Researches On The Discharge Channel Wall Segmenting And Magnetic Shielding Effect In Hall Thruster

Hall thruster with advantages such as high specific impulse,high efficiency and high reliability,etc.,has been widely used in spacecraft orbital transfer,north-south position retention,attitude control and other propulsion tasks.Hall thruster has strong interaction between plasma and the channel wall,and also has big surface-volume ratio,which causes severe wall erosion,and affects thruster performance.Scientists have carried out a lot of scientific researches on thruster wall material and electromagnetic field configuration,but the physical mechanism needs to be further explored due to the complicated plasma discharge process in the channel.In this paper,we arrange a graphite electrode material at different positions in Hall thruster ionization region and use magnetic shielding electromagnetic field configuration to enhance thruster discharge performance.The focusing process of the plasma beam and the discharge characteristics are investigated,which provides theoretical basis and method for the optimization of the channel wall material arrangement and the design of the magnetic field configuration.In this paper,a axisymmetric two-dimensional physical model is established according to Hall thruster channel size and discharge process.PIC simulation method is used to study the influences of the segmented biased electrode on the potential distribution,ion number density distribution,and plasma-wall collision frequency.The results shows that,when the bias voltage of the segmented electrode is equal to the anode voltage,arrangement of segmented electrodes at the end of the ionization region can shorten the acceleration region,the equipotential lines are perpendicular to the wall,the ion-wall collision frequency decreases,and the thruster specific impulse increases.When the starting position of the segmented electrode is at L0 = 19 mm and the bias voltage of the electrode is 18 V higher than the anode voltage,the discharge parameters such as potential,particle number density and electron temperature change distinctly.The accelerating region expands axially and the ionization locates near the anode.The ion focusing effect is obvious,the ionization rate increases and the wall corrosion decreases,the thruster specific impulse significantly increases.When L0=21 mm and the bias voltage of the electrode is 43 V higher than the anode voltage,the ion-wall collision frequency significantly increases along with the erosion.When the segmented electrode is located near the center of the ionization region(L0= 9,12 mm),even if the electrode bias voltage is 60 V higher than the anode voltage,the plasma discharge parameters merely change.The electromagnetic field distribution of Hall thruster discharge channel directly affects propulsive efficiency by controlling the plasma beam.In this paper,the variation of the particle-wall collision frequencies,the specific impulse and the push power ratio with different magnetic shielding configurations are numerically studied.The results show that compared with the magnetic field distribution of the traditional Hall thruster,by applying magnetic shielding field configurations,the electron temperature increases and the electron-wall collision frequency decreases.Therefore the wall erosion decreases correspondingly,and the specific impulse increases.Especially when the channel wall is entirely magnetic shielding material and the zero magnetic field is located near the anode in the channel,the axial electric field is strong and thus the ion acceleration and focusing are improved.