Multi-Line Diagnosis Of Ionization Parameter In Hall Thruster Channel

Hall-effect thruster (HET) is a kind of plasma propulsion devise which is used widely in spaceflight. Due to their high efficiency, high specific impulse, long lifetime and high reliability, they are suitable for station keeping, orbit modifying, power compensating and survey of deep space of various space vehicles. The physical processes are very complex in which ionization is an essential process in improvement of HET's performance. Working substance's being fully ionized or not and ions'being vertically spilled out or not both effect HET's efficient seriously. HET has narrow channel and complex electromagnetic field in it, which make it exclusive to use spectral diagnose for all kinds of plasma parameters. Spectral diagnose is also important because its real-time, portable.In this work, we start from basically formative processes of rare gases'inner energy level, discussed the establishment of spectral omission model and expatiate theoretically and measured experimentally the effect of radiation trapping effect. In compared with double-lines diagnostic method, we propose multi-lines method and analyze it uncertainty.Collisional radiative model (CRM) in HET's channel is established according to all kinds of particle collision process in it. Coupling process of rare gases'energy level which is different from other atoms is jK coupling. The coupling process established level's quantum number. According to levels'transition rules, only specific transitions between level are which include excitation, ionization and spontaneous emission of atoms allowed. In HET's channel, there exist complex energy-transfer processes between photons, electrons, atoms, ions etc. By some simple assumption, we can attribute atom energy levels'population to electrons'collision with atoms in ground state and metastable. The channel of atoms'excitation by electrons is characterized by cross section. We consumed all excited atoms are de-excited by spontaneous emission, and then collisional radiative model in the channel is established.Apart from the main collision processes included in above model, atoms'absorption of photons are also need to be considered, which is radiation trapping effect. In plasma, because of atoms crowd, photons radiated from an atom may be reabsorbed by another same atom's specific energy level, which make energy level's population changed on the whole. We estimate radiation trapping effect in HET channel and find it cannot be neglected especially for near- anode area. Effect of radiation trapping is reflected mainly in the increase of electron impact apparent cross section and changing of transition from the same upper level to different lower levels. The former is mentioned in many papers recently and the latter is verified by our experiment and we find the change trend of different levels is various. According to these discuss, we propose two methods to eliminate the effects of irradiative trapping: taking use of apparent cross section in channel's pressure and taking place spectral radiation with level's population.Then we proposed multi-line method natively. We establish population uilibrium equation for ten levels which contain specific parameter group according to its property and solve these equations classified. We firstly use 2p_6¹0's population equation to get electrons'temperature, atoms'density multiplied with electrons temperature, ratio of 1s₅ metastable's density to ground's density. Then by 2p_3⁴'s population equation, we can calculate 1s₃ metastable's density to ground's density. We can also use 2p_1,2,5's population equation to calculate electrons'temperature and compare with these result. By these parameters, we can obtain ions'total generation rate along with channel and then obtain working gas's utilization rate. We compare our result with it measured by Faraday probe.Finally, we analyze uncertainty of multi-line method. It is an exact process to measure absolute spectral irradiative intensity in which track junking, spectrometer etc. will introduce uncertainty to our result. After calibration of the diagnostic system, we can obtain absolute intensity and then we measure its uncertainty of fluctuation with time dependence with spectral intensity. Uncertainty can also be introduced by electron energy distribution function (EEDF). We compare Maxwell EEDF and Bugrova (EEDF)'s influence to excitation rate.