Electron Beam Experiments at High Altitudes

Experiments with the electron gun on the SCATHA satellite produced evidence of beam-plasma interactions, and heating of the low energy electrons around the satellite. These experiments were conduct ed near geosynchronous orbit, in the dusk bulge, and plasma sheet, with one short operation in the lobe regions, providing a range of ambient plasma densities. The electron gun was operated at 50 eV, with beam currents of 1, 10 and 100 μA . Also, a filament emitter was used in a mode where it was biased -100 V w i t h r e s p e c t t o the satellite, at a current setting of 20 i A . Data from electrostatic analyzers and the DC electric field experiment show that the satellite charged to near the beam energy in sunlight, at sufficiently high beam currents. The electrostatic analyzers showed distribution functions which had peaks, or plateaus at energies greater than the satellite potential. These measurements indicate heating of the ambient plasma, at several Debye lengths from the satellite (several 10's of meters), with the heated plasma then accelerated into the satellite. It is likely that at times the 'ambient' cold plasma is in fact the photoelectron sheath generated by the satellite.