Dust Particle Properties in a Dual-Frequency Driven Sheath

We study characteristics of a single dust particle in a duai-frequency capacitively coupled plasma sheath, such as charging and suspending processes, using a collisionless self-consistent model. Also, the movement of the dust grain with time is investigated for the various radii and initial velocities. The numerical results show that, after several microseconds, the charging process of the dust particle reaches equilibrium, and the grain obtains its equilibrium position, In addition, it is found that the parameters of the low-frequency source impact on the charging and suspending processes of the dust grain significantly.     

Dust Lattice Waves of Dusty Plasma Chain with an External Magnetic Field

Dust lattice waves of a one-dimensional plasma crystal chain with an external magnetic field are investigated. When the magnetic field is in the vertical direction （θ- 0）, perpendicular to the chain, the vertical transverse mode is not affected, while the horizontal transverse mode is coupled with the longitudinal mode. In the high frequency range, we obtain an ‘upper-hybrid＇ dust lattice mode and in the low frequency range, we obtain a ＇lower-hybrid＇ dust lattice mode. Between the two modes, a ＇gap＇ is formed. When the magnetic field is oriented to the chain （0 = π/2）, the longitudinal mode is not affected while both the horizontal and vertical transverse modes are shifted due to the effect of the magnetic field.     

A fluid model of the current-voltage characteristics of an electron emitting electrode immersed in a two electron temperature plasma

The current voltage characteristics of a negatively biased electron emitting electrode immersed in a two-electron temperature plasma are analyzed by a simple one dimensional fluid model. Based on the assumption that the electron density in the pre-sheath region obeys the Boltzmann law the Bohm criterion is derived in the form of a transcendental equation for the Mach number, which can have up to 3 solutions. According to these solutions the ion velocity at the sheath edge can be determined either by the hot or by the cool electron temperature. When it is determined by the cool electron temperature and the hot electron temperature is high enough the critical electron emission current from the collector can have a very pronounced local maximum and a minimum when regarded as a function of the electrode potential. Because of that the current voltage characteristics of the electrode may exhibit up to 3 different floating potentials. This result is in good agreement with the experimental observations reported in [J. Appl. Phys. 63, 5674 (1988)].     

Oscillation modes in Coulomb clusters with variable charges

The mode spectra of small N=3 and N=7 clusters of dust particles with fluctuating charges are analyzed. It is demonstrated that the main effect related to the charge fluctuations is a splitting of the spectrum modes. The splitting depends the value of the charge variance. It is found that the most affected mode is the fundamental pure rotational mode. The least affected modes are pure translational ones while other modes demonstrate mixed response to the variance of the charge fluctuations.     

Ion-acoustic dressed solitons in electron-positron-ion plasmas

Expanding the Sagdeev potential to include fourth-order nonlinearities of electric potential and integrating the resulting energy equation, an exact soliton solution is determined for ion-acoustic waves in an electron-positron-ion (e-p-i) plasma system. This exact solution reduces to the dressed soliton solution obtained for the system using renormalization procedure in the reductive perturbation method (RPM), when Mach number (M) is expanded in terms of soliton velocity (λ) and terms up to order of λ² are retained in the analysis. Variation of shape, velocity, width and product (P) of amplitude (A) and square of width (W²) for the KdV soliton, core structure, dressed soliton, and exact soliton are graphically represented for different values of fractional positron concentration (p). It is found that for a given value of the fractional positron concentration (p) and amplitude of soliton, the velocity of the dressed soliton is faster and width is narrower than the KdV or exact soliton, and agrees qualitatively with the experimental observations of Ikezi et al. for small amplitude solitons in the plasma free from positron component. Among all these structures, the product P(AW²) is found to be lowest for the dressed soliton and it decreases as Mach number of soliton or fractional positron concentration in the plasma increases.     

Effects of positron density and temperature on ion acoustic dressed solitons in an electron–positron–ion plasma

Ion acoustic dressed solitons in a three component plasma consisting of cold ions, hot electrons and positrons are studied. Using reductive perturbation method, Korteweg–de Vries (KdV) equation and a linear inhomogeneous equation, governing respectively the evolution of first and second order potentials are derived for the system. Renormalization procedure of Kodama and Taniuti is used to obtain nonsecular solutions of these coupled equations. It is found that electron–positron–ion plasma system supports only compressive solitons. For a given amplitude of soliton on increasing the positron concentration, velocity of the KdV as well as dressed soliton increases. For any arbitrary values of soliton's amplitude and positron concentration, velocity of the dressed soliton is found to be larger than that of the KdV soliton. For small amplitude of solitons, the width of KdV as well as dressed soliton decreases as positron concentration increases and width of dressed soliton is found to be larger than that of the KdV soliton. However, for a large value of soliton's amplitude as concentration of positrons increases, instead of decreasing width of dressed soliton starts to increase.     

Lattice Wave of Magnetized Spherical Dust in Radio-Frequency Sheath with Negative Ions

Lattice wave of magnetized spherical dust in radio-frequency sheath with negative ions is investigated. The dispersion relation of two-dimensional hexagonal lattice horizontal wave and the influence of negative ions and magnetic field intensity on the wave are also investigated. The results show that for two-dimensional hexagonal horizontal lattice wave, negative ions reduce the wave frequency at the range of long-wavelength, whereas raising the wave frequency at the range of short-wavelength and magnetic field contributes to dropping the wave frequency a little.     

Nonplanar Ion-Acoustic Solitons in Electron-Positron-Ion Quantum Plasmas

The propagation of nonplanar quantum ion-acoustic solitary waves in a dense, unmagnetized electron-positronion （e-p-i） plasma are studied by using the Korteweg-de Vries （KdV） model. The quantum hydrodynamic （QHD） equations are used taking into account the quantum diffraction and quantum statistics corrections. The analytical and numerical solutions of KdV equation reveal that the nonplanar ion-acoustic solitons arc modified significantly with quantum corrections and positron concentration, and behave differently in different geometries.     

Propagation and Interaction of Ion-Acoustic Solitary Waves in a Two-Dimensional Plasma Consisting of Isothermal Electrons and Hot Ions

We study the propagation and interaction of ion-acoustic solitary waves in a simple two-dimensional plasma by using the extended Poincare Lighthill-Kuo perturbation method. We consider the interaction between two ion-acoustic solitary waves with different propagation directions in such a system, and obtain two Korteweg-de Vries equations for small but finite amplitude solitary waves along both ξ and η trajectories. The effects of the ratio of ion temperature σ the ratio of heat capacity γ and the colliding angle a on the amplitude, the width of the new nonlinear wave created by the collision between two solitary waves are studied. The effects of these parameters on both the colliding solitary waves are examined as well. It is found that all the above-mentioned parameters have significant effects on the properties of these nonlinear waves.     

Electrostatic Nonlinear Structures in Dissipative Electron--Positron--Ion Quantum Plasmas

Low frequency （in comparison to ion plasma frequency） ion-acoustic shocks and solitons in superdense electronpositron-ion quantum plasmas are studied. The quantum hydrodynamic model is used incorporating quantum Bohm forces and Fermi-Dirac statistical corrections to derive the deformed Korteweg de Vries-Burgers （dKdVB） equation in weakly nonlinear limit. The travelling wave solution of dKdVB equation is presented and results are discussed in different limits. It is found that shock height increases with increase of quantum pressure, positron concentration and dissipation. Further, it is seen that the width of soliton decreases with increase of quantum pressure     

Low-Frequency Relaxation Oscillations in Capacitive Discharge Processes

Low-frequency （2.72-3.70 Hz） relaxation oscillations at 100 mTorr at higher absorbed power were observed from time-varying optical emission of the main discharge chamber and the periphery. We interpret the low frequency oscillations using an electromagnetic model of the slot impedance with parallel connection variational peripheral capacitance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions.     

Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

Linear and nonlinear electrostatic waves in unmagnetized electron-positron-ion (e-p-i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e-p) plasma in the presence of ions. The small amplitude electrostatic Korteweg-de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e-p-i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e-p-i plasmas are also discussed.     

Numerical Simulation of Dust Void Evolution in Complex Plasmas with Ionization Effect

We develop the nonlinear theory of dust voids [Phys. Rev. Lett. 90 （2003） 075001], focusing particularly on effects of the ionization, to investigate numerically the void evolution under cylindrical coordinates [Phys. Plasmas 13 （2006） 064502]. The ion velocity profile is solved by a more accurate ion motion equation with the ion convection and ionization terms. It is shown that the differences between the previous result and the one obtained with ionizations are significant for the distributions of the ion and dust velocities, the dust density, and etc., in the void formation process. Furthermore, the ionization can slow down the void formation process effectively.     

Comparison between Dual Radio Frequency- and Pulse-Driven Sheath near Insulating Substrates

We carry out a comparison between the characteristics of radio frequency- and pulse-sheath near insulating substrates driven by dual frequency （DF） sources making use of the fluid model in which the self-bias voltage on the electrode is obtained consistently under a current balance condition. The results show that the combination of the higher and lower frequency source modulate the characteristics of the radio-frequency- and pulse-sheath： the higher frequency makes the physical quantities oscillate fast while the slow oscillating contour of variation in physical quantities is modulated by the lower frequency source. However, there are some differences between the capacity of mitigating the charging effects on the surface of the insulator, i.e., the pulsed driven plasma gains an advantage over the radio-frequency driven one because the insulating surface to neutralize the positive charge the ＇off＇ state of the pulse allow more electrons to reach due to the incident ion as the pulse being in the pulse＇s duty. In addition, the ion energy distribution （IED） bombarding the surface of the insulator has a range of energy for the radio-frequency bias while that for the pulse bias is discontinuous.     

Relativistic Magnetosonic Soliton in a Negative-Ion-Rich Magnetized Plasma

Two-dimensional (2D) relativistic magnetosonic solitons in the negative-ion-rich plasma consisting of positive ions Ar⁺, negative ions SF₆^- and electrons are investigated in the presence of an applied magnetic field B₀ and can be described by a Kadomtsev--Petviashvili (KP) equation in the weakly relativistic limit. The ratio of positive ion density to negative ion density has a marked influence on the amplitude Φ_m and width W of the steady-state KP soliton. The interaction law of the nontrivial solitons with rich web structure is studied by the Wronskian determinant method.     

Effect of Thermionic Emission on Dust-Acoustic Solitons in a Dust-Electron Plasma

The effects of thermionic emission on dust-acoustic solitons with a very small but finite amplitude in a dustelectron plasma are studied using the reductive perturbation technique. The self-consistent variation of dust charge is taken into account. It is shown that the thermionic emission could significantly increase the dust positive charge. The dependences of the phase velocity, amplitude, and width of such solitons on the dust temperature and the dust work function of dust material are plotted and discussed.     

Global Wave Solution of generalized MHD Equations in a Cylindrical Plasma

The linear eigenstate problem of generalized magnetohydrodynamics(MHD) equations in a cylindrical plasma is discussed. The effects of finite frequency and finite pressure perturbation lead to an important result: the resonant layer of the shear Alfven waves is not a singular layer. In this paper, the MHD equations are reduced to four differential equations of first order for perturbed quantities. An analytical dispersion relation for a homogeneous plasma cylinder is obtained. The K. Appert theory is a limiting case of our theory     

Dynamic nature of the ion wake in dusty plasmas

The dynamic nature of the ion wake formed downstream a dust particle immersed in a plasma with flowing ions has been investigated via Particle-in-Cell simulation. It is found that the wake oscillates in time and the motion is characterized by some dominant frequencies. By means of signal processing analysis, three harmonics are detected (two at low frequencies and one at high frequencies) and compared to the characteristic plasma frequencies given by the dispersion relations for ions and electrons. Good matching is found between the high frequency harmonic and the electron plasma frequency, and between the low frequency harmonics and the ion acoustic and ion plasma frequencies.     

Reflection of Electromagnetic Waves by a Nonuniform Plasma Layer Covering a Metal Surface

Reflection coefficients of electromagnetic waves in a nonuniform plasma layer with electrons, positive ions and negative ions, covering a metal surface are investigated by using the finite-difference-time-domMn method. It is shown that the reflection coemcients are influenced greatly by the density gradient on the layer edge, layer thickness and electron proportion, i.e., the effect of the negative ions. It is also found that low reflection or high attenuation can be reached by properly choosing high electron proportion, thick plasma layer, and smooth density gradient in the low frequency regime, but sharp density gradient in the high frequency regime.