Electron Gyro Time Measurement Technique for Determining Electric and Magnetic Fields

The paper describes the technique the Electron Drift Instrument (EDI) on CLUSTER employs to measure the flight times of the electrons between the time they are emitted and the time they return after having completed a gyration in the ambient magnetic field. In the presence of an electric field two different trajectories exist which return to the detector, and thus there are two possible flight times. Their difference is a measure of the electric field, while their average is determined solely by the magnetic field. EDI uses beams which are modulated with selectable frequency and pseudo-noise coded. A set of correlators determines the time delay of the received electron counts. An auto-tracking feature allows to follow time variations caused by changes in magnetic and/or electric fields.