A Characterization of Plasma Fluctuations within a Hall Discharge

Abstract—Experimental results are presented for studies of low (2–20 kHz) and intermediate-frequency (20–100 kHz) oscillations in crossed-field closed electron-drift Hall discharges. Conditional sampling using two electrostatic probes is used to identify and ex-tract properties of coherent structures associated with the prop-agation of azimuthal and longitudinal instabilities within the dis-charge channel. The azimuthal component phase velocities are de-termined for a wide range of wave frequencies and over character-istic regimes of operation of these devices. A variety of propagation modes are observed and analyzed, including the appearance of an induced mode due to the presence of the probes themselves. This later result is believed to be the first direct evidence of how fluc-tuations can be influenced in these Hall discharges using relatively simple actuation methods. Index Terms—Hall discharges, Langmuir probes, plasma insta-bilities, plasma propulsion. I