finite amplitude, oblique, hydromagnetic waves in a cold collision-free plasma. It is shown that the equations admit steady solutions which describe flow through a front. Ahead of the front, the flow is uniform, but behind the front the magnetic field and flow variables oscillate irregularly in a random manner. The fronts are called ‘quasi-shocks’, although they have more in common with the laminar-turbulent transition of fluid mechanics than with the classical shock wave. The structure of the quasi-shocks is examined, and estimates are made for the mean values behind the front. The relevance of the quasishocks to the so-called ‘collision-free shock’ is considered, and comparison is made with the ‘bow shock’ on the solar wind near the earth. It is shown that the quasi-shock is consistent with some of the observed data.
Production of superthermal electrons by electrostatic plasma oscillations
Authors: Fredricks R. W.
Published: March 2009

The beam-plasma interaction which has been proposed by Stix is examined both by approximate analysis and by integration of the non-linear equations of motion which describe the interaction of an individual electron with a monochromatic large amplitude electrostatic plasma wave. The quasi-stochastic model of the large amplitude plasma waves, introduced by Stix (1964), has been used in the calculations by programming a random phase function into the argument of the periodic plasma wave function. It is found that electrons are subject to a quasi- cyclotron acceleration which proceeds to a higher energy in the stochastic case than the limit found in the non-stochastic case (a phase-coherent plasma wave). This behaviour is interpreted in terms of a limit cycle phenomenon, and the stochastic phase shift appears to push electrons across these limit cycles. It is also found that favoured groups of electrons in a 2eV plasma excited by a 5 keV beam in a2000 Gauss field can achieve energies in the range 85 to 170 keY in less than a nanosecond by a single acceleration occurring in one plasma wave coherence length L‖ as defined by Stix.
Propagation along the magnetic field of a pulse current originated disturbance in a cold two-fluid plasma
Authors: Lewak G.J.
Published: March 2009

The propagation, along the magnetic field, of a point disturbance in a cold two fluid linear plasma is solved asymptotically in various space-time régimes. The main disturbance is a pulse front travelling at approximately the Alfvén speed divided by the electron to ion mass ratio. Its proffle envelope is an Airy function. It oscillates at the mean of the gyro-frequencies and is effiptically polarized. The disturbances remaining behind this front are of two kinds: an oscillation at the sum of the gyro-frequencies which is circularly polarized and represents the ‘extraordinary’ wave, and an oscillation at the ion gyro-frequency which is elliptically polarized with changing eccentricity and orientation of axis.
Interaction of electromagnetic fields with warm slightly ionized magneto-plasmas
Authors: De Barbieri O. , Maroli C.
Published: March 2009

The problem concerning the interaction of electromagnetic fields with a warm, slightly ionized magneto-plasma is analysed by means of the multiple time scales asymptotic technique. Only initial value problems in an infinite plasma are here considered in detail. It is shown how the full set of Vlasov–Maxwell equations, modified through a standard Boltzmann collision integral to take account of the elastic electron-neutral encounters, can be reduced, in the basic limit assumed, to a set of two coupled non-linear integro-difl�erential equations for the dominant terms of the longitudinal fields and of the electron distribution function. Once the initial conditions are specified, the behaviour of the transverse initial field is also described. A particular example has been given for the so-called progressing-wave initial conditions.
Surface waves of a magnetoactive plasma
Authors: Jungwirth K. , Petržílka V. A.
Published: March 2009

It is proved in the surface potential waves approximation that not oniy a bounded plasma with flows along the magnetostatic field, but also a plasma with a finite ‘longitudinal temperature’ of the electrons can be unstable against axially asymmetric perturbations of magnetohydrodynamic type. The branches of surface oscillations of a cold plasma, and the conditions for their excitation by an admixture of electrons with a sufficiently high ‘longitudinal temperature’ in various geometrical configurations, are also derived in the aper.
Collision and ionization effects in a plasma sheath
Authors: Hu Pung Nien , Ziering Sigi
Published: March 2009

This paper examines analytically the transition domain between collisionless and collision dominated flows in the environment of a plasma sheath. The onset of collisions also brings into focus the concurrent effects due to ionization, which are retained in the theory. An integral method of iteration is established, and the dominant correction terms due to collision and ionization effects are obtained. Various limiting cases are examined.
On oscillating electric dipoles immersed in a hot plasma
Authors: Watson S. R.
Published: March 2009

In this paper the electric fields of an infinitesimal dipole oscillating in a hot plasma are derived in the absence of an external magnetic field; explicit expressions are obtained by making an approximation on the background electron velocity distribution function. These results are applied to investigate the resonance observed at the plasma frequency, and to estimate the radiation resistance of the dipole.