This work, based on an EU-funded project, NEMESIS, is aiming at developing electride-based cathode technology which is compatible with all kinds of electric propulsion systems requiring neutralization. Its target is to demonstrate and validate the performance of a novel C12A7:e-electride material as electron emitter instead of traditional thermionic emitters such as lanthanum hexaboride, LaBe, or barium oxide, BaO. In this study, a fair comparison between LaBe and C12A7:e-samples was performed both addressing pure material characterization parameters as well as comparing performance as cathodes under different architectures and operational conditions. In this case, a current/cathode power ratio around 3 mA/W was obtained when using the C12A7:e-sample in a plasma environment with Ar, which is approximately one order of magnitude higher compared to the LaB6 sample.
Abstract-The design and performance of a novel direct current neutralizer for electric propulsion applications are presented. The neutralizer exploits an E×B discharge to enhance ionization via electron-neutral collisions. Tests are performed with helium, argon, xenon, air and water vapour as working gases. The I-V characteristics and extraction parameters are measured for both atomic and molecular gases. The maximum partial power efficiency is 4.2 mA/W in argon, 2.7 mA/W in air and 2 mA/W in water vapour. The typical utilization factor is below 1 and the power consumption is less than 120 W. A semi-empirical model is derived to predict the performance of direct current plasma cathodes using atomic gas. A comparison with existing plasma cathodes and conventional LaB6 cathodes is presented and design optimisations aimed at improving the performance are proposed.
The ion plume of a 72 mm diameter Hall Effect Thruster operated on mixtures of xenon/nitrogen and xenon/air is investigated by means of a Wien filter (or E × B probe). The dependence of the velocities of the plume ions (Xe + , Xe 2+ , Xe 3+ , O + 2 , O + , N + 2 and N +) on the operating parameters of the thruster (anode voltage, anode power, mass flow rate and magnetic field) is explored. The most probable ion acceleration voltages, the ion current and density fractions of the multi-propellant, multi-species ion beam, are computed from the Wien filter spectra through a dedicated post-processing analysis. The knowledge of these properties is fundamental for understanding the contribution of each ion species to the propulsive performance metrics of the thruster when operated on these molecular gas mixtures.
This work, based on an EU-funded project (NEMESIS), is summarising some of the results from the project activities on the research and development on electride-based cathode technology compatible with all kinds of electric propulsion (EP) systems requiring neutralization or electron emission. Further information describing in detail the performed tests and captured measurements can be found in the referenced documents of each section. Different cathode architectures and several emitter configurations with traditional and with alternative propellants are being developed and tested within the project, all of them using C12A7:e-electride material as thermionic electron source. Findings and conclusions derived from these multiple designs are allowing to figure out some of the key factors that determine the best performance of C12A7:e-electride based cathodes. In this work, a discussion of some of these key design and operation factors will be presented based both on the material characterization parameters, and on the performance tests carried out for the different cathode designs.
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