| Due to their high efficiency, high specific impulse, long lifetime and high reliability, Hall Thrusters already become the research focus of the international electrical propulsion. However, due to the complex physical process, researchers are not clear to some physical mechanism, which limit the furuter improvement of the thruster.In Hall thrusters, the magnetic field is designed to control the movement of electrons, while ionization and ion acceleration are indirectly controled. Therefore, electron is the direct control factor in Hall thrusters. In order to understand the inner physical mechanism in Hall thruster, it is necessary to understand electron's behavior and the influence of electrons on performance firstly. In this thesis, the Particle in Cell (PIC) method is used to simulate the electron behaviors in Hall thrusters. The special behaviors of electrons due to the influence of sheath and magnetic field are considered.In this thesis, the PIC method is depiced in detail at first. Due to unacceptable amount of calculation, the PIC model should be simplified at first. Based on the analysis of the exiting simplified model, a new simplified method is proposed to accelerate the simulation and maintain the accuracy of the model. In the process of PIC simulaton, the stability problem was found. The control system design method is used to analyze the stability problem of PIC method. A new stability algorithm is proposed to improve the stability. Based on these works, the PIC simulated code is finished.The influence of electrons on thruster performance mainly depends on the electron conductivity. So the electron Near Wall Conductivity (NWC) is analyzed firstly. Focusing on the influence of the wall condition and magnetic field on NWC, the real condition of wall and magnetic field is used to study the NWC. The simulated results showed that the magnetic mirror effect due to magnetic lens can influence the electron behavior, the NWC is influenced accordingly. The theoretical analysis is also used to analyze the influence of magnetic mirror effect on NWC. After that, the PIC code is used to analyze the influence of wall groove on NWC. The numerical results found that the wall groove can strengthen the NWC. At the same time, the simulated results shown that electric potential would be anisomerous when considering grooves, which can be used to explain the anomalous erosion phenomena in Hall thrusters.The electron behaviour during the electron cyclotron motion is also study in the thesis. The influences of magnetic field gradient on electron behaviour are analyzed. The mechanism of magnetic field gradient's influence on electron mobility is found during the numerical simulation. After that, the fully PIC method is used to simulate the influence of magnetic field gradient on plasma distribution. The plasma distribution and thruster performance were found be influenced when altering the magnetic field gradient due to the change of electron behaviour. The simulated results are in accord with the experimental resultsAt last, the research results on electron behaviour are sucessfuly used in the model to predict the thruster performance. The ingnition process and pre-ionization in buffer chamber are simulated by PIC code. By simulating those physical phenomena, the current peak was found during the ignition, and the influence of various factors on current peak was analyzed. The design method to increase the pre-ionization in buffer chamber is proposed. The simulated results can be used to design and optimize the thruster.
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