碘工质射频离子推力器栅极系统束流特性仿真

Ion beam characteristics of iodine RF ion thruster optical system

为分析碘工质射频离子推力器束流特性,应用粒子云网格算法(PIC),对碘工质射频离子推力器栅极系统进行三维数值仿真。碘工质电离产物中除了大量存在的I^(+),还包含少量I^(+)_(2)、I^(2+)、I^(3+)几种多价离子。对添加多价离子前后束流特性的仿真结果进行对比,得出该栅极系统离子空间分布、电势分布、离子相空间分布以及束流、束流发散角,并对变密度工况下束流大小进行统计。计算结果表明,程序能较好地模拟离子在栅极系统中的运动情况:添加多价离子后,等离子体悬浮电势有所上升,鞍点电势有所下降,但整体电势分布的变化幅度较小;添加多价离子后束流大小略有增加,束流发散角略有减小,通过理论分析可知仿真所得理论推力及理论比冲均有小幅度增加;放电室等离子体数密度增加到约2.4×10^(17)m^(-3)时,该栅极系统达到了束流引出的极限,后续增大等离子体密度引出束流不增反降。模拟结果可以为碘工质射频离子推力器栅极系统的设计提供参考。

Based on the particle-in cell(PIC)method,a numerical simulation on iodine RF ion thruster optics system was carried out to analyze characteristics of ion beam.Besides substantial I^(+),ionization products of iodine contain a little multivalent ions including I^(+)_(2),I^(2+),I^(3+).Comparison of ion beam characteristics′simulation results with and without addition of multivalent ions obtained spatial distribution of ions,potential distribution,phase space distribution,beam current and divergence angle.The results show that the program can simulate the motion of ions in optics system properly.With addition of multivalent ions,plasma potential increases and saddle point potential declines,though the variation range of the whole potential distribution is limited.The charge-to-mass ratio of the ion group increases slightly with addition of multivalent ions,therefore beam current increases and divergence angle declines a little.Both thrust and specific impulse increase slightly through theoretical analysis.When the plasma density in discharge chamber increases to about 2.4×10^(17)m^(-3),the optics system reaches the limit of beam extraction,and extracted beam current decreases instead of increasing with proceeding increase of plasma density.The simulation results can provide a reference for design of RF ion thruster optics system.