1994 Volume 46 Issue 8 Pages 693-711
The electric field detector (EFD) on board GEOTAIL measures the electric field by two different techniques, one by the probe technique and the other by electron beam technique. The probe technique (EFD-P) gives electric field in the plane perpendicular to the satellite spin axis by measuring the voltage difference between the two sphere probes; each deployed 50 meters from the spacecraft in the opposite direction. The electron beam technique (EFD-B), measures the drift motion of the gyration center of artificially emitted electrons to obtain the electric field. The drift motion of the electrons is measured by two methods, one by measuring the drift motion itself and the other by measuring the time of the return flight of electrons to the spacecraft. To realize these measurements, EFD is equipped with two additional capabilities. One is the capability to measure the spacecraft potential relative to the ambient plasma and the other is that to control the spacecraft potential by emitting ions. The reliability of the electric field measurements can be improved greatly by employing the probe and beam techniques at the same time. The potential control of the spacecraft enables the plasma detectors onboard GEOTAIL to measure low energy ions which would otherwise be repelled by the positive potential of the spacecraft. This article describes the outline of the electric field experiments on GEOTAIL with emphasis on the principles of the measurements, the configuration of the hardware, the raw data processing, as well as the preliminary results from the initial operation with the intention of providing the basis for the studies which use the GEOTAIL electric field data.
