Initial Results from the Cluster Electron Drift Instrument

We present an overview of initial results from the electron drift instrument (EDI) on the Cluster mission. EDI measures the local electron drift velocity by firing two weak electron-beams perpendicular to the magnetic field, and detecting their return after one or more gyro orbits. Depending on the magnitudes of the drift velocity and magnetic field, the measurement uses either a time-of-flight or "triangulation" technique to deduce the drift velocity. EDI inherently measures both components of the drift velocity in the plane perpendicular to the magnetic field, indpendent of the orientation of the spacecraft spin-axis. The measured drift velocity, from which we deduce the electric field, is usually dominated by the ExB drift. However EDI uses two different beam energies to identify the grad-B contribution to the drift.