Numerical simulations and experiments have been conducted to investigate the effects of a filter on low frequency oscillation in Hall thrusters. With one-dimensional quasineutral hydrodynamic model, the effects of filter components are studied by way of simulation computations. The simulation results show that with proper filter parameters, low frequency oscillation can be stabilized. Further, an eigenvalue study of the linear stability has been performed and the stability conditions according to filter parameters are given. Finally, the theoretical analysis is validated qualitatively through experiments.

The characterization of coupling oscillation in a Hall thruster is experimentally studied by varying magnetic flux density or discharge voltage to obtain the relationship between discharge parameters and coupling oscillation. The dispersion relation of coupling oscillation is deduced using a 2D collisionless quasi-neutral fluid model and the factors having their effects on coupling oscillation are obtained. Experimental results and theoretical analysis indicate that coupling oscillation increases with magnetic flux density, discharge voltage or coupling intensity coefficient. The instability has a very large wave number within a frequency spectrum ranging from hundreds of kilohertz to megahertz.

It was found through the experiments made with an Aton-type Hall thruster that some of the propellant was ionized in the buffer chamber by “quick electrons.” This ionization is called “preionization” to discriminate it from the ionization in the discharge channel. The effect of preionization on low frequency oscillation was experimentally studied by changing the electric field intensity in the buffer chamber. The relationship between low frequency oscillation and preionization ratio was investigated through numerical simulation using a one-dimensional quasineutrality hydrodynamic model. The results obtained indicate that the amplitude of low frequency oscillation decreases as the preionization ratio increases. It was found through the analysis and numerical simulation of the physical process of low frequency oscillation that the positive feedback of electron density was the main cause of low frequency oscillation. The increase of preionization ratio decreases the amplitude of the feedback variation thereby reducing the amplitude of low frequency oscillation.

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The mechanism of low frequency oscillations in Hall thrusters is usually explained using the predator-prey type model, but the reasonable boundary conditions for the model have not been given. Analyses on thrusters' model equations show that besides the processes of neutral replenishment and ionization avalanche, the effects of dynamic electric field are also necessary for low frequency oscillations. The dynamic electric field reflects the interaction of ionization zone with acceleration zone, and is embodied in boundary conditions of the predatorprey type model. Furthermore, a basic predator-prey type model with reasonable boundary conditions and complete physical mechanism is proposed. And the effects of electric field on low frequency oscillations are verified by experiment.