Dynamics of Fractal Ice Grains in Cryogenic Plasmas

Ice grains formed in a cryogenically cooled plasma exhibit fractal morphologies that drive distinct collective dynamics. By measuring and quantifying the dynamics of these grains in a plasma afterglow, we observe a new fundamental dynamical regime induced by fractal scalings of ice mass and collisional cross section. In this regime, grains become more coupled to flows of gas and ions as they get larger, while the influence of gravity remains comparatively small, even as the grains reach millimeter sizes. These dynamics are unattainable by compact spheres, and thus inaccessible to dusty plasma models that assume spherical grains, challenging models for systems ranging from laboratory nanoparticle synthesis to astrophysical dust transport.