Electric field measurements using the electron beam technique at low altitudes

Abstract

The electron beam technique determines the perpendicular electric field by using a weak beam of electrons to measure the E × B drift. An advantage of the technique is that it can measure the component of the electric field along the spin axis of a rotating spacecraft without the use of booms. Because the magnetic field is quite strong at ow altitudes, the measured quantity, the displacement of the beam after one gyration, is quite small - a few mm for moderate electric fields. This limits the lowest fields that the technique can measure to about 20 mV/m. For such small fields, offsets and distortions of the signal the same size as or greater than the actual signal from the electric field must be subtracted and the data must be smoothed. Nonetheless, the technique does measure electric fields which compare favorably with the electric fields determined by the double probe technique.