Objectif
Electric propulsion is nowadays a well-established concept for space applications. Among all proposed electric propulsive devices such as arcjet, magneto plasma dynamic thruster, gridded ion engine and Hall Effect Thruster (HET), the latter is currently recognized as an attractive propulsion means for long duration missions and for maneuvers that require a large change of velocity. Hall effect thrusters, also called stationary plasma thrusters, are advanced propulsion devices that use an electric discharge with magnetized electrons to ionize and accelerate a propellant gas. Due to interesting features in terms of propellant ejection speed and efficiency, HET are now employed for missions like geo-stationary satellite orbit correction and station keeping. The use of high power Hall thrusters for orbit transfer maneuvers would also offer significant benefits in terms of launch mass, payload mass and operational life. Furthermore, Hall effect thrusters appear as good candidates to be employed as the primary propulsion engine for space probes during interplanetary trips, as demonstrated by the successful SMART-1 mission of the European Space Agency. In spite of interesting performances in terms of thrust and specific impulse (Isp), current Hall effect thrusters suffer from a relatively low thrust efficiency, especially at high power, as well as a lack of flexibility in terms of operation conditions. A high efficiency allows a better use of the electrical power available onboard the spacecraft. It is also necessary to minimize thruster power losses. Flexibility is crucial for missions like platform orbit transfer and deep space exploration. Indeed, depending on the stage of the missions, the spacecraft maneuver necessitates either a high thrust level or a high Isp level. Modern HET can be operated over a broad range of power, however, it is not possible so far to control the thrust and the Isp in an independent manner. In this project, we proposed a novel approach in order to improve standard HET performances in terms of Isp and efficiency and to push away limits that arise from the overlapping of ionization and acceleration regions. Instead of changing dimensions or magnetic map or designing a two-stage thruster, we suggest to locally supply the thruster discharge with additional energy. The main objective of this project is therefore to investigate the influence of Radio Frequency power input on performances and physical characteristics of HETs. The idea is to apply RF power by means of antennas (inductive coupling) and electrodes (capacitive coupling) in an upstream region of the discharge chamber of a standard HET in order to locally modify the electron temperature. The expected consequences are twofold: the ionization degree rises and ions gain thermal energy, which in turn can be converted into kinetic energy. It should then be possible to better control both the thrust and the Isp and to improve the thruster efficiency and versatility.
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ORLÉANS
France