Waves In Complex Plasma Research Articles

Propagation characteristics of nonlinear dust acoustic solitary waves in complex plasma with nonthermal electrons and trapped ions

The propagation characteristics of nonlinear dust acoustic solitary waves in a complex plasma system with nonthermal electrons and trapped ions are investigate in this work. The nonlinear dispersion relation of dust acoustic waves is obtained by using the linear method, and the two-dimensional autonomous system governing the motion of nonlinear dust acoustic waves is derived by using the Sagdeev potential method. At the same time, the specific expression of the Sagdeev potential function is obtained based on the Sagdeev potential equation. The numerical simulations are used to analyze the phase portraits of the two-dimensional autonomous system, revealing the linear periodic wave orbits, nonlinear periodic wave orbits, and homoclinic orbits co-existing in the complex dusty plasma system with nonthermal electrons and trapped ions. Furthermore, from the variations of the Sagdeev potential function with different system parameters it follows that only the compressive solitary waves exist in this complex plasma system. The significant influences of various system parameters on the amplitude, width, and waveform of the nonlinear dust acoustic solitary wave in the complex plasma system are discussed in detail. The results demonstrate that the Mach number, the nonthermal electrons and trapped ions, undisturbed dust particle number density, temperature, and charge have important effects on the propagating characteristics of the nonlinear dust acoustic solitary waves in a complex plasma with nonthermal electrons and trapped ions.

Dispersion relation for the dust ionization and dust acoustic waves in the gas discharge complex plasma

A theoretical approach is developed for the dust ionization (DIW) and dust acoustic waves (DAW) propagating in the cloud of microparticles in the low-pressure gas discharge under microgravity conditions. The theory explores the fluid approximation for the microparticle subsystem of complex plasma combined with the kinetic equation for the ions. In the one-dimensional approximation, the wave equation is obtained whose solution defines the dispersion relation for the waves in complex plasma involving the oscillations of microparticles. Obtained dispersion relation unifies both the dust ionization and the dust acoustic waves (DIW and DAW, respectively). According to this dispersion relation, the effect of microparticles on the recombination rate leads to a number of peculiarities. Among them are existence of the minimum frequency, above which the wave propagation is possible, a weak dependence of the DIW wave number on the frequency, and a high phase velocity of DIW as compared to DAW. It is demonstrated that no instability of DIW is possible, whereas DAW can reveal instability under proper conditions. Calculation results correlate with those obtained in a recent experiment.

Spatial distribution of dust density wave properties in fluid complex plasmas.

Complex plasmas consist of microparticles embedded in a low-temperature plasma and allow investigating various effects by tracing the motion of these microparticles. Dust density waves appear in complex plasmas as self-excited acoustic waves in the microparticle fluid at low neutral gas pressures. Here we show that various properties of these waves depend on the position of the microparticle cloud with respect to the plasma sheath and explain this finding in terms of the underlying ion-drift instability. These results may be helpful in better understanding the propagation of dust density waves in complex plasmas and beyond, for instance, in astrophysical dusty plasmas.

Nonlinear dispersion relation for dust-acoustic waves in complex plasmas.

Nonlinear dispersion relation for the finite-amplitude dust acoustic modes is obtained taking into account resonant particle trapping in the wave. The kinetic model predicts a frequency shift scaling ∝sqrt[ϕ] relative to the linear dispersion relation with ϕ being the wave amplitude of the electrostatic potential. The species contributions to the nonlinear frequency shift have opposite sign: positive for trapped electrons and ions and negative for particles. It is shown that the relative importance of these contributions depends on the electron-to-ion or particle temperature ratio, particle charge, and Havnes parameter. In typical complex plasma experiments, the kinetic frequency shift is dominated by the positive ion contribution. As a result, the nonlinear modification of the dispersion relation affects the wave dispersion properties and may provide the acoustic-like behavior to the wave number domain kλ_{Di}∼1.

The Suprathermal Particles and Charge Fluctuation Effects on Waves in Complex Plasma

In the frame of kinetic theory we investigated the effects of suprathermal particles and dust charge fluctuations due to the inelastic collision between the dust grains and plasma particles by calculating the longitudinal dielectric permittivity in an unmagnetized dusty plasma on the wave modes propagating in a complex plasma. The ion and electron distribution were assumed to be Maxwell and Kapa distribution in the systems. It was shown that the wave frequency can be analyzed for various values of the spectral index K and the dust charge fluctuations. The landau damping rate and Propagation rate in dust charge fluctuation presence increase

Bifurcation analysis of ion-acoustic waves in an adiabatic trapped electron and warm ion plasma

Bifurcation analysis of ion-acoustic waves in complex plasmas in the presence of adiabatic trapped electrons and warm ions is studied. Using bifurcation theory of dynamical structure, the Hamiltonian system inculpated electrostatic potential is derived. Effects of physical parameters, such as T and , are shown on the analytical solitary wave solution. The numerical results show that parameters T and affect significantly on nonlinear electrostatic solitary waves. By adding an external periodic perturbation to unperturbed Hamiltonian system, we investigate quasiperiodic structure of the perturbed Hamiltonian system.

Magnetic field effects and waves in complex plasmas

Magnetic fields can modify the physical properties of a complex plasma in various different ways. Weak magnetic fields in the mT range affect only the electrons while strong fields in the Tesla regime also magnetize the ions. In a rotating dusty plasma, the Coriolis force substitutes the Lorentz force and can be used to create an effective magnetization for the strongly coupled dust particles while leaving electrons and ions unaffected. Here, we present a summary of our recent experimental and theoretical work on magnetized complex plasmas. We discuss the dynamics of dust particles in magnetized discharges, the wave spectra of strongly coupled plasmas, and the excitations in confined plasmas.

Dust Density Waves in Weak Electric Fields: Effect of the Dust Number Density

We report on modifications of the dispersion relation, describing dust density waves in complex plasmas subjected to weak electric fields due to variations of the equilibrium dust densities. The calculations show the essentially different wave dispersion and predict the existence of cutoff wavenumbers, corresponding to aperiodically growing dust density perturbations. The theory explains the preferential range of wavenumbers where the dust density waves can be effectively excited.

Cluster Agglomeration Induced by Dust-Density Waves in Complex Plasmas

Experimental results showing the agglomeration of large carbonaceous particles in a dusty plasma are reported. Experiments were performed in a capacitively coupled rf argon plasma. Acetylene was injected to produce dust particles. When a sufficient amount of nanoparticles is present in the cathodic sheath, self-excited dust-density waves occur. The latter ones induce the motion of larger clusters, which vertically oscillate with the displacement of wave fronts. In some cases, the relative velocity of large particles was high enough to overcome the Coulomb repulsion forces, and agglomeration can be observed. The mechanisms underlying this process are discussed.

Dust acoustic waves in complex plasmas at elevated pressure

The bi-Yukawa effective interaction potential with different screening constants is employed to calculate dust static correlation functions in the hyper-netted chain approximation and to generalize the theory of dust acoustic waves within the non-perturbative moment approach complemented by hydrodynamic considerations. For the bi-Yukawa interaction potential the sound speed becomes significantly wavenumber-dependent, an additional soft diffusion-like mode is predicted, and the static dielectric function is shown to take negative values. The results can be applied to non-equilibrium dusty plasmas at elevated pressure.

Critical point and sound waves in complex plasmas

An equation of state for particles in complex plasmas, which includes contributions from plasma background fields and interparticle interactions (electric repulsion and “ion shadow” attraction), is obtained. Using this equation, experimental parameter regimes for the observation of liquid-vapor transitions and a critical point are examined. In addition, it is demonstrated that as in binary fluids, sound waves in complex plasmas do not exhibit critical behavior. Thus, criticality in complex plasmas may have more in common with binary fluids rather than ordinary fluids.

Effect of secondary electron emission and other sources on the propagation of dust ion acoustic waves in a complex plasma with positively charged dust grains

The effect of secondary electron emission on dust ion acoustic wave (DIA) propagation has been investigated based on orbit motion limited (OML) theory of dust grain charging. The emitted secondaries are assumed to have the same temperature of that of the ambient plasma electrons so that the plasma is effectively composed of three components: The ions, electrons and the varying charged dusts. Together with the effect of secondary electron emission, the effect of ion and electron capture and ionization of neutral atoms and recombination have been included in the ion and electron fluid equations. Small amplitude perturbation is considered about a charge neutral steady state. It is seen that for the positively charged dust grains, waves are purely damped about the equilibrium. The frequency and damping decrement of DIA waves in complex plasmas with positively charged dust grains are determined.

Non-linear waves in complex plasma

The combined effects of the non-adiabatic dust charge fluctuation and the inhomogeneous of equilibrium dust density and charging on non-linear dust acoustic waves are presented theoretically. By the perturbation method, a variable coefficients Korteweg–de Vries–Burgers equation governing the non-linear waves is derived. It is shown that both solitary waves and shock waves (both oscillatory and monotone shock) can exist in this complex plasma .

The application of the constants of motion to nonlinear stationary waves in complex plasmas: a unified fluid dynamic viewpoint

Perturbation reductive procedures, as used to analyse various weakly nonlinear plasma waves (solitons and periodic waves), normally lead to the dynamical system being described by KdV, Burgers' or a nonlinear Schrödinger-type equation, with properties that can be deduced from an array of mathematical techniques. Here we develop a fully nonlinear theory of one-dimensional stationary plasma waves, which elucidates the common nature of various diverse wave phenomena. This is accomplished by adopting an essentially fluid dynamic viewpoint. In this unified treatment the constants of the motion (for mass, momentum and energy) lead naturally to the construction of the wave structure equations. It is shown, for example, that electrostatic, Hall–magnetohydrodynamic and ion–cyclotron–acoustic nonlinear waves all obey first-order differential equations of the same generic type for the longitudinal flow field of the wave. The equilibrium points, which define the soliton amplitude, are given by the compressive and/or rarefactive roots of a total plasma ‘energy’ or ‘momentum’ function characterizing the wave type. This energy function, which is an algebraic combination of the Bernoulli momentum and energy functions for the longitudinal flow field, is the fluid dynamic counterpart of the pseudo-potentials, which are characteristic of system structure equations formulated in other than fluid variables. Another general feature of the structure equation is the phenomenon of choked flow, which occurs when the flow speed becomes sonic. It is this trans-sonic property that limits the soliton amplitudes and defines the critical collective Mach numbers of the waves. These features are also obtained in multi-component plasmas where, for example, in a bi-ion plasma, momentum exchanges between protons and heavier ions are mediated by the Maxwell magnetic stresses. With a suitable generalization of the concept of a sonic point in a bi-ion system and the corresponding choked flow feature, the wave structures, although now more complicated, can also be understood within this overall fluid framework. Particularly useful tools in this context are the momentum hodograph (an algebraic relation between the bi-ion speeds and the electron speed, or magnetic field, which follows from the conservation of mass, momentum and charge-neutrality) and a generalized Bernoulli energy density for each species. Analysis shows that the bi-ion solitons are essentially compressive, but contain the remarkable feature of the presence of a proton rarefactive core. A new type of soliton, called an ‘oscilliton’ because embedded spatial oscillations are superimposed on the classical soliton, is also described and discussed. A necessary condition for the existence of this type of wave is that the linear phase velocity must exhibit an extremum where the phase speed matches the group speed. The remarkable properties of this wave are illustrated for the case of both whistler waves and bi-ion waves where, for the latter, the requisite condition is met near the cross-over frequencies. In the case of the whistler oscilliton, which propagates at speeds in excess of one half of the Alfvén speed (based on the electrons), an analytic solution has been constructed through a phase-portrait integral of the system in which the proton and electron dynamics must be placed on the same footing. The relevance of the different wave structures to diverse space environments is briefly discussed in relation to recently available high-time and spatial resolution data from satellite observations.

Waves in Complex Plasmas With Dust Distributions (Charge/Size/Mass) Revisited

Polydisperse dust, as in astrophysical observations, occurs in a range of sizes, compositions, charges, and masses, with corresponding changes to linear dispersion laws. At the fluid level the charged dust can be treated as a discrete collection of different fluids or as the continuous limit over a charge range. On the other hand, one global dust fluid needs appropriate model equations, derivable from a Klimontovich or extended Vlasov approach, in which charge, mass, and/or size enter as extra phase space variables. Due to differing charge-to-mass weightings, this is sometimes quite involved. An extended kinetic theory allows for a more correct picture, including possible microscopic damping mechanisms, but quickly becomes very unwieldy. An intermediate procedure is to use results for monodisperse dust and integrate afterwards over dust distributions. This cannot be applied blindly, so that it is necessary to check results on their applicability and consistency. Selected applications have been treated for parallel electromagnetic, oblique electrostatic (and possibly self-gravitational), and fluid dust-Bernstein modes, to illustrate the methodological aspects of this part of dusty plasma physics.

Ion-acoustic waves in a complex plasma with negative ions.

A self-consistent theory of linear waves in complex laboratory plasmas containing dust grains and negative ions is presented. A comprehensive model for such plasmas including source and sink effects associated with the presence of dust grains and negative ions is introduced. The stationary state of the plasma as well as the dispersion and damping characteristics of the waves are investigated. All relevant processes, such as ionization, diffusion, electron attachment, negative-positive ion recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dust particles, as well as charging collisions with the dusts, are taken into consideration.

Influence of electromagnetic radiation on the shock structure formation in complex plasmas

Electromagnetic radiation effects are calculated for the case of the solar radiation spectrum in the vicinity of the Earth. The influence of the photoelectric effect on the propagation of nonlinear waves in complex plasmas is studied when the dust grains acquire large positive charges. Exact solutions to nonlinear equations in the form of steady-state shocks that do not involve electron-ion collisions are found, and the conditions for their existence are obtained. In contrast to the classical collisionless shock waves, the dissipation due to the dust charging involves the interaction of the electrons and ions with the dust grains in the form of microscopic grain currents and the photoelectric current. The nonsteady problem of the evolution of a perturbation and its transformation into a nonlinear wave structure is considered. The evolution of an intense, initially nonmoving region with a constant increased ion density is investigated. It is shown that the evolution of a rather intense nonmoving region with a constant increased ion density can result in the formation of a shock wave. In addition to the compressional wave, a rarefaction region (dilatation wave) appears. The presence of a dilatation wave finally leads to the destruction of the shock structure. The possibility is discussed of the observation of shock waves related to dust charging in the presence of electromagnetic radiation in active rocket experiments, which involve the release of a gaseous substance in the Earth's ionosphere in the form of a high-speed plasma jet at altitudes of 500–600 km.

Nonlinearly coupled inertial Alfvén and dust acoustic waves in complex plasmas

The nonlinear coupling between finite amplitude inertial Alfvén (IA) and dust acoustic (DA) waves in a complex plasma is considered. By employing a multi-fluid dusty plasma model, which includes the effects of the ponderomotive force on the DA waves, a system of coupled equations is derived and used to study modulational instabilities of a constant amplitude IA wave. The results may have relevance to nonlinear phenomena involving IA and DA waves in low-temperature laboratory and space plasmas.