Plasma wave observations during electron and ion gun experiments

Abstract

Experiments in charge control on the AF/NASA P78-2 (SCATHA) satellite were conducted with ion and electron emitters in the inner magnetosphere. These experiments were monitored with plasma wave instruments capable of high temporal and frequency resolution in the 0-6 kHz frequency range. Electron gun experiments were studied to determine if there were plasma wave signatures consistent with inferences of electron heating made previously from analysis of electron data. One clear set of observations was found which indicated strong plasma waves near the electron gyrofrequency (fce). Such waves would be expected to heat ambient low energy electrons, as previously inferred. Ion gun experiments revealed two distinct classes of behavior. Non-neutralized ion beam operation at 1 ma, 1 kV resulted in arcing signatures (spiky in time, broad frequency range), coincident with induced satellite potentials of -600 to 9 0 0 V. This signature disappeared when the accelerating voltage was switched off, or the beam was neutralized (at which time the satellite body approached potentials of a few volts). The signal is attributed to arcing between differentially charged surfaces. Operations without an acceleration voltage had the affect of shielding the electric antenna from spacecraft generated interference signals. -