Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites (more than 120 in orbit to date). Moreover, they can offer a cost-effective solution for interplanetary journey, as proved by the recent ESA SMART-1 mission to the Moon. The main limiting factor of the HETs lifetime is the erosion of the annular channel ceramics walls. In order to provide a better understanding of the energy deposition on the insulated walls, a laser irradiation study has been carried out on a PPS100-ML thruster during its run in the PIVOINE-2G ground test facility (CNRS Orléans, France). Two distinct approaches have been followed: continuous wave fiber laser irradiation (generation of thermal defects) and nanosecond pulsed laser ablation (generation of topological defects). The irradiated zones have been monitored in situ by IR thermography and optical emission spectroscopy and further investigated ex situ by scanning electron microscopy and profilometry.

Hall Effect Thrusters (HETs) are promising electric propulsion devices for the station-keeping of geostationary satellites and for interplanetary missions. The main limiting factor of the HET lifetime is the erosion of the annular channel ceramic walls. Erosion monitoring has been performed in the laboratory using optical emission spectroscopy (OES) measurements and data treatment based on the coronal model and the actinometric hypothesis. This study uses laser ablation of the ceramic wall in a running HET in order to introduce controlled amounts of sputtered material in the thruster plasma. The transient laser-induced breakdown plasma expands orthogonally in a steady-state plasma jet created by the HET discharge. The proposed spectroscopic method involves species from both plasmas (B, Xe, Xe+). The optical emission signal is correlated to the ablated volume (measured by profilometry) leading to the first direct validation of the actinometric hypothesis in this frame and opening the road for calibration of in-flight erosion monitoring based on the OES method.

The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET) to limit the plasma discharge play an important role but yet completely not understood and controlled. In order to investigate the effect of an energy flux on the wall we performed tests with a nanosecond pulsed laser to simulate the energy deposition on BNSiO2 (usual dielectric material for HETs). The tests have been carried out with the second harmonic (532 nm) of a Q-switched (10 ns) Nd:YAG laser focused on the samples placed in a vacuum chamber (10-6 Torr). The energy/pulse range explored has been 5 – 320 mJ, leading to fluences of 1 – 1000 J/cm2. The modifications induced by laser irradiation on the BNSiO2 targets have been analysed by profilometry and scanning electron microscopy. The plasma created by laser ablation has also been characterized by optical and spectral methods. The present paper presents preliminary results of these combined investigations.

The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET) to limit the plasma discharge play an important role but yet completely not understood and controlled. In order to investigate the effect of an energy flux on the wall we performed tests with a nanosecond pulsed laser to simulate the energy deposition on BNSiO2 (usual dielectric material for HETs). The tests have been carried out with the second harmonic (532 nm) of a Q-switched (10 ns) Nd:YAG laser focused on the samples placed in a vacuum chamber (10-6 Torr). The energy/pulse range explored has been 5

In this contribution, we present a new method to predict the ceramic erosion of the thruster channel inner walls. Silicon substrats are introduced into the channel of the PPSX000-ML Hall Effect Thruster (laboratory model) before four hours of firing for five sets of tooling ceramics in the PIVOINE french facility. The deposition layers of the sputtered ceramics by impinging ions are measured by means of profilometry after firing. Geometrical 1D model has been developed in order to determine the quantity of material sputtered. Thus evolution of the ceramic wear along the thruster virtual lifetime has been determined until 6000 to 7000 hours. OES erosion measurements were performed during tests using the silicon substrats. Good correlation was obtained between the substrat and spectroscopic methods.

This paper is focused on experimental studies of a high power pulsed magnetron discharge stabilized by low current pre-ionization. Time resolved studies were performed for a Cu target by optical emission spectroscopy and electrical measurements for different pressures of Ar buffer gas. Due to the elimination of the statistical delay time and a fast discharge current rise the quasi-stationary state was reached in 6 mu s. The quasi-stationary state is characterized by an extremely high and pressure independent discharge current density of similar to 10 A cm(-2) and stable Cu+ and Cu++ emissions. Such fast discharge dynamics permits the magnetron cathode current to be driven with a pulse of duration of the order of a few mu s, significantly shorter than in other devices. During this short time, the plasma does not have time to undergo the transition from the glow to the arc discharge even at the extremely high cathode loads met in our case. Different stages of the fast discharge development are identified and the composition of the magnetized plasma as a function of the pressure is discussed in detail.

The Ionized Physical Vapour Deposition technique has been developed since 1990 as an improvement of the magnetron sputtering technique to obtain more conformal and dense deposited layers. Amongst the different methods developed to ensure the ionization of the sputtered vapour, the superimposition of an Inductively Coupled Plasma to a magnetron cathode is the most used method. However, the use of an internal radio-frequency (RF) coil to create the additional ionization may lead to contamination of the deposited layers by the material of the coil. We report in this paper a set of experiments that allowed us to control the film deposition pollution. We compared the flux of particles sputtered from the magnetron and deposited on the coil, with the flux of atoms sputtered by ions from the RF coil. In our experiments, the magnetron material is titanium and the coil material is stainless steel.

The dynamic behavior of the Hall effect thruster plasma plume is investigated after ultrafast current ignition driven by a metal-oxide-semiconductor field-effect transistor 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.

To investigate the generation and transport of ions during and after a high power current pulse applied on magnetron cathode, we performed spectroscopic measurements with time and space resolution. The microwave antennas placed between target and substrate ensure proper conditions of current pulse development, ion transport and., by re-exciting sputtered species, allows spectroscopic emission measurements of species transported towards the substrate. Measured data are presented and discussed.

In this contribution, we present a real time optical method to control the ceramic erosion of the thruster channel inner walls. OES measurements were performed on a SPT100-ML (laboratory model) during tests using permanent magnets instead of magnetic coils in the PIVOINE french facility. Different magnet/coil configurations was studied for different discharge parameters as discharge voltage, mass flow rate, chamber pressure, and coil current. Join to LIF and Fabry-Perot ion velocity measurements very helpful informations has been obtained about potential map evolution with discharge parameters.

Specific features of Hall thrusters, which are advanced electric propulsion devices for space applications, in terms of thrust, specific impulse, efficiency and lifetime make them suitable candidates for missions like geo-stationary satellite orbit correction and station keeping. A large research program devoted to the investigation of physical processes connected to the working of Hall thrusters has been carried out in France for many years. One of the current research topic concerns the erosion phenomena induced by the created plasma. Indeed, erosion of the ceramic insulators of a Hall thruster is always considered as a critical point as the main limiting factor for the thruster lifetime. It is clear that a better understanding as well as a better monitoring of wear processes of the insulators is necessary in order to employ Hall thrusters for long term missions like interplanetary journeys. By comparing experiments and numerical outcomes, it appears that present models describing erosion mechanisms, solely based on ion bombardment, do not explain the overall losses of insulator material and the periodic pattern observed at the channel outlet. The peculiar wear of the insulators could find its origin in the so-called "anomalous erosion" phenomenon. It is most likely that electrons play a major role in such an erosion process, however, the way they act and the deep reason for the formation of a network of longitudinal streaks are still to be clarified. In terms of erosion monitoring, to observe the light emitted by atoms sputtered from insulators appears to be a promising way of real-time controlling the wear of the ceramic walls.

In this paper, which deals with physical processes and problems that are involved in magnetron discharges used for the deposition of thin films and material coatings, we emphasize the aspects connected to discharge physics: energy deposition, behaviour of the discharge in reactive gases in connection with plasma–surface interactions. We also present recent works on ionized physical vapour deposition (IPVD) in which the usual PVD magnetron sputtering is assisted by an additional discharge in order to ionize the sputtered neutral vapour and to achieve a better control and quality of the deposited material in industrial applications. We restrict ourselves to planar magnetrons.

A new type of plasma reactor for thin film deposition has been designed : a magnetron sputtering device assisted by microwave applicators to ionize the sputtered vapor of the magnetron, in order to improve the deposition process (film quality, recovery of the layers,...). The reactor consists in a planar rectangular magnetron cathode (22 cm x 9 cm) and on two coaxial-type microwave applicators located perpendicularly to the substrate-magnetron axis, on both sides of the sputtered vapor flow. This reactor can operate on a wide range of pressures : from about 1 mTorr to 500 mTorr. Langmuir probes measurements have shown that electron density created by the microwave devices can reach 10(12) cm(-3) (typically at 30 mTorr). Results presented here are for a chromium target. The ionized chromium emission, non visible with the magnetron alone, appears clearly when the microwave devices are powered on and increases with the microwave power. Neutral chromium was detected by optical absorption. A first interpretation of these results is developed.

A high speed electronic switch of discharge current has been used as a diagnostic tool of closed electron drift thrusters. Analysis of transients in discharge current and plasma spectral emissions leads to an evaluation of electron energy and density losses. Low energy excitation processes populating excited states from ion and neutral metastables are evidenced. Measurements of mean electron axial velocity are compared with neutral collision transport across magnetic field. Finally a strong correlation is evidenced between angular distribution of ejected ions and localization of the ionization zone in the thruster channel.

This paper presents some aspects of the research developed in the frame of a coordinated program launched in France in 1996 and devoted to plasma thrusters for space technologies. Relevant results of physical studies have been selected from the literature with the addition of recent original results. The thrusters within the scope of this research are diagnostic equipped versions of industrial realizations, in a thrust level range of 0.1 N and electrical power 1.5 kW. The optical and electrical diagnostics concern studies of the thruster plasma and of the thruster plume. Transient phenomena in these two regions, related to discharge current fluctuations or oscillations on a typical time scale of 40 µs, have been space-time characterized. This has been achieved by developing a large panel of diagnostics including RFEA, Langmuir probes, OES, fast camera imaging and electron drift Hall current probe. They lead to a coherent representation of these phenomena , in rather good qualitative agreement with 1D modelling. But they emphasize also the importance of 2D effects. Insights obtained through combined LIF (on Xe+ ions) and OES diagnostics are also presented. They concern the ionization-acceleration region in the thruster plasma, where intrusive diagnostics are disturbing in nature, and open a new step for a significant improvement of the detailed understanding of these thrusters. Such improvements are required when looking at the final goal of a predicable modelling simulation able to help the design of optimized structures at various thrust levels, in spite of the important work devoted to these devices in the former USSR and by Russian teams in Moscow at the MIREA, MAI-RIAME and KOURCHATOV Institutes.

The results of measurements made on an ATON-class Hall thruster in the French PIVOINE facility are presented. Diagnostics consist in optical emission spectroscopy, fast imaging, Langmuir probes arid ion energy analyser. The aim of this work was to compare the characteristics of the plasma in the channel and in the plume between two modes, called swallow tail and spike modes.