ALBERT

Description: We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio & Plasma Wave Science (RPWS) instruments onboard Cassini during the Ring-Grazing orbits. The numerous ring passage observations show a consistent picture as follows: 1) Beyond 0.1R S above and below the equator the electron and ion densities are quasi-neutral with a distribution similar to the one obtained in the plasma disk. 2) A sharp ion density enhancement occurs at |Z|〈0.1R S , to more than 200 cm -3 at the equator, while the electron density remains low only to values of 50 cm -3 . The electron/ion density ratio is ≦0.1 at the equator. 3) Micrometer sized dust has also been observed at the equator. However, the region of intense dust signals is significantly narrower (|Z|〈0.02R S ) than the enhanced ion density regions. 4) The electron temperature (T e ) generally decreases with decreasing Z with a small T e enhancements near the equator. We show that the dust size characteristics are different depending on the distance from the equator, and the large micrometer sized grains are more perceptible in a narrow region near the equator where the power law slope of the dust size distribution becomes less steep. As a result, different scale heights are obtained for nanometer and micrometer grains. Throughout the ring, the dominant part of the negative charges is carried by the small nanometer sized grains. The electron/ion density ratio is variable from orbit to orbit, suggesting changes in the dust charging over time scales of weeks.