Research On Plume Simulation Method And Plume Characteristics Of Hall Thruster

Hall thruster is an electric propulsion device with high efficiency,high specific impulse and long life.During the operation of Hall thruster,plasma plume will be formed at its tail.Because the plume contains a large number of charged particles,its diffusion in space will affect the electromagnetic field environment of the spacecraft,and the high-energy ions will hit the spacecraft surface,causing torque,thermal deposition,erosion and other effects on the spacecraft surface.Therefore,it is necessary to study the plume of Hall thruster systematically.The plume research of Hall thruster mainly includes ground test,in orbit test and numerical simulation.Ground test measurement is limited by experimental conditions,while the cost of on orbit flight test is relatively high.So at present,numerical simulation method is widely used,combined with the test results for comprehensive analysis.According to different research problems,plume simulation can be divided into near field plume simulation and far field plume simulation.In recent years,the plume calculation model has been gradually improved and optimized with the development of thruster research and plume problem research.However,the current calculation model still has certain limitations.This is mainly reflected in the fact that the current near-field plume model cannot investigate the position of the cathode,the lack of research on erosion products in the plume composition,and the thruster outlet boundary depends on the results of the experiment in the far field plume calculation.Therefore,it is necessary to further improve the plume calculation model.In this dissertation,based on the above research background,firstly,the improvement of the calculation model is carried out.And on this basis,the systematic research work is carried out for the problems of near field plume and far field plume.Because the simulation size span is too large,it is impossible to use a single numerical simulation code to realize the overall simulation of thruster and far-field plume.Therefore,the simulation of plume needs to model the near-field plume and the far-field plume respectively.In this dissertation,the full particle-in-cell simulation method is adopted for near-field plume simulation,and the hybrid simulation method is adopted for far-field plume simulation.Then according to the needs of cathode position research in near field plume simulation,the cathode boundary model is optimized,and a hybrid cathode boundary model is proposed.Meanwhile,the applicability of the model is extended by using the plume simulation results of the near field plume simulation instead of the experimental results as the thruster outlet boundary of the far field plume simulation.The location and accuracy of the outer boundary of the plume are verified.The optimization design of magnetic field and electric field is an important means for beam control of thruster plume.In this dissertation,the beam control of electromagnetic field in plume region is simulated.For the magnetic field,previous studies have shown that there is a matching problem between the magnetic field in the plume and the cathode.Therefore,starting with the position relationship between cathode and magnetic field,this dissertation investigates the influence of magnetic field on electron motion and electron conduction.It is found that the electrons emitted from the cathode will be bound by the magnetic field after entering the plume region,so as to form a virtual cathode.The discharge difference under the condition of internal and external cathode is mainly related to the formation position of virtual cathode.The simulation results show that the cathode is located inside and outside the magnetic separatrix,and there is an obvious difference in electron conduction near the magnetic separatirx above the plume.Combined with the electron trajectory,it is found that the formation of electron conduction difference is mainly affected by the magnetic tip on the outer magnetic pole.Meanwhile,through the comparison of thrust and plume divergence angle under different external cathode conditions,it is found that the existence of magnetic interface can effectively inhibit plume divergence,and the design of this magnetic field can be applied to plume beam control.On this basis,the influence of the position and angle of the magnetic separatirx on the beam control is further investigated.The results show that the design scheme of properly deflecting the magnetic separatirx to the channel direction can effectively reduce the plume divergence angle and improve the performance of the thruster.For the research of beam control of electric field,the influence of additional electrode in plume region on discharge is simulated in this dissertation.The results show that the existence of additional electrode can effectively inhibit the radial diffusion of ions.Meanwhile,the presence of additional electrode will increase the potential of the nearby region,resulting in the enhancement of ion bombardment on the outer magnetic pole.The erosion problem is an important content in the research of Hall thruster.In the past,erosion research mainly focused on the research of lifespan,and there were few studies on the pollution of erosion products in the plume.And the erosion products are difficult to detect in experiments due to their relatively low proportions.Therefore,it is necessary to carry out research on the movement of erosion products.In this dissertation,based on the previous research,the movement of erosion products was simulated.In this dissertation,the erosion model,the movement and collision model of erosion products are added to the near-field plume calculation model.So the near-field plume calculation model has the ability to simulate erosion products.On this basis,the effects of neutral gas axial velocity and radial gas supply position on wall erosion were simulated and analyzed.The research results show that the reduction of the axial velocity of the neutral gas will increase the wall erosion.The change of the gas supply position will cause the uneven radial distribution of the neutral gas in the channel.Meanwhile,it will affect the angular sputtering coefficient and energy sputtering coefficient on the inner and outer wall surfaces,and will have a significant impact on the range and intensity of wall erosion.Through the simulation of the movement and collision of the erosion products,it is found that the distribution of B atoms is mainly located at the outlet of the thruster,which corresponds to the larger erosion rate at this position,and its density is three orders of magnitude lower than that of Xe⁺ions.The peak value of B⁺ions is mainly located in the middle of the thruster exit,and its density is one order of magnitude lower than that of B atoms.And the divergence degree of B⁺ions in the plume region is higher than that of Xe⁺ions.Finally,the plume pollution of a typical spacecraft model is simulated.The results of the near field plume simulation are used as the thruster outlet boundary conditions.And in this chapter,two different thruster installation angles are considered in the three-dimensional modeling.Through the far-field plume simulation,the pollution of Hall thruster plume to spacecraft under different plume divergence angles is compared and analyzed,and the torque,thermal deposition,erosion effects on solar panels are evaluated.The results show that the change of thruster installation angle has a significant impact on the spacecraft pollution.The distribution of the thruster beam ions is relatively concentrated,and the back flow ions will diffuse to the surrounding environment.A reasonable installation angle can effectively avoid the erosion of spacecraft and solar panels by beam ions.Through the evaluation of the torque,thermal deposition and erosion effects on the solar panel,it is found that the effect of the torque and thermal deposition on the solar panel caused by the plume is relatively small.The deposition rate of B⁺ions is on the order of 10^-12m/Kh,which is about 6 orders of magnitude lower than the erosion rate of Xe⁺ions.The erosion products have relatively little impact on spacecraft pollution.