Collisionless bounce resonance heating in dual-frequency capacitively coupled plasmas.

We present the experimental evidence of the collisionless electron bounce resonance heating (BRH) in low-pressure dual-frequency capacitively coupled plasmas. In capacitively coupled plasmas at low pressures when the discharge frequency and gap satisfy a certain resonant condition, the high energy beamlike electrons can be generated by fast sheath expansion, and heated by the two sheaths coherently, thus the BRH occurs. By using a combined measurement of a floating double probe and optical emission spectroscopy, we demonstrate the effect of BRH on plasma properties, such as plasma density and light emission, especially in dual-frequency discharges.

Wave spectra of two-dimensional dusty plasma solids and liquids.

Brownian dynamics simulations were carried out to study wave spectra of two-dimensional dusty plasma liquids and solids for a wide range of wavelengths. The existence of a longitudinal dust-thermal mode was confirmed in simulations, and a cutoff wave number in the transverse mode was measured. Dispersion relations, resulting from simulations, were compared with those from analytical theories, such as the random-phase approximation (RPA), the quasilocalized charged approximation (QLCA), and the harmonic approximation (HA). An overall good agreement between the QLCA and simulations was found for wide ranges of states and wavelengths after taking into account the direct thermal effect in the QLCA, while for the RPA and HA, good agreement with simulations was found in the high and low-temperature limits, respectively.

Self-diffusion in 2D dusty-plasma liquids: numerical-simulation results.

We perform Brownian dynamics simulations for studying the self-diffusion in two-dimensional (2D) dusty-plasma liquids, in terms of both mean-square displacement and the velocity autocorrelation function (VAF). Superdiffusion of charged dust particles has been observed to be the most significant at an infinitely small damping rate gamma for intermediate coupling strength, where the long-time asymptotic behavior of VAF is found to be the product of t;{-1} and exp(-gammat). The former represents the prediction of early theories in 2D simple liquids and the latter the VAF of a free Brownian particle. This leads to a smooth transition from superdiffusion to normal diffusion, and then to subdiffusion with an increase of the damping rate. These results well explain the seemingly contradictory observations scattered in recent classical molecular dynamics simulations and experiments of dusty plasmas.

Image force on a charged projectile moving over a two-dimensional strongly coupled Yukawa system.

We use both analytical theory and numerical simulations to study the image force on a charged particle moving parallel to a two-dimensional strongly coupled Yukawa system. Special attention is paid to the effects of strong correlation and nonlinear response in the Yukawa system on the dependences of the image force on the particle velocity and its distance from the Yukawa system. Those effects are elucidated by comparing the results obtained from a Brownian dynamics simulation with those from linear-dielectric-response theories based on both the quasilocalized charge approximation and the standard Vlasov random phase approximation.

Energy loss of a charged particle moving over a 2D strongly coupled dusty plasma.

We use molecular dynamics (MD) simulation to evaluate the energy loss of a charged projectile moving parallel to a two-dimensional strongly coupled dusty plasma and compare the results with those obtained from the quasilocalized charge approximation (QLCA) and the Vlasov-random phase approximation. Good agreement is found between the QLCA and MD results when the projectile-dust coupling is weak. In the opposite regime, nonlinear effects in the dust-layer response render the QLCA model increasingly inadequate for calculating the energy losses at low projectile speeds.

Excitation of Mach cones and energy dissipation by charged particles moving over two-dimensional strongly coupled dusty plasmas.

We present a theoretical model for studying the interactions of charged particles with two-dimensional strongly coupled dusty plasmas, based on the quasilocalized charge approximation in which the static pair distribution function of a dust layer is determined from a molecular dynamics simulation. General expressions are derived for the perturbed dust-layer density, the induced potential in plasma, and the energy loss of a charged particle moving parallel to the dust layer. Numerical results show that the structure of Mach cones, excited in the dust layer by the charged particle, strongly depends on the plasma parameters such as the coupling parameter, the screening parameter, and the discharge pressure, as well as on the particle speed. In addition, it is found that the energy dissipation suffered by slow charged particles can be significantly enhanced in strongly coupled dusty plasmas when compared to the dissipation in weakly coupled plasmas.

Theoretical study of laser-excited Mach cones in dusty plasmas.

A two-dimensional hydrodynamic model for a monolayer of dust particles is used to study the Mach cones excited by a moving laser beam through dusty plasmas. Numerical results for the density perturbation and the velocity distribution of dust particles exhibit both compressional and shear-wave Mach cones. It is found that the compressional Mach cones exist in cases of both supersonic and subsonic excitations, and that they consist of multiple lateral or transverse wakes. On the other hand, realization of single shear-wave Mach cones depends closely on the excitation technique, the laser scanning speed, and the discharge pressures. It is found that, when the scanning direction of the laser beam is perpendicular to the laser force, a transition from multiple compressional Mach cones to a single shear Mach cone can be achieved either by lowering the scanning speed or by increasing the discharge pressures.

Induced potential of a dust particle in a collisional radio-frequency sheath.

A hydrodynamic model is established to study the interactions of a dust particle with a radio-frequency (rf) sheath, taking into account the influence of the spatial inhomogeneity of the (rf) sheath, as well as the influence of the ion-neutral collisions. Numerical results are obtained for the charge on the dust particle and for the spatial distribution of the induced potential around this particle, based on a self-consistent modeling of the sheath parameters such as the sheath electric field, the ion velocity, and the ion and electron densities. The induced potential exhibits the familiar oscillatory structure of a wake potential, which is, however, strongly damped due to the collisional effects. The spatial inhomogeneity of the rf sheath gives rise to a further damping of the induced potential, as well as to a reduction of the oscillations at large distances from the dust particle.

Self-consistent nonlinear resonance and hysteresis of a charged microparticle in a RF sheath.

A self-consistent model is proposed to study nonlinear phenomena, such as secondary resonance and hysteresis in the vertical oscillations of a charged microparticle in a radio-frequency sheath. The motion of a single microparticle in the sheath is simulated by solving Newton's equation in which various forces acting on the particle are taken into account. The particle charging and the sheath electric field are described by a self-consistent model of the collisional radio-frequency sheath dynamics. It is found that the nonlinearity is related to the particle's charge, the sheath electric field, and the external excitation force, as well as the ion drag force and neutral-gas friction on the particle.