Thesis Defense Announcement
Herff College of Engineering announces the Final Thesis Defense of
for the Degree of Master of Science
February 15, 2019 at 4:15 PM in Engineering Science Building, Room 317
Advisor: Ranganathan Gopalakrishnan
Coulombic Collisions in Aerosols and Dusty Plasmas
ABSTRACT: Determination of the charge on particles (grains) in aerosol and dusty plasma systems are a key part of describing their dynamics that takes place within them. The large difference in size and mobility between ions and electrons results in grains which accumulate negative and positive charge at different rates. Moreover, the grains within these aerosol systems are typically surrounded by neutral gas molecules whose density depends on the pressure of the system. These gas molecules play an important role in determining the trajectories of the ions and the rate constant at which they are collected by the grain, referred to as the collision kernel H. The value of H obtained from the classical continuum approach (continuum limit) breaks down as collisions with gas molecules become rare at lower pressures, while a description for H derived from kinetic theory (free-molecular limit) only works when neutral gas molecules are absent altogether (vacuum). The Langevin equation is used to simulate ensemble of ion trajectories in the transition regime of gas pressures. The particle-ion hitting time distribution is found to be accurately described by the Gumbel distribution. The aforementioned understanding of the hitting time distribution is used to develop a model to calculate the collision rate as a function of the diffusive Knudsen number and a non-dimensional parameter representing the strength of the coulombic interaction between the ion and grain.