Physics – Plasma Physics
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..dppf3i105f&link_type=abstract
American Physical Society, Division of Plasma Physics Meeting, November 16-20, 1998 New Orleans, LA, abstract #F3I.1.05
Physics
Plasma Physics
Scientific paper
Investigations of outer space show the importance of dust and dust structures for formation of stars, planet systems, planetary rings and for processes in the upper atmosphere layers (in magnetosphere, ionosphere etc). Under the space conditions an intensive UV-radiation can charge dust particles due to a photoemission. The micron sized dust particles can take a positive charge Zp of the order of 102-104 e (electron charges). The interaction between the dust particles leads to ordered structures (strongly-coupled system) including liquid- and solid-like forms of matter, where the particles are arranged just as atoms are in actual condensed matter. The objective of the space experiment was to study the possibility of ordered structure formation under UV-radiation of Sun. To do this, the experimental studies of particle ensemble behavior were made in the Russian space station "Mir" under conditions of microgravity. The particle charge was induced by solar radiation. Investigation of charged particle formation in these conditions allows to obtain new experimental data that impossible to realize under the Earth gravity. The purpose of the preliminary calculations was to find the conditions of the formation of particle ordered structures. It is supposed that the particle charge is induced by UV-radiation under microgravity conditions. As a result we obtained: (1) the necessary conditions of the formation of ordered structures of charged particles (type of neutral gas and its pressure, particle density, substance and size); (2) value of charge and coupling parameter needed for formation of ordered structures on exposure to solar radiation typical time of the formation of ordered structures under microgravity conditions. The calculations demonstrated the possibility of ordered structure formation under experimental conditions. The experiment was carried out with the dust particles placed in a cylindrical neon-filled glass tube. The tube was positioned near the illuminator of the space station "Mir" to provide the solar exposure of dust particles inside the tube. Observations of dust particles were made by illuminating with a laser sheet. Individual particles were seen with a CCD video camera fitted with a macro objective. Dust grains used in our experiments are bronze spheres of 70-120 mm diameter. We made the measurements at 0.01 Torr and 40 Torr neon pressure. The measurements were carried out by the following way. First, the tube experiences a dynamic action (shaking). Second, the particle system relaxes to the initial condition. The results of the measurements reveal that on exposure to solar radiation, bronze particles were charged and acquired a charge of the order of 104 e. The strong correlation between particle positions was not observed. Nevertheless, the pair correlation function obtained demonstrates the formation of short range order (liquidlike) structures under microgravity.
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