Collaborative Research: Fundamental Charging Processes of Dust in Complex Plasmas

University Of Alabama In Huntsville, Huntsville AL

Investigators

Abstract

Complex plasmas, also known as dusty plasmas, consist of ions, electrons and charged dust, tiny solid particles much smaller than the width of a human hair. Dusty plasmas have long been of interest in the astrophysics community, due to the fact that dust and ionized gas are found in most space environments, including the clouds from which stars and planets form, comet tails, planetary rings, and noctilucent clouds in the earth's ionosphere. Dusty plasmas are also present on Earth in applied settings. They are formed in the chemically active gases used in industrial plasma processing devices to create computer chips, contaminating the end product and reducing overall yield. Dust contamination within fusion devices is also an issue, since dust produced through erosion of the containment walls raises both safety (operating instabilities) and health (long-term contamination) concerns. The formation of dust crystals, clusters and strings in laboratory plasmas has also proven to be a capable analog for atomic and molecular systems. Charging of dust grains is a unique and important aspect of dusty plasmas. Understanding the physics behind this charging and subsequent formation of dust structures immersed within plasma has proven to require nuanced details. The charge acquired by the dust grains is determined by the plasma environment, but the charged particles in turn influence this environment. Local variations in the charge, either over the surface of a single dust grain or the multiple dust grains comprising a larger structure, can affect both the grain's local dynamics and the evolution of the overall system. Many situations introduce asymmetries into this problem, making the charge difficult to describe analytically. Complicating factors include variations in space (due to geometry of the dust structure or of the plasma environment) as well as variations in time (due to the response of the plasma to the moving dust grains or stochastic charging processes). The dust charge is also extremely difficult to determine in experiments. Thus, the primary objective of this research is to determine how variations in charge in both time and space influence and respond to the dynamics and configuration of dust particles in plasma environments. In order to accomplish this goal, numerical modeling techniques will be combined with laboratory experiments to provide a proper understanding of the processes governing the system behavior. Numerical models will be used to model temporal and spatial charge variation over the dust structures, including stochastic effects to resolve the variations in time due to the discrete nature of the plasma particles. The charging will also be linked to numerical models of the plasma environment which define the response of the plasma to boundary conditions and the dust itself. Simultaneously, laboratory experiments will employ state-of-the-art techniques to control and confine the dust within dust clouds, strings, clusters, and aggregates in order to use them as in situ probes to measure the local plasma environment.