Laser injection of ultra-short electron bursts for the diagnosis of Hall thruster plasma

Abstract

The present developments of Hall thrusters for satellite control and space mission technologies represent a new step towards their routine use in place of conventional thermal thrusters. In spite of their long R and D history, the complex physics of the E × B discharge at work in these structures has prevented, up to now, the availability of predictive simulations. The electron transport in the accelerating layers of these thrusters is one of the remaining challenges in this direction. From the experimental point of view, any diagnostics of electron transport and electric field in this critical layer would be welcome for comparison with code predictions. Appropriate diagnostics are difficult, due to the very aggressive local plasma conditions. This paper presents the first step in the development of a new tool for characterization of the plasma electric field in the very near exhaust thruster plume and comparison with simulation code predictions.The main idea is to use very short bursts of electrons, probing local electron dynamics in this critical plume area. Such bursts can be obtained through photoelectric emission induced by a UV pulsed laser beam on a convenient target. A specific study, devoted to the characterization of the electron burst emission, is presented in the first section of the paper; the implementation and testing of the injection of electrons in the critical layer of Hall thruster plasma is described in the second section. The design and testing of a fast and sensitive system for characterizing the transport of injected bursts will be the next step of this program. It requires a preliminary evaluation of electron trajectories which was achieved by using simulation code. Simulation data are presented in the last section of the paper, with the full diagnostic design to be tested in the near future, when runs will be available in the renewed PIVOINE facility. The same electron burst injection could also be a valuable input in the present discussion on the physics of the 5-10 MHz instability observed in almost all Hall thrusters.

Doubly‐Charged Xe Ions Evidenced by Time Resolved RPA Measurement in the Far Field Plume of a Low‐Power HET

“…The main features and the performance of the PPI thruster were investigated both in the small vacuum chamber of the GREMI laboratory [13] with pumping speed (xenon) of 3000 L/s at 8 10 −5 mbar and in the large scale French test facility PIVOINE [14] with pumping speed higher than 100,000 L/s. The results obtained in these two vacuum chambers were extensively reported by Leufroy et Al [15].…”