2.4.1 spase://CNES/Instrument/CDPP-AMDA/Geotail/EFD EFD Geotail Electric Field Detector 2019-05-05T12:34:56.789 The objectives of this investigation are studies of (1) the large scale configuration of the electric field in the magnetotail, (2) tail electric field variations during substorms, (3) the electric field in the plasma sheet, (4) the electric field near the magnetopause and in the plasma mantle at locations tailward of those covered by similar measurements on ISEE 1, (5) micropulsation and low frequency wave measurements at frequencies covering the local gyrofrequency (.LT.1Hz) and lower hybrid frequency (.LT.10Hz) in the tail, (6) plasma density as deduced from measurement of the floating potential of the spacecraft, and (7) electric field comparisons (with the aid of the other spacecraft in the ISTP program) at different points along the same magnetic field line, at different points along a common boundary, or in different regions of the magnetosphere. The instrument consists of two orthogonal double probes, each of which is a pair of separated spheres on wire booms that are located in the satellite spin plane and whose difference of potential is measured. The separation distances between the pair of sensors are variable and as great as 160 m tip-to-tip. One operating mode involves length ratios of the two antennas of about 2:1 in order to verify instrument operation through showing that the electric field signature is proportional to the boom length. A second reason for two pairs of wire booms in the satellite spin plane is the requirement for measurements having a time resolution far better than the satellite spin period. spase://SMWG/Person/Koichiro.Tsuruda PrincipalInvestigator spase://SMWG/Person/Forrest.S.Mozer CoInvestigator ISTP site at NASA/GSFC https://pwg.gsfc.nasa.gov/geotail.shtml Geotail mission description and contacts DoubleSphere Electric Field Detector spase://CNES/Observatory/CDPP-AMDA/Geotail