Efficient electron sources are crucial for any space-based mission, especially when using electric thrusters. In many respects, hollow cathodes are a baseline technology due to their power-efficient electron emission in the desired current range and the potentially long lifetime of these emitters. However, the delicate design of the heater, with the associated constraints on its operation, and the high degradation of state-of-the-art materials to new propellant options under evaluation for electric space propulsion systems, are severe limitations of current systems. To address some of the most pressing challenges with cathodes, a heaterless plasma-based cathode using the emitter material C12A7 electride has been developed and is described in this thesis. The cathode has been developed with the requirements of an electrodynamic tether demonstration mission in mind.
C12A7 electride is an electrically conductive ceramic that has recently attracted much attention as a potential electron emitter in hollow cathodes. However, there appear to be significant challenges with the material itself, requiring careful design evaluation and thorough testing to gain a sufficient understanding of the material's behavior. Most importantly, material degradation in the harsh environment of a plasma.
Throughout the thesis, an optimized electride material was developed and tested, yielding a ceramic-metal composite with greatly improved plasma performance compared to pure C12A7 electride material. In addition, a special design of a plasma-based cathode was developed and described, which respects the unique properties of the material and allows convenient operation, and thus characterization and optimization of the cathode. Several milestones have been achieved, including endurance operation for nearly \num{1000} hours, successful operation with a Hall-effect thruster, characterization of the cathode in the discharge current range of \qtyrange{0.2}{2}{\A}, reduction of the flow rate required for ignition and operation down to \qty{2}{\sccm}, and heaterless ignition cycling for up to \num{3300} cycles with a single insert.
The observed performance of the cathode was eventually compared with performance data reported in the literature using state-of-the-art materials and showed reasonable comparability. In particular, advantages over state-of-the-art cathodes were identified in terms of ignition behavior: Requiring only \qty{2}{\sccm} of krypton and a potential of less than \qty{400}{\V}, and reaching steady-state operation in less than a few tens of milliseconds, the performance was better than reported in the literature. Combined with the acceptable discharge performance, these results motivate the further development of such an electride cathode for space applications. Due to the simplicity of such a cathode, applications for a wide range of industrial processes may also be considered.:1 - Introduction
2 - Cathode Theory
3 - C12A7 Electride
4 - Scope of Development
5 - Design Development
6 - Thruster Operation
7 - Endurance Operation
8 - Electride Cathode for Low Current EDT Operation
9 - Additional Tests with the Electride Cathode
10 - Discussion of Results and Further Steps
11 - Conclusion
Bibliography
Appendix
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:88418 |
| Date | 04 December 2023 |
| Creators | Drobny, Christian |
| Contributors | Tajmar, Martin, Lozano, Paulo, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
Page generated in 0.0136 seconds