Investigation of DC and RF biased gridded ion thruster plume phenomena

Overview & Synopsis

In recent years, two promising technologies emerged to improve the performance and decrease the cost of ion thrusters; RF biasing of ion acceleration grids and the use of iodine as a propellant.These techniques may represent a significant technological step forward; however, when using either of them, the physical processes in the plasma generation and especially on the downstream plasma plume are intricate, having significant implications on the device's performance.The main goal of this work was to elucidate the physics of the plasma plume when using these technologies through a numerical and experimental approach.A dedicated numerical model of the plume was developed to study RF grid biasing, which allowed a determination of the behavior of several phenomena and the expansion of previous numerical work.A prototype using RF grid biasing was also investigated experimentally, which was operated at the highest values of acceleration energy and frequency to date, demonstrating that it can generate a well-neutralized plume with acceptable performance and provide initial benchmark data available for this type of thruster.The experiments also showed an excellent agreement with the numerical and theoretical predictions, which confirmed both the correctness of the model developed here, and previous works, and being an important advancement towards developing a flight prototype.For iodine, the characteristics of the plume and the thruster performance were measured and compared to xenon, showing unique and, in several cases, better characteristics.A new automated instrument to determine the ion beam profile was developed, and to improve the quality of experiments and increase the knowledge base on iodine plasmas, the secondary electron emission yield of iodine ions was measured for the first time.During this work, the thruster tested was launched onboard a space mission, which permitted a comparison of ground and flight results with excellent agreement obtained.