Plasma wave observations during Ion Gun Experiments

Abstract

Experiments in charge control on the AF/NASA P78‐2 (SCATHA) satellite were conducted with a plasma/ion source 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. Ion gun experiments revealed two distinct classes of behavior. Nonneutralized 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 −900 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. An additional feature was noted in the 100‐kHz channel of the wave receiver. During emission of dense, low‐energy plasma, a signal is generated which may be at the upper hybrid, or plasma frequency for the local plasma.

Ionospheric Physics

“…On both the space shuttle STS‐3 and SpaceLab‐2 flights the electron generator (FPEG) and a plasma monitor (PDP), respectively produced and observed enhanced VLF emissions [Farrell et al, 1988; Frank et al, 1989; Reeves et al, 1988, 1990]. Goerke et al, [1990] observed VLF emissions generated by an electron beam gun on a Nike Black Brant V sounding rocket; similarly, Winglee and Kellogg [1990] reported electromagnetic wave emissions generated by beams, and Olsen et al, [1990] studied plasma waves generated by ion beams on the SCATHA satellite. The role of coherent Cerenkov radiation driven by bunching of the electron beam was developed theoretically by Farrell et al, [1989] and Pickett et al, [1989].…”

Discharging spacecraft through neutral gas release: Experiment and theory

“…For example, at negative charging levels the low mobility of positive ions impedes their ability to act as neutralizing return current. Another source of payload charging is ion beam emission [Kaufmann et al, 1989;Roth et al, 1983], but typically, the currents are small, and charging has not been observed above a few hundred volts [Olsen et al, 1990]. However, electron beam sources employed in many space experiments are capable of relatively large currents, and they can also cause high-voltage charging.…”