Effect of ion flows on heating and instabilities in weakly coupled dusty plasmas

Auburn University, Auburn AL

Investigators

Abstract

Dusty (complex) plasmas are four-component plasma systems that consist of ions, electrons, neutral particles, and the addition of a fourth species, charged microscopic particles or "dust". The charged dust, which is typically composed of micron- or nanometer-sized particles, fully interacts and self-consistently modifies the properties of the surrounding plasma. Once primarily focused on astrophysical phenomena such as planetary rings or interstellar dust, the growth of laboratory studies of the role of charged microparticles in plasmas has offered a unique opportunity to observe plasma physics phenomena at the kinetic level. As a result, this field has become, over the last two decades, a robust scientific enterprise within the larger field of plasma science. In laboratory studies, the microparticles become charged through the collection of ions and electrons from the background plasma. This process alters the ion and electron distributions in the plasma. Furthermore, in the presence of flows in the plasma, particularly ion flows, not only are the charging conditions of the microparticles modified, but the flows alter the force balance that allows the microparticles to remain suspended in the plasma and provide a free energy source for heating the microparticles and driving instabilities. Thus, a continuing challenge to the understanding of dusty plasmas remains the interaction between the charged microparticles and the ions. However, a complete model of this ion drag force remains elusive and an essential piece of information for resolving the differences among the models "the ion drift velocity" is often difficult to obtain in many experiments. Most studies of ion-dust interactions infer the ion flow either from collected currents on probes or by the response of the dust particles to an applied perturbation. In this investigation, the PI proposes to directly and independently measure both the ion flow and the dust response to determine the correlation between these two parameters. To accomplish this, the PI?s group will utilize its unique capabilities for optical measurements of microparticle velocities using two-dimensional and stereoscopic particle imaging velocimetry (PIV). PIV facilitates measurements of microparticle transport and the velocity space distribution function of the microparticle component of the plasma. Furthermore, through a collaboration with Prof. Earl Scime's group at West Virginia University and access to the Auburn Fusion Laboratory's dye laser system, the PI proposes to use laser induced fluorescence (LIF) to directly measure ion flow velocities in the plasma. Additionally, complementary studies using Prof. Robert Merlino's Dusty Plasma Device at the University of Iowa will allow a verification of the measurements performed at the PI's laboratory at Auburn University. Consequently, this proposed work offers a unique opportunity to address a number of outstanding questions of importance to the dusty plasma community. Specifically, this project will investigate two specific aspects of ion-dust interactions: (a) testing a proposed model of dusty plasma heating that occurs via an ion-dust two-stream instability; and (b) characterizing how ion flow acts as a trigger for the generation of dust acoustic waves. This proposed research project has several opportunities to have a broader impact. The PI will continue to actively engage undergraduate and graduate students and post-doctoral scholars in hands-on research training. The PI has a successful track-record of student training and will continue encourage and include student participation in publications, national and international conferences, and laboratory outreach activities. Additionally, this work will support collaborative activities among different researchers within the dusty plasma community (e.g., at Auburn and Iowa) and establish a new partnership (with WVU), thereby strengthening the community of researchers involved in basic plasma science. Furthermore, this project will provide continuing support for many of the public outreach activities that have been undertaken by the PI's laboratory to illuminate the physics of plasmas and dusty plasmas. Funds for this award are provided by the Physics Division and the Office of Multi-disciplinary Activities within the NSF's Mathematics and Physical Sciences Directorate, Combustion, Fire, and Plasma Systems within NSF's Engineering Directorate, and the Office of Fusion Energy Sciences of the DoE within the context of the NSF/DOE Partnership in Basic Plasma Science and Engineering.