Energetic particles in the Earth's magnetotail or: Cluster and Regatta as a dispersiometer

Energetic particles in the Earth's magnetotail carry information about the site and origin of their acceleration, i.e., about the dynamics of the main magnetospheric plasma reservoir. Despite several previous attempts to use this information, a separation of temporal and spatial effects in energetic particle observations was almost impossible. The multi-satellite Cluster and Regatta A missions will provide a new chance to solve this problem, if their relative positions in the tail are chosen appropriately. If so, the combination of Cluster and Regatta A energetic particle analyzers may act as a dispersiometer. To prepare its data interpretation, theoretical models of magnetotail particle acceleration are discussed with the two main sources, the more or less stationary dawn-dusk electric field, induced by the flowing solar wind and impulsive fields, related to fast changes in the tail magnetic field.