无中和器离子推力器的发展现状、关键技术及展望

Development status,key technologies,and prospects of neutralizer-free ion thrusters

离子推力器具有高比冲和高效率等优势,是目前应用最广泛的电推力器之一,但亦存在着系统结构复杂、关键部件繁多等缺点.无中和器离子推力器可以消除对中和器的依赖,实现离子推进系统结构的简化,从而减小推力器体积和重量并提高系统可靠性.本文首先归纳了传统离子推力器的原理、优势及限制,引出了无中和器离子推力器的概念,对其基本原理、技术优势及分类进行了介绍;随后从等离子体源的束流自中和技术出发,总结了无中和器离子推力器的发展现状;结合空间应用需求以及无中和器离子推力器的工作特点,分析了无中和器离子推力器的关键技术,提出应将工质选择、等离子体机理研究、磁过滤装置和栅极系统设计以及栅极射频电压灵活调控方法这四方面作为其研究重点,同时应该发展并完善新的推力器参数测量方法,进一步明确无中和器离子推力器的工作特性.

The ion thruster is one of the most widely used electric thrusters and is famous for its high specific impulse and efficiency,but there are some shortcomings of the conventional ion thruster,such as the complex structure and the difficulty of miniaturization.One of the most attractive solutions to make up for these shortcomings is the neutralizer-free ion thruster which can reduce the volume and mass of the ion propulsion system and improve the system reliability by canceling the neutralizer system.In this review,the principles,strengths,and weaknesses of the conventional ion thruster are summarized,which leads to the concept of the neutralizer-free ion thruster.Combined with the operations of ion thrusters in real space missions,the advantages of removing neutralizer systems are analyzed.According to the neutralization methods,the neutralizer-free ion thruster can be divided into two types which are the electronegative ion thruster and RF(radio-frequency)ion thruster based on the self-bias effect.At present,the neutralizer-free ion thruster is mainly developed in Europe,Japan,and the United States of America.Researchers in China also perform some numerical and experimental studies on the neutralizer-free ion thruster,but there is still no report on the relatively mature prototype model.Lastly,based on the application requirements of the space propulsion and characteristics of the neutralizer-free ion thruster,the key technologies of the neutralizer-free ion thruster are discussed:(1)For the sake of prolonging the service life and improving the beam performance,the choice of propellant in neutralizer-free ion thrusters,especially the electronegative ion thruster where the propellant should be electronegative,needs more consideration than conventional ion thrusters.(2)The voltages applied on the grid system are generally AC voltages.Thus,to extract the collimated ion beams with high neutralization degree,the determination of the frequency and amplitude of grid voltages should consider many factors,such as the propellant type,insulation design,and plasma properties.(3)The adjustment of the working mode becomes more complex in the neutralizer-free ion thruster,since it is more difficult to adjust the AC grid voltage than conventional DC grid voltages and the relationship between the AC grid voltage and thruster performance also needs further investigations.(4)The magnetic filter plays an important role in the electronegative ion thruster,but it should be optimized because it increases the volume and weight of the thruster and weakens the advantages of the neutralizer-free ion thruster.(5)The ionion plasma in the electronegative ion thruster and the sheath near the grid with AC voltages make the plasma characteristics in the neutralizer-free ion thruster quite different from the conventional ion thruster.It is critical to perform more studies on the plasma physics of the neutralizer-free ion thruster to better design the thruster and adjust its performance.Accordingly,it’s concluded that the investigations of the choice of the propellant,design of the magnetic filter and grid system,plasma physics,and flexible regulation method of the grid voltage should be focused on.Moreover,to further understand the performance of the neutralizer-free ion thruster,new methods for diagnosing this new type of thruster need to be developed.