Characterization of n_e in the presence of ice in the Water-Ice Dusty Plasma Experiment at Caltech

The Water-Ice Dusty Plasma Experiment at Caltech generates a low-temperature, capacitively coupled RF plasma in which injected water vapor nucleates and forms negatively charged ice grains. This system provides a laboratory model for processes relevant to the upper atmosphere and astrophysical environments. When the electrodes are cooled below 200K, a substantial decrease in ne occurs within 15 ms after water injection, suggesting absorption of electrons by ice grains or free radicals. Significant variation in intensity and time-scale of these fluctuations motivates expanding the parameter space evaluated in order to quantify and understand free electron absorption and establish its relationship to ice nucleation. This project involves using a hairpin probe—a type of microwave resonator used to measure plasma permittivity [1]–to measure time-resolved ne before and after water injection into the device. System conditions are set by adjusting chamber pressure, regulating electrode temperature with cryocoolers, and tuning the RF power supply. Ongoing work focuses on determining the behavior of the ne drop in the discharge while varying either pressure, temperature, or power. Consistent response to the change in parameters may provide insight into the source of the drop and the ideal conditions for ice nucleation.

Citations:

[1] R. L. Stenzel, Rev. Sci. Instrum. 47, 603 (1976)