Experimental Assessment of the Performance of an Electron Cyclotron Resonance Acceleration (ECRA) Thruster Operated with Iodine

The growing demand for compact and efficient space propulsion systems has accelerated the development of alternative propellants and thruster technologies. Among these, iodine has emerged as a promising candidate for electric propulsion due to its high storage density, low ionization energy, and significantly lower cost compared to xenon. The work presented here was conducted during a six-month internship at the Physics Instrumentation and Space Department, in the Lightning, Plasmas, and Applications unit at ONERA center in Palaiseau, France. The aim of the study was to investigate the use of iodine in an Electron Cyclotron Resonance Acceleration (ECRA) thruster, originally designed and patented at ONERA for xenon use. The internship was structured in three main phases. First, a literature review was conducted to deepen understanding of electric propulsion technologies, the advantages and limitations of using iodine versus xenon, and the current state-of-the-art of iodine-based propulsion systems. Next, the core of the internship consisted in developing a dedicated experimental setup for iodine operation. This included modifications to the heating system for the iodine feed-through fluid line, thruster assembly, cryogenic system, and plasma diagnostic setup to ensure reliable iodine testing. Finally, the performance of the ECRA thruster was evaluated with iodine, xenon, argon, and nitrogen. Thrust, specific impulse, and efficiency were estimated from the ion current density measured using a Faraday probe for all tested propellants. Despite the uncertainties associated with the ion energy estimation, preliminary results indicate a comparable operational behavior of the ECRA thruster with both iodine and xenon. With ECRA operating at 30 W, iodine and xenon deliver the highest thrust, varying between 150 and 350 µN, and display similar trends in the evolution of thrust as a function of flowrate. Xenon delivers the highest overall performance, with Isp up to 240 s and TTPR above 10 mN/kW, while Iodine, at lower operating pressure, follows closely, with similar peak TTPR values at a lower Isp of around 180 s. Iodine at higher pressure exhibits reduced performance, with a peak Isp of around 150 s, reflecting the degradation of ECRA performance when operating pressure increases. At the end of the work, the influence of iodine plasma composition on performance estimation is also discussed, identifying key challenges for future research with iodine: precise measurements of ion energy and plasma composition.