In spite of its high cost, xenon gas is known as both the most efficient and commonly used propellant for plasma thrusters in space technologies. Argon, a gas by far less costly, is widely used in other technologies, but a much lower efficiency of ionization, as obtained for example in closed electron drift thrusters, prevents its use in R&D programs and development of space thrusters. This paper shows that a drastic increase in argon ionization can be obtained in a low power thruster when only a few percent of xenon are added in the argon flow. Besides the increase in the ion beam current in the plume generated by the thruster, a net increase in the ion kinetic energy is observed. These two features are of interest in terms of thrust efficiency. These results, obtained for a small size closed electron drift thruster, could be even more spectacular for higher power devices, suggesting further investigations for space propulsion and/or ion source applications.

A low power Hall Effect Thruster (HET), based on a permanent magnet circuit, was investigated in the GREMI laboratory facility. The thruster operated in the working range between 50 and 300 W and the previously measured thrust is between 4 and 16 mN for an anodic efficiency respectively between 15% and 27%. The pulsed character of the thruster current is an important feature of this HET. The ion current's bursts are recorded at 30 and 70 cm from the exit plane in the thruster plume and are time-resolved, which lead to a preliminary analysis of the time of flight (TOF) phenomena. This paper presents a detailed study of these bursts of ion current in the plume. The total ion current is shown to be a superposition of 2 distinct contributions of charged species.In complement, a controlled single current interruption in stable anodic current condition leads to exactly the same features than in oscillating mode. This crucial verification garantees the validity of the time of flight origine of the two distinct contributions.Then, the slower one is the more intense and is proportional to the ion Xe+ current whereas the faster one could be attributed either to doubly-charged Xe ++ or to superfast Xe + . The work presents a way to determine unambiguously the nature of the fast contribution by recording the Retardated Potential Analyser ( RPA) signals at various repelling grid potentials with respect to time. The energy distribution of the 2 wellseparated contributions are reconstructed and confirms the contribution of doubly-charged xenon ions (Xe ++ ) in the plume. This way of RPA collecting data and interpretation presents the main advantage to be an easy way for the identification of the nature of the charged species in the plume.