A fundamental experimental study is proposed for nonequilibrium dynamics, viscoelastic behavior, and waves in strongly-coupled dusty plasma. Strongly-coupled plasma is ionized gas in which the interparticle potential energy is greater than the particle kinetic energy. Under these conditions, plasma behaves like a crystal or liquid, unlike more familiar weakly-coupled plasmas which behave like a gas. Dusty plasma consists of micron-size particles of solid matter suspended in a plasma consisting of electrons and ions. Due to collecting electrons and ions from the plasma, particles become highly charged. Typically, Q = -10,000 e for a 10 micron diameter sphere. This large charge produces a large interparticle repulsion. This large repulsion, combined with cooling the particles with gas drag, provides strong coupling. The size of the particles allows direct imaging and particle tracking using video micrography. Experiments are done with both 2D and 3D suspensions of microspheres. For 2D, the electric field of a plasma sheath levitates particles in the presence of gravity, yielding a single layer of particles. Discoveries made with this 2D system will help in understanding 2D physics in other areas of physics as well. For 3D, forces due to gas temperature gradients are applied to offset gravity, yielding a 3D suspension called a "Coulomb ball." Laser beams can push and manipulate particles in different ways to heat them, drive shear flows, and excite waves. A combination of this manipulation and gas friction provides a driven-dissipative system. This allows nonequilibrium systems to be studied experimentally at a fundamental level that is usually possible only in theory.
An experimental program is proposed for these fundamental physics topics: * Nonequilibrium fluctuations in 2D * Equilibration of 3D expanding plasma * Viscoelastic 2D physics * Interfaces in 3D under extreme shear. * Solitary waves in 2D crystal. Other impacts of the research activity include: * K12 outreach presentations in the "Hawk-Eyes on Science" series. * Participation of faculty of a non-PhD-granting institution. * Incorporating research topics in the teaching curriculum
This proposal was submitted to the NSF-DoE Partnership in Plasma Science and Engineering joint solicitation 08-589. This award is being funded by the Plasma Physics Program in the Division of Physics.
We carried out laboratory experiments and data analysis of laboratory experiments on the topic of strongly coupled dusty plasmas. We also carried out numerical simulations to support the experiments. A dusty plasma is a four-component mixture of neutral gas molecules, negative electrons, positive ions, and negatively charged small particles of solid matter. The latter, which are termed dust particles, have such large charges that they interact strongly, and tend to arrange themselves in an ordered structure similar to the way that molecules arrange themselves in a crystal or a liquid. The dust particles are so large that they allow video imaging of their motion, so that they can be tracked as they move about. This video imaging enables a study of many phenomena, such as melting and viscoelasticity, that are of great practical interest in normal matter but cannot be similarly studied because the constituent molecules are too small to image. In this way, strongly coupled dusty plasmas serve as a model system for the study of more common forms of matter. Results were reported in 19 publications in refereed journals, which are available to the public at the PI's website: http://dusty.physics.uiowa.edu. Titles of these publications are listed below: Gas flow driven by thermal creep in dusty plasma Experimental investigation of dust density waves and plasma glow Evolution of shear-induced melting in dusty plasma Dusty plasma diagnostics methods for charge, electron temperature and ion density Viscoelastic response of Yukawa liquids Viscoelasticity of 2D liquids quantified in a dusty plasma experiment Mode coupling for phonons in a single-layer dusty plasma crystal Identifying anomalous diffusion and melting in dusty plasmas Observation of the spatial growth of self-excited dust-density waves Development of nonlinearity in a growing self-excited dust-density wave Viscosity calculated in simulations of strongly-coupled dusty plasmas with gas friction Errors in particle tracking velocimetry with high-speed cameras Polygon construction to investigate melting in 2D strongly-coupled dusty plasma Viscosity obtained from the Green-Kubo relation using experimental data for a 2D dusty plasma. Synchronization and Arnold tongues for dust density waves Particle chains in a dilute dusty plasma with subsonic ion flow Cutoff wave number for shear waves and Maxwell relaxation time in Yukawa liquids Frequency-dependent shear viscosity of a liquid 2D dusty plasma Longitudinal viscosity of two-dimensional Yukawa liquids
