NUMERICAL CALCULATION CODE FOR DESIGN OF CUSPED ION THRUSTERS

开发了尖端离子推力器的数值计算程序，用于推力器性能的评估和燃烧室设计的优化。该程序可用于计算具有任意磁场配置的圆柱形离子推进器的离子生产成本和推进剂利用效率。该程序由四个计算部分组成；即用于1)计算施加到放电室的磁场方向和强度的部分。2)计算离子和中性原子的网格透明度。3)计算初级电子限制时间，4)计算被提取为离子束的离子的比例。在第一部分中，使用有限元方法的二维磁场分析程序来计算磁场构型。第二，建立了一个二维离子光学程序，用于计算离子轨迹和优化网格系统的设计。第三部分采用蒙特卡罗方法建立了电荷粒子动力学模型，计算了放电室中初级电子的轨道，进而计算了约束时间。在最后的计算部分，采用了基于等离子体扩散方程的等离子体流动模型来计算提取离子的分数。将其与基于质量、电荷和能量守恒方程的放电室模型相结合，可以计算等离子体的性质，进而计算推进器的性能。给出了几个数值结果，并与几个离子推进器的实验结果进行了比较。结果表明，该程序是优化燃烧室几何形状和磁场结构以获得良好性能的有效工具。

A numerical calculation code for cusped ion thrusters was developed to estimate thruster performance and to optimize chamber design. This code can be used to calculate both ion production cost and propellant utilization efficiency for a cylindrical ion thruster having any magnetic field configuration. This code is composed of four calculation sections; namely ones that are used 1) to compute the direction and strength of magnetic fields applied to the discharge chamber. 2) to compute grid transparencies to ions and neutral atoms. 3) to compute primary electron confinement time, and 4) to compute the fraction of ions produced that are extracted as an ion beam. In the first section, a two-dimensional magnetic analysis code using the Finite Element Method was employed to compute the magnetic field configuration. In the second, a tow-dimensional ion optics code is uded to compute ion trajectries and to optimize the grid system design. In the third section, a charge particle kinetic model using the Monte Carlo Method was employed to compute orbits of primary electrons in the discharge chamber and then to compute the confinement time. In the last calculation section, a plasma flow model based on plasma diffusion equation is used to compute the extracted-ion fraction. Combing these with the discharge chamber model base on the conservation equations of mass, charge, and energy, one can compute plasma properties and then calculate the thruster performance. Several numerical results were shown and compared with experimental results obtained in several ion thrusters. From the results, it is concluded that this code is a useful tool of optimizing the chamber geometry and the magnetic field configuration for good thruster performance.