Development of a RF cathode to improve the thruster’s neutralization capabilities
RF cathodes are sources of electron current that can be employed as neutralizers in electric thrusters6. These devices consist of a discharge chamber where plasma is generated via an RF antenna. An ion collector (i.e., an electrode) is placed inside the source to bias the plasma and to sustain the electron current which is extracted from an orifice on the end-plate of the cathode. Provided that no insert material is necessary to sustain the discharge via the thermionic effect, RF cathodes present much lower contamination and erosion issues if compared to classical hollow cathodes[1]. This advantage is critical to enable the widespread diffusion of solid and liquid propellants (i.e., I2 or H2O) in the frame of the electric propulsion for SmallSats.
Nonetheless, there is a lack in literature regarding the physical mechanisms that drive the performance (i.e., maximum extracted current) of RF cathodes, hindering a proper optimization of these devices. Therefore, a thorough analysis is necessary to investigate aspects as the material selection for the ion collector and the optimization of the RF antenna. After that, an optimized RF cathode compatible with iodine propellant will be designed, realized and tested. Particular care will be put in the investigation and definition of proper interfaces with the other sub-systems (e.g., fluidic line). In this way, it will be possible to pave the way for the definition of standards to couple this neutralizer with a generic concept of electric thruster. Moreover, a feasibility study will be focused at investigating the scaling of the RF cathode toward low-medium power applications. To sum up, the main goals associated to SO-1 are:
- Development of an optimized RF cathode propelled with iodine.
- Thorough numerical analysis and experimental characterization to deepen the physical understanding of the plasma dynamics in a RF cathode. This point will enable the optimization of the device as well as the acquisition of the know-how to scale the cathode at a generic current rate.
- Analysis and definition of the thermal, mechanical and electrical interfaces of the RF cathode. In this way, it will be possible to realize a building-block applicable on a generic concept of electric thruster.
- Development of a component capable to increase the lifetime of electric propulsion systems, presenting a much lower contamination and erosion compared to other types of cathodes.
Thanks to the expertise in handling RF plasma sources and iodine propellant, UNIPD shall be the partner responsible of the achievement of these goals. Moreover, the suite of numerical codes available at UNIPD and UNIBO and the diagnostic tools developed at CNRS will allow to deepen the physical understanding of RF cathodes.