The Electron Drift Instrument (EDI) is an active experiment intended to measure the electron drift velocity. The measurements are based on sensing the displacement of a weak beam of electrons after one gyration in the ambient magnetic field. This displacement, referred to as the drift step, is directly proportional to the drift velocity. The drift velocity, in turn, is controlled by the ambient electric field and/or gradients in the magnetic field. By measuring the drift velocity at two different electron energies, one can derive, separately, the electric field and the magnetic field gradient.
To make the measurements, two electron beams are independently swept in the plane perpendicular to the magnetic field B while those firing directions and electron times of flight are recorded for which return beams are sensed by the detectors on the opposite side of the spacecraft. The drift step can then be determined from the two beam directions via triangulation, or from the difference in times of flight. The triangulation method is applicable for small drift steps, the time-of-flight technique for large drift steps.
Sweeping the beams in the plane perpendicular to B until hits are recorded by the associated detectors, implies that the hits are not usually equidistant in time. Thus the sampling rate of the measurements is not fixed. When measurements at two different electron energies are made, and significant magnetic field gradients are present, it takes at least twice as long to gather the relevant information. Furthermore, the strength of the return signal might not always be sufficient for detection, particularly at times when the ambient electron background is strong. When this happens, there will be gaps in the data. Gaps can also be expected at times when strong wave activity in the ambient medium disrupts the beams.
In NM, one set of firing directions and time of flights are transmitted every 64 ms. In BM1 telemetry, this interval is reduced to 16 ms. These times set the maximum time-resolution of the drift measurements. The time resolution is reduced if no valid measurement occurred in some of the intervals.
This description has been obtained from Section 3.3 of the ''Users Guide to the Cluster Science Data System'', DS-MPA-TN-0015.
Version:2.4.0
The Electron Drift Instrument (EDI) is an active experiment intended to measure the electron drift velocity. The measurements are based on sensing the displacement of a weak beam of electrons after one gyration in the ambient magnetic field. This displacement, referred to as the drift step, is directly proportional to the drift velocity. The drift velocity, in turn, is controlled by the ambient electric field and/or gradients in the magnetic field. By measuring the drift velocity at two different electron energies, one can derive, separately, the electric field and the magnetic field gradient.
To make the measurements, two electron beams are independently swept in the plane perpendicular to the magnetic field B while those firing directions and electron times of flight are recorded for which return beams are sensed by the detectors on the opposite side of the spacecraft. The drift step can then be determined from the two beam directions via triangulation, or from the difference in times of flight. The triangulation method is applicable for small drift steps, the time-of-flight technique for large drift steps.
Sweeping the beams in the plane perpendicular to B until hits are recorded by the associated detectors, implies that the hits are not usually equidistant in time. Thus the sampling rate of the measurements is not fixed. When measurements at two different electron energies are made, and significant magnetic field gradients are present, it takes at least twice as long to gather the relevant information. Furthermore, the strength of the return signal might not always be sufficient for detection, particularly at times when the ambient electron background is strong. When this happens, there will be gaps in the data. Gaps can also be expected at times when strong wave activity in the ambient medium disrupts the beams.
In NM, one set of firing directions and time of flights are transmitted every 64 ms. In BM1 telemetry, this interval is reduced to 16 ms. These times set the maximum time-resolution of the drift measurements. The time resolution is reduced if no valid measurement occurred in some of the intervals.
This description has been obtained from Section 3.3 of the ''Users Guide to the Cluster Science Data System'', DS-MPA-TN-0015.
| Role | Person | StartDate | StopDate | Note | |
|---|---|---|---|---|---|
| 1. | PrincipalInvestigator | spase://CNES/Person/CDPP-Archive/Goetz.Pachmann |