Growth and phase of ice grains formed in a cryogenically cooled RF plasma*

In the Water-Ice Dusty Plasma Experiment at Caltech, microscopic grains of ice are spontaneously created within a cryogenically-cooled RF-powered weakly ionized plasma. FTIR absorption spectroscopy shows that the ice phase can be either crystalline or amorphous. This spectroscopy is then used to examine how the ice phase depends on background gas temperature, plasma parameters, and time. The FTIR absorption spectrum also enables measurement of optical constants which can then be used to determine the characteristic grain size at which electromagnetic radiation scatters from the ice grains. These spectroscopic results indicating grain size are compared to direct microscope imaging of the dust grains, linking the microstructure to macroscopic behavior.