Wave emissions from dc and modulated electron beams on STS 3

The first active beam-plasma experiments utilizing the space shuttle were carried out in March 1982 as part of the NASA Office of Space Science mission on the third space shuttle flight. A fast pulse electron generator emitted a 1-keV, 100-mA electron beam in either a continuous (dc) mode or an on/off modulated mode in the ELF to HF frequency range. Stimulated electrostatic and electromagnetic waves and associated plasma effects were measured with the plasma diagnostics package as it was maneuvered through and near the beam by the remote manipulator system. For the dc beam the wave spectrum was electrostatic, was peaked in the 300- to 500-Hz range with a spectral density of 4 × 10^−-3 V² m^−-2 Hz^−-1, and was unpolarized. Above the nominal lower hybrid resonance frequency the intensity decreased but was polarized. Strong emissions near the electron gyrofrequency and the plasma frequency were occasionally detected. The background spectrum was similar to the dc case for VLF and ELF modulations, but the emissions at the modulation frequency were more electromagnetic and more intense with field strengths of up to 1 V m^−-1.