A Water-Ice Dusty Plasma Experiment at Caltech

The Water-Ice Dusty Plasma Experiment at Caltech investigates the nucleation and dynamics of water-ice dust grains in a plasma, with parameters relevant to the upper atmosphere and space environments such as protoplanetary disks. Capacitively-coupled RF electrodes create a weakly-ionized plasma, into which water is injected through a leak valve and nucleates spontaneously to form quickly growing ice grains. The electrodes are attached to cryocoolers, which allow precise control of the neutral temperature to under 70 K. The ice grains were previously observed to have an elongated fractal structure reaching up to 100 microns in length, with specific geometry and growth rate highly sensitive to the ambient conditions. The ice grains are imaged using both laser diffraction and a long-distance microscope for various pressures and neutral temperatures.