Investigation of the Effect of Ice Grain Size on RF Harmonic Structure in a Weakly Ionized Plasma

The Caltech Ice Dusty Plasma Experiment studies the dynamics of ice grains suspended in a weakly ionized plasma at T=80-150K. The dusty plasma is a capacitively coupled discharge driven at a radio frequency (rf) of 13.56 MHz. Nonlinear sheath oscillations generate harmonics of the driving frequency. For a silane-argon dusty plasma, it had been observed that the amplitude of these harmonics abruptly changes as the dust particles transition from an accumulation to a coagulation growth mechanism. Investigations of the silane-argon plasma utilize similar nucleation and growth models applicable to the Caltech Dusty Ice Plasma Experiment at equivalent size scales (nanometers), so the analysis is expected to be transferable. The effects of the ice grains on the plasma plan to be examined by monitoring the Fourier Transform of the time-varying voltage at the powered electrode. While the ice grains are on the order of nanometers, the charge accumulated by the grains is insufficient to alter the plasma’s impedance. Consequently, when the ice grains are at this size scale, variations in the rf harmonics should directly correlate with the growth mechanism. Analysis of the rf harmonics will be used to isolate ice grain nucleation and growth and assess working models for the phenomena.