Accurate freezing and melting equations for the Lennard-Jones system

Analyzing three approximate methods to locate liquid-solid coexistence in simple systems, an observation is made that all of them predict the same functional dependence of the temperature on density at freezing and melting of the conventional Lennard-Jones system. The emerging equations can be written as $T={\mathcal A}\rho^4+{\mathcal B}\rho^2$ in normalized units. We suggest to determine the values of the coefficients ${\mathcal A}$ at freezing and melting from the high-temperature limit, governed by the inverse twelfth power repulsive potential. The coefficients ${\mathcal B}$ can be determined from the triple point parameters of the LJ fluid. This produces freezing and melting equations which are exact in the high-temperature limit and at the triple point, and show remarkably good agreement with numerical simulation data in the intermediate region.Comment: 6 pages, 1 figur

Ionization enhanced ion collection by a small floating grain in plasmas

It is demonstrated that the ionization events in the vicinity of a small floating grain can increase the ion flux to its surface. In this respect the effect of electron impact ionization is fully analogous to that of the ion-neutral resonant charge exchange collisions. Both processes create slow ion which cannot overcome grain' electrical attraction and eventually fall onto its surface. The relative importance of ionization and ion-neutral collisions is roughly given by the ratio of the corresponding frequencies. We have evaluated this ratio for neon and argon plasmas to demonstrate that ionization enhanced ion collection can indeed be an important factor affecting grain charging in realistic experimental conditions.Comment: 7 pages, 1 figure, submitted to Physics of Plasma

Effect of strong wakes on waves in two-dimensional plasma crystals

We study effects of the particle-wake interactions on the dispersion and polarization of dust lattice wave modes in two-dimensional plasma crystals. Most notably, the wake-induced coupling between the modes causes the branches to "attract" each other, and their polarizations become elliptical. Upon the mode hybridization the major axes of the ellipses (remaining mutually orthogonal) rotate by $45^\circ$. To demonstrate importance of the obtained results for experiments, we plot spectral densities of the longitudinal and transverse waves revealing distinct fingerprints of the mixed polarization. Furthermore, we show that at strong coupling the hybrid mode is significantly shifted towards smaller wave numbers, away from the border of the first Brillouin zone (where the hybrid mode is localized for a weak coupling).Comment: 10 pages, 6 figure

The Bohm sheath criterion in strongly coupled complex plasmas

A modification of the classical Bohm sheath criterion is investigated in complex plasmas containing Boltzmann electrons, cold fluid ions and strongly coupled microparticles. Equilibrium is provided by an effective 'temperature' associated with electrostatic interactions between charged grains. Using the small-potential expansion approach of the Sagdeev potential, a significant reduction of the ion Bohm velocity is obtained for complex plasma parameters relevant for experiments. The result is of consequence for all problems involving ion drag on microparticles, including parametric instability, structure formation, wave propagation, etc

Shielding of a small charged particle in weakly ionized plasmas

In this paper we present a concise overview of our recent results concerning the electric potential distribution around a small charged particle in weakly ionized plasmas. A number of different effects which influence plasma screening properties are considered. Some consequences of the results are discussed, mostly in the context of complex (dusty) plasmas.Comment: This is a short review pape

Agglomeration of microparticles in complex plasmas

Agglomeration of highly charged microparticles was observed and studied in complex plasma experiments carried out in a capacitively coupled rf discharge. The agglomeration was caused by strong dust density waves triggered in a particle cloud by decreasing neutral gas pressure. Using a high-speed camera during this unstable regime, it was possible to resolve the motion of individual microparticles and to show that the relative velocities of some particles were sufficiently high to overcome the mutual Coulomb repulsion and hence to result in agglomeration. After stabilising the cloud again through the increase of the pressure, we were able to observe the aggregates directly with a long-distance microscope. We show that the agglomeration rate deduced from our experiments is in good agreement with theoretical estimates. In addition, we briefly discuss the mechanisms that can provide binding of highly charged microparticles in a plasma.Comment: submitted to Phys. Plasm

Channeling of particles and associated anomalous transport in a 2D complex plasma crystal

Implications of recently discovered effect of channeling of upstream extra particles for transport phenomena in a two-dimensional plasma crystal are discussed. Upstream particles levitated above the lattice layer and tended to move between the rows of lattice particles. An example of heat transport is considered, where upstream particles act as moving heat sources, which may lead to anomalous heat transport. The average channeling length observed was 15 - 20 interparticle distances. New features of the channeling process are also reported

Wake-mediated propulsion of an upstream particle in two-dimensional plasma crystals

The wake-mediated propulsion of an "extra" particle in a channel of two neighboring rows of a two-dimensional plasma crystal, observed experimentally by Du et al. [Phys. Rev. E 89, 021101(R) (2014)], is explained in simulations and theory. We use the simple model of a pointlike ion wake charge to reproduce this intriguing effect in simulations, allowing for a detailed investigation and a deeper understanding of the underlying dynamics. We show that the nonreciprocity of the particle interaction, owing to the wake charges, is responsible for a broken symmetry of the channel that enables a persistent self-propelled motion of the extra particle. We find good agreement of the terminal extra-particle velocity with our theoretical considerations and with experiments.Comment: 7 pages, 4 figures, PRL (https://journals.aps.org/prl/), updated version with correct author affiliation