Design And Characteristics Of A Long-life Hall Thruster With An Externally Loaded Magneitc Field

With the rapid development of aerospace science and technology in recent years,space missions and directions have shown significant changes in long-term characteristics.The development needs of future aerospace missions indicate that the transformation of electric propulsion from auxiliary propulsion to main propulsion is taking place.Meanwhile,huge development opportunities and severe application challenges have put forward very strict requirements on the working life of space propulsion,so long-life space propulsion is an inevitable development trend in the future.Hall thruster,as a typical space propulsion device using magnetic field confined plasma to generate power,has outstanding advantages such as high speci fic impulse and high efficiency.However,its working life has always been the main factor limiting its development to a broader space.Therefore,the research on long life has become an active field in the related research of Hall thruster.The fundamental reason for the end of the life of the Hall thruster is the bombardment and erosion of the discharge channel wall and magnetic circuit system by high energy ions,which eventually leads to the discharge failure of the Hall thruster.The magnetic field is the key factor to control the plasma,so the design of magnetic field is also the most important direction to realize the long life design of Hall thruster.In this paper,the concept of the long-life Hall thruster with an externally loaded magnetic field is proposed in the field of magnetic field design.For this new type of Hall thruster,the life characteristics,discharge characteristics and performance are studied from the perspective of long-term operation of the entire channel erosion,and the physical mechanisms are clarified.This paper demonstrates how to eliminate the key factor that limit the life of Hall thruster through magnetic field design,and then proposes the concept of the long-life Hall thruster with an externally loaded magnetic field.Starting from the sputtering erosion of the channel wall by high-energy ions,the most direct factor limiting the life of Hall thruster,the factors affecting the wall erosion rate are analyzed.Then,by comparing the magnetic field configuration characteristics of the first-generation SPT-100 and the second-generation ATON Hall thruster,the effectiveness of ATON Hall thruster’s magnetic field lines curved toward the anode and magnetic field with the large gradient in reducing the ion beam divergence are analyzed.Therefore,compared with SPT-100 Hall thruster,the strength of high-energy ions sputtering on the channel wall is weakened,and the length of the erosion zone is reduced.What’s more,the limitations of ATON Hall thruster in realizing long life design are analyzed.According to the enlightenment of the magnetic field design of ATON Hall thruster in the aspect of life promotion,the design idea of eliminating the factors limiting the lifetime of the Hall thruster is proposed by properly controlling the high energy ion region.The feasibility and method of magnetic circuit realization of the externally loaded magnetic field are demonstrated by analyzing the magnetic circuit structure and simulating with FEMM magnetic field simulation software.Therefore,the concept of the long-life Hall thruster with an externally loaded magnetic field is put forward from the perspective of magnetic field design.The magnetic field design analysis to realize the long-life design of the Hall thruster has improved the design theory of the long-life requirement in the practical application of the Hall thruster.Aiming at the design verification problem of the long-life Hall thruster with an externally loaded magnetic field,the influence of magnetic field externally loaded degree on the life characteristics and performance of thruster is studied by Particle-in-Cell(PIC)simulation and experiment method.Experiment and simulation results have indicated that the increase of externally loaded degree has positive significance for the long life design of Hall thruster.Through the influence of magnetic field externally loaded degree on the sputtering characteristics of channel wall,it is indicated that there is a design lower limit of magnetic field externally loaded degree to realize the long life design of Hall thruster.However,the increase of magnetic field externally loaded degree will have a negative impact on the performance of Hall thruster,so there is an optimal value of magnetic field externally loaded degree.The research on the magnetic circuit design method and the degree of externally loaded magnetic field has important guiding significance for the magnetic field design of the long-life Hall thruster.PIC simulation and experiment are used to study the channel design problem with the condition of magnetic field externally loaded,and discharge characteristics and performance differences with the channel walls in the initial desig n and late erosion.Experiment results have indicated that the discharge channel design of the externally loaded magnetic filed Hall thruster should ensure that the end of the channel coincides with the position of the maximum magnetic field strength,such a channel design scheme can ensure better discharge stability and performance of the thruster.What’s more,the equivalence of channel design between the oustside loading magnetic field Hall thruster and the traditional Hall thruster is proposed.Due to the high energy ion sputtering on the channel wall,the experiment results indicate that the channel length and morphology of the externally loaded magnetic field Hall thruster change gradually with the increase of the working time of the thruster.Compared with the initial channel design,the discharge stability and performance of the thruster in the late erosion of discharge channel will be reduced.Further more,the similarity and difference between the externally loaded magnetic field Hall thruster and Magnetic shielding Hall thruster are discussed.PIC simulation results indicate that increasing the curvature of the lens-type magnetic field is helpful to control the ionization of the working gas in the main flow region of the discharge channel,and shorten the length of the erosion zone.The research related to the channel design in this paper has important practical value to realize the long-life Hall thruster engineering application with the optimal total impulse.The research on the influence of the channel walls in the initial design and late erosion on thruster discharge process is significent for further understanding of thruster discharge characteristics in long-term working range.The influence of the externally loaded magnetic field on electron and ion movement behavior is studied by the method of PIC simulation and experim ent.The influences of the magnetic field strength and gradient on the anode ring temperature distribution are studied via experimental measurement,and the results indicate that the intersection of the cusp magnetic field and the anode ring is the main wa y of electron deposition to anode.PIC simulation results indicate that the discharge stability and performance of the thruster decrease in the channel late erosion period,which is the result of the influence of channel change on the electron and ion movement behavior.The shortening of the channel and the change of gradually expanding morphology increase the electron loss and the escape loss of working gas.Meanwhile,the increase of electron temperature will lead to the deterioration of the equipotentialization effect of magnetic force lines,which intensifies the divergence loss of the ion beam,and reduces the performance of the thruster and increases the discharge oscillation.Experiment results have indicated that a appropriate inward inclination of the strong magnetic field is required to suppress the radial ion motion and optimize the performance in the externally loaded magnetic field Hall thruster.The research of the influence of magnetic field on the electron and ion movement behavior is significant to understand the discharge characteristics of the externally loaded magnetic field Hall thruster,and has important practical value for ion beam divergence loss control in the channel late erosion period.