Experimental Objectives The main scientific objectives of SEP AC experiment are to study: (1) Vehicle charging and charge neutralization. (2) Beam plasma physics. (3) Beam-atmosphere interactions. (1) Vehicle charging and its neutralization. By electron beam injection from a spacecraft, electrical charge is built-up on the spacecraft. It is neutralized by the electron current from the ambient plasma in the neighbourhood. The experiment aims at revealing the nature of vehicle charging in the space plasma. The charge neutralization by the plasma and neutral beam injection during the beam emission will clarify the mechanism of the charge neutralization in space. (2) Beam plasma physics. The magnetosphere provides a gigantic natural plasma laboratory, in which SEP AC instruments can perform various active experiments by injecting the high power electron beam, high density plasma and neutral gas plume. Such activ^ experiments are important not only to geo-astrophysical interests, but also they contribute much to the knowledge of fundamental processes in plasma physics. (3) Beam-atmosphere interaction. This experiment is intended to make artificial auroral airglow excitations and modification of ionospheric parameters. Cooperation with ground-based observatories is especially important. The specific items to be studied are: • Input-output experiment of auroral excitations, • Spatial structure of auroral arc formation, • Electron echo experiment, • Ionospheric Ne and Te perturbations, • Plasma beam propagation and shock waves, • Artificial airglow excitation.
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