The Supra-Thermal Plasma Analysers on the ESA GEOS Satellites

Abstract

The GEOS suprathermal plasma analyzers measure differential fluxes of electrons and protons with energies less than 500 eV in the magnetosphere. Hemispherical electrostatic analyzers are boom-mounted with a novel sensor bias control in order to overcome difficulties associated with electron emission from spacecraft surfaces and the consequent charging. Data examples are presented to demonstrate how well the design aims have been fulfilled and to illustrate how the operational flexibility of the experiment permits a wide variety of particle distributions to be measured in the plasmasphere, plasma trough, plasma sheet, and magnetosheath. The technique also yields information on spacecraft surfaces and photoelectron sheath characteristics.