The Improvement And Characteristic Study Of Low Frequency Oscillation Model For Hall Thruster

The Hall Thruster is a plasma jet source, which ionizes propellant gas andaccelerates ions under the effects of electric and magnetic fields. The low frequencyoscillation, resulted from the instability of ionization, is a key characteristic for aworking thruster and also a basic issue concerning the microscopic mechanisms andmacroscopic properties. numerical simulation is an important method to describethe oscillation. The results of the existing model are not in good agreement with theexperimental properties, and it’s necessary to be further improved. In this thesis, theexisting model is revised according to the discrepancy of the physical properties indifferent sectors, therefore a new model is proposed, which is more coherent withthe experiments.The Partial Differential Equations (PDE) system is established on the basis ofBoltzmann equation. The equations are nondimensionalized and numerical solutionsare obtained by difference method. Considering the discrepancy of the change of ionnumber density, the change of atom number density and the discharge currentbetween the existing model and experiments, the quasi-neutral assumption is revised,and wall combination as well as anomalous conduction are introduced into the newmodel, all of the above are on the basis of the disparate physical properties betweenthe near-anode zone and the ionization-acceleration zone. The description of typicalparameters from the new model consists with the experimental results.The ionization of neutral gas and the acceleration of ions are the mainprocesses in the channel, and the low frequency oscillation is the direct reflexion ofthe ionization characteristics. According to the new model, the low frequencyoscillation is studied from the ionization state by changing the operating parameters.The distribution of ionization intensity and the shift of ionization positon isdescribed by changing the discharge voltage, mass flow rate and magnetic fluxdensity respectively. At the same time, the discharge current characteristic is given.The intrinsic links between the low frequency oscillation and ionization is given byanalyzing the simulation results.The relevance of operating parameters and ionization state is also studiedthrough experiments. Spectrum method is adopted to measure ionization intensity,and the data is processed with the corona model which is adapted to the thin plasma.Based on the optimal working conditions, the experiments are performed bychanging working parameters. It is shown that the oscillation is the process of the alternative domination between the neutral gas inflating and ionization by analyzingthe simulation results and experimental results.