• Hall thrusters
• low-temperature plasmas
• plasma oscillations
• plasma physics
• electric propulsion
• zero-dimensional model
• 0D model
• alternative propellants
• numerical simulations
• electron mobility
• ionization instability
• breathing mode

Electric propulsion systems have gained significant popularity in space missions due to their high efficiency, specific impulse, and long operational lifespan. Among them, the Hall thruster stands out as a crucial example employed in various applications, including geostationary satellite station-keeping, deep space exploration, and interplanetary missions. Despite its advantages over conventional chemical propulsion systems, Hall thrusters face challenges, notably the breathing mode instability, which can negatively impact their performance and even lead to catastrophic failure. The breathing mode, characterized by longitudinal oscillation of the discharge current and plasma quantities that occurs at a relatively low frequency (5-35 kHz), can reduce thrust, efficiency, and damage the thruster.

This thesis addresses the problem of the breathing mode instability and its impact on Hall thrusters when using different propellants. The research is motivated by the desire to enhance propulsion capabilities for space missions that demand superior performance and extended thruster lifespan. By maintaining a Hall thruster in a stable operational mode, overall thruster performance is improved, resulting in higher specific impulse and reduced propellant consumption. The study utilizes a well-established 0D numerical model of plasma dynamics to simulate the behavior of Hall thrusters under various propellants. The investigation involves the introduction of artificial propellants, Aprop1 and Aprop2, between reference propellants (xenon, krypton, and argon) through linear interpolation, allowing for continuous simulations and parameter variations. The model is assessed for stability and oscillatory behavior across different propellants, anode temperatures, and magnetic field intensities.

Results reveal that transitioning from xenon to argon gradually leads to an enlarged unstable region on the stability plot, indicating higher susceptibility to instability. Moreover, argon exhibits greater sensitivity to changes in anode temperature and magnetic field intensity compared to xenon and krypton. Increasing the anode temperature proves beneficial in enhancing a Hall thruster's ability to withstand breathing mode instability, especially for argon. The influence of magnetic field intensity on thruster stability is demonstrated, with each propellant having a magnetic field intensity that minimizes growth rate and oscillation frequency. The tuning of the 0D model against an experimentally validated 1D model emphasizes the significance of ion dynamics modeling for precise predictive simulations. The findings provide valuable insights into the breathing mode phenomenon in Hall thrusters and its dependence on various parameters. This research contributes to advancing space propulsion technology by optimizing thruster performance and stability when utilizing different propellants.