The field of complex plasmas provides a rich field for inquiry into the areas of space and laboratory physics. The ability of dust grains immersed in a plasma environment to organize themselves into complex structures provides insights into the physics of systems as diverse as the formation of planets in protoplanetary disks to the structure and phase transitions of crystalline solids. Recent astronomical evidence has shown that our planetary system is not unique in the galaxy. Rather, it seems more the rule than the exception for a star to be accompanied by orbiting planets. The planets must necessarily form from the disk of gas and dust left over from the formation of the parent star. Thus the formation of planets initially depends on how micron-sized grains, immersed in a plasma and radiative environment, are able to collide, stick and organize themselves into larger, more robust structures which may then agglomerate under gravitational interactions. The objective of this research is to develop a detailed model for the coagulation of charged fractal aggregates in a protoplanetary disk. This will be achieved by a combination of numerical modeling and experimental research directed at furthering the understanding of the microphysics involved in the charging and coagulation of fractal aggregates.
The charging and growth of fractal aggregates are necessarily linked and must be included self-consistently to correctly model the interaction of charged aggregates. The charge distribution on aggregates influences their orientation as they collide and stick, which in turn determines how open or compact the fractal structure is, a major influence on the coagulation rate. Numerical models will be used to determine the charge and charge arrangement on irregular dust aggregates. The results of the charging models can then be incorporated into existing coagulation models. New algorithms will be added to the coagulation models to allow for the dipole-dipole interactions between charged grains, the coupling of the fractal grains to the gas environment, and include various collision outcomes (sticking without restructuring, crushing, disruption, etc.) to determine limits on fractal grain growth. Laboratory experiments run concurrently with the numerical simulations will provide a check on theoretical models and provide additional data to improve the models.
The results of this project will provide new and fundamentally original information about the self-assembly and growth of charged dust grains. This project will have implications not only for understanding dust growth as an initial step towards planet formation, but will also contribute to the understanding of the self-ordering and growth of dust in controlled laboratory plasma environments, such as those found in plasma semi-conductor manufacturing and magnetically confined plasma fusion experiments. Grain aggregation is also an important process in understanding atmospheric processes both here on earth and on other bodies in the solar system. The coagulation of charged grains may also prove relevant to understanding processes such as catalysis and pollution control. Graduate, undergraduate, technical, and high school students working on this project will receive training and experience that will prepare them for careers in academia, industry, or government laboratories. They will learn not only physical principles and experimental protocols, but will also develop critical skills such as computation and modeling, practical experience with vacuum systems, instrumentation and diagnostics, and technical writing and presentation skills.
