The lifetime of electric propulsion (EP) thrusters depends particularly on the erosion characteristics of operation relevant components, for instance, the grid hole erosion of gridded ion thrusters or the channel wall erosion of Hall effect thrusters. Here two tools for in situ erosion measurements are presented, a triangular laser head for surface profiling and a telemicroscope for high-resolution optical imaging. Both can give access to radial and axial erosion parameters. The measurements can be done in situ without the need for breaking the vacuum and dismounting the thruster, which reduces thruster testing time considerably. In situ measurements can also help to ensure reproducibility of thruster performance conditions and can improve statistics of thruster characterization. The present work describes the fundamentals of both techniques in detail, selected experimental setups are presented, their performance is characterized and critically evaluated. The capabilities and limitations related to erosion measurements of EP thrusters are, exemplary, demonstrated for a gridded ion thruster RIT-22 and a Hall effect thruster SPT-100D.

The application of an electric propulsion diagnostic system for in situ thermal characterization of electric thrusters is studied, as described previously. Exemplarily, the surface temperature profile of the accelerator grid of a gridded ion thruster RIT-22 is obtained and characterized. In situ pyrometer line scans in combination with precise measurements of geometrical grid parameters are demonstrated. The accelerator grid surface temperature of the firing thruster is obtained by a model calculation that requires the knowledge of geometrical grid parameters, such as hole diameter, distance between holes, or grid shape. These parameters are also measured in situ with a telemicroscope for high-resolution optical imaging and a triangular laser head for surface profile scanning. The distance between grid surface and pyrometer optics are precisely monitored with the support of the triangular laser head, for which the position is fixed with respect to the pyrometer. The distance measurement allows for correcting the measurement spot size of the pyrometer. The temperature profiles at three different beam power levels (1250, 2250, and 4000W), and warm-up and cool-down phases demonstrate the capabilities of the complex equipment. It is found that thermal steady state is reached after 4 h of thruster firing. Furthermore, it is shown that the accelerator grid surface temperature increases almost linearly with increasing beam current.

The sputter yield is an important material parameter not only for varioussurface treatment techniques, but also for electric spacecraft propulsion.Many satellite or thruster components might be subject of erosion due toenergetic and/or related secondary ions. In order to estimate the lifetimeof these components the sputter yield under xenon ion incidence has to beknown in dependence on ion energy and incidence angle, mainly in the lowenergy region (i.e. below 1500 eV). However, for many materials related toelectric propulsion the supply of sputter yield data in literature is quitepoor. Therefore, in this study the sputter yields of molybdenum, titanium,tungsten, silver and aluminium was investigated under xenon ion incidence.

RIT-μX (Elegant BB) is a radio frequency ion thruster especially designed for the demands of high precision formation flying missions and the needs of fine and ultrafine drag control. The thruster design bases on the experience in more than 40 years radio frequency ion thruster development. The RIT-μX thruster and system development has been performed in the frame of ESA's GST program. This publication is focused on the results of the thruster functional test program. During the functional test campaign the basis performance (Isp, Thrust, Power consumption) as well as advanced parameters (Thrust resolution, Controllability, Thrust Noise) have been investigated.

A first qualitative approach to the importance of the divergence angle and angular distribution of the ions within the broad beam (here called internal beam parameters) on the pattern formation by low-energy ion beam erosion is presented. Si (100) surfaces were irradiated with Kr+, with an ion energy of 2 keV, using a Kaufman type broad beam ion source. It is found that the operating parameters of the broad beam ion source which are responsible for the angular distribution of the ions also affect the pattern formation. Especially, the effect of the acceleration voltage, discharge voltage, grid distance and operation time on the transition from ripple to dot pattern with increasing ion beam incidence angle were analyzed. The results represent additional evidence about the significance of the internal beam parameters and the need of the further investigation of their role on the pattern formation by low-energy erosion.

The importance of the ion incidence angle in self-organized pattern formation during low energy Xe+ ion beam erosion of silicon is elaborated. By a small step variation of the ion incidence angle, a variety of nanostructured patterns can develop. In this context, the angular distribution of ions within the ion beam is explored as an additional parameter controlling the evolution of the surface topography. Due to a controlled variation of these two parameters, hitherto unknown phenomena are found: (i) formation of rotated ripples, (ii) continuous transitions between patterns, and (iii) long range square ordered dot pattern.

A 13.56MHz radio frequency plasma bridge neutralizer (rf-PBN) for ion thruster applications as well as ion beam surface processing of insulating materials is presented. The energy for the plasma excitation is inductively coupled into the plasma chamber. Because no components are located inside the plasma, the lifetime of the rf-PBN is expected to be very long. A compact tuning system adapts the input power to the plasma impedance. The electron current may be controlled over a wide range by the rf input power. An electron current of up to 1.6A has been extracted.

Introduction Ion beam sources are widely used in material processing, especially for ion beam etching and ion beam assisted deposition [1, 2]. Using of ion beams for electric spacecraft propulsion is already applied and continuously improved [3, 4], e.g. SMART-1, DEEP SPACE-1. Knowledge about the beam properties, e.g. ion-energy distribution, ion-current density and their profiles, is necessary for all applications. Therefore, plenty of work has been spent in the improvement of ion sources [5, 6] and development of beam diagnostics. In this paper we characterize the performance of an electron cyclotron resonance (ECR) microwave (MW) broad beam ion source [1] using different diagnostics. The beam properties such as density, energy and respective the profile are investigated using Faradaycups and retarding-field analyzers. Axial and radial profiles of beam energy and density as functions of source parameters are measured. The results from different diagnostics are checked for consistency and discussed.

This article describes the validation of our extraction grid erosion modeling for gridded ion thrusters. Experimental data from three life tests of different thruster sizes and operation conditions was available. For all test cases, an excellent agreement was achieved between experimental and simulated data, which increased the confidence in the lifetime predictions of the code for space missions.

We performed angle and energy dependent sputter yield measurements of various prospective carbon ion thruster grid materials under xenon ion incidence in the energy range 200-1 400 eV and at normal and oblique incidence up to 70 degrees. Materials investigated are high-density graphite of various grain sizes, carbon-carbon material and pyrolytic graphite. No significant difference between the various carbon materials with respect to sputter yield was found.

RIT-µX is a radio frequency ion engine for micro propulsion applications. The ionization of the propellant by electro magnetic fields offers inherently highest thrust control, -stability and resolution. The function principle of the engine and the specific advantages are explained and the layout of a propulsion system is presented. Potential missions are described and selected test results are given.

Ion thrusters or broad beam ion sources are widely used in electrostatic space propulsion and in high-end surface modification processes.A short historical review of the roots of electric space propulsion is given. In the following, we introduce the electrostatic ion thrusters and broad beam ion sources based on different plasma excitation principles and describe the similarities as well as the differences briefly. Furthermore, an overview on source plasma and ion beam characterisation methods is presented. Apart from that, a beam profile modelling strategy with the help of numerical trajectory codes as basis for a special grid system design is outlined. This modelling represents the basis for the adaptation of a grid system for required technological demands. Examples of model validation demonstrate their reliability. One of the main challenges in improvement of ion beam technologies is the customisation of the ion beam properties, e.g. the ion current density profile for specific demands. Methods of an ex-situ and in-situ beam profile control will be demonstrated.Examples for the use of ion beam technologies in space and on earth - the RIT-10 rescue mission of ESA's satellite Artemis, the RIT-22 for BepiColombo mission and the deposition of multilayer stacks for EUVL (Extreme Ultra Violet Lithography) mask blank application are provided in order to illustrate the potential of plasma-based ion beam sources. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

§** †† ‡‡ §§ Electric Propulsion based on gridded ion thruster technology is the key for several upcoming missions. Namely the European Space Agency ESA's corner stone mission BepiColombo to the Sun's nearest planet mercury is a representative for these type of missions. Beside harsh thermal and radiation environment the required total impulse and engine lifetime is a challenge for the electric propulsion system. Astrium GmbH BL Equipment and Propulsion proposes its new ion thruster RIT-22 based on cathodless radiofrequency technology for this mission. In 2006 a successful 3,000h test was extended for another 2,000h. The 5,000h Endurance test demonstrates the compliance between egine performance and mission requirements. This paper describes the ion engine, the test setup and the test facility. One section is devoted to the control software which bases on the flight proven architecture for ARTEMIS. Test results are given and the life time prediction is presented.

We present the energy-selective mass spectroscopy (ESMS) as a very useful tool for the characterisation of the discharge chamber plasma and the ion beam. The beam composition, particularly the content of multiply charged ions and contaminations can be studied. From the energy distributions, information on the plasma properties and processes occurring in the plasma and the beam can be obtained. Modification of the spectrometer to allow the analysis at higher ion energies (up to 5 keV) is described. First results of the characterisation of the RIT-22 ion thruster are presented. The basics of radio-frequency ionisation are well understood. Nevertheless, more detailed knowledge of the discharge processes would allow for further performance improvements. Therefore, fast non-intrusive diagnostic methods are from growing interest. Optical methods like LIF and OES were successfully established for plasma monitoring of ion engines and plasma thrusters. In contrast to Langmuir probe measurements, optical diagnostics give access to neutral particles also. Although these methods offer many advantages their implementation is challenging. In respect to measurements on flight-hardware the above methods have one decisive disadvantage: hardware modifications (e.g. optical viewports or windows) are required. Here, we present an interesting non-intrusive approach to the plasma properties - the energy selective mass spectrometry (ESMS) or, as it is sometimes called plasmamonitor. Observing the ionic species, their densities and energy distributions in the beam gives meaningful insights into the discharge chamber. For that the ion thruster to be examined remains as is. Besides the access to discharge parameters this beam diagnostic delivers detailed information of the ion beam too. The angular distribution of ion emission and their energy can be investigated not only from beam ions, but also from secondary ions. The divergence angle can be deduced. These results are from crucial interest with respect to thruster-spacecraft interaction, e.g. the impact of energetic ions on solar cells.

The design of experiments approach is used to build models of the extracted beamlet current and divergence in dependence on grid parameters and plasma density employing a beamlet simulation code. Appropriate polynomial degrees for the input parameters are determined which result in a mean deviation of the models from additional simulated data of less than 4%. The derived models are obtained at a low computational effort and are helpful in designing and optimizing ion source extraction systems.

We present a modular microwave excited electron cyclotron resonance type linear ion source concept that allows the adaptation of the ion beam dimensions to the requirements of the particular application. The ion beam current density profile is controlled by dividing the middle grid of a triple-grid system into segments of 2cm width. Each segment is separately switched between the negative accelerator grid voltage and a positive blocking voltage. By adjusting the pulse-to-pause ratio of each segment, the current density profile can be controlled from a homogeneous profile up to nearly arbitrary profiles. This ion source enables an in situ adaptation of ion beam profile. The application of a 2m linear ion source for hardening of stainless steel tools and the homogenization of the beam profile by segmented grids are demonstrated.

Ion beam and grid erosion simulation prove their usefulness in ion thruster development and optimisation. The experimental validation of the simulation is of very high importance. This paper describes the validation process of the IOM grid erosion modelling with strong attention on the modelling of the grid geometrical changes due of grid erosion processes. Experimental data from 3 life tests was available: the 2.800 h sub-scale accelerated wear test performed at IOM, the 20.000 h life test of the RIT-10 ion thruster for ARTEMIS and the 3.000 h endurance test of the RIT-22 EM thruster. For all test cases an excellent agreement was achieved between experimental and simulated data.

New Grid Systems for Ion Engines" is a project in the frame of The European Space Agency ESA's Technology Research Program (TRP) aiming on a further improvement of grid systems for ion engines with respect to performance, lifetime and reliability. A consortium of European electric propulsion specialists works together on a project consisting of three phases. In the study phase improvement and validation of numerical tools for grid design was performed. In parallel, standard and advanced grid materials were investigated. From the most potential materials subscale grids were manufactured, tested and assessed. During the design phase a grid system for the BepiColombo mission and a subscale grid for future high specific impulse engines were designed and manufactured. Meanwhile the also the validation phase which contains the intensive endurance test of the grid systems is nearly completed. This paper summarizes the results of the three study phases and a first conclusion is drawn.

The Design of Experiments (DoE) approach is used to build models of beamlet parameters as the extracted beamlet current, beamlet divergence and the perveance limit in dependence on grid parameters and plasma density employing our well-approved beamlet simulation code. Appropriate polynomial degrees for the input parameters are determined which result in a mean deviation of the models from additional simulated test data of less than 4%. The derived models are obtained at a low computational effort and are helpful in designing and optimizing ion source extraction systems.