Determining the Ice Phase, Nucleation Process, and Electromagnetic Interaction Properties of the Ice Grains in an Ice Dusty Plasma

California Institute Of Technology, Pasadena CA

Investigators

Abstract

The award supports an experimental study of water ice grain formation in a weakly ionized plasma environment. Plasma - a gas containing free electrons and ions - can be weakly ionized so that the gas is almost all neutral atoms and molecules with only one part in a million consisting of the electrically charged particles. This experimental research program will study a weakly-ionized plasma where the neutral gas is arranged to be extremely cold, such as -300F. When a small amount of water vapor is injected into such plasma, it is found that tiny grains of ice spontaneously form, become electrically charged, and are suspended in the plasma. The ice grains range in size from nanometers to hundreds of micrometers depending on experimental conditions. The new study will provide information relevant to situations that occur in nature such as the protoplanetary disk that existed in the early stage of solar system evolution, the diffuse rings of Saturn, and terrestrial noctilucent clouds that can form at 50-mile altitudes in polar regions. The project has two main goals. The first is to determine how the ice grain infrared absorption spectrum varies with temperature. At the extremely cold temperatures found in many astrophysical situations, ice can be in an amorphous phase and so have a different infrared absorption spectrum from the crystalline ice of ordinary experience. The second main goal is determining why and how ice nucleates in a plasma. For terrestrial atmospheric conditions it is well established that ice nucleation requires a core of non-ice solid material, such as carbon or silicate, on which ice forms as a coating. However, laboratory plasma experiments do not contain any non-ice material and preliminary evidence is that the weakly-ionized plasma catalyzes ice nucleation. The investigation will explore how the weakly-ionized plasma environment may enable ice nucleation and will be guided by a theoretical prediction that high-energy plasma electrons, a tiny minority of all free electrons, may play a key role in the process. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.