Existence domains for nonlinear structures in complex two-ion-temperature plasmas

in Journal of Physics : A Mathematical & General (2006), 39(12), 3137-3146

The existence domains for one-dimensional acoustic solitons and double layers in complex (dusty) plasmas with two ion temperatures are obtained, using the fluid dynamic paradigm with a general polytropic ... [more ▼]

The existence domains for one-dimensional acoustic solitons and double layers in complex (dusty) plasmas with two ion temperatures are obtained, using the fluid dynamic paradigm with a general polytropic equation of state. Dust-acoustic solitons are considered in a four-component plasma of negative dust grains, cool and very hot ions, and very hot electrons. Whereas in a dust-ion-electron plasma only negative potential solitons are supported, the presence of a second ion component allows positive potential solitons to occur as well. The existence domain in parameter space is delineated, in particular, also for the reduced three-component case in which there are no free electrons, all electrons being adsorbed onto the dust grains. Next, the ion-acoustic regime is considered. Both positive and negative potential dust-ion acoustic solitons and double layers are found, and their existence conditions in the parameter space of cool ion density and Mach number derived. [less ▲]

Ion- and dust-acoustic solitons in dusty plasmas: Existence conditions for positive and negative potential solutions

in Physics of Plasmas (2005), 12(8), 8

The usual description of dust-modified ion-acoustic and dust-acoustic solitons in plasmas containing negative dust is in terms of Boltzmann distributions for the hotter species. In the dust-modified ion ... [more ▼]

The usual description of dust-modified ion-acoustic and dust-acoustic solitons in plasmas containing negative dust is in terms of Boltzmann distributions for the hotter species. In the dust-modified ion-acoustic regime, besides positive potential solitons, negative structures can also be generated, for electrons with a polytropic index gamma(e)not equal 1, as well as for Boltzmann electrons, subject to conditions that are not too stringent. These general conditions were previously either ignored or given for weakly nonlinear solutions only. In the dust-acoustic domain in plasmas with negatively charged dust, however, only negative potential solitons can occur, even when the lighter species have non-Boltzmann distributions. For Boltzmann electrons only an infinite dust compression limits the soliton amplitudes and corresponding Mach numbers, whereas for gamma(e)not equal 1, the electron density, too, can be a limiting factor for the existence domain of such solitons. (c) 2005 American Institute of Physics. [less ▲]

Acoustic solitons in dusty plasmas revisited

in AIP Conference Proceedings (2005), (799), 502-5

The usual description of dust-modified ion-acoustic and dust-acoustic solitons in plasmas containing negative dust is in terms of Boltzmann distributions for the hotter species. In the dust-modified ion ... [more ▼]

The usual description of dust-modified ion-acoustic and dust-acoustic solitons in plasmas containing negative dust is in terms of Boltzmann distributions for the hotter species. In the dust-modified ion-acoustic regime, besides positive potential solitons, negative ones can also be generated, for non-Boltzmann as well as for Boltzmann electrons, subject to very mild conditions that were previously ignored or given for weakly nonlinear solutions only. In the dust-acoustic domain in plasmas with negatively charged dust, however, only negative potential solitons can occur, even when the lighter species have non-Boltzmann distributions [less ▲]

Potential hill electron-acoustic solitons and double layers in plasmas with two electron species

in Physics of Plasmas (2005), 12(4), 10

In the description of (high-frequency) electron-acoustic solitons in a plasma consisting of positive ions, cool electrons, and hot electrons, the dynamics of the ions plays no essential role and can be ... [more ▼]

In the description of (high-frequency) electron-acoustic solitons in a plasma consisting of positive ions, cool electrons, and hot electrons, the dynamics of the ions plays no essential role and can be eliminated from the treatment, the ions merely providing a constant positive background. It is widely believed that in such a plasma only potential dip solitary waves can be generated. In a potential dip the cooler electrons are compressed and the hotter electrons rarefied, both being driven towards their sonic points, the cooler ones from above, the hotter ones from below. This transonic feature gives rise to the solitary wave. However, it is shown that the restriction to potential dip solitons is due to the neglect of the inertia of the hot electrons, implicitly or explicitly assumed by most-authors. If hot electron inertia is retained, there exists a parameter range where-potential hill solitary waves are formed, with both electron species being driven away from their sonic points This has important consequences for the reinterpretation of several astrophysical phenomena involving two-electron plasmas. (c) 2005 American Institute of Physics. [less ▲]

Solitary waves in self-gravitating molecular clouds

in Astronomy and Astrophysics (2005), 438(1), 23-29

Molecular clouds are self-gravitating fluids that support different waves and contain highly nonlinear clumps and filaments, for which explanations have been sought in terms of solitons. The present paper ... [more ▼]

Molecular clouds are self-gravitating fluids that support different waves and contain highly nonlinear clumps and filaments, for which explanations have been sought in terms of solitons. The present paper explores the possibility that several ( neutral) species with different thermal speeds coexist, as in a molecular cloud consisting of gas and dust, or of a mixture of normal matter and dark matter. It is shown that this model can support soliton formation, both with humps or dips in the self-gravitational potential. The existence domain has been given in terms of the hot species Mach number and fractional mass density, in a gas-dynamic description which emphasizes the constraints coming from the sonic and neutral points, and from the limits due to infinite compression or total rarefaction. One species is compressed while the other is rarefied, allowing the system to reach a mass neutral point outside equilibrium. In this way, solitons are possible without invoking interaction with a weakly ionized cloud component or involving envelope solitons that are not really stationary structures. [less ▲]

Gas-dynamic description of electrostatic solitons

in Journal of Plasma Physics (2004), 70

The nonlinear propagation of electrostatic solitary structures in unmagnetized multispecies plasmas is studied in the wave frame, where they are stationary, via the recently developed McKenzie approach as ... [more ▼]

The nonlinear propagation of electrostatic solitary structures in unmagnetized multispecies plasmas is studied in the wave frame, where they are stationary, via the recently developed McKenzie approach as an alternative to the more usual Sagdeev pseudo-potential method. This way of looking at the problem brings out the gas-dynamic aspects, which then allow a straightforward characterization of the solitary wave possibilities in terms of the species' own sonic points and of the global charge neutral points. A qualitative discussion of ion-, dust- and electron-acoustic solitary waves is given in terms of these concepts and the results are contrasted with those obtained by other methods. Ion-acoustic solitons can be shown to always be compressive, without invoking simplifying assumptions such as cold ions or Boltzmann electrons. Beam-plasmas can also be studied, as in the elect non-acoustic solitary wave model for the spiky structures of the broadband electrostatic noise observed in the auroral regions of the Earth's magnetosphere. Such solitons always show a potential dip. [less ▲]

Magnetosonic modes with a beam of dust or secondary ions

in Physics of Plasmas (2004), 11(10), 4589-4595

Charged dust particles on near-Keplerian orbits in planetary rings drift relative to the corotating background plasma, and this relative streaming may drive dust-modified magnetosonic waves unstable ... [more ▼]

Charged dust particles on near-Keplerian orbits in planetary rings drift relative to the corotating background plasma, and this relative streaming may drive dust-modified magnetosonic waves unstable. Using a magnetofluid model, this situation is revisited, and it is shown that a correct description can be obtained at frequencies and Doppler shifts that are small compared to the electron gyrofrequency. An excellent agreement is reached between the analytical approximation and the numerical solution of the full or reduced dispersion law. A very low-frequency, small wave number beam instability may occur at supermagnetosonic beam velocities of the dust component, but, based on the existing data, is unlikely to play a role in planetary rings. Instability is also found for submagnetosonic speeds, which might be relevant to Saturn's E ring. (C) 2004 American Institute of Physics. [less ▲]

Large amplitude solitary electromagnetic waves in electron-positron plasmas

in Physics of Plasmas (2004), 11(6), 3078-3082

Waves in electron-positron plasmas have fundamentally different dispersion characteristics due to the equal charge-to-mass ratios between negative and positive charges, which mix different timescales, and ... [more ▼]

Waves in electron-positron plasmas have fundamentally different dispersion characteristics due to the equal charge-to-mass ratios between negative and positive charges, which mix different timescales, and are of interest in understanding aspects of pulsars and active galactic nuclei, where astrophysical electron-positron plasmas occur. Earlier systematic nonlinear treatments of parallel propagating electromagnetic waves via a reductive perturbation analysis had indicated unusual results, namely a vector equivalent of the modified Korteweg-de Vries equation. The latter is nonintegrable except in the case of linear polarization when it becomes equivalent to the scalar (integrable) modified Korteweg-de Vries equation. Here large amplitude purely stationary nonlinear solitary waves are studied in their own reference frame via the McKenzie approach. The behavior of the wave magnetic field can be expressed through an energy integral that involves the Mach number of the structure. Possible solitons are super-Alfvenic and occur symmetrically for positive or negative fields, owing to the obvious symmetry between positive and negative charges with the same mass. The limits on the allowable Mach numbers and soliton amplitudes have also been computed. (C) 2004 American Institute of Physics. [less ▲]

Whistler oscillitons revisited: the role of charge neutrality?

in Nonlinear Processes in Geophysics (2004), 11(4), 447-452

When studying transverse modes propagating parallel to a static magnetic field, an apparent contradiction arises between the weakly nonlinear results obtained from the derivative nonlinear Schrodinger ... [more ▼]

When studying transverse modes propagating parallel to a static magnetic field, an apparent contradiction arises between the weakly nonlinear results obtained from the derivative nonlinear Schrodinger equation, predicting envelope solitons (where the amplitude is stationary in the wave frame, but the phase is not), and recent results for whistler oscillitons, indicating that really stationary structures of large amplitude are possible. Revisiting this problem in the fluid dynamic approach, care has been taken not to introduce charge neutrality from the outset, because this not only neglects electric stresses compared to magnetic stresses, which is reasonable, but could also imply from Poisson's equation a vanishing of the wave electric field. Nevertheless, the fixed points of the remaining equations are the same, whether charge neutrality is assumed from the outset or not, so that the solitary wave solutions at not too large amplitudes will be very similar. This is home out by numerical simulations of the solutions under the two hypotheses, showing that the lack of correspondence with the DNLS envelope solitons indicates the limitations of the reductive perturbation approach, and is not a consequence of assuming charge neutrality. [less ▲]

Electromagnetic modes in dusty plasmas with charge and mass distributions

in Physics of Plasmas (2003), 10(4), 956-962

Electromagnetic modes in dusty plasmas are studied for polydisperse dust grains with a distribution in charge and mass. Owing to the different charge and mass weightings of the velocities, there occurs an ... [more ▼]

Electromagnetic modes in dusty plasmas are studied for polydisperse dust grains with a distribution in charge and mass. Owing to the different charge and mass weightings of the velocities, there occurs an infinite chain of equations of motion, coupled through the magnetic part of the Lorentz force. Depending on the frequency and associated convergence regimes, one has to close the chain in ascending or in descending order. Both series together lead to the polydisperse dispersion law that is a generalization of monodisperse or size distributed dust. Power-law distributions typical for heliospheric plasmas are discussed as an application. (C) 2003 American Institute of Physics. [less ▲]