Interaction between Metallic Microparticles and Mesospheric Plasma

Abstract: SCRAP is a student experiment that aims to validate theories on electron density fluctuations induced by the presence of dust particles connected to the phenomenon of polar mesospheric summer echoes (PMSE). Radar echoes are to be measured from a dust cloud of metallic microparticles released into the mesosphere above northern Sweden using a sounding rocket in spring 2015. This report presents a subproject of selecting the best size, amount and material of the dust particles to be used. A collisionless model describing the charging of and wave backscattering from the dust cloud has been compiled and applied for typical mesospheric conditions. The results indicate that the charging is dominated by photoelectric emission, leading to a positive steady-state charge number between about 10 and 1000 in less than 24 s. The particle characteristics are shown to be measurable by computing the scattering cross-section originating in the propagation of dust acoustic waves. The choice of optimal particle parameters depends on two competitive effects. For large particles of high density and low photoelectric yield, the measured signals will be stronger but also broader in the frequency spectrum. Of the alternatives considered, silver particles of 0.1 m radius are found to be the best choice.