Molecular-dynamics simulations of viscosity and diffusion in a 2d dusty plasma

Summary form only given. Simulations are reported to model transport processes in two-dimensional layers of dust suspended in a plasma. These simulations are motivated by recent experiments, where the viscosity and diffusion coefficients of charged microspheres in a plasma were measured by tracking the motion of individual particles. Molecular-dynamics (MD) simulations were carried out for charged particles interacting through a screened-Coulomb interaction. The particles moved in a two-dimensional plane, mimicking the microspheres in the experiment which are levitated in a horizontal plane above the electrode of an RF glow discharge plasma. The kinetic temperature of the particles was controlled using a software thermostat. The particle equation of motion was integrated using periodic boundary conditions. In the temperature range that was investigated, the particles were strongly-coupled but not in a crystalline lattice. They flowed easily, but interacted mainly with nearest neighbors, like molecules in a liquid. In this liquid phase, the viscosity coefficient was found to have a minimum, unlike most simple liquids. This minimum is attributed to the contributions of potential energy and kinetic motion, which vary with temperature. Also reported are values of the diffusion coefficient as a function of temperature. It is found that a valid diffusion coefficient exists in this 2D liquid only at low temperatures near the freezing transition and at high temperatures where it is a non-ideal gas. At intermediate temperatures particle motion is super-diffusive as shown by the mean-squared displacement (MSD) method