Characterization of a Low Current LaB6 Heaterless Hollow Cathode with Krypton Propellant
Jain, Prachi Lalit
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A first-generation LaB6 heaterless hollow cathode with a flat-plate anode is experimentally investigated. The cathode is characterized using krypton as propellant at varying flow rates, discharge currents and cathode-anode distances. Voltage probes, used to make direct voltage measurements in the ignition circuit, are the only diagnostic tool used experimentally. A plasma model is used to infer plasma parameters in the cathode emitter region. The cathode characterization results are consistent with those obtained during previous investigations of 1 A-class LaB6 hollow cathode with krypton. A peak-to-peak anode voltage criterion is used to identify the discharge modes and the occurrence of mode transition. Fourier analysis of the keeper and anode voltage waveforms carried out to study the discharge mode behavior reveals resonant frequencies ranging from 40 to 150 kHz. Lastly, post-test visual observations of the cathode components show signs of emitter poisoning and keeper erosion.
General Audience Abstract
Recent years have seen rapid growth in the development of both stand-alone satellites and satellite constellations. A critical component of these satellites is the on-board propulsion system, which is responsible for controlling their orientation with respect to the object of interest and keeping the spacecraft in the assigned orbit. Generally, electric propulsion systems are used for this purpose. These types of propulsion systems use electrical power to change the velocity of satellite, providing a small thrust for a long duration of time as compared to chemical propulsion systems. Certain types of electric thrusters utilize a hollow cathode device as an electron source to start-off and support the thruster operation. In this research, a non-conventional hollow cathode for low power applications is developed and tested. The main characteristic of the developed cathode is the heaterless configuration, which eliminates the heater module used in conventional cathodes to enable the cathode to reach its operational temperature. The absence of a heater reduces the complexity of the cathode and the electrical power system. The cathode utilizes an electron emitter material which is insensitive to impurities and air exposure. Additionally, unlike typical electric thrusters which use xenon as the fuel, this cathode uses krypton which is similar to xenon but is less expensive. The presented work includes an overview of electric propulsion and the hollow cathode operation, followed by a detailed discussion of the heaterless hollow cathode design, the experimental setup and the test results. Several noteworthy findings regarding cathode operation are included as well. This research shows that the non-conventional heaterless hollow cathode and its operation with krypton have the potential to improve the overall thruster performance by reducing the weight and the cost, thus contributing to an integral aspect of satellite on-board propulsion.
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