Study On Influencing Factors Of Multi-parameters And Mechanisms Of Low Frequency Oscillation

Hall thruster is a widely used space propulsion device.It will have low frequency oscillation during discharge,which is caused by the ionization and supplemental inhomogeneity of the working fluid.The existence of low frequency oscillation will degrades the performance of the thruster and reduces reliability.In this paper,the ionization process of the Hall thruster with the side slit of the discharge channel is captured by a high-speed camera.The variation of the light intensity is used to study the change of the ionization in the thruster channel.The curve of the ionization distribution along the axial direction is obtained by the normal fitting method,and the ionization related parameters such as the maximum point position of the ionization intensity and the width of the main ionization region are found.The time domain analysis of the parameters such as the maximum point position of the ionization intensity and the width of the main ionization region is carried out.By comparing the time-domain characteristics with the time-domain characteristics of discharge current,it is found that the parameters such as the maximum point position of the ionization intensity and the width of the main ionization region oscillate with the same cycle and regularity together with the discharge current.The parameters such as the maximum point position of the ionization intensity and the width of the main ionization region increase with the increase of the discharge current,and decrease with the decrease of the discharge current.Secondly,by changing the self-parameters of thruster such as discharge voltage,anode flow rate,excitation current and cathode parameters such as keeper current and cathode flow rate,the effects of operating parameter changes on low frequency oscillation,the maximum point position of the ionization intensity and the width of the main ionization region are studied.The results show that the average value of the parameters such as the discharge current,the maximum point position of the ionization intensity and the width of the main ionization region will change regularly with the parameters of the thruster itself,and the standard deviation of the parameters such as the maximum point position of the ionization intensity and the width of the main ionization zone is positively correlated with the standard deviation of the current.That is,as the oscillation of the discharge current increases,the oscillation of the parameters such as the maximum point position of the ionization intensity and the width of the main ionization region is also enhanced.Changing cathode flow rate has a greater influence on the low frequency oscillation than changing the keeper current.That is,changing the electron emission density of the cathode is more likely to affect the low frequency oscillation than changing the electron temperature of the cathode region.Thirdly,change the shell,power supply negative,keeper,ground connection network and grounding structure,and study the influence of grounding mode change on parameters such as low frequency oscillation and the maximum point position of the ionization intensity and the width of the main ionization region.The experimental results show that the change of the connection network and grounding structure will not change the parameters of the discharge current and the maximum point position of the ionization intensity and the width of the main ionization region,but changes the average values of the discharge current and the maximum point position of the ionization intensity and the width of the main ionization region.The change of the connection network and the grounding structure changes the correlation between the standard deviation of the parameters such as the maximum point position of the ionization intensity,the width of the main ionization region,and the standard deviation of the discharge current.Finally,in order to improve the physical mechanism of low frequency oscillation,the transient behavior of plasma parameters in the ionization channel during thruster discharge is studied.The simulation results show that the oscillation of the parameters such as plasma density,electron temperature and space potential is the same as the oscillation period of the discharge current.The time-domain characteristics of plasma density and electron temperature were experimentally studied by the modulation signal method and the double Langmuir probe method.The results were the same as the simulation results.Through the above research,the understanding of the low frequency oscillation characteristics of the Hall thruster has been expanded.