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Title: Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment

Abstract

The grain growth process in the Caltech water–ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (i) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μ m, (ii) the major axis length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (i.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ∼0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.

Authors:
; ;  [1]
  1. Applied Physics and Materials Science, Caltech, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22661323
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 837; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COLLISIONS; DENSITY; DISTRIBUTION; DUSTS; FRACTALS; GRAIN GROWTH; ICE; LENSES; MICROSCOPES; MOLECULES; PLANETS; PLASMA; PROTOPLANETS; SATELLITES; VELOCITY; WATER

Citation Formats

Marshall, Ryan S., Chai, Kil-Byoung, and Bellan, Paul M. Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5D11.
Marshall, Ryan S., Chai, Kil-Byoung, & Bellan, Paul M. Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment. United States. doi:10.3847/1538-4357/AA5D11.
Marshall, Ryan S., Chai, Kil-Byoung, and Bellan, Paul M. Wed . "Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment". United States. doi:10.3847/1538-4357/AA5D11.
@article{osti_22661323,
title = {Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water–Ice Dusty Plasma Experiment},
author = {Marshall, Ryan S. and Chai, Kil-Byoung and Bellan, Paul M.},
abstractNote = {The grain growth process in the Caltech water–ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (i) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μ m, (ii) the major axis length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (i.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ∼0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.},
doi = {10.3847/1538-4357/AA5D11},
journal = {Astrophysical Journal},
number = 1,
volume = 837,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}
  • The ({alpha}+{ital d}) breakup of 60 MeV {sup 6}Li scattered from {sup 208}Pb has been measured inside the grazing angle for c.m. energies of the fragments between 100 keV and 1.5 MeV. We find the integrated cross sections to be in agreement with Coulomb excitation theory, but the angular correlations of nonresonant breakup exhibit significant deviations from this theory. This shows that the measured breakup cross section cannot be related by first-order Coulomb excitation theory to the astrophysically relevant {sup 4}He({ital d},{gamma}){sup 6}Li capture reaction.
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