Particle-in-cell simulation for effect of anode temperature on discharge characteristics of a Hall effect thruster

Propellant gas flow has an important impact on the ionization and acceleration process of Hall effect thrusters （HETs）. In this paper, a particle-in-cell numerical method is used to study the effect of the anode temperature, i.e., the flow speed of the propellant gas, on the discharge characteristics of a HET. The simulation results show that, no matter the magnitude of the discharge voltage, the calculated variation trends of performance parameters with the anode temperature are in good agreement with the experimental ones presented in the literature. Further mechanism analysis indicates that the magnitude of the electron temperature is responsible for the two opposing variation laws found under different discharge voltages. When the discharge voltage is low, the electron temperature is low, and so is the intensity of the propellant ionization; the variation of the thruster performance with the anode temperature is thereby determined by the variation of the neutral density that affects the propellant utilization efficiency. When the discharge voltage is high, the electron temperature is large enough to guarantee a high degree of the propellant utilization no matter the magnitude of the anode temperature. The change of the thruster performance with the anode temperature is thus dominated by the change of the electron temperature and consequently the electron-neutral collisions as well as the electron cross-field mobility that affect the current utilization efficiency.

Spectrum Diagnosis for Fuchsia Plume of Hall Effect Thruster with Xenon as Propellant

The colour of the Hall effect thruster＇s plume is often light-green, and sometimes a fuchsia plume appears during experiments. Based on a spectrum and colour analysis, and a comparison with normal plumes, a conclusion is made that the density of the Xe ions and the temperature of electrons are low when the plume appears fuchsia. In this condition, most of the components of the plume are Xe atoms, and the ionization rate of the propellant is low.

Thrust estimate method of an on-orbit Hall thruster using Hall drift current

In order to realize the thrust estimation of the Hall thruster during its flight mission,this study establishes an estimation method based on measurement of the Hall drift current.In this method,the Hall drift current is calculated from an inverse magnetostatic problem,which is formulated according to its induced magnetic flux density detected by sensors,and then the thrust is estimated by multiplying the Hall drift current with the characteristic magnetic flux density of the thruster itself.In addition,a three-wire torsion pendulum micro-thrust measurement system is utilized to verify the estimate values obtained from the proposed method.The errors were found to be less than 8%when the discharge voltage ranged from 250 V to 350 V and the anode flow rate ranged from 30 sccm to 50 sccm,indicating the possibility that the proposed thrust estimate method could be practically applied.Moreover,the measurement accuracy of the magnetic flux density is suggested to be lower than 0.015 mT and improvement on the inverse problem solution is required in the future.

Effect of Magnetic Mirror on the Asymmetry of the Radial Profile of Near-Wall Conductivity in Hall Thrusters

Considering the actual magnetic field configuration in a Hall thruster, the effect of magnetic mirror on the radial profile of near-wall conductivity （NWC） is studied in this paper. The plasma electron dynamic process is described by the test particle method. The Monte Carlo scheme is used to solve this model. The radial profile of electron mobility is obtained and the role of magnetic mirror in NWC is analysed both theoretically and numerically. The numerical results show that the electron mobility peak due to NWC is inversely proportional to the magnetic mirror ratio and the asymmetry of electron mobility along the radial direction gets greater when the magnetic mirror is considered. This effect indicates that apart from the disparity in the magnetic field strength, the difference in the magnetic mirror ratio near the inner and outer walls would actually augment the asymmetry of the radial profile of NWC in Hall thrusters.

Correlation Method of Average Plasma Velocity Measurement in Hall-Effect Thrusters

A new method to measure the average plasma velocity in a Hall-effect thruster is presented. The method is brought forward in virtue of the characteristics of low frequency oscillation induced by the propellant ionization in the channel and the oriented movement feature of the plasma density out of the channel. The method, equivalent to the correlation method generally used in the signal processing field, provides a solution to the problem of specific impulse measurement on a timescale of hundreds of microseconds and makes the time evolution of average plasma velocity clear. The comparison between the measured value and the calibrated value shows that the relative error is about 3%.

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages.To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition,a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages.The results show that when the discharge voltage is high,the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition;with the gradual strengthening of the ignition process,the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases.The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.

磁场对霍尔推力器气体电离率的影响规律研究

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Bmax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Bmax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Bmax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Bmax下对电离碰撞产生限制程度不同。

Experiment of Hall thruster plume effects on different ground experimental conditions

Reducing the influence of back-sputtering effect can effectively improve the accuracy of the measurement of the Hall thruster plume effect.Quartz crystal microbalance(QCM)was used to measure the deposition and sputtering distribution of HET-40 thruster plume on two different experimental conditions:case1,using liquid nitrogen heat sinks and case 2,without using liquid nitrogen heat sinks.Meanwhile,X-ray photoelectron spectroscopy(XPS)was used to analyze the composition of the QCM surface after two experiments.The results of the two experiments showed that the sputtering rate under the condition of case 1 was slightly higher than case 2.Especially within the range of 90°to 110°relative to the thruster axis,case 1 experiment result showed sputtering effect,while case 2 experiment showed deposition effect.Through analysis of the experimental results,it can be found that using liquid nitrogen heat sink to reduce the temperature of the inner wall surface of vacuum chamber can effectively adsorb the particles sputtered by the plume and reduce the concentration of back-sputtering particles,leading to the above phenomenon.

霍尔效应推力器羽流的PIC/MCC模拟(英文)

采用粒子网格单元与蒙特卡洛碰撞相结合的方法，建立霍尔效应推力器羽流的二维轴对称模型。模型中电子作为流体处理且服从等熵假设，离子（Xe＋和Xe2＋）采用粒子描述，中性原子为背景气体。自洽电势通过求解非准中性、线性化Poisson方程获得。模拟结果与实验数据相比较表明，模型能够可靠预估羽流的物理特性；粒子入射发散角为30°-40°时模拟结果与实验数据吻合较好；倒流区离子数密度可达10^14m^-3，会对飞行器表面造成损害；且等离子体密度和电子温度沿轴线方向衰减很快。

霍尔推力器通道宽度对电离特性的影响

为了研究霍尔推力器通道宽度对电离特性的影响,采用以数值模拟为主、实验验证为辅两种手段相结合的方式。所建立的数学模型是基于蒙特卡洛方法的二维完全动力学粒子模型,实验选择了与等离子体无接触的光谱诊断方法。计算和实验两方面的结果都发现随着宽度的增加,电子电离工质气体的速率增加,电离更加有效,而且电离区域变得集中的规律。通过进一步的计算发现,电离特性的明显差异和电子与壁面碰撞频率随宽度增加而减小,电子温度随之升高有着密切关系。电子温度升高一方面会对电离特性起到促进作用,另一方面也会使电离消耗的能量增加。由于稳态时的电子温度是由电子能量平衡机制决定的,因此对电子能量平衡方程进行深入分析之后发现,在研究通道宽度影响电离特性这一物理问题上,电子在壁面上的能量损失是决定电子温度的主导因素,而电离损失仅属于次要因素,宽度增加有利于改善推力器的电离特性。

真空室氢组分背压对霍尔推力器等离子体束聚焦特性的影响研究

基于光谱方法和羽流探针诊断方法，研究分析了氢组分压力对霍尔推力器束流聚焦特性和振荡特性的影响。研究结果表明，随着罐内氢组分压力的提高，通道内氢的特征谱线强度增强，相比 pH=0Pa， pH=0.04Pa下最大HI=652.6nm相对谱线强度增加了8-9倍。氢组分向通道内的返流影响通道内的工质电离和离子加速过程，进而导致推力器束流特性变差，且伴随着低频振荡增大。当 p H=0.04Pa时，羽流发散半角为41.5°，相比pH=0Pa条件下增加了24.5°。

亚稳态原子对霍尔推力器电离影响的光谱诊断

霍尔推力器(HET)是一种先进的电推进装置,在航天领域有着广泛应用。为了衡量亚稳态原子对于推力器电离过程的影响,提高相应电离计算模拟模型的准确性,应用发射光谱线强度比计算方法来确定HET通道中包含亚稳态原子贡献的氪原子有效电离速率。实验发现,考虑亚稳态院子的贡献后,氪原子有效电离速率相对于未考虑亚稳态贡献的基态原子电离速率高,在15～20eV的电子温度范围内增加最多,大约11%。计算结果说明亚稳态原子的存在使得HET通道内氪原子具有较高的有效电离速率,所以在HET电离模型中必须引入亚稳态的贡献项。

微波霍尔推力器表面波等离子体源的实验研究

在微波霍尔推力器中,微波通过窗口耦合到霍尔加速通道,在通道底部介质板附近产生表面波等离子体以抑制振荡。表面波等离子体能否顺利产生将直接影响推力器本身的性能,为此,开展微波霍尔推力器表面波等离子体源的真空实验研究。在不同微波输出功率条件下,分别以氪、氩气为工质,以陶瓷和石英材料为介质板,通过改变流量,得到了表面波等离子体的产生规律。采用朗缪尔探针,实验诊断了介质板附近的表面波等离子体密度。实验结果表明:和陶瓷介质板相比,石英介质板对微波的损耗低,表面波更容易稳定产生;朗缪尔探针的诊断结果表明,石英介质板附近等离子体的电子密度高于对应的临界电子密度,证明本实验等离子体为表面波等离子体。

磁场对高电压霍尔推力器性能影响研究

为研究磁场构型、磁场强度对高电压霍尔推力器主要性能的影响机理,以HET-200推力器为对象,采用固定磁场构型和不固定磁场构型两种方案进行实验研究。结果表明,在不固定构型的情况下增强磁场,放电电流存在两个极小值,效率也存在相应的两个极大值;但当固定磁场构型时,则放电电流只有一个最小值,效率也只有一个最大值。以最优效率下的磁场构型为基准,获得了磁场与电压、磁场与流量的匹配关系分别为B_(r, max)∝V^(0.7),B_(r, max)∝m。

分布式嵌套霍尔电推进设计与容错控制

空间电推进相比于传统化学推进,具有运行时间长、高比冲、小推力且功率比冲均可调节等优势。首先基于霍尔效应推进器基本工作原理引出嵌套式霍尔电推进概念,并设计出一个额定推力为2N的双通道嵌套式霍尔推力器,再对其各项性能参数如阳极比冲、放电电压、放电电流、阳极质量流率、功率等进行设计计算。最后,提出了一种基于滑模控制的容错控制方法,用于分布式嵌套霍尔电推进控制系统,并对其进行仿真分析。

霍尔效应推力器放电双稳态机理研究

实验发现霍尔效应推力器在自励磁模式下具有两个稳定的放电工作点,且运行过程中在这两个工作点上往复跳变,很大程度上影响了推力器通道内等离子体的放电物理过程及其综合性能.本文结合推力器放电磁安特性曲线与励磁电流曲线的相互关系,给出了推力器放电双稳态特性形成的物理机理.在此基础上提出了通过改变励磁电流曲线斜率,使推力器稳定工作于单放电工作点的方法,结合—维动态流体模型给予了物理解释,并通过实验加以验证.