Instrument for the determination of drift velocity of the plasma - GEOS-experiment S 329

The considered instrument measures the velocity of the satellite with respect to the surrounding medium. In the case of the GEOS satellite, the measured motion corresponds to a superposition of the unknown plasma motion and the known satellite motion. In principle, the drift velocity of the plasma can be calculated. However, large measurement errors occur generally in connection with the limited measurement accuracy and large differences between the satellite orbital velocity and the slow rate of plasma motion. The principles of operation of the instrument are discussed, giving attention to the orbits of the electrons which are introduced into the plasma with the aid of an electron gun and the characteristics of the electron-detecting device.