Ion acceleration in the magnetic nozzle of an ECR thruster: comparison of experimental measurements with a quasi 1D kinetic model

Proceeding of: Space Propulsion Conference, SP 2018,14-18 mayo, SevillaThis paper presents experimental results on the magnetic nozzle of the 50 W Electron Cyclotron Resonance (ECR) thruster of ONERA, consisting of a 27 mm diameter ECR cavity and a fully divergent magnetic nozzle, created by a Neodymium permanent magnet. The diagnostics installed are a cylindrical Langmuir probe to measure plasma potential, plasma density and electron temperature, and a Laser Induced Fluorescence set-up to measure the mean ion kinetic energy. Both the ion velocity and plasma potential profiles seem to be independent of the mass flow rate when normalized with the electron temperature estimated at the sonic transition of the plasma flow. This sonic transition appears to be slightly shifted downwards of the thruster exit. Results are compared with a supersonic collisionless kinetic 1D model where electron dynamics account for magnetic mirror effects and potential barriers, while ions are treated as a fluid cold species.This work was made in the framework of project MINOTOR that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730028. This work was additionally supported by the Spanish R D National Plan (Grant No. ESP2013-41052-P)