Effect of strong wakes on waves in two-dimensional plasma crystals (original) (raw)
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Wave mode coupling due to plasma wakes in two-dimensional plasma crystals: In-depth view
Physics of Plasmas, 2011
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.
Coupling of Noncrossing Wave Modes in a Two-Dimensional Plasma Crystal
Physical Review Letters, 2017
We report an experimental observation of coupling of the transverse vertical and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex plasma crystal in the absence of mode crossing. A new large diameter rf plasma chamber was used to suspend the plasma crystal. The observations are confirmed with molecular-dynamics simulations. The coupling manifests itself in traces of the transverse vertical mode appearing in the measured longitudinal spectra and vice versa. We calculate the expected ratio of the trace to the principal mode with a theoretical analysis of the modes in a crystal with finite temperature and find good agreement with the experiment and simulations.
Coupled dust-lattice modes in complex plasmas
Physical Review E, 2005
The coupling between transverse and longitudinal dust-lattice modes due to the particle-wake interactions and vertical dust charge gradient is considered. It is shown that the dust-lattice waves can be subjected to a specific instability, the criterion for which has been derived. This instability can explain experimentally observed spontaneous excitation of vibrational modes in a plasma crystal when the pressure is decreased below a critical value.
Polarization of wave modes in a two-dimensional hexagonal lattice using a complex (dusty) plasma
Physical Review E, 2003
Wave spectra corresponding to the random particle motion in a monolayer Yukawa crystal were studied for various directions of propagation. It was found that there are two wave modes with a polarization alternating between the longitudinal and transverse. In the long-wavelength regime, the modes became purely longitudinal and transverse as was known before. In the short-wavelength regime the spectra strongly depended on the wavelength and the direction of propagation. The results obtained from the experiment, theory, and simulation agreed well with each other.
Direct Observation of Mode-Coupling Instability in Two-Dimensional Plasma Crystals
Physical Review Letters, 2010
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.
Physics of Plasmas, 2009
The propagation of nonlinear dust-lattice waves in a two-dimensional hexagonal crystal is investigated. Transverse (off-plane) dust grain oscillatory motion is considered, in the form of a backward propagating wavepacket whose linear and nonlinear characteristics are investigated. An evolution equation is obtained for the slowly varying amplitude of the first (fundamental) harmonic, by making use of a two-dimensional lattice multiple scales technique. An analysis based on the continuum approximation (spatially extended excitations, compated to the lattice spacing) shows that wavepackets will be modulationally stable and that dark-type envelope solitons (density holes) may occur, in the long wavelength region. Evidence is provided of modulational instability and of the occurrence of bright-type envelopes (pulses) at shorter wavelengths. The role of second neighbor interactions is also investigated, and is shown to be rather weak in determining the modulational stability region. The effect of dissipation, assumed negligible in the algebra throughout the article, is briefly discussed.
Modulational Instability of Dust-Lattice Waves in a Plasma Crystal
Physica Scripta, 1998
A nonlinear Schro dinger equation for the propagation of a dust-lattice wave in a one-dimensional chain of a plasma crystal is derived by using the KrylovĂBogoliubovĂMitropolsky (KBM) perturbation technique. The resulting equation is then analyzed to obtain a nonlinear dispersion relation for the wave envelope. It has been found that the dust-lattice wave is modulationally unstable for long wavelength perturbations and the modulationally unstable wave propagates as an envelope soliton. The importance of this investigation in present-day laboratory experiments for dust-plasma crystallization is pointed out.
Nonlinear modulation of transverse dust lattice waves in complex plasma crystals
Physics of Plasmas, 2004
The occurrence of the modulational instability in transverse dust lattice waves propagating in a one-dimensional dusty plasma crystal is investigated. The amplitude modulation mechanism, which is related to the intrinsic nonlinearity of the sheath electric field, is shown to destabilize the carrier wave under certain conditions, possibly leading to the formation of localized envelope excitations. Explicit expressions for the instability growth rate and threshold are presented and discussed.
Ion-wake-induced anomaly of dust lattice mode in the presence of an external magnetic field
We report a theoretical investigation of the dust lattice (DL) mode in two-dimensional Yukawa crystals in the presence of asymmetric ion flow and an external magnetic field perpendicular to the crystal plane. Two mutually perpendicular modes are found to be coupled due to Lorentz force. Interaction among the dust grains along the vertical direction of ion flow is strongly affected due to the formation of an ion wake. This causes anisotropy in interaction strength along two mutually perpendicular directions. Both hybrid modes are studied as characteristics of different ion flow speeds and magnetic field strengths. The study shows a fluctuation in DL mode frequency driven by the strength of the particle-wake interaction. The effect of ion flow on polarization of the hybrid wave amplitudes is discussed in detail. Results show a possible mechanism of anomalous phase transition in dusty plasma.
Charge gradient effects on modulated dust lattice wave packets in dusty plasma crystals
Iranian Journal of Physics Research, 2012
Nonlinear Dust lattice modes are studied in a hexagonal two-dimensional dusty plasma lattice, in presence of charge gradient of dust particles. In this lattice, such gradients affect nonlinear behavior of dust lattice waves. The amplitude modulation of off-plane transverse dust lattice wave packets is investigated considering the anisotropy of interactions, caused by the height-dependent charge variations. A nonlinear Schrodinger equation described time evolution of modulated off-plane transverse dust lattice wave packet. Calculations show that the charge gradient changes the stability condition of the solution of the nonlinear Schrodinger equation.