ECHO 7: An electron beam experiment in the magnetosphere

Abstract

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., [1988] have analyzed ELF wave generation observed during the previous flight, ECHO 6, and referenced recent papers under the ECHO program.

Comparison of Echo 7 field line length measurements to magnetospheric model predictions

“…At the heart of the Echo 7 experiment was the on-board electron accelerator, described by Winckler et al [1989]. The electron gun was a space-charge-limited diode, so the emitted current was related to the acceleration voltage as V3/2; 40-kV acceleration corresponded to 225-mA injected current.…”

“…For purposes of conjugate echo detection, both of those subpayloads carried a set of four scintillators sensitive to electrons > 1 keV; and two large-geometry-factor Toroidal Electron Detectors (TEDs), electrostatic spectrometers capable of measuring electron energies from 2 to 40 keV with 7.5% full width energy resolution [Nemzek, 1990]. Additional details about Echo 7, including preliminary analysis of data returned by a host of other detectors, are given by Winckler et al [1989].…”

The interaction of an artificial electron beam with the Earth's upper atmosphere: Effects on spacecraft charging and the near‐plasma environment

“…Common for the BPD, BPI, and PD is the fact that theories, at present, do not allow quantitative estimates of the magnitude of return currents or the energy spectra of return current electrons arising from these interactions. While the observation of suprathermal electrons and electrostatic wave turbulence often in the past have been taken as evidence for BPI [Winckler et al, 1989], it has not been possible to quantify this effect in terms of the active return current component generated through this process. We will show, however, that this is possible for the BAI and that substantial fluxes of suprathermal electrons are generated through this process at typical sounding rocket altitudes.…”

Imaging of artificial aurora in the upper atmosphere

“…In addition, space experiments in which electron beams were emitted are a conventional technique used to investigate natural electron beam processes. For example, electron beams have been used to trace magnetic fields to investigate the structure of the magnetosphere [e.g., Winckler et al, 1989;Hallinan et al, 1990], to probe the local electric fields [Melzner et al, 1978;Junginger et al, 1984], and to generate electromagnetic waves by beam modulation [Burch et al, 1993].…”