Various ways of generating and sensing test particles for measurements of electric and magnetic fields in space plasmas are discussed. Some of these methods involve the test particles traversing great distances and are thus relatively immune from the local plasma disturbances invariably caused by the presence of a spacecraft. One technique is to send test particles on trajectories which bring them back to a detector on the same spacecraft after one or more gyro motions in the ambient magnetic field. It is shown that by measuring the angles of these trajectories and the times of flight as a function of the test particle energy, not only can the ambient electric field be determined over a wide dynamic range, but the magnetic field magnitude and the gradient of the magnitude can also be determined. The special and demanding requirements of a detector for gathering magnetically returned test particles have required the creation of a new and novel design.

Auroral arcs often extend for more than a thousand kilometers with little deviation of their relative position within the auroral oval. At high altitudes, the outer limits of the plasmasphere are usually marked by sharp decreases in the cold plasma densities. It is suggested that some auroral arcs follow the ionospheric trace of these boundary shells.

Abstract. We have used vector measurements of the electron drift velocity made by the Electron Drift Instrument (EDI) on Cluster between February 2001 and March 2006 to derive statistical maps of the high-latitude plasma convection. The EDI measurements, obtained at geocentric distances between ~4 and ~20 RE over both hemispheres, are mapped into the polar ionosphere, and sorted according to the clock-angle of the interplanetary magnetic field (IMF), measured at ACE and propagated to Earth, using best estimates of the orientation of the IMF variations. Only intervals of stable IMF are used, based on the magnitude of a "bias-vector" constructed from 30-min averages. The resulting data set consists of a total of 5862 h of EDI data. Contour maps of the electric potential in the polar ionosphere are subsequently derived from the mapped and averaged ionospheric drift vectors. Comparison with published statistical results based on Super Dual Auroral Radar Network (SuperDARN) radar and low-altitude satellite measurements shows excellent agreement between the average convection patterns, and in particular the lack of mirror-symmetry between the effects of positive and negative IMF By, the appearance of a duskward flow component for strongly southward IMF, and the general weakening of the average flows and potentials for northerly IMF directions. This agreement lends credence to the validity of the assumption underlying the mapping of the EDI data, namely that magnetic field lines are equipotentials. For strongly northward IMF the mapped EDI data show the clear emergence of two counter-rotating lobe cells with a channel of sunward flow between them. The total potential drops across the polar caps obtained from the mapped EDI data are intermediate between the radar and the low-altitude satellite results.

A synaptic view of Cluster FGM, CIS, EDI, and PEACE observations of the near-Earth neutral line region during 1800–1830UT on 13 September 2002 is discussed. Associated with the flow reversal and a thin cross-tail current sheet, a clear signature of a quadrupolar magnetic field is observed, which indicates the formation of the Hall current system around the X line in the large-scale picture. Associated with this magnetic field structure, low energy field-aligned electron beams mainly directed toward the X line are observed. High resolution data of FGM and EDI further show the fine structure of the low energy electron beams near the plasma sheet–lobe boundary. The beam becomes much more intense in the narrower region associated with the small magnetic field disturbances. In some cases, complicated bi-directional or oppositely directed beams are observed.

EDI measures the drift velocity of artificially injected electron beams. From this drift velocity, the perpendicular electric field and the local magnetic field gradients can be deduced when employing different electron energies. The technique requires the injection of two electron beams at right angles to the magnetic field and the search for those directions within the plane that return the beams to their associated detectors after one or more gyrations. The drift velocity is then derived from the directions of the two beams and/or from the difference in their times-of-flight, measured via amplitude-modulation and coding of the emitted electron beams and correlation with the signal from the returning electrons. After careful adjustment of the control parameters, the beam recognition algorithms, and the onboard magnetometer calibrations during the commissioning phase, EDI is providing excellent data over a wide range of conditions. In this paper, we present first results in a variety of regions ranging from the polar cap, across the magnetopause, and well into the magnetosheath.Key words. Electron drift velocity (electric fields; plasma convection; instruments and techniques)

We examine two crossings of three Cluster satellites from the polar cap into the high-latitude plasma sheet at midnight local time, using data from the Electron Drift Instrument (EDI). EDI measures the full electron drift velocity in the plane perpendicular to the magnetic field for any field and drift directions. The context of the measured convection velocities is established by their relation to the intense enhancements in 1 keV electrons, also measured by EDI, as the satellites move from the polar cap into the plasma sheet boundary. In both cases presented here, the cross B convection in the polar cap is anti-sunward (toward the nightside plasma sheet) with a small duskward component. As the satellites enter the plasma sheet boundary region, the dawn-dusk convective flow component reverses its sign, and the flow in the meridianal plane (toward the center of the plasma sheet) drops substantially. The relatively stable convection in the polar cap becomes highly variable as the PSBL is encountered. The timing and sequence of the boundary crossings by the Cluster satellites are consistent with a relatively static structure on a time scale of the few minutes in satellite separations. In one of the two events, the plasma sheet boundary has a spatially separate structure that is crossed by the satellites before entering the plasma sheet.Key words. Magnetospheric physics (electric fields; magnetopause, cusp and boundary layers; instruments and techniques)

We present the first triangulation measurements of electric fields with the electron drift instrument (EDI) on Equator-S. We show results from five high-data-rate passes of the satellite through the near-midnight equatorial region, at geocentric distances of approximately 5–6 RE, during geomagnetically quiet conditions. In a co-rotating frame of reference, the measured electric fields have magnitudes of a few tenths of mV/m, with the E × B drift generally directed sunward but with large variations. Temporal variations of the electric field on time scales of several seconds to minutes are large compared to the average magnitude. Comparisons of the “DC” baseline of the EDI-measured electric fields with the mapped Weimer ionospheric model and the Rowland and Wygant CRRES measurements yield reasonable agreement.

We present the first electron time-of-flight measurements obtained with the Electron Drift Instrument (EDI) on Equator-S. These measurements are made possible by amplitude-modulation and coding of the emitted electron beams and correlation with the signal from the returning electrons. The purpose of the time-of-flight measurements is twofold. First, they provide the drift velocity, and thus the electric field, when the distance the electrons drift in a gyro period becomes sufficiently large. Second, they provide the gyro time of the electrons emitted by the instrument, and thus the magnitude of the ambient magnetic field, allowing in-flight calibration of the flux-gate magnetometer with high precision. Results of both applications are discussed.

The electron drift technique is based on sensing the drift of a weak beam of test electrons that is caused by electric fields and/or gradients in the magnetic field. These quantities can, by use of different electron energies, in principle be determined separately. Depending on the ratio of drift speed to magnetic field strength, the drift velocity can be determined either from the two emission directions that cause the electrons to gyrate back to detectors placed some distance from the emitting guns, or from measurements of the time of flight of the electrons. As a by-product of the time-of-flight measurements, the magnetic field strength is also determined. The paper describes strengths and weaknesses of the method as well as technical constraints.

Music and the Magnetosphere Carl E. Mcilwain, Carl E. Mcilwain Department of Physics, and Center for Astrophysics and Space Sciences, University of California at San DiegoSearch for more papers by this author Carl E. Mcilwain, Carl E. Mcilwain Department of Physics, and Center for Astrophysics and Space Sciences, University of California at San DiegoSearch for more papers by this author Book Editor(s):C. Stewart Gillmor, C. Stewart GillmorSearch for more papers by this authorJohn R. Spreiter, John R. SpreiterSearch for more papers by this author First published: 01 January 1997 https://doi.org/10.1029/HG007p0129Citations: 2Book Series:History of Geophysics AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Discovery of the Magnetosphere, Volume 7 RelatedInformation

The Electron Drift Instrument (EDI) measures the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and the gradient in the magnetic field, and these quantities can, by use of different electron energies, be determined separately. As a by-product, the magnetic field strength is also measured. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument.