The Study On Steady Lifie Limit Mechanism And Development Method Of Hollow Cathode

The hollow cathode is the core component of the electric propulsion system and is mainly responsible for the work of the electron source and the neutralizer.Due to the special nature of the aerospace system,hollow cathodes are required to have extremely high lifetime and reliability,and stable steady-state characteristics.The steady-state characteristics o f the cathode mainly include macroscopic characteristics(discharge voltage,discharge current,cathode pressure,cathode oscillation,heat transfer characteristics,corrosion characteristics)and a series of microscopic characteristics(plasma density,electron temperature,electron density).These characteristics reflect the working status and stabilit y of the cathode and have an important role in measuring the life of the cathode.Therefore,it is of great significance to study the steady-state discharge characteristics of the hollow cathode.A short-term life test was carried out for the existing hollow cathode,and the evolut ion regularity of the steady state characteristics of the hollow cathode under two currents was measured.The experiment found that cathode voltage,internal gas pressure,temperature distribution,and discharge oscillation did not change much with time in the short term,but corrosion occurred at the materials such as the contact pole and tungsten top,leading to a rapid decrease i n the life of the hollow cathode.By comparison,it can be seen that the hollow cathodes work in the plume mode and the point mode under the two currents respective ly,while the discharge characteristics of the cathode in the plume mode are extremely unsta ble,the surface of the contact pole and the corrosion are severe,and the reliable life of the cathode is shortened.The main measure of the cathode mode is the oscillation of the cathode.Aiming at the obvious corrosion phenomenon of the cathode in the e xperiment,the oscillation characteristics of the cathode under different working condit ions were analyzed,and the difference of the oscillation characteristics of the cathode in the plume mode and the point mode was analyzed.The three-probe measurement was used to measure the transient changes in electron temperature and electron density at the cathode,and the effect of cathode mode and oscillation on the energy distribution of the cathode ions was measured using RPA.Further analys is shows that as the extraction current increases,the increase in cathode oscillations results in an increase in high-energy ions and an increase in the ion flux of the bombarded material.This is a major factor in cathode emitters,tungsten t ip-holes,and tentative sputtering corrosion..In order to reduce the corrosion rate of the material and prolong the life of the cathode,the method of controlling the amplitude of the hollow cathode discharge oscillation and reducing the ion energy is studied.When the hollow cathode and the Hall thruster are coupled to discharge,there is a magnetic field.Therefore,the magnetic field influence study is first carried out.It is found that the axial magnetic fie ld can control the discharge oscillation to suppress the high energy ions because it can increase the conduction of electrons to the anode.Increasing the supply air flow reduces the anode voltage and reduces the amplitude of the oscillation,thereby suppressing the generation of high energy ions.The capacitance of the discharge loop reduces the voltage oscillation and increases the current oscillation.The inductance acts on the opposite side of the capacitor,but both can reduce the high energy ions by phase adjustment.There is no reliable on-line monitoring method for material corrosion during hollow cathode discharge,but the corrosion state of the material is an important feature to characterize the life of the cathode.For this reason,a method based on the emission intensity of corrosion material and on-line monitoring of cathode corrosion products is presented..By comparing with the characteristic line of thorium,the characteristic line of the corroded material of the emitter is selected,and the variation law of the luminescence intensity of the material under different working conditions is obtained.The result shows that the amplitude of the cathode discharge oscillation increases and the luminescence intensity increases significantly.Finally,the paper presents an improved design for the stable application of the method.