多级会切磁场推力器的羽流结构及模式转变机理研究

Multi-cusped field thruster is a new type of plasma propulsion device. The plasma confinement in multi-cusped field could significantly decrease the erosion degree of discharge channel, and the thruster features its long-life time. Through a 20 years’ rapid development, this kind of thruster has reached its space application stage. At present, the divergent plume is not well optimized and becomes a common problem, which severely restricts the performance improvement of the thruster. In view of this problem, a study on the plume structure and mode transition mechanisms in this project is proposed. A new research method in which the plume should be divided into several angle regions by the space non-continuity characteristics of ion energy distribution functions is first put forward. The changing characteristics of ion energy distribution functions in different angle regions with the change of ionization degree in each stage will be studied to discover the relationship between plume regions and each ionization regions. Then the plume structures in different operating modes would be confirmed. On the other hand, mode transitions induced by the change of different characteristic parameters will be invested. Then, the common characteristics among different mode transitions could be obtained. On this basis, the ion groups in plume region will be separated and extracted by the characteristics of each ionization region. The competitive relationships among multi-ionization regions in different mode transitions will be analyzed by quantitative experiments and numerical simulations, and the mode transition mechanisms would be studied.

多级会切磁场推力器是一种新型的等离子体电推进装置。该推力器利用会切磁场对等离子的约束能够大幅降低壁面的离子侵蚀，使其表现出显著的长寿命性能优势。经过二十年的快速发展，该推力器发展到了空间应用阶段。羽流发散的现象已成为目前限制该类推力器性能提升的普遍问题。对此，本项目提出了多级会切磁场推力器羽流结构及模式转变机理的研究工作。首次提出了利用离子能量分布函数的非连续性对羽流进行分区的研究方法，并将通过羽流区离子电流随电离级强度变化规律的实验研究建立羽流分区与各电离区之间的对应关系，进而探究不同模式下推力器的羽流结构。另一方面，还将对多个特征参数变化所引起的多种模式转变过程进行研究，从中探索模式转变过程的共性变化规律。在此基础上，根据各电离区特征对羽流区离子群体进行提取，通过定量实验研究和数值模拟相结合的方法探讨推力器多电离区的竞争关系，研究羽流模式的转变机理。

本项目围绕多级会切磁场推力器的羽流结构、模式转变过程、模式转变机理、高性能推力器设计开展了较为全面的理论与实验研究工作。首先，利用离子能量非连续性对羽流进行分区，研究推力器在不同放电模式下的羽流结构，建立起羽流分区与电离区的对应关系，进而实现推力器电离级的优化; 其次，研究多特征参数变化所引起的模式转变过程，获得羽流模式转变过程的一般性规律，提出了利用图像差分技术获取电子传导路径影像的实验方法，证实了两类电子传导路径的客观必然性。设计阴极耦合实验，利用双探针联合测试方法论证电子传导路径对羽流模式转变过程的影响规律，明确推力器羽流模式转变的诱导机制。再次，提出离子电流分区与特征提取方法，研究多电离区竞争对羽流模式转变特性的影响规律，证实推力器电离竞争机制是驱动羽流模式转变的重要原因。研究推力器模式转变过程中电离区和加速区之间的弱耦合规律，证实推力器电离加速的弱耦合机制是拓展羽流模式调节范围的根本原因。探究电子多路径传导、多电离区竞争、电离加速弱耦合之间的关系，得出推力器羽流模式的转变机理。最后，开展推力器工程化应用研究。提出基于电子传导的高效电离加速匹配方法，突破羽流聚焦关键技术，研制国内首台5kW高比冲多级会切磁场推力器，额定推力达到180 mN，最高比冲达到3200s，性能指标与国际先进水平相当。以超低轨卫星的应用为背景，将模式宽范围调节方法应用于吸气式电推进，研制1kW吸气式电推力器，实现5.8 mN ~ 24.2 mN推力连续调节，可满足超低轨卫星大气阻力补偿需求。

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