Dr. rer. nat. Dennie Lange

A particle-in-cell (PIC) simulation study of the charging processes of spherical dust grains in a magnetized plasma environment is presented. Different magnetic field strengths with corresponding electron/ion gyration radii of smaller, the same or larger size than the grain radius and the plasma Debye length are examined. The charging currents are significantly reduced in the presence of a magnetic field, resulting in a more negative grain floating potential. The simulation results are compared with a modified orbital motion limited (OML) theory. For very small gyration radii, the simulation results are in good agreement with the modified OML approach for both magnetized electron and ion charging currents.

As the largest in our solar system the Jovian magnetosphere is treated in the literature as the dominant source of a few-MeV electrons, which have been measured by various spacecraft. In particular, observations obtained with Ulysses have significantly broadened the available data base. We simulated the transports of MeV electrons in the heliosphere on the basis of a time-dependent, three-dimensional modulation model. For this purpose, the cosmic rays, the Jovian and the Saturnian electron sources have been, for the first time, considered together in the simulation of electron fluxes. At 1 MeV the intensities along the Ulysses and the Cassini trajectories are clearly influenced by the presence of Kronian electrons. Our results reveal that the electrons from the Kronian magnetosphere,as the second largest, cannot be neglected in the very-low MeV energy range.

We report on the modelling of the time-dependent transport of a few MeV electrons in the heliosphere. These low-energetic electrons, observed with the Kiel Electron Telescope (KET) on board the Ulysses spacecraft, are for the first time simulated over a complete solar activity cycle on the basis of a time-dependent three-dimensional modulation model. It is demonstrated that the solar activity has an effect especially at high heliographic latitudes being observed by Ulysses. Both galactic cosmic rays and the Jovian electron source are considered for the simulation of the electron fluxes within the heliosphere. A time-dependent anisotropic diffusion tensor was also tested in order to figure out from KET observations the variation of the release rate of low-energetic electrons from the Jovian magnetosphere.