• Dissociation of iodine
• Hall thruster
• SPT-100

Hall thrusters are widely used in space propulsion due to their efficiency, reliability, and heritage in long-duration missions. Traditionally, xenon has been the propellant of choice because of its high atomic mass and inert properties. However, iodine has recently emerged as a viable alternative to xenon, offering advantages such as higher storage density, lower cost, and its diatomic nature, hence providing additional chemical species like molecular positive ions, negative atomic ions, neutral molecules, neutral atoms, and atomic ions. The plasma dynamics inside a hall thruster causes highly complex instabilities, particularly low-frequency breathing mode oscillations that cause discharge current fluctuations. Alongside efforts to stabilise these oscillations using an RLC low-pass filter, this study also investigates how thermal dissociation of iodine at the anode influences overall thruster performance.
A one-dimensional numerical fluid model was employed to simulate the plasma discharge inside the Hall thruster, accounting for multiple species and their interactions. To further enhance system stability, an RLC-based low-pass filter was developed using MATLAB and Simulink, aimed at reducing high-frequency breathing mode oscillations and preventing current backflow from the thruster to the power supply. The filter model was integrated with the main thruster model to evaluate its impact. Simulations were performed for iodine across different mass flow rates under two configurations: one where dissociation occurs near the anode due to high temperature, and another where dissociation is delayed and allowed to occur only through plasma processes. For comparison, xenon-fed thruster behaviour was also analysed under similar discharge conditions.
The results show that the filter effectively prevents backflow of the current and thus protecting the power supply. However, the high-frequency discharge current fluctuations within the breathing mode persist even after introducing the RLC filter. This confirms that such oscillations are inherent to Hall thruster operation and appear to be governed by internal plasma instabilities rather than external electrical conditions, as they are not directly dependent on the anode voltage. Crucially, it was observed that when iodine dissociation occurred downstream in the plasma rather than at the anode, the thruster demonstrated improved performance in terms of thrust and thrust-to-power ratio. This improvement is attributed to the presence of molecular ions, which increased the average mass of the expelled ions.
In conclusion, this research highlights the opportunity to leverage thermal dissociation behaviour in iodine-fed Hall thrusters as a performance-optimisation mechanism. Combined with suitable filtering techniques, careful control over dissociation location offers a promising design strategy for future electric propulsion systems employing iodine.