Spontaneous formation of nonspherical water ice grains in a plasma environment

Abstract

[1] Saturn's rings, terrestrial polar mesospheric clouds, and astrophysical molecular clouds are all dusty plasma environments where tiny grains of water ice are an important constituent. Existing models typically assume that the ice grains are spherical and then invoke various arguments about the normal distribution or the power law dependence of grain number density on grain radius. Using a laboratory plasma in which water ice grains spontaneously form, we investigated the validity of the traditional assumption that these grains are spherical. We found that in certain cases at low ambient pressures, water ice grains in the laboratory dusty plasma are not spherical but instead are highly elongated, i.e., ellipsoidal. Preliminary analysis suggests that electrical forces associated with the dusty plasma environment are responsible for the nonspherical shape. Citation: Chai, K.-B., and P. M. Bellan (2013), Spontaneous formation of nonspherical water ice grains in a plasma environment, Geophys. Res. Lett., 40,[6258][6259][6260][6261][6262][6263]

Study on morphology and growth of water–ice grains spontaneously generated in a laboratory plasma

“…In order to investigate the possibility of non-spherical ice grains, we built a laboratory apparatus and used this apparatus to investigate the morphology of water-ice grains in a plasma. Initial results show that water-ice grains are spontaneously generated in a plasma environment and grow nonspherically if the neutral pressure of the background weakly ionized plasma is low (Chai and Bellan, 2013). We report in this paper measurements made to provide an improved understanding of the underlying physics of nonspherical growth.…”

“…Fig. 1 shows a photo of the water-ice dusty plasma; a detailed description is given elsewhere (Chai and Bellan, 2013). The apparatus incorporates design features of a previously existing experiment at the Max-Planck-Institute for Extraterrestrial Physics (Shimizu et al, 2010) but differs in two important aspects: the inter-electrode separation is adjustable and water vapor is directly injected into an argon plasma instead of forming water molecules in a plasma created from a fill of D 2 and O 2 .…”

Formation and Alignment of Elongated, Fractal-Like Water-Ice Grains in Extremely Cold, Weakly Ionized Plasma

“…Detailed information about the experimental design and operation is described in Chai & Bellan (2013) and is briefly summarized here. Two electrically floating, parallel-plate aluminum electrodes in a small vacuum chamber have cold fingers extending out of the vacuum chamber.…”

Dynamics of nonspherical, fractal-like water-ice particles in a plasma environment

“…studied the charging and rotation of nonspherical aggregates using a laboratory experiment and a simulation code 19 . Recently, the experiments developed at Caltech and KAERI have successfully created nonspherical dust particles in a plasma environment 20 – 22 and hence they provide a good opportunity to study the dynamics of nonspherical particles. In this work, by using a laboratory experiment which can produce nonspherical water-ice particles in a plasma environment we report the dynamical properties of nonspherical, fractal-like water-ice particles.…”