Dynamics of Strongly Coupled Complex Plasma Systems with Directed Ion Flow

Baylor University, Waco TX

Investigators

Abstract

This research project will investigate wakes, a phenomenon widely encountered in nature and spanning a range of length scales. Wakes are observed in the bow shock of a neutron star speeding through interstellar gas, in cloud patterns as air flows past ocean islands, and behind rocks in flowing streams. Cyclists take advantage of the wake created by their teammates, riding close behind each other to conserve energy. This research investigates the wakes formed by positively charged ions flowing past negatively charged dust particles in a complex plasma. The micron-sized dust particles in a complex (dusty) plasma have the ability to self-organize into a wide variety of structures. Much like drafting cyclists, dust particles trapped in the flowing plasma tend to line up downstream of each other. The energy savings due to dust alignment in the wakefield has an effect on the dynamics and the stability of dust structures. Complex plasmas are an excellent system for studying dynamic effects such as structure formation, as they allow direct observation at easily accessible space and time scales. An investigation of the modes of oscillation and structural transitions in a complex plasma can also provide insight into the dynamics of other finite systems which cannot be easily imaged. Many dusty plasma experiments utilize dust grains suspended in the sheath formed between the plasma and a bounding surface. The electric fields present in the sheath accelerate the plasma ions towards the bounding surface, leading to an ion wake downstream of the grains. The primary objective of this research is to investigate the effect of the plasma wakefield interaction on the self-organization, dynamics, and phase transitions in self-assembled dust structures within a complex plasma environment. This research merges computational and experimental techniques. A dynamic computational simulation is needed, as forces, charges, and wakes all change with particle location and the proximity of other particles. Numerical models will provide self-consistent calculations of dynamics, charging and anisotropic screening of dust particles in an ion flow. Charging and wakefield formation will be linked to the plasma environment, defining the response of the plasma to boundary conditions. At the same time, experimental techniques are needed that can produce specific particle structures in a controlled manner. Laboratory experiments will employ state-of-the-art techniques designed to control and confine the dust within dust clouds, strings, clusters, and crystals with defined characteristics. Experimentally, dust particles will also be used as in situ probes to measure the local plasma environment providing data for use in the numerical models.