Thermophoresis of micron-sized water ice aerosols in an RF plasma afterglow

The ice grains in the Caltech Water-Ice Dusty Plasma Experiment exhibit complex dynamic motion due to a balance of thermophoretic, electric, gravity, and drag forces. When the RF power is shut off, grains move from their equilibrium positions as the electric force vanishes, and the thermophoretic force is dominant. As each electrode's temperature can be varied independently, the thermophoretic force is precisely controlled, and effect on the grain motion can be thoroughly investigated. A high-speed camera fitted with a microscope lens is used to directly image the grains, and the force balance in the afterglow is obtained through particle tracking. Effect of the grain's highly-nonspherical fractal shapes on their experienced thermophoretic and drag forces are investigated