Numerical Study On Background Magnetic Field Optimization And Its Effect On Plasma Characteristics In Hall Thruster

As more and more missions in space exploration are committed, many advanced propulsion technologies are developed. In these thrusters, hall thruster is widely used due to its high efficiency, high specific impulse, long life time and low thrust. The physical process in hall thruster is very complex and many physical mechanisms are not clear yet. To improve the performance of hall thruster, it is important to figure out these physical mechanisms. Moreover, it is difficult to commit experiment for the thruster is very small. Therefore, it is necessary to do theoretical and simulation research. In this paper, the magnetic field in hall thruster is simulated. Based on the background magnetic field calculated, the plasma in hall thruster is simulated using two-dimensional fluid simulation.The magnetic field can restrain the movement of electrons, while ions cannot be constrained for they are much heavier than electrons. Thus, the magnetic field can affect the distribution of potential and then affect the performance of hall thruster. In history, the promotion of hall thruster’s performance is always related to the improvement of magnetic field configuration. Therefore, it is necessary to study the factors affecting magnetic field configuration. In this paper, the effect of magnetic screen, magnetic pole and trim coil on magnetic field configuration is studied using numerical simulation method. The results show that the width between magnetic screen and magnetic pole can affect magnetic intention and magnetic mirror ratio. When inside magnetic pole is higher, the magnetic lines near exit plane are parallel to it, which is benefit to improve the performance of hall thruster. The trim coil current can affect the magnetic intention and the position of magnetic zero point. The magnetic mirror ratio increases as the current increases. The gradient of magnetic field increases with the distance between the coil and anode decreasing.In hall thruster, the physical processes related to electrons such as electron conduction, electron drift and collision have significant influence on hall thruster’s performance. In this paper, a two-dimensional fluid simulation method is applied to study the effect of magnetic field on electron movement. Owing to the big difference between ions and elections in terms of time scale, drift-diffusion approximate is applied to ions, while for electrons general fluid model is used. The numerical results show that when magnetic intention is greater than a certain value, magnetic field constrains axial electron conduction well. The azimuthal velocity of electrons first increases and then decreases as the magnetic intention increases. The distribution of plasma and its variation with time have significant influence on hall thruster’s performance. To do related research, a two-dimensional fluid model is applied. As the time scale concerned is relatively long, drift-diffusion approximate is applied to both electrons and ions. According to the results,a high frequency oscillation in MHz band shows up. When magnetic screen exits, the frequency decreases. When the angle between magnetic lines and exit plane becomes lager, irregular oscillation with higher frequency becomes prominent. Magnetic configuration with zero magnetic point suppresses the irregular oscillation and makes the MHz band oscillation’s frequency become lager. Magnetic configuration with magnetic lines convex to anode makes plasma be concentrated in the central of thruster. Magnetic configuration with zero magnetic point makes the peak of plasma density away from anode.