Research On Azimuthal Oscillation Characteristics Of Plasma Discharge In Hall Thruster

In the measurement of the conduction current of the Hall thruster,it is found that the total electron current is higher than the electron current generated by the classical conduction of heavy particles colliding with electrons.So there are other abnormal electron conduction mechanisms.Bohm conduction and near-wall conduction are two abnormal conduction mechanisms present in Hall thrusters.Due to the large surface area of the Hall thruster,secondary electron emission effects and sheath oscillation problems occur when electrons collide with the wall.The problem of near-wall conduction caused by this has been considered as the main cause of abnormal electron conduction current.However,the research found that the sum of the near-wall conduction and the classical conduction current is not enough to explain the total electron current of the Hall thruster.Therefore,this topic will focus on the electron conduction problem caused by the plasma oscillation phenomenon in the Hall thruster.By establishing a numerical calculation model with r-? as the research plane,the effects of different discharge parameters and different wall conditions on the azimuthal oscillation characteristics of the plasma were studied.Firstly,based on the actual structure of the Hall thruster,a 2.5D-3V particle simulation program with a r-? as the research plane was established.According to the dispersion relation,it is verified that the obtained azimuthal wave simulated by the model belongs to the range of ion acoustic wave.In order to speed up the calculation,the model is processed by reducing the ion mass and increasing the vacuum dielectric constant.The simulation results are compared with the theoretical solutions,and the model verification results are obtained.Then,according to the difference of various power thrusters,the axial,radial and azimuthal lengths of the thrusters are changed.The influence of size effect on the azimuthal oscillation of thruster is studied,and reasonable model parameters are determined for further study.Next,based on the discharge parameters of the Hall thruster,the effects of different axial electric field intensity and radical magnetic field intensity on the azimuthal oscillation of plasma discharge were studied.It is confirmed that the azimuthal oscillation is caused by the electron Hall drift.It is found that stable azimuthal wave requires a matching relationship between electric field and magnetic field.According to the different atomic densities of different discharge regions of Hall thrusters,and the plasma density of ionization in different regions are different,the influence of background atom density and plasma density on azimuthal oscillation characteristics is studied.Finally,based on the established particle model,the effects of metal grounding and suspension,and the influence of suspended metal wall and insulating wall on the azimuthal oscillation of the plasma are simulated.The potential drop and oscillation near the insulation wall and the variation of the parameters related to the azimuthal wave in the simulated discharge area are obtained.At the same time,the effects of different wall materials on the azimuthal oscillation characteristics of the plasma were simulated.