Dmitry Samsonov

Molecular-Dynamics Simulations of Dynamic Phenomena in Complex Plasmas

Complex plasmas consist of micrometer-sized spheres immersed into an ordinary ion-electron plasma. They exist in solid, liquid, and gaseous states, sustain particle-mediated waves, and exhibit a range of nonlinear and dynamic effects. Here, we present a numerical study of nonlinear-wave steepening (tsunami effect), interaction of solitons, and shock-wave propagation in monolayer complex plasmas. The simulated results are found to be in a good agreement with the experiments. It was also found that the simulation using a tenth-order confinement potential produced more homogeneous lattices with fewer defects than that with the conventional parabolic potential.

Ideal Gas Behavior of a Strongly Coupled Complex (Dusty) Plasma

In a laboratory, a two-dimensional complex (dusty) plasma consists of a low-density ionized gas containing a confined suspension of Yukawa-coupled plastic microspheres. For an initial crystal-like form, we report ideal gas behavior in this strongly coupled system during shock-wave experiments. This evidence supports the use of the ideal gas law as the equation of state for soft crystals such as those formed by dusty plasmas.

Tracking shocked dust: State estimation for a complex plasma during a shock wave

We consider a two-dimensional complex (dusty) plasma crystal excited by an electrostatically-induced shock wave. Dust particle kinematics in such a system are usually determined using particle tracking velocimetry. In this work we present a particle tracking algorithm which determines the dust particle kinematics with significantly higher accuracy than particle tracking velocimetry. The algorithm uses multiple extended Kalman filters to estimate the particle states and an interacting multiple model to assign probabilities to the different filters. This enables the determination of relevant physical properties of the dust, such as kinetic energy and kinetic temperature, with high precision. We use a Hugoniot shock-jump relation to calculate a pressure-volume diagram from the shocked dust kinematics. Calculation of the full pressure-volume diagram was possible with our tracking algorithm, but not with particle tracking velocimetry.

Three-dimensional structure of Mach cones in monolayer complex plasma crystals.

The structure of Mach cones in a crystalline complex plasma has been studied experimentally using an intensity sensitive imaging, which resolved particle motion in three dimensions. This revealed a previously unknown out-of-plane cone structure, which appeared due to excitation of the vertical wave mode. The complex plasma consisted of micron sized particles forming a monolayer in a plasma sheath of a gas discharge. Fast particles, spontaneously moving under the monolayer, created Mach cones with multiple structures. The in-plane cone structure was due to compressional and shear lattice waves.

High-Speed Imaging of a Shock in a Complex Plasma

The motion of particles in a complex (dusty) plasma agitated by a shock wave was resolved with a high-speed video camera. The shock melted the initially crystalline monolayer. Macroscopic parameters such as number density, kinetic temperature, and flow velocity were determined. The shock caused a 30-fold jump in kinetic temperature. The width of the shock front was found to be on the order of the interparticle distance.

Steepening of solitons (tsunami effect) in complex plasmas

The effect of soliton steepening has been observed experimentally and numerically in a complex plasma. Complex plasmas are mixtures of micron-sized microspheres with ion-electron plasmas. Formed in the sheath of a gas discharge they often form monolayer hexagonal quasi-crystals. A soliton propagating in a monolayer with decreasing number density gains amplitude even in the presence of a damping force. This effect is similar to tsunami formation. The results were found to differ from the prediction of the Korteweg-de Vries equation by up to a factor of 1.7.

Defect dynamics in complex plasmas: Interactions between solitons and penta-hepta defects (dislocations)

We report an experimental and numerical study of the dynamic behavior of dislocations in two-dimensional strongly coupled plasma crystals excited by compressional solitary waves. Complex plasmas are mixtures of micron-sized particles with ion-electron plasmas. Confined in the sheath of a gas discharge they often form hexagonal quasi-crystals. It was found that the penta-hepta defect either moved in small increments due to elastic deformation caused by the wave or experienced large jumps from one pair of particles to the next. The elastic displacement occurred primarily in the direction of the wave, whereas the jumps were in the direction parallel to Burgers vector of the dislocation.

Tracking dust: tracking and state estimation for dusty plasmas

Complex (dusty) plasmas - consisting of micron-sized grains within an ion-electron plasma - are a unique vehicle for studying the kinematics of microscopic systems. Although they are mesoscopic, they embody many of the major structural properties of conventional condensed matter systems (fluid-like and crystal-like states) and they can be used to probe the structural dynamics of such complex systems. Modern state estimation and tracking techniques allow complex systems to be monitored automatically and provide mechanisms for deriving mathematical models for the underlying dynamics - identifying where known models are deficient and suggesting new dynamical models that better match the experimental data. This paper discusses how modern tracking and state estimation techniques can be used to explore and control important physical processes in complex plasmas: such as phase transitions, wave propagation and viscous flow.

Visualizing a Dusty Plasma Shock Wave via Interacting Multiple-Model Mode Probabilities

Particles in a dusty plasma crystal disturbed by a shock wave are tracked using a three-mode interacting multiple model approach. Color-coded mode probabilities are used to visualize the shock wave propagation through the crystal.

Dislocations dynamics during plastic deformations of complex plasma crystals

The internal structures of most periodic crystalline solids contain defects. This affects various important mechanical and thermal properties of crystals. Since it is very difficult and expensive to track the motion of individual atoms in real solids, macroscopic model systems, such as complex plasmas, are often used. Complex plasmas consist of micrometer-sized grains immersed into an ion-electron plasma. They exist in solidlike, liquidlike, and gaseouslike states and exhibit a range of nonlinear and dynamic effects, most of which have direct analogies in solids and liquids. Slabs of a monolayer hexagonal complex plasma were subjected to a cycle of uniaxial compression and decompression of large amplitudes to achieve plastic deformations, both in experiments and simulations. During the cycle, the internal structure of the lattice exhibited significant rearrangements. Dislocations (point defects) were generated and displaced in the stressed lattice. They tended to glide parallel to their Burgers vectors under load. It was found that the deformation cycle was macroscopically reversible but irreversible at the particle scale.