Three-dimensional FEM-PIC Simulation Of Ion Extraction With The Collision Effect

Ion thruster has many advantages,such as high specific impulse,high efficiency,long life,and less consumption of propellant.It has been widely used in space missions such as main propulsion system of deep space exploration,position control and orbit transfer of geostationary orbit satellite.The optics system is an important part of the ion thruster.The extraction process of ion beam in the grid system is very important.It will affect thrust performance and efficiency of the ion thruster,and it will even cause the failure of grid structure due to grid erosion.However,so far,because the grid structure is fine,the process of ion extraction is complicated,and many of these physical mechanisms are poorly understood,studying process of the ion extraction in depth is of great significance to explore to physical mechanism of grid and optimize for the thruster life performance.Aiming at the above research background and research demand,this paper aims to carry out three-dimensional FEM-PIC simulation of ion extraction with the collision effect.The main work and innovation include:1.Firstly,the research background,the research significance and development of ion thruster are introduced.Secondly,the working principle of ion thruster and the important role of ion optics system are summarized,and the significance of ion extraction research is pointed out.Finally,the development of the numerical simulation method of ion optics system at home and abroad is expounded,which lays a foundation for the topic selection of the paper.2.The most commonly used numerical simulation methods for ion extraction are described in this paper: FD-PIC method and IFE-PIC method.The shortcomings of these two methods are found by comparing and summarizing them,so the numerical simulation method adopted in this paper is FEM-PIC simulation algorithm.3.This paper adopts FEM-PIC algorithm to establish a mathematical model of three-dimensional ion extraction,and uses MCC method to add CEX collision effect.The calculation of FEM-PIC algorithm is based on unstructured mesh and it mainly includes that adopting FEM algorithm to solve the potential of mesh node,adopting the interpolation algorithm to calculate electric field of the ion position,adopting the ion movement updating algorithm to drive ion to move,and using the base function allocation algorithm to allocate charge.4.In certain parameters of the grid structure and voltage etc,a two-dimensional mathematical model and three-dimensional mathematical model were studied.The simulation results show that the presence of CEX ions will affect the focusing of beam ions.The barrel erosion is mainly caused by the beam ions which have poor focusing state and CEX ions impacting on the acceleration grid hole.The pits-and-grooves erosion is mainly caused by CEX ions impact on the downstream surface of acceleration grid,and for the porous model,the edge hole is more vulnerable to erosion than the center hole.5.By comparing the influence of different emission current density,different voltage of screen grid and different voltage of acceleration grid on the ion passing rate of screen grid and the collision probability of acceleration grid,it is found that it is necessary to coordinate the setting of these parameters to design an ion optics with good performance.