磁场对霍尔推力器气体电离率的影响规律研究

Effects of magnetic field on gas ionization rate in Hall thrusters

关键词:  霍尔推力器  磁场  电子运动路程  碰撞短板效应  数值模拟

Key words:  Hall thruster  Magnetic field  Electron motion path  Cask effect of the collision  Numerical simulation

摘要:

霍尔推力器的通道磁场是推力器核心设计因素，对工质电离率和性能有重要影响作用。为深入揭示通道中线磁感应强度峰值B_max对气体电离率的影响规律与机制，以数值模拟方法进行研究。数值模型采用单元粒子方法（PIC）结合蒙特卡洛碰撞（MCC）方法，同时考虑电子的近壁传导作用。为验证数值模型的精度和修正模型中的经验参数，在真空罐内开展推力测量试验，以推力的测量值和计算值进行对比，修正后的模型计算误差可控制在7.5%以内。在此基础上，针对霍尔推力器通道不同的B_max对中性气体电离率的影响规律和机理进行数值分析，发现电离率对应B_max的变化曲线存在4个阶段：缓慢升高、急速升高、浮动不变和逐渐降低，原因为电子运动路程和激发碰撞的“短板效应”在不同B_max下对电离碰撞产生限制程度不同。

Abstract:

The magnetic field in the channel is one of the core designing factors in Hall thrusters， and it has been exerted a significant effect on both the gas medium ionization rate and the performance. In order to determine the influence law and the mechanism of the gas medium ionization rate caused by the changes of the B_max （the peak of the magnetic induction intensity） along the channel center line， a numerical model was employed. This model in the present study involved the particle-in-cell model （PIC）， the Monte-Carlo-collision model （MCC）， and the electron-wall conduction model. To justify and rectify the empirical parameters of the model， a thrust measurement test was conducted in the vacuum chamber， and the comparison of the measurement and calculation results was used to examine the model accuracy. The relative error of the corrected model was less than 7.5%. On the basis above， the influence law and relevant mechanism of the neutral gas ionization rate changing caused by different B_max has been analyzed by the numerical model. It has been found that there are four phases in the ionization rate vs B_max curve： slow rise， rapid rise， invariableness and gradual decline. Furthermore， the causing reason is that the electron motion path and the cask effect of the excitation collision exerts respectively a different impact on the ionization collision frequency at different condition of B_max.