Measurements and theory of driven breathing oscillations in a Hall effect thruster

Breathing mode oscillations in Hall effect thrusters occur depending on the operation parameters such as discharge voltage, anode mass flow, and magnetic field. Time-dependent laser-induced fluorescence 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 field 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 fluctuate in time and is in-phase with the electric field 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 field during the oscillation.