Plasma Diagnosis In Plume Region Of Hollow Cathode Based On Langmuir Probe And Emission Spectrum

Because of its high jet speed,electric propulsion can save a lot of fuel for satellites.It has been widely used in space missions such as Orbital changes,resistance compensation,and satellite networking.This requires thrusters to work stably for thousands or even tens of thousands of hours.As the electron source and neutralizer,the hollow cathode is the key component of the existing two mainstream electric propulsion-Hall thruster and ion thruster.The failure and performance degradation of the hollow cathode will directly lead to the scrapping of the propulsion system.The hollow cathode works by coupling the plume area of thruster and cathode,and conducts electrons from the inside of the hollow cathode into the ion jet area.Therefore,the hollow cathode plume parameter distribution is very important.It directly affects the neutralization of ions and the performance of the thruster,which makes carrying out research on the plasma parameters,measurement methods and parameter characteristic changes in the hollow cathode plume area urgently.Based on the above requirements,this paper has carried out the Langmuir probe and emission spectroscopy diagnostic study of the plasma in the hollow cathode plume area.The main contents are as follows:Firstly,the diagnosis mechanism of the Langmuir probe and the emission spectroscopy method is compared and analyzed for the characteristics of the hollow cathode plume.The dynamic model of the Langmuir probe measurement is mainly introduced.The effect of charged particles on the absorption electric field of the probe is mainly analyzed by singleparticle method.The Baum boundary model is also analyzed,and a method for calculating the plasma density using ion current and electron temperature is obtained,which makes the probe method more accurate to measure the plasma parameters in the hollow cathode plume area.For the measurement of plasma parameters by spectroscopy,the collision excitation radiation model of xenon atoms is analyzed,and the method of calculating plasma parameters based on the model is analyzed.At the same time,different collision radiation cross-sections are compared,and the gas use range and availability are analyzed.It provides theoretical support for the application of the following two methods.Secondly,in response to the hollow cathode plume measurement requirements,the test platform was improved,including the fiber optic connector through the vacuum tank and the circuit structure of the Langmuir probe.The measurement circuit and volt-ampere characteristics acquisition method of various probes were compared and analyzed.Aiming at the emission spectrum of the plume area,the excitation process and the main reaction equations of the xenon ions are analyzed.The collision-radiation model is used to calculate the electron temperature and other parameters in the hollow cathode plume area,which provides good experimental conditions for the subsequent measurement of plasma parameters.In this process,the information of the xenon atom 788.7nm,823.2nm,828.0nm,and 881.9nm spectral lines are needed.Based on the completion of the theory and platform,the Langmuir probe and emission spectrum measurement of plasma parameters were carried out for the steady-state discharge conditions in the small-sized hollow cathode plume area.Firstly,process the parameters of the typical Langmuir probe data,including data fitting,semi-logarithmic fitting,and calculating the electronic distribution function of the first and second derivatives,and obtain the typical values of plasma parameters(spatial potential,electron temperature,plasma density)as well as their changing regularity with current and gas flow under different working conditions in the hollow cathode plume area.Secondly,the typical emission intensity distribution of the hollow cathode plume area under xenon at different working conditions was collected by spectroscopy,according to which,the different spectral intensities,ratio of energy levels and electron temperature of the large-size hollow cathode were obtained.The electronic temperature results obtained by the two measurement methods are basically close and remain basically unchanged within the rated working range,which meets the application requirements of electric propulsion for a wide range of hollow cathode parameters and high stability.