| Hall thruster is a kind of electric propulsion device with high efficiency,high specific impulse and high reliability,which has been widely used in the aerospace field to provide power for the orbit transfer,position maintenance and attitude adjustment of spacecraft.At present,the propellant used in Hall thrusters is mainly xenon,and the typical specific impulse is about 2000～3000s,which is generally less than the 3000～4000s specific impulse of ion thrusters.Additional,the natural reserve of xenon is small,which makes it expensive and limited for large-scale application.The physical properties of krypton are similar to that of xenon,but its reserves are abundant,and the price is low,simultaneously the theoretically specific impulse is higher,so krypton is one of the best alternatives to xenon,and the research on krypton becomes one of the hotspots in the field of electric propulsion.In addition,Space X has officially applied the Krypton Hall thruster in its Starlink constellation network.The research of Krypton Hall thruster has a long history,and the research results show that Krypton has obvious advantage of high specific impulse and is suitable for working with high power density and high voltage.But the physical characteristics of krypton lead to poor ionization characteristics and low ionization efficiency,and it adversely affects the acceleration process of krypton ions,which leads its plume to diverge and the ion wall collision loss to increase.Ultimately,it affects the performance and thermal stability of the Hall thruster.Additional,in order to take advantage of the high specific impulse of the krypton,it is necessary to increase the discharge voltage,but it brings greater challenges to the improvements of working performance and thermal stability of the krypton Hall thruster.Therefore,based on the above research background and contradiction analysis,this article takes the engineering application of the high specific impulse krypton Hall thruster as the ultimate goal,and aims to solve the performance improvement and working thermal stability problems of the krypton.Finally,designing and verifying engineering applications of high specific impulse krypton Hall thruster base on research results.Firstly,the characteristic analysis and optimization research on the ionization process of the Krypton Hall thruster are carried out.By analyzing the ionization process of propellant,it is found that the influencing factors affecting the process are mainly particle parameters such as electron energy,electron density,and atom density.Modifying the macroscopic input parameters has certain optimization effects on above particle parameters,but the effects are limited.In addition,the demand for high voltage due to high specific impulse make the anode flow rate reduced due to the power limitation,so the neutral atom density decreases,which intensifies the contradiction of full ionization of krypton.Based on the analysis of the movement process of krypton atoms,this paper proposes a method for controlling the flow of neutral gas — rotating supply,which effectively reduces the axial velocity of the neutral atoms,thereby increasing the neutral atom density.It is found by the image diagnosis method after the rotating supply that the ionization zone of the krypton was narrowed,and the ionization center position moved to the focal point of the focused electromagnetic field,so the krypton ionization characteristics were optimized.Simultaneously,the performance measurement results showed that the ionization efficiency of the krypton was improved,and the overall performance of the thruster has improved significantly.Secondly,theoretical research and optimization design are carried out for working performance problem of krypton with high voltage brought by the high specific impulse demand.The working efficiency of the Hall thruster have a "efficiency peak" problem with the increase of the discharge voltage,which limits the efficiency improvement of the Krypton Hall thruster under high discharge voltage,as well as the upper limit value of the discharge voltage for stable working.The latter directly affects the improvement of the specific impulse.By the theoretical analysis,the exponential increase in wall energy loss of krypton ions under high voltage is the main reason for the "efficiency peak" problem.Therefore,the peak-pushed-outside magnetic field is adopted to achieve the purpose of pushing the ionization zone and acceleration zone of the krypton to the outside of the discharge channel,reducing the wall loss of krypton ions,increasing the the efficiency peak value and the corresponding discharge voltage value.Additional,it increases the upper limit value of the discharge voltage for the stable working of the thruster.Then,the working thermal stability characteristics of the krypton Hall thruster under high voltage are studied.Compared with the xenon,the wall energy deposition power ratio of the krypton Hall thruster is larger,and the high discharge voltage further intensifies the thermal deposition problem of the krypton.It is found by PIC simulation analysis that the ion energy,ion density and ion velocity distribution near the discharge channel outlet wall are the main factors affecting the wall energy deposition.The peakpushed-outside magnetic field and chamfered channel wall can respectively effectively reduce the area and ion flux of the krypton bombarding the wall,thereby achieving the purpose of reducing the loss of the krypton ions on the wall.In addition,a variety of design methods represented by the outer loop control method of low-frequency oscillation have optimized effects on the focus of the krypton ion beam,thereby reducing the wall heat flow deposition and improving the working efficiency of the thruster.Finally,based on the optimization results of the ionization process,acceleration process and thermal stability of the krypton,a high specific impulse krypton Hall thruster— HKT-110 is designed by combining with the inside cathode technology,thermal structure design,flow field,magnetic field and electric field design,etc..And discharge characteristics and performance verification,as well as engineering performance assessment,are conducted.HKT-110 achieves anode efficiency of 43.4%,anode specific impulse of 3865 s,and thrust of 92.5m N under the discharge voltage of 1000 V and anode power of 4k W.At the same time,the thruster achieves the high thrust working mode under low discharge voltage.Compared with Hall thrusters of the same power level,HKT-110 has greater advantages in specific impulse and anode efficiency.At the same time,taking the DFH-5 all-electric propulsion satellite platform mission as an example,it is found by the analysis that the engineering application of the high specific impulse krypton Hall thruster has obvious advantages. |
