【作者】 鄂鹏；

【导师】 于达仁； 王晓钢；

【作者基本信息】 哈尔滨工业大学 ， 动力机械及工程， 2009， 博士

【摘要】 霍尔推力器是一种为航天器在轨运行提供微小推力的动力装置,具有高效率、高比冲以及高可靠性等优点,广泛地应用于航天器的轨道提升、位置保持、姿态控制等推进任务。近年来,随着大型卫星平台建设、微小卫星组网、深空探测等航天技术的不断发展,相应地对霍尔推力器的性能也提出了更高的要求,推动了其技术发展。霍尔推力器依靠磁场抑制电子轴向输运以建立强电场,从而实现等离子体束流加速,因而磁场是影响推力器放电特性及性能水平的关键因素之一,也是推力器性能优化的重要设计自由度。本文主要围绕磁场对推力器放电特性的影响规律展开研究,在此基础上进一步研究磁场对电子输运过程的控制,从而为磁场优化设计提供理论依据。本文的主要工作包括以下五个方面:1.基于磁场影响霍尔推力器运行的物理机理,系统地总结了霍尔推力器对磁场强度、磁场梯度的要求,将霍尔推力器放电通道内磁场的主要分布特点归结为出口处磁场强度和强场区轴向磁场梯度这两个量化参数,从而为分析磁场对霍尔推力器放电特性和电子输运过程的影响,得出与实际工况相匹配的磁场优化选择范围提供了研究思路。2.根据霍尔推力器对磁场强度和磁场梯度选择的物理要求进行了实验设计,采用光谱仪、多栅探针、实时频谱分析仪等测量仪器分别研究了磁场强度和磁场梯度对霍尔推力器放电特性的影响规律,并从分析推进剂的电离特性、离子流的加速特性和强场区的等离子体振荡特性入手,总结了磁场强度和磁场梯度的优选范围。3.在不同工况下(放电电压和推进剂质量流量),采用推力器的磁安特性和多栅探针伏安特性计算得出了放电通道出口截面处电子传导电流大小,并依据电子传导电流与当地磁场强度的关系分析了主导电子传导机制,通过F检验法进行了显著性分析和验证。4.分析了霍尔推力器通道内电子的能量耗散及加热机制,通过研究不同磁场强度下电子传导电流与电子温度的关系得出了电子的主导加热机制,此外,在霍尔推力器放电实验中首次发现了发生于特定磁场强度范围内的反常电子加热现象,并对这一现象所伴随的不同价态粒子组分变化进行了分析。5.基于优化磁场的选择很大程度上要依赖于外部的实验条件,针对外部真空背压对磁场选择的影响进行了分析。首先论述了真空背压影响推力器运行的机理——羽流效应、放电效应和表面沉积效应,然后设计实验研究不同真空背压下的推力器放电特性,分析真空背压大小对推进剂电离和加速过程的影响规律,据此最后给出了与推力器工况以及真空罐体几何尺寸相匹配的参考真空背压上下限。更多还原

【Abstract】 Hall Thruster is a kind of propulsion devices providing micro thrust for the on-orbit operation of spacecrafts. Due to its high efficiency, high specific impulse and high reliability, Hall thruster has been widely applied in many propulsion missions including orbit transfer, station keeping, and attitude control etc. In recent years, with the development of space technology such as large satellite platform, micro-satellite net and deep space exploration, the performance of the Hall Thrusters is left open to be improved as well.Strong axial electric field is built through applied magnetic field to prevent electrons transport along the channel of Hall thrusters, and then the ion flux can be accelerated effectively, so that magnetic field not only plays a great role in affecting the discharge characteristics and performance of Hall thrusters, but also acts as an important DOF (degree of freedom) for optimization design. In this paper, researches mainly focus on the influences of magnetic field affects the discharge characteristics of Hall thrusters, and base on this work, the control rules of magnetic field on electrons transport has been investigated, and thereby providing fundamental theories for designing optimized magnetic field.The main work in this paper is divided into following five parts:1. According to the physical mechanisms that magnetic field affect the operation of Hall thrusters, requirements of the magnetic field intensity and magnetic field gradient for Hall thrusters were systematically summarized. The distribution of magnetic field in discharge channel of Hall thrusters can come down to two quantitative parameters: magnetic field intensity in exit plane and axial magnetic field gradient in strong field zone, thus a research thought that analyzing the effect of magnetic field on discharge characteristics and electrons transport processes put forward, and thereby, optimized range of magnetic field matched to actual working conditions can be acquired.2. Experimental setups were designed according to the physical requirements of magnetic field intensity and axial gradient for Hall thrusters. The effects of magnetic field intensity and axial gradient on discharge characteristics of Hall thrusters were investigated respectively by using spectrometer, multi-grid probe, real-time spectrum analyzer and other measuring instruments, and started with analyzing ionization of propellants, acceleration of ion flux and plasma oscillation in strong filed zone, the optimized range of magnetic field strength and axial gradient were summarized.3. Electron conductive current in exit plane at different working conditions which refers to different discharge voltage or propellant mass flow was calculated by using magneto-ampere character and voltage-ampere character of Hall thruster and multi-grid probe respectively, and then the dominant electron conductive mechanism was analyzed according to the relations between electron current and local magnetic field intensity, finally the significant analysis was conducted by F test method.4. Electron energy dissipation and heating mechanisms in channel of Hall thruster were analyzed. The dominant electron heating mechanism was investigated through analyzing the relations between electron conductive current and electron temperature under different magnetic field intensity. Moreover, during the discharge experiments of Hall thruster, an anomalous electron heating phenomenon in particular range of magnetic field intensity was firstly discovered, and research work has been done on the changing of the particle proportions with different valences.5. Since the choosing of optimized magnetic field depends largely on external experiment conditions, the effects of vacuum backpressure on choosing magnetic field were analyzed. Firstly, the mechanisms of vacuum backpressure on the operation of Hall thrusters including plume effect, discharge effect, and surface deposition effect were discussed. Secondly, experimental research was conducted to investigate the discharge characteristics of Hall thruster under different backpressures, and then the influences of backpressure on ionization and acceleration processes of propellants were analyzed. Finally, the upper and lower limit of vacuum backpressure which matched actual working conditions of thrusters and the dimensions of vacuum tank were given.更多还原