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Double-stage Hall Current Thruster with Inductive RF Source - Experimental Study of Operation and Low Frequency Instabilities

by Laurence Laffont - published on , updated on

Alexandre GUGLIELMI’s thesis defense intitled « Propulseur à courant de Hall double étage à source RF inductive – Étude expérimentale du fonctionnement et des instabilités basses fréquences » (Double-stage Hall current thruster with inductive RF source - Experimental study of operation and low frequency instabilities) will be held on Thursday, November 26th, at the Amphithéâtre Le Chatelier - building 2A of Paul SABATIER University.

His work has been supervized by Freddy Gaboriau and Jean-Pierre Boeuf, as welle as observants from CNES, Claude Boniface and Alberto Rossi.

Jury:
Mr Jean-Pierre BOEUF - University of Toulouse III - Paul Sabatier - Thesis Supervisor
Mrs Sedina TSIKATA - ICARE Laboratory– CNRS UPR 3021 - Rapporteur
Mr Gilles CARTRY- PIIM Laboratory UMR 7345 - Rapporteur
Mr Freddy GABORIAU - University of Toulouse III - Paul Sabatier - Thesis Co-Supervisor
Mr Olivier PASCAL - University of Toulouse III - Paul Sabatier - Reviewer
Mr Stéphane MAZOUFFRE - ICARE Laboratory – CNRS UPR 3021 - Reviewer
Mr Alberto ROSSI - CNES - Guest

YouTube Live link: https://youtu.be/3LalRdUzAsU .

Abstract:
Unlike chemical thrusters, electric Hall current thrusters are small motors used for station keeping, orbiting, as well as for interplanetary missions. Often characterized by low thrusts, their advantage is to have a very high ejection speed and a specific impulse.
The principle is based on the ionization of a rare gas (Xe, Kr) by a potential difference applied through a magnetic barrier. The locally weaker electronic conductivity in the barrier leads to the creation of an electric field in this area. The ions are then subjected to this field and are therefore accelerated up to speeds that may exceed several tens of km/s. The electric field at this barrier is then responsible for the acceleration of the ions and therefore, simultaneously, for the thrust and the specific impulse.
In order to modify independently these two parameters, a double stage Hall thruster (ID-Hall, Inductive Double stage HALL thruster) has been developed. The first step is the ionization stage, consisting of an independent plasma source (ICP source), and the second step is the acceleration in the area with the magnetic barrier. Using different diagnosises (ionic flux probe, retarding potential analyzer, high speed camera, current-voltage probes, etc.) as welle as a numerical model (HALLIS), we were able to characterize the plasma, its instabilities, and thruster performance.
In spite of the singular magnetic mapping of this thruster, the characteristics in single stage operation are comparable to those of conventional Hall current thrusters. In a dual-stage operation, the RF source significantly affects the transportation of electrons within the thruster. Additionnally, other double-stage results show that at low discharge voltages, the discharge current is lower than at single stage. The energy of the extracted ions is higher in double stage and the ion current decreases with increasing RF power but remains close to the ion current in single stage.
This study was carried out in Xenon and Argon. Low-frequency oscillations of large amplitudes (Breathing Mode) were experimentally observed, analyzed by time-resolved probing and compared to results obtained by the model. Other azimuthal instabilities (Rotating Spokes) have also been identified and studied electrically as well as by imaging. As soon as the source is active, at low RF power, these previous instabilities are strongly attenuated, while at higher power, other azimuthal instabilities appear (Striations). These azimutal instabilities were also studied around the source alone, by imaging with different gases and using a PIC-MCC particle model.

Keywords:
Propulsion, Plasma, Double-stage, Diagnosis, Modelisation, Instabilities