Performance and plume evolutions during the lifetime test of a Hall-effect thruster

To demonstrate the qualifications of the thruster lifetime, performance and reliability design, an 8000-h ground test of a Hall-effect thruster was conducted. Except for the ignition stage, the thruster operated at the nominal condition with a gas flow rate of 53.7 sccm and a discharge current of 4.2 A. In this paper, the research focuses on the evolutions of the thruster performance parameters and plume plasma properties during the long-duration (about 8240 h) test. An optical imaging system was developed to observe the erosion configuration of the insulator rings. The far-field diagnostic instruments consisted of a Langmuir probe, a Faraday probe and a Retarding Potential Analyzer. These probes were configured to measure the local plasma potential, plasma density, ion current density and ion energy. The results show that the thrust value first increases and then decreases during the first 2000 h. At the stage ranging from 2000 to 8240 h, the thrust value shows a slowly rising trend on the whole and stabilizes at the end. The thruster plume exhibits the phenomena of beam expansion and beam contraction at the early-to-mid lifetime stage and the mid-to-late lifetime stage, respectively. During these two periods, the relevant variations of the plume plasma parameters are related to the erosion configuration of the insulator ceramic walls. It also suggests that the evolutions of the thruster performance are largely determined by the properties of the plume plasma, especially the behaviours of the beam ions.