Researches On The Discharge Characteristics Of Channel Wall Segmenting In Hall Thruster

Hall thruster is a kind of device providing small thrust for spacecraft in orbit, which shows outstanding performance on the efficiency, the specific impulse and the reliability. Therefore it is widely applied to achieve the spacecraft promote task such as orbital transfer, station keeping, and attitude control. The wall material formation of Hall thruster discharge channel has a significant impact on plasma dynamic characteristics. Though numerous experiments and simulation researches have been carried out by researchers, but the mechanism of segmented wall material and the influences on discharge characteristics of thruster are still unclear due to the complicated physical interaction process between the plasma and the walls of discharge channel. In this paper, two kinds of segmented wall methods are adopted to research the physical mechanism of influences on discharge characteristics of Hall thruster, which includes applying segmented low secondary electron emission graphite electrode and insulated wall at the channel exit. By researching and analyzing the segmented wall method, it can provide a theoretical basis and optimization methods for further selection and design of channel wall material.In this paper, a two-dimensional physical model according to Hall thruster discharge channel is established using the particle-in-cell (PIC) method. The influences of segmented graphite electrode on discharge characteristics such as ion density, electric potential distribution and ionization rate are investigated. It is found that, with the increasing of segmented electrode length, the equipotential lines bend towards the channel exit, the radial electric potential drop, radial velocity and radial flow of ions are increased, the electron temperature, collision frequency between electron and wall surface and discharge current are also enhanced. Based on these researches, the influence of discharge voltage on the physical parameters with non-segmented and segmented electrode are also investigated, such as electric potential, ionization rate, electron temperature distribution and so on. The results show that, with the increase of discharge voltage (during 250-650 V), the acceleration region moves slightly towards anode, the electron temperature in discharge channel is enhanced, and the electron temperature saturation is observed between 400-450 V. However, when the discharge voltage increases to 700 V, the acceleration region shows little axial expansion for the segmented electrode case, the electron temperature and discharge current are greatly increased, and the specific impulse is reduced which means the performance of Hall thruster is decreased.Based on the analyses of the discharge characteristics of Hall thruster with low secondary electron emission segmented graphite electrode, the influences of segmented insulating material with low secondary electron emission on the discharge characteristics of Hall thruster are investigated. It is found that, when the segmented insulating wall length is set below 3 mm at the exit, the acceleration region is shortened, the axial electric potential gradient is enhanced, and collision frequency between ions and walls is reduced. Besides, ionization rate and specific impulse are enhanced. Therefore, the efficiency of Hall thruster is improved.