71 research outputs found
Thermodynamics of Yukawa fluids near the one-component-plasma limit
Thermodynamics of weakly screened (near the one-component-plasma limit)
Yukawa fluids in two and three dimensions is analyzed in detail. It is shown
that the thermal component of the excess internal energy of these fluids, when
expressed in terms of the properly normalized coupling strength, exhibits the
scaling pertinent to the corresponding one-component-plasma limit (the scalings
differ considerably between the two- and three-dimensional situations). This
provides us with a simple and accurate practical tool to estimate thermodynamic
properties of weakly screened Yukawa fluids. Particular attention is paid to
the two-dimensional fluids, for which several important thermodynamic
quantities are calculated to illustrate the application of the approach.Comment: Submitted to Phys. Plasma
Observation of particle pairing in a two-dimensional plasma crystal
The observation is presented of naturally occurring pairing of particles and
their cooperative drift in a two-dimensional plasma crystal. A single layer of
plastic microspheres was suspended in the plasma sheath of a capacitively
coupled rf discharge in argon at a low pressure of 1 Pa. The particle dynamics
were studied by combining the top-view and side-view imaging of the suspension.
Cross analysis of the particle trajectories allowed us to identify naturally
occurring metastable pairs of particles. The lifetime of pairs was long enough
for their reliable identification.Comment: 5 pages, 4 figure
Synchronization of particle motion in compressed two-dimensional plasma crystals
The collective motion of dust particles during the mode-coupling induced
melting of a two-dimensional plasma crystal is explored in molecular dynamics
simulations. The crystal is compressed horizontally by an anisotropic
confinement. This compression leads to an asymmetric triggering of the
mode-coupling instability which is accompanied by alternating chains of
in-phase and anti-phase oscillating particles. A new order parameter is
proposed to quantify the synchronization with respect to different directions
of the crystal. Depending on the orientation of the confinement anisotropy,
mode-coupling instability and synchronized motion are observed in one or two
directions. Notably, the synchronization is found to be direction-dependent.
The good agreement with experiments suggests that the confinement anisotropy
can be used to explain the observed synchronization process.Comment: 6 pages, 4 figure
First direct measurement of optical phonons in 2D plasma crystals
Spectra of phonons with out-of-plane polarization were studied experimentally
in a 2D plasma crystal. The dispersion relation was directly measured for the
first time using a novel method of particle imaging. The out-of-plane mode was
proven to have negative optical dispersion, comparison with theory showed good
agreement. The effect of the plasma wakes on the dispersion relation is briefly
discussed.Comment: submitted to Physical Review Letter
Wave mode coupling due to plasma wakes in two-dimensional plasma crystals: In-depth view
Experiments with two-dimensional (2D) plasma crystals are usually carried out
in rf plasma sheaths, where the interparticle interactions are modified due to
the presence of plasma wakes. The wake-mediated interactions result in the
coupling between wave modes in 2D crystals, which can trigger the mode-coupling
instability and cause melting. The theory predicts a number of distinct
fingerprints to be observed upon the instability onset, such as the emergence
of a new hybrid mode, a critical angular dependence, a mixed polarization, and
distinct thresholds. In this paper we summarize these key features and provide
their detailed discussion, analyze the critical dependence on experimental
parameters, and highlight the outstanding issues
Direct observation of mode-coupling instability in two-dimensional plasma crystals
Dedicated experiments on melting of 2D plasma crystals were carried out. The
melting was always accompanied by spontaneous growth of the particle kinetic
energy, suggesting a universal plasma-driven mechanism underlying the process.
By measuring three principal dust-lattice (DL) wave modes simultaneously, it is
unambiguously demonstrated that the melting occurs due to the resonance
coupling between two of the DL modes. The variation of the wave modes with the
experimental conditions, including the emergence of the resonant (hybrid)
branch, reveals exceptionally good agreement with the theory of mode-coupling
instability.Comment: 4 pages, submitted to Physical Review Letter
Nonlinear regime of the mode-coupling instability in 2D plasma crystals
The transition between linear and nonlinear regimes of the mode-coupling
instability (MCI) operating in a monolayer plasma crystal is studied. The mode
coupling is triggered at the centre of the crystal and a melting front is
formed, which travels through the crystal. At the nonlinear stage, the mode
coupling results in synchronisation of the particle motion and the kinetic
temperature of the particles grows exponentially. After melting of the
crystalline structure, the mean kinetic energy of the particles continued to
grow further, preventing recrystallisation of the melted phase. The effect
could not be reproduced in simulations employing a simple point-like wake
model. This shows that at the nonlinear stage of the MCI a heating mechanism is
working which was not considered so far.Comment: 6 pages, 4 figure
Forced mode-coupling instability in two-dimensional complex plasmas
It is demonstrated experimentally that the wake-mediated resonant coupling of the in-plane and out-of-plane collective motion in two-dimensional plasma crystals can be induced by applying various types of external forcing. When the forcing is sufficiently strong, it can trigger the mode-coupling instability leading to the melting of the crystalline monolayer. The experimental observations are supported by numerical analysis of the forced collective dynamics of particles with the wake-mediated interactions. The reported results show the universal nature of the wake-mediated mode coupling (also occurring for the " forced " wave modes) and confirm characteristic features of the mode-coupling instability predicted theoretically by Ivlev et al. [Phys. Rev. Lett. 113, 135002 (2014)]
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