The SEPAC artificial aurora

Abstract

The Space Experiments with Particle Accelerators (SEPAC) and the Atmospheric Emission Photometric Imager (AEPI) were flown on the ATLAS‐1 shuttle mission in the spring of 1992. In a series of artificial aurora experiments, SEPAC injected electron beam pulses (6.25 keV, 1.2 A) into the Earth's upper atmosphere while the AEPI camera recorded optical emissions in white light continuum and 4278 Å. The intensity, overall size, and structure of the artificial auroras have been compared to results from a two‐stream code which models collisional and transport properties of natural and artificial electron beams. Using the curvature of the magnetic field to resolve the altitude dependence of observed optical emissions, it is found that the beam reaches 110–130 km altitude and excites emissions at intensities that are consistent with model calculations (1 kR). However, it is also concluded that the near‐field intensity (5 kR) exceeds model estimates by one order of magnitude. It is argued that this unexpected enhancement is caused by emissions generated within the first 10's of kilometers of the Orbiter by suprathermal electron fluxes at levels that are orders of magnitude larger than predicted by the purely collisional model. It is suggested that the enhanced flux is due to wave‐particle interactions heating the ambient plasma.