Research On Coupling Oscillation Between Magnetic Field And Discharge In Hall Thrusters

In order to adapt the technology requirements of survey of deep space and interplan-etary travel, it is an inexorable trend in the development of spacecraft propulsion fieldthat electric propulsion takes the place of chemical propulsion. Hall thruster is one of theelectric propulsion. As a typical magnetically confined plasma discharge device, variouskinds of plasma instabilities might exist in the discharge process of Hall thrusters. Theplasma instabilities may cause the loss of charged particle or the increase of transportcoefficient. Therefore, the research of various kinds of plasma instabilities which aim todiscover the physical mechanism, the characterization and seek for the stabilizing methodis always the center of magnetically confined plasma physics.Hall thruster as a typical magnetically confined plasma discharge device has thetypical ?→E×?→B crossed electric and magnetic field configuration. The typical character-ization of Hall thruster and the key of Hall thruster concept forming is that electrons isconfined by magnetic field and drift in the coaxial geometry channel. The effect of Hallcurrent oscillation and the physical effects went with it on the process of discharge , thedesign of magnetic field and performance optimizing is an important and basic physicalissue. In this thesis, through the experimental research and theoretical analysis and aim-ing at the plasma oscillation in Hall thruster, a new mode plasma oscillation: CouplingOscillation was discovered in the experiments. Centering on this new plasma oscillationphenomenon, the research work was concentrated on the physical mechanism, character-ization, in?uencing factors and the effect on the magnetic field design and performanceof Hall thrustersFirstly, in order to study the plasma oscillation phenomenon comprehensively, thelow frequency discharge oscillation was researched. The characterization of low fre-quency discharge oscillation in plume was studied with probes and results indicate that theoscillation of plasma parameters in the plume exhibits the same frequency as a low fre-quency discharge current oscillation and is synchronous in the circumferential directionat the time scale of the low frequency discharge current oscillation. The time delay of theoscillation in different axial positions is related to the propagation of plasma density alongthe axial direction. The oscillation of Xe+has the same frequency as the low frequency discharge current oscillation, but the oscillation of Xe2+ or a high-valence ion is morecomplex and scattered due to their instability in the ionization process. It is therefore con-cluded that the low frequency oscillation of plasma parameters in the plume is stronglyrelated to the low frequency discharge current oscillation and the ionization process ofa neutral atom. On the stabilizing of low frequency discharge oscillation, The effect ofpreionization on low frequency oscillation was experimentally studied by changing theelectric field intensity in the buffer chamber the amplitude of low frequency oscillationdecreases as the preionization ratio increases. It was found through the analysis of thephysical process of low frequency oscillation that the positive feedback of electron den-sity was the main cause of low frequency oscillation. The increase of preionization ratiodecreases the amplitude of the feedback variation thereby reducing the amplitude of lowfrequency oscillation. In the study of filter, it is discovered that low frequency dischargecurrent oscillation of two inductors with the same nominal value is extremely different.To decide the general characteristic of thruster inductors in applications, relationship be-tween the frequency characteristic of inductors and low frequency oscillation is studiedin experiments with the same operation conditions. Experiment results indicate that asthe corner frequency of inductors increases, the discharge current low frequency oscilla-tion declines at first and then slightly turns up after a certain frequency. Through analysisfrom the perspective of control system, advantageous frequency characteristics of thrusterinductors in filter are suggested. The research about the low frequency oscillation expandsome acknowledges and fill in some gaps of Hall thruster plasma oscillation.Secondly, beginning with Hall current which is the typical and basic physical ef-fect in the discharge process of Hall thruster, the effect of the coupling between magneticcircuit and Hall current on the static magnetic field is evaluated with the electromag-netic induction theory based on the discussion of the importance of magnetic field designand the mean characterization of optimized magnetic field. A new plasma oscillationmode due to the coupling between discharge circuit and magnetic circuit was discovered,which was named coupling oscillation. The frequency of coupling oscillation was studiedthrough the experiments of changing discharge parameters, measuring with open-circuitcoils and measuring internal channel; and the physical mechanism was clarified with the-oretical analysis combined with the experiments of magnetic circuit resonant frequencymeasurement. Thirdly, in order to study characterizations of coupling oscillation, a Hall thrusterwas experimentally studied by varying magnetic ?ux density or discharge voltage to ob-tain the relationship between discharge parameters and the magnitude of coupling oscil-lation through connecting coils in series to obtained one-factor analysis and combinedwith the data processing method. Based on the analysis of magnetic field distribution ofelectric current loop, the dispersion relation with respect to the perturbation of magneticfield was deduced and the in?uencing factors of coupling oscillation were defined andobtained. The experimental results and theoretical analysis results by dispersion relationtally closely with each other. Additionally, checking the parameter of coupling intensity,it can be concluded that coupling intensity is proportional to the turns and the cross-sectional area of coils and inversely proportional to the resistance coefficient of magneticcoils and the coupling oscillation has a very high wave number values with a frequencyspectrum in the range of several MHz. The work expands acknowledges of couplingoscillation.Lastly, in term of the limitations of ampere turns equivalent in static magnetic fielddesign, the different coupling oscillation intensity was formed with different turns of coils.Based on the studied of physical mechanism and characterization of coupling oscilla-tion, the effect of coupling oscillation on the performance of a Hall thruster was studied.Results indicated that the increase of coupling oscillation intensity cause the ?uctuationadded and the electron current and plume divergence angle increase with its effect. There-fore, the performance of Hall thrusters was reduced. The effect of coil current ?uctuationon the static magnetic field was evaluated on the P70-type Hall thruster with the help ofFEMM and the principle of magnetic field design with respect to coupling oscillation wasprovided.