微型电推进技术在微纳卫星的(质量＜100kg)轨道维护、姿态控制、卫星编队飞行等航天任务中占有重要地位。离子液体电喷雾推进器(ILET)作为一种重要的解决方案，具有体积小、重量轻、比冲高、推力连续可调、推力精度高、不需要中和器等优点。与脉冲等离子体推进器(PPT)、真空电弧推进器(VAT)、场发射电推进器(FEEP)等其他微型推进器相比，ILET作为空间引力波探测卫星的推进装置具有巨大的潜力。

根据ILET发射极结构的不同，可分为外部润湿型、毛细管型和多孔介质型。外部润湿型通过改变发射极的结构和材料，与离子液体实现完全浸润，并在发射极外表面形成液膜，达到连续浸润发射极的目的，由此保证连续发射。毛细管型则需要一个由微泵、微阀、微流道、管路和储液装置组成的主动供液系统。多孔介质型是通过材料孔隙间液体的毛细力被动供给液体的。这三种供液方式都面临着ILET发射极浸润的问题。浸润效果对ILET的工作方式、推力的一致性和稳定性以及推力噪声都有很大的影响。因此，研究发射极外部液体的浸润模式、液面构型、浸润速度和浸润效果对提高ILET的性能尤为重要。本文的主要内容包括以下四个部分：探究大气环境下复合式外部润湿型发射极浸润弯月面的理论解与仿真解；数值模拟静电场中复合式外部润湿型发射极被离子液体电润湿的过程；研制外部润湿型发射极并对单针ILET的束流进行测试；研制出可扩展的外部润湿型发射极阵列并搭建束流、推力和比冲测试系统对其性能进行测试。

首先，提出了一种新型针-毛细管离子液体电喷雾推进器发射极结构，并对供液和无供液条件下发射极的浸润效应进行了数值模拟和理论分析。发射极物理尺寸L、d、θ、β以及离子液体与结构之间的接触角α、γ共同决定了弯月面的构型。通过分析各变量对浸润的影响，总结出了一套完整的发射极浸润规律。此外，在供液条件的数值模拟中发现了浸润弛豫和周期性浸润振荡的现象，为发射极结构的优化设计提供了重要依据。考虑到Bond<<10^-2和推力器工作在空间环境中，液体主要受表面张力和粘性力的影响。同时，离子液体与结构形成的弯月面满足旋转轴对称和常平均曲率曲面的假设，从而得到准静态弯月面，即Delaunay曲面的数学解析表达式。对数值模拟结果和解析解进行了拟合，得到了较好的一致性和较小的拟合偏差。此外，还探讨了将不同的弯月面拟合到相应的Delaunay曲面上的分类推论。

其次，深刻剖析离子液体在静电场中的流体动力学机理是保证离子液体电喷推力器获得良好润湿性的理论基础。稳定并持续的电润湿发射极与推力的噪声、分辨率及其稳定性有十分密切的联系。所以，急切需要探索离子液体在静电场电润湿发射极的规律来提升推力器的性能。本文继而提出了一种由v形刀刃状发射极和方形毛细管复合而成的发射极结构。对正常重力和大气条件下的发射极电润湿进行了数值模拟和发射实验，探索了离子液体层在发射极外表面扩散的过程。离子液体的物理性质和发射极尺寸d1、d2、θ共同决定了电润湿速度、润湿电压阈值和液层厚度。通过分析各种变量对电润湿的影响，总结出离子液体电喷雾推进器完整的发射极电润湿规律，为优化发射极结构提供了重要依据。考虑发射极尺度和Bond≈1，静电场中的弯月面主要受重力、表面张力、粘滞力和电泳力的影响。因此，值得注意的是，电泳力是用麦克斯韦应力张量法计算的，该方法将离子液体作为介电介质，以保证半月板的连续性。数值模拟结果与实验结果相吻合。实验证明，本文所采用的方法能够较准确地模拟液相层破裂形成离子发射前的发射极电润湿过程。

再次，提出了一种制造外部润湿型发射极的新方法。该方法采用低速线切割(LSWC)与电化学腐蚀相结合的方法，通过三步法制备外部润湿型发射极。首先，通过LSWC对钨长方体进行成形，得到发射体的几何形状。其次，用超强酸清洗发射器，去除严重阻碍离子液体湿润发射极的氧化层。最后，采用电化学刻蚀法在发射体表面刻蚀微通道。通过上述步骤制备的钨发射极可获得优异的润湿性，其微通道可降低壁面与离子液体的接触角，增强离子液体沿发射极爬升的毛细力。离子液体在发射极表面扩散成均匀的液膜，保证稳定连续的流量供应，使推进器能够长时间工作在低噪声、高分辨率、高推力功率比的纯离子发射模式下。通过对酸洗前后各元素的定量和定性分析，证明了去除氧化层的可行性。采用金相显微镜和轮廓仪对发射极的微观形貌进行了测量和观察，包括微通道的结构和尺寸、针尖的尺寸和液膜的厚度。通过反复观察和评价，记录了最优的刻蚀参数，包括交流电压的幅值和频率、刻蚀时间、发射极浸入溶液的深度和NaOH溶液的浓度。为了比较外部润湿型发射极和多孔型发射极的性能，采用相同的工艺分别制备了两种发射极。在发射试验中，总结了束流电流、束流分辨率和束流噪声、点火可靠性和发射时间等方面的结论。发射实验表明，外部润湿型发射极具有更好的润湿性，且微通道不易被电化学反应产物堵塞，保证具有较好的发射性能。

最后，研发出可扩展的外部润湿型发射极阵列，对其束流特性进行了测试，实验证明外部润湿型发射极阵列可以实现稳定持续的发射，并能实现束流的多级调控，单个阵列模块分别发射阴阳离子的最大束流均可以达到800μA。单个阵列模块的分辨率优于3μA，束流噪声小于1μA，最大功率2W，可以实现以1Hz阴阳离子交替发射的工作模式。启动时束流响应时间在百毫秒量级，在正常发射期间以50v和100v为电压增量采集束流台阶，发现束流有很好的电压跟随性，即极快的束流响应。每3个拥有相似伏安特性曲线的阵列模块成为1组，总共3组。每组的最大束流可以达到2mA，功率小于5.5W。搭建了闭环控制的微推力和比冲的测量系统，最大推力144μN，对应比冲1588s，推力分辨率优于0.1μN。

Micro-electric propulsion technology occupies an important position in space missions such as micro-nano satellites (mass<100kg) orbit maintenance, attitude control, and satellite formation flying. As an important solution, ILET (Ionic Liquid Electrospray Thruster) has demonstrated its advantages of small size, light weight, high specific impulse, continuously adjustable thrust, high thrust accuracy and no need for neutralization. Compared with other micro thrusters such as PPT (Pulsed Plasma Thruster), VAT (Vacuum Arc Thruster), and FEEP (Field Emission Electric Propulsion Thruster), ILET has great potential as a propulsion device for space gravitational wave detection satellites.

According to the difference of ILET emitter structure, it can be classified into externally wetted type, capillary type and porous media type. The externally wetted type achieves complete infiltration with the ionic liquid by changing the structure and material of the emitter, and forms a liquid film on the external of the emitter to achieve the purpose of continuously infiltrating the emitter to ensure continuous emission. The capillary type requires a liquid supply system composed of a micro pump, a micro valve, a micro flow channel, a pipeline, and a liquid storage device for initiative supply. The porous media type passively supplies liquid by the capillary force of the liquid between the material pores. These three liquid supply modes all face the problem of ILET emitter infiltration. The infiltration effect has a great influence on the working mode of thruster, the consistency and stability of thrust and the thrust noise. Therefore, studying the liquid spreading pattern on the emitter external, liquid surface configuration, infiltration speed and effect is particularly important for improving the performance of ILET. The thesis includes the following four main parts. The theoretical solution and simulation solution of hybrid emitter infiltration meniscus under atmospheric environment. The simulation of electrowetting process of hybrid emitter by ionic liquid in electrostatic field. The externally wetted emitter is developed and the beam current testing of single needle ILET is carried out. An expandable externally wetted emitter array is developed and the beam current, thrust and specific impulse testing systems are built to obtain its performance.

First, The thesis proposes a new emitter structure of needle-capillary ionic liquid electrospray thruster and carries out numerical simulation and theoretical analysis of the emitter infiltration effect under the conditions of liquid supply and no liquid supply. Emitter physical dimension L, d, θ, β and the contact angle α, γ between the ionic fluid and the structure jointly determine the configuration of meniscus. Through analyzing the influence of various variables on the infiltration, a complete emitter infiltration law of needle-capillary ILET is summarized. In addition, the phenomena of infiltration relaxation and periodical infiltration vibration were found in the numerical simulation of the liquid supply conditions, which provided an important basis for the optimal design of the emitter structure. Considering Bond<<10^-2 and working in a space environment, the liquid is mainly affected by surface tension and viscous force. Meanwhile, the meniscus formed by the ionic fluid and the structure satisfies the hypothesis of rotational axis symmetry and constant mean curvature surface, thereby obtaining the mathematical analytical expression of the quasi-static meniscus, the Delaunay surface. The numerical simulation results and analytical solutions were fitted, an excellent consistency was obtained with a small fitting deviation. Besides, the classification inferences of fitting different meniscus to the corresponding Delaunay surface are explored.

Secondly, it is the theoretical basis to analyze the hydrodynamics mechanism of ionic liquid in electrostatic field to ensure that the ionic liquid electrospray thruster possesses good wettability. Stable and continuous electrowetting emitter is closely related to thrust noise, resolution and stability. Therefore, it is urgent to explore the law of ionic liquid electrowetting emitter in electrostatic field to improve the performance of thruster. The article proposes a new hybrid emitter structure which consists of a V-blade emitter and a square capillary. It also carries out numerical simulation of the emitter electrowetting under normal gravity and atmospheric conditions and emission experiments to explore the process of ionic liquid layer spreading on the external surface of emitter. The dimension of emitter d1, d2, θ and the physical properties of ionic liquids jointly determine the electrowetting velocity, the threshold of wetting voltage and liquid layer thickness. By analyzing the influence of various variables on the electrowetting, a complete emitter electrowetting law of ionic liquid electrospray thruster is summarized which provide an important basis for the optimization of the emitter structure. Considering the scale of emitter and Bond≈1, the meniscus in the electrostatic field is mainly affected by gravity, surface tension, viscous force and electrophoretic force. Accordingly, it is worth noting that electrophoretic force is calculated by the Maxwell stress tensor method that treats ionic liquids as dielectric to ensure the continuity of the meniscus. Although it can satisfy the electrowetting study at the macro scale, the interaction between anions and cations at the micro scale is ignored. The numerical simulation results and the experimental results are correlatively. It is proved that the method used in this article is accurate enough to simulate electrowetting before liquid layer breaking up to form ion emission.

Subsequently, the micro-newton thrust generated by ionic liquid electrospray thruster (ILET) can be used for drag-free control, attitude precise control, networking and formation flight of micro-nano satellites or spacecraft. Fabrication of high-quality emitters is one of the key technologies for the application of ILET. A new method for fabricating externally wetted emitter is presented in this article. This method uses low-speed wire cutting (LSWC) combined with electrochemical etching, and the externally wetted emitter is fabricated by three steps. First, the tungsten cuboid is shaped by LSWC to get the geometry of the emitter. Secondly, the emitter is cleaned by super acid to remove the oxide layer that seriously prevents the ionic liquid from wetting the emitter. Finally, microchannels are etched on the emitter surface by electrochemical etching. The tungsten emitter fabricated by the above steps can obtain excellent wettability, and its microchannel can reduce the contact angle between the wall and the ionic liquid, and enhance the capillary force that promotes the ionic liquid to climb along the emitter. The ionic liquid is spread into a uniform liquid film on the emitter surface to ensure a stable and continuous flow supply, so that the thruster can work in pure ionic emission mode for a long time with low noise, high resolution and high thrust power ratio. The quantitative and qualitative analysis of all elements before and after pickling emitter proves the feasibility of removing oxide layer. The morphology features of the emitter are measured and observed by metallographic microscope and profilometer, including the microchannel structure and its size, tip size and the thickness of liquid film. Through repeated observation and evaluation, the optimal etching parameters are recorded, including the amplitude and frequency of AC voltage, the etching time, the depth of emitter immersing in solution and the concentration of NaOH solution. In order to compare the performance of externally wetted emitter and porous emitter, the same process is used to fabricate two kinds of emitter. The conclusions about beam current, the resolution and noise of beam current, ignition reliability and emission time are summarized during the emission testing. The emission tests indicate that the externally wetted emitter has more outstanding performance, which depends on its better wettability and the fact that the microchannels are not easily blocked by the products of electrochemical reaction.

Finally, an expandable externally wetted emitter array is developed, and its beam current characteristics are tested. Experiments show that the externally wetted emitter array can achieve stable and continuous emission and multistage beam current regulation, and the maximum beam current of a single array module can reach 800μA. The resolution of a single array module is better than 3μA, the beam current noise is less than 1μA, the maximum power is 2W, and the working mode of alternating ion and anion emission can be realized at 1Hz. The beam current response time is in the order of hundreds of milliseconds at startup, and the beam current steps are collected with voltage increments of 50v and 100v during normal launch. It is found that the beam current has very good voltage following, that is, very fast beam current response. Every three array modules with similar V-I characteristic curves become one group, and there are three groups in total. The maximum beam current of each group can reach 2mA and the power is less than 5.5W. A closed-loop controlled micro-thrust and specific impulse measurement system is established. The maximum thrust was 144μN, corresponding to 1588s specific impulse, and the thrust resolution can be better than 0.1μN.