Particle beams released from space vehicles provide a unique way to study many problems in basic plasma physics in the ionosphere and magnetosphere. Electron beams, for example, may act as probes or tracers in the large-scale magnetosphere but also generate waves, plasma heating, and current systems in the local ionosphere. Such experiments are a natural extension of laboratory plasma physics to a regime where there are no walls, but where a high degree of control may still be achieved.
The first electron beam experiment in space was the Hess Artificial Aurora Experiment [Hess et al., 1971], which was launched in 1969 from the NASA Wallops Island Range, Wallops Island, Va., not only to generate auroral streaks but to map magnetic field lines between conjugate regions above the Earth's surface. This was followed in 1970 by ECHO 1, also from Wallops. Since that time, a multitude of electron beam experiments have been carried out on sounding rockets, and some at orbiting altitudes on the Space Shuttle. In the ECHO program, six additional experiments have been flown, culminating in ECHO 7, which is the subject of this paper and the last of the series. The history of the subject up to 1980 has been covered in a review paper [Winckler, 1980]. Particle beams in space plasmas were the subject of an extensive symposium in 1981 [Grandal, 1982]. This symposium includes a review of ECHO results [Winckler, 1982]. Abe et al.,  have analyzed ELF wave generation observed during the previous flight, ECHO 6, and referenced recent papers under the ECHO program.