524 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 33, NO. 2, APRIL 2005 CCD Images of Hall Effect Thruster Plume Dynamics After Ultrafast Current Ignition V. Vial, S. Mazouffre, M. Prioul, D. Pagnon, and A. Bouchoule Abstract—The dynamic behavior of the Hall effect thruster plasma plume is investigated after ultrafast current ignition driven by a metal–oxide–semiconductor field-effect tranistor MOSFET power switch. Time-resolved optical measurements performed with a gated intensified charged coupled device (CCD) camera allow to reconstruct the plume temporal features. Images of the ion beam reveal oscillations in plasma light intensity linked to “breathing” instabilities. The observed periodic variations of the beam divergence originate from the displacement of the ionization layer within the thruster magnetic barrier. Index Terms—Breathing modes, hall thruster, optical emission, plasma instabilities. H ALL EFFECT THRUSTERS (HET), also called sta- tionary plasma thrusters or closed electron drift thrusters, are advanced propulsion devices that uses an electric discharge to ionize and accelerate a propellant gas [1]. At present, they are employed for missions like satellite orbit correction and station keeping. The additional utilization of high-power Hall thrusters for orbit topping or raising would also offer significant benefits in terms of launch mass, payload mass and operational life. Moreover, Hall thrusters appear as good candidates to be used as the primary propulsion engine for space probes during interplanetary journey, as confirmed by the successful SMART-1 mission from ESA. The basic physics of a HET implies a magnetic barrier in a low-pressure direct current (dc) discharge generated between an external hollow cathode and an anode that also acts as gas distributor [1]. The anode is located at the rear of a hollow annular ceramic channel that confines the discharge. A set of solenoids provides a radially directed magnetic field of which the strength is highest near the channel exhaust. The magnetic field is chosen weak enough not to disturb the ion motion, but strong enough to slow down the electron’s axial motion. The discharge voltage drop is mostly concentrated in the near-exit section of the channel due to the low electron conductivity in this restricted area. The locally induced axial electric field has two main effects. First, it drives a high electron azimuthal cur- rent that is responsible for the efficient ionization of the supplied Manuscript received July 1, 2004; revised October 11, 2004. This work was supported by the research group CNRS/CNES/SNECMA/Universities 2759 “Propulsion Spatiale à Plasma.” V. Vial and A. Bouchoule are with the GREMI Laboratory, University of Or- léans, 45067 Orléans, France. S. Mazouffre is with the Laboratoire d’Aérothermique, CNRS, 45071 Or- léans, France (e-mail: mazouffre@cnrs-orleans.fr). M. Prioul is with SNECMA moteurs, 77552 Moissy-Cramayel, France. D. Pagnon is with the LPGP Laboratory, University of Paris-Sud, 91405 Orsay, France. Digital Object Identifier 10.1109/TPS.2005.845363 Fig. 1. Anode discharge current oscillations (ac mode) as a function of time after ultrafast externally driven current ignition. Curve originates from the average over 256 waveforms. Mean frequency oscillation is 24.5 kHz. Full circles indicate times at which thruster plume CCD images are taken (see Fig. 2). gas (usually xenon). Second, it accelerates the created ions that form the thruster plasma plume. When operating near 1.3 kW, a ejects ions at 20 km/s, and generates 90 mN of thrust with an efficiency in excess of 50%. Examination of a Hall thruster response to ultrafast current in- terruptions driven by an optically controlled metal–oxide–semi- conductor field-effect transistor (MOSFET) power switch has proven to be a powerful way to untangle part of the complexity of such a magnetized plasma medium [2]. The switch allows fast cancellation and generation of ion and electron currents, as well as electric field on a time scale (around 100 ns) shorter than any characteristic time scale for non turbulent transport phenomena. Among others, this approach based on a pulse perturbation has recently permitted [2]: 1) to determine the electron drift current, 2) to better understand transient ionization phenomena oc- curring inside the thruster channel, 3) to analyze the ion beam composition and angular energy distribution. In this paper, high-speed two-dimensional (2-D) mapping of thruster plasma light is employed to reconstruct both ion beam density and plume divergence temporal fluctuations after a fast current ignition that follows a discharge shut down phase. A laboratory model SPT-100 HET is operated at 300-V applied voltage and 5.42-mg/s xenon flow rate. As shown in Fig. 1, the current ignition follows a 10- s power-off time period during which the plasma fully vanishes [2]. A gated 0093-3813/$20.00 © 2005 IEEE