Transient phenomena in closed electron drift plasma thrusters: insights obtained in a French cooperative program

This paper presents some aspects of the research developed in the frame of a coordinated program launched in France in 1996 and devoted to plasma thru sters for space technologies. Relevant results of physical studies have bee n selected from the literature with the addition of recent original results . The thrusters within the scope of this research are diagnostic equipped v ersions of industrial realizations, in a thrust level range of 0.1 N and el ectrical power 1.5 kW. The optical. and electrical diagnostics concern stud ies of the thruster plasma and of the thruster plume, Transient phenomena i n these two regions, related to discharge current fluctuations or oscillati ons on a typical time scale of 40 mus, have been space-time characterized. This has been achieved by developing a large panel of diagnostics including RFEA, Langmuir probes, OES, fast camera imaging and electron drift Hall cu rrent probe. They lead to a coherent representation of these phenomena, in rather good qualitative agreement with 1D modelling. But they emphasize als o the importance of 2D effects. Insights obtained through combined LIF (on Xe+ ions) and OES diagnostics are also presented. They concern the ionizati an-acceleration region in the thruster plasma, where intrusive diagnostics are disturbing in nature, and open a new step for a significant improvement of the detailed understanding of these thrusters. Such improvements are re quired when looking at the final goal of a predicable modelling simulation able to help the design of optimized structures at Various thrust levels, i n spite of the important work devoted to these devices in the former USSR a nd by Russian teams in Moscow at the MIREA, MAI-RIAME and KOURCHATOV Instit utes.