Time-resolved variations of the ion velocity distribution function (IVDF) are measured in the cylindrical Hall thruster using a novel heterodyne method based on the laser-induced fluorescence technique. This method consists in inducing modulations of the discharge plasma at frequencies that enable the coupling to the breathing mode. Using a harmonic decomposition of the IVDF, one can extract each harmonic component of the IVDF from which the time-resolved IVDF is reconstructed. In addition, simulations have been performed assuming a sloshing of the IVDF during the modulation that show agreement between the simulated and measured first order perturbation of the IVDF.

Breathing mode oscillations in Hall eect thrusters occur depending on the operation parameters such as discharge voltage, anode mass ow, and magnetic eld. Time-dependent laser-induced uorescence is used to measure the ion velocity distribution functions (IVDFs) with a modulating anode voltage. [Diallo et al. RSI 2015] Experimental results suggest that the IVDFs vanish or shifts its peak to a small velocity near the maximum peak of the discharge current oscillation. A zero-dimensional plasma global model [Hara et al. PoP 2014] is used to analyze the ionization oscillation mode by forcing the electric eld to oscillate with a certain strength and frequency. In this model, the neutral atom continuity equation, the ion continuity and momentum equations, and electron energy equation are taken into account. Global model suggests that the ion mean velocity can uctuate in time and is in-phase with the electric eld oscillation. A 1D hybrid simulation shows that there can be a region where ion distribution exists in slow velocity (∼1000 m/s) due to reversed electric eld during the oscillation.

Coherent m = 0 breathing oscillations in a cylindrical Hall thruster are driven by imposing a sinusoidal modulation of the applied anode potential. Using high speed imaging and total discharge current measurements to monitor fluctuations, 11 kHz oscillations are driven at 13 V AC . The resulting discharge provides a test-bed to perform laser-induced fluorescence measurements of the time-dependent ion velocity distribution using a novel heterodyne approach. Development of the diagnostic and characterization of induced oscillations could be relevant steps to understand the naturally occurring breathing mode and rotating spoke oscillations in Hall thrusters.

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