Electrons in the Geomagnetic Tail

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9312467 Ashour-Abdalla The proposed theoretical investigation is to calculate electron distributions in the geomagnetic tail to the Earth's magnetosphere and to evaluate the local and global problem of charge neutrality between electrons and ions. Although the dynamics of ions in the magnetotail has been the subject of extensive theoretical investigations using single particle orbit calculations, hybrid simulations, and magnetohydrodynamic fluid simulations, electron dynamics have been virtually ignored. Yet, the most fundamental aspect of a plasma - the establishment and maintenance of charge neutrality - depends on electron behavior. Some electrons move at high speeds and rapidly traverse large volumes of space; the establishment of local charge neutrality depends on both the global sources and sinks of electrons and the large scale structure of the electric and magnetic fields in the tail. Until now, no scientific methodology has existed capable of addressing global transport and calculating the local distributions of electrons in the tail. In the proposed large scale kinetics approach, starting from various source regions, electrons will be allowed to propagate throughout the entire volume of the magnetotail along trajectories which are determined using model electromagnetic fields to represent the tail configuration. The local electron distribution function will be calculated by summing the contributions of each trajectory passing through the local spatial region, and the electron density will be compared to the local ion density (which is similarly calculated by the large scale kinetics technique) to determine the extent of charge neutrality violation. Parallel electric fields will be added to the electromagnetic field model, and will be adjusted to obtain the closet reasonable balance between electron and ion charge densities. The potential significance of this proposed is profound in that, with its success we could for the first time directly asses s the problem of charge neutrality in a space plasma, determine the large scale potential electric fields required to maintain charge neutrality, and establish the extent to which charge neutrality demands the exchange of electrons between the tail plasma and the ionosphere. ***