Dispersion relations of Yukawa fluids at weak and moderate coupling

In this paper we compare different theoretical approaches to describe the dispersion of collective modes in Yukawa fluids when the inter-particle coupling is relatively weak, so that kinetic and potential contributions to the dispersion relation compete. Thorough comparison with the results from molecular dymamics simulation allows us to conclude that in the regime investigated the best description is provided by the sum of the generalized excess bulk modulus and the Bohm-Gross kinetic term.Comment: 9 pages, 7 figure

Self-diffusion in single-component Yukawa fluids

It was suggested in the literature that the self-diffusion coefficient of simple fluids can be approximated as a ratio of the squared thermal velocity of the atoms to the "fluid Einstein frequency," which can thus serve as a rough estimate of the friction (momentum transfer) rate in the dense fluid phase. In this article we test this suggestion using a single-component Yukawa fluid as a reference system. The available simulation data on self-diffusion in Yukawa fluids, complemented with new data for Yukawa melts (Yukawa fluids near the freezing phase transition), are carefully analyzed. It is shown that although not exact, this earlier suggestion nevertheless provides a very sensible way of normalization of the self-diffusion constant. Additionally, we demonstrate that certain quantitative properties of self-diffusion in Yukawa melts are also shared by systems like one-component plasma and liquid metals at freezing, providing support to an emerging dynamical freezing indicator for simple soft matter systems. The obtained results are also briefly discussed in the context of the theory of momentum transfer in complex (dusty) plasmas.Comment: 6 pages, 3 figure

Nanoparticle formation and dynamics in a complex (dusty) plasma: from the plasma ignition to the afterglow.

Complex (dusty) plasmas are a subject of growing interest. They areionized gases containing charged dust particles. In capacitively-coupled RF discharges, dust growth can occur naturally and two methods can be used to grow dust particles: chemically active plasmas or sputtering. The growth of dust particles in argon discharges by RF sputtering and the effect of dust particles on theplasma have been investigated from the plasma ignition to the afterglow. It was shown that plasma and discharge parameters are greatly affected by the dust particles. Furthermore, plasma instabilities can be triggered by the presence of the dust particles. These instabilities can be due to dust particle growth or they can be instabilities of a well established dust cloud filling the interelectrode space. When the discharge is switched off, the dust particles act like a sink for the charge carrier and consequently affect the plasma losses. It was shown that the dust particles do keep residual chargeswhich values are greatly affected by the diffusion of the charge carriers and especially the transition from ambipolar to free diffusion

Brownian-like motion of a single dust grain in a radio-frequency plasma discharge comparison of experiments and simulations

Bronwnian-like motion of a single dust-grain in a radio frequency plasma has been studied by different research groups. The rise of the particles temperature above “room temperature” is attributed to e.g. random fluctuations of the particle charge and fluctuations of the electrical field. Additional disturbance might occur due to gas density variations, temporal variation of the particles mass and particle interaction with the illuminating laser light. In addition, a nonoptimal frame rate of the optical diagnostic system and pixel locking can lead to an incorrect estimation of the particle kinetic temperature. Our experiments are conducted in a weakly ionized radio-frequency gas discharge at a low neutral gas pressure and power. A single micron sized spherical particle is trapped in a harmonic-like potential trap in the sheath of the lower driven electrode [1]. Its twodimensional planar motion is recorded with a long-distance microscope and a high-resolution camera. From the measured particle positions we derive the probability density function, the velocity autocorrelation function and the mean squared displacement. We obtain a particle kinetic temperature above 350 K, a neutral gas damping time of about 0.5 sec and a resonance frequency of 1-2 Hz. Anisotropic oscillation of the particle occurs, leading to angle dependent temperatures along the x and y direction in the plane of the recorded images, which can be explained by the presence of an asymmetric horizontal potential trap. Experimental observations are compared with our simulations using md simulations and the Ornstein-Uhlenbeck stochastic process

On the long-waves dispersion in Yukawa systems

International audienceA useful simplification of the quasilocalized charge approximations (QLCA) method to calculate the dispersion relations in strongly coupled Yukawa fluids is discussed. In this simplified version, a simplest possible model radial distribution function, properly related to the thermodynamic properties of the system, is used. The approach demonstrates good agreement with the dispersion relations obtained using the molecular dynamics simulations and the original QLCA in the long-wavelength regime. (C) 2016 AIP Publishing LLC