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Accueil du site > Thèmes de recherche > Propulsion spatiale & écoulements à grande vitesse > 3.1 Propulsion spatiale > 3.1.1 Propulsion électrique

3.1.1 Propulsion électrique

Research activities of the Electric Propulsion team are mostly focused on the in-depth examination of the physics of various low-pressure discharges. The aims are twofold and concern on the one hand, the improvement of existing thrusters for satellites and interplanetary spacecrafts and, on the other hand, the design of innovative ion sources for the next generation of electric propulsion devices.

3.1.1.1 Physics of Hall effect thrusters
A Hall effect thruster is an advanced propulsion device that uses a low-pressure magnetized discharge to ionize and accelerate a propellant gas. All activities related to this subject are performed in the frame of a joint-research program (GDR 3161, Propulsion à Plasma dans l’Espace) between the CNRS, the CNES, the Snecma company and several Universities.

  • Transport phenomena of ions and atoms within the E×B discharge as well as in the plume near-field of various thrusters are investigated by means of Laser Induced Fluorescence spectroscopy (TH14). Measurements of the ion velocity allow to reconstruct the electric field distribution. Parts of these studies were carried out in the frame of the ANR project Teliopeh. Last year, we managed to reveal the time evolution of the electric field at low-frequency by way of a pulse-counting technique. Recently, we characterized the ion azimuthal trajectory and 25 we proposed a comprehensive picture of the atom flow in a Hall thruster (ACL138, 139, 148, 149, 153, 154, 157, 159, 160 ; ACLN10, ASCL7).
  • The influence of the magnetic field topology, a key parameter, is examined by measuring discharge properties (electron parameters, ion energy, plasma potential…) and thruster performances for various configurations of the Snecma-built PPS®1350-ML thruster (ACL149. In a few months, the PPS-Flex, a dedicated source especially built to provide “exotic” field maps, will be available.
  • The electron density and temperature as well as the plasma potential are determined in the plume far field using Langmuir probes and emissive probes. Such data are crucial for critically assessing plasma-spacecraft interactions. We are currently developing a technique for time-resolved measurements as well as an original setup to realize measurements in the high-energy core of the discharge (ACL136 ; ACLN11).
  • The construction of scaling laws and the development of sizing methodology presently represent a large part of the ICARE activities in the electric propulsion area. Dedicated experiments are carried out in the recently-built NExET test-bench with a low-power thruster equipped with magnets. Besides, in the frame of the EU FP7 HiPER project, we are responsible for the design of a 20 kW Hall thruster able to deliver 1 N of thrust (ACL137).
  • Other activities are the following : thermal imaging of HET cavity and assessment of power deposited to the dielectric walls (ACL144, 145), analysis of electron turbulence and plasma fluctuations (ACL152 ; ACLN11) and development of plasma plume diagnostics for facilities of the European Space Agency.

3.1.1.2 Investigation of innovative Hall thruster designs
In order to improve the performance level of a HET, we suggested in 2006 to add energy in the thruster cavity by means of a Radio Frequency wave. The idea of a RF-enhanced HET was investigated within an EU FP6 INTAS project (2006-2009) that included several Russian laboratories. The consortium demonstrated that localized energy injection has a significant impact on the thrust and the beam divergence. A low-power thruster with inductive RF coupling is now under development at ICARE to pursue along that promising path. Such a concept may also be of great interest for propellants with high ionization energy.

3.1.1.3 Ion-ion plasma-based thrusters
Both Hall effect thrusters and gridded ion engines, although based on two different ion acceleration strategies, suffer from two main drawbacks : the need of an external electron gun to neutralize the ion beam and the creation of slow ions that interact with the spacecraft elements like solar panels. A new concept termed PEGASES and patented in 2007 by P. Chabert from the Ecole Polytechnique, avoids the two obstacles thanks to the use of both positive and negative ions. In 2009 we initiated a collaborative research program with the LPP to further develop the PEGASES concept and to build, on a long range, a flight demonstrator. These activities are presently supported by Astrium. Our task mostly consists in studying the continuous (opposed to pulsed) production of a high-density ion-pair plasma from an electronegative gas. For that purpose, an inductively-coupled RF reactor equipped with a versatile magnetic trap was constructed. In addition, a second prototype of the PEGASES with an acceleration stage will soon be tested in the cryogenic NExET bench which was especially built for these experiments.

3.1.1.4 Other activities in the field of plasma physics
Cooperation with LPIIM (Marseille) : Investigation by LIF spectroscopy of de-excitation of metastable atoms on a metal surface in a low-pressure multipolar device.

Cooperation with LPP (Ecole Polytechnique) : Study of neutral depletion phenomenon in a helicon device ; measurements of Ar atom temperature as a function of the magnetic field strength and comparison with numerical simulations.

Cooperation with the University of Opole (Poland) : Hyperfine structure of several Xe and Kr atomic lines (ACL14)] ; physics of expanding plasmas (ACL147, 161 ; ACLN9).

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