Time-resolved ion velocity measurements in a high-power Hall thruster using laser-induced fluorescence with transfer function averaging

• Published in: Applied physics letters 2020-06, Vol.116 (23)
• Main Authors: Chaplin, V. H., Lobbia, R. B., Lopez Ortega, A., Mikellides, I. G., Hofer, R. R., Polk, J. E., Friss, A. J.
• Format: Article
• Language: English
• Subjects: Acceleration; Applied physics; Discharge; Electric potential; Hall effect; Ion velocity; Laser induced fluorescence; Lasers; Magnetic shielding; Oscillations; Time measurement; Transfer functions; Voltage; Waveforms
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0007161

We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces taken at different laser wavelengths, measurement axes, and positions in the plasma, achieving a measurement bandwidth of ∼ 100   kHz. For breathing-mode like global oscillations, the results are shown to be robust to the choice of either discharge current I d ( t ) or cathode-to-ground voltage V c g ( t ) as the reference waveform input to the transfer function. At discharge voltage V d = 600   V, a nearly periodic, impulsive oscillation in the acceleration zone position was accompanied by a ≳ 100   V peak-to-peak oscillation in the near-plume plasma potential. Smaller amplitude, aperiodic oscillations in the mean ion velocities were detected at V d = 300   V.