Plasma and dust interaction in the magnetosphere of Saturn

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: The Cassini spacecraft orbits Saturn since 2004, carrying a multitude of instruments for studies of the plasma environment around the planet as well as the constituents of the ring system. Of particular interest to the present thesis is the large E ring, which consists mainly of water ice grains, smaller than a few micrometres, referred to as dust. The first part of the work presented here is concerned with the interaction between, on the one hand, the plasma and, on the other hand, the dust, the spacecraft and the Langmuir probe carried by the spacecraft. In Paper I, dust densities along the trajectory of Cassini, as it passes through the ring, are inferred from measured electron and ion densities. In Paper II, the situation where a Langmuir probe is located in the potential well of a spacecraft is considered. The importance of knowing the potential structure around the spacecraft and probe is emphasised and its effect on the probe's current-voltage characteristic is illustrated with a simple analytical model. In Paper III, particle-in-cell simulations are employed to study the potential and density profiles around the Cassini as it travels through the plasma at the orbit of the moon Enceladus. The latter part of the work concerns large-scale currents and convection patterns. In Paper IV, the effects of charged E-ring dust moving across the magnetic field is studied, for example in terms of what field-aligned currents it sets up, which compared to corresponding plasma currents. In Paper V, a model for the convection of the magnetospheric plasma is proposed that recreates the co-rotating density asymmetry of the plasma.