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磁场作为霍尔推力器的关键设计参数之一, 其通过直接影响电子输运、中性原子电离、等离子体分布等微观行为, 间接影响推力器的宏观性能. 目前, 针对霍尔推力器磁场影响的研究更多的是关注放电通道内磁场大小以及分布的影响, 而对羽流区磁场的影响研究相对较少. 基于此, 本文利用二维粒子-流体混合模型研究了霍尔推力器羽流区的轴向磁场分布对推力器性能的影响. 结果表明, 在放电通道内轴向磁场分布不变的情况下, 改变羽流区的轴向磁场梯度对推力具有显著的影响. 放电通道中的电势降随着羽流区轴向磁场梯度的减小而减小, 羽流区电场以及放电通道中的离子数密度峰值则随着羽流区轴向磁场梯度的减小而增大. 增大羽流区的磁感应强度, 有助于推力器性能的提升. 更明确地说, 羽流区的磁场梯度存在一个临界值, 当羽流区轴向磁场梯度大于临界值时, 推力随羽流区轴向磁场梯度的减小而增大. 当羽流区轴向磁场梯度小于临界值时, 推力随羽流区轴向磁场梯度的减小而轻微的减小. 通过对不同羽流区磁场分布下的等离子体电势、电场、离子数密度, 以及电离率分布的比较表明, 羽流区磁场通过影响电子迁移率改变电场的分布, 而电场分布的改变则会对推力产生影响. 本文的研究结果将对霍尔推力器性能优化, 以及磁场设计提供理论支撑.As one of the key design parameters of Hall thruster, magnetic field indirectly influences the macroscopic performance of the thruster by directly affecting electron transport, neutral atom ionization, plasma distribution and other microscopic behaviors. At present, the research on the influence of Hall thruster’s magnetic field focuses mostly on the size and distribution of the magnetic field in the discharge channel, but less on the influence of the plume magnetic field on the thruster. Based on this, the effect of plume region axial magnetic field profile on the performance of Hall thruster is studied by using two-dimensional hybrid simulation. The research results show that the axial magnetic field gradient in the plume region has a significant influence on the thruster performance, when the magnetic field characteristics (magnetic field topology and magnetic field intensity) in the discharge channel remain unchanged. The potential drop in the discharge channel decreases with the axial magnetic field gradient in the plume region decreasing. However, the electric field in the plume region and the peak ion number density in the discharge channel increase with the axial magnetic field gradient in the plume region decreasing. Overall, the performance of the thruster is improved by increasing the magnetic field strength in the plume region. More specifically, there is a critical value of axial magnetic field gradient in the plume region. When the axial magnetic field gradient in the plume region is greater than the critical value, the thrust increases with the axial magnetic field gradient decreasing. When the axial magnetic field gradient of the plume region is less than the critical value, the thrust decreases slightly with the axial magnetic field gradient decreasing. The comparison of plasma potential, electric field, ion number density, and ionization rate distribution under different magnetic field distributions in the plume region shows that the effect of plume magnetic field on thrust is to affect the spatial electric field distribution by affecting the mobility of electrons, thus causing the thrust to change due to electric field. The research results of this paper will provide theoretical support for improving the performance of hall thrusters and designing magnetic fields.
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