Time-Resolved Ion Velocity Measurements In A High-Power Hall Thruster Using Laser-Induced Fluorescence With Transfer Function Averaging

We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5kW 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 ofsimilar to 100kHz. For breathing-mode like global oscillations, the results are shown to be robust to the choice of either discharge currentI d( t ) or cathode-to-ground voltageVc g( t ) as the reference waveform input to the transfer function. At discharge voltageV d = 600V, a nearly periodic, impulsive oscillation in the acceleration zone position was accompanied by agreater than or similar to 100V peak-to-peak oscillation in the near-plume plasma potential. Smaller amplitude, aperiodic oscillations in the mean ion velocities were detected atV d = 300V.