Experiments in magnetic nozzle thruster plasma plumes

This talk presents several experiments, carried out in the plume of an Electron Cyclotron Resonance thruster (ECRT) developed at ONERA, aimed at gaining a better understanding of the plasma acceleration and demagnetization in a diverging magnetic field, also called magnetic nozzle.

First, a two-axis Laser Induced Fluorescence (LIF) setup was used to measure the two components of the ion velocity field in the plasma production region, called the source, and the plasma acceleration region, called the plume, of the device. These measurements were linked to the electron dynamics in the nozzle through a fluid model. Second, in order to extend the measurements to regions farther away in the plume, a directional faraday cup has been developed. This electrostatic diagnostic, which measures the local angular distribution of ion current density, allowed to define and determine the plasma demagnetisation location, or detachment point, in the plume of the ECRT. This experimental characterization supports the theories of diverging ion detachment, and shows that the ions that are detached from the magnetic field lines follow linear trajectories. Besides, together with plasma potential measurements performed with an emissive probe that allowed to evaluate the structure of the electric field in the plume, these results also highlighted the rotation of the magnetized electrons in the nozzle and their influence on the ejection of the ions.