Dusty Plasma Liquid Research Articles

How does the supercooled dusty plasma liquid relax microscopically after quenching?

For the liquid quenched to the glass forming state, its dynamics becomes slow, associated with the emergence of heterogeneities in structure and motion. The microscopic transient relaxation of the supercooled liquid towards a new equilibrium after deep quenching still remains an open challenging issue. In this work, our recent studies on this issue through direct tracking particle motion of a dusty plasma liquid after quenching are briefly reviewed. The spatiotemporal evolutions of multi-scale dynamics on the multi-scale heterogeneous network with increasing waiting time, their self-similar power law scaling behaviour of the observed behaviours, are presented and discussed. With the suppressed thermal agitation after quenching, the structural memory of the multi-scale patchwork which only allows the slow strain energy release and cascading through structural rearrangement is the key for the slow power law relaxation with large fluctuations.

Correlating Structural Order with Structural Rearrangement in Dusty Plasma Liquids: Can Structural Rearrangement be Predicted by Static Structural Information?

Whether the static microstructural order information is strongly correlated with the subsequent structural rearrangement (SR) and their predicting power for SR are investigated experimentally in the quenched dusty plasma liquid with microheterogeneities. The poor local structural order is found to be a good alarm to identify the soft spot and predict the short term SR. For the site with good structural order, the persistent time for sustaining the structural memory until SR has a large mean value but a broad distribution. The deviation of the local structural order from that averaged over nearest neighbors serves as a good second alarm to further sort out the short time SR sites. It has the similar sorting power to that using the temporal fluctuation of the local structural order over a small time interval.

Transient slowing down relaxation dynamics of the supercooled dusty plasma liquid after quenching

The spatiotemporal evolutions of microstructure and motion in the transient relaxation toward the steady supercooled liquid state after quenching a dusty plasma Wigner liquid, formed by charged dust particles suspended in a low pressure discharge, are experimentally investigated through direct optical microscopy. It is found that the quenched liquid slowly evolves to a colder state with more heterogeneities in structure and motion. Hopping particles and defects appear in the form of clusters with multiscale cluster size distributions. Via the structure rearrangement induced by the reduced thermal agitation from the cold thermal bath after quenching, the temporarily stored strain energy can be cascaded through the network to different newly distorted regions and dissipated after transferring to nonlinearly coupled motions with different scales. It leads to the observed self-similar multiscale slowing down relaxation with power law increases of structural order and structural relaxation time, the similar power law decreases of particle motions at different time scales, and the stronger and slower fluctuations with increasing waiting time toward the new steady state.

Shear viscosity and diffusion motion of two-dimensional dusty plasma liquids

A molecular dynamics method for studying diffusion motion and shear viscosity is presented for two-dimensional (2D) plasma liquids. The calculations obtained by using the mean-squared displacement (MSD), velocity autocorrelation function (VACF) and the shear autocorrelation function indicate that there is a diffusive motion for the lower coupling range of strongly coupled liquid states. In the MSD test, both states of a transition phase from normal diffusion to superdiffusion, and the extreme superdiffusion at intermediate coupling strength are dependent on screening strengths. The simulation data show that the position of extreme superdiffusion shifts towards higher coupling with an increase in screening strength, and the superdiffusion is nearly in a constant motion for higher coupling. A smooth transition from normal diffusion to superdiffusion exhibits the existence of superdiffusion at intermediate coupling strengths in the VACF test. A valid shear viscosity exists only at the intermediate and higher coupling parameters. It seems that the present calculations cannot establish a coupling between the viscosity and diffusion in 2D Yukawa liquids.

Thermal Conductivity of Three‐Dimensional Yukawa Liquids (Dusty Plasmas)

AbstractAn improved method is proposed to investigate the behavior of a Yukawa liquid under the action of an external field strength using computer simulated nonequilibrium molecular dynamics. The thermal conductivity calculations with appropriate normalizations, in the limit of low value field strengths, are estimated over a wide range of the Coulomb coupling and screening strengths. The new simulations provide more reliable data for the thermal conductivity than the previously known results for the Yukawa liquids. The calculations show that the thermal conductivity is dependent on both the Coulomb coupling and screening parameters in the three‐dimensional (3D) Yukawa liquids. The low value field strength simulation data are found to obey the universal and quasiuniversal scaling. It is shown that the homogenous nonequilibrium method can be used to predict the thermal conductivity in Yukawa systems and to understand the fundamental features of 3D dusty plasma liquids (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Projectile channeling in chain bundle dusty plasma liquids: Wave excitation and projectile-wave interaction

The microscopic channeling dynamics of projectiles in subexcitable chain bundle dusty plasma liquids consisting of long chains of negatively charged dusts suspended in low pressure glow discharges is investigated experimentally using fast video-microscopy. The long distance channeling of the projectile in the channel formed by the surrounding dust chain bundles and the excitation of a narrow wake associated with the elliptical motions of the background dusts are demonstrated. In the high projectile speed regime, the drag force due to wake wave excitation increases with the decreasing projectile speed. The excited wave then leads the slowed down projectile after the projectile speed is decreased below the resonant speed of wave excitation. The wave-projectile interaction causes the increasing projectile drag below the resonant speed and the subsequent oscillation around a descending average level, until the projectile settles down to the equilibrium point. Long distance projectile surfing through the resonant crest trapping by the externally excited large amplitude solitary wave is also demonstrated.

Crystal and liquid structures in strongly nonideal dusty plasmas under laboratory and microgravity conditions

This review presents the results obtained in a cycle of interrelated experimental works that have a priority character in the study of dusty plasma crystals and liquids under laboratory and microgravity conditions (on board the Mir Orbital Complex and the International Space Station) over wide ranges of temperatures and pressures: in a DC glow-discharge plasma and a low-pressure RF discharge plasma at room and cryogenic temperatures, in a nuclear-excited plasma and an UV-induced plasma, and in a thermal plasma at atmospheric pressure.

Cooperative microexcitations in 2+1D chain-bundle dusty plasma liquids

Through direct visualization at the discrete level, the microexcitations in cold 2+1D dusty plasma liquids formed by negatively charged dusts suspended in low pressure gaseous discharges were experimentally investigated, in which the downward ion flow wake field induces strong vertical coupling and chain bundle structure. It is found that the horizontal structure and motion are similar to those of the two-dimensional liquid. Different types of basic cooperative chain excitations: straight vertical chains with small amplitude jittering, chain tilting-restraightening, bundle twisting-restraightening, and chain breaking-reconnection, are observed. The region with good (poor) horizontal structural order prefers the straight (tilted or broken) chains with little (large) titling and tilting rate.

Investigation of non-Newtonian behavior of dusty plasma liquid

AbstractThe paper presents experimental investigation of flow of dusty plasma medium formed by macroparticles in argon plasma. The dependences of the coefficient of shear viscosity of such liquid on the external force causing the flow of dusty plasma liquid and on the pressure of plasma-generating gas are studied. It is found that the viscosity of the dusty plasma medium decreases with increasing shear stress and increases with increasing pressure of buffer gas. An experimental investigation of the dynamics of macroparticles in an unperturbed liquid dusty plasma medium as a function of coupling parameter is performed; in so doing, formations of particles whose motion is correlated are observed in the region of high values of coupling parameter. It is assumed that the non-Newtonian pattern of dusty plasma liquid may be due to the emergence of crystal-like dusty plasma clusters in the ‘liquid’ phase. An experimental investigation of a crystalline dusty plasma structure under the effect of laser radiation is performed; in so doing, a macroscopic flow of the crystalline dusty plasma structure is observed under the effect of shear stress. The mechanism of formation and subsequent annihilation of edge misfit dislocations is observed and the threshold pattern of such flow is established; the threshold value of power of laser radiation is determined.

Wave-Particle Dynamics of Wave Breaking in the Self-Excited Dust Acoustic Wave

The wave-particle microdynamics in the breaking of the self-excited dust acoustic wave growing in a dusty plasma liquid is investigated through directly tracking dust micromotion. It is found that the nonlinear wave growth and steepening stop as the mean oscillating amplitude of dust displacement reaches about 1/k (k is the wave number), where the vertical neighboring dust trajectories start to crossover and the resonant wave heating with uncertain crest trapping onsets. The dephased dust oscillations cause the abrupt dropping and broadening of the wave crest after breaking, accompanied by the transition from the liquid phase with coherent dust oscillation to the gas phase with chaotic dust oscillation. Corkscrew-shaped phase-space distributions measured at the fixed phases of the wave oscillation cycle clearly indicate how dusts move in and constitute the evolving waveform through dust-wave interaction.

Steady-shear-enhanced microdiffusion with multiple time scales of confined, mesoscopic, two-dimensional dusty-plasma liquids

We experimentally investigate the multitime scale diffusion and the spatiotemporal behaviors of the degrees of enhancement for the longitudinal and the transverse diffusions in a confined mesoscopic quasi-two-dimensional dusty-plasma liquid sheared by two parallel counterpropagating laser beams. The steady external drive directly enhances the longitudinal cooperative hopping, associated with the shear bands that have high shear rate near boundaries. It drastically excites the slow hopping modes to high fluctuation level in the outer band region, accompanied by the enhanced superdiffusion. Through cascaded many-body interaction, the excitation flows from the outer region toward the center region, from the longitudinal modes to the transverse mode, and from the slow hopping modes to the fast caging modes, which are in better contact with the thermal bath. It causes the weaker enhancement of fluctuation level, and diffusion for the center region and the fast modes. The boundary confinement further breaks the system symmetry and enhances anisotropy. It has much stronger effect on the suppression of the transverse hopping modes than the longitudinal hopping mode. The degrees of enhancement of the fluctuations by the shear stress are highly anisotropic for the large amplitude slow modes, especially in the outer region but are more isotropic in the inner band.

Solitary wake field microdynamics of the pulsed laser induced microbubbles in three-dimensional dusty plasma liquids

The Eulerian/Lagrangian dynamics in the narrow wake field of the dusty plasma bubble is explored by directly tracking dust motion at the microscopic level. The bubble is induced by the focused laser pulse ablation in three-dimensional quiescent dusty plasma liquids operated in the pressure higher than the critical pressure for the self-excitation of dust acoustic wave by the downward ion wind. It is found that, after bubble expansion ceases, the collective excitation maintains its width and travels downward as a solitary wave, led by an ultrasonic rarefaction front contributed by the dust motion below the lower boundary, and trailed by the few compressional crests with descending crest heights and speeds in the narrow wake, under the symmetry breaking by the downward ion flow. The quick damping of the waves propagating along other directions leads to a narrow wake. Increasing the background pressure causes the more isotropic collapsing of the bubble without wake field oscillation. The role played by dust motion on interacting with and sustaining the wake field evolution is identified and discussed.

Dynamical Heterogeneities in 2D Dusty Plasma Liquids at the Discrete Level

AbstractDown to the discrete microscopic level, the liquid is neither homogeneous nor completely disordered. The interplay of mutual coupling and thermal agitation makes the system support short range structural order, and avalanche‐type cooperative hopping excitations which lead to structural arrangement. The rich dynamical behaviors of spatio‐temporal heterogeneities are still poorly understood because of the lack of proper tools for direct visualization. The dusty plasma liquid can be self‐organized by negatively charged micrometer sized dusts suspending in a low‐pressure rf discharge background. Its sub‐mm inter‐particle distance and the tens of second thermal relaxation time make it a proper system to mimic and understand the generic spatio‐temporal behaviors of the liquid at the discrete kinetic level through direct optical video‐microscopy. In this paper, we briefly review the recent studies on the dynamical heterogeneities of the cold 2D dusty plasma liquids at the discrete level. The effects of mutual interaction, thermal agitation, external shear, and tight confinement on micro‐motion, anomalous diffusion, avalanche‐type excitations of hopping clusters and defect clusters, structural ordering and rearrangement, and visco‐elastic responses are presented and discussed (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Two-dimensional dusty plasma crystals and liquids

Strongly coupled plasmas - in which the average potential energy per particle dominates over the average kinetic energy - appear in a wide variety of physical systems. Among these systems, dust plasma crystals and liquids realized in low-pressure gas discharges by dispersing mesoscopic grains into the plasma have attracted a lot of attention during the past years. We describe the experimental realization of the quasi-two-dimensional dust system, summarize the basics of the computer simulation and theoretical approaches capable of their description in the liquid and solid phases. We discuss the properties of the dynamical density and current correlation spectra, generated by molecular dynamics simulations, and address the issues associated with the existence of different phases and transport coefficients (e.g. superdiffusive behavior) in the low-dimensional systems under study.

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.

Dusty-Plasma Liquid in the Statistical Theory of the Liquid State

Measurements in dusty plasmas were carried out to find the region of validity of approximate relation in statistical theory of liquid states. The integral equations with the Percus-Yewick and the hypernetted-chain closures as well as the superposition approximation were chosen as the objects for investigation. The range of validity of these approaches was obtained by the use of experimental methods for analysis of spatial correlation of dust particles in plasma.

A Note on the Possibility of Generating a Dense Dusty Plasma Liquid

Recently, there has been interest in the properties of strongly coupled dusty plasmas in the liquid phase. Here, we consider theoretically a possible way to generate and detect a dense dusty plasma liquid. The idea is to use noble metal submicron dust particles and detect the dust by scattering at the surface plasmon resonance frequency of the dust. Parameters that may be relevant to possible laboratory dusty plasma experiments are discussed.

Viscosity of a dusty plasma liquid

We present the results of our experimental study of the flow of a dusty plasma liquid produced by macroparticles in an argon plasma. The dependences of shear viscosity for such a liquid on the magnitude of the external force inducing the dusty plasma liquid flow and on the plasma-generating gas pressure are analyzed. We have established that the viscosity of a dusty plasma medium decreases with increasing shear stress in it, while the viscosity of such a liquid increases with buffer gas pressure. The flow of a dusty plasma liquid under the action of an external force has been found to resemble the plastic deformation of a Bingham body. We suggest that the formation of crystal-like dusty plasma clusters in a “liquid” phase can be responsible for the non-Newtonian behavior of the dusty plasma liquid flow.

Memory and persistence correlation of microstructural fluctuations in two-dimensional dusty plasma liquids

We investigate the temporal memory and persistence time correlations of microstructural order fluctuations in quasi-two-dimensional dusty plasma liquids through directly monitoring particle positions. The persistence length of the ordered and the disordered microstates both follow power-law distribution for the cold liquid. The correlation probabilities of the persistence lengths in different pairs of fluctuating cycles show that an order-disorder-order and a disorder-order-disorder sequence are more likely to have the long-short-long or short-long-short persistent lengths combination. The persistence time correlation lasts for several fluctuating cycles. The correlation memory is stored in the surrounding heterogeneous network through mutual coupling. Increasing thermal noise level deteriorates the memory and leads to the less correlated stretched exponential distribution of the persistent length.